Synthesis And Photoluminescence Properties Of Carbon Quantum Dots

Carbon quantum dots (CDs) are new carbon nanomaterials with the size within 20 nanometers discovered in 2004. Because of its high fluorescent intensity, well stability, resistance to photo-bleaching, broad excitation wavelengths and narrow emitting peak shape, emission wavelength would be changed by particle sizes, structures and components, and doped materials of carbon quantum dots. Due to their good biocompatibility, precise biological target and low toxicity and so becomes ideal substitute of traditional semiconductor quantum dots in biological imaging and biological labeling and other fields, which can be directly used for cell labeling. Due to the simple preparation process, cost low, easy functionalization and industrialization of carbon quantum dots, make it in many fields shown great potential applications such as fluorescence sensing, environmental detection, photo catalysis, optoelectronic devices and so on. Moreover, it also bring new and broad space for development in biomedical, optoelectronic devices, green lighting, film display and other disciplines.In this thesis, we focus on the synthesis of carbon quantum dots by hydrothermal treatment of fresh lemon juice and orange juice, and study on their photoluminescence properties. Moreover the surface morphology, microstructure and crystalline state photoluminescence characteristics of carbon quantum dots were characterized and analyzed by TEM, XRD, XPS, UV-Vis absorption spectra, and PL spectra for exploring their luminescence mechanism. Furthermore, CDs were employed to carry out biological imaging and to mark human lung cancer cells base of their biological compatibility, low cell toxicity and excellent photoluminescence properties. The main works in the thesis are as follows:1. The optimal process parameters for the synthesis of photoluminescence carbon quantum dots is constant temperature heating for 150 min at 120℃. In this condition, we got the carbon quantum dots with uniform size distribution, nice monodisperse, high crystalline and well stability, and the CDs are stable in aqueous solutions.2. The synthesis of carbon quantum dots is carbonization procedures of ascorbic acid, citric acid and saccharides that belong to the main component of lemon juice and orange juice. Carbon quantum dots are become aggregation, deformation, non-uniform distribution when the time of constant temperature heating is prolonged during the synthesis of CDs.3. In the optimum process we got the carbon quantum dots with the size distribution of 2-6 nm and an average diameter of ～3 nm, and the clear crystal lattice. The UV-Vis absorption spectrum of CDs shows two absorption peaks at 202 nm and 290 nm, and imply that the absorption strong on the UV but visible have none. We found a large number of oxygen functional groups on the surface of carbon quantum dots which are beneficial to the surface modification and functionalization, and also is conducive to the solution in water.4. Photoluminescence of carbon quantum dots has the characteristics of excitation dependent photoluminescence that emission peaks put up small red shift with the increase of the excitation wavelength, the strongest emitting peak at 482 nm and appearing color of bluish green. The carbon quantum dots were applied in human lung adenocarcinoma cell markers and marked lung adenocarcinoma cells can observe with biologic photomicroscopes. Our results show that fluorescence images of human lung adenocarcinoma cells marked by CDs are clear and similar morphology to their bright field images under optical microscopes.