Striking antithermal quenching and waterproofness of Mn4+-doped fluoride phosphors induced by synergy of double coating and single passivation

Manganese (IV) (Mn4+)-doped fluoride phosphors generally suffer two pressing problems, thermal quenching (TQ) and poor water resistance. This study reports striking luminous intensity enhancement, anti-TQ property, and waterproofness of Mn4+-doped potassium fluosilicate phosphors induced by synergy of double coating and single passivation (coating with hydroxylated graphene quantum dots (GQDs), passivation with H2O2, and coating with K2SiF6). The luminous intensity of the phosphor is approximately 163% of that of K2SiF6:Mn4+. The integrated emission intensity at 150oC is 129.3% higher than that at 30oC. The emission intensity remains 93.2% of the initial value after immersion in water for 480 min. These results are attributed to energy transfer from GQDs to Mn4+ and the formation of a stable Mn-free shell layer. In particular, the white light-emitting diodes produced using the phosphors maintained 99.6% luminescence efficiency after 240 h of operation in high-temperature, high-humidity environments. We believe that this study provides a feasible approach to simultaneously enhance the thermal stability and waterproofness of Mn4+-doped fluoride phosphors.