Substitutional site and defect structure of Ni2+ in LiNbO3 crystal studied from the optical and electron paramagnetic resonance spectra

The energy levels (which are related to optical spectra) and effective spin-Hamiltonian parameters (g factors g(//) g(perpendicular to) and zero-field splitting D which are measured by electron paramagnetic resonance (EPR) spectra) of Ni2+ ion in LiNbO3 are calculated from the complete diagonalization (of energy matrix) method. In the calculations, the Ni2+ ion is suggested to replace Li+ ion with the local relaxation in LiNbO3. This point is in disagreement with the opinions in many previous papers in which the substitutional site and structural data of Ni2+ at Nb5+ site are used to explain the experimental data obtained by the optical and EPR spectra. The present calculated results are also consistent with the experimental values. The reasonableness of the substitutional site and defect structure of Ni2+ at Li+ site is discussed.