Enhanced phase miscibility and luminescence by inducing oxygen vacancies in Ce1−xEuxO2−δ under a strongly reducing atmosphere

A novel synthetic process was used to achieve complete solid solubility in micrometer-sized Ce1−xEuxO2−δ (x=0.15, 0.3) particles at temperatures ≤1300 °C with enhanced photoluminescence. The most important part of this process was to reduce the sample under 10 Torr H2 gas at 1300 °C. The reduced micrometer-sized particles (x=0.15, 0.3) showed a single fluorite phase (Fm-3 m, a≈5.45 Å). Oxidizing in air at temperatures >1300 °C resulted in the decomposition of this single phase into two fluorite phases with different lattice parameters. An acute increase in the oxygen vacancy concentration by the reduction process was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The oxygen vacancies and Eu3+ ions migrated to the particle surface during the oxidation process. An excess of oxygen vacancies plays a key role in producing complete solubility as well as enhancing the photoluminescence intensity. The reduction process adopted in this study is quite effective in producing an excess of oxygen vacancies, increasing the Ce3+/Ce4+ ratio, and enhancing the phase miscibility, which fortify the local asymmetry environments of Eu3+ ions.