A search for extra-high brightness laser-driven color converters by investigating thermally-induced luminance saturation

Abstract

To achieve extra-high brightness laser lighting, the bottleneck of thermally-induced luminance saturation that phosphor materials (i.e., color converters) usually suffer from under high power density laser excitation must be broken. However, the mechanisms for thermal saturation are not fully understood yet. Here, thermal saturation of typical Ce³⁺-doped garnet phosphor ceramics was systematically investigated by considering the balance among heat generation, dissipation and resistance of color converters. With increasing Ce concentration (0.0167 → 0.433%), the thermal saturation threshold decreases due to more heat generation (i.e., 3.97 → 6.73 W at an incident laser power of 6.73 W). A tunable saturation threshold (2–49 W mm⁻²) was observed by a chemical substitution strategy because of the difference in the thermal resistance and heat generation. The sample thickness exerts a complex influence on the saturation threshold accompanied by increased heat generation and enhanced heat dissipation corroborated by a broader temperature distribution curve. Based on these investigations, a high-flux white light of 2347.9 lm is obtained with robust YAG:Ce ceramics irradiated with a high power density of 31.94 W mm⁻². Moreover, a promising green color converter able to withstand a blue laser power density of 49 W mm⁻² was discovered for laser displays with an output luminous flux of 3967.3 lm. This work provides a principle to design and/or select phosphor materials with high thermal saturation thresholds, thus accelerating the rapid development of laser-driven lighting and displays.