Remarkable changes in the photoluminescent properties of Y2Ce2O7:Eu3+ red phosphors through modification of the cerium oxidation states and oxygen vacancy ordering

A new series of red phosphors based on Eu3+-doped yttrium cerate [Y1.9Ce2O7:0.1Eu3+, Y2Ce1.9O7:0.1Eu3+ and Y2Ce2−xO7:xEu3+ (x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.50)] was prepared via a conventional solid-state method. The influence of the substitution of Eu3+ at the aliovalent site on the photoluminescent properties was determined by powder X-ray diffraction, FT Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy with energy-dispersive spectroscopy, UV-visible absorption spectroscopy, photoluminescence spectroscopy and lifetime measurements. The substitution of Eu3+ at the Ce4+ site induces a structural transition from a defect fluorite to a C-type structure, which increases the oxygen vacancy ordering and the distortion of the Eu3+ environment, and decreases the formation of Ce3+ states. In contrast, phosphors with isovalent substitution at the Y3+ site exhibit the biphasic nature of defect fluorite and a C-type structure, thereby increasing the number of Ce3+ oxidation states. These modifications resulted in remarkable changes in the photoluminescent properties of Y2Ce1.9O7:0.1Eu3+ red phosphors, with emission intensities 3.8 times greater than those of the Ce0.9O2:0.1Eu3+ and Y1.9Ce2O7:0.1Eu3+. The photoluminescent properties of Y2Ce2−xO7:xEu3+ were studied at different Eu3+ concentrations under excitation with blue light. These phosphors emit intense red light due to the 5D0–7F2 transition under excitation at 466 nm and no concentration quenching is observed with up to 50 mol% Eu3+. They show increased lifetimes in the range 0.62–0.72 ms at Eu3+ concentrations. The cation ordering linked to the oxygen vacancy ordering led to the uniform distribution of Eu3+ ions in the lattice, thus allowing higher doping concentrations without quenching and consequently increasing the lifetime of the 5D0 states. Our results demonstrate that significant improvements in the photoluminescence properties can be achieved by the structural alteration of a fluorite CeO2 to a C-type lattice.