Investigations of EPR parameters and defect models for three Yb~(3+) impurity centers in ThO_2 and CeO_2 crystals

摘要

The electron paramagnetic resonance (EPR) parameters (g_(ll) factors g_(ll), g_⊥ and hyperfine structure constants ~(171)A_(ll), ~(171)A_⊥, ~(173)A_(ll) and ~(173)A_⊥) for three Yb3+ centers, one cubic (center I) and two trigonal (centers II and III), in ThO_2 and CeO_2 crystals are studied from a complete diagonalization (of energy matrix) method. In the method, the Zeeman and hyperfine interaction terms are added to the classical Hamiltonian and the crystal-field parameters are calculated from the empirical superposition model. From the studies, the EPR parameters for these Yb~(3+) centers in ThO_2 and CeO_2 crystals are reasonably explained, the defect model for the trigonal Yb~(3+) center II suggested in the previous paper is confirmed and the defect structure of center II are also obtained. The theoretical hyperfine structure constants A of two Yb isotopes for centers II and III are suggested and remain to be checked by further experiments. The results are discussed.