Simultaneous NIR Emission and Thermal Stability Enhancement in Garnet‐Type NIR Phosphors through the Synergistic Effect of Lattice Distortion and Enhanced Rigidity

Abstract Even though there have been significant advancements in the development of Cr 3+ ‐activated near‐infrared (NIR) phosphors, the challenge still remains to develop highly efficient and thermally stable NIR phosphors. Here, the Ca 4‐x Zn x HfGe 3 O 12 :0.03Cr 3+ solid solution phosphors with 834–806 nm NIR emission are constructed by substituting Zn 2+ for Ca 2+ , thereby facilitating the formation of [ZnO 6 ] luminescence site. The coexistence of [HfO 6 ] and [Zn/CaO 6 ] luminescence centers is confirmed through DFT calculation, time‐resolved photoluminescence (TRPL) spectroscopy, and low‐temperature‐photoluminescence (77 K) spectroscopy. The formation of [ZnO 6 ] effectively resolves the issue of lattice mismatch between Cr 3+ and Ca 2+ . Furthermore, the simultaneous enhancement of luminescence intensity and thermal stability is realized through a synergistic combination of lattice distortion and rigidity enhancement. By optimizing the substitution concentration of Cr 3+ , the internal quantum efficiency (IQE) of 92% and an external quantum efficiency (EQE) of 29% are finally achieved. Meanwhile, the thermal stability is also enhanced from 59%@400 K (x = 0) to 81%@400 K (x = 0.8). The developed NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) exhibit promising prospects in the fields of security, biomedicine, non‐destructive testing and rapid identification.