Origins of heat and luminous saturation in LuAG:Ce thin films for high-power laser lighting

The performance of high-power laser-driven lighting systems is fundamentally limited by an insufficient understanding of the mechanisms governing heat generation and luminous saturation in color-converting materials. In this study, Ce-doped Lu₃Al₅O₁₂ (LuAG:Ce) thin films, synthesized through spray pyrolysis across a doping range of 0.1-4.0 mol%, are systematically investigated to elucidate these effects. Heat generation, resulting from the Stokes shift, is found to scale with both Ce concentration and excitation power density, emerging as a critical factor that constrains luminescence output. At an optimized doping level of 2.5 mol% Ce, the films achieve a luminous flux of 1618.3 lm and exhibit a saturation threshold of 28 W·mm^-2 under ambient conditions. Incorporation of water cooling reduces the local laser spot temperature by approximately 42.3 °C at the same excitation intensity, effectively raising the saturation threshold to 32 W·mm^-2 and increasing luminous flux to 1938.6 lm, representing a 19.8% enhancement. These results demonstrate that non-radiative transitions, arising from thermal quenching, lead to luminous saturation. Collectively, this study clarifies the origins of heat generation and luminous saturation in LuAG:Ce films under high-power laser excitation and underscores the critical roles of Ce doping optimization and heat dissipation in enhancing solid-state lighting performance.