Red-emitting phosphors APF6:Mn4+ (A = Cs+, Rb+, K+): synthesis, luminescent properties and application in solid-state lighting
A series of APF6:Mn4+ (A = Cs+, Rb+, K+) phosphors with single phases were obtained via a simple ion exchange method. These phosphors can possess red emission with broad excitation band in the blue regions. Meanwhile, the optimized concentration of Mn4+ in APF6:Mn4+ were investigated. The Racah parameters B and C of Mn4+ in APF6:Mn4+ are also calculated. The results indicate that Mn4+ in CsPF6:Mn4+ experiences the weakest crystal field among APF6:Mn4+. The phosphor CsPF6:Mn4+ prepared with the HPF6/K2MnF6 molar ratio of 10:1 has the strongest red-emission and the highest external quantum efficiency of 50.4 % among these samples. Meanwhile, it has the high thermal-quenching resistance and its emission intensity at 160 oC is about 1.1 times higher than that at room temperature. This sample also can remarkablely improve color rendering index and decrease the colour rendering index of white light-emitting diodes (w-LEDs). Hence, CsPF6:Mn4+ could be a red-emitting phosphor for warm w-LEDs.