Some Optical properties for Ag x( Ga 0.4 Se 0.6 ) 100 - x system (x?=?2.5, 5.0, 7.5, 10.0 and 12.5)

Thin films for Agx(Ga0.4 Se0.6)100-x (x=2.5, 5, 7.5, 10 and12.5 at. %) which prepared by thermal evaporation technique in room temperature, The optical properties of Agx(Ga0.4Se0.6)100-x films as a function of Ag-content were studied by measurements (for spectrum range 400-1100 nm). Transmittance, T and reflectance, R were measured. The extinction coefficient, k and the refractive index, n were found to be practically dependence on the film composition, optical energy gap (Eg opt), dispersion energy (Ed), oscillator energy (Eo) as well as, the high frequency dielectric constant () and the lattice dielectric constant (L). The optical gap, Eg opt decreases (2.7: 2.4 eV) as the Ag-content increase (2.5:12.5at%), this decrease was attributed to the increase of the density of localized states according to Mott and Davis model. ..