Two- and three-dimensional models for analysis of optical absorption in tungsten disulphide single crystals

The optical energy gaps of WS2 single crystal were determined from the analysis of the absorption spectrum near the fundamental absorption edge at room temperature using light parallel to c-axis incident normally on the basal plane. On the basis of two- and three-dimensional models it was found that both direct and indirect hand transitions took place in WS2 and the indirect transition was of the allowed type. The optical energy gaps corresponding to both transitions were determined and the phonon energies associated with the indirect transitions estimated. The implications of the results have been discussed.