Investigations of the spin-Hamiltonian parameters for Er3+ at the Th4+ site in ThGeO4

The spin-Hamiltonian (SH) parameters g factors g(parallel to), g(perpendicular to) and the hyperfine structure parameters A(parallel to) and A(perpendicular to) for Er3+ at the tetragonally distorted dodecahedral Th4+ site in ThGeO4 are theoretically investigated by using the perturbation formulas of the SH parameters for a 4f(11) ion in tetragonal symmetry. In these formulas, the contributions to the SH parameters from the second-order perturbation terms and the admixture of various energy levels are taken into account. The related crystal-field parameters are calculated from the geometrical relationship of the impurity center and the superposition model. Based on the studies, the lowest Kramers doublet is found to be Gamma(7), rather than Gamma(6) suggested in the previous work. The calculated SH parameters for Gamma(7) doublet in this work are smaller than those obtained for Gamma(6) doublet in the previous work and in good agreement with the observed values. The various contributions to the SH parameters are discussed. (c) 2004 Elsevier B.V. All rights reserved.