Growth and characterization of CdAl2S4 and CdAl2Se4 single crystals

Single crystals of CdAl2S4 and CdAl2Se4 showing high transparency were grown by the chemical vapour transport method. Their composition was proven by microprobe analysis. Structural investigations were done by Rietveld refinements and are in good agreement with known structure data. From transmittance and reflectance measurements the energy of the band gap was estimated. Assuming a direct nature of the corresponding optical transition the following values were obtained: E-g = 3.82 eV (RT), E-g = 3.94 eV (85 K) for CdAl2S4 and E-g = 2.95 eV (RT), E-g = 3.07 eV (85 K) for CdAl2Se4 respectively.