Highly Crystalline Y3Al5O12:Ce3+ Phosphor‐in‐Glass Film: A New Composite Color Converter for Next‐Generation High‐Brightness Laser‐Driven Lightings

Abstract As a successor to the light‐emitting‐diode (LED), the laser diode (LD) forecasts a brighter future for energy‐saving solid‐state lighting (SSL). Aiming for high‐performance white LD, herein, a brand‐new material form for Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) garnet, that is, the integrated composite of YAG:Ce phosphor‐in‐silica glass ceramic/phosphor‐in‐silica ceramic (PiSGC/PiSC) film‐on‐sapphire plate (SP), following an “amorphous → polycrystalline” phase transformation mechanism, is developed. Remarkably, nearly full crystallization from glass in a controllable manner can be achieved. The in situ precipitated SiO 2 microcrystals with high thermal conductivity (TC) favor to build efficient local heat dissipation network inside this opto‐functional composite, and therefore, substantially increase luminescence saturation threshold and luminous brightness under blue LD irradiation. Upon material optimization, bright and directional white light is generated with luminous flux (LF) of 1350 lm@10.5 W mm −2 , correlated color temperature (CCT) of 7916 K, and color rendering index (CRI) of 69.3, enabling the application in high‐brightness long‐distance illumination scenarios. This smart material design highlights the combined merits of admirable luminescent properties from YAG:Ce@SiO 2 ceramic, ultrahigh TC from sapphire single crystal, as well as, low cost, facile preparation, scalable manufacturing inherited from glass.