INFRARED LUMINESCENCE AND VIBRONIC COUPLING IN ZNTE-FE2+

Samples of crystalline ZnTe with different concentrations of iron were prepared by the vertical high-pressure Bridgman method. Absorption an d emission spectra were recorded at liquid-helium temperature in the r egion of the T-5(2)(D)reversible arrow(5)E(D) infrared transitions of substitutional Fe2+(d(6)) ions. In the range between 2400 and 2520 cm( -1) a rich structure is observed showing more lines than predicted by plain crystal-field theory. The explanation of all these lines is foun d after introducing a vibronic Jahn-Teller term to the Hamiltonian. A linear coupling between the doubly degenerate vibrational mode epsilon to the electronic orbitals of the ionic multiplet D-5 is added to the electronic and vibrational terms of the Hamiltonian. A diagonalizatio n follows using just one free parameter: the Jahn-Teller energy repres enting the strength of the coupling. The corresponding value is 3 cm- (1), which is identical to the one already reported for CdTe: Fe2+. Th e calculated spectrum is in good agreement with the one determined exp erimentally. Measurements of the absorption spectra support conclusion s drawn earlier about a Jahn-Teller coupling also for the excited mult iplet. Finally a prediction of how the far-infrared would look like is also given.