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arXiv · 2605.10160

Ytterbium charge state and stabilization in the Ba(Ca)F$_2$ host by electron paramagnetic resonance and infrared photoluminescence

David John·Shelja Sharma·Marius Stef·Gabriel Buse·Zdeněk Remeš·Anna Artemenko·Sergii Chertopalov·Vineet Sikarwar·Alan Mašláni·Jafar Fathi·Jakub Pilař·Tomáš Hostinský·Jan Zich·Tomáš Mates·Brenda Natalia Lopez Nino·Michal Hlína·Karol Bartosiewicz·Marina Konuhova·Anatoli Popov·Ján Lančok·Maksym Buryi
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Abstract

Lanthanide-doped fluorides are promising materials for advanced photonic and quantum applications due to their wide bandgap, low phonon energy, and chemical stability. In this work, we present a systematic comparative study of ytterbium incorporation at low doping levels (0.05--0.2 mol\%) in BaF$_2$ and CaF$_2$ single crystals, focusing on the interplay between host lattice properties, charge-state stabilization, and defect formation mechanisms. Using a combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), transmittance, and infrared photoluminescence (IR PL), we explore how host lattice properties affect the stabilization of Yb$^{3+}$ and Yb$^{2+}$ ions. XRD confirmed cubic phase purity and lattice parameter stability in both hosts, while XPS revealed surface chemical composition variations associated with charge-compensating defects and trace impurities. EPR spectra indicated that BaF$_2$ favored perturbed Yb$^{3+}$ environments with increasing dopant levels, while CaF$_2$ maintained predominantly unperturbed sites, suggesting a more favorable ionic match for Yb$^{2+}$. Photothermal deflection spectroscopy (PDS) and IR PL results showed host-specific optical responses, with CaF$_2$ exhibiting crystal-field splitting and broader local field effects. These results reveal a clear decoupling between long-range structural stability and local lattice perturbations, and demonstrate that host cation identity governs the balance between Yb$^{2+}$ and Yb$^{3+}$ stabilization as well as defect-driven optical behavior. This offers valuable insights for optimizing rare-earth-doped fluoride crystals in laser, scintillator, and quantum device applications.

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David John, Shelja Sharma, Marius Stef, Gabriel Buse, Zdeněk Remeš, Anna Artemenko, Sergii Chertopalov, Vineet Sikarwar, Alan Mašláni, Jafar Fathi, Jakub Pilař, Tomáš Hostinský, Jan Zich, Tomáš Mates, Brenda Natalia Lopez Nino, Michal Hlína, Karol Bartosiewicz, Marina Konuhova, Anatoli Popov, Ján Lančok, Maksym Buryi. 2026-05-11. Ytterbium charge state and stabilization in the Ba(Ca)F$_2$ host by electron paramagnetic resonance and infrared photoluminescence. https://doi.org/10.1016/j.optmat.2026.118242

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