REDISTRIBUTION OF CR3-CR CRYSTALS( IONS FROM LI+ TO NB5+ SITES IN ZNOCODOPED LINBO3)

This Letter reports on the optical spectroscopy properties of Cr3+ ion s in codoped ZnO:LiNbO3:Cr crystals. Experimental techniques such as o ptical absorption, luminescence, time-resolved spectroscopy and electr on paramagnetic resonance have been used to investigate the site occup ied by the Cr3+ ions. Two Cr3+ centres located in Li+ and Nb5+ sites ( Cr-LI(3+) and Cr-Nb(3+) centres, respectively) were observed, dependin g on its relative concentrations of the ZnO content in the samples. Fo r ZnO concentrations below 4.7%, the majority of centres correspond to Cr-Li(3+) centres, whereas, for a ZnO concentration above this thresh old both centres coexist, but with the Cr-Nb(3+) centres being more pr edominant. The emission bands, excitation spectra and lifetimes associ ated with both centres are reported. (C) 1998 Elsevier Science B.V. Al l rights reserved.