Structural, Linear and Third Order Nonlinear Optical Properties of Sol-Gel Grown Ag-CdS Nanocrystalline Thin Films

Pure and Ag doped CdS nanocrystalline films with different Ag doping concentrations were successfully grown on glass substrates by a sol-gel spin coating method. Ag doping was performed using silver acetate aqueous solution with 0.01, 0.02 and 0.03M concentrations via ion exchange. The influences of Ag doping on structural, vibrational, morphological, linear and third order nonlinear optical properties of CdS nanocrystalline films were studied. The x-ray diffraction patterns of the films exhibited a broad peak centered at an angle 2=26.5 degrees along the (111) plane, which confirms the cubic structure and formation of nanocrystalline films. Raman spectra of films demonstrate a shift in longitudinal optical phonon vibrations as compared to the bulk counterpart. Pure CdS film shows high transmittance (83%) in the visible and near infrared (NIR) regions. With Ag doping, a significant red shift in the band edge and reduction in the transmittance of the films in visible and NIR regions were observed. However, the films doped with Ag showed appreciable transmittance in visible region for window layer applications. A significant effect on optical parameters such as absorption index, refractive index, and optical dielectric constant was observed after Ag doping. The nonlinear optical properties of films were enhanced with incorporation of Ag atoms into the CdS binary system. The values of nonlinear optical susceptibility ((3)) and refractive index n(2) were found to increase with increasing Ag concentration and were estimated to be in the range of 2.92x10(-10)-1x10(-7)esu and 1.00x10(-9)-2.00x10(-7)esu, respectively. These values suggest that these films can be potential candidates for nonlinear optical device applications.