Advancing Red-Emitting Fluoride Phosphors for Highly Stable White Light-Emitting Diodes: Crystal Reconstruction and...

Mn⁴⁺-activated fluoride red phosphors exhibit excellent luminescence properties. However, a persistent technical challenge lies in their poor moisture resistance. Current strategies primarily focus on surface modifications to effectively shield the [MnF₆]^2- species from water molecules while neglecting the underlying structure of the fluoride matrix. In this study, we introduce Si⁴⁺ and Ge⁴⁺ ions into the K₂TiF₆:Mn⁴⁺ crystal to create covalent fluoride solid solutions, namely, K₂Ti_1-SiF₆:Mn⁴⁺ and K₂Ti_1-GeF₆:Mn⁴⁺, through crystal reconstruction. The findings reveal that the incorporation of Si⁴⁺ leads to increased particle size, enhanced luminescence intensity (by 40%), and improved moisture resistance. Furthermore, after undergoing 1000 h of aging at high temperature and high humidity conditions, the white LED featuring the K₂Ti_0.97Si_0.03F₆:Mn⁴⁺ phosphor demonstrates remarkable durability by retaining 90% of its initial luminous efficacy. This performance surpasses that of the device utilizing the K₂TiF₆:Mn⁴⁺ phosphor, which only retains 74% of its original efficacy. The crystal reconstruction method and covalent enhancement strategy proposed in this work contribute to enhancing the luminescence efficiency and moisture resistance of fluoride phosphors, thereby offering new insights for advancing the development of high-efficiency and highly stable white light LED devices.