Crystal field energy levels, spin-Hamiltonian parameters and local structures for the Cr3+ and Mn4+ centers in La3Ga5SiO14 crystals

The crystal field energy levels (obtained from optical spectra) together with the spin-Hamiltonian parameters g//, g⊥ and D (obtained from EPR spectra) for 3d3 ions Cr3+ and Mn4+ at the trigonal octahedral Ga3+ sites in La3Ga5SiO14 crystals are computed from the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model. The model takes into account the contributions due to the spin-orbit parameter of central dn ion (in the traditional crystal field theory) and that of ligand ions via covalence effect. The calculated results are in rational accord with the experimental values. The calculations also imply that the covalence of (MnO6)8− center in La3Ga5SiO14 crystals is stronger than that of (CrO6)9− center, and the impurity-induced local lattice relaxation for (MnO6)8− center is larger than that for (CrO6)9− cluster because of the larger size and charge mismatch for Mn4+ replacing Ga3+ in La3Ga5SiO14 crystals.