Zero-field splitting of tetrahedral Co²⁺in the trigonal crystal field

Abstract

A new high-order perturbation formula for the zero-field splitting of the 4A2 ground state of d3,7 ions in a trigonal field is derived on the basis of the weak-field approximation. The formula obtained is shown to be a good approximation for the cases where the cubic field parameter Dq is less than the Racah electrostatic parameter B and is thus especially suitable for tetrahedral Co2+ complexes. By using it, the zero-field splitting of ZnO:Co2+ is calculated from a parametrised d orbit and the parameters are determined from the optical spectra. The result agrees well with the experimental finding.