Magneto-optical properties of the Van Vleck semimagnetic semiconductor Cd1-xFexSe. I. The electronic structure of Fe2+

The electronic structure of the Fe2+ ion diluted in a CdSe matrix has been investigated within the manifold of the 25 wave functions corresponding to the (3d6)5D free-ion ground-state configuration, regrouped to form trigonal-field functions as a basis. The 25x25 matrices for the Fe2+ Hamiltonian and spin operator S are given. In this representation, the selection rules on the coupling of the eigenstates by an external magnetic field and by S have been derived from group-theoretical considerations. The spin-orbit parameter λ and the trigonal distortion v' have been determined from the Raman spectra which exhibit sharp excitations at 13 and 17.6 cm-1, due to internal transitions of Fe2+ ions from their ground state to the first two excited states. The result is λ=-95.3 cm-1 and v'=43.2 cm-1. A good agreement is found between theory and experiment on the selection rules for the observation of resonant Raman scattering, and the Raman shifts as a function of the magnetic field H<6 T applied in both parallel and perpendicular directions to the c axis