Optical bleaching of <f>Cr3+</f> luminescence in near stoichiometric <f>LiNbO3</f> crystals codoped with MgO

The emission intensity of the R-line of <f>Cr3+</f> ions in near stoichiometric <f>LiNbO3</f>crystals codoped with MgO has been studied at a low temperature under excitation of the <f>4A2→4T1</f> transition. The R-line emission intensity associated with <f>Cr3+</f> ions in the <f>Nb5+</f> site, <f>[Cr]Nb</f> centre, was observed to decrease with the illumination time whereas the <f>Cr3+</f> ions located in the Li site, <f>[Cr]Li</f> centres, are optically stable. This selective bleaching is explained by considering the photoionization of <f>Cr3+</f> ions in <f>Nb5+</f> sites and the formation of <f>Nb4+</f>. [Copyright &y& Elsevier]