Achieving Ultrahigh Thermal Stability in Cr-Activated Garnet Phosphors through Electron Migration between Thermally Coupled Levels.

Recently, Cr-activated near-infrared (NIR) phosphors have received much more attention due to their excellent photoluminescence (PL) properties. However, most of them suffer from poor thermal stability which limits further application. Herein, a novel LuCaGaSnO:Cr phosphor with broadband NIR emission (λ = 750 nm) is synthesized successfully. Despite the good luminescence property, its PL intensity decreases obviously with temperature ( = 79%). To improve the thermal stability, a series of LuCaGaSnO:Cr ( = 0-1.0) solid solutions with tunable thermal quenching performance have been designed. It is found that the fluorescence intensity ratio (FIR) of T → A to E → A [(T)/(E)] transitions (i.e. electron occupation) decreases monotonously with increasing [Lu-Ga] co-substitution, resulting from a strengthened crystal field strength and increased energy difference between T and E energy levels. Benefiting from the various thermal population and energy difference Δ', the PL thermal quenching behavior of LuCaGaSnO:Cr can be adjusted easily, and the corresponding mechanism is explored in detail. Most notably, the emission intensity of LuCaGaSnO:Cr at 425 K can reach up to 142% compared with that at 300 K, which may be the best for Cr-activated NIR phosphors. This work may provide an alternative path for the development of thermally stable broadband NIR phosphors.