Near-Infrared-Emitting K₂CaP₂O₇:Cr³⁺ with Outstanding Thermal Stability

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have great potential as next-generation NIR light sources for a wide range of applications. However, the development of NIR-emitting phosphors that simultaneously produce long wavelength and broadband emission with high thermal stability continues to be a challenge. Here, we design a broadband NIR phosphor, Cr³⁺-activated K₂CaP₂O₇. Under an optimal 460 nm excitation, it shows broadband NIR emission in the range of 650 to 1200 nm. More importantly, it demonstrates outstanding anti-thermal quenching (anti-TQ) performance, i.e., even enhanced luminescence intensity at 150 °C, which is 180% of that measured at room temperature. Using a combination of first-principles calculations and experimental analysis, the mechanism of the distinctive anti-TQ is clarified as the thermally induced energy transfer from energy levels of oxygen vacancy defects to Cr³⁺ 3d excited state centers. In addition, we have showcased the potential multifunctional applications of this tunable NIR-emitting phosphor in nondestructive NIR spectroscopy detection and night vision. It is expected that the exciting results from the Cr³⁺-activated K₂CaP₂O₇ will contribute to a better understanding of how crystal defects affect luminous materials and encourage further research into defect control to create thermally stable phosphors with practical use.