Nonlinear Zeeman behavior of Cu2+ centers in ZnS and CdS explained by a Jahn-Teller effect

The copper defect is that transition-metal impurity in II-VI compounds for which the most complete set of information has been compiled so far experimentally and theoretically. This makes it a favored system to study the mechanisms determining the optical spectra. The interpretation of the observed Cu2+ transitions in ZnS and CdS crystals is made using a coupling of the electronic states to a local vibrational mode of E symmetry and a moderate Jahn-Teller effect with a Huang-Rhys factor of S = 0.8 for ZnS and S = 1.1 for CdS. We report on parameter-free calculations of the magnetic-field splitting of Cu2+ centers in II-VI compounds, which show a general agreement with the observed spectra. For ZnS:Cu2+ the calculated g factors agree with the observed values, though a stronger nonlinear behavior with respect to the magnetic field had been found for some of the calculated energy levels. For CdS:Cu2+ the nonlinear behavior of the magnetic-field splitting is also reproduced by the calculation and the g factors agree for the (2)E excited-state doublets, whereas there are some differences for the g factors of the T-2(2) ground-state doublets, which are due to the neglect of the T-2 mode coupling in the Jahn-Teller calculation.