Ethanol-Induced Deposition of a Passivation Layer to Enhance the Water Resistance and Luminescent Properties of K2TiF6: Mn4+ Phosphors

Poor moisture resistance represents a critical bottleneck restricting the practical application of K2TiF6:Mn4+ phosphors in white light-emitting diodes. In this work, phosphorous acid was employed as a reducing agent to eliminate surface Mn4+ species and passivate the phosphor surface, followed by ethanol-induced surface deposition. This approach successfully constructed a thick K2TiF6 matrix coating layer on the phosphor particles. After 6 h of water immersion, the treated phosphors maintained 88.1% of their initial fluorescence intensity; even after boiling treatment, the internal quantum yield still reached as high as 76.8%. WLED devices encapsulated with the modified phosphors exhibited outstanding stability during continuous operation for 432 h under high-temperature and high-humidity conditions. This effective surface modification strategy significantly broadens the application prospects of Mn4+-doped fluoride red phosphors in WLEDs.