Mn4+-activated (K1-Cs )2NbF7 red phosphors with high color purity and excellent moisture resistance for WLEDs

Recently, Mn4+-activated fluoride red phosphors have received intensive attention due to their excellent luminescence properties. However, poor moisture resistance hinders their commercial application. Herein, (K1-xCsx)2NbF7:Mn4+ phosphors were designed and synthesized. All the obtained samples are rod-like microcrystals with monoclinic phase structure, Cs+-doping concentration has little influence on the microstructure while significantly impacts their luminescence properties. Specially, the composition optimized (K1-xCsx)2NbF7:Mn4+ (x = 0.3) phosphor has the color purity of 94.20%, the quantum yield of 53.90% and the decay lifetime of 3.59 ms. More importantly, the optimized phosphor can maintain 83.20% of the initial emission intensity after being immersed in distilled water for 1440 min, showing the excellent moisture resistance. A warm WLED with high CRI of 85 and low CCT of 4362 K is achieved by coating the obtained optimized red phosphor in chip. Our work demonstrates that the (K1-xCsx)2NbF7:Mn4+ red phosphors possess a great potential application in warm WLEDs.