Tunable optical nonlinearities of MWCNTs with core-satellite ZnS-Au structure

In order to modulate the nonlinear optical (NLO) properties of multi walled carbon nanotubes (MWCNTs) and make them applicable to ultrafast nonlinear optical devices, we fabricated a core satellite ZnS-Au nanostructure on the surface of MWCNTs via the solvothermal method. The structure and morphology of the MWCNTs-Au-ZnS product were characterized by means of the XRD, SEM and XPS, which showed that the ZnS-Au nanoassemblies were combined along with the MWCNTs through C S covalent bond and partial ionic bond. The optical nonlinearities of the MWCNTs-Au-ZnS system were investigated using the Z-scan technique under the excitation of 532 nm ps laser pulses and kinetically analyzed using the pump-probe transient absorption spectroscopy. The results showed that the saturation absorption (SA) coefficient and the third-order nonlinear susceptibility of the MWCNTs-Au-ZnS system were adjustable with the variation of the core-satellite structure. The intensity of the saturation absorption was tuned downward below that of the pure MWCNTs, while the susceptibility of the system was tuned upward above that of the pure MWCNTs, which were attributed to the combined action of two-photon absorption of ZnS, charge transfer in the system, trap states provided by Au and charge delocalization varying with the size. These tunable nonlinearities will expand the applications of the MWCNTs-Au-ZnS system in photonic devices.