Single Particle Spectroscopic Study On Zero Dimension Nanoparticles

Recently,with the expansion of low-dimensional nanomaterials and the improvement of their properties,the application of low-dimensional nanomaterials in optoelectronic devices,biomedicine and other fields has been developing bring much convenience to our daily life.Among them,zero-dimensional nanoparticles are one of the most hot research materials.Their excellent optoelectronic properties are closely related to the special particle size and intrinsic structure,which have been endowed with rich physical and chemical properties.Therefore,it has potential application in many fields such as lasers,biological imaging,and nano-sensor.Although the types of zero-dimensional nanoparticles are constantly enriched,but the low dimension and small size also make the material possessing the complicated structure structures related with morphology and chemical components Difference of properties between individual particles is significant.To understand the complex chemical and physical processes involved in the interior of zero-dimensional nanoparticles,the difficulty is that traditional ensemble measurements only provide averaged information of the samples,which is very useful for homogeneous molecules but hinders deep insights into the different properties of nanoparticles caused by heterogeneity of individual paritcles.Single molecule/particle spectroscopy can be used to investigate the specific particles at the single molecule or single particle level,eliminating the average effect.Understanding the differences between different molecules or particles helps comprehend the fundamental relationship between structure and properties.In this thesis,with the help of single particle spectroscopy,we studied several kinds of zero-dimensional nanoparticles to deeply understand the luminescent processes of nanoparticles and to explore their luminescent mechanism as well as the energy or charge transfer between quantum dots and other materials.The main contents are listed as follows:?1?Luminescence blinking is a unique phenomenon frequently occurred in the single nanoparticles,which limits their applications in the fields of labelling,tracing and single photon source etc.In order to solve this blinking effect,we synthesized non-blinking Cs₄Pb Br₆ nanoparticles and investigated the photostability and thermal stability of individual nanoparticles.We found that the fluorescent intensity of Cs₄Pb Br₆nanoparticles remained almost unchanged under the continuous illumination by laser.Besides,the fluorescent intensity and lifetime of single naonoparticles showed good linear relationships with temperature in the range of 20?45°C,indicating potential applications as thermal sensors in nanometer scale.The sensitivity reached up to 2%/°C and 3%/°C for intensity and lifetime,respectively.?2?Graphene quantum dots?GQDs?combine the special physical properties of graphene and the excellent optical properties of quantum dots,which are widely used in many fields.However,due to the complexity of material structure and composition,there is no consensus on the photoluminescence mechanism of GQDs.Thus,we first investigated the GQDs without doping and GQDs doped with nitrogen?denoted as IGQDs?by single particle spectroscopy.It was found that the emission spectra of single GQDs or IGQDs were very narrow than solution state,and showed diversity of the spectral shapes,peak positions and peak widths.Comparing the results of single particles and the solution phase,it is found that the broad emission spectrum of the solution phase is only the result of the coexistence of multiple particles.In addition,by analyzing the relationship between GQDs/IGQDs size and luminescence performance,we excluded the size effect on the fluorescent properties and proposed that the origin of the luminescence is the defect states.The narrow emission spectra also showed the potential application of single GQD in the monochromatic light emitting devices.Then,we further investigated the excitation spectra ranging from 450 nm to 520nm of individual GQDs with the help of the recently-developed single particle excitation spectroscopy technology,and it was found that the excitation spectra of the particles were heterogeneous.The distribution of luminescence particles under different excited wavelength in the same sample was also observed by optical imaging in situ.We found that the different particles were selectively excited at different excitation wavelengths,revealing the heterogeneity of not only the emission properties but the absorption capabilities of these particles.Taking advantage of above results,we successfully explained the controversial mechanism of the excitation wavelength dependence of GQDs.?3?Macroscopical optical and electrical characterization showed the potential of the polymer quantum dot/hole transport material?Pdots/HTM?system in the field of photoelectrochemical detection in the future,and the enhancement of optoelectronic properties was attributed to the high efficiency of hole extraction at the Pdots/HTM interface.In order to further study the hole transport kinetics on the interface,we observed the fluorescence properties of Pdots with the change of HTM concentration at the single particle level,and the effect of concentration could be observed sensitively.With the increasing HTM-to-Pdots ratios,the distribution of the on-state lifetimes shifts to the shorter lifetime region.This work use single particle technique to reveal the interaction between hole transfer and blinking dynamics,which plays a vital role in understanding interface charge transfer in the field of solar cells.