Measurement And Analysis Of The PL-lifetime Of PbSe QDs

Semiconductor nanocrystal quantum dots(QDs)is a new type of nano artificial materials.In recent years,researchers have made some works on the unique fluorescence properties of QDs.It is concluded that a series of wonderful optical,electrical and magnetic properties of QDs are associated with the QDs size.In this dissertation,we focus on the relation between the fluorescence properties or photoluminescence(PL)lifetime with QDs size.PL-lifetime is a primary property of QDs for the photoelectric field,especially for the gain of optoelectronic devices doped by QDs.Because of the size effects,surface effects and complex structure,the study on the PL-lifetime of QDs becomes difficult.In addition,the PL-lifetime of QDs is related to the material doped in QDs.At present,there are some defects in the most popular method for testing the PL-lifetime of PbSe QDs.The PL-lifetime data obtained by these methods are discrete because too many factors,such as the size of QDs,the material doped in QDs,testing temperature,which affect the PL-lifetime of QDs.As a result,the PL-lifetime of PbSe QDs obtained by these methods range widely.Therefore,the research on the PL-lifetime of PbSe QDs is needed.In this dissertation,we measure the spectra and PL-lifetime of PbSe QDs at room temperature based on the fluorescence effect of PbSe QDs.The diameter of PbSe QDs used in the experiment is 2.7~5.7 nm.The absorption and PL spectra of PbSe QDs with different sizes and doped in organic solvent-hexane are measured by spectrometer.The diameter of PbSe QDs is measured by transmission electron microscopy(TEM).According to the analysis of data obtained in the experiment,we present two empirical formulas of the first absorption-peak wavelength and PL-peak wavelength varying with the size of PbSe QDs.The PL-lifetime of PbSe QDs are determined by analyzing transient PL-decay curves,which depend on both the surface defect and the size of QDs.The measured PL-lifetime ranges 1.44~11.96 ?s,which can be determined from two cases,i.e.,the PL transition is only either a direct interband transition or a defected state transition for the particle size of 2.7~5.7 nm used in this paper.Further,there is evidence to show that the PL-lifetime is weakly dependent on the size of PbSe QDs,following a linear expression.As an example,the averaged PL-lifetime is among 7.17~6.72 ?s for the diameter of 2.7~5.7 nm of PbSe QDs.We also present an empirical formula of the averaged lifetime varying with the size of PbSe QDs.According to the study in this dissertation,we quantitatively analyze the spectra and PL-lifetime of PbSe QDs varying with the particle size under this experimental condition.And we also give three empirical formulas to describe the rules.These empirical formulas have an important significance on designing gain devices and sensors doped by PbSe QDs.