Experimental linear and calculated nonlinear optical properties of SeTePb glassy films

Se90Te8Pb2 and Se90Te4Pb6 compositions have been prepared in bulk and thin film forms. Transmittance and reflectance have been measured for the investigated films over the wavelength range (500-2500 nm). The studied films are transparent where no light absorbed or scattered at the longer wavelength region, while they are absorbing at shorter wavelengths. The optical constants have been determined from the analysis of the transmittance and reflectance data using Murmann,s exact equations. The observed decrease in refractive index (n) values with Pb content is attributed to the increase of polarizability with Pb addition. Analysis of refractive index data yields some important parameters. An increase of Pb content in the studied film samples enlarge the Urbach's energy Ee values from 0.071 to 0.12 eV, which considered due to increase of the disorder defect localized states. These localized states arise due to the high difference in atomic radii of Te and Pb atoms. The optical transitions are found to be indirect with optical energy gap decreasing from 1.7 to 1.19 eV with increasing Pb content. The nonlinear optical susceptibility and the nonlinear refractive index are calculated from the obtained data and their dependence of Pb content is discussed as well.