Near‐Unity and Zero‐Thermal‐Quenching Far‐Red‐Emitting Composite Ceramics via Pressureless Glass Crystallization

Abstract Laser‐driven (LD) lighting is emerging as the next‐generation high‐power solid‐state lighting technology. All‐inorganic color converters with high quantum efficiency (QE), small thermal quenching, high thermal conductivity, and high thermal and chemical stabilities are crucial to coping with the enormous heat generated in LD lighting. Although luminescent translucent ceramics are the most promising class of color converters, only green/yellow‐emitting ones with satisfactory performance are developed before. Here, a far‐red‐emitting composite ceramics Y 3 Al 5 O 12 (YAG)–Al 2 O 3 :Cr 3+ with near‐unity internal QE and zero‐thermal quenching are prepared via pressureless glass crystallization, where the inside light scattering is finely tuned by simply manipulating the temperature to induce controllable grain growth. The commonly used inert matrix Al 2 O 3 here becomes an optically active component as YAG, thus alleviating the undesired concentration quenching while maintaining strong light absorption. Therefore, a high‐power LD far‐red lighting source with luminescence saturation threshold up to 21.4 W mm −2 is demonstrated, which may find broad applications in plant growth lighting, solar simulators, and phototherapy.