Highly Moisture-Stable and Enhanced Luminescence-Efficient Mn⁴⁺-Activated Red-Emitting Fluoride Phosphors via a Bi-hydrogen-Bond Organic Coating

A facile and eco-friendly ethanol-thermal method has been developed to improve the moisture resistance and luminescence efficiency of Mn4+-activated fluoride phosphors using oleylamine (OAm) as an organic coating layer. The luminescence efficiency of K2SiF6:Mn4+ phosphors was significantly enhanced after coating with the internal quantum efficiency increasing from 86.2 to 94.2%. Additionally, after being soaked in deionized water, the luminescence intensity of KSFM@OAm remained at 85.2% of its initial value, while that of non-coated KSFM decreased to 15.4%. This is due to the formation of a complete and uniform OAm coating layer that isolates KSFM crystals from humidity in the environment by forming bi-hydrogen bonds (-N-HF) between -NH2 in OAm and fluorine-terminal groups in KSFM. White light-emitting devices fabricated with commercial Y3Al5O12:Ce3+ and OAm-coated KSFM exhibit bright white light with an excellent correlated-color temperature (CCT = 4546 K), color rendering index (Ra = 89.7 and R9 = 85), luminous efficiency (LE = 155.1 lm/W), and color stability (Delta E = 6.1 x 10(-3)), indicating that OAm-coated KSFM may be a promising red phosphor for WLEDs.