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

Recently, Mn 4+ -activated fluoride red phosphors have received intensive attention due to their excellent luminescence properties. However, poor moisture resistance hinders their commercial application. Herein, (K 1- x Cs x ) 2 NbF 7 :Mn 4+ 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 (K 1- x Cs x ) 2 NbF 7 :Mn 4+ ( 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 (K 1- x Cs x ) 2 NbF 7 :Mn 4+ red phosphors possess a great potential application in warm WLEDs.