The effect of pressure on the optical properties of 2H and 4H SnS₂

A study is presented of the optical absorption edge of 2H-SnS 2 and 4H-SnS 2 at 77K and 273K and as a function of hydrostatic pressure. The results are interpreted to show that for both polytypes the lowest energy optical transition is an indirect one (E g ) and that the first direct transition (E o ) follows closely to higher energies. The results show that polytypism is significant in determining both the magnitude of the energy gaps and their pressure coefficients. This suggests that layer-layer interactions are very important for the electron states responsible for the band gaps.