Spectrally tunable near-infrared photoluminescence in MP3O9:Cr3+ (M = Al, Ga, In) phosphate phosphors

Modulation of the octahedral crystal field environment of Cr³⁺ is an effective approach to achieve tunable emission. Here, we prepared a series of broadband MP₃O₉:Cr³⁺ (M = Al, Ga, In) near-infrared (NIR) phosphors, and cubic AlP₃O₉:Cr³⁺ (APO-c:Cr³⁺) and monoclinic AlP₃O₉:Cr³⁺ (APO-m:Cr³⁺) phosphors were prepared by controlling the synthesis temperature. The emission wavelength was tuned from 787 nm for APO-c:Cr³⁺ to 894 nm for monoclinic InP₃O₉:Cr³⁺ (IPO:Cr³⁺) by regulating the M ion and reducing the crystal field intensity. Excitingly, the MP₃O₉:Cr³⁺ (M = Al, Ga, In) family shows excellent thermal stability; the emission intensity of APO-c:Cr³⁺, APO-m:Cr³⁺ and monoclinic GaP₃O₉:Cr³⁺ (GPO:Cr³⁺) can still maintain 95.6%, 86% and 86% of that at room temperature when heating to 423 K, respectively. An NIR LED device was prepared by incorporating GPO:Cr³⁺ and a blue light LED, demonstrating the potential application in night vision and non-destructive testing.