A facile and environmentally friendly ion exchange-assisted surface passivation (IASP) strategy is presented for synthesizing red emitting Mn⁴⁺-activated fluoride phosphors. A substantial, pristine Mn⁴⁺-free shell layer, applied as a coating to Mn⁴⁺ doped potassium fluorosilicate K₂SiF₆:Mn⁴⁺ (KSFM) phosphors, enhances both water resistance and luminescence efficiency. The stability test of fluoride in water at ambient temperature and boiling water demonstrates that IASP-treated KSFM phosphors are highly water resistant. Furthermore, both the negative thermal temperature (NTQ) fitting results and the photoluminescence (PL) decay confirm that the IASP process effectively passivates surface defects, leading to enhanced luminescence performance. The maximum internal quantum yield (QY_i) of the IASP-KSFM phosphor is 94.24%. A white LED realized a high color rendering index (CRI) of 93.09 and luminous efficiency (LE) of 149.48 lm/W. This work presented a novel technique for the development of stable fluoride phosphors and has the potential to increase the use of KSFM phosphors in plant supplementary lighting systems and white light-emitting diodes.

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.

Poor moisture resistance represents a critical bottleneck restricting the practical application of K2TiF6:Mn4+ phosphors in white light-emitting diodes (WLEDs). 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 hours of water immersion, the treated phosphors maintained 88.11% of their initial fluorescence intensity; even after boiling treatment, the internal quantum yield (IQY) still reached as high as 76.78%. WLED devices encapsulated with the modified phosphors exhibited outstanding stability during continuous operation for 432 hours 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.