Studies On Third-order Nonlinear Optical Properties Of Graphene And Selenide Composite Materials

The third-order nonlinear?NLO?optical properties which was an important part of nonlinear opticalresearch,has been widely valued.The NLO material was used in the optical parametric oscillator,passive optical limiter and other nonlinear optical devices on the application of great guidance.Therefore,it is very important to study the third-order nonlinear optical properties of materials and to promote the nonlinear optical properties of materials.Semiconductor nanomaterials are limited to the order of nanometers due to their geometricaldimensions,and have special band structure and quantum confinement effects,which make them possess better optical properties than bulk materials and become a hot research topic in nonlinear materials.ZnSe and Bi₂Se₃,which are direct bandgap group II-VI semiconductors,have attracted unique attention for their unique thermal,electrical,optical and chemical properties.However,due to the tendency of these materials to agglomerate,the third-order nonlinear optical properties of the same kind of material vary greatly depending on the specific surface area and particle radius.Therefore,they can be hydrogen-bonded or covalently bonded and modified to other materials,thereby preventing agglomeration between materials,so that it has better third-order nonlinear optical properties.Graphene,as a kind of hexagonal lattice structure with carbon atoms as sp² hybrid,is atwo-dimensional inorganic nanomaterial.With its rich source,high mechanical strength,stable planar structure,excellent thermal and electrical conductivity and fast electron transport rate,high specific surface area and other properties,graphene has become an ideal inorganic non-metallic nanomaterial to preparation of composite materials and cause widespread concern.Because of its strong third-order nonlinear optical properties,graphene and semiconductor nanocomposites can not only solve the problem of easy aggregation and dispersion of semiconductor nanomaterials,but also enhance the third-order nonlinear optical properties of monomeric materials.Making the performance of composite materials greatly improved.Therefore,it is of great practical significance to study the third-order nonlinear optical properties of graphene and selenide composites.In order to further study the enhancement effect of the third-order nonlinear optical properties ofgraphene and selenide,and lay the foundation for the future application of materials on nonlinear optical devices,this paper studied the preparation,characterization and third-order nonlinear optical properties of graphene and semiconductor nanomaterial ZnSe and Bi₂Se₃ in the following aspects:Firstly,graphite oxide was used as a raw material to prepare graphene oxide by a modified Hummersmethod,and the graphene oxide with high oxygen content was obtained.The basic research on graphene oxide reduction by hydrazine hydrate was carried out.Due to the rich source of graphite powder,the experimental costs are low and samples are easier to obtain.After non-linear measurement of the sample,the results show that the sample has the third-order nonlinear optical properties.Secondly,the synthesis of graphene nanomaterials and ZnSe quantum dots?QDs?composites and thethird-order nonlinear optical effects were studied.Preparation of ZnSe QDs and their composites by controlling the amount of hydrazine hydrate by thermochemical reaction.The samples were characterized by X-ray diffraction,UV-visible absorption spectrum,Fourier transform infrared spectroscopy,transmission electron microscopy and Raman spectroscopy.The experimental results show that the X-ray diffraction peaks of ZnSe QDs correspond to the?111?,?220?and?311?crystal planes,respectively,indicating that they have a sphalerite structure.Transmission electron microscopy of the topography shows that simple QDs easily reunion,and they can be well dispersed in the graphene surface.At the same time single-beam Z-scan technology is used for measuring non-linearity optical characteristics.The results show that the third-order nonlinear optical effect of the composite is enhanced.The nonlinear optical effects of composite materials with different morphologies vary greatly.The nonlinear optical effect of the composites is due to the synergistic effect of the charge transfer between graphene and ZnSe and the enhancement of the linear absorption coefficient.However,due to the different degree of structural defects,the degree of enhancement is different.Thirdly,investigation of the third-order nonlinear optical effect of graphene nanomaterials and Bi₂Se₃QDs composites.Preparering of Bi₂Se₃ QDs and their composites by controlling the reaction time in the absence of any shielding gas at high temperature by thermal injection.The UV-visible absorption spectra of the samples were also characterized.It was found that the absorption peaks of the composites were obviously red-shifted.The structure and morphology of the samples were characterized by X-ray diffraction,Fourier transform infrared spectroscopy,Raman spectroscopy and transmission electron microscopy.The results show that the size of Bi₂Se₃ QDs is about 10 nm.The nonlinear optical effect of the sample was tested by Z-scan technique.The results of the test and analysis show that the peak shape distribution of the Z-scan open-aperture is symmetrical under the laser pulse of 532 nm and 38 ps.The result shows that the sample has saturated absorption phenomenon.At the same time,the third-order nonlinear optical properties of the composite material are enhanced compared with that of the Bi₂Se₃ QDs.This will provide more valuable parameters for the later exploration of the application of these materials in the optical limiter and so on.