| Nanotechnology is the creation and utilization of materials, devices, and systems through the control of matter on the nanometer-length scale. Nanoparticles are one of the most important part of nanomaterials. They show size tunable properties due to quantum confine effects and surface effects. These new properties will lead to new, high-performance products and technologies that were not possible before.Since the size of most important biomolecules, such as protein of DNA etc., are similar to the nanoparticles, the using of nanoparticles as biotechnological tool are particularly attractive. one of such application is using fluorescent semiconductor as labels for biological tagging experiments. Biological tagging is one of the most widely employed techniques for diagnostics and visualization. It appears as though for many applications, the colloidal nanocrystals are advantageous as labels, when compared to existing organic dyes. This has led to rapid commercialization of the new nanotechnology. For this reason, the development of a successful synthetic scheme of high quality nanocrystals is very important. My dissertation works aim to develop a versatile synthetic method of doped nanocrystals with high fluorescent properties. In chapter 2, water soluble ZnS:Mn nanocrystals with MPA (3-mercaptopropionic acid) as stabilizer were synthesized. The MPA molecules coordinate with Zn ion on the nanocrystals surface and form negative charge layer which stabilized the nanocrystals in water. TEM, XRD, and absorption spectroscopy are employed to study the structure and optical properties of the obtained ZnS:Mn nanocrystals. The coordination of Zn ion with MPA helps efficient doping of Mn and thus makes the process reproducible as compared to the common co-precipitation method. To obtain a high luminescent intensity, post-preparative treatments are performed. It is found that the surface states of the nanocrystals play important roles in the enhancement of the luminescent intensity. Through surface absorption of oxygen or S2- ion, the 590 nm luminescence of doped Mn can be enhanced while the 420 nm ZnS-related luminescence is quenched. The ZnS:Mn nanocrystals show a pH-sensitive luminescence. Since the changing of pH will affect the coordination between MPA and the Zn ion on the nanocrystals surface.In chapter 3, we synthesized a serials of water-soluble Mn doped ZnxCd1-xS nanocrystals with MPA (3-mercaptopropionic acid) as stabilizer. XPS, ICP, and XRD measurements were employed to confirm that the composition of the obtained nanocrystals is homogeneous. These alloyed nanocrystals show composition tunable optical band gap energy. The absorption spectra of the alloyed nanocrystals gradually shift to short wavelength with increasing of the Cd ion content. The luminescent properties of the alloyed nanocrystals also changed with the particle composition. By using EPR measurements, we found that Mn ion can only be doped efficiently into the alloyed nanocrystals at a low Cd concentration. When the Cd concentration is high, Mn ion will form MnS clusters in the nanocrystals which will quench the 590 nm luminescence and lead to a low luminescence efficiency.In chapter 4, water-soluble ZnS:Cu nanocrystals were synthesized and microwave hydrothermal method were introduce to improve the photoluminescent properties. The obtained ZnS:Cu nanocrystals show a bright green luminescence at 510 nm. The doped Cu ion disturbs the crystal lattice of ZnS nanocrystals and forms new energy levels which acted as new recombination center of excited electron and holes. By using microwave hydrothermal method, the crystallinity of ZnS:Cu nanocrystals was well improved and the doped efficiency of Cu was enhanced. The size of ZnS:Cu nanocrystals can be controlled by tuning the power of the microwave or reacting time. From the XPS data, we found that more Cu2+ ions were reduce to Cu+ by microwave irradiation. This will enhance the luminescence of doped Cu ion and quenched the ZnS-related luminescence which lead to a more symmetrical l...
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