Ultrafast Nonlinear Optical Properties Of Sulfide Two-Dimensional Materials And Porphyrin Systems

In recent years,with the research on two-dimensional(2D)materials and organic nonlinear optical materials,people turned their attention to heterojunction materials composed of different 2D materials and heterojunction materials composed of 2D materials and other nonlinear optical materials.By selecting materials with different abilities of electron donor and acceptor,heterojunction materials with different properties of charge carrier inside the materials can be composed.It is expected that through the relationships among electron excitations,migrations,relaxations,physical and chemical properties,instructions for synthesization and production materials with better properties can be established.In this paper,the researches of 2D sulfides and porphyrins are introduced,the nonlinear optical properties and ultrafast dynamics of hybrid materials composed by acceptor electron 2D sulfides and electron donor porphyrins are investigated.The nonlinear optical absorptions(NLA)of 2D Mo S2 and WS2 are investigated by using the Z-scan technique.It is found that under low intensity excitation of femtosecond laser at 515 nm,Mo S2 and WS2 exhibit saturable absorption,with increase of intensity,the nonlinear absorption of Mo S2 changes to reverse saturation absorption(RSA),whereas the NLA of WS2 keeps unchanged.The nonlinear optical parameters(absorption cross sections and relaxation times)are obtained through the theoretical fitting of the experimental results.On the other hand,10 kinds of porphyrins are synthezed,which are characterized by absorption spectra and fluorescence spectra.It is found that,for the porphyrins in absence of metal atoms,there is S band around 420 nm,and there are four weaker Q bands from 500 to 675 nm.For the porphyrins in presence of metal atoms,there is S band around 420 nm,and there are one weaker Q bands from 540 to 560 nm.The NLA and ultrafast dynamics of these porphyrins are investigated by using the Z-scan and pump-probe technique,respectively.Under the excitation of laser at 515 an 532 nm,all these porphyrins exbihit RSA,the porphyrin with four benzene rings exhibit the strongest RSA,with the increase of thienyls and nitrobenzophenone,the RSA of porphyrin decreases,the decrease of RSA by nitrobenzophenone is stronger than that of thienyl.The porphyrins filled with zinc atom exhibit stronger RSA and longer relaxation time comparing to that of porphyrins filled with copper atom.The porphyrins filled with copper atom do not increase the RSA comparing to that of porphyrins in absence of metal atom.The relaxation time of porphyrins filled with copper atom is increased comparing to that of porphyrins in absence of metal atom.Based on these results,relationships between the periphery substituent groups,internal metal atoms,as well as the nolinear absorption cross sections and life times of the energy level are established.By mixing the 2D sulfides and porphyrins,heterojunction materials composed of 2D sulfide and porphyrin through the Van Der waals bonding are obtained.The NLA and ultrafast dynamics of these heterojunction materials are investigated.By comparing to 2D sulfides and porphyrins,it is found that the porphyrin that adsorbed on the surface of 2D sulfide absorbes photon and excites electron.The excited electron postinjects into 2D sulfide.The influence of charge transfer to the nonlinar optical properties are analyzed by energy level model.