Showing 1–46 of 46 results for author: Manna, L

Scalable Conformal MoSx Catalyst for Efficient Hydrogen Evolution at Industrial-Level Current Density in Alkaline Electrolyzers

Authors: Yong Zuo, Sebastiano Bellani, Meysoun Jabrane, Gabriele Saleh, Thi-Hong-Hanh Le, Michele Ferri, Davide Salusso, Zhanzhao Li, Valentina Mastronardi, Marilena I. Zappia, Manjunath Chatti, Mirko Prato, Silvia Dante, Francesco Bonaccorso, Yongsheng Han, Liberato Manna

Abstract: The development of simple and scalable fabrication strategies for cost-effective electrodes is crucial to advance water splitting in alkaline water electrolyzers (AWEs). Here, we present a coating-annealing method to conformally coat a MoSx catalyst layer onto a porous Ni foam (NF) substrate. By controlling the annealing process, the composition of the MoSx layer could be tuned from MoS2 to MoS3 a… ▽ More The development of simple and scalable fabrication strategies for cost-effective electrodes is crucial to advance water splitting in alkaline water electrolyzers (AWEs). Here, we present a coating-annealing method to conformally coat a MoSx catalyst layer onto a porous Ni foam (NF) substrate. By controlling the annealing process, the composition of the MoSx layer could be tuned from MoS2 to MoS3 and its catalytic performance for hydrogen evolution reaction (HER) in alkaline media was optimized. The MoS3@NF synthesized by this method achieved industrially relevant HER current densities of 200 mA/cm2 at a low overpotential of 246 mV, maintaining stable operation for over 240 h. The MoS3@NF cathode, combined with a stainless steel anode, enabled an alkaline water electrolyzer (AWE) cell to operate steadily at 1.96 V and 1 A/cm2 for 1000 h. This performance surpasses that of most of the previously reported water electrolyzers employing MoSx-based cathodes. Our work demonstrates the potential of MoS3 (with its abundant edge-sulfur atoms serving as active sites) as a high-performance cathode material for industrial AWEs. △ Less

Submitted 10 June, 2026; originally announced June 2026.

Comments: 57 pages, 29 Figures

Journal ref: Chem Catalysis 6, 101763, 2026 (2026)

Metal Halide Perovskite/Chalcohalide Heterojunctions for the Photoinduced Oxidative Coupling of p-substituted Thiophenols

Authors: Anna Cabona, Stefano Toso, Alejandro Cortés-Villena, Ignacio Rosa-Pardo, Mirko Prato, Michele Ferri, Julia Perez-Prieto, Ilka Kriegel, Liberato Manna, Raquel E. Galian

Abstract: The introduction of a semiconductor-semiconductor junction is an effective strategy to enhance the photocatalytic performance of perovskite nanocrystal-based systems. Herein, we optimized the synthesis of CsPbX3/Pb4S3X2 (X= Cl, Br, I) perovskites-chalcohalides heterostructures, whose band alignment can be tuned by halide composition. As a proof-of-concept, we evaluated the photooxidative coupling… ▽ More The introduction of a semiconductor-semiconductor junction is an effective strategy to enhance the photocatalytic performance of perovskite nanocrystal-based systems. Herein, we optimized the synthesis of CsPbX3/Pb4S3X2 (X= Cl, Br, I) perovskites-chalcohalides heterostructures, whose band alignment can be tuned by halide composition. As a proof-of-concept, we evaluated the photooxidative coupling of p-substituted thiophenols at room temperature, under visible-light, air, and without sacrificial electron donor. Notably, CsPbBr3/Pb4S3Br2 achieved up to 94 % selectivity toward disulfide (p-OCH3 thiophenol with a turnover number of 14300) highlighting the crucial role of the type-II heterojunction to promote charge separation and efficient electron delocalization across the junction. △ Less

Submitted 8 June, 2026; originally announced June 2026.

Comments: 55 pages, 35 figures

Journal ref: ACS Applied Nano Materials 2026 9 (11), 4841-4847

Interfacial Reconstructions and Engineering in III-V@II-VI Core-Shell Quantum Dots

Authors: Jordi Llusar, Abdessamad El Adel, Luca De Trizio, Liberato Manna, Zeger Hens, Ivan Infante

Abstract: In core/shell quantum dots (QDs), the interface between semiconductors of different chemical character largely determines their optoelectronic properties. In III-V/II-VI systems, this boundary involves pronounced chemical and electronic discontinuities that can generate trap states even under complete surface passivation. Using density functional theory on atomistic models of InAs/CdSe QDs, we sys… ▽ More In core/shell quantum dots (QDs), the interface between semiconductors of different chemical character largely determines their optoelectronic properties. In III-V/II-VI systems, this boundary involves pronounced chemical and electronic discontinuities that can generate trap states even under complete surface passivation. Using density functional theory on atomistic models of InAs/CdSe QDs, we systematically reconstruct atomic arrangements at the surface and interface to evaluate how local coordination and interfacial dipoles influence the electronic structure. Abrupt interfaces induce charge imbalance and band-gap collapse, whereas introducing an alloyed interlayer that mixes core and shell atoms and vacancies restores energetic alignment and yields delocalized band-edge states, consistent with experimental findings. We also introduce a charge-flow analysis that quantifies charge redistribution across the QD, providing a framework for realistic modeling of interlayer formation and predictive design of defect-free interfaces in core@shell architectures. △ Less

Submitted 15 May, 2026; originally announced May 2026.

Comments: 27 pages, 4 figures

Journal ref: ACS Energy Letters 11 5 (2026) 3945-3952

Deterministic nucleation of nanocrystal superlattices on 2D perovskites for light-funneling heterostructures

Authors: Umberto Filippi, Alexander Schleusener, Simone Lauciello, Roman Krahne, Dmitry Baranov, Liberato Manna, Masaru Kuno

Abstract: Semiconductor heterostructures that combine components with different dimensionality provide an interesting way to manipulate the physical properties of the resulting material. Two-dimensional lead halide perovskites crystallize as flat microcrystals and have efficient in-plane exciton mobility, while perovskite nanocrystals are efficient emitters with a tunable bandgap that can self-assemble into… ▽ More Semiconductor heterostructures that combine components with different dimensionality provide an interesting way to manipulate the physical properties of the resulting material. Two-dimensional lead halide perovskites crystallize as flat microcrystals and have efficient in-plane exciton mobility, while perovskite nanocrystals are efficient emitters with a tunable bandgap that can self-assemble into microscopic superlattices. However, combining such intricate architectures into heterostructures has been challenging due to the mismatch in solubility properties and the challenging transfer procedures. Here we realize heterostructures where CsPbBr3 nanocrystal superlattices are deterministically grown along the faces of PEA2PbBr4 two-dimensional layered perovskite microcrystals. The growth can be limited to the lateral faces of the microcrystals and result in core-crown epitaxial heterostructures, or extended to the vertical direction leading to core-shell-like structures. The growth method is simple yet effective and versatile, and promises to be expanded to a large variety of other materials. We demonstrate that these heterostructures can be employed as efficient light-harvesting systems. In fact, energy can be transferred from the two-dimensional microcrystal domain to the superlattices, enabling switching between linear and non-linear carrier recombination regimes by tuning the excitation fluence. Moreover, by exploiting the lifetime shortening of CsPbBr3 nanocrystal emission upon sample cooling, we ensure that energy transfer occurs after the biexcitonic and single-excitonic decays of the nanocrystals, effectively extending the radiative recombination of superlattices. △ Less

Submitted 19 March, 2026; originally announced March 2026.

Synthesis and Structural Analysis of an Emissive Colloidal Argyrodite Nanocrystal: Canfieldite Ag8SnS6

Authors: Francisco Yarur Villanueva, Victor Quezada Novoa, Pascal Rusch, Stefano Toso, Maxwell W. Terban, Yurii P. Ivanov, Joaquin Carlos Chu, Maxine J. Kirshenbaum, Ehsan Nikbin, Maria J. Gendron Romero, Mirko Prato, Giorgio Divitini, Jane Y. Howe, Mark W. B. Wilson, Liberato Manna

Abstract: We resolve a phase identification controversy in the Ag-Sn-S material system by unraveling the polymorphic structure of nanocrystals within the argyrodite material family. Argyrodites are a class of superionic materials used in their bulk form for applications in solid-state batteries and thermoelectrics, where their advantageous properties relate to their polymorphism. However, despite their well… ▽ More We resolve a phase identification controversy in the Ag-Sn-S material system by unraveling the polymorphic structure of nanocrystals within the argyrodite material family. Argyrodites are a class of superionic materials used in their bulk form for applications in solid-state batteries and thermoelectrics, where their advantageous properties relate to their polymorphism. However, despite their well-studied bulk applications, the limited exploration at the nanoscale has left considerable potential for the discovery of emerging properties due to size effects. Further, phase identification presents a prominent challenge to the study of polymorphs in superionic conductors and related mate-rials. In this work, we synthesize canfieldite-like (Ag8SnS6) nanocrystals to understand their formation and structural behavior at the nanoscale. We observe the emergence of emissive, meta-stable, cluster-like species. Then, high-resolution transmission electron microscopy reveals indistinguishable polymorphs of canfieldite due to identical heavy-atom frameworks. However, using synchrotron X-ray total scattering for pair distribution function analysis, we uncover structural distortions, showing a pseudo-orthorhombic configuration that likely gives rise to the red emission. Further, we investigate the optical properties and structure of Ag8SnS6 nanocrystals upon the addition of Zn2+, the cation of interest in the canfieldite vs. pirquitasite (Ag2ZnSnS4) phase identification controversy. We show that Zn2+ is incorporated in the canfieldite-like structure through the replacement of Ag+, boosting the emission. Our results solve a standing phase identification challenge and uncover fundamental insights for the synthesis and structure of canfieldite nanocrystals, laying the ground for the exploration of other argyrodite materials with emerging properties at the nanoscale. △ Less

Submitted 27 February, 2026; originally announced February 2026.

Comments: 28 pages, 23 figures

Journal ref: J. Am. Chem. Soc. 2025, 147, 32, 29413-29422

A Nanocrystal Synthesis Derived Approach to Silver Bismuth Iodide Layered Double Perovskites with Aliphatic Amines: (CnH(2n+1)NH3)4AgBiI8

Authors: Pascal Rusch, Ann Mary Antony, Meenakshi Pegu, Meysoun Jabrane, Gabriele Saleh, Arghyadeep Garai, Aswin Asaithambi, Simone Lauciello, Sergio Marras, Serena De Negri, Pavlo Solokha, Liberato Manna

Abstract: Lead-free iodide double perovskites are an interesting class of materials since they combine a relatively low toxicity (compared to the lead counterpart) with the small bandgap typical of iodide-based perovskite structures. Their reported number is small due to their lower structural stability compared to the chloride and bromide analogues, hence their difficult synthesis. The structural constrain… ▽ More Lead-free iodide double perovskites are an interesting class of materials since they combine a relatively low toxicity (compared to the lead counterpart) with the small bandgap typical of iodide-based perovskite structures. Their reported number is small due to their lower structural stability compared to the chloride and bromide analogues, hence their difficult synthesis. The structural constraints that limit stability, on the other hand, can be much relieved in layered, organic-inorganic perovskites. Following this line of thought, we report here a successful fast precipitation route to iodide layered (CnH(2n+1)NH3)4AgBiI8 (n = 10, 12, and 14) double perovskites that borrow concepts from the synthesis of colloidal nanocrystals. X-ray diffraction studies revealed for these compounds a monoclinic crystal structure containing edge-sharing alternated [AgI6] and [BiI6] octahedra. These materials have experimental band gaps of 2.1 eV, as also corroborated by theoretical calculations. We have also investigated their phase transitions by thermal analysis and temperature-dependent diffraction and found them to be similar to their lead-based layered perovskite counterparts. △ Less

Submitted 27 February, 2026; originally announced February 2026.

Comments: 54 pages, 32 figures

Journal ref: Chem. Mater. 2026, 38, 2, 900-909

Anti-Thermal Quenching Phosphors based on Metal Halides

Authors: Baowei Zhang, Liberato Manna

Abstract: Thermal quenching (TQ) generally occurs in phosphors and is ascribed to the activation of non-radiative transitions at elevated temperatures. This effect limits the use of most phosphors in high-power/high-temperature applications, such as outdoor lighting and laser systems. To achieve anti-TQ properties, structural design of phosphors is required. This usually follows two guidelines: (1) increasi… ▽ More Thermal quenching (TQ) generally occurs in phosphors and is ascribed to the activation of non-radiative transitions at elevated temperatures. This effect limits the use of most phosphors in high-power/high-temperature applications, such as outdoor lighting and laser systems. To achieve anti-TQ properties, structural design of phosphors is required. This usually follows two guidelines: (1) increasing lattice rigidity to minimize thermal expansion; (2) converting thermal energy into radiative transitions to compensate for the non-radiative losses. While metal oxides and metal nitrides dominate the field of commercial anti-TQ phosphors, metal halides - despite their inherently soft lattices - have shown remarkable progress as anti-TQ phosphors in recent years. Here, we review the advances in anti-TQ metal halides (covering the time span from 2017, when first reports have appeared, till today) and discuss their mechanisms and applications. We argue that the low synthesis temperatures of metal halides and their high photoluminescence quantum yields (PLQYs) make them promising candidates as anti-TQ phosphors. Furthermore, since the rich optical-physical processes underlying the anti-TQ effect in soft-lattice in metal halides are only now beginning to be unraveled, this creates opportunities for many fundamental investigations. △ Less

Submitted 26 February, 2026; originally announced February 2026.

Comments: 14 pages, 9 figures

Journal ref: B. Zhang and L. Manna, ACS Energy Lett. 2026, 11, 1, 345-355

The Predictive Power of Chemical Bonding Analysis in Materials: a Perspective on Optoelectronic Properties

Authors: Gabriele Saleh, Liberato Manna

Abstract: Chemical bonding governs how atoms interact to form compounds, thereby determining their physicochemical properties. Despite being an elusive concept, chemical bonding has led to the development of models and tools to explain and predict the behavior of chemical species. This perspective addresses the adoption of chemical bonding analysis to the study of optoelectronic materials, emphasizing the i… ▽ More Chemical bonding governs how atoms interact to form compounds, thereby determining their physicochemical properties. Despite being an elusive concept, chemical bonding has led to the development of models and tools to explain and predict the behavior of chemical species. This perspective addresses the adoption of chemical bonding analysis to the study of optoelectronic materials, emphasizing the im-portance of its predictive aspect. After reviewing the evolution of chemical bonding models from the first Lewis formulation to the present day, the perspective discusses material classes and chemical bonding phenomena most relevant for light harvesting and emission. We delve into metal halide perovskites and structurally related materials, given their central role in optoelectronic research. Various aspects of chemical bonding in these materials are surveyed, from the structure-property relationship to the rationalization of their electronic properties through molecular orbital diagrams. Two chemical bonding features are particularly important for optoelectronic materials: the ns2 lone pairs of the cations typically found in these materials (e.g. Pb, Sb, Bi) and the antibonding nature of valence and/or conduction bands. We discuss in depth the models to predict the implications of these two phenomena on optoelectronic properties. We also explore chalcohal-ides, a class of materials whose optoelectronic properties are recently emerging. From the chemical bonding perspective, these materials display intriguing phenomena due to the interplay of various types of chemical bonds. Finally, we discuss our vision on the role of chemical bonding analysis in the future of materials science, including synergies and antitheses with machine learning. △ Less

Submitted 25 February, 2026; originally announced February 2026.

Comments: 9 figures, 17 pages

Journal ref: G. Saleh and L. Manna, J. Am. Chem. Soc. 2025, 147, 51, 46705-46719

Permanent Lattice Compression of Lead-Halide Perovskite for Persistently Enhanced Optoelectronic Properties

Authors: Karunakara Moorthy Boopathi, Beatriz Martín-García, Aniruddha Ray, Joao M. Pina, Sergio Marras, Makhsud I. Saidaminov, Francesco Bonaccorso, Francesco Di Stasio, Edward H. Sargent, Liberato Manna, Ahmed L. Abdelhady

Abstract: Under mild mechanical pressure, halide perovskites show enhanced optoelectronic properties. However, these improvements are reversible upon decompression, and permanent enhancements have yet to be realized. Here, we report antisolvent-assisted solvent acidolysis crystallization that enables us to prepare methylammonium lead bromide single crystals showing intense emission at all four edges under u… ▽ More Under mild mechanical pressure, halide perovskites show enhanced optoelectronic properties. However, these improvements are reversible upon decompression, and permanent enhancements have yet to be realized. Here, we report antisolvent-assisted solvent acidolysis crystallization that enables us to prepare methylammonium lead bromide single crystals showing intense emission at all four edges under ultraviolet light excitation. We study structural variations, edge-vs-center, in these crystals using micro-X-ray diffraction and find that the enhanced emission at the edges correlates with lattice compression compared to in the central areas. Time-resolved photoluminescence measurements show much longer-lived photogenerated carriers at the compressed edges, with radiative component lifetimes of ca. 1.4 us, 10 times longer than at the central regions. The properties of the edges are exploited to fabricate planar photodetectors exhibiting detectivities of 3x10^13 Jones, compared to 5x10^12 Jones at the central regions. The enhanced lifetimes and detectivities correlate to the reduced trap state densities and the formation of shallower traps at the edges due to lattice compression. △ Less

Submitted 22 January, 2026; originally announced January 2026.

Journal ref: ACS Energy Letters 2020, 5 (2), 642-649

Heterostructure Design in Two-Dimensional Perovskites by Sequential Recrystallization

Authors: Mehrdad Faraji, Alexander Schleusener, Sirous Khabbaz Abkenar, Andrea Griesi, Mattia Lizzano, Sudhir Kumar Saini, Aswin V. Asaithambi, Liberato Manna, Matteo Lorenzoni, Mirko Prato, Giorgio Divitini, Roman Krahne

Abstract: Low-dimensional metal halide perovskites provide exciting opportunities to fabricate new semiconductor materials. Semiconductor technology relies on electronic heterojunctions, and cost-efficient and flexible approaches to realize functional heterostructures are of fundamental importance. Lateral heterostructures define the energy landscape in the plane of the semiconducting lattice in such 2D mat… ▽ More Low-dimensional metal halide perovskites provide exciting opportunities to fabricate new semiconductor materials. Semiconductor technology relies on electronic heterojunctions, and cost-efficient and flexible approaches to realize functional heterostructures are of fundamental importance. Lateral heterostructures define the energy landscape in the plane of the semiconducting lattice in such 2D materials, representing an ideal platform to tailor energy barriers and to control charge carrier flow. Here, we demonstrate a versatile one-pot synthesis to fabricate a large variety of 2D perovskite heterostructures based on different halides and/or metal cations. Exploiting sequential crystallization of different 2D perovskites, and playing with the composition and injection events of the materials, enables the design of diverse heterostructure architectures including multiple heterojunctions. We obtain crystalline quality of the heterojunctions, multicolor emission, and optical coupling between the different heterostructure regions. We foresee that the design freedom of our method will stimulate the development of novel optoelectronic devices where electronic band engineering is crucial. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Comments: 33 pages main text, 6 figures, followed by supplementary information with 26 figures

Structure Prediction of Ionic Epitaxial Interfaces with Ogre Demonstrated for Colloidal Heterostructures of Lead Halide Perovskites

Authors: Stefano Toso, Derek Dardzinski, Liberato Manna, Noa Marom

Abstract: Colloidal epitaxial heterostructures are nanoparticles composed of two different materials connected at an interface, which can exhibit properties different from those of their individual components. Combining dissimilar materials offers opportunities to create several functional heterostructures. Yet, assessing structural compatibility (the main prerequisite for epitaxial growth) is challenging w… ▽ More Colloidal epitaxial heterostructures are nanoparticles composed of two different materials connected at an interface, which can exhibit properties different from those of their individual components. Combining dissimilar materials offers opportunities to create several functional heterostructures. Yet, assessing structural compatibility (the main prerequisite for epitaxial growth) is challenging when pairing complex materials with different lattice parameters/crystal structures. This complicates both the selection of target heterostructures for synthesis and the assignment of interface models when new heterostructures are obtained. Here, we demonstrate Ogre as a powerful tool to accelerate the design and characterization of colloidal heterostructures. To this end we implemented developments tailored for the efficient prediction of epitaxial interfaces between ionic/polar materials, which encompass most colloidal semiconductors. These include pre-screening candidate models based on charge balance at the interface and using a classical potential for fast energy evaluations, with parameters automatically extracted from the input bulk structures. These developments are validated for CsPbBr3/Pb4S3Br2 heterostructures, where Ogre produces interface models in agreement with density functional theory and experiments. Furthermore, we use Ogre to rationalize the templating effect of CsPbCl3 on the growth of lead sulfochlorides, where perovskite seeds induce the formation of Pb4S3Cl2 rather than Pb3S2Cl2 due to better epitaxial compatibility. Combining Ogre simulations with experimental data enables us to unravel the structure and composition of the hitherto unsolved CsPbBr3/BixPbySz interface and assign a structure to many other reported metal halide/oxide based interfaces. The Ogre package is available on GitHub or via the OgreInterface desktop application, available for Windows, Linux and Mac. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: 103 pages, 48 figures

Journal ref: ACS Nano 2025, 19, 5, 5326-5341

Exogenous Metal Cations in the Synthesis of CsPbBr3 Nanocrystals and their Interplay with Tertiary Amines

Authors: Zhanzhao Li, Luca Goldoni, Ye Wu, Muhammad Imran, Yurii P. Ivanov, Giorgio Divitini, Juliette Zito, Iyyappa Rajan Panneerselvam, Dmitry Baranov, Ivan Infante, Luca De Trizio, Liberato Manna

Abstract: Current syntheses of CsPbBr3 halide perovskite nanocrystals (NCs) rely on over-stoichiometric amounts of Pb2+ precursors, resulting in unreacted lead ions at the end of the process. In our synthesis scheme of CsPbBr3 NCs we replaced excess Pb2+ with different exogenous metal cations (M) and investigated their effect on the synthesis products. These cations can be divided into two groups: group 1 d… ▽ More Current syntheses of CsPbBr3 halide perovskite nanocrystals (NCs) rely on over-stoichiometric amounts of Pb2+ precursors, resulting in unreacted lead ions at the end of the process. In our synthesis scheme of CsPbBr3 NCs we replaced excess Pb2+ with different exogenous metal cations (M) and investigated their effect on the synthesis products. These cations can be divided into two groups: group 1 delivers monodisperse CsPbBr3 cubes capped with oleate species (as for the case when Pb2+ is used in excess) and with photoluminescence quantum yield (PLQY) as high as 90% with some cations (for example with M= In3+); group 2 yields irregularly shaped CsPbBr3 NCs with broad size distributions. In both cases, the addition of a tertiary ammonium cation (didodecylmethyl ammonium, DDMA+) during the synthesis, after the nucleation of the NCs, reshapes the NCs to monodisperse truncated cubes. Such NCs feature a mixed oleate/DDMA+ surface termination with PLQY values up to 90%. For group 1 cations, this happens only if the ammonium cation is directly added as a salt (DDMA-Br) while for group 2 cations this happens even if the corresponding tertiary amine (DDMA) is added, instead of DDMA-Br. This is attributed to the fact that only group 2 cations can facilitate the protonation of DDMA by the excess oleic acid present in the reaction environment. In all cases studied, the incorporation of M cations is marginal and the reshaping of the NCs is only transient: if the reactions are run for a long time the truncated cubes evolve to cubes. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Comments: 39 pages, 43 figures

Journal ref: Journal of the American Chemical Society 2024, 146, 20636-20648

Core@Shell AgBr@CsPbBr3 Nanocrystals as Precursors to Hollow Lead Halide Perovskite Nanocubes

Authors: Zhanzhao Li, Yurii P. Ivanov, Anna Cabona, Andrea Fratelli, Stefano Toso, Saptarshi Chakraborty, Giorgio Divitini, Ilka Kriegel, Sergio Brovelli, Liberato Manna

Abstract: We report the synthesis of colloidal core@shell AgBr@CsPbBr3 nanocubes by a one-pot approach, where the nucleation and growth of AgBr nanocrystals occurs rapidly after the injection of chemical precursors. This is immediately followed by the overgrowth of CsPbBr3, delivering AgBr@CsPbBr3 nanocubes of several tens of nanometers in size, with the volume of the AgBr core being only a small fraction o… ▽ More We report the synthesis of colloidal core@shell AgBr@CsPbBr3 nanocubes by a one-pot approach, where the nucleation and growth of AgBr nanocrystals occurs rapidly after the injection of chemical precursors. This is immediately followed by the overgrowth of CsPbBr3, delivering AgBr@CsPbBr3 nanocubes of several tens of nanometers in size, with the volume of the AgBr core being only a small fraction of the overall nanocrystal volume. The formation of a core@shell geometry is facilitated by the epitaxial compatibility between AgBr and CsPbBr3 along multiple crystallographic directions. Exchange with Cl-ions leads to Ag@CsPbCl3 nanocubes, whereas exchange with I-ions leads to hollow CsPbI3 nanocubes, due to selective etching of the AgBr (or Ag) core region by the I-ions diffusing in the nanocubes. These hollow CsPbI3 nanocubes can then be converted into hollow CsPbBr3 and CsPbCl3 nanocubes by halide exchange. The optical emission properties of the hollow CsPbX3 (X=Cl, Br, I) nanocubes are in line with those expected from large, non-hollow halide perovskite nanocrystals, indicating that the small hollow region in the cubes has no major influence on their optical properties. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Comments: 22 pages, 21 figures

Journal ref: Journal of the American Chemical Society 2025, 147, 23192-23201

Synthesis, Growth Mechanism, and Photocatalytic Properties of Metallic-Bi/Bi13S18Br2 Nano-Bell Heterostructures

Authors: Anna Cabona, Stefano Toso, Andrea Griesi, Martina Rizzo, Michele Ferri, Pascal Rusch, Giorgio Divitini, Julia Perez-Prieto, Raquel E. Galian, Ilka Kriegel, Liberato Manna

Abstract: We report the synthesis of bell-shaped Bi/Bi13S18Br2 metal/semiconductor heterostructures as a photocatalyst based on non-toxic and Earth-abundant elements. Their unique morphology arises from a multi-step growth process, involving 1) the nucleation of Bi13S18Br2 nanorods, 2) the reduction of a metallic-Bi domain on their surface induced by N,N-didodecylmethylamine, and 3) the heterostructure accr… ▽ More We report the synthesis of bell-shaped Bi/Bi13S18Br2 metal/semiconductor heterostructures as a photocatalyst based on non-toxic and Earth-abundant elements. Their unique morphology arises from a multi-step growth process, involving 1) the nucleation of Bi13S18Br2 nanorods, 2) the reduction of a metallic-Bi domain on their surface induced by N,N-didodecylmethylamine, and 3) the heterostructure accretion by a localized reaction at the Bi/Bi13S18Br2 interface promoted by Ostwald ripening. These heterostructures display remarkable stability in polar solvents, remaining almost unaffected by prolonged exposure to isopropanol and water, and exhibit high photocatalytic efficiency for the degradation of organic dyes (i.e., Rhodamine-B and Methylene Blue) under visible-light irradiation, with good recyclability. Additionally, preliminary tests demonstrate CO2 reduction capabilities, which make them promising for both the photocatalytic degradation of pollutants and photo-electro CO2 conversion. The straightforward synthesis process and the use of non-toxic and earth-abundant elements offers significant potential for sustainable energy conversion technologies. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Comments: 41 pages, 32 figures

Journal ref: ACS Materials Letters, 2025, 7, 1707-1716

Improving the Stability of Colloidal CsPbBr3 Nanocrystals with an Alkylphosphonium Bromide as Surface Ligand Pair

Authors: Meenakshi Pegu, Hossein Roshan, Clara Otero-Martinez, Luca Goldoni, Juliette Zito, Nikolaos Livakas, Pascal Rusch, Francesco De Boni, Francesco Di Stasio, Ivan Infante, Luca De Trizio, Liberato Manna

Abstract: In this study, we synthesised a phosphonium-based ligand, trimethyl(tetradecyl)phosphonium bromide (TTP-Br), and employed it in the post-synthesis surface treatment of Cs-oleate-capped CsPbBr3 NCs. The photoluminescence quantum yield (PLQY) of the NCs increased from 60% to more than 90%, as a consequence of replacing Cs-oleate with TTP-Br ligand pairs. Density functional theory calculations reveal… ▽ More In this study, we synthesised a phosphonium-based ligand, trimethyl(tetradecyl)phosphonium bromide (TTP-Br), and employed it in the post-synthesis surface treatment of Cs-oleate-capped CsPbBr3 NCs. The photoluminescence quantum yield (PLQY) of the NCs increased from 60% to more than 90%, as a consequence of replacing Cs-oleate with TTP-Br ligand pairs. Density functional theory calculations revealed that TTP+ ions bind to the NC surface by occupying Cs+ surface sites and orienting one of their P-CH3 bonds perpendicular to the surface, akin to quaternary ammonium passivation. Importantly, TTP-Br-capped NCs exhibited higher stability in air compared to didodecyldimethylammonium bromide-capped CsPbBr3 NCs (which is considered a benchmark system), retaining 90% of their PLQY after six weeks of air exposure. Light-emitting diodes fabricated with TTP-Br-capped NCs achieved a maximum external quantum efficiency of 17.2 %, demonstrating the potential of phosphonium-based molecules as surface ligands for CsPbBr3 NCs in optoelectronic applications. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Breaking the Boundaries of the Goldschmidt Tolerance Factor with Ethylammonium Lead Iodide Perovskite Nanocrystals

Authors: C. Meric Guvenc, Stefano Toso, Yurii P. Ivanov, Gabriele Saleh, Sinan Balci, Giorgio Divitini, Liberato Manna

Abstract: We report the synthesis of ethylammonium lead iodide (EAPbI3) colloidal nanocrystals as another member of the lead halide perovskites family. The insertion of an unusually large A-cation (274 pm in diameter) in the perovskite structure, hitherto considered unlikely due to the unfavorable Goldschmidt tolerance factor, results in a significantly larger lattice parameter compared to the Cs-, methylam… ▽ More We report the synthesis of ethylammonium lead iodide (EAPbI3) colloidal nanocrystals as another member of the lead halide perovskites family. The insertion of an unusually large A-cation (274 pm in diameter) in the perovskite structure, hitherto considered unlikely due to the unfavorable Goldschmidt tolerance factor, results in a significantly larger lattice parameter compared to the Cs-, methylammonium- and formamidinium-based lead halide perovskite homologues. As a consequence, EAPbI3 nanocrystals are highly unstable, evolving to a non-perovskite delta-EAPbI3 polymorph within one day. Also, EAPbI3 nanocrystals are very sensitive to electron irradiation and quickly degrade to PbI2 upon exposure to the electron beam, following a mechanism similar to that of other hybrid lead iodide perovskites (although degradation can be reduced by partially replacing the EA+ ions with Cs+ ions). Interestingly, in some cases during this degradation the formation of an epitaxial interface between (EAxCs1-x)PbI3 and PbI2 is observed. The photoluminescence emission of the EAPbI3 perovskite nanocrystals, albeit being characterized by a low quantum yield (around 1%), can be tuned in the 664-690 nm range by regulating their size during the synthesis. The emission efficiency can be improved upon partial alloying at the A site with Cs+ or formamidinium cations. Furthermore, the morphology of the EAPbI3 nanocrystals can be chosen to be either nanocube or nanoplatelet, depending on the synthesis conditions. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Comments: 44 pages, 22 Figures

Journal ref: ACS Nano 2025, 19, 1, 1557-1565

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications

Authors: Ying Liu, Francesco Di Stasio, Chenghao Bi, Jibin Zhang, Zhiguo Xia, Zhifeng Shi, Liberato Manna

Abstract: Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability and adjustable optical properties. NIR emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) over 20% and a device stability of over 10,000 h. Such resul… ▽ More Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability and adjustable optical properties. NIR emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, we summarize several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, and assess their recent advancements. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. We also highlight the various applications of NIR-emitting metal halides and provide an outlook for the field. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Comments: 53 pages, 10 figures

Journal ref: Advanced Materials, 2024, 2312482

Light-Emitting Diodes based on Metal Halide Perovskite and Perovskite Related Nanocrystals

Authors: Ying Liu, Zhuangzhuang Ma, Jibin Zhang, Yanni He, Jinfei Dai, Xinjian Li, Zhifeng Shi, Liberato Manna

Abstract: Light-emitting diodes (LEDs) based on halide perovskite nanocrystals have attracted extensive attention due to their considerable luminescence efficiency, wide color gamut, high color purity, and facile material synthesis. Since the first demonstration of LEDs based on MAPbBr3 nanocrystals were reported in 2014, the community has witnessed a rapid development in their performances. In this review,… ▽ More Light-emitting diodes (LEDs) based on halide perovskite nanocrystals have attracted extensive attention due to their considerable luminescence efficiency, wide color gamut, high color purity, and facile material synthesis. Since the first demonstration of LEDs based on MAPbBr3 nanocrystals were reported in 2014, the community has witnessed a rapid development in their performances. In this review, we provide a historical perspective of the development of LEDs based on halide perovskite nanocrystals and then present a comprehensive survey of current strategies to high-efficiency lead-based perovskite nanocrystals LEDs, including synthesis optimization, ion doping/alloying and shell coating. We then review the basic characteristics and emission mechanisms of lead-free perovskite and perovskite-related nanocrystals emitters in environmentally friendly LEDs, from the standpoint of different emission colors. Finally, we cover the progress in LED applications and provide an outlook of the opportunities and challenges for future developments in this field. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Comments: 95 pages, 15 figures

Journal ref: Advanced Materials 2025, 2415606

Halide Perovskite-Chalcohalide Nanocrystal Heterostructures as a Platform for the Synthesis and Investigation of the CsPbCl3-CsPbI3 Epitaxial Interface

Authors: Nikolaos Livakas, Irina Skvortsova, Juliette Zito, Yurii P. Ivanov, Aswin Asaithambi, Andrea Toma, Annick De Backer, Muhammad Imran, Sandra Van Aert, Giorgio Divitini, Ivan Infante, Sara Bals, Liberato Manna

Abstract: Halide exchange in lead-based halide perovskites has been studied extensively. While mixed Cl-Br or Br-I alloy compositions can be formed with no miscibility gaps, this is precluded for mixed Cl-I compositions, due to the large difference in Cl and I ionic radii. Here, we exploit perovskite-chalcohalide CsPbCl3-Pb4S3Cl2 heterostructures to study the Cl-I exchange and isolate new types of intermedi… ▽ More Halide exchange in lead-based halide perovskites has been studied extensively. While mixed Cl-Br or Br-I alloy compositions can be formed with no miscibility gaps, this is precluded for mixed Cl-I compositions, due to the large difference in Cl and I ionic radii. Here, we exploit perovskite-chalcohalide CsPbCl3-Pb4S3Cl2 heterostructures to study the Cl-I exchange and isolate new types of intermediate structures. The epitaxial interface between the Pb4S3Cl2 chalcohalide and the CsPbCl3 perovskite domain significantly influences the intermediate stages of halide exchange in the perovskite domain, leading to coexisting CsPbCl3 and CsPbI3 domains, thereby delivering segmented CsPbI3-CsPbCl3-Pb4S3Cl2 energetically favorable heterostructures, with partial iodide alloying of the CsPbCl3 domain and at the perovskite-chalcohalide interface. The I:CsPbCl3 domain between CsPbI3 and Pb4S3Cl2 enables a gradual lattice expansion across the heterostructure. This design accommodates interfacial strain, with a 5.6% mismatch at the CsPbCl3-CsPbI3 interface and a 3.4% mismatch at the perovskite-chalcohalide interface. Full halide exchange leads to CsPbI3-Pb4S3Cl2 heterostructures. Both in intermediate and fully exchanged heterostructures, the CsPbI3 domain is emissive. In the intermediate structures, the band alignment between the two perovskite domains is type-I, with carriers photogenerated in the CsPbCl3 domain quickly transferring to the CsPbI3 domain, where they can recombine radiatively. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Nanocrystals Heterostructures based on Halide Perovskites and Metal Sulfides

Authors: Nikolaos Livakas, Juliette Zito, Yurii P. Ivanov, Clara Otero Martínez, Giorgio Divitini, Ivan Infante, Liberato Manna

Abstract: We report the synthesis of nanocrystal heterostructures composed of CsPbCl3 and PbS domains sharing an epitaxial interface. We were able to promote the growth of a PbS domain (in competition with the more commonly observed Pb4S3Cl2 one) on top of the CsPbCl3 domain by employing Mn2$^+$ ions, the latter acting most likely as scavengers of Cl$^-$ ions. Complete suppression of the Pb4S3Cl2 domain gro… ▽ More We report the synthesis of nanocrystal heterostructures composed of CsPbCl3 and PbS domains sharing an epitaxial interface. We were able to promote the growth of a PbS domain (in competition with the more commonly observed Pb4S3Cl2 one) on top of the CsPbCl3 domain by employing Mn2$^+$ ions, the latter acting most likely as scavengers of Cl$^-$ ions. Complete suppression of the Pb4S3Cl2 domain growth was then achieved by additionally selecting an appropriate sulfur source (bis(trimethylsilyl)sulfide, which also acted as scavenger of Cl$^-$ ions), and reaction temperature. In the heterostructures, emission from the perovskite domain was quenched, while emission from the PbS domain was observed, pointing to a type-I band alignment, as confirmed by calculations. These heterostructures in turn could be exploited to prepare second-generation heterostructures through selective ion exchange on the individual domains (halide ion exchange on CsPbCl3, cation exchange on PbS). We demonstrate the cases of Cl$^-$ to Br$^-$ and Pb2$^+$ to Cu$^+$ exchanges, which deliver CsPbBr3@PbS and CsPbCl3@Cu2-xS epitaxial heterostructures, respectively. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Sinusoidal Displacement Describes Disorder in CsPbBr3 Nanocrystal Superlattices

Authors: Umberto Filippi, Stefano Toso, Matheus G. Ferreira, Lorenzo Tallarini, Yurii P. Ivanov, Francesco Scattarella, Vahid Haghighat, Huaiyu Chen, Megan O. Hill Landberg, Giorgio Divitini, Jesper Wallentin, Cinzia Giannini, Liberato Manna, Dmitry Baranov

Abstract: Disorder is an intrinsic feature of all solids, from crystals of atoms to superlattices of colloidal nanoparticles. Unlike atomic crystals, in nanocrystal superlattices a single misplaced particle can affect the positions of neighbors over long distances, leading to cumulative disorder. This elusive form of collective particle displacement leaves clear signatures in diffraction, but little is know… ▽ More Disorder is an intrinsic feature of all solids, from crystals of atoms to superlattices of colloidal nanoparticles. Unlike atomic crystals, in nanocrystal superlattices a single misplaced particle can affect the positions of neighbors over long distances, leading to cumulative disorder. This elusive form of collective particle displacement leaves clear signatures in diffraction, but little is known about how it accumulates and propagates throughout the superlattice. Here we rationalize propagation and accumulation of disorder in a series of CsPbBr3 nanocrystal superlattices by using synchrotron grazing incidence small- and wide-angle X-ray scattering. CsPbBr3 nanocrystals of colloidal softness S in the range of 0.3-0.7 were obtained by preparing particles with different sizes and ligand mixtures, consisting of oleic acid and primary amines of variable lengths. Most diffraction patterns showed clear signatures of anisotropic disorder, with multilayer diffraction characteristics of high structural coherence visible only for the {100} axial directions and lost in all other directions. As the softness decreased, the superlattices transitioned to a more ordered regime where small-angle diffraction peaks became resolution-limited, and superlattice multilayer diffraction appeared for the (110) diagonal reflections. To rationalize these anisotropies in structural coherence and their dependence on superlattice softness, we propose a sinusoidal displacement model where longitudinal and transverse displacements modulate nanocrystal positions. The model explains experimental observations and advances the understanding of disorder in mesocrystalline systems as they approach the limits of structural perfection. △ Less

Submitted 13 September, 2025; originally announced September 2025.

Journal ref: ACS Nano, 2026

Investigating the convergence properties of iterative ptychography for atomic-resolution low-dose imaging

Authors: Tamazouzt Chennit, Songge Li, Hoelen L. Lalandec Robert, Christoph Hofer, Nadine J. Schrenker, Liberato Manna, Sara Bals, Timothy J. Pennycook, Jo Verbeeck

Abstract: This study investigates the convergence properties of a collection of iterative electron ptychography methods, under low electron doses ($<$ 10$^3$ $e^-/A^2$) and gives particular attention to the impact of the user-defined update strengths. We demonstrate that carefully chosen values for this parameter, ideally smaller than those conventionally met in the literature, are essential for achieving a… ▽ More This study investigates the convergence properties of a collection of iterative electron ptychography methods, under low electron doses ($<$ 10$^3$ $e^-/A^2$) and gives particular attention to the impact of the user-defined update strengths. We demonstrate that carefully chosen values for this parameter, ideally smaller than those conventionally met in the literature, are essential for achieving accurate reconstructions of the projected electrostatic potential. Using a 4D dataset of a thin hybrid organic-inorganic formamidinium lead bromide (FAPbBr$_{3}$) sample, we show that convergence is in practice achievable only when the update strengths for both the object and probe are relatively small compared to what is found in literature. Additionally we demonstrate that under low electron doses, the reconstructions initial error increases when the update strength coefficients are reduced below a certain threshold emphasizing the existence of critical values beyond which the algorithms are trapped in local minima. These findings highlight the need for carefully optimized reconstruction parameters in iterative ptychography, especially when working with low electron doses, ensuring both effective convergence and correctness of the result. △ Less

Submitted 26 September, 2025; v1 submitted 9 July, 2025; originally announced July 2025.

Ultrafast Superradiant Scintillation from Weakly Confined CsPbBr3 Nanocrystals

Authors: Matteo L. Zaffalon, Andrea Fratelli, Zhanzhao Li, Francesco Bruni, Ihor Cherniukh, Francesco Carulli, Francesco Meinardi, Maksym V. Kovalenko, Liberato Manna, Sergio Brovelli

Abstract: Efficiency and emission rate are two traditionally conflicting parameters in radiation detection, and achieving their simultaneous maximization could significantly advance ultrafast time-of-flight (ToF) technologies. In this study, we demonstrate that this goal is attainable by harnessing the giant oscillator strength (GOS) inherent to weakly confined perovskite nanocrystals, which enables superra… ▽ More Efficiency and emission rate are two traditionally conflicting parameters in radiation detection, and achieving their simultaneous maximization could significantly advance ultrafast time-of-flight (ToF) technologies. In this study, we demonstrate that this goal is attainable by harnessing the giant oscillator strength (GOS) inherent to weakly confined perovskite nanocrystals, which enables superradiant scintillation under mildly cryogenic conditions that align seamlessly with ToF technologies. We show that the radiative acceleration due to GOS encompasses both single and multiple exciton dynamics arising from ionizing interactions, further enhanced by suppressed non-radiative losses and Auger recombination at 80 K. The outcome is ultrafast scintillation with 420 ps lifetime and light yield of ~10'000 photons/MeV for diluted NC solutions, all without non-radiative losses. Temperature-dependent light-guiding experiments on test-bed nanocomposite scintillators finally indicate that the light-transport capability remains unaffected by the accumulation of band-edge oscillator strength due to GOS. These findings suggest a promising pathway toward developing ultrafast nanotech scintillators with optimized light output and timing performance. △ Less

Submitted 7 December, 2024; v1 submitted 3 December, 2024; originally announced December 2024.

Size-dependent multiexciton dynamics governs scintillation from perovskite quantum dots

Authors: Andrea Fratelli, Matteo L. Zaffalon, Emanuele Mazzola, Dmitry Dirin, Ihor Cherniukh, Clara Otero Martinez, Matteo Salomoni, Francesco Carulli, Francesco Meinardi, Luca Gironi, Liberato Manna, Maksym V. Kovalenko, Sergio Brovelli

Abstract: The recent emergence of quantum confined nanomaterials in the field of radiation detection, in particular lead halide perovskite nanocrystals, offers potentially revolutionary scalability and performance advantages over conventional materials. This development raises fundamental questions about the mechanism of scintillation itself at the nanoscale and the role of particle size, arguably the most… ▽ More The recent emergence of quantum confined nanomaterials in the field of radiation detection, in particular lead halide perovskite nanocrystals, offers potentially revolutionary scalability and performance advantages over conventional materials. This development raises fundamental questions about the mechanism of scintillation itself at the nanoscale and the role of particle size, arguably the most defining parameter of quantum dots. Understanding this is crucial for the design and optimisation of future nanotechnology scintillators. In this work, we address these open questions by theoretically and experimentally studying the size-dependent scintillation of CsPbBr3 nanocrystals using a combination of Monte Carlo simulations, spectroscopic, and radiometric techniques. The results reveal and unravel a complex parametric space where the fine balance between the simultaneous effects of size-dependent energy deposition, (multi-)exciton population, and light emission under ionizing excitation, typical of confined particles, combine to maximize the scintillation efficiency and time performance of larger nanocrystals due to greater stopping power and reduced Auger decay. The remarkable agreement between theory and experiment produces a fully validated descriptive model that unprecedentedly predicts the scintillation yield and kinetics of nanocrystals without free parameters, providing the first fundamental guide for the rational design of nanoscale scintillators. △ Less

Submitted 25 September, 2024; originally announced September 2024.

Ultrasmall CsPbBr3 Blue Emissive Perovskite Quantum Dots using K-alloyed Cs4PbBr6 Nanocrystals as Precursors

Authors: Clara Otero Martinez, Matteo L. Zaffalon, Yurii Ivanov, Nikolaos Livakas, Luca Goldoni, Giorgio Divitini, Sankalpa Bora, Gabriele Saleh, Francesco Meinardi, Andrea Fratelli, Sudip Chakraborty, Lakshminarayana Polavarapu, Sergio Brovelli, Liberato Manna

Abstract: We report a colloidal synthesis of blue emissive, stable cube-shaped CsPbBr3 quantum dots (QDs) in the strong quantum confinement regime via a dissolution-recrystallization starting from pre-synthesized (KxCs1-x)4PbBr6 nanocrystals which are then reacted with PbBr2. This is markedly different from the known case of Cs4PbBr6 nanocrystals that react within seconds with PbBr2 and get transformed into… ▽ More We report a colloidal synthesis of blue emissive, stable cube-shaped CsPbBr3 quantum dots (QDs) in the strong quantum confinement regime via a dissolution-recrystallization starting from pre-synthesized (KxCs1-x)4PbBr6 nanocrystals which are then reacted with PbBr2. This is markedly different from the known case of Cs4PbBr6 nanocrystals that react within seconds with PbBr2 and get transformed into much larger, green emitting CsPbBr3 nanocrystals. Here, instead, the conversion of (KxCs1-x)4PbBr6 nanocrystals to CsPbBr3 QDs occurs in a time span of hours, and tuning of the QDs size is achieved by adjusting the concentration of precursors. The QDs exhibit excitonic features in optical absorption that are tunable in the 420 - 452 nm range, accompanied by blue photoluminescence with quantum yield around 60%. Detailed spectroscopic investigations in both the single and multi-exciton regime reveal the exciton fine structure and the effect of Auger recombination of these CsPbBr3 QDs, confirming theoretical predictions for this system. △ Less

Submitted 18 June, 2024; originally announced June 2024.

Journal ref: ACS Energy Letters 2024

Exciton-photocarrier interference in mixed lead-halide-perovskite nanocrystals

Authors: Esteban Rojas-Gatjens, Quinten A. Akkerman, Liberato Manna, Ajay Ram Srimath Kandada, Carlos Silva-Acuña

Abstract: The use of semiconductor nanocrystals in scalable quantum technologies requires characterization of the exciton coherence dynamics in an \emph{ensemble} of electronically isolated crystals in which system-bath interactions are nevertheless strong. In this communication, we identify signatures of Fano-like interference between excitons and photocarriers in the coherent two-dimensional photoluminesc… ▽ More The use of semiconductor nanocrystals in scalable quantum technologies requires characterization of the exciton coherence dynamics in an \emph{ensemble} of electronically isolated crystals in which system-bath interactions are nevertheless strong. In this communication, we identify signatures of Fano-like interference between excitons and photocarriers in the coherent two-dimensional photoluminescence excitation spectral lineshapes of mixed lead-halide perovskite nanocrystals in dilute solution. Specifically, by tuning the femtosecond-pulse spectrum, we show such interference in an intermediate coupling regime, which is evident in the coherent lineshape when simultaneously exciting the exciton and the free-carrier band at higher energy. We conclude that this interference is an intrinsic effect that will be consequential in the quantum dynamics of the system and will thus dictate decoherence dynamics, with consequences in their application in quantum technologies. △ Less

Submitted 6 May, 2024; v1 submitted 18 February, 2024; originally announced February 2024.

Comments: Submitted to The Journal of Chemical Physics. The Supplemental Materials document SI.pdf can be downloaded from the Tex Source link

Journal ref: J. Chem. Phys. 160, 221101 (2024)

The fate of optical excitons in FAPbI3 nanocube superlattices

Authors: Alessandra Milloch, Umberto Filippi, Paolo Franceschini, Selene Mor, Stefania Pagliara, Gabriele Ferrini, Franco V. A. Camargo, Giulio Cerullo, Dmitry Baranov, Liberato Manna, Claudio Giannetti

Abstract: Understanding the nature of the photoexcitation and ultrafast charge dynamics pathways in organic halide perovskite nanocubes and their aggregation into superlattices is key for the potential applications as tunable light emitters, photon harvesting materials and light-amplification systems. In this work, we apply two-dimensional coherent electronic spectroscopy (2DES) to track in real time the fo… ▽ More Understanding the nature of the photoexcitation and ultrafast charge dynamics pathways in organic halide perovskite nanocubes and their aggregation into superlattices is key for the potential applications as tunable light emitters, photon harvesting materials and light-amplification systems. In this work, we apply two-dimensional coherent electronic spectroscopy (2DES) to track in real time the formation of near-infrared optical excitons and their ultrafast relaxation in CH(NH2)2PbI3 nanocube superlattices. Our results unveil that the coherent ultrafast dynamics is limited by the combination of the inherent short exciton decay time ~40 fs and the dephasing due to the coupling with selective optical phonon modes at higher temperatures. On the picosecond timescale, we observe the progressive formation of long-lived localized trap states. The analysis of the temperature dependence of the excitonic intrinsic linewidth, as extracted by the anti-diagonal components of the 2D spectra, unveils a dramatic change of the excitonic coherence time across the cubic to tetragonal structural transition. Our results offer a new way to control and enhance the ultrafast coherent dynamics of photocarrier generation in hybrid halide perovskite synthetic solids. △ Less

Submitted 19 July, 2024; v1 submitted 30 January, 2024; originally announced January 2024.

Journal ref: ACS Photonics 2024, 11, 3511-3520

Halide perovskite artificial solids as a new platform to simulate collective phenomena in doped Mott insulators

Authors: Alessandra Milloch, Umberto Filippi, Paolo Franceschini, Michele Galvani, Selene Mor, Stefania Pagliara, Gabriele Ferrini, Francesco Banfi, Massimo Capone, Dmitry Baranov, Liberato Manna, Claudio Giannetti

Abstract: The development of Quantum Simulators, artificial platforms where the predictions of many-body theories of correlated quantum materials can be tested in a controllable and tunable way, is one of the main challenges of condensed matter physics. Here we introduce artificial lattices made of lead halide perovskite nanocubes as a new platform to simulate and investigate the physics of correlated quant… ▽ More The development of Quantum Simulators, artificial platforms where the predictions of many-body theories of correlated quantum materials can be tested in a controllable and tunable way, is one of the main challenges of condensed matter physics. Here we introduce artificial lattices made of lead halide perovskite nanocubes as a new platform to simulate and investigate the physics of correlated quantum materials. The ultrafast optical injection of quantum confined excitons plays the role of doping in real materials. We show that, at large photo-doping, the exciton gas undergoes an excitonic Mott transition, which fully realizes the magnetic-field-driven insulator-to-metal transition described by the Hubbard model. At lower photo-doping, the long-range interactions drive the formation of a collective superradiant state, in which the phases of the excitons generated in each single perovskite nanocube are coherently locked. Our results demonstrate that time-resolved experiments span a parameter region of the Hubbard model in which long-range and phase-coherent orders emerge out of a doped Mott insulating phase. This physics is relevant for a broad class of phenomena, such as superconductivity and charge-density waves in correlated materials whose properties are captured by doped Hubbard models. △ Less

Submitted 15 March, 2023; originally announced March 2023.

Journal ref: Nano Lett. 2023, 23, 22, 10617-10624

Control of electronic band profiles through depletion layer engineering in core-shell nanocrystals

Authors: Michele Ghini, Nicola Curreli, Matteo B. Lodi, Nicolò Petrini, Mengjiao Wang, Mirko Prato, Alessandro Fanti, Liberato Manna, Ilka Kriegel

Abstract: The understanding of depletion layers is of major importance to control the optical and electronic properties of metal oxide (MO) nanocrystals (NCs). Here, we show that depletion layer engineering is the main mechanism of photodoping of MO NCs. We show that the introduction of different electronic interfaces induces a double-bending of the electronic bands and a distinct carrier density profile. W… ▽ More The understanding of depletion layers is of major importance to control the optical and electronic properties of metal oxide (MO) nanocrystals (NCs). Here, we show that depletion layer engineering is the main mechanism of photodoping of MO NCs. We show that the introduction of different electronic interfaces induces a double-bending of the electronic bands and a distinct carrier density profile. We found that the light-induced depletion layer modulation and bending of the bands close to the surface of the nanocrystal is the main mechanism responsible for the storage of extra electrons after photodoping in MO NCs. We support our results by a combined experimental and theoretical approach in the case of Sn:In2O3/In2O3 core-shell NCs, in which we compare numerical simulations with empirical modeling and experiments. This allows not only to extract the main mechanism of photodoping in MO NCs but also to engineer the charge storage capability of MO NCs after photodoping. Our results are transferable to other core-multishell systems, opening up a novel direction to control the optoelectronic properties of nanoscale MOs by designing their energetic band profiles through depletion layer engineering. △ Less

Submitted 28 August, 2021; originally announced August 2021.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications and Their Optical Properties

Authors: Javad Shamsi, Alexander S. Urban, Muhammad Imran, Luca De Trizio, Liberato Manna

Abstract: Metal halide perovskites represent a flourishing area of research, driven by both their potential application in photo-voltaics and optoelectronics, and for the fundamental science underpinning their unique optoelectronic properties. The advent of colloidal methods for the synthesis of halide perovskite nanocrystals has brought to the attention inter-esting aspects of this new type of materials, a… ▽ More Metal halide perovskites represent a flourishing area of research, driven by both their potential application in photo-voltaics and optoelectronics, and for the fundamental science underpinning their unique optoelectronic properties. The advent of colloidal methods for the synthesis of halide perovskite nanocrystals has brought to the attention inter-esting aspects of this new type of materials, above all their defect-tolerance. This review aims to provide an updated survey of this fast-moving field, with a main focus on their colloidal synthesis. We examine the chemistry and the ca-pability of different colloidal synthetic routes to control the shape, size and optical properties of the resulting nano-crystals. We also provide an up to date overview of their post-synthesis transformations, and summarize the various so-lution processes aimed at fabricating halide perovskite-based nanocomposites. We then review the fundamental optical properties of halide perovskite nanocrystals, by focusing on their linear optical properties, on the effects of quantum confinement and, then, on the current knowledge of their exciton binding energies. We also discuss the emergence of non-linear phenomena such as multiphoton absorption, biexcitons and carrier multiplication. At last, we provide an outlook in the field, with the most cogent open questions and possible future directions. △ Less

Submitted 28 October, 2020; originally announced October 2020.

Temporal Evolution of Self-Assembled Lead Halide Perovskite Nanocrystal Superlattices: Effects on Photoluminescence and Energy Transfer

Authors: Dmitry Baranov, Antonio Fieramosca, Ruo Xi Yang, Laura Polimeno, Giovanni Lerario, Stefano Toso, Carlo Giansante, Milena De Giorgi, Liang Z. Tan, Daniele Sanvitto, Liberato Manna

Abstract: Excitonic/electronic coupling and cooperative interactions in self-assembled lead halide perovskite nanocrystals were reported to give rise to a collective low energy emission peak with accelerated dynamics. Here we report that similar spectroscopic features could appear as a result of the nanocrystal reactivity within the self-assembled superlattices. This is demonstrated by using CsPbBr3 nanocry… ▽ More Excitonic/electronic coupling and cooperative interactions in self-assembled lead halide perovskite nanocrystals were reported to give rise to a collective low energy emission peak with accelerated dynamics. Here we report that similar spectroscopic features could appear as a result of the nanocrystal reactivity within the self-assembled superlattices. This is demonstrated by using CsPbBr3 nanocrystal superlattices under room temperature and cryogenic micro-photoluminescence spectroscopy. It is shown that keeping such structures under vacuum, a gradual contraction of the superlattices and subsequent coalescence of the nanocrystals occurs over several days. As a result, a narrow, low energy emission peak is observed at 4 K with a concomitant shortening of the photoluminescence lifetime due to the energy transfer between nanocrystals. When exposed to air, self-assembled CsPbBr3 nanocrystals develop bulk-like CsPbBr3 particles on top of the superlattices. At 4 K, these particles produce a distribution of narrow, low energy emission peaks with short lifetimes and excitation fluence-dependent, oscillatory decays, resembling the features of superfluorescence. Overall, the reactivity of CsPbBr3 nanocrystals dramatically alters the emission of their assemblies, which should not be overlooked when studying collective optoelectronic properties nor confused with superfluorescence effects. △ Less

Submitted 6 August, 2020; originally announced August 2020.

Comments: 50 pages, 26 figures

Journal ref: ACS Nano 2021, 15, 1, 650-664

Bandgap in orthorhombic thin lead halide perovskite (CsPbBr3) nanosheets measured from STEM-EELS

Authors: Rosaria Brescia, Stefano Toso, Quentin Ramasse, Liberato Manna, Clive Downing, Arrigo Calzolari, Giovanni Bertoni

Abstract: Inorganic lead halide perovskites are promising candidates for optoelectronic applications, due to their bandgap tunability, high photoluminescence quantum yield, and narrow emission line widths. In particular, they offer the possibility to vary the bandgap as a function of the halide composition and dimension/shape of the crystals at the nanoscale. Here we present an aberration-corrected scanning… ▽ More Inorganic lead halide perovskites are promising candidates for optoelectronic applications, due to their bandgap tunability, high photoluminescence quantum yield, and narrow emission line widths. In particular, they offer the possibility to vary the bandgap as a function of the halide composition and dimension/shape of the crystals at the nanoscale. Here we present an aberration-corrected scanning transmission microscopy (STEM) study of extended nanosheets of CsPbBr3 directly demonstrating their orthorhombic crystal structure and their lateral termination with Cs-Br planes. The bandgaps from individual nanosheets are measured by monochromated electron energy loss spectroscopy (EELS). We find an increase of the bandgap starting at thicknesses below 10 nm, confirming the less dramatic effect of 1D confinement in nanosheets compared to the 3D confinement observed in quantum dots, as predicted by density functional theory calculations and optical spectroscopy data from ensemble measurements. △ Less

Submitted 31 July, 2020; originally announced July 2020.

Journal ref: Nanoscale Horizons 2020

Directional Anisotropy of the Vibrational Modes in 2D Layered Perovskites

Authors: Balaji Dhanabalan, Yu-Chen Leng, Giulia Biffi, Miao-Ling Lin, Ping-Heng Tan, Ivan Infante, Liberato Manna, Milena P. Arciniegas, Roman Krahne

Abstract: The vibrational modes in organic/inorganic layered perovskites are of fundamental importance for their optoelectronic properties. The hierarchical architecture of the Ruddlesden-Popper phase of these materials allows for distinct directionality of the vibrational modes withrespect to the main axes of the pseudocubic lattice in the octahedral plane. Here, we study the directionality of the fundamen… ▽ More The vibrational modes in organic/inorganic layered perovskites are of fundamental importance for their optoelectronic properties. The hierarchical architecture of the Ruddlesden-Popper phase of these materials allows for distinct directionality of the vibrational modes withrespect to the main axes of the pseudocubic lattice in the octahedral plane. Here, we study the directionality of the fundamental phonon modes in single exfoliated Ruddlesden-Popper perovskite flakes with polarized Raman spectroscopy at ultralow-frequencies. A wealth of Raman bands is distinguished in the range from 15-150 cm-1 (2-15 meV), whose features depend on the organic cation species, on temperature, and on the direction of the linear polarization of the incident light. By controlling the angle of the linear polarization of the excitation laser with respect to the in-plane axes of the octahedral layer, we gain detailed information on the symmetry of the vibrational modes. The choice of two different organic moieties, phenethylammonium (PEA) and butylammonium (BA) allows to discern the influence of the linker molecules, evidencing strong anisotropy of the vibrations for the (PEA)2PbBr4 samples. Temperature dependent Raman measurements reveal that the broad phonon bands observed at room temperature consist of a series of sharp modes, and that such mode splitting strongly differs for the different organic moieties and vibrational bands. △ Less

Submitted 17 April, 2020; originally announced April 2020.

Comments: 25 pages, 4 figures

Journal ref: ACS Publications 2020

Octapod-shaped CdSe nanocrystals hosting Pt with high-mass activity for the hydrogen evolution reaction

Authors: Leyla Najafi, Sebastiano Bellani, Andrea Castelli, Milena P. Arciniegas, Rosaria Brescia, Reinier Oropesa-Nuñez, Beatriz Martín-García, Michele Serri, Filippo Drago, Liberato Manna, Francesco Bonaccorso

Abstract: The design of efficient electrocatalysts for electrochemical water splitting with minimal amount of precious metal is crucial to attain renewable and sustainable energy conversion. Here, we report the use of a network of CdSe branched colloidal nanocrystals, made of a CdSe core and eight CdSe pods (so-called octapods), able to host on their pods Pt particles, and thus catalyzing water splitting re… ▽ More The design of efficient electrocatalysts for electrochemical water splitting with minimal amount of precious metal is crucial to attain renewable and sustainable energy conversion. Here, we report the use of a network of CdSe branched colloidal nanocrystals, made of a CdSe core and eight CdSe pods (so-called octapods), able to host on their pods Pt particles, and thus catalyzing water splitting reactions. Thanks to the octapod shape, the resulting Pt-hosting network is mechanically trapped onto carbon nanotube buckypaper, providing mechanically flexible and binder-free electrodes. We found that such hierarchical configuration maximizes the mass activity and the utilization efficiency of Pt for the hydrogen evolution reaction (HER). At a potential of -0.15 V vs. reversible hydrogen electrode, the Pt/octapod network-based electrodes display a Pt mass activity on the HER of 166 A mg-1 and 42 A mg-1 in acidic and alkaline media, respectively. These values correspond to turnover frequencies of 168 s-1 and 42 s-1, respectively, which are in that order 14 and 21 times higher compared to commercially available Pt/C benchmarks. The strong chemical and mechanical interactions between the Pt and the octapod surface, along with pod-aided adhesion of the Pt/octapod network to the buckypaper, result in a long-term durability (>20 h) of the HER-activity in both media. These results experimentally prove that the exploitation of our network of branched nanocrystals hosting Pt particles can circumvent the durability issues of the catalysts while adopting either ultralow Pt loadings or benchmarking carbon-supported Pt nanocrystals. Our work opens up prospects for using porous networks made by branched nanocrystals as catalysts with ultralow amount of noble metals and controlled catalytic properties. △ Less

Submitted 17 March, 2020; originally announced March 2020.

Journal ref: Chemistry of Materials, 2020

Imaging localized plasmon resonances in vacancy doped Cu3-xP semiconductor nanocrystals with STEM-EELS

Authors: Giovanni Bertoni, Rosaria Brescia, Luca De Trizio, Liberato Manna, Quentin Ramasse

Abstract: Copper binary compounds are often intrinsic p-type semiconductors due to the presence of Cu(I) vacancies, with corresponding hole carriers in the valence band. If the free carrier concentration is high enough, localized plasmon resonances can be sustained in nanocrystals, with frequencies in the infra-red (<1 eV), with respect to the typical resonances seen in the visible range in the case of meta… ▽ More Copper binary compounds are often intrinsic p-type semiconductors due to the presence of Cu(I) vacancies, with corresponding hole carriers in the valence band. If the free carrier concentration is high enough, localized plasmon resonances can be sustained in nanocrystals, with frequencies in the infra-red (<1 eV), with respect to the typical resonances seen in the visible range in the case of metals (Ag, Au, ...). The localization of the resonances can be demonstrated with scanning transmission electron energy loss spectroscopy (STEM-EELS) by combining high spatial and high energy resolutions. Here we demonstrate that Cu(I) vacancies can be directly measured from the STEM images in Cu(3-x)P hexagonal nanocrystals. Two localized resonances can be seen from STEM-EELS, which are in agreement with the resonances calculated from the vacancy concentration obtained from the STEM. △ Less

Submitted 12 July, 2019; originally announced July 2019.

Comments: 10 pages, 3 figures

Journal ref: ACS Materials Letters 2019

Ultrafast THz probe of photo-induced polarons in lead-halide perovskites

Authors: Eugenio Cinquanta, Daniele Meggiolaro, Silvia G. Motti, Marina Gandini, Marcelo J. P. Alcocer, Quinten Adriaan Akkerman, Caterina Vozzi, Liberato Manna, Filippo De Angelis, Annamaria Petrozza, Salvatore Stagira

Abstract: We study the nature of photo-excited charge carriers in CsPbBr3 nanocrystal thin films by ultrafast optical pump - THz probe spectroscopy. We observe a deviation from a pure Drude dispersion of the THz dielectric response that is ascribed to the polaronic nature of carriers; a transient blueshift of observed phonon frequencies is indicative of the coupling between photogenerated charges and stretc… ▽ More We study the nature of photo-excited charge carriers in CsPbBr3 nanocrystal thin films by ultrafast optical pump - THz probe spectroscopy. We observe a deviation from a pure Drude dispersion of the THz dielectric response that is ascribed to the polaronic nature of carriers; a transient blueshift of observed phonon frequencies is indicative of the coupling between photogenerated charges and stretching-bending modes of the deformed inorganic sublattice, as confirmed by DFT calculations. △ Less

Submitted 12 December, 2018; originally announced December 2018.

Journal ref: Phys. Rev. Lett. 122, 166601 (2019)

Broadband Defects Emission and Enhanced Ligand Raman Scattering in 0D Cs3Bi2I9 Colloidal Nanocrystals

Authors: Giuseppe M. Paterno', Nimai Mishra, Alex J. Barker, Zhiya Dang, Guglielmo Lanzani, Liberato Manna, Annamaria Petrozza

Abstract: Excitonic 0D and 2D lead-halide perovskites have been recently developed and investigated as new materials for light generation. Here we report broadband (> 1 eV) emission from newly synthesised zero-dimensional (0D) lead-free colloidal Cs3Bi2I9 nanocrystals. We investigate the nature of their emissive states as well as the relative dynamics which are currently hotly debated. In particular, we fin… ▽ More Excitonic 0D and 2D lead-halide perovskites have been recently developed and investigated as new materials for light generation. Here we report broadband (> 1 eV) emission from newly synthesised zero-dimensional (0D) lead-free colloidal Cs3Bi2I9 nanocrystals. We investigate the nature of their emissive states as well as the relative dynamics which are currently hotly debated. In particular, we find that the broadband emission is made by the coexistence of emissive excitons and sub-bandgap emissive trap-states. Remarkably, we observe evidence of enhanced Raman scattering from the ligands when attached to the nanocrystals surface, an effect that we preliminary attribute to strong exciton-ligands electronic coupling in these systems. △ Less

Submitted 19 November, 2018; originally announced November 2018.

Contactless photo-induced carrier density control in nanocrystal MoS2 hybrids

Authors: Ilka Kriegel, Nicholas J. Borys, Kehao Zhang, Adam W. Jansons, Brandon M. Crockett, Kristopher M. Koskela, Edward S. Barnard, Erika Penzo, James E. Hutchison, Joshua A. Robinson, Liberato Manna, P. James Schuck

Abstract: The ultrathin nature of two-dimensional monolayer semiconductors yields optoelectronic properties which are highly responsive to changes in free-carrier density, making it imperative to masterfully control their doping levels. We report a new photo-doping scheme that quasi-permanently dopes the monolayer MoS2 to extents competing with electrostatic gating. The photo-doping is achieved by coupling… ▽ More The ultrathin nature of two-dimensional monolayer semiconductors yields optoelectronic properties which are highly responsive to changes in free-carrier density, making it imperative to masterfully control their doping levels. We report a new photo-doping scheme that quasi-permanently dopes the monolayer MoS2 to extents competing with electrostatic gating. The photo-doping is achieved by coupling monolayer MoS2 with indium tin oxide nanocrystals that can store multiple electrons per nanocrystal after UV illumination. In the hybrid structure, the photo-generated valence band holes in the nanocrystals are filled by MoS2 electrons, photo-doping the MoS2 with holes. Reductions in carrier density by ~6x10^12 cm^-2 are observed, equivalent to the storage of ~40 electrons per nanocrystal. Long-range changes proliferating up to 40 micrometers away from the localized photodoping result from local bandstructure variations in MoS2. These studies reveal novel all-optical carrier density control in monolayer semiconductors, enabling remote-control of local charge density and innovative energy storage technologies. △ Less

Submitted 28 January, 2019; v1 submitted 12 October, 2018; originally announced October 2018.

Exfoliation of Few-Layer Black Phosphorus in Low-Boiling-Point Solvents and Its Application in Li-Ion Batteries

Authors: Antonio Esau Del Rio Castillo, Vittorio Pellegrini, Haiyan Sun, Joka Buha, Duc Anh Dinh, Emanuele Lago, Alberto Ansaldo, Andrea Capasso, Liberato Manna, Francesco Bonaccorso

Abstract: The liquid-phase exfoliation (LPE) of black phosphorus (BP) is a strategic route for the large-scale production of phosphorene and few-layer BP (FL-BP) flakes. The exploitation of this exfoliated material in cutting-edge technologies, e.g., in flexible electronics and energy storage, is however limited by the fact that the LPE of BP is usually carried out at a high boiling point and in toxic solve… ▽ More The liquid-phase exfoliation (LPE) of black phosphorus (BP) is a strategic route for the large-scale production of phosphorene and few-layer BP (FL-BP) flakes. The exploitation of this exfoliated material in cutting-edge technologies, e.g., in flexible electronics and energy storage, is however limited by the fact that the LPE of BP is usually carried out at a high boiling point and in toxic solvents. In fact, the solvent residual is detrimental to device performance in real applications; thus, complete solvent removal is critical. Here, we tackle these issues by exfoliating BP in different low boiling-point solvents. Among these solvents, we find that acetone also provides a high concentration of exfoliated BP, leading to the production of FL-BP flakes with an average lateral size and thickness of c.a. 30 and 7 nm, respectively. The use of acetone to produce less defective few-layer BP flakes (FL-BPacetone) from bulk crystals is a straightforward process which enables the rapid preparation of homogeneous thin films thanks to the fast solvent evaporation. The ratio of edge to bulk atoms for the BP flakes here produced, combined with the use of low-boiling-point solvents for the exfoliation process suggests that these thin films are promising anodes for lithium-ion batteries. To this end, we tested Li-ion half cells with FL-BPacetone anodes achieving a reversible specific capacity of 480 mAh/g at a current density of 100 mA/g, over 100 charge/discharge cycles. Moreover, a reversible specific capacity of 345 mAh/g is achieved for the FL-BPacetone-based anode at a high current density (i.e., 1 A/g). These findings indicate that the FL-BPacetone-based battery is promising with regards to the design of fast charge/discharge devices. Overall, the presented process is a step forward toward the fabrication of phosphorene-based devices. △ Less

Submitted 7 May, 2018; originally announced May 2018.

Comments: 30 pages, 11 images

Single-mode lasing from colloidal water-soluble CdSe/CdS quantum dot-in-rods

Authors: Francesco Di Stasio, Joel Q Grim, Vladimir Lesnyak, Prachi Rastogi, Liberato Manna, Iwan Moreels, Roman Krahne

Abstract: Core-shell CdSe/CdS nanocrystals are a very promising material for light emitting applications. Their solution-phase synthesis is based on surface-stabilizing ligands that makes them soluble in organic solvents, like toluene or chloroform. However, solubility of these materials in water provides many advantages, such as additional process routes and easier handling. So far, solubilization of CdSe/… ▽ More Core-shell CdSe/CdS nanocrystals are a very promising material for light emitting applications. Their solution-phase synthesis is based on surface-stabilizing ligands that makes them soluble in organic solvents, like toluene or chloroform. However, solubility of these materials in water provides many advantages, such as additional process routes and easier handling. So far, solubilization of CdSe/CdS nanocrystals in water that avoids detrimental effects on the luminescent properties, poses a major challenge. This work demonstrates how core-shell CdSe/CdS quantum dot-in-rods can be transferred into water using a ligand exchange method employing mercaptopropionic acid (MPA). Key to maintaining the light-emitting properties is an enlarged CdS rod diameter, which prevents potential surface defects formed during the ligand exchange from affecting the photophysics of the dot-in-rods. Films made from water-soluble dot-in-rods show amplified spontaneous emission (ASE) with a similar threshold (130 microJ/cm2) as the pristine material (115 microJ/cm2). To demonstrate feasibility for lasing applications, self-assembled micro lasers are fabricated via the coffee-ring effect that display single-mode operation and a very low threshold of around 10 microJ/cm2. The performance of these micro lasers is enhanced by the small size of MPA ligands, enabling a high packing density of the dot-in-rods. △ Less

Submitted 2 May, 2018; originally announced May 2018.

Comments: 20 pages, 4 figures, published paper with supporting information

Journal ref: Small 11, 1328, 2015

Plasmonic Doped Semiconductor Nanocrystals: Properties, Fabrication, Applications and Perspectives

Authors: Ilka Kriegel, Francesco Scotognella, Liberato Manna

Abstract: Degenerately doped semiconductor nanocrystals (NCs) are of recent interest to the NC community due to their tunable localized surface plasmon resonances (LSPRs) in the near infrared (NIR). The high level of doping in such materials with carrier densities in the range of 1021 cm^-3 leads to degeneracy of the doping levels and intense plasmonic absorption in the NIR. The lower carrier density in deg… ▽ More Degenerately doped semiconductor nanocrystals (NCs) are of recent interest to the NC community due to their tunable localized surface plasmon resonances (LSPRs) in the near infrared (NIR). The high level of doping in such materials with carrier densities in the range of 1021 cm^-3 leads to degeneracy of the doping levels and intense plasmonic absorption in the NIR. The lower carrier density in degenerately doped semiconductor NCs compared to noble metals enables LSPR tuning over a wide spectral range, since even a minor change of the carrier density strongly affects the spectral position of the LSPR. We focus on copper chalcogenide NCs and impurity doped metal oxide NCs as the most investigated alternatives to noble metals. We shed light on the structural changes upon LSPR tuning in vacancy doped copper chalcogenide NCs and deliver a picture for the fundamentally different mechanism of LSPR modification of impurity doped metal oxide NCs. We review on the peculiar optical properties of plasmonic degenerately doped NCs by highlighting the variety of different optical measurements and optical modeling approaches. These findings are merged in an exhaustive section on new and exciting applications based on the special characteristics that plasmonic semiconductor NCs bring along. △ Less

Submitted 20 January, 2017; originally announced January 2017.

Comments: 97 pages, 33 figures

Colloidal Synthesis of Strongly Fluorescent CsPbBr3 Nanowires with Width Tunable down to the Quantum Confinement Regime

Authors: Muhammad Imran, Francesco Di Stasio, Zhiya Dang, Claudio Canale, Ali Hossain Khan, Javad Shamsi, Rosaria Brescia, Mirko Prato, Liberato Manna

Abstract: We report the colloidal synthesis of strongly fluorescent CsPbBr3 perovskite nanowires (NWs) with rectangular section and with tuneable width, from 20 nm (exhibiting no quantum confinement, hence emitting in the green) down to around 3 nm (in the strong quan-tum-confinement regime, emitting in the blue), by introducing in the synthesis a short acid (octanoic acid or hexanoic acid) together with al… ▽ More We report the colloidal synthesis of strongly fluorescent CsPbBr3 perovskite nanowires (NWs) with rectangular section and with tuneable width, from 20 nm (exhibiting no quantum confinement, hence emitting in the green) down to around 3 nm (in the strong quan-tum-confinement regime, emitting in the blue), by introducing in the synthesis a short acid (octanoic acid or hexanoic acid) together with alkyl amines (octylamine and oleylamine). Temperatures below 70 °C promoted the formation of monodisperse, few unit cell thick NWs that were free from byproducts. The photoluminescence quantum yield of the NW samples went from 12% for non-confined NWs emitting at 524 nm to a maximum of 77% for the 5 nm diameter NWs emitting at 497 nm, down to 30% for the thinnest NWs (diameter ~ 3nm), in the latter sample most likely due to aggregation occurring in solution. △ Less

Submitted 25 October, 2016; originally announced October 2016.

Comments: 5 pages, 4 figures

Journal ref: Chemistry of Materials 2016

Assembly-mediated Interplay of Dipolar Interactions and Surface Spin Disorder in Colloidal Maghemite Nanoclusters

Authors: A. Kostopoulou, K. Brintakis, M. Vasilakaki, K. N. Trohidou, A. P. Douvalis, A. Lascialfari, L. Manna, A. Lappas

Abstract: Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of $\sim$ 13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the i… ▽ More Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of $\sim$ 13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the increasing volume fraction, $φ$, of the inorganic magnetic phase that goes from individual colloidal nanoparticles ($φ$= 0.47) to clusters ($φ$= 0.72). The frozen-liquid dispersions of the latter exhibit weak ferrimagnetic behavior at 300 K. Comparative Mossbauer spectroscopic studies imply that intra-cluster interactions come into play. A new insight emerges from the clusters temperature-dependent ac susceptibility that displays two maxima in $χ$''(T), with strong frequency dispersion. Scaling-law analysis, together with the observed memory effects suggest that a superspin glass state settles-in at T$_{B}$ $\sim$ 160-200 K, while at lower-temperatures, surface spin-glass freezing is established at T$_{f}$ $\sim$40- 70 K. In such nanoparticle-assembled systems, with increased $φ$, Monte Carlo simulations corroborate the role of the inter-particle dipolar interactions and that of the constituent nanoparticles surface spin disorder in the emerging spin-glass dynamics. △ Less

Submitted 20 November, 2013; v1 submitted 18 November, 2013; originally announced November 2013.

Plasmonics in heavily-doped semiconductor nanocrystals

Authors: Francesco Scotognella, Giuseppe Della Valle, Ajay Ram Srimath Kandada, Margherita Zavelani-Rossi, Alberto Comin, Stefano Longhi, Liberato Manna, Guglielmo Lanzani, Francesco Tassone

Abstract: Heavily-doped semiconductor nanocrystals characterized by a tunable plasmonic band have been gaining increasing attention recently. Herein, we introduce this type of materials focusing on their structural and photo physical properties. Beside their continuous-wave plasmonic response, depicted both theoretically and experimentally, we also review recent results on their transient, ultrafast respons… ▽ More Heavily-doped semiconductor nanocrystals characterized by a tunable plasmonic band have been gaining increasing attention recently. Herein, we introduce this type of materials focusing on their structural and photo physical properties. Beside their continuous-wave plasmonic response, depicted both theoretically and experimentally, we also review recent results on their transient, ultrafast response. This was successfully interpreted by adapting models of the ultrafast response of gold nanoparticles. △ Less

Submitted 5 June, 2013; originally announced June 2013.

Comments: 20 pages review paper, 15 figures

Journal ref: Eur. Phys. J. B (2013) 86: 154

Self assembly of highly fluorescent semiconductor nanorods into large scale smectic liquid crystal structures by coffee stain evaporation dynamics

Authors: Concetta Nobile, Luigi Carbone, Angela Fiore, Roberto Cingolani, Liberato Manna, Roman Krahne

Abstract: We deposit droplets of nanorods dispersed in solvents on substrate surfaces and let the solvent evaporate. We find that strong contact line pinning leads to dense nanorod deposition inside coffee stain fringes, where we observe large-scale lateral ordering of the nanorods with the long axis of the rods oriented parallel to the contact line. We observe birefringence of these coffee stain fringes… ▽ More We deposit droplets of nanorods dispersed in solvents on substrate surfaces and let the solvent evaporate. We find that strong contact line pinning leads to dense nanorod deposition inside coffee stain fringes, where we observe large-scale lateral ordering of the nanorods with the long axis of the rods oriented parallel to the contact line. We observe birefringence of these coffee stain fringes by polarized microscopy and we find the direction of the extraordinary refractive index parallel to the long axis of the nanorods. △ Less

Submitted 20 January, 2009; v1 submitted 30 December, 2008; originally announced December 2008.

Comments: 11 pages, 6 figures and supporting information

Confined optical phonon modes in polar tetrapod nanocrystals detected by resonant inelastic light scattering

Authors: R. Krahne, G. Chilla, C. Schueller, L. Carbone, S. Kudera, G. Mannarini, L. Manna, D. Heitmannb, R. Cingolani

Abstract: We investigated CdTe nanocrystal tetrapods of different sizes by resonant inelastic light scattering at room temperature and under cryogenic conditions. We observe a strongly resonant behavior of the phonon scattering with the excitonic structure of the tetrapods. Under resonant conditions we detect a set of phonon modes that can be understood as confined longitudinal-optical phonons, surface-op… ▽ More We investigated CdTe nanocrystal tetrapods of different sizes by resonant inelastic light scattering at room temperature and under cryogenic conditions. We observe a strongly resonant behavior of the phonon scattering with the excitonic structure of the tetrapods. Under resonant conditions we detect a set of phonon modes that can be understood as confined longitudinal-optical phonons, surface-optical phonons, and transverse-optical phonons in a nanowire picture. △ Less

Submitted 21 December, 2005; originally announced December 2005.

Comments: 12 pages, 4 figures

Journal ref: Nano Lett.; (Letter); 2006; 6(3); 478-482.