Optical spectrum, local lattice structure and EPR g factors for Cr3+ impurity ions in MgTiO3 and LiTaO3

On the basis of the 120x120 complete energy matrices for a d3 configuration ion in a trigonal ligand field, for Cr3+ ions doped in MgTiO3 and LiTaO3, the local structures and EPR g factors of the octahedral (CrO6)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=Mg2+, Ta5+) ions are obviously different, after Cr3+ replacing the M, the local lattice structures around the Cr3+ ions are quite similar and close to those of the Cr2O3. This may be ascribed to the fact that the octahedral Cr3+ center in MgTiO3:Cr3+ and LiTaO3:Cr3+ systems and that in Cr2O3 exhibit similar octahedral (CrO6)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 Cr3+ ions doped in MgTiO3 and LiTaO3