Epitaxial growth: Via anti-solvent-induced deposition towards a highly efficient and stable Mn⁴⁺ doped fluoride red phosphor for application in warm WLEDs

The poor moisture-resistant property of the commercial narrow band red-emitting K₂SiF₆:Mn⁴⁺ phosphor restricts its practical application in high performance warm WLEDs. Herein, we report epitaxial growth via simple ethanol-induced deposition to enhance the luminescence and moisture resistance of K₂SiF₆:Mn⁴⁺. Specifically, an appropriate amount of ethanol at the end of the synthesis leads to epitaxial growth of a K₂SiF₆:Mn⁴⁺ shell. The resultant K₂SiF₆:Mn⁴⁺@K₂SiF₆:Mn⁴⁺ presents higher photoluminescence intensity due to a high Mn⁴⁺ critical concentration in the K₂SiF₆:Mn⁴⁺ epitaxial shell. Furthermore, the epitaxial growth of the K₂SiF₆ shell on K₂SiF₆:Mn⁴⁺ is designed to conquer the moisture resistance. As expected, the formed K₂SiF₆:Mn⁴⁺@K₂SiF₆ retains 82% of the initial emission intensity after being immersed in water for 4 h and 90% after being exposed to high temperature and humidity (85 °C, 85%) for 10 days. By employing K₂SiF₆:Mn⁴⁺@K₂SiF₆ as a red phosphor, a packaged white LED exhibits excellent performance with a CRI of 96.5, a CCT of 2879 K and a luminous efficacy of 119.74 lm W^-1. More importantly, this fabricated WLED device retains high luminous efficacy and undergoes minor chromatic coordinate changes when aged at high temperature and humidity (85 °C, 85%). Therefore, these findings not only illustrate the effect of ethanol addition on the photoluminescence intensity of Mn⁴⁺ doped phosphors in the synthesis process, but also provide a facile strategy to improve the moisture resistance of K₂SiF₆:Mn⁴⁺ for warm WLEDs in the future.