All-Inorganic Green Synthesis of Small-Sized and Efficient K 2 SiF 6 :Mn 4+ Phosphor for Mini-LED Displays.

High-resolution liquid crystal display (LCD) backlight requires a color conversion layer featuring micrometer light-emitting particles and a uniform morphology. The widely used commercial red-emitting K 2 SiF 6 :Mn 4+ phosphor, showing promise as a light-conversion candidate, faces limitations due to its toxic synthesis process, large particle size, and poor moisture resistance. We successfully demonstrated an efficient substitution of the highly toxic HF/TEOS/KHF 2 solvent system with a commonly used HCl/SiO 2 /KF solvent system to synthesize the small-sized K 2 SiF 6 :Mn 4+ phosphor. Additionally, surface passivation was performed to enhance the luminescence intensity and resistance to moisture, denoted as K 2 SiF 6 :Mn 4+ @CaF 2 . Accordingly, the K 2 SiF 6 :Mn 4+ @CaF 2 phosphor presents a high luminescence efficiency (99.87%/32.84% IQE/EQE) with an average particle size of ∼2.67 μm. Notably, after exposure to 85% humidity and 85 °C temperature for 3 h, the luminescence intensity remains at 47.4% for K 2 SiF 6 :Mn 4+ @CaF 2 , while 21.2% for pristine K 2 SiF 6 :Mn 4+ , and only 3.5% for K 2 SiF 6 :Mn 4+ synthesized by TEOS. These advancements hold great potential for improving high-resolution LCD backlighting, particularly for displays with micron-level pixels, opening up new possibilities for enhanced display technology.