High Thermal Conductivity BN Substrate YAG:Ce³⁺ Phosphor Glass Films for a Laser-Driven Lighting Device

The development of laser-driven lighting is progressing toward achieving high-power and high-brightness capabilities. However, all-inorganic color converters still face significant challenges arising from heat accumulation. Herein, we propose an effective approach to enhance the thermal conductivity of the light converter by closely sintering Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor-glass films on a highly thermally conductive BN substrate (abbreviated as PBNC) for localized heat dissipation. This results in a significant increase in the luminescence saturation threshold when exposed to blue laser irradiation. The laser bearing capacity of PBNC is effectively optimized by adjusting the ratio of phosphor to glass and the thickness of the BN substrate. Under a laser irradiation level of 4.47 W/mm2 for 3 min, the maximum surface temperature of the PBNC is 92 °C, representing a significant reduction of 44 °C compared to that of the phosphor-glass film on the AlN substrate (136 °C). A laser-driven lighting device employing a PBNC with a thickness of 2.5 mm gives a luminous flux of 590.4 lm and luminous efficacy of 173.6 lm/W under a laser power density of 5.07 W/mm2. These findings confirm that the BN substrate enhances the thermal conductivity of phosphor-glass films, enabling them to become highly promising color converters for laser-driven lighting.