Local structures in the superionic conductorY3+-dopedCeO2studied using site-selective spectroscopy

Luminescence spectra of ${\mathrm{Eu}}^{3+}$ ions in ${\mathrm{Y}}^{3+}$-doped ${\mathrm{CeO}}_2$ crystals are measured as a function of excitation wavelength for samples of various ${\mathrm{Y}}^{3+}$ concentrations. ${\mathrm{Eu}}^{3+}$ ions, which partially substitute for ${\mathrm{Y}}^{3+}$ ions, act as a structural probe. It is found that six different sites of ${\mathrm{Eu}}^{3+}$ ions exist in this material. A local-structure model is proposed for these sites and experimental results are well explained with this model. The dopant-concentration dependence of the luminescence spectra reveals that the defect center of the oxygen vacancy associated with one ${\mathrm{Y}}^{3+}$ ion is closely related to the ionic conducting mechanism in this sytem.