Highly Quantum Efficient and Thermally Stable Near‐Infrared‐Emitting K‐β‐Al₂O₃:Cr³⁺ Phosphor

Abstract Near‐infrared (NIR) phosphors are enablers for NIR phosphor‐converted light‐emitting diodes (pc‐LEDs). However, fewer NIR‐emitting phosphors with both high internal/external quantum efficiency (IQE/EQE) and thermal stability are discovered, which obstructs the promotion of NIR pc‐LEDs. Herein, by partially replacing Al³⁺ in K‐β‐Al₂O₃:2Cr³⁺ with Ga³⁺, the photoluminescence (PL) intensity of the solid solution K_1+δ(Al_0.4Ga_0.6)₁₁O₁₇:2Cr³⁺, (KA_0.4G_0.6O:Cr) phosphor is increased 2.75 and 1.25 times that of end‐members K_1+δAl₁₁O₁₇:2Cr³⁺ (KAO:Cr) and K_1+δGa₁₁O₁₇:2Cr³⁺ (KGO:Cr). The IQE/EQE of optimal KA_0.4G_0.6O:Cr reaches 88.9%/50.8% with high thermal stability (77.4%@150 °C). The PL intensity enhancement is due to the Al/Ga‐6O octahedral volume and distortion variation caused by the substitution of Ga³⁺ for Al³⁺ in K_1+δ(Al_1‐y,Ga_y)₁₁O₁₇:2Cr³⁺ (KA_1‐yG_yO:Cr), which leads to the forbidden d–d transition being broken and crystal field strength varied. Finally, a NIR pc‐LED device fabricated based on KA_0.4G_0.6O:Cr NIR‐emitting phosphor and blue chip reaches an electro‐optical efficiency of 16.3% under a drive current of 100 mA. Meanwhile, non‐destructive detection and plant germination applications of the NIR pc‐LED are demonstrated. These results prove that KA_0.4G_0.6O:Cr is a promising NIR phosphor for diverse applications.