An Ultra-High Yield of Spherical K2NaScF6:Mn4+ Red Phosphor and its Application in Ultra-Wide-Color-Gamut Liquid Crystal Displays
Mn4+-activated narrow-band red-emitting fluoride phosphors are an efficient red compensator to widen the color gamut and improve the color quality of pc-WLEDs for backlight display applications. However, the low synthetic yields and extremely nonuniform, irregular morphologies of these fluorides seriously restricted their practical industry applications. Here, a novel Mn4+-doped narrow-band red-emitting phosphor K2NaScF6:Mn4+ was prepared through a simple co-precipitation route. High-resolution synchrotron XRD and its Rietveld refinement reveals that K2NaScF6:Mn4+ crystallized in the space group "Fm" "3" @#x0305;"m" with a cubic structure and the octahedral Sc3+ sites were occupied by Mn4+, resulting in a very small amount of alkali metal cation vacancies for charge compensation. The electronic band gap of K2NaScF6 was calculated to be 6.46 eV by DFT calculations, which ensured the location of Mn4+ energy levels in the host band gap and was verified by DRS results. Unlike the previous reported Mn4+-activated fluorides, K2NaScF6:Mn4+ has an ultra-high synthetic yield (~100%) and a uniform spherical morphology with extremely narrow size distribution (~1.17 μm). Excess of KHF2 and the extremely low solubility of K2NaScF6 are proved to be responsible for the high synthetic yield of K2NaScF6:Mn4+. Under blue light illumination, the K2NaScF6:Mn4+ exhibits intense sharp-line red fluorescence peaked at 630 nm. Meanwhile, the ZPL intensity could be tailored through control of the Mn4+ amount in K2NaScF6 matrix. By employing the efficient and stable K2NaScF6:Mn4+ as an efficient red emitter, two pc-WLEDs with ultra-wide color gamut (Rec. 2020 value of 95.1% and NTSC value of 127.3% for LED-1, Rec. 2020 value of 96.7% and NTSC value of 129.5% for LED-2) were obtained successfully. These results suggest great potential of K2NaScF6:Mn4+ as a red-emitting phosphor for applications in high-quality backlight displays, and this work may open a perspective for researchers to design new luminescence materials with high synthetic yield and uniform spherical morphology.