Optical properties of amorphous Ge_x_Sb40 − _x_Se60 (_x_=22.5, 25, 27.5, 30 and 32.5 at.%) thin films prepared by electron beam evaporation have been measured in the visible and near-infrared spectral region. The variations of the electronic energy gap (_E_g) with composition are discussed on the basis of both the overall mean bond energy and the topological model based on the ... Read more