The optical absorption of substitutional ${\mathrm{Fe}}^{2+}$ ions in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$Te compounds has been measured in the far infrared (10–80 ${\mathrm{cm}}^{\mathrm{-}1}$) at temperatures from 5 to 300 K. Electronic transitions inside the ${}_{}{}^5{}_{}{}^{}$E multiplet of ${\mathrm{Fe}}^{2+}$ are observed at low temperature, but the crystal-field model is not sufficient to explain the experimental features. Calculations of the ${}_{}{}^5{}_{}{}^{}$E electron states are performed, taking into account the Jahn-Teller interaction with the vibrations of the host lattice. The electron-phonon coupling is approximated by a single pair of E modes corresponding to TA(L) phonons. Energies and oscillator strengths for electric- and magnetic-dipole transitions from the ground state to excited levels are calculated within the Jahn-Teller model. An excellent quantitative agreement is obtained with the low-temperature absorption lines for a Jahn-Teller energy of 2.5 ${\mathrm{cm}}^{\mathrm{-}1}$, an effective spin-orbit splitting λ=-101.9 ${\mathrm{cm}}^{\mathrm{-}1}$, a spin-spin interaction coefficient ρ=0.18 ${\mathrm{cm}}^{\mathrm{-}1}$, and a phonon energy of the TA(L) mode (28±0.5 ${\mathrm{cm}}^{\mathrm{-}1}$) quite consistent with the neutron-scattering results. The high-temperature far-infrared absorption spectra give also evidence for a local mode of Fe in CdTe and for a two-phonon process involving the TA(X) mode of CdTe (35±0.5 ${\mathrm{cm}}^{\mathrm{-}1}$).

• Received 9 December 1991

DOI:https://doi.org/10.1103/PhysRevB.46.2183