Defect model and electron paramagnetic resonance parameters of a FeZn+-X complex defect in ZnS crystal

The electron paramagnetic resonance (EPR) parameters (g factors gparallel, gperpendicular and zero-field splitting D) of the approximately tetragonal defect centre FeZn+-X in cubic ZnS crystal are calculated from high-order perturbation formulae based on the two spin-orbit coupling parameter model for the EPR parameters of the 3d7 ion in tetragonal symmetry. From the calculations, we suggest that the associated defect X (which is at the interstitial site on a (100) axis, but its origin and nature remain unknown) in this centre has a negatively charged state (i.e. an anion). The slightly monoclinic distortion of this defect centre is attributed to a further anion S2- vacancy Vs2- in the vicinity of defect X owing to charge compensation. The defect model is discussed