Toward Laser‐Driven Lighting with High Overall Optical Performance: Thermally Robust Composite Phosphor‐in‐Glass Film

Abstract For laser‐driven white light sources, phosphor‐in‐glass films (PiGFs), typically sintered onto substrates with high‐thermal conductivity, are developed and emerged as the leading materials. However, compared to other all‐inorganic color converters, such as single crystals, transparent ceramics, PiGF suffers from a low saturation threshold, poor thermal stability and limited irradiation durability, which restricts its practical applications. To overcome these limitations, in this study, a series of h‐BN‐YAG:Ce 3+ PiGF is developed on opaque Al 2 O 3 /transparent Al 2 O 3 (B‐Y PiGF@o/t‐Al 2 O 3 ) by directly incorporating high‐thermal‐conductivity fillers into the PiGF. The selective incorporation of h‐BN establishes a local heat conduction network, significantly increasing the saturation threshold and luminous flux. Through optimization, a maximum luminous flux of 6015.46 ± 14.46 lm with a saturation threshold of 16.15 ± 0.48 W mm −2 is achieved in reflective excitation mode, outperforming previous high‐performance PiGFs. The addition of h‐BN both enhanced heat dissipation and improved the uniformity of white light output in transmissive excitation mode, addressing the “yellow ring” effect commonly seen in laser‐driven lighting. The application potential of the developed composite has been proven ranging from automotive headlights to medical lighting, offering a path toward enhanced brightness, more efficient, and operational‐stable next‐generation lighting technologies.