CHARGE COMPENSATION AND SITE-SELECTIVE LUMINESCENCE OF CR-3+-LINBO3

Spectroscopic studies are reported of Cr3+:LiNbO3 and of Cr3+-doped MgO-LiNbO3, With different Cr3+ doping levels. A knowledge of the defect structure of melt grown crystals enables an assignment of the R-line structure of Cr3+ ions to independent optical centres involving Nb5+ and Li+ ion sites. Site-selective laser s py of Cr3+-doped LiNbO3 confirms that charge compensation for Cr3+ ions occupying Li+ and Nb5+ sites is not via exchange coupled nearest-neighbour pairs of Cr3+ (Li+)-Cr3+(Nb5+) ions. The R lines observed using photoluminescence are shown to be inhomogeneously broadened by disorder.