Broadband near-infrared luminescence properties of fluoride phosphor K3AlF6:Cr3+

Near-infrared light can be widely used in non-destructive testing, sensing, and night vision. Recently, phosphor-converted LED (pc-LED) based on near-infrared (NIR) phosphor have attracted considerable interest. In this work, tetragonal structured K3AlF6:Cr3+ phosphors were synthesized using the co-precipitation method. Cr3+ ions occupy the octahedral position, and its Dq/B value (the parameter describing the crystal field strength) is calculated to be 2.08, suggesting a weak crystal field. Upon blue light excitation (430 nm), a broadband NIR emission is observed in the range of 650–900 nm, corresponding to the spin-allow 4T2 → 4A2 transition. Increasing Cr3+ concentration, red-shift is observed in its NIR emission with the maximum emission intensity at 5 mol