| Nanocrystals are one of the most important part 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.Fluorescent semiconductor nanocrystals are of great interest for both fundamental research and technical applications, due to their unique properties. Since the size of most important biomolecules, such as protein of DNA etc., are similar to the nanocrystals, the using of nanocrystals as biotechnologicals 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.Fluorescent semiconductor nanocrystals have several inheret functional advantages compared to organic dyes. The photoluminescence(PL) emissionsof high-quality semiconductor nanocrystals are narrow, symmetric, and strongly size-dependent. These spectral features make it possible to carry out multiple labeling with a single-laser setup. All those features have attracted tremendous interest in exploring novel materials based on semiconductor nanocrystals.CdTe nanocrystals was chosen because it was a representative example of fluorescent semiconductor nanocrystals that has been used in numerous applications, such as in light-emitting devices, photoelectrochemical cells, photonic and biological labels. My dissertation works focused on the preparation and primary surface modification of fluorescent CdTe nanocrystals.The main chapters are outlined as followings.In chapter2, a series of CdTe nanocrystals with TGA(thioglycolic acid)as stabilizer were synthesized in aqueous solution. The TGA molecules coordinate with Cd 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 CdTe nanocrystals. Control of luminescent properties and shape of nanocrystals has been playing a critical role in this very active field. The effects on luminescent properties of CdTe nanocrystals were studied under a series of reaction conditions, such as the change of pH value, the amount of TGA added, the ratio of reaction precursor (Cd + to Te ") in detail. The relative optimal conditions were found for synthesis of different sized CdTenanocrystals.In chapter 3, CdTe nanocrystals were prepared in aqueous solution by the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid .The photoluminescence efficiency of CdTe nanocrystals strongly depends on the pH value of the colloidal solution. Upon addition of IN HC1 acid , the fluorescence intensity of a CdTe colloidal solution increased slowly until the solution became neutral, then it increased drastically when the solution was adjusted into the acidic range. The optical spectroscopy studies imply that the pH-dependent behavior of the CdTe nanocrystals fluoresce is caused by structural changes on the surface rather than the size of the nanocrystals. The changing of pH will affect the coordination between TGA and the Cd ion on the nanocrystals surface. Additionally , the luminescence responses of CdTe crystals to important metal ions were investigated . It is found that the TGA-stabilized CdTe nanocrystals show a copper ion-sensitive luminescence. Copper ion can drastically quench the luminescence of CdTe nanocrystals with TGA as stabilizer. |
