| Quantum dots are the crystal that between the molecules and block material, the electronic structure is different from discrete molecular level and the continuous band structure of the materials, but it is special band structure between them. The size and shape of quantum dot can be controled by changing the reaction time, temperature, pH, ligand, and so on. Quantum dot’s unique properties are based on its own quantum effect, when the particle size becomes into nanometer level, size confinement will cause size effect, macroscopic quantum tunnel effect, quantum confinement effect and surface effect. Comparing with the traditional organic dyes, quantum dots have broad and continuous absorption spectra, narrow and symmetric fluorescence emission spectra, size tunable, excellent luminescent properties and optical stability. At the same time, quantum dots with high quantum yield and strong resistance to photobleaching capacity. Because of its unique optical properties, quantum dots not only can be used in studying molecular biology, cell living imaging, genomics, molecular probe, drug screening, biological macromolecular interactions, but also can be used for light color diodes, solar cellsand, etc.At present, preparation of quantum dots is divided into the organic phase and aqueous phase. In the organic phase, the temperature of the system can be adjusted in wide range, quantum dots have a higher fluorescence quantum yield, good monodispersity and stability, narrow fluorescence FWHM. But the size of oil-soluble quantum dots are too large, and with high cost, low operational safety. In aqueous phase, the quantum dots with excellent advantage, such as, simple, inexpensive, non-toxic reagents, good biocompatibility, etc. In this paper, we do the major research on preparation of a novel one-pot synthesis of UV-Blue ZnSe quantum dots, ZnxCd1-xSe quantum dots, CdSe quantum dots in aqueous solution, and experiment consists of the following there parts:1. Na2SeO3was used instead of Se powder as Se source, chosen glutathione(GSH) as ligand in experiment, Zn(Ac)2-2H2O as Zn source, UV-Blue ZnSe quantum dots with stable optical properties were prepared by optimizing the molar ratio of Zn:GSH:Se, pH, temperature, reflux time of the precursor. This quantum yield of ZnSe prepared is19%, which chosed quinine sulfate (quantum yield of55%) as reference material. Also, XRD and TEM show the ZnSe QDs are zinc cubic structure particles with good particle size distribution.2. Based on the first synthesis of ZnSe with excellent luminescent properties and optical stability, CdCl2·2.5H2O is used instead of Zn(Ac)2·2H2O, white ZnxCd1-xSe quantum dots were prepared by optimizing the reflux time, molar ratio of Cd/Zn, temperature. By observing absorption spectrum and fluorescence spectra at the different conditions, discuss the formation of ZnxCd1-xSe quantum dots, rather than forming separate CdSe and ZnSe nanoparticles or core-shell structure CdSe/ZnSe nanoparticles. The XRD and TEM figures show that ZnxCd1-xSe quantum dots are zinc cubic structure particles with an average diameter of3nm. Connecting ZnxCd1-xSe quantum dots with different concentration of hemoglobin, the fluorescence intensity reduced gradually, which laid a foundation for the application of ZnxCd1-xSe quantum dots in biological and medical.3. Based on the second part, CdCl2·2.5H2O partly replaced Zn(Ac)2-2H2O, the ZnxCd1-xSe quantum dots with stable optical properties have be synthesized. In the third part, Zn(Ac)2-2H2O was replaced completely by CdCl2·2.5H2O, the yellow CdSe quantum dots was prepared at150℃, pH12.0, and at about1h. The fluorescence intensity of CdSe quantum was adjusted by changing the temperature, molar ratio of Se/Cd. These CdSe quantum dots can be kept in the refrigerator for several months and do not precipitate, indicating that quantum dots with good optical stability. |
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