Mn⁴⁺-Activated Oxyfluoride CsNaWO₂F₄ Phosphor: Enhancement in the Water Stability and Thermal-Quenching Resistance

Mn⁴⁺-activated oxyfluoride phosphors play an important role in solid-state lighting and display areas due to the suitable red-light emission. However, the hydrolysis and thermal quenching of the phosphors restrict their practical applications. In this work, we prepared a novel CsNaWO₂F₄:Mn⁴⁺ oxyfluoride phosphor with high water stability and better thermal-quenching resistance; similar phosphors X₂WO₂F₄:Mn⁴⁺ (X = Na, Cs) were used as reference. A new structure model and CIF files were established by simulation. Theoretical calculations and experiments were performed to investigate the increase in water stability and thermal-quenching resistance. The luminous properties are also discussed in detail. The results show that CsNaWO₂F₄:Mn⁴⁺ exhibits a superior moisture resistance, maintaining 92.2% of the initial intensity when soaked in deionized water for 1 h and 81.7% for 24 h. A favorable thermal-quenching resistance is obtained compared with the reference, retaining about 50% of its initial intensity at 373 K. Furthermore, the WLED device fabricated with as-prepared CsNaWO₂F₄:Mn⁴⁺ phosphors, YAG:Ce³⁺ phosphors, and a 455 nm chip achieved a correlated color temperature (CCT) of 4701 K, a color rendering index (Ra) of 81.9, and a lumen efficiency of 142.52 lm/W.