Study On Nonlinear Optical Property Adjustment Of Graphene And MOF Materials

With the rapid development of the Internet,digital traffic jam has become a potential threat to the development of information technology.For data centers,metro networks and supercomputing facilities,building ultra-fast photonic devices has become an urgent need.Undoubtedly,this problem needs to be solved from the fundamental chemistry of photonic materials and the collaborative innovation of device engineering.Nonlinear optical(NLO)materials play an important role in the development of photonic platforms,which has attracted a lot of attention.A large number of materials with excellent nonlinear responses have been discovered,such as carbon materials including graphene and carbon nanotubes,and porous materials including metal-organic framework(MOF)and covalent organic framework(COF).However,these known nonlinear materials have gradually failed to meet the needs of practical application.We need to adjust the nonlinear response of materials by internal adjustment(such as molecular structure adjustment)or external adjustment of materials(such as functionalization of these materials by combining with other materials or doping metal ions)to meet the needs of practical applications.In this paper,graphene,which is representative of carbon materials,and MOF,which is representative of porous materials,are selected to systematically study the influence of internal and external adjustment of materials on the nonlinear response of materials.The main research work of this paper is as follows:First,the external adjustment of graphene is carried out by hydrothermal method.In this paper,graphene was functionalized by recombination of Ni doped Zn S nanoparticles with graphene.Morphology characterization confirmed that the Ni doped Zn S nanoparticles anchored on the surface of graphene can effectively avoid the accumulation of nanoparticles,and the Zn S nanoparticles can form a close contact with the surface of graphene.External adjustment of graphene was mainly carried out in two ways:(1)composite of graphene with Ni doped Zn S nanoparticles;(2)composite of graphene with different size Zn S nanoparticles.The Z-scan results showed that the maximum nonlinear absorption coefficient,nonlinear susceptibility and nonlinear refractive index of Ni-Zn S/RGO among all the products were obtained at Ni doping concentration of 2.5% and Zn S size of 110?nm(growth time 2?h),which were 25,18 and 23 times of those of RGO.Due to the charge transfer between Zn S and graphene,and the introduction of impurity level forming a significant trap effect inhibits electronic hole pairs of composite,the NLO properties of composites were significantly improved compared with graphene.Second,a simple hydrothermal method is designed for internal adjustment of MOF material in this paper.Two kinds of MOF materials were synthesized by controlling the amount of trifluoroacetic acid.The XPS results showed that the coordination of metal and ligand in MOF material could be effectively improved by adding trifluoroacetic acid as an auxiliary agent.The Z-scan results showed that the MOF without trifluoroacetic acid showed a simple saturated absorption response,while the MOF with trifluoroacetic acid showed a switch from saturated absorption to reverse saturated absorption with the increase of light intensity.The first-principles calculations and pump detection analysis showed that different coordination amounts led to different charge transfer amounts from metal to organic ligands,resulting in different nonlinear responses.This work provides a reference for precise adjustment of nonlinear response of MOF materials.Third,a simple one-step hydrothermal synthesis method is proposed to adjust the nonlinear response of MOF materials externally by anchoring Zn S nanoparticles on MOF nanosheets.The morphology of Zn S nanoparticles on Cu-TCPP nanosheets showed good dispersion and uniform size.The XPS results showed that Zn S and Cu-TCPP were coupled by S-O bond.Z-scan results showed that Zn S/Cu-TCPP composites have higher nonlinear responses compared to Cu-TCPP.The ultrafast carrier dynamics analysis further confirmed that the effective electron transfer(ET)from excited MOF to Zn S greatly promoted the charge separation process in MOF,extended the carrier relaxation time and led to stronger nonlinear response.