Aqueous Synthesis And Optical Properties Of Fluorescent Chalcogenide Nanocrystals

The domain of Life Sciences is undergoing a dramatic transformation by nanotechnology. It is a new research field for biology as the size of nanoparticles smaller than most of organs in the organism. Biolabeling is an important tool to realize the role of biomolecular in cell, tissue and organ in the living. The applications of biolabeling in the biological fields become a hot research area because of the nanoscale resolution and molecular sensitivity. But there are some drawbacks, such as absorption, low penetrability and special resolution. Moreover, interference from blood or tissue autofluorescence will influence the biolabeling. Near-infrared(NIR) fluorescence quantum dots(QDs) with fantastic optical properties, such as broad excitation, narrow emission, size-dependent photoluminescence and unusual photochemical stability, are suitable for bioimaging. They involve low absorption and relatively low autofluorescence with NIR emission. However, there are still several unsolved problems when using the NIR QDs, such as leakage of heavy metal ions and toxicity in the process of organic synthesis. Most of bright NIR QDs are synthesized in the organic solvent that is hazardous to the environment and the health. Thus, aqueous synthesis of less toxic and more environmentally friendly NIR QDs has attracted considerable attention. Focusing on aqueous synthesis of highly luminescent nanocrystals, this dissertation investigated the synthesis and optical properties of several NIR chalcogenide nanoparticles. The main research results of this dissertation are listed below:(1) CuGaSe2 QDs have been prepared directly in aqueous media by a hot injection method. The method is simple and rapid. It can avoid further surface modification or ligand exchange, which will decrease the fluorescence emission of the product. The QDs are spherical, with uniform particle size and good dispersion. The reaction time has a great influence on the crystallinity of the sample. After reaction 30 min, the QDs become good crystallization, with high emission at about 600 nm. The mass of mercaptopropionic acid(MPA) can influence the photoluminescent(PL) intensity by reducing the surface defect and possessing surface passivation.(2) Ag2 Se QDs have been prepared directly in aqueous media by hot injection method. The QDs are spherical, with uniform particle size and good dispersion. The PL emission of Ag2 Se QDs can tune by different Ag:Se molar ratio, as control the particle size. The quantum yield(QY) of Ag2 Se QDs is 31 %. A ZnSe shell is used to reduce the surface defect. The QY of Ag2Se/ZnSe QDs is about 42 %. The stability is enhanced obviously after storing 30 days. The Ag2Se/ZnSe QDs with low cytotoxic could be used as good cell labels, showing great potential applications in bio-imaging.(3) AgInSe2 QDs have been prepared directly in aqueous media by one-pot hot-injection method. The QDs are spherical, with uniform particle size and good dispersion. The strongest QY is 10.3 %. Adding the Zn2+ ions can increase the QY and stability by decreasing the defect of AgInSe2 QDs. The QY of AgInSe2/ZnSe is 31 %. The PL emission of AgInSe2 QDs can tune by different Ag:In molar ratio. These QDs with low cytotoxicity show favorable applications for in vitro optical imaging as versatile fluorescent probes.(4) CuFeS2 QDs have been prepared in diethylene glycol(DEG) by one-pot hot-injection method. The QDs are spherical, with uniform particle size and good dispersion. The strongest QY is 5.2 %. After storing 30 days, the QDs still have good red emission. The magnetization curve of the CuFeS2 QDs clearly depicts a typical weakly magnetic behavior. The obtained CuFeS2 QDs with low cytotoxicity show favorable applications for in vitro optical imaging as versatile fluorescent probes. Thus, CuFeS2 QDs may possess the potential to serve for bioapplications as dual-imaging agents.(5) Red emission LaPO4:Eu nanocrystals have been realized through an aqueous method by using microwave irradiation(MW) and microfluidic system. The LaPO4:Eu nanocrystals obtained by MW are good dispersion, narrow size distribution and highly luminescent. The QY is 21 %. Then, CuFeS2 QDs have been prepared by this method. The QDs are spherical, with uniform particle size and good dispersion. The particle size of the samples is only 2 nm, even synthesizing by long reaction time. The QY of CuFeS2 QDs prepared in the microfluidic system is about 7.1 %, higher than the samples synthesized in the three-necked flask. The stability is enhanced obviously by this method. After storing 30 days, the QY still remains up 6.5 %.