Linear and non-linear optical properties of Ag doped ZnS thin film
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Un-doped and Silver (Ag) doped zinc sulfide (ZnS) thin films were deposited on glass substrate by thermal evaporation method in the vacuum chamber with different doping concentrations. The structural properties of the thin films were analyzed by X-ray diffraction patterns. There is no peaks corresponding to impurities and Ag2O were detected which suggests that Ag ions were well incorporated in the ZnS lattice structure. On the other hand the intensity of the diffraction peaks increases with the increasing dopant concentration. This might be due the change in electronic density in the crystallographic position of Ag doped ZnS. UV measurement shows a blue shift due to the quantum confinement effect by incorporation of Ag2+ ions in ZnS thin films. The band gap values of ZnS and Ag doped ZnS nanostructures were calculated from transmission data. Photoluminescence (PL) measurements at room temperature show a PL peak at around 450 nm for all thin films. The PL intensity decreases with increasing Ag2+ ions concentration. The nonlinear optical measurements were carried out using Z-scan technique. The results reveal that the films exhibit self-defocusing nonlinearity. There is an increment in the nonlinear refractive index with increasing Ag2+ ions concentration in ZnS thin films. Open aperture Z-scan measurement shows two-photon absorption within the medium. The measurements confirm that the more concentration of Ag dopant also makes it possible to increase the nonlinear absorption coefficient. These results show that ZnS:Ag thin films are promising candidate for various potential applications in the field of nonlinear optics.
KeywordsZnS Thin film PL Nonlinear refractive index
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