Hydrofluoric Acid-Free Broadband Near-Infrared Phosphors K₂LiMF₆:Cr³⁺ with Zero-Thermal Quenching: Structure, Luminescence, and Application

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are considered promising light sources for night vision, food analysis, biomedicine, and plant growth. Yet, the application potential of this technology is vulnerable to the function degradation of the phosphors used, such as thermal quenching, which needs to be addressed urgently. Herein, the NIR phosphors K₂LiMF₆:Cr³⁺ (M = Al, Ga, In) with a cubic double-perovskite structure synthesized by a green hydrofluoric acid-free hydrothermal method exhibit outstanding thermal stability. Under 450 nm excitation, the as-synthesized K₂LiMF₆:Cr³⁺ phosphors all exhibited broadband NIR emission covering 650-1000 nm peaking at 755-780 nm. The prepared K₂LiAlF₆:Cr³⁺ phosphor shows a unique zero-thermal quenching performance (I_{423 K}/I_{298 K} = 102%). The comprehensive effects of a wide band gap, large thermal energy barrier, weak electron-phonon coupling effect, and high structural rigidity are responsible for the suppression of thermal quenching in this material. The output power of the NIR pc-LED device reached 285 mW at 100 mA. This series of phosphors has promise in night vision and bioimaging applications.