Photoluminescence from indented MgO crystals using a near ultraviolet/visible Raman microscope

Using a Renishaw ultraviolet/visible Raman microscope and excitation radiation of 325 nm from a HeCd laser, photoluminescence investigations have been made in the wavelength region 325–726 nm of indentended MgO crystals of 99.9% and 99.99% purity. It was found that the plastic deformation caused considerably enhanced photoluminescence from within the indentation as well as from the plastically deformed region around it. In both types of crystal, the photoluminescence consisted of a strong band at 375 nm and a much weaker and broader band at 525 nm. The strongest luminescence was obtained from within the indentation, clearly indicating the absence of radiative quenching. On annealing the indents at 1000 °C in vacuum for 2 h, the relative intensity of the 375 nm band decreased, whereas the relative intensity of the 525 nm band increased. It has been suggested that the 375 and the 525 nm bands are probably due to the F+ and F centers, respectively, and that the relative number density of the F+ centers increases with increasing plastic strain. The effect of the annealing is to convert F+ to F centers, and to cause an overall decrease in the total number density of color centers.