The effects of distortion on the spectra of a Cu2+ion in a tetrahedral crystal field

A theoretical study of a Cu 2+ ion in a trigonally distorted tetrahedral crystal field has been made in order to account for the observed magnetic resonance properties of ZnO:Cu. Large values for the hyperfine constants A and B have recently been found. This contrasts sharply with the absence of hyperfine structure in the magnetic resonance observed in the only other example reported of Cu 2+ in a tetrahedral field, namely copper (αα' bromo-) dipyrromethene, where tetragonal distortion exists. It was shown that the experimental results for the latter crystal could be explained through hybridization of the free-ion 3d 8 4p( 2 D) excited state with the 3d 9 ground state. The present investigation makes the same assumption and demonstrates that the differences between the two examples may largely be attributed to the differences in the distortion of the crystal field from that formed by a pure tetrahedron. The data for ZnO:Cu indicate that the hole under consideration spends approximately 7½% of its time in a 4p and 67½% of its time in a 3d wave function attached to the central copper nucleus. The orbital motion associated with the ground state accounts for the large values for A and B .