Theoretical study of EPR spectra and local structure for (NiO6)10− cluster in LiNbO3:Ni2+ and Al2O3:Ni2+ systems

For a d8 configuration ion, the 45×45 complete energy matrix, which contains the electron-electron repulsion interaction, the ligand-field interaction, the spin-orbit coupling interaction as well as the Zeeman interaction, has been established. By diagonalizing the complete energy matrix, the local lattice structure, EPR parameters (D, g//, g⊥) and optical absorption spectra for Ni2+ ions doped in LiNbO3 and Al2O3 have been investigated. The local structure distortion parameters ΔR, Δθ1 and Δθ2 are determined for LiNbO3:Ni2+ and Al2O3:Ni2+ systems, simultaneously. These results show that local structure of (NiO6)10− cluster exhibits an elongation distortion in both LiNbO3:Ni2+ and Al2O3:Ni2+ systems, in spite of the different reasons of the elongation in both systems. In addition, we have found that the orbit reduction effect is very important to understand the anisotropic g-factors for Ni2+ ions doped in LiNbO3 and Al2O3 crystals.