Energy band structure and Frenkel excitons in PbGa2S4

Optical reflection spectra are measured and calculated in PbGa2S4 crystals in the region of resonances related to excitons with large oscillator strength and binding energy (Frenkel excitons). The splitting of the upper valence band in the center of the Brillouin zone due to crystal field (Δcf) and spin orbit (Δso) interaction are determined. Optical reflection spectra are measured and calculated according to Kramers–Kronig relations in the region of 3–6 eV in Е⊥с and Е∥с polarizations, and the optical constants n, k, ε1 and ε2 are determined. The observed electronic transitions in PbGa2S4 crystals are discussed in the frame of theoretical energy band structure calculation for thiogallate crystals.