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 nonradiative 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.

High operating temperatures generally degrade the luminous performance of color converters used in high-power, laser-driven white lighting systems. This study demonstrated that the operating temperature of LuAG:Ce films can be significantly reduced, particularly under high-power laser excitation near the saturation threshold. This improvement was achieved by enhancing the crystallinity and increasing the Ce³⁺ content in LuAG:Ce films. LuAG:Ce films, approximately 22.17 μm in thickness, were deposited on sapphire substrates via spray pyrolysis techniques. The crystallinity was controlled by the annealing temperature, while the Ce³⁺ content was regulated by the annealing atmosphere. Compared with those with a crystallinity of 75.5%, the air-annealed films with a crystallinity of 87.4% exhibited a remarkable 95.6 °C decrease in operating temperature under 18 W/mm² blue laser excitation. Additionally, the incorporation of a higher Ce³⁺ content through CO annealing led to a further reduction in the operating temperature. By lowering the operating temperature, LuAG:Ce films on sapphire substrates exhibit enhanced luminous performance and thermal stability under prolonged high-power laser excitation, which could inspire the design and development of advanced color converters for laser lighting applications.