Investigations on the g factors of the ground and excited states for Cu2+ ions in ZnO crystal

摘要

The g factors g// and g⊥ of the ground Γ_6(~2T_2) and excited Γ_(4,5)(~2E), Γ_6(~2E) states for trigonal Cu~(2+) centres in ZnO crystals are calculated from three theoretical methods, the complete diagonalization (of the energy matrix) method, the second-order perturbation method (PTM-I) and the simplified second-order perturbation method (PTM-II, this method was described in an earlier paper). These methods are based on the cluster approach in which the spin-orbit coupling parameters Χ, Χ' and the orbital reduction factors k, k' are calculated from a semi-empirical molecular orbital method. The crystal-field parameters used in the calculations are obtained from the superposition model and so the defect structure of Cu ~(2+) centres in ZnO can be acquired. The calculated g factors from the three methods are in reasonable agreement with the experimental values and the defect structure of Cu~(2+) centres in ZnO is acquired. It appears that in some cases the approximate PTM can be applied in the studies of g factors of various states. The conditions that the PTM are ineffective are discussed.