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Topology of chemical ordering and influence on optical band gap in ternary Se-In-Bi chalcogenide glasses

Mosimanegape Thobega, Stephen T. Sathiaraj, Kelebogile Maabong and Cosmas M. Muiva

Spectrophotometric measurements were performed on flash evaporated amorphous Se90-XIn10BiX (x= 0, 2, 4, 6, 8, 10) thin films. The complex dielectric constant (ε) was determined from n and k spectra and was observed to increase with Bi content. The optical band gap (Eg opt) values were determined from the experimental data and compared against the theoretical ones obtained from the Shimakawa model which is based on the Random Band Network (RBN) theory. There was close correlation between the Eg opt values obtained from the two methods. The observed strong dependence of the optical band gap on Bi additive was explained on the basis of topological and chemical bond energy modifications and increased density of localized states in the mobility gap.