INFRARED LUMINESCENCE AND APPLICATION OF A VIBRONIC-COUPLING HAMILTONIAN TO THE LEVEL STRUCTURE OF CDTE-FE2+

Samples of crystalline CdTe doped with two different concentrations of iron were prepared by the vertical high-pressure Bridgman method. Abs orption and emission spectra were recorded at liquid-helium temperatur e in the region of the 5T2(D) reversible 5 E(D) infrared transitions o f substitutional Fe2+(d6) ions. Especially in the range between 2200 a nd 2300 cm-1, a rich structure is resolved comprising more lines than predicted from plain crystal-field theory. The explanation of all the important lines is found after introducing a vibronic Jahn-Teller term to the Hamiltonian. A linear coupling between the double-degenerate v ibrational mode is-an-element-of (or gamma3) to the electronic orbital s of the atomic multiplet of symmetry 5D leads to the diagnonalization of the total Hamiltonian in a set of vibronic functions. Just one fre e parameter is used in the adjustment: the so-called Jahn-Teller energ y representing the strength of the coupling. The corresponding value t hat we report here is 3 cm-1. The energies thus found are in good agre ement with the positions of the observed lines in the spectra. With th e final wave functions we can calculate the relative intensities of th e most important transitions and approximate theoretical line shape. T his is also in good agreement with the experiment. Using these same en ergies and wave functions a calculation was performed to explain data existing in the literature about far-infrared absorption for the syste m CdTe:Fe2+. Again, good agreement between experiment and theory is fo und.