The low-energy absorption and reflectivity of Hg2P2S6 and Hg2P2Se6

Absorption and reflectivity measurements have been performed on Hg2P2S6 and Hg2P2Se6 samples in the energy range from 1.6 to 5.5 eV at room temperature. Optical absorption results indicate that the absorption edge arises from a direct transition for both compounds. The reflectivity spectra show a striking similarity: two maxima are present in both materials for photon energies greater than that of the absorption edge; These structures have been interpreted as direct allowed interband transitions. The interpretation is based on the so-called transition metal weakly interacting model. In order to indicate the possible electronic transitions responsible for the observed reflectivity structures, a schematic energy level diagram is proposed for both compounds.