The Jahn-Teller interaction and 3d⁹ions at tetrahedral sites

Experimental data on 3d 9 ions (Cu 3+ and Ni + ) at tetrahedral sites is reviewed and compared to the predictions of crystal field theory including the effects of covalency, 4p configurational mixing and the Jahn-Teller effect. Of the copper centres considered, only for the case of ZnO is this theory found acceptable and to make the optical and epr results consistent it is necessary to include second order Jahn-Teller effects. The first order reduction factor for angular momentum is found to be about 0.1. The hyperfine effect is explained using a reduction in the magnitude of the contact term caused by 4p mixing, as has previously been found in tetragonally distorted complexes.