Study On Third-order Nonlinear Optical Properties Of Two-dimensional Metal-organic Framework

With the increasing demand for communication capacity and high-speed data processing in communication technology,traditional electronic wired communication has been replaced by optical fiber communication.At present,the optical fiber communication has successfully realized all-optical signal transmission.However,the conversion between optical and electrical signals still relies on electronic methods,which severely limits the rate of optical communication.All-optical modulation is expected to break the "electronic bottleneck" and has become a hot field in current information technology.The third-order nonlinear optical material is an essential medium for all-optical modulation,and its performance largely determines the exchange rate and energy consumption in all-optical modulation.Theoretical researches have shown that the two-dimensional(2D)MOFs own excellent photoelectric properties and have great potential in all-optical modulation.However,there are relatively few studies on the nonlinear optical properties of 2D MOFs,and there is no direct experimental proof.Therefore,we mainly did the following work on the direct measurement of the nonlinear optical properties of 2D MOFs:(1)In measuring the nonlinear optical properties of the materials,it is usually necessary to disperse the materials in an organic solvent in order to achieve better dispersibility and uniformity.However,the organic solvent itself has a certain nonlinear optical effect,which will affect interpretation of the measurement results of the material.Therefore,we first used Spatial cross-phase modulation(SXPM)technology to study the nonlinear optical properties of commonly used organic solvents.The results shows that organic solvents(alcohols,formic acid and acetic acid)with-OH and-COOH functional groups have obvious thermo-optical nonlinear effects in the near-infrared band.It is also found that aldehydes and ketones samples added with water or nitric acid produce obvious nonlinear effects because products with-OH and-COOH are produced due to the nucleophilic addition reaction.Taking acetone as an example,the real-time visual observation of the nucleophilic addition reaction of acetone is realized by monitoring the changes over time of the diffraction pattern generated under SXPM.This research can provide a guide in selecting suitable organic solvents when measuring the nonlinear optical effects of the materials.(2)The nonlinear optical properties of 2D Cu-MOF and 2D Zn-MOF materials(1,4-copper/zinc phthalate,CuBDC and ZnBDC)were measured using spatial self-phase modulation(SSPM)and SXPM.The dichloromethane is chosen as the solvent,because no obvious nonlinear optical effect is observed from dichloromethane in the near-infrared band.The results indicate that the 2D Cu-MOF exhibits a large nonlinear optical coefficient(n2=5.20×10-11m2/W,?(3)=8.24×10-11(e.s.u.)).On the contrary,2D Zn-MOF did not show obvious nonlinear optical effects under the same conditions.The main reason is that 2D Cu-MOF has a variable number of valence electrons and empty 3d atomic orbitals,which can form a larger conjugated system through d-? interaction,enhancing the nonlinearity of 2D Cu-MOF materials.Furthermore,the all-optical modulation performance of 2D Cu-MOF was tested using SXPM,and the results show that 2D Cu-MOF material can successfully realize the on-off control of the probe beam through the signal beam.This work experimentally proves the feasibility of 2D MOFs in all-optical modulation,and also provides a reference for the design of 2D MOFs with high nonlinear optical coefficients in the future.In this study,the method of spatial phase modulation was used to measure and study the nonlinear optical properties of 2D MOFs,which provides a direct experimental basis for the application of two-dimensional MOFs to all-optical modulation.This is of meaning for exploring the application potential of 2D MOFs in the fields of optics,photonic circuits and optical communications.