Energy level structure for the infra-red luminescence of cadmium sulphide and zinc sulphide

Banded emission spectra in the 1.3-2.3 μm range and the corresponding excitation spectra have been examined for both zinc sulphide (cubic and hexagonal) and cadmium sulphide. To explain the experimental results and to be consistent with other published experimental evidence a new model has been proposed. On this model the luminescent centre has an energy level in the forbidden zone of the energy band scheme and excitation of the infra-red emission occurs when an electron is excited to this level either from the p-state valence band or the lower lying s-state valence band. Banded infra-red emission occurs when the electron returns to the p-state valence band (which is split by crystal-field and spin-orbit effects).