Research Chiral Optics And Ultrafast Optics Of Heterostructure Semiconductors Nanocrystals

Compared with simple structured semiconductor nanocrystals(NCs),core-shell semiconductor heterostructure can be formed by the epitaxial growth of one or more shells onto the core.This method can eliminate the dangling bonds on the surface and effectively reduce the non-radiative recombination caused by surface defects.These nanocrystals not only have high quantum efficiency and photothermal stability,but also have a long fluorescence lifetime,indicating that they have very broad prospects in various application,such as new solar photovoltaic devices,light emitting diodes,biological imaging,photodetectors,and nano lasers.As an emerging optically active material,semiconductor heterostructure modified by chiral molecules have attracted widespread attention.Chiral semiconductor heterostructure have unique optical properties,including chiral optics and ultrafast nonlinear optical behavior.Chiral optical behavior,such as circular dichroism,circularly polarized luminescence,has great application prospects in the fields of circularly polarized light-emitting devices,fluorescent probes,and chiral recognition.In addition,compared with traditional organic molecules,fluorescent probes based on inorganic semiconductor heterostructure have the advantages of long fluorescence lifetime and strong multiphoton absorption.Therefore,inorganic semiconductor heterostructure has bright application prospects in high-resolution fluorescence imaging.However,there are few studies on chiral optics and ultrafast nonlinear optical behaviors of chiral semiconductor heterostructure,which severely limits their applications in related fields.Based on this,using a variety of spectroscopic techniques,including absorption spectroscopy,fluorescence spectroscopy,fluorescence lifetime spectroscopy,circular dichroism,circular polarization luminescence,Z-scan technique,multiphoton excited fluorescence spectroscopy and femtosecond transient absorption spectroscopy,this theis deeply study the chiral opticsr and ultra-fast nonlinear optical behavior of semiconductors heterostructure.The detailed research contents include:(1)The chiral optical behavior of the cysteine ligand caped CdSe/CdS dot/rod nanocrystals in water solution and polyvinyl alcohol(PVA)films have been investigated.It has been found that the anisotropy factors of circular dichroism and circularly polarized luminescence of nanocrystals in PVA film are improved by an order of magnitude compared with those in solution.(2)The ultrafast kinetics and multiphoton absorption behavior of cysteine caped CdSe/CdS dot/rod nanocrystals in aqueous solution have been studied.The experimental results show that the nanocrystals have very large two-photon and threephoton absorption cross-sections in the first and second biological windows.Besides,the CdSe/CdS dot/rod nanocrystals in PVA film have giant two-photon and threephoton absorption coefficients,indicating that these materials have important application prospects in nonlinear chiral photonics.Interestingly,the nanocystals can efficiently generate singlet oxygen generation with a efficiency as high as 35%.In addition,we have successfully demonstrated two-photon fluorescence lifetime imaging and photodynamic therapy of these nanocrystals.The excellent optical properties of these water-soluble CdSe/CdS dot/rod nanocrystals indicate that they have bright prospects in nonlinear bioimaging applications.(3)The linear and nonlinear optical behavior of type II ZnSe/CdS/ZnS core/shell /shell nanocrystals.Femtosecond transient absorption spectroscopy has been used to reveal the ultrafast processes occurring at the interface between ZnSe and CdS,such as the injection of photo-induced electrons into the CdS shell and the injection of photoinduced holes into the ZnSe core and subsequent relaxation.Finally,Z-scan technique has been used to determine their multiphoton absorption cross-sections at different wavelengths.Excellent optical behavior of this kind of type II heterostructure indicate it should have important applications in optoelectronic devices and fluorescence imaging.