Studies of the EPR g factors and the local structure for the trigonal Nd 3+ center in LiNbO 3:Nd 3+ crystal

Abstract

In this paper, the perturbation formulas of the EPR g factors g ∥ and g ⊥ for a 4f 3 ion in trigonal symmetry are established. In these formulas, the contributions to the g factors from the second-order perturbation terms, the admixtures of various states and covalency effect are taken into account. The above formulas are applied to the trigonal Nd 3+ center in LiNbO 3, with the related crystal-field parameters obtained from the local structural parameters of the impurity center. Based on the studies, one can find that the impurity Nd 3+ may not occupy the ideal Li + site, but undergo an off-center displacement Δ Z (≈−0.28 Å) away from the center of the oxygen octahedron along the C 3 axis. The above displacement Δ Z is comparable with that (≈−0.40 Å) obtained from Rutherford backscattering spectrometry (RBS) experiment. In addition, the calculated g factors (and also the anisotropy Δ g (= g ⊥− g ∥)) based on the Δ Z show reasonable agreement with the observed values. The contributions to the g factors and the local structure of this impurity center are also discussed.