Highly Regular, Uniform K3ScF6:Mn4+ Phosphors: Facile Synthesis, Microstructures, Photoluminescence Properties, and Application in Light-Emitting Diode Devices.

A new generation of red phosphors of complex fluoride matrices activated with Mn4+ has gained a broad interest in getting high color quality and low color temperature of solid-state white light-emitting diodes (WLEDs). However, besides their instability toward moisture, the extremely irregular and nonuniform morphologies of these phosphors have limited their practical industry applications. In the present study, a novel type of K3ScF6:Mn4+ red phosphor with highly regular, uniform, and high color purity was obtained successfully through a facile coprecipitation route under mild conditions. The crystal structure was identified with aids of the powder X-ray diffraction, Rietveld refinement, and density functional theory calculations. The prototype crystallizes in the space group Fm3 m with a cubic structure, and the lattice parameters are fitted well to be a = b = c = 8.4859(8) Å and V = 611.074(2) Å3. The Mn4+ ions occupy Sc3+ sites and locate at the centers of the distorted ScF6 octahedrons. A wide band gap of approximately 6.15 eV can provide sufficient space to accommodate impurity energy levels. Unlike most other Mn4+ ion-activated fluoride phosphors, the as-prepared K3ScF6:Mn4+ phosphors demonstrate highly uniform and regular morphologies with shapes transforming from cube to octahedron with increasing Mn4+ ion concentration. Under blue light excitation, the as-prepared K3ScF6:Mn4+ sample exhibits intense sharp-line red fluorescence (the strongest peak located at 631 nm) with high color purity. An excellent recovery in luminescence upon heating and cooling processes implies high stability of K3ScF6:Mn4+. Furthermore, a warm WLED fabricated with blue GaN chips merged with the mixture of K3ScF6:Mn4+ and the well-known commercial YAG:Ce3+ yellow phosphors exhibits wonderful color quality with lower correlated color temperature (3250 K) and higher color-rendering index ( Ra = 86.4). These results suggest that the K3ScF6:Mn4+ phosphor possesses stupendous potentiality for practical applications.