Preparation And Nonlinear Optical Limiting Performances Of Carbon Nanodots Doped Composite Gel Glasses

Carbon nano-dots(CNDs)exhibit excellent nonlinear optical limiting properties under nanosecond and picosecond laser pulses irridiation.However,most of the researches are mainly concentrated on the liquid matrix,which significantly limits the practical application process.In addition,single-component optical limiting materials can not fulfill the requirements of ideal optical limiting materials,such as fast response speed,low optical limiting threshold,and broadband protection,and so on.However,construction composite materials by covalent or non-covalent based on different limiting mechanisms often can obtain improved optical limiting performance,owing to the coordinated optimization and complementary advantages between the components.In present work,CNDs,one kind of single optical limiting material,was prepared by hydrothermal method using heparin sodium as a carbon source.Two-component optical limiting material,i.e.,CNDs coated graphene(GO)composites(CNDs/GO),was successfully synthesized by a facile one-step electrochemical method.Meanwhile,CNDs and CNDs/GO were introduced into organically-modified silica(SiO2)gel glass matrices by sol-gel method.The resulted composite gel glasses presented high transparency and good thermal stability.The composition,morphologis,structures and linear optical properties of CNDs,CNDs/GO and their composite gel glasses were systematically characterized.Subsequently,the nonlinear optical limiting properties of CNDs,CNDs/GO and their composite gel glasses were studied by Z-scan method,and the nonlinear optical limiting mechanisms of CNDs and CNDs/GO in liquid and solid substrates were also explored.The resluted CNDs present uniform size and good dispersion.Meanwhile,plenty of functional groups,such as carboxyl groups and hydroxyl groups,are presense on the surface of CNDs.The CNDs displayed excitation-wavelength-dependent fluorescence behaviors,the emission peaks are red-shifted as the excitation wavelength increases.The open-apertures results showed that the CNDs presented an energy-dependent optical limiting charateristics in the liquid-phase matrix,which would transfer from saturation absorption to reverse saturation absorption with the increased irradiated laser influence.The optical limiting mechanisms of CNDs in liquid matrix were found to be nonlinear absorption(NLA)and free carrier absorption.The CNDs can homogeneously assemble on the surface of oxide graphene by a facile one-step electrochemical method.The loading of CNDs has no significantly influcenc in the structure of GO,but it enhances its fluorescence performance obviously.Furthermore,the nonlinear optical limiting performance of GO can be effectively enhanced after archored of CNDs.The improvment in optical limiting performances is mainly due to the complementary advantages between NLA and nonlinear scattering(NLS)and the charge/energy transfer between CNDs and GO.The introduction of CNDs and CNDs/GO into SiO2 gel glass has little effect on the composition of the SiO2 matrix,but changed its surface characteristics and pore structure,and therefore improved the thermal stability of the matrix.However,the fluorescences of CNDs and CNDs/GO were quenched after introduced into the solid matrix.Compared to the liquid phase matrix,the nonlinear optical limiting properties of CNDs and CNDs/GOs were improved after incorporated into the solid matrix.The optical limiting of CNDs in the solid matrix was attributed to NLA,while the CNDs/GO in solid matrix could be ascribed to NLA and NLR.All above results could provide experimental and theoretical basis to explore the application of CNDs and CNDs/GO in the field of nonlinear optical limiting.