Preparation, Modification And Properties Of ZnS And Its Doped Semiconductor Quantum Dots

For doping ion in doped nanocrystal can create new energy level or slightly perturb the main energy level, and form new electron-hole recombination center, it can contribute to special optical, electrical or magnetic performance of doped nanocrystal. In addition, doped quantum dots not only retain the advantages of normal quantum dots, such as adjustable wide absorption spectrum, narrow and symmetrical emission spectrum, resistance to photobleaching, but also solve self-quenching problems of the normal quantum dots with a large stokes displacement. These properties endow doped quantum dots with great advantages that are promising in the field of biological fluorescent labeling, optical sensing, nano-photoelectric device and optical coding.The oil-soluble ZnS and Mn-doped ZnS quantum dots with high quantum yield and chemical stability were synthesized via a high-boiling solvent without oxygen and water through a facile and inexpensive synthetic process. The optical properties and micro structures of quantum dots were well discussed by UV-vis、PL、XRD、 TEM、EDX and other characterization.The technology of phase transfer catalysis technology was employed here in the preparation of solvent-free quantum dots. Cationic quaternary ammonium salt (NPEQ), containing oxygen ethylene chain and acting as phase transfer reagent, was coated on the surface of water-soluble quantum dots terminated with carboxylic acid salt anion, and the solvent-free oil-soluble quantum dots ionic liquid was prepared, which was favorable to the compatibility of solid inorganic quantum dots and polymer matrix. The analysis shows that dispersibility of the quantum dots ionic liquid modified by NPEQ was better than that of the water-soluble quantum dots. Moreover, the quantum dots ionic liquid retained good fluorescence quality and the fluorescence quantum yield was even higher than the water-soluble counterpart. And it also had high thermal stability and low melting point, presenting good flowability in absence of any solvent.By investigating the three essential demands that the donator-acceptor couple has to meet, the energy matching between ZnS quantum dots and fluorescein isothiocyanate (FITC) was analysed carefully. Mercaptoethylamine was chosen to conduct a surface modification on ZnS quantum dots. IR analysis showed that there were a large number of amino groups on the surface of water-soluble quantum dots after modification. TEM analysis revealed that monodispersion of the modified quantum dots declined, and reunion occured, but the lattice fringe was clear which indicated that structure of the quantum dots had not been destructed. Analysis of optical properties suggested that the quantum dots had a good fluorescence performance after converted into water-soluble, but the fluorescence quantum yield decreased. The energy transfer efficiency and occurrence between ZnS quantum dots and FITC have been studied, and the influence of various pH and QDs/FITC concentration raito were taken into account.