NEAR AND FAR-INFRARED TRANSITIONS OF FE2-VI SEMICONDUCTORS - DYNAMIC JAHN-TELLER INTERACTION( IN CUBIC II)

Optical-absorption and emission measurements of doubly ionized iron in CdTe, ZnTe, ZnSe and ZnS have been analyzed by means of a vibronic co upling model. The model [1] is based on the crystal-field theory, incl uding spin-orbit and spin-spin interactions and Jahn-Teller couplings of the orbital doublet and triplet states of Fe2+ with overtones of ph onons of Gamma(3) and Gamma(5) symmetries, respectively. Starting from the 25 spin-orbit wave functions appropriate to the orbital doublet a nd triplet manifolds, the symmetry-adapted vibronic basis is construct ed and used to diagonalize the Hamiltonian matrix formed out of five b locks of symmetry Gamma(1), Gamma(2), Gamma(3), Gamma(4) and Gamma(5). Phonon overtones up to N=6 for the Gamma(3) phonon and up to N=10 for the Gamma(5) phonon were included to ensure convergence of the energy values and eigenfunction of the vibronic states. The available measur ed positions and relative intensities of the spectral lines in the nea r and far infrared are accounted for within the experimental accuracy. It is shown that the above mentioned iron based II-VI compounds (ZnS: Fe2+ excepted) exhibit a strong dynamic Jahn-Teller coupling of the up per orbital triplet state with phonons of Gamma(5) symmetry and that t he spin-orbit interaction between the orbital doublet and triplet stat es of Fe2+ is essential to explain the data.