Near-infrared study of radiation damage in ion-irradiated cerium dioxide and cerium-gadolinium dioxide

•We report diffuse reflectivity FTIR spectra of ceria and ceria-gadolinia sintered samples irradiated with heavy ions.•Pristine ((Ce, Gd)O2-x) samples for a variable Gd2O3 content were also measured in the same conditions.•The FTIR bands of irradiated samples are assigned to Ce vacancies and not to O vacancies.•These data are analyzed on the basis of ab initio calculations of point defects in ceria.•The respective roles of electronic excitations and elastic collisions in defect formation are discussed. Radiation damage is studied in ion-irradiated sintered CeO2 and (Ce, Gd)O2-x samples. Near Infra-red (NIR) spectra were recorded at room temperature for wavenumbers between 2800 and 11,000 cm−1 (i.e. ∼0.9–3.57 µm in wavelength and ∼0.35–1.36 eV in photon energy). Measurements were carried out by using the diffuse reflectivity mode for all of these sintered samples. Samples were irradiated with 100-MeV Kr, 200-MeV Xe, and 36-MeV W ions up to 1 × 1014 cm−2. A sintered (Ce, Gd)O2-x sample for 5 mol% Gd2O3 was also irradiated with 12-MeV Ar ions at 2 × 1014 cm−2. Four broad absorption bands centered at 3700, 4100, 6000, and 7600 cm−1 (i.e. ∼0.46, 0.51, 0.74, and 0.94 eV) are deduced from fits of the FTIR spectra for the ion-irradiated sintered CeO2 and (Ce, Gd)O2-x samples accompanied by a change in color from ivory to green. No such bands are recorded for the virgin (Ce, Gd)O2-x samples with 5, 10, and 15 mol% Gd2O3 with an increasing amount of oxygen vacancies. Absorption bands are tentatively assigned to electronic transitions involving cerium vacancy levels in the band gap, also observed under high-energy electron irradiation. The possible effects of either electronic excitations or nuclear collisions in this damage process are discussed.