Flux-assisted low-temperature synthesis of Mn4+-doped unusual broadband deep-red phosphors toward warm w-LEDs

Abstract Rare-earth free ions, especially Mn4+, doped phosphors with red emission have become a research hotspot. To achieve high-performance phosphor-converted warm w-LEDs, blue light activable Mn4+-doped phosphors with broadband red emission rather than the commonly sharp ones are highly desired. In this work, we report a novel Mn4+-doped Li2Mg3TiO6 phosphor prepared by the conventional solid-state reaction and the synthesis temperature is remarkably lowered from 1300 °C to 950 °C with the addition of LiF flux. The fluorescence properties were well characterized by steady and transient state spectroscopies. The occupation of Mn4+ ions for the center of octahedral sites leads to a blue light excitable phosphor showing unusual broadband deep-red emission. The addition of LiF enhances the Mn4+ emission intensity and 0.1 mol% Mn4+-doped phosphor attains the highest red emission intensity with the maximum PLQY = 35.1%. The Mn4+ emission presents good thermal resistance demonstrated by high-temperature dependent fluorescence and activation energy ΔE = 0.369 eV. The as-obtained red phosphor enables the fabrication of a warm w-LED device by the combination of commercial YAG yellow phosphor and blue LED (BLED) chip, giving CIE(x, y) = (0.307, 0.337), CRI = 83.9 and CCT = 5258 K. This work provides a promising candidate Li2Mg3TiO6:Mn4+ as broadband deep-red phosphor for warm w-LEDs as well as a method to effectively lower the preparation temperature.