Novel Red-Emitting Microwave-Assisted-Sintered LiSrPO₄: Eu³⁺ Phosphors for Application in Near-UV White Light-Emitting Diodes

Abstract

Novel red-emitting LiSr_1−x PO₄:xEu³⁺ phosphors with various concentrations (x = 0.03, 0.05, 0.07, 0.1) of Eu³⁺ ions were synthesized by microwave-assisted sintering at 1200°C for 3 h in air. The microstructural and luminescent characteristics of the LiSrPO₄:Eu³⁺ phosphors were investigated and are discussed here. x-Ray diffraction (XRD) results showed that the prepared LiSr_1−x PO₄:xEu³⁺ phosphors presented an impurity phase of Eu₂O₃ when the Eu³⁺ ions exceeded x = 0.05. Photoluminescence (PL) results showed a series of emission states ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃, and ⁵D₀ → ⁷F₄ (corresponding to the typical 4f → 4f intraconfiguration forbidden transitions of Eu³⁺) with a major emission peak at around 617 nm. The optimum concentration of Eu³⁺ for LiSr_1−x PO₄:xEu³⁺ prepared by microwave-assisted sintering was found to be 0.05. The lifetime values of LiSr_1−x PO₄:xEu³⁺ phosphors with doping concentrations of Eu³⁺ ions of 0.03, 0.05, 0.07, and 0.1 were found to be 3.32 ms, 3.30 ms, 2.84 ms, and 2.60 ms, respectively. Moreover, the chromaticity values (x, y) of all of the LiSr_1−x PO₄:xEu³⁺ phosphors were located in the red region (0.65, 0.34).