POLARIZATION SPECTROSCOPY OF CR3+ IONS IN LINBO3 SINGLE-CRYSTALS - EFFECT OF MG2+ IONS

This paper discusses the polarized absorption and luminescence spectra of Cr3+-doped LiNbO3 and Cr3+-doped MgO:LiNbO3 single crystals. In Cr3+-LiNbO3 the broad-band 4A2, 4T2 absorption transition is strongly sigma-polarized as anticipated for sites with C3 (nearly C3v) local symmetry. For this same material the sharp R-lines associated with the 4A2 <--> 2E transitions are also sigma polarized, due to admixing of the almost degenerate 4T2 and 2E excited state levels. In contrast with this behaviour, both 4A2 <--> 4T2 and 4A2 <--> 2E transitions in Cr3+-MgO:LiNbO3 are observed to be pi-polarized, suggesting that the local symmetry of Cr3+ centres is perturbed by the close proximity of Mg2+ ions.