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

Radiation damage is studied in ion-irradiated sintered CeO₂ and (Ce, Gd)O_2-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)O_2-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)O_2-x samples accompanied by a change in color from ivory to green. No such bands are recorded for the virgin (Ce, Gd)O_2-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.