Photoluminescence properties of solid solutions of YNbO<sub>4</sub>, GdNbO<sub>4</sub> and LuNbO<sub>4</sub>

The photoluminescence properties of solid solutions of YNbO4, GdNbO4, and LuNbO4 were investigated to determine the rare earth composition that maximizes the intrinsic luminescence intensity. All samples exhibited a monoclinic β-fergusonite-type structure without impurity phases. The intrinsic luminescence intensity followed the order of GdNbO4, YNbO4 and LuNbO4, with GdNbO4 showing significantly low intensity due to concentration quenching and self-absorption by Gd3+. Among the solid solutions, (Y,Lu)NbO4 showed higher luminescence intensity than LuNbO4, with Y0.75Lu0.25NbO4 exhibiting the highest intensity, approximately 42 % higher than LuNbO4. Fluorescence lifetime measurements of (Y,Lu)NbO4 showed single-component decay curves with lifetimes ranging from 3.3 to 4.3 µs, with no significant differences or correlation with luminescence intensity.