| Quantum dots (QDs), also referred to as semiconductor nanocrystals, have currently attracted great interest for application in biolabeling and electro-optical applications, due to their unique optical and electrical properties. Compared with organic dyes, QDs have a narrow and tunable emission spectrum, good photostability, chemical stability, and high brightness. The absorption spectra of nanocrystals with different sizes all extend from the onset to deep UV. These spectral features make it possible to carry out multiple labeling with a single-laser setup. QDs prepared by traditional non-aqueous synthesis can't be directly applied in bio-labeling. Compared with the non-aqueous synthesis, aqueous synthesis is much cheaper, less toxic, better water-soluble and bio-compatible. Unfortunately, the conventional aqueous synthesized QDs have much lower QY. Core/shell nanocrystals formed by growing a lattice-matched, higher band gap material on the top of the core have a higher quantum yield. In the thesis, the preparation of water-soluble core/shell CdSe/CdS and CdTe/CdS nanocrystals, as well as bionic assembly of CdTe nanocrystals with polymer were investigated, and some innovative results were abtained. The major contents are as follows:(1) Water-soluble core/shell CdSe/CdS nanocrystals were prepared, using MPA as stabilizer, and their properties were characterized by means of TEM, UV-visible absorption spectroscopy and fluorescence spectroscopy. The mean size of CdSe/CdS nanocrystals is 8 nm, and it has an absorption perk at 390 nm and a wide fluorescence spectra. When the molar ration of Cd: Se: MPA was 1:1:2.4, the concentration of precursors (Cd) was 1.25 mM, and the pH of Cd precursor solution was about 8.0, CdSe/CdS nanocrystals had the strongest photoluminescence. In the range of 0 to 6 hours, fluorescence intensity of CdSe/CdS became stronger, but emission wavelength didn't change.(2) A series of water-soluble core/shell CdTe/CdS nanocrystals were prepared, using MPA as stabilizer, their properties were characterized by means of TEM, UV-visible absorption spectroscopy and fluorescence spectroscopy, and their QY was caculated. The mean size of CdTe/CdS nanocrystals was 8 nm, and it had an absorption perk of excitonic luminescence and a narrow emission perk with 40 nm FWHM. With the prolonging of refluxed time, the PL perk position shifted to a longer wavelength, and the fluorescence intensity became stronger. The QY of CdTe/CdS nanocrystals were measured by using Rhodamine 6G as a reference standard, and the maximal quantum yield was up to 50%.(3) CdTe/PDDA multilayer films were prepared through layer-by-layer self-assembly technic, and their properties were characterized by means of AFM, XPS, UV-visible absorption spectroscopy and fluorescence spectroscopy. Further more, the influence of number of dipping cycles and different sizes of nanocrystals to the property of films were investigated. As-prepared CdTe/PDDA multilayers had a strong photoluminescence. A linear growth of absorbance with the number of dipping cycles was abserved. However, the strong perk in the fluorescence spectra against the number of double layers showed non-linear function and had a perk value. With the increasing of nanocrystals size, the PL perk position shifted to a longer wavelength, and the fluorescence intensity became stronger. CdTe nanocrystals embedded in the films could be seen through AFM. XPS spectra further inproved the presence of CdTe nanocrystals.(4) A series of Gemini surfactants' properties at the air/water interface were investigated by forming Langmuir film spread on pure water and in the queous subphase containing CdTe nanocrystals. We found that Gemini (16-s-16) (s=6, 8, 12) surfactant formed counter-U structure, when it spreaded on pure water. The area of molecule declined when Gemini surfactant spreaded on the aqueous subphase containing CdTe nanocrystals. Nonarods can be found through TEM measurements.
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