High-Stable Narrow Red Emitting Homogeneous K₂SiF₆:Mn⁴⁺@K₂SiF₆ Composite Phosphor for White LEDs: Green Synthesis and Water-Resistant Mechanism

Poor water resistance and non-green synthesis remain a great challenge for commercial narrow red emitting A2MF6:Mn4+ (A=alkali metal ion; M=Si, Ge, Ti) for solid state lighting and display. We develop here a simple and green growth route to synthesize homogeneous K2SiF6:Mn4+@K2SiF6 (KSFM@KSF) red emitting composite phosphor with excellent water resistance and high efficiency without the usage of toxic and volatile HF solution. After immersed into water for 6 hours, the as-obtained water-resistant products maintain 76% of the original emission intensity while the non-water-resistant ones steeply drop into 11%. Under 85% humidity and 85 oC for 504 h (21 days), the as-obtained water-resistant products remain 80-90%, much higher than 30-40% for the non-water-resistant products. Surface deactivation enabled growth mechanism was proposed, comprehensively investigated in detail. This composite structure strategy was also successfully used to treat KSFM prepared by other methods. We believe that it will open the opportunity for excellent anti-moisture narrow red emitting A2MF6:Mn4+ to be environment-friendly synthesized in large scale toward white LED industry adoptions.