Studies On Third-order Nonlinear Optical Property Of Metal Selenides And Graphene Composites

Third-order nonlinear optics is a subject that studies nonlinear effects of interaction between hard light and materials.With the development of science and technology,nonlinear optical materials play an increasingly important role in daily life and industrial production.Finding good-performance nonlinear optical materials play a vital role in improving performance of optical limiters,optical switches,and optical storage.Therefore,researching nonlinear optical materials with higher performance has become the goal,which are pursued by more and more researchers.Due to small particle size of semiconductor nanomaterials,it has excellent properties such as quantum size effect and surface effect which are not available in bulk materials,and it has more potential in the field of nonlinear optics than bulk materials.Graphene is a kind of crystalline material made of carbon atoms that have been hybridized to sp2 orbital,which can exist independently in nature.Graphene is also a kind of very thin material with two-dimensional structure.Due to its special form of electronic hybridization,graphene has stable planar structure,high specific surface area,excellent electricity,heat,light and etc.This makes it become ideal carrier for metal selenide semiconductor materials.Metal selenide semiconductor nanoparticles are attached to graphene nanosheets by chemical bonds to form composites,which can not only effectively solve the problem of easy agglomeration of nanoparticles,but also enhance the third-order nonlinear optical properties of the materials.In this dissertation,cadmium selenide(Cd Se),Zinc selenide(Zn Se)and cadmium selenide coated zinc selenide(Zn Se/Cd Se)core-shell semiconductor nanoparticles and graphene composites were prepared.The third-order nonlinear optical properties of these composites and their influence factors were investigated.The main research contents of this article are divided into the following aspects:1.Preparation and third-order nonlinear optical properties of Cd Se and graphene composite materials.The composite materials of Cd Se nanoparticles and graphene with different concentrations were prepared by low temperature hydrothermal method,and the composite materials were tested by X-ray diffraction,scanning electron microscopy,Fourier infrared change and Raman spectroscopy.The results show that Cd Se was uniform dispersed on graphene sheets,the oxygen-containing functional groups(such as hydroxyl and carboxyl groups)in graphene play a decisive role in the dispersion of Cd Se.The third order nonlinear optical properties of Cd Se nanoparticles and graphene composites were measured by Z scanning technique.The results show that the composites exhibit reverse saturable absorption and self-focusing.In addition,the third-order nonlinear polarizability of the composite material is significantly improved,which is mainly due to the good dispersion of Cd Se nanoparticles on graphene and the synergistic effect between them.2.Preparation and third-order nonlinear optical properties of Zn Se and graphene composite materials.A new simple hydrothermal method was found to synthesize Zn Se and its graphene composites.This method is environmental friendly and not causes any pollution to environment.In this way,we investigated the effects of different reaction times on Zn Se and composites.Zn Se,composites and graphene have been successfully prepared by this method,which can be proved through X-ray diffraction and Fourier infrared spectroscopy.The element distribution and element content ratio of the materials were analyzed by scanning electron microscopy.It was found that the particle size of the synthesized Zn Se monomer reached the micron level and formed microsphere structure,while the particle size of Zn Se particle in the composite material was at the nanometer level.Finally,it was concluded that graphene had inhibitory effect on the growth of Zn Se.The Z-scan technique was used to measure the third-order nonlinear optical properties of Zn Se microspheres and their composites at laser wavelength of 532 nm.The results show that nonlinear absorption response of Zn Se microspheres changes from saturation absorption to reverse saturable absorption with reaction time extending.Due to the flexible structure of graphene sheets,the third-order nonlinear properties of nanocomposites are effectively improved,making the nonlinear optical properties of composites stronger than Zn Se monomers.3.Preparation and third order nonlinear optical properties of Zn Se/Cd Se core-shell nanoparticles and graphene composites.Zn Se/Cd Se core-shell particles and graphene composites were prepared by hydrothermal method which was simple and environmentally friendly.The concentration of core-shell nanoparticles in the composite was controlled by changing the amount of graphene.Through characterization and analysis of their morphology and structure,the results show that the core-shell nanoparticles are uniformly dispersed on the graphene sheet and the size is consistent,the size is about 56.09 nm;The Z-scan test of materials were carried out by laser with wavelength of 532 nm and pulse width of 30 ps.The results show that the composite materiasl exhibit saturation absorption and positive nonlinear refraction,and can be used in laser Q-switching and other fields.This dissertation is divided into five chapters.The first chapter introduces the development of nonlinear optics,metal-selenide semiconductor nanoparticles and graphene and how to calculate the third-order nonlinear parameters of materials by Z-scan technology.The second chapter mainly introduces the third-order nonlinear optical properties of composite materials with different concentrations of Cd Se nanoparticles;The third chapter explores the third-order nonlinear optical properties of Zn Se microspheres and composites with different synthesis time.The fourth chapter introduces the third-order nonlinear optical properties of Zn Se/Cd Se core-shell nanoparticles and graphene composites.The fifth chapter is about the summary and prospect.