Cubic and rhombohedral Ba₄Lu₃F₁₇:Er³⁺ in transparent glass ceramics: Crystallization and upconversion luminescence

Novel Er³⁺ doped glass ceramics containing Ba₄Lu₃F₁₇ nanocrystals were successfully prepared by heat treatment of melt-quenched glasses. Highly efficient upconversion luminescence was detected under near-infrared excitation and it was at least two orders of magnitude higher than that in the precursor glass. The activator content in the crystalline phase was estimated using polycrystalline Ba₄Lu₃F₁₇ with different Er³⁺ content as the reference and it was found to be higher than in similar glass ceramics. The structure and thermal analysis of the glass ceramics revealed the formation of cubic and rhombohedrally distorted cubic modifications of Ba₄Lu₃F₁₇. Phase transition between the two modifications was studied using site selective spectroscopy of Er³⁺ as a structural probe. Unusually efficient incorporation of Er³⁺ ions in the Ba₄Lu₃F₁₇ nanocrystals combined with the low phonon energy of the fluoride crystals make this material a desirable host for upconversion luminescence.