Optical spectrum, local lattice structure and EPR g factors for Cr 3+ impurity ions in MgTiO 3 and LiTaO 3

Abstract

On the basis of the 120×120 complete energy matrices for a d 3 configuration ion in a trigonal ligand field, for Cr 3+ ions doped in MgTiO 3 and LiTaO 3, the local structures and EPR g factors of the octahedral (CrO 6) 9− clusters have been studied, respectively. By simulating the calculated optical spectra and the EPR spectra data to the experimental results, local structure parameters are obtained. The calculated results show that although the local lattice structures around the M (M=Mg 2+, Ta 5+) ions are obviously different, after Cr 3+ replacing the M, the local lattice structures around the Cr 3+ ions are quite similar and close to those of the Cr 2O 3. This may be ascribed to the fact that the octahedral Cr 3+ center in MgTiO 3:Cr 3+ and LiTaO 3:Cr 3+ systems and that in Cr 2O 3 exhibit similar octahedral (CrO 6) 9− clusters. Moreover, the corresponding theoretical values of the optical spectra have been reported. It is also found that the orbital reduction factor k is very important to understand the EPR g factors for Cr 3+ ions doped in MgTiO 3 and LiTaO 3.