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

Abstract

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 ${\mathrm{Cu}}^{2+}$ 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 ${\mathrm{Cu}}^{2+}$ centers in II-VI compounds, which show a general agreement with the observed spectra. For ZnS:${\mathrm{Cu}}^{2+}$ 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:${\mathrm{Cu}}^{2+}$ 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 $^{2}$${\mathit{T}}_{2}$ ground-state doublets, which are due to the neglect of the ${\mathit{T}}_{2}$ mode coupling in the Jahn-Teller calculation. \textcopyright{} 1996 The American Physical Society.