Rapidly constructed water-resistant composite shell of fluoride red phosphors K2GeF6:Mn4+ by in-situ passivation

White light emitting diodes assembled with Mn4+-doped fluoride red light phosphors are perfect photoconversion devices, but their low water stability prevents them from being used in commercial lighting displays. In this work, in order to increase the moisture resistance of the K2GeF6:Mn4+ (KGFM) phosphor, the Mn4+-free composite shell was prepared by in-situ passivation method with reducing agent SnCl2, and K2GeF6:Mn4+@ K2GeF6, K2SnF6 (PKGFM) with moisture resistance was achieved, which the shell also prevents the energy transfer to the surface defects of the phosphor. The thermal stability and luminescence decay time of the PKGFM are enhanced after surface modification, and IQE was raised from 94.37 % to 96.08 %. After immersion in water for 480 min, the luminescence intensity of the modified phosphors was 91.65 % of its initial, and IQE could still maintain 94.58 %. The WLED prepared with PKGFM was aged at high temperature (85 °C) and high humidity (85 %), after aging for 288 h, the luminous efficiency of the WLED could maintain 83 % of the initial value, and its CCT and CRI were 2979 K and 89.5, indicating that it has excellent color stability. The aging test results further demonstrate that the PKGFM phosphor contained with the Mn4+-free composite shell has good moisture resistance.