The Optical Spectrum of HgI2

The optical spectra of tetragonal HgI 2 single crystals were investigated at 4.2 K and 79 K in 2∼6 eV region of photon energy. The main part of the dichroic optical spectra is well described by the optical transition from three p -like valence bands, which are split due to spin orbit interaction and crystal field perturbation, to an s -like conduction band. The optical structures, which seem to be due to exciton series, were observed in the fundamental absorption edge for an ordinary light. The tail part of the absorption edge was well expressed by Urbach Rule.