Experimental Measurement Of Photoluminescence Lifetime Of PbS Quantum Dots

Compared with the traditional organic dyes and bulk materials,nanocrystal quantum dots(QDs)have attracted much attention in recent years for unique optical properties,such as tunable fluorescence wavelength varying with QDs size,broad-band spectra with large absorption coefficient,tremendous photo-stability and so on.Photoluminescence(PL)lifetime is one of basic properties of QDs,which characterizes atomic-energy levels of QDs and radiation relaxation processes.Due to the special properties,such as energy dispersion,surface effect and quantum size effect,it is difficult to study PL lifetime.In addition to the particle size,temperature,background material and the other factors can also affect the PL lifetime of QDs.At present,most reported works of the PL lifetime are limited in single factor,such as the particle size,temperature,and background material.Moreover,the reported data are too discrete to gain available recognition.Above all,the researches on the PbS QD PL-lifetime should be further explored.In this dissertation,we used the double kinds of PbS QDs with 2.35~5.61 nm diameter provided by two companies for comparing and to get reliable results in experiments.Using the spectrophotometer(Shimadzu Corporation,UV-3600)and steady-transient state fluorescence spectrometer(British Edinburgh,FLS920 and FLS980),the absorption spectra,PL emission spectra and the transient PL decay curves of PbS QDs were obtained.The PL lifetime of PbS QDs dispersed in different background materials and with different particle sizes were measured at room temperature.The results show that the PL lifetime is strong dependent on the QDs size and sensitive with the background material.For example,as the particle size increases from 2.35 nm to 5.61 nm,the PL lifetime of PbS QDs decreases from 2.57 ?s to 0.71 ?s.An empirical formula describing PL lifetime varying with particle size can be expressed as?=7.64exp(7)-d7.88(8)-3.08(?s).PL lifetimes of PbS QDs dispersed in UV glue within the low temperature(7K)and room temperature were obtained.There is evidence to show that the PL lifetime of PbS QDs is weakly dependent on temperature.At 200 K,the maximum lifetime is up to 3.42 ?s.In the temperature range of 7~300 K,the average PL lifetime is 2.27?1.15 ?s.The images of the particle size,morphology and distribution of PbS QDs were obtained by using the transmission electron microscopy(TEM).Based on the experimental data,we obtained an empirical formula characterizing the first absorption peak wavelength varying with the particle size.In summary,we study the PL lifetime of PbS QDs varying with the particle size,temperature and background material respectively.Two empirical formulas related with the absorption peak wavelength and the PL lifetime varying with the particle size is presented.It can be expected that the systematic work with basic optical data and formulas will be significant for the design of Pb S QD doped sensors and optoelectronic devices in the future.