A green synthetic route to the highly efficient K2SiF6:Mn4+narrow-band red phosphor for warm white light-emitting diodes.

Mn4+‐activated fluoride red‐emitting narrow‐band phosphors have been successfully used in wide color‐gamut white LEDs for liquid crystal display (LCD) backlights. However, highly concentrated and toxic HF is usually used in their synthesis, causing environment and safety issues. In this work, we proposed a HF‐free green method, that is, using NH4F/HCl instead of HF, to synthesize a series of A2XF6:Mn4+ (A = K, Na, Rb, Cs; X = Si, Ge, Ti) phosphors. The microstructure, photoluminescence (PL) properties, thermal quenching, and applications of the synthesized phosphors were investigated. Using the proposed approach, the phosphors generally showed a pure phase, a particle size ranging from 5 to 45 μm, and some characteristic sharp emission lines of Mn4+ in the red spectral range. The internal quantum efficiency was varied in a broad range of 69%‐94% under the 460 nm excitation, depending on the composition of the fluoride host. Among these compositions, K2XF6:Mn4+ (X = Ge and Ti) phosphors even had a similar external quantum efficiency (>60%) with commercial ones. By combining K2GeF6:Mn4+ (narrow‐band red) and β‐sialon:Eu2+ (narrow‐band green) with a blue LED, a white light‐emitting diode (wLED) backlight with a color gamut of 87.7% National Television System Committee Standard, color temperature of 8423 K, and a luminous efficacy of 110.8 lm/W was demonstrated. These results indicate that the synthetic method proposed in this work is universal for preparing highly efficient fluoride phosphors used in wLEDs.

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