Optical reflectivity of ion-irradiated cerium dioxide sinters
Résumé
Reflection spectra of cerium dioxide sintered samples were measured in the UV-visible range after irradiation with various heavy ions (2.4-MeV Cu, 5-MeV W, 10-MeV W, 36-MeV W, 100-MeV Kr, and 200-MeV Xe). Differential reflectance spectra of irradiated samples after subtraction of the reference sample spectrum are fit with six broad Gaussian bands centered at about 1.2, 2.2, 2.8, 4.0, 4.8, and 6.2 eV. The growth curves of most bands show a saturation behavior versus ion fluence. Reflection spectra are consistent with UV-visible absorption spectra of electron-irradiated ceria single crystals for photon energies lower than and#61566;3.2 eV, corresponding to the optical gap. Spectra are tentatively analyzed on the basis of charge transfer bands and 4f and#61614; 5d transitions related to Ce3+ ion in the distorted environment formed by irradiation. More insight on defect formation is given by reflection spectra rather than the absorption ones due to the limit in absorption of the optical gap. These data are also discussed with reference to the radiation damage processes by electronic excitations and nuclear collisions in ceria.