Enhanced photoluminescence of a HF free novel NIR phosphor of K2ZnF4:Cr3+ by lithium ion doping

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have been attracting considerable attention as a new solid-state light source for night vision technology and biological imaging applications. Nevertheless, the requirement for toxic and concentrated HF in the previous synthesis of fluoride phosphors may cause environmental pollution and safety problems. Here, we report a feasible HF-free green synthesis method using a two-step process to prepare the Cr3+ source and a series of Cr3+, Li+ doped NIR phosphors using aqueous solution and methanol solution. X-ray diffraction analysis indicates that the pure target material was successfully synthesized. The luminescence intensity of K2ZnF4:Cr3+,Li+ is 2.58 times improved compared with K2ZnF4:Cr3+. Furthermore, the prepared phosphors show broadband emission in the range of 650 to 1000 nm, with a full width at half-maximum (FWHM) of 139 nm peaking at 783 nm. The NIR output power of the pc-LED fabricated with the K2ZnF4:Cr3+,Li+ phosphor and a 450 nm blue chip reaches 1007 mW at 320 mA. This work provides a promising phosphor for application as a NIR light emitting diode and has important implications for the green synthesis of HF-free Cr3+-doped fluorides in the future.