The Deep Impurity Conduction Band Charge Transfer Transition In ZnSe:Co

Abstract

Novel absorption and luminescence features observed in ZnSe:Co were described briefly in a recent paper. The associated transitions involve three high energy excited states, L, M and N, of Co|£. This is established from the appearance of these transitions in the excitation spectra of the4T2->4A2infrared luminescence of C o|£ and the observation of luminescence from the lowest excited state L to four different spin quartet states of Co2+whose energy separations are accurately known from infrared absorption. The present paper contains a m uch more complete account of the experiNovel absorption and luminescence features observed in ZnSe: Co were described briefly in a recent paper. The associated transitions involve three high energy excited states, L, M and N, of Co|£. This is established from the appearance of these transitions in the excitation spectra of the 4T 2 -> 4A2 infrared luminescence of C o|£ and the observation of luminescence from the lowest excited state L to four different spin quartet states of Co2+ whose energy separations are accurately known from infrared absorption. The present paper contains a much more complete account of the experimental properties of these new transitions, including a detailed study of the magneto-optical properties and behaviour under uniaxial stress of transition L and its satellites. Among three possible models for the new states, two are discarded, particularly in view of the weak phonon coupling and the symmetric positive form of the L, M and N absorption lines. The remaining model is closely associated with the impurity -> conduction band charge transfer process since the excited states are described w ith two weakly interacting parts, the Co3+im purity core and a relatively weakly bound electron in three different syfnmetric excited states. The symmetry and F-value of excited state L are readily described by a Hamiltonian containing spin—orbit and exchange in teraction terms. However, the properties of the lower satellite L ' (2.363 eV) indicate a vibronic character which requires a dynamic Jahn-Teller interaction term . The parameters of the model required by experiment appear reasonable.