All-Inorganic Green Synthesis of Small-Sized and Efficient K2SiF6:Mn4+ 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 K₂SiF₆:Mn⁴⁺ 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/KHF₂ solvent system with a commonly used HCl/SiO₂/KF solvent system to synthesize the small-sized K₂SiF₆:Mn⁴⁺ phosphor. Additionally, surface passivation was performed to enhance the luminescence intensity and resistance to moisture, denoted as K₂SiF₆:Mn⁴⁺@CaF₂. Accordingly, the K₂SiF₆:Mn⁴⁺@CaF₂ 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 K₂SiF₆:Mn⁴⁺@CaF₂, while 21.2% for pristine K₂SiF₆:Mn⁴⁺, and only 3.5% for K₂SiF₆:Mn⁴⁺ 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.