Temperature Dependent near Infrared Spectroscopy of Electron Irradiated Ceria Single Crystals.

The FTIR absorption bands of virgin and electron-irradiated CeO single crystals were measured from 20 K to 500 K between 4000 cm and 12,000 cm (830 nm to 2500 nm). Three broad bands centered at about 6100 cm (0.75 eV), 7000 cm (0.87 eV), and 10,500 cm (1.3 eV) were recorded above 100 K for the 2.5 MeV electron energy. Two smaller bands at about 4300 cm (0.53 eV) and 5500 cm (0.68 eV) were also recorded below 100 K. Similar broad bands centered at about 4100 cm (0.52 eV), 6400 cm (0.79 eV), 7600 cm (0.94 eV), and 10,500 cm (1.3 eV) are also found for the 1.4 MeV electron energy above 300 K. The evolution of these absorption bands was followed as a function of temperature. The plots of band intensity ratios show a thermally activated process corresponding to the ionization of the deep electronic levels of point defects in the band gap of ceria of 26,000 cm (3.2 eV). These five bands are assigned to the different charge states (0, -1, -2, -3, -4) of the Ce vacancies produced by elastic collisions above 1.0 MeV.