Unusual, broad red emission of novel Ce³⁺-activated Sr₃Sc₄O₉ phosphors under visible-light excitation

Most conventional white light emitting diodes (white-LEDs) that are widely used as a new lighting system in next generation lights with Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺)-based phosphors have a low colour rendering index (CRI) because the YAG:Ce³⁺ phosphor shows a weak emission intensity in the red spectral region. Therefore, discovering a red-emitting phosphor with a high-efficiency is quite important to enhance the CRI of white-LEDs. In this study, we successfully discovered a novel, red-emitting Ce³⁺-activated Sr₃Sc₄O₉ phosphor that can be excited by blue-light irradiation at 425 nm. A crystal structure of the host material was first determined by Rietveld refinement, which indicated that it should be isostructural with Ba₃Ln₄O₉ (Ln = Sc, Y and Dy-Lu). As the Ce³⁺ content increased, the X-ray diffraction patterns shifted to a lower angle, which suggested that the Ce³⁺ ion could substitute Sc in the Sr₃Sc₄O₉ host. Under UV and blue-light excitation, the Ce³⁺-activated Sr₃Sc₄O₉ phosphor exhibited a broad emission band with a maximum peak at 620 nm, and its full width half maximum (FWHM) was 180 nm (4530 cm^-1). The highest emission intensity was obtained for Sr₃(Sc_0.997Ce_0.003)₄O₉, and the internal quantum efficiency of this phosphor under excitation at 425 nm was 53%. To the best of our knowledge, the emission band of the Ce³⁺-activated Sr₃Sc₄O₉ phosphor is the longest wavelength for a reported Ce³⁺-activated oxide phosphor.