Ultrafast third-order nonlinear optical response of Ag modified ZnSe/ZnS core-shell structure quantum dots composite films

ZnSe/ZnS/Ag composite films were prepared on quartz substrates by magnetron sputtering and spin coating techniques.The morphology of Ag nanoparticles (NPs) with different sputtering powers and the dispersion of ZnSe/ZnS quantum dots (QDs) at different concentrations were observed by SEM and TEM. The linear absorption spectra shows the composite films which modified by Ag NPs had a blue shifted compared with the single ZnSe/ZnS QDs.The Z-scan results showed that the saturated absorption(SA) characteristics of the composite films modified by Ag NPs were significantly enhanced.The SA intensity of the composite films can be adjusted by appropriate increase the concentration of QDs, increasing the sputtering power of Ag NPs and incident laser power.By calculating the nonlinear absorption coefficients of the composite films under different conditions, it is found that increasing the excitation power is the most effective way to improve the SA property of the composite films. Compared with the single ZnSe/ZnS QDs, the βeff value of the composite films is increased by 104 orders of magnitude, which makes the ZnSe/ZnS QDs more widely used in the field of nonlinear optical devices.