Photoconductivity and Luminescence Caused by Band-Band and by ${\mathrm{Cr}}^{3+}$ Crystal Field Absorptions in Cd${\mathrm{Cr}}_2$${\mathrm{S}}_4$

By photoconductivity measurements the direct band edge has been located at 2.5 eV. With decreasing temperature this edge shows a blue shift, also below $T_C$. Irradiation at the energies of ${\mathrm{Cr}}^{3+}$ crystal field transitions causes both luminescence and photoconduction. The latter shows a strong magnetic field dependence near $T_C$. An energy-level model for Cd${\mathrm{Cr}}_2$ ${\mathrm{S}}_4$ is proposed. In the model the energy difference between conduction-and valence-band extrema is considerably smaller (about 1.6 eV) than the optical band gap.