| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 95 === In this thesis, we study the optical properties of single CdSe/ZnS colloidal quantum dot. One of the interesting phenomenons of single quantum dot is the fluorescence intermittency. Due to the ionization of quantum dot by Auger, thermal, or tunneling process, the bright and dark phenomena alternatively exist. The effects of excitation power and surrounding matrix on the blinking behavior were studied. We also investigated the influences of quantum dot size and organic ligand conjugation on the optical properties of quantum dot. For excitation power dependence study, it shows that the emissive time interval and the blinking frequency of fluorescence intermittency dramatically changes by excitation power, however, the non-emissive time interval is independent of excitation power. In addition, the radiative lifetime decreases while the excitation power was increased. Moreover, the fluorescence intermittence behavior was suppressed when the surrounding matrix was changed from insulation glass cover-slip to conducting gold nano-particles, and also the fluorescence intensity could be enhanced by the plasmon resonance. For quantum dot size dependent investigation, no correlation was observed between quantum dot size and fluorescence intermittency.
In addition, the TOPO (trioctylphosphine oxide), HDA (hexadecylamine), and PA (pylamine) organic ligands were conjugated to the CdSe/ZnS and CdSe quantum dot surface. For QD clusters, the TOPO-HDA conjugated quantum dot has the lowest fluorescence intensity than the others. On the contrary, it is the highest in CdSe/ZnS QD. On the other hand, for the single QD, the fluorescence intermittency for the TOPO-HDA-PA ligand conjugated QD has larger emissive/non-emissive ratio. Besides, we use Kohlrausch-William-Watts stretching exponential function for radiative decay curve fitting to determine the degree of lifetime distribution. We found that the TOPO-HDA ligand conjugated QD has largest lifetime distribution in bare CdSe case, but smallest one for CdSe/ZnS. After TOPO-HDA ligand conjugated, adding the PA ligand would reduce lifetime distribution for both CdSe and CdSe/ZnS quantum dot. The comparison of integrated fluorescence of single quantum dots is corresponding to that of ensemble average.
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