Temperature Dependent Photoluminescence Spectrum With Multiple Peaks In PbS Quantum Dots

Seeking for these potential features of quantum dots,in decades,a lot effort was made by scientists.The stability of quantum dots(QD)has been remarkably promoted,and so does the process of making it.Its potential cannot be ignored in some specific applications such as photodiode and photodetector for the very single wavelength light,solar battery that has a high quantum efficiency(with multiexciton or carrier multiplication it can be possible)while the absorbing spectrum cover the all wavelength that the sun emits.But,there are still some mechanisms that need further study since the mechanisms in quantum dots are numerous,for instance,influence of defect and transporting mechanism of carrier and bright/dark exciton level and etc.,which has a compete with each other,and the consequence of the compete are complicated due to the input wavelength,frequency,temperature and more.They are not completely predicted by the current theory.the thesis mainly carried out the following work based on Photo-carrier radiometry:1.A Photoluminescence theoretical model of QD that based on signal of photocarrier radiometry(PCR)is founded.2.To study the mechanisms that affect the lifetime of quantum dot excitons through the photoluminescence spectra of PbS quantum dots under excitation light of different modulation frequencies and different temperatures.By analyzing the photoluminescence spectrum signals at different temperatures,it was found that: first,temperature will change the number of phonons in the material,thereby affecting the probability of excitons passing through radiative recombination and non-radiative recombination.F?rster resonance energy transfer(FRET),and the temperature has a significant effect on the position of the photoluminescence peak of the sample,but due to incomplete experimental results,the cause of this phenomenon needs to be further studied.3.By measuring the photoluminescence signals of the quantum dot samples of single particle diameter and mixed particle diameter at different luminescence peaks.It was found that the average lifetime of excitons of single and mixed particle diameter samples would increase with temperature;for a single particle size sample,because the particle size corresponds to a narrow band gap,a small band gap means that the exciton transition probability is large,thus the exciton lifetime is shorter;but for the mixed particle size sample,this conclusion is invalid due to the effects of re-absorption and FRET.Both phenomena will cause large-sized quantum dots to absorb energy from small-sized quantum dots,so their average exciton lifetime extend.4.To study the effect of temperature changes on the relaxation mechanism of quantum dot exciton through temperature scanning.It was found that as the temperature decreases,the non-radiative recombination of the excitons is suppressed,and more excitons relax to the ground state through radiation recombination,resulting in an increase in photoluminescence intensity;as the temperature increases,the phase of the PCR signal The phase lag of the position relative to the incident excitation light gradually decreases,indicating that the exciton relaxes in the quantum dot for a longer time at low temperature,so under the same external conditions and excitation light frequency,the carriers involved in the radiation recombination in the quantum dot The higher the concentration,the greater the amplitude of the signal.In summary,the exciton lifetime of single particle and mixed particle quantum dot samples under excitation light of different modulation frequencies and different temperatures was measured by PCR method.By studying the relationship between those lifetimes,we can further understand the relationship between several quantum dot exciton transport mechanisms.