Chalcogenide glasses belonging to the GexS94 - xBi6 system (14 x 28.33 at%) have been prepared from high purity constituent elements. Thin films of the same materials have been deposited by vacuum thermal evaporation. Optical absorbance measurements have been performed on the as-deposited films. The allowed optical transition is found to be indirect and the corresponding optical gaps, Eg, are determined. The variation of Eg with the average coordination number, r, is also investigated. The observed Eg - r dependence is discussed on the basis of the chemical bonding between the constituents and the rigidity percolation threshold behavior of the network.

PHYSICA STATUS SOLIDI B-BASIC RESEARCH, Volume 239 Issue 1, Pages 251 - 256