The perturbation formulas of electron paramagnetic resonance parameters (g factors g||, g and hyperfine structural constants A|| and A) for the lowest Kramers doublet Γ6 or Γ7 of 4I15/2 of 4f11 ion in trigonal symmetry were established. In these formulas, the second-order perturbation contributions were considered in addition to the first-order perturbation contributions considered in the previous works. Based on these formulas, the EPR parameters and the defect structures of two trigonal Er3+ centers in LiNbO3 and MgO or ZnO co-doped LiNbO3 crystals were studied. It was found that in order to reach a good fit between calculations and experiments, the Er3+ ions in centers I and II do not occupy exactly the Li+ and Nb5+ sites, respectively, but were displaced along the C3 axis away from the center of O octahedron by about 0.039nm for center I and towards the center of octahedron by about 0.030nm for center II.

EPR Parameters and Defect Structures for Two Trigonal Er3+ Centers in LiNbO3 and MgO or ZnO Co-Doped LiNbO3 Crystals. S.Y.Wu, W.C.Zheng: Physical Review B, 2002, 65[22], 224107 (6pp)