Redistribution of Cr3+ ions from Li+ to Nb5+ sites in ZnO codoped LiNbO3:Cr crystals

This Letter reports on the optical spectroscopy properties of Cr3+ ions in codoped ZnO:LiNbO3:Cr crystals. Experimental techniques such as optical absorption, luminescence, time-resolved spectroscopy and electron paramagnetic resonance have been used to investigate the site occupied by the Cr3+ ions. Two Cr3+ centres located in Li+ and Nb5+ sites (CrLi3+ and CrNb3+ centres, respectively) were observed, depending on its relative concentrations of the ZnO content in the samples. For ZnO concentrations below 4.7%, the majority of centres correspond to CrLi3+ centres, whereas, for a ZnO concentration above this threshold both centres coexist, but with the CrNb3+ centres being more predominant. The emission bands, excitation spectra and lifetimes associated with both centres are reported.