Lowering operating temperatures in high-power laser-excited LuAG:Ce films by improving crystallinity and increasing Ce³⁺ content

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.