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

Abstract

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 Ca₃Y_2-2x(ZnZr)_xGe₃O₁₂:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn²⁺-Zr⁴⁺] for [Y³⁺-Y³⁺] played a critical role as reductant to promote the valence transformation from Cr⁴⁺ to Cr³⁺, resulting from the reconstruction of octahedral sites for Cr³⁺. The introduction of [Zn²⁺-Zr⁴⁺] 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.