Luminescence properties of Eu2+- and Ce3+-doped CaAl2S4 and application in white LEDs

The Eu2+- and Ce3+-doped CaAl2S4 phosphors were comparatively synthesized by conventional solid-state reaction and the evacuated sealed quartz ampoule. The X-ray diffraction (XRD) patterns show that the sample with better crystalline quality was prepared by the evacuated sealed quartz ampoule, resulting in the enhancement of the emission intensity of Eu2+ ion by a factor of 1.7. The intensive green LEDs were also fabricated by combining CaAl2S4:Eu2+ with near-ultraviolet InGaN chips (λem=395 nm). The dependence of as-fabricated green LEDs on forward-bias currents shows that it presents good chromaticity stability and luminance saturation, indicating that CaAl2S4:Eu2+ is a promising green-emitting phosphor for a near-UV InGaN-based LED. In addition, the optical properties of CaAl2S4:Ce3+ were systematically investigated by means of diffuse reflectance, photoluminescence excitation and emission, concentrating quenching and the decay curve.