| Semiconductor nanocrystals (NCs) have many unique optoelectronic properties, for example, the bandgap of NCs can be tuned by its size, their emission band is narrow and symmetric, different emissions of NCs'can be excited simultaneously by a single excitation source for their continuous absorption spectra, and so on. Thus, NCs have promising and extensive applications in bio-labeling, bio-imaging, optical coding, laser, fluorescence display, and so on. During the resent two decades, there have been great improvements in the field of NCs, and NCs have been playing an important and active role in bio-label area. However, there is still a long way to go to realize NCs'supposed extensive applications in other areas. To realize these applications, it requires NCs have high quality with narrow size distribution, high stability and high quantum yield (QY) on the one hand; on the other hand, it is necessary to combine NCs with various matrix structures to enhance NCs'stability and to integrate their functions. It is challenging to improve the quality of NCs to meet the application requirements, and resolve the problems that lie in the combination of NCs with different polymer structures, such as the oxidation, decomposition, and aggregation of NCs and the resulting quenching of emission.The first chapter of the thesis reviews the properties of NCs and the developments in the area ofâ…¡-â…¥NCs in recent two decades, including the improvement on the synthesis methods, the evolution on NCs compositions and structures, the exploration of the growth kinetics, the methods to combine NCs with matrix materials and their applications. In the end, the design of the thesis is proposed according to the actuality and the problems that remain to be resolved in this area, which is to prepare stable magic-size NCs with single size distribution and narrow bandgap emission and explore reliable and facile method to combine NCs with various polymer micro-structures and lay foundation for extending their applications.The second chapter aims at narrowing down the size distribution of NCs and explores methods to synthesize magic-size CdS NCs. By systematical tuning the experimental parameters, such as, the feed ratio of reactants, reaction temperature and reaction time, a CdS magic-size NCs family with UV absorption at 378 nm was obtained. The magic-size NCs have bandgap emission at 378 nm with nearly zero Stokes shift, and the full width at half maximum have been narrowed to less than 10 nm. The growth kinetics of magic-size CdS NCs were investigated by monitor the isothermal growth process, and it is found that the stability difference between regular NCs and magic-size NCs governed the exclusive generation of magic-size NCs. Solid state nuclear magnetic resonance spectroscopy, X-ray diffraction, 1H-Diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance and transmission electron microscopy were used to characterize the composition, structure and size of the magic-size NCsThe third to the fifth chapter deals with the methods to combine NCs with various polymer matrix structures, such as microspheres, fibers and micro-capsules. Surface-modifying of the NCs, enhancing the interaction between NCs and polymer matrix, avoiding the NCs in the polymerization process and using proper physical process were applied to prevent the oxidation, decomposition and aggregation of NCs in the matrix and make the combination of NCs with polymer micro-structures controllable. These composite structures will extend the applications of NCs in areas such as bio-label, fluorescence display, waveguide and smart materials.The third chapter deals with the methods to combine aqueous CdTe NCs with different size-scaled spheres. As for the synthesis of nanometer-size composite spheres, 40 nm to 100 nm positively charged polystyrene spheres were prepared by adding cationic monomer to emulsifier free emulsion system of styrene, then negatively charged CdTe NCs were adsorbed onto the spheres by static interaction. The amount of CdTe NCs on the spheres was controlled by the feed ratio of NCs to the spheres. NCs preserved good fluorescence properties. Although NCs were on the sphere's surface, they were more stable than bare NCs. The polymer nanosphere can be used as the carrier of NCs in preparing transparent film. Rayleigh scattering was reduced for the small size of the spheres, and the transparency of the film was guaranteed; also, the mobilization of NCs on the spheres's surface avoided NCs'aggregation and their fluorescence properties were preserved.The above method is very successful in preparing nanometer composite spheres; however, it is difficult to extend the size to sub-micrometer scale. To overcome this problem, acrylic acid was added to the emulsifier free emulsion polymerization system of styrene and a series of polystyrene spheres in the size range of 200 nm to 600 nm were prepared with narrow size distribution. Negatively charged CdTe were extracted to organic solution by cationic surfactant and swollen into the spheres. The swollen efficiency was near 100%. Not only single colored NCs were swollen into the spheres in a controllable way, but also multi-color NCs were swollen into the spheres with desired intensity ratio. NCs were confined to the spheres, water or even organic solution could not wash the NCs out.Emulsion polymerization is not applicable any more to prepare micrometer composite spheres. Here, we used post-process method to obtain spheres in micrometer scale. Polymerizable cationic surfactant was used to copolymerize with styrene to prepare cationic polystyrene polymer and extract negatively charged CdTe to form a CdTe NCs-polymer composite. Then the organic composite solution was emulsified into micrometer droplet. After the organic solvent evaporated completely, high fluorescent micrometer composite spheres were obtained.The fourth chapter deals with the process of aqueous CdTe NCs-polymer blending solution into polymer nanofibers by electrospinning method. NCs had surprisingly as good dispersibility in the fibers as in water, which was totally different with other composite materials from blending solution. The reason why NCs have so good dispersity was investigated, and it is found that the fast evaporation of the solvents because of the large specific surface area of the fibers, together with the effect of electric field caused the fast solidification of polymer chains and the freeze of NCs in their places. In this way, not only single color emission, but also multicolor emissions of NC-polymer composite fibers can be obtained in a well controllable way. Electrospinning method is also applicable to prepare other NC-polymer composite from blending solution. The application of the composite fibers in the area of responsive materials was investigated. NCs could grow in the solid fibers when treated above the glass transition temperature of the composite while the relaxation of polymer chains brought NCs to bump. For the growth rate was dependent on growth temperature it could be used in heat detector and used for heat induced fluorescence patterns.The fifth chapter deals with the incorporation of CdSe/ZnS NCs into poly (cucurbit(6)uril) (poly(CB)6) capsules. Ally-CB6 which can self-assembly into capsules during polymerization with di-thiol molecules was first prepared by a two steps modification of CB6. Mercapto-acid was used to cap CdSe/ZnS by ligand exchange and the NCs were introduced into the UV light irradiation polymerization system. For the interaction of NCs with dithiol, NCs were all brought into the capsules. NCs stand the polymerization conditions and preserved high fluorescence. The liability to surface modification of the host molecules of CB6 makes it possible to be use in bio-systems.To sum up, a lot of fundamental work on the preparation of high quality NCs and incorporation of NCs into various polymer micro-structures has been done and it lays foundation for the extension of applications of NCs.
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