Theoretical calculations and photoluminescence properties of Sr4Al14O25:Mn4+ red phosphors doped with Li+

The absence of high-efficiency oxide red phosphors restricts the development of high-performance solid-state lighting. In this work, a series of Li⁺ doped Sr₄Al₁₄O₂₅:Mn⁴⁺ (SAO-Li⁺) red phosphors were prepared. Theoretical calculation results indicate that Li⁺ is inclined to occupy the gap 2 position. The low concentration Li⁺ gap doping has almost no influence on the Sr₄Al₁₄O₂₅ structure, and a 0.4 mol Li⁺-doped sample exhibits a pure phase with regular morphology. With increasing Li⁺ doping content, the luminescence intensities of phosphors increase first and then decrease. 0.4 mol is found to be the optimal concentration. The fluorescence lifetime continues to decrease with the increase in the Li⁺ doping content and a mutation occurs at 0.5 mol Li⁺. Phosphor doping with Li⁺ can improve the thermal quenching resistance. The WLED device encapsulated with SAO-0.4Li and YAG:Ce³⁺ phosphors prepared showed a correlated color temperature of 4667 K, a color rendering index of 82, and a light efficiency of 137.34 lm W^-1 at a driving current of 20 mA. The above results indicate that the use of a SAO-0.4Li⁺ phosphor is expected for application in warm WLEDs.