F + and F centers in α-Al2O3 by electron-induced x-ray emission spectroscopy and cathodoluminescence

Study of an α-Al2O3 single crystal by electron-induced x-ray emission spectroscopy and cathodoluminescence is reported. The relative intensities of optical emissions due to F+ and F centers have been determined as a function of the parameters of the electron beam and the annealing of the sample. It is shown that the F+ centers, i.e., the oxygen vacancies with one trapped electron, are predominant when the density of the incident electron beam increases. Similar variation is observed when the electron energy varies from 1 to 4 keV. From the comparison between x-ray and optical spectra, the F+ centers are determined to be stable defects in the bulk of the sample.