Valence conversion and site reconstruction in nearinfrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared(NIR)-emitting phosphors.Here,we designed a“kill two birds with one stone”strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca_(3)Y_(2-2x)(ZnZr)_(x)Ge_(3)O_(12):Cr garnet system by chemical unit cosubstitution,and revealed universal structure-property relationship and the luminescence optimization mechanism.The cosubstitution of[Zn^(2+)-Zr^(4+)]for[Y^(3+)-Y^(3+)]played a critical role as reductant to promote the valence transformation from Cr^(4+)to Cr^(3+),resulting from the reconstruction of octahedral sites for Cr^(3+).The introduction of[Zn^(2+)-Zr^(4+)]unit also contributed to a rigid crystal structure.These two aspects together realized the high internal quantum efficiency of 96%and excellent thermal stability of 89%@423 K.Moreover,information encryption with“burning after reading”was achieved based on different chemical resistance of the phosphors to acid.The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision.This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.