Description:
The specular reflectivity of CdCr2Se4 single crystals has been measured within the spectral energy interval 0.03 eV–12 eV at room temperature. The spectral dependence of the real and imaginary part of the dielectric constant has been obtained from a Kramers-Kronig analysis of the experimental data. From an ionic model of the spinel structure using the Born-Haber cycle the energies of the various bands and localized levels have been derived also as a function of the structure parameter u. This now enables a comparison of the optical absorption with calculated energy differences. Furthermore, the results of the pressure shift of the absorption edge and the compressibility are used to reduce the possibilities of electronic transitions at the absorption edge. For the magnetic red shift in the Cr spinels a new mechanism is proposed involving the observed dependence of the structure parameter u on the magnetic order.