Growth and spectroscopy of Er3+-doped Na5Y9F32 (5NaF∙9YF3) crystal

We report on the growth, structure and spectroscopy of an Er³⁺ -doped Na₅Y₉F₃₂ (5NaF∙9YF₃) crystal featuring significant inhomogeneous spectral broadening. Single-crystals of Na₅Y₉F₃₂ doped with 0.22 – 9.63 at.% Er3+ were grown by the Czochralski method. Er:Na5Y9F32 exhibits a cubic fluorite-type structure (a = 5.4881(2) Å for 5.59 at.% Er³⁺ doping). The most intense Raman band of this material is found at ~404 cm^-1 . Er³⁺ ions in Na₅Y₉F₃₂ exhibit a broad and smooth emission band owing to the ⁴ I_11/2 → ⁴ I_13/2 transition with a maximum stimulated-emission cross-section of 0.42×10^-20 cm₂ at 2708 nm. According to the Judd-Ofelt analysis, the radiative lifetime of the ⁴ I_11/2 multiplet is 10.0 ms and the luminescence branching ratio β( ⁴ I_11/2 → ⁴ I_13/2) is 17.6%. The luminescence lifetimes of the ⁴ I_11/2 and ⁴ I_13/2 Er³⁺ states were studied as a function of the doping concentration. For 5.59 at.% Er doping, they are 7.72 ms and 6.69 ms, respectively, representing a favorable ratio for mid-infrared laser operation.