An Efficient Red Phosphor Li+, Mn4+ Co-Doped Sr4Al14O25 for Warm White Light Emitting Diodes

Abstract

Non rare earth-based Sr_{4– x /2}Li _x Al_{14 –0.01 ×4/3}Mn_0.01O₂₅ red phosphors were prepared by solid-state reaction at 1,400 °C in air. The crystal structure of the phosphors was characterized by X-ray diffraction, and its luminescent properties were investigated. The excitation spectrum had two broad excitation bands, which showed that the phosphor was effectively excited by both near-ultraviolet light and the commercially available blue light of light emitting diode (LED) chips. Simultaneously, Sr_{4– x /2}Li _x Al_{14 –0.01 ×4/3}Mn_0.01O₂₅ presented two emission peaks, which were assigned to the ²E → ⁴A₂ transitions of Mn⁴⁺ and a phonon sideband transition, and the dominant emission was located at 654 nm. The fluorescent intensities of the phosphors were influenced by the Li⁺ doping content. With optimized concentration of Li⁺ in the phosphor, the emission intensity of Sr_{4 –0.05/2}Li_0.05Al_{14 –0.01 ×4/3}Mn_0.01O₂₅ increased by 90% compared with that of Sr₄Al₁₄O₂₅:0.01 Mn. The chromaticity coordinates of Sr_{4 –0.05/2}Li_0.05Al_{14 –0.01 ×4/3}Mn_0.01O₂₅ located in the deep red region, and were about (0.72, 0.28), so, the phosphor was promising in warm white light emitting diode.