Nonlinear Optical Limiting Performances Of MoS₂@MWCNTs Composite Materials

Transition-metal dichalcogenides（TMDC）materials exhibit great potential for various applications of nonlinear photonic devices such as optical switch,mode locking laser,and optical limiter.However,the properties of monomer materials such as narrow protective band,high limiting threshold,and low damage threshold limit wider applications.The optical limiting performance can be improved by combining two optical limiting materials together and coordinating and optimizing the bonds of different optical limiting mechanisms.Herein,different morphologies and sizes low dimensional molybdenum disulfide（MoS₂）was decorated on multi walled carbon nanotubes（MWCNTs）.The successful fabrication of the unique MoS2@MWCNT heterostructure has been confirmed by field emission scanning electron microscopy（SEM）,transmission electron microscope（TEM）,X-ray diffraction（XRD）,Raman spectrum,X-ray photoelectron spectroscopy（XPS）and Solid UV diffuse reflection spectrum（UV-vis DRS）.The nonlinear optical（NLO）and optical limiting（OL）responses of MoS₂/MWCNT heterostructure together with MoS₂ and MWCNTs were investigated by Z-scan technique equipped with a 532 nm nanosecond and picosecond pulsed laser source.Finally,the optical limiting mechanism of composite materials and their potential in future optical and optoelectronic applications are discussed.The main content is as follows:（1）Multi-walled carbon nanotubes loaded with molybdenum disulfide nanosheets were successfully synthesized by glucose assisted hydrothermal method（MoS₂-NS@MWCNTs）.MoS₂ nanoflower loaded MWCNTs and MoS₂ nanosheet loaded MWCNTs can be synthesis with the change of glucose content.Under nanosecond laser light,the OL threshold of MoS₂@MWCNTs with nanoflower shaped heterostructures is 0.53 J/cm²,while the OL threshold of MoS₂@MWCNTs with core-shell structures is0.41 J/cm²,which is lower or equivalent to the OL threshold of common transition metal dihalides or graphene like compounds,And can effectively avoid laser damage to human eyes.On the picosecond time scale,the optical limiting mechanism is due to nonlinear absorption（NLA）and nonlinear refraction（NLR）,but on the nanosecond time scale with the addition of nonlinear scattering（NLS）from MWCNTs.And the enhancement in NLO and OL performances could be ascribed to the photo induced interface charge transfer between MoS2 and MWCNTs and the unique structure in MoS₂@MWCNT heterostructure as well as the coupling of heterostructure morphology.This material has great potential for prospective optical limiting applications.（2）Molybdenum disulfide quantum dots were successfully modified on the surface of MWCNTs using ultrasonic method and van der Waals force MoS₂-QDs@MWCNTs Nano composite materials.The unique optical properties of quantum dots increase the third-order nonlinear polarizability,which is 2.74 times higher than that of MWCNTs and 4.53 times higher than that of MoS₂-QDs.This material exhibits excellent nonlinear optical limiting performance,with an optical limiting threshold of 0.73 J/cm²,which is3.02 times higher than the MWCNT of the monomer.the Z-scan curve of MoS₂-QDs is studied Under nanosecond pulse excitation.It is found that there is a competition between saturated absorption（SA）and reverse saturated absorption（RSA）with the input energy increases.Finally,the application potential in the field of optical limiting detection is explored.