Hot lines in the infrared absorption spectra of Fe²⁺ in III-V compounds

We attempt an explanation of the main features of the high-temperature infrared absorption spectra of Fe²⁺ in III-V compounds (GaAs and GaP). We consider a linear Jahn-Teller interaction with two lattice modes of E symmetry, having energies in the range of acoustical and optical phonons, respectively. The upper vibronic states originating from all electronic states of the free ion must be considered to cope with the many possible transitions that arise at temperatures that populate several low-energy vibronic levels. We use Lanczos-recursion procedures to find energies and wave functions. A comparison with experimental energies and intensities is performed. A discussion comparing present findings with previous results based only on cold lines is also done.