Research Photophysical Process Of Inorganic Perovskite Nanocrystals

Perovskite nanocrystals are new optoelectronic materials developed in recent years.They have wide application prospects in light-emitting diodes,solar cells,photodetectors and nonlinear optical devices.However,there is still a lack of in-depth and detailed research on the fundamental photophysical processes of perovskite NCs,such as ultrafast nonlinear optics and chiral optical behavior,which will seriously limit their relevant applications.Ultrafast nonlinear optics is the most advanced part of transient optics,which develops with the appearance of ultrashort pulse laser.The development of ultrashort pulse laser and ultrafast nonlinear optical phenomena promote each other.Ultrafast nonlinear optical materials have promising applications in laser technology,optical communication,all-optical switching,optical information storage and 3D imaging.Chiral optical behavior,such as circular dichroism and circularly polarized fluorescence,is a new field developed in recent years.It shows bright application prospects in 3D display,circularly polarized laser,molecular recognition,fluorescent probe and chiral optical switcher.Therefore,the in-depth study of the basic photophysical processes of perovskite NCs in ultrafast nonlinear optics and chiral optics is of great significance for the realization of their relevant applications.Based on this,this thesis will synthesize several kinds of all-inorganic perovskite NCs and studies on the influences of perovskite NCs'size,components and dimension on their photophysical properties,using various spectral tools?absorption spectrum,fluorescence spectrum,time-resolved spectrum,low temperature fluorescence spectrum,transient absorption spectrum,multiphoton fluorescence spectrum,Z-scan technique,circular dichroism spectrum and circular polarized luminescence spectrum etc.?.The research content of this paper includes the following parts.?1?the ultrafast nonlinear optical behavior of blue emitting perovskite NCs,that is,CsPbCl₃ and CsPb(Cl_0.53Br_0.47)₃,was systematically studied using Z-scan technique.The experimental results show that CsPb(Cl_0.53Br_0.47)₃ NCs have significantly enhanced nonlinear optical behavior due to its structural asymmetry and relative instability.More interestingly,CsPb(Cl_0.53Br_0.47)₃ NCs also have promising applications in all-optical switching.?2?The influence of perovskite NCs'dimension on their multiphoton absorption behavior was studied.The experimental results show that the two-dimensional quantum confinement effect of CsPbBr₃ nanosheets can enhance their volume normalized multiphoton absorption cross section by 1-3 orders of magnitude compared with their cubic counterparts.In addition,we also found that the material dimension has a significant impact on Mn²⁺doped CsPbCl₃ NCs'exciton coupling effect,multiphoton absorption and energy transfer behavior.The exciton-phonon coupling effect and two-photon absorption behavior of CsPbBr_2.7I_0.3 two-dimensional nanosheets,the cubic NCs of CsPbBr_2.7I_0.3 and CsPbI₃ were studied systematically.Experimental results show that compared with cubic NCs,two-dimensional nanosheets have higher fluorescence color purity and higher volume normalized two-photon absorption cross section.?3?We studied the intrinsic circular dichroism and circular polarized luminescence spectra of CsPbBr_2.7I_0.3 two-dimensional nanosheets.The experimental results show that the chiral optical behavior of nanosheets is due to the asymmetry caused by abundant surface defects on their surface.In addition,we successfully prepared perovskite cubic NCs with excellent chiral optical behavior by substituting the surface ligand oleic acid molecules into chiral 1,2-diaminocyclohexane molecules,using post-synthetic ligand exchange?achiral ligand/chiral ligand?method.Additionally,we carried out a detailed and in-depth study on their relevant physical mechanism.