Study On Oxidation And Photo Recovery Process Of Water Soluble CdSe / ZnS Quantum Dots

Semiconductor quantum dot as a florescent material has long been the focus of many research groups from various disciplines for its special characters and advantages like tunable emission wavelength, broad absorption band and high quantum yield. From the beginning of the success of its synthesis, semiconductor quantum dots have been applied in many fields. Recent application in biology and medical diagnosis includes cell labeling, targeted drug delivery and photo dynamic treatment. Besides its importance in multidiscipline research, the optical behavior of the fluorescent semiconductor material itself has also gained many interests, one of which is the photo-luminescence enhancement. When the semiconductor quantum dots are irradiated, the brightness of the fluorescence will increase. This very aspect of the fluorescence of the quantum dots involves various mechanisms, which still needs further exploration on the surface character of quantum dot. In this thesis, we use the commercial core-shell CdSe/ZnS quantum dots, which enjoy better optical stability and higher quantum yield. After the core-shell quantum dots are oxidized by some strong oxidizing agent, their fluorescence are quenched and then a radiation-healing effect is found, which means that photons help the oxidized and core-shell quantum dots neutralize and be fluorescent again.Several factors affect the speed of the healing process, the intensity of the radiation, the wavelength of the radiation laser and the chemical environment. The brightness of quantum dots recovers faster with larger intensity and shorter wavelength of the laser radiation and with reducing agent like Dithiothreitol (DTT) in the surrounding than without. The quenching and recovery of the core-shell quantum dot by oxidizing agent and laser radiance respectively provides us a very good way to explore the surface character of quantum dot and their mechanisms.