A near-infrared phosphor doped with Cr3+ towards zero-thermal-quenching for high-power LEDs

Cr3+-doped phosphors show significant application potential in near-infrared (NIR) light-emitting diodes (LEDs). However, the development of thermally stable and efficient NIR phosphors still faces enormous challenges. Herein, NIR phosphors K2NaMF6:Cr3+ (M3+ = Al3+, Ga3+, and In3+) were synthesized by the hydrothermal method. The represented K2NaAlF6:Cr3+ phosphor can be effectively excited by blue light (∼430 nm) to present broadband emission at half a maximum of 96 nm peaking at ∼ 728 nm. Meanwhile, the K2NaAlF6:Cr3+ phosphor exhibits excellent internal quantum efficiency (IQE = 68.08%) and nearly zero-thermal-quenching behavior, which is able to maintain 96.5% emission intensity at 150 °C of the initial value at 25 °C. The NIR phosphor-converted LED was fabricated based on K2NaAlF6:Cr3+ phosphor and a blue LED chip, showing a NIR output power of 394.39 mW at 300 mA with a high photoelectric conversion efficiency of 10.9% at 20 mA. Using the high-power NIR LED as a lighting source, transparent and quick veins imaging as well as non-destructive testing were demonstrated, suggesting the NIR phosphor has a wide range of practical applications.