PHOTOLUMINESCENCE FROM INDENTED MGO CRYSTALS USING A NEAR ULTRAVIOLETVISIBLE RAMAN MICROSCOPE/

Using a Renishaw ultraviolet/visible Raman microscope and excitation r adiation 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 de formation caused considerably enhanced photoluminescence from within t he indentation as well as from the plastically deformed region around it. In both types of crystal, the photoluminescence consisted of a str ong band at 375 nm and a much weaker and broader band at 525 nm. The s trongest luminescence was obtained from within the indentation, clearl y indicating the absence of radiative quenching. On annealing the inde nts at 1000 degrees C in vacuum for 2 h, the relative intensity of the 375 nm band decreased, whereas the relative intensity of the 525 nm b and 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 pl astic strain. The effect of the annealing is to convert F+ to F center s, and to cause an overall decrease in the total number density of col or centers. (C) 1997 American Institute of Physics.