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

Abstract

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, K2Ti1–x Si x F6:Mn4+ and K2Ti1–y Ge y F6: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 K2Ti0.97Si0.03F6: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.

Millimeter-Sized K2MnF6:Si4+, NH4+ Red-Luminescent Crystals with High Absorption Efficiency (AEmax of 93.5%) and External Quantum Efficiency (EQEmax of 68.9%) Grown by Cooling-Induced Crystallization

“…Red-luminescent Mn 4+ -activated fluoride phosphors, typically K 2 SiF 6 :Mn 4+ , have been commercially used in white light-emitting diodes (WLEDs) backlights for liquid crystal displays to achieve a wide color gamut . However, the fluoride phosphors exhibit poor moisture resistance as the [MnF 6 ] 2– groups, especially those at the particle surface and grain boundary, are prone to undergo hydrolysis. , This would lead to the formation of Mn-(hydro)­oxides, causing a severe decrease of the luminescence efficiency. One way is to develop oxide-based red phosphors − with high stability such as Sr 3 TaO 5.5 :Eu 2+ ; alternatively, a series of strategies have been utilized for the fluoride phosphors to improve the waterproofness.…”