| Quantum dots,also known as semiconducting nanocrystals,have found wide application in many fields such as fluorescent labels,photocatalysis,and light-emitting LED because of their unique photochemical properties.Early research was focused on Cd-type quantum dots such as CdS,CdTe,they are used as fluorescent probes because of their high fluorescence efficiency,especially for imaging and sensors,but the biological toxicity of Cd-based quantum dots have limited its application in the analysis and detection of organisms.Compared with Cd-based quantum dots,Zn-based quantum dots have lower toxicity and better fluorescence performance,as a blue-light materials with wide-band gaps in the ultraviolet to blue region,ZnSe is recognized as an icdeal host for doping transition metals.Compared to cadmium-based QDs synthesized in aqueous solution,the toxicity of ZnS,ZnSe QDs is much lower,indicating that they can be used as fluorescent markers for cell and tissue imaging.By doping metal ions in the ZnSe quantum dots,the fluorescence characteristics of the quantum dots can be modified,Besides,inorganic molecular shell layer is epitaxially grown on the surface of the microspheres to passivate the surface defects of the quantum dots to enhance fluorescence intensity and stability;Suitable surface modifiers can make quantum dots water solubility and biocompatibility.Therefore,the main purpose of this paper is to synthesize water-soluble ZnSe-doped core/shell quantum dots with good stablility,high quantum yield,low toxicity,and biocompatibility in the aqueous phase,and results achieved as following:(1)Water-soluble Ag:ZnSe/ZnSe QDs were synthesized by epitaxial growth method with L-cysteine as the modifier through coating the surface of Ag:ZnSe QDs with a ZnSe shell.X-ray powder diffraction(XRD),transmission electron microscopy(TEM),infrared spectrum(IR),ultraviolet-visible absorption spectrum(UV-Vis)and photoluminescence spectrum(PL)were applied to characterize the morphology,structure,composition,and optical properties of the as-prepared quantum dots.The results showed that spherical Ag:ZnSe/ZnSe quantum dots were successfully synthesized,the fluorescence quantum yield of the quantum dots reached up to 20.59%.When the ratio of n(ZnSe:Ag):n(ZnSe)is 1:0.2,solution pH is 10,and the reaction time is one hour,the quantum dots with good fluorescence have been achieved.Compared with Ag:ZnSe,the stability of the Ag:ZnSe/ZnSe quantum dots has been improved.(2)The co-precipitation method was used to synthesize water-soluble Ag:ZnSe/ZnSe/ZnS quantum dots with L-cysteine as the modifier.The structure and fluorescence properties were characterized by TEM,XRD,EDX,IR,UV-Vis,PL instruments.The Ag:ZnSe/ZnSe/ZnS with a diameter of 3.6 nm was successfully synthesized,the fluorescence quantum yield reached up to 24.84%.When pH=10,reaction for 1.5 hours,the n(Ag:ZnSe):n(ZnSe):n(ZnS)=1:0.2:0.2,n(ZnSe):n(ZnS)=1:1,the best fluorescence intensity of the quantum dots was achieved.Compared to the Ag:ZnSe/ZnSe quantum dots,the stability of the Ag:ZnSe/ZnSe/ZnS quantum dots is greatly improved.(3)Ag:ZnSe/SiO2-NH2 nanoparticles have been successfully prepared by Stober method through coating a layer of Si02 on the surface of Ag:ZnSe quantum dots.The Ag:ZnSe/SiO2-NH2 nanoparticles are analyzed using infrared spectroscopy,ultraviolet-visible spectroscopy,transmission electron microscopy,X-ray diffraction powder diffraction,fluorescence spectroscopy,etc.The Ag:ZnSe/SiO2-NH2 is spherical particles with average size of 30 nm.The fluorescence quantum yield of Ag:ZnSe/SiO2-NH2 reached up to 13.34%.Under ultraviolet light irradiation,the fluorescence intensity of Ag:ZnSe/SiO2-NH2 remains unchanged for a long time.Compared with Ag:ZnSe,the stability of the Ag:ZnSe/SiO2-NH2 is greatly improved. |
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