Achieving moisture-stable red emission in core-shell-structured Mn4+-Doped fluoride phosphors for white LEDs

Mn 4+ -doped fluoride phosphors are promising red emitters for WLEDs owing to their narrow-band emission and high color purity. However, their practical applications are hindered by severe moisture sensitivity arising from the hydrolysis of [MnF 6 ] 2- units. In this study, a reduction-assisted surface recrystallization strategy using ascorbic acid (AA) was employed to construct an Mn 4+ -free inorganic shell, effectively suppressing hydrolysis and protecting the luminescent centers. The AA-modified Na 2 SiF 6 :6 %Mn 4+ phosphor retained 88.84 % of its emission intensity after 16 days in deionized water and 86.77 % after 6 h of boiling water exposure, whereas the unmodified sample exhibited negligible emission under the same conditions. Additionally, the AA modification led to a 130 % increase in emission intensity, an internal quantum efficiency of 97.6 %, and superior thermal stability with 97.62 % luminescence retention at 423 K. WLEDs fabricated with the AA-modified phosphor demonstrated enhanced luminous efficacy, color rendering, and long-term reliability under high-temperature and high-humidity conditions. This work provides a simple and scalable route to environmentally robust Mn 4+ -activated red phosphors, offering practical potential for next-generation solid-state lighting.