An-Najah Staff

Chalcogenide glasses belonging to the Ge_xS_{94 − x}Bi₆ 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, E_g, are determined. The variation of E_g with the average coordination number, 〈r〉, is also investigated. The observed E_g − 〈r〉 dependence is discussed on the basis of the chemical bonding between the constituents and the rigidity percolation threshold behavior of the network.