Studies On Third Order Nonlinear Optical Property Of Mn S And Its Graphene Composites

Emergence of hard light sources has made the emerging discipline,which is nonlinear optics,begin to develop.Nonlinear optics plays an important role in the fields of laser technology,optoelectronic technology,optical limiting,optical modulation and communication technology.In recent years,with continuous advancement of science and technology,the property of nonlinear optical materials,such as nonlinear refraction and absorption property,has gradually failed to meet requirements in practical applications.Therefore,exploring new nonlinear optical materials and making their nonlinear property controllable become an important direction for researchers.Semiconductor nanomaterials show superior characteristics on photoelectricity and nonlinearitye,they have important application potential in the manufacture of optoelectronic devices and nonlinear devices.Semiconductor nanomaterial can be combined with carbon materials such as carbon nanotubes and graphene through physical or chemical methods.Graphene is two-dimensional structure containing only carbon atoms with hexagonal lattice structure and thickness of one carbon atom.It has attracted much attention in many fields such as energy,materials,physics and chemistry.Fast electron migration and conductivity,excellent thermal,electrical,and mechanical property make graphene also be good based material for semiconductor nanoparticle.Covalent bonds exist between semiconductor nanoparticles and graphene,which can make semiconductor nanomaterials to distribute on its surface,and can greatly improve performance of composite material.The main contents of this paper are:First,MnS nanoparticles were prepared by hydrothermal method,and size and crystal form of MnS nanoparticles were changed by controlling hydrothermal time.It is of great significance to study the reason why semiconductor materials have adjustable third order optical nonlinearity through changing crystal and size.Z-scan technique was used to test size-limited NLO(nonlinear optical)property with laser pulse of 30 ps at 532 nm.Nanoparticles of different crystal forms exhibit different nonlinear optical responses.Because yMnS has narrower energy band than aMnS,it has higher fluorescence quantum yield and better nonlinear response.As size of aMnS nanoparticles decreases,two-photon absorption and nonlinear refraction are increased.The maximum NLO susceptibility of nanoparticles is 3.09×10-12 esu.The max susceptibility is about nine times higher than minimum value.However,when size is further reduced,susceptibility of nanoparticles is reduced.This trend can be explained by effect of light-induced dipole moment.Moreover,defects in ?MnS nanoparticles also have influence on NLO property.Results show that MnS nanoparticles have potential application value in optical confinement and optical modulation.Second,we explored nonlinear optical property of graphene-?MnS.The graphene-?MnS was prepared by hydrothermal method.By controlling hydrothermal time,the size of composite material is changed,and size increases with time extending.The attachment of aMnS on graphene surface changes all kinds of property compared with pure nanoparticles.The Z-scan technique was used to test three order nonlinear optical property of material using picosecond laser.It was found that nonlinear response of composite material was significantly enhanced and composite materials with different synthesis times exhibited different nonlinear responses and certain trend.This may be due to the change in stacking state of aMnS nanoparticles on graphene surface,resulting in changes in NLO response.The results show that graphene-?MnS composites have potential applications in manufacture of photonic devicesThird,we explored nonlinear optical property of graphene-yMnS.yMnS nanoparticles and graphene are combined by covalent bond.The distribution of particles and oxygen-containing groups on graphene-yMnS surface is controlled by changing the amount of graphene oxide added in composite material.A variety of characterization methods are used to characterize composite to obtain structural information.The results show that material has good wurtzite structure,the size of yMnS nanoparticles is around 100 nm,and there may be electron transport between nanoparticles and graphene.The Z-scan technique is used to test third order nonlinear optical property of composite material through picosecond laser,so we can explore the mechanism of nonlinear response of composite material.The results show that nonlinear optical property of graphene-yMnS composites are significantly enhanced with covalently connected.The enhancement of nonlinear response stems from synergistic effect in the local electric field between yMnS nanoparticles and graphene,including local field theory and charge transfer.And the non-radiative defects in graphene-yMnS also influence NLO property,which is the important reason that increase of susceptibility is limited in one magnitude.As the amount of graphene oxide added in graphene-yMnS increases,the susceptibility of composite decreases first and then increases.After yMnS nanoparticles are combined with graphene oxide under high temperature and pressure,oxygen-containing groups on surface of graphene oxide are gradually reduced,sp3 clusters are gradually transformed into sp2 domains.The dispersion of yMnS on graphene may change surface state and density of defects.So nonlinear response of material decreases first and then increases.The experimental results show that the composite materials have potential applications in manufacture of optical limiters and all-optical devicesFinally,the main work of this dissertation is summarized and the future work is prospected,and problems and basic ideas to be further solved are pointed out.