Control of defect formation and ordering in Eu3+ doped RE2Ce2O7 (RE = La, Y, and Gd) red phosphor

Abstract

The control of defect formation and ordering in the lattice on the photoluminescence properties of Eu3+ doped RE2Ce2O7 is studied by the incorporation of some rare earth elements (RE = Y, La, Gd) in the system. Structural studies divulge all the compositions to crystallize into a fluorite type structure with the space group Fm3m. Raman mode analysis supplements the confirmation of the fluorite structure and further indicates an oxygen vacancy ordering in the lattice from Y to Gd. The defect formation of Ce3+ concentration from the x-ray photoelectron spectroscopy analysis shows dependence on the type of rare earths. The ordering in the lattice is associated more with the trapping/repelling of oxygen vacancy based on the rare earth. In other words, the defect formation is minimum for Gd by trapping more oxygen vacancies and maximum for the Y system due to more disorders in the lattice. The Ce3+ concentration and the ordering greatly affected the absorbance and luminescence properties. Thus, the Gd system with more ordering and less defect formation exhibited enhanced red emission of Eu3+ (612 nm), which is more than 1.8 times that of La based phosphors and 11 times better than Ce0.9O2:0.1Eu3+. Also, studies on the effect of Eu3+ concentration in the Gd2−xCe2O7:xEu3+ system indicated further improvements in the red emission intensity along with a high asymmetric ratio, good chromaticity coordinates (0.66, 0.35), and high color purity (97.6%). This study demonstrates that the role of ordering associated with defect formation plays significantly in determining the luminescence properties.