EPR parameters and defect structures for two trigonalEr3+centers inLiNbO3and MgO or ZnO codopedLiNbO3crystals

Abstract

In this paper, the perturbation formulas of EPR parameters (g factors g(parallel to),g(perpendicular to) and hyperfine structural constants A(parallel to) and A(perpendicular to)) for the lowest Kramers doublet Gamma(6) or Gamma(7) of I-4(15/2) of 4f(11) ion in trigonal symmetry are established. In these formulas, the second-order perturbation contributions are 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 codoped LiNbO3 crystals are studied. It is 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 are displaced along the C-3 axis away from the center of oxygen octahedron by about 0.039 nm for center I and towards the center of octahedron by about 0.030 nm for center II. The reasonableness of the local lattice distortions and the contributions from the second-order perturbation terms are discussed.