Third-Order Nonlinear Optical Properties Of Graphene,Black Phosphorus Composites

With the continuous development of science and technology,information technology has penetrated into people’s economy,education,social life and other fields.As opposed to optical information processing and storage,optical communication,etc.,the development of efficient optoelectronic devices is an important driving force for the development of information technology.In the development of optoelectronic devices,non-linear optical materials are favored by researchers for their excellent optoelectronic properties.Non-linear materials have already been used in optoelectronic devices,but continuous research and preparation of non-linear optical materials with excellent optoelectronic properties are needed to obtain efficient optoelectronic devices.Two-dimensional layered materials have a wide range of applications in the field of optoelectronic devices due to their diverse energy band structure and wide optical response range.Graphene and black phosphorus,as two-dimensional layered materials,are widely used in saturable absorbers,photoelectric modulators and other optoelectronic devices due to their strong non-linear response and broadband saturable absorption.Based on the excellent optoelectronic properties of graphene and black phosphorus monomers,researchers have doped them with other non-linear materials as matrix materials in the hope of obtaining composites with better non-linear properties and applying them to the development of high-performance optoelectronic devices.This paper therefore adopts a doping method to prepare graphene and black phosphorus composites,and systematically investigates the third-order nonlinear optical properties and the intrinsic mechanism of nonlinear enhancement of graphene and black phosphorus composites.The details of the research in this paper are as follows:Firstly,the third-order nonlinear optical properties of ZrO₂/RGO composites were systematically investigated.The ZrO₂/RGO composites were prepared by hydrothermal method.By characterizing the structure and morphology of the composites,a uniform distribution of ZrO₂ on the graphene surface in the composite samples was obtained.The third-order non-linear optical properties of the composites with different mass ratios of ZrO₂ to graphene were investigated by Z-scanning technique,and the ZrO₂/RGO composites were obtained to have saturable absorption and self-focusing（positive non-linear refraction）properties.Also,the saturation absorption intensity of the composites changes when the mass ratio of ZrO₂to graphene is varied.When the mass ratio of ZrO₂ to graphene is 4:1,the third-order nonlinear polarizability of the composites reaches 13.27×10^-12 esu,which is about 5 times higher compared to graphene monomer.It indicates that the nonlinear properties of the ZrO₂/graphene composites are enhanced.The intrinsic mechanism of the enhanced third-order nonlinear properties of the composites was investigated by establishing a charge transfer model,and it was obtained that the enhanced nonlinear properties of the composites were due to the suppression of electron-hole pair compounding by the involvement of defective energy levels in the charge transfer process of the composites.This study provides a theoretical basis for the application of ZrO₂/RGO composites in optoelectronic devices.Secondly,a low temperature seed growth method was used to prepare AuNRs/BPNFs composites and to investigate the third order non-linear optical properties of the composites.The length-to-diameter ratio of AuNRs in the composites was varied by controlling the addition of Ag NO₃ solution and HCl solution to obtain composites with different length-to-diameter ratios.The morphological and structural characterization showed that gold nanoparticles and gold nanorods were attached on the surface of the black phosphorus nanosheets in the composites.The third-order non-linear optical properties of the composites were investigated at 532 nm using picosecond Z-scanning techniques.The nonlinear saturable absorption properties of the AuNRs/BPNFs composites were obtained to be superior to those of the BPNFs monomer.The transient absorption spectra and carrier dynamics of the samples were analyzed,and it was obtained that the ultra-fast charge transfer in the composite samples enhanced the saturation absorption of the composites.Based on the saturable absorption properties of the composites,Q-locked mode tests were performed on the composite samples using a Q-locked mode system,and a stable Q-locked,mode-locked pulse sequence was obtained for the composite samples at laser wavelengths of 1550 nm and 1064 nm and power of 200 m W.This study provides a theoretical and experimental basis for the application of AuNRs/BPNFs composites in Q-locked devices.Thirdly,the third-order non-linear optical properties of BPQDs composites with Ni₂（OH）₂（L4）（metal hydroxide organic backbone material,MHOF）were investigated.The BPQDs/Ni₂（OH）₂（L4）composites were prepared by hydrothermal method and the morphological and structural characterization of the composite samples was carried out to obtain the attachment of BPQDs to the surface of Ni₂（OH）₂（L4）sheets in the composites.The nonlinear optical properties of the samples were investigated using Z-scan technique,and the results showed that BPQDs,Ni₂（OH）₂（L4）sheet and BPQDs/Ni₂（OH）₂（L4）exhibited nonlinear saturation absorption properties,and the nonlinear saturation absorption intensity of BPQDs/Ni₂（OH）₂（L4）was better than that of BPQDs,Ni₂（OH）₂（L4）monomer.The effect of charge transfer between BPQDs and Ni₂（OH）₂（L4）on the enhancement of the non-linear properties of the composite samples was analyzed by developing a charge transfer model.This experiment provides a theoretical basis for further research on the application of BPQDs/Ni₂（OH）₂（L4）composites in optoelectronic devices.