Optical Transmission Enhancement of Ionic Crystals via Superionic Fluoride Transfer: Growing VUV-Transparent Radioactive Crystals
Authors:
Kjeld Beeks,
Tomas Sikorsky,
Fabian Schaden,
Martin Pressler,
Felix Schneider,
Björn N. Koch,
Thomas Pronebner,
David Werban,
Niyusha Hosseini,
Georgy Kazakov,
Jan Welch,
Johannes H. Sterba,
Florian Kraus,
Thorsten Schumm
Abstract:
The 8 eV first nuclear excited state in $^{229}$Th is a candidate for implementing an nuclear clock. Doping $^{229}$Th into ionic crystals such as CaF$_2$ is expected to suppress non-radiative decay, enabling nuclear spectroscopy and the realization of a solid-state optical clock. Yet, the inherent radioactivity of $^{229}$Th prohibits the growth of high-quality single crystals with high $^{229}$T…
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The 8 eV first nuclear excited state in $^{229}$Th is a candidate for implementing an nuclear clock. Doping $^{229}$Th into ionic crystals such as CaF$_2$ is expected to suppress non-radiative decay, enabling nuclear spectroscopy and the realization of a solid-state optical clock. Yet, the inherent radioactivity of $^{229}$Th prohibits the growth of high-quality single crystals with high $^{229}$Th concentration; radiolysis causes fluoride loss, increasing absorption at 8 eV. We overcome this roadblock by annealing $^{229}$Th doped CaF$_2$ at 1250$\unicode{x2103}$ in CF$_4$. The technique presented here allows to adjust the fluoride content without crystal melting, preserving its single-crystal structure. Superionic state annealing ensures rapid fluoride distribution, creating fully transparent and radiation-hard crystals. This approach enables control over the charge state of dopants which can be used in deep UV optics, laser crystals, scintillators, and nuclear clocks.
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Submitted 29 February, 2024; v1 submitted 21 December, 2023;
originally announced December 2023.