| The analysis of fluorescence lifetime of quantum dots is of great significance for revealing the optical properties and realizing the application of quantum dots in optoelectronic devices and biomedicine.Fluorescence decay curve fitting method based on time-correlated single photon counting is a conventional method for measuring fluorescence lifetime of quantum dots.The method obtains the fluorescence decay curve of quantum dot by timecorrelated single photon counting technique,and uses a single exponential or multi-exponential decay function to fit it to obtain fluorescence lifetimes.Time-correlated single photon counting devices of picosecond-scale time resolution and pulsed light sources of picosecond pulse width have been used to measure fluorescence lifetimes on the order of sub-nanosecond.However,fluorescence decay curve fitting method cannot eliminate the effects of dark counts and background light from the experimental system,resulting in reduced fitting accuracy of fluorescence lifetimes.Increasing the number of fitted photons can alleviate this adverse effect to some extent,but inevitably reduces the time resolution and speed of fluorescence lifetime measurement.Therefore,it is increasingly necessary to find a new alternative that can achieve accurate,fast measurement of fluorescence lifetimes with high time resolution.The main research contents of this thesis are as follows:1.A new method for measuring the fluorescence lifetimes of quantum dots based on single photons modulation is proposed.The method utilizes the pulsed laser to naturally modulate the fluorescence of the quantum dots.According to the nonlinear correspondence between the amplitude of the modulation frequency signal and the fluorescence lifetime,the fluorescence lifetime of the quantum dots can be measured with high accuracy,speed and time resolution.2.The analytical relationship between the amplitude of the pulse repetition frequency spectrum signal and the fluorescence lifetime in the single dynamic process of quantum dots is deduced theoretically.By performing discrete Fourier transform on the arrival time of fluorescent photons,a pulse-repetition frequency spectrum signal with high SNR can be obtained in the frequency domain.According to the theoretical analytical relationship,we can obtain a unique fluorescence lifetime.3.Fluorescence lifetimes of quantum dots are measured by single photon modulation spectrum method.The experimental results show that the singlephotons modulation spectrum method can improve the accuracy of fluorescence lifetime measurement by more than one order of magnitude compared to the traditional fluorescence decay curve fitting method when the fluctuation error is 5%.When the fluctuation error and the deviation error are both not more than 5%,the single photons modulation spectrum method can increase the speed and time resolution of measurement by more than four times.4.The dynamic properties of quantum dots are studied by single photons modulation spectrum method.The method can reduce the number of photons required for fluorescence lifetime analysis to about 2 k(with an error of not more than 5%).Based on this,we obtained the fluorescence lifetime trajectory corresponding to the fluorescence trajectory of the quantum dots in real time,which realized the rapid acquisition and visual representation of the dynamics information of quantum dots by using only a small number of photons. |
