Site-selective spectroscopy of Cr3+ in congruent co-doped LiNbO3 : Cr3+: ZnO crystals

This work reports the energy levels of chromium ions for different sites in congruent LiNbO3 crystals doped with ZnO. Optical absorption and luminesce nce (fluorescence and excitation) experimental techniques were used. For cr ystals with Zn2+ concentration less than 4.7%, optical signals correspond t o Cr3+ ions substituting for Li+ ions; for higher Zn2+ concentration, signa ls show two components coming from different sites for active Cr3+ ions. It is accepted that these two components can be assigned to Cr3+ ions substit uting for Li+ ions and Cr3+ ions substituting for Nb+ ions. The energy leve ls of the former site are reported for the first time in this work; the T-4 (2) and T-4(1) levels lie 13 421 cm(-1) and 19 550 cm(-1) above the (4)A(2) ground level, respectively. Analysis of the excitation spectra was the key result for achieving the resolution of the new site.