Study on the covalence effect of the transition-metal in solids and its application for the electron states of ZnS:Co 2+ crystal

Abstract

In the investigation of optical and magnetic properties of the semiconductors containing transition-metal ions, the one-electron orbital cannot be treated as a pure d-orbital because of a strong covalence. In the energy matrix, the covalence could be described by two covalent factors ( N t and N e) associated with the t 2g and e g orbits. This paper studied the contribution of the covalent factors for d 7 electric and d 3 hole systems on the basis of a semi-SCF model and the complete energy matrix diagonalization procedure (CDP). Both the matrices of electrostatic interaction and the crystal field potential are described in generalized forms. In these forms, d 7 electron system cannot be respected as d 3 hole system because their energy matrices are different. N t and N e are not identical in the molecular orbit (MO) calculation, but a numerical calculation shows that the difference in numerical values should be small, because Racah electrostatic parameter A plays giant role when the covalence effect considered, which means that the conventional B, C and Δ scheme of crystal theory is a good approximation. These conclusions are then extended to the application of ZnS:Co 2+, the energy levels and g-factor are explained uniformly.