CdS Third-Order Nonlinear Optical Properties Of Composites With Graphene And MOF

Two-dimensional layered materials have become frontier materials in the research of optoelectronics and other fields,owing to their unique structure and rich variety.Due to their reduced thickness compared with physical phase materials,they possess novel and rich physical and chemical properties.As a result,research in the fields of materials,energy,condensed matter physics,and photonics is flourishing.Nonlinear optics plays a crucial role in modern optics,with applications in high-tech fields such as optical communication,optical storage,and laser systems.Currently,two-dimensional layered materials are the focus in nonlinear optics research.Graphene is a prime example,with its unique electronic properties,ultra-high carrier mobility,and broadband saturable absorption properties.Materials such as two-dimensional metal-organic frameworks(MOFs),similar to graphene,also show great potential in the nonlinear field due to their diverse and adjustable structures.However,their structural constraints limit their application potential.To address this issue,this paper investigates various heterostructures prepared by growing semiconductor materials on graphene and MOF surfaces.The study systematically investigates the effect of charge transfer between heterojunctions on nonlinear response,exploring the intrinsic mechanism of enhanced nonlinear response.The research results are as follows:First,we systematically investigated the nonlinear enhancement mechanism of graphene semiconductor composites.To this end,we synthesized RGO modified at different concentrations(0%-10%)of Mn-doped semiconductor CdS nanoparticles(RGO/CdS:Mn)using the solvent thermal method.We aimed to study the changes in the nonlinear optical properties of graphene.We characterized the structure,morphology,and basic physical properties of RGO,CdS,RGO/CdS,and RGO/CdS:Mn using various basic characterization techniques.The results revealed that the uniform attachment of Mn-doped CdS nanoparticles to the graphene surface effectively inhibited the agglomeration exhibited by pure CdS.We used the Z-scan technique to test the composite’s nonlinear response.The results showed that the 10% Mndoped RGO/CdS:Mn composite had the largest nonlinear response.The nonlinear susceptibility and saturation absorption coefficient were 15.3 and 26 times higher than those of RGO,respectively.We attribute the intrinsic mechanism of the enhanced nonlinear response to the charge transfer between and within the components and the trap effect arising from Mn doping,which effectively inhibited the photogenerated electron pair recombination.The significantly improved optical nonlinearity of RGO/CdS:Mn composites lays the foundation for their potential application in photonic devices.The excellent saturable absorption characteristics of RGO/CdS:Mn composites indicate their potential application in the field of saturable absorbers and mode-locked lasers.Second,a simple one-step hydrothermal method was designed to anchor CdS nanoparticles to the surface of MOF nanosheets.In this study,a high surface area and highly stable MOF material was chosen as the base material to construct a CdS/Cu-TCPP heterojunction.Compared to other carboxylic acid chelating groups(such as terephthalate)in traditional MOFs,the porphyrin group in Cu-TCPP used in this work has a larger π conjugate system,leading to higher π-d orbit overlap with the metal node,which accelerates the charge transfer from the ligand to the metal node and effectively inhibits charge recombination,providing sufficient electrons for the photoresponse process.SEM and TEM tests confirmed the successful construction of the heterojunction,which improved the dispersion of CdS.XPS and linear absorption spectra further verified the effective charge transfer between CdS and Cu-TCPP.Finally,picosecond laser Z scan tests showed that the CdS/Cu-TCPP heterojunction greatly improved the NLO response of CdS nanoparticles.This study successfully prepared the CdS/Cu-TCPP heterojunction using a simple one-step hydrothermal method,which improved the dispersion of CdS nanoparticles and effectively inhibited photogenerated electron-hole pair recombination,thus greatly enhancing the NLO response of CdS.These new findings will enrich the knowledge of heterojunction nonlinear optical materials and provide promising strategies for designing nonlinear optical devices that can satisfy practical applications.Third,a one-step hydrothermal method was used to prepare a CdS/Zn-TCPP composite by replacing Cu atoms in Cu-TCPP with Zn atoms.SEM and TEM tests revealed that CdS was densely distributed on the surface of Zn-TCPP nanosheets and exhibited agglomeration.XPS tests showed charge transfer between CdS nanoparticles and Zn-TCPP nanosheets.Z scan results showed that both Zn-TCPP and CdS/Zn-TCPP showed a transition from RSA to SA,but not SA to RSA as in Cu-TCPP.However,the nonlinear parameters of the composite were not much higher than those of pure CdS and Zn-TCPP.This is because the agglomeration of CdS nanoparticles in the surface distribution of Zn-TCPP adversely affected the nonlinear response of the composite,despite the charge transfer between CdS and Zn-TCPP suppressing the recombination of light electron pairs in Zn-TCPP.This chapter’s work demonstrates the importance of good nanoparticle dispersion in composites for their nonlinear response.