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

For a d(8) configuration ion, the 45 x 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(parallel to), g(perpendicular to)) and optical absorption spectra for Ni2+ ions doped in LiNbO3 and Al2O3 have been investigated. The local structure distortion parameters Delta R, Delta theta(1) and Delta theta(2) 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. Published by Elsevier Ltd.