Optical property and band structure of layered sulfide La1−xYxCuS2

The system La1−xYxCuS2 has been prepared by a stoichiometric solid-state reaction of La2S3, Y2S3, Cu, and S at 1223 K. La1−xYxCuS2 in the range of x from 0 to 0.25 crystallizes in the LaCuS2 structure type, which is a layered structure. The optical band gap for La1−xYxCuS2 changes slightly between 2.23 eV and 2.26 eV, deduced from their absorption spectra. From a band structure calculation, the optical transitions for La1−xYxCuS2 mainly arise from the valence orbits of Cu and S atoms.