| Fluorescent quantum dots?QDs?,because of its unique quantum confined effect and show all kinds of novel physical and chemical properties,has been widely used in biomedical labeling,light-emitting diodes and sensors.So far,the cadmium chalcogenide such as CdTe,CdS and CdSe,etc.have been successfully synthesized and used as versatile fluorescent bioprobes for imaging and sensing applications.However,the biotoxicity of the cadmium chalcogenide have restricted their further application.By contrast,the biotoxicity of the zinc chalcogenide can be significantly reduced.So more attention has been paid to the zinc chalcogenide,especially ZnSe quantum dots.Meanwhile,ZnSe quantum dots has a broadband gap and it is the ideal blue light-emitting semiconductor materials.ZnSe has unique fluorescence properties,doped with metal ions and coated with inorganic shell or organic shell on core quantum dots can not only improve the quantum efficiency but also improve chemical stability and the fluorescence lifetime.Moreover,a suitable modifier may make the quantum dots more water soluble,biocompatible and the ability to couple with biological macromole-cules.Therefore,the main research content of this paper is to synthesis water-soluble L-cysteine-modified doped ZnSe core/shell quantum dots in aqueous solution,which has good stability,low toxicity,high luminous efficiency and biocompatibility.The results are listed as following:1)ZnSe quantum dots was prepared successfully via simple and green method using L-cysteine as a modifier in aqueous solution.The reaction conditions such as the oil bath temperture,reflux time,the amount of modifier,different ratio of zinc and selenium,pH value on the fluorescence properties were investigated.In addition,the stability and photoinduced effects of ZnSe quantum dots were further studied.Many advanced techniques,such as X-ray power diffraction?XRD?,fourier transform infrared spectrum?IR?,transmission electron microscopy?TEM?,photoluminescence spectrum?PL?,energy dispersive X-ray analysis?EDX?and UV-Vis absorption spectrum?UV-Vis?were applied to investigate the structure,component,morphology,size and optical property of the quantum dots.Results indicate that ZnSe quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water solubility and biocompatibility.After illuminated with indoor natural light,the quantum efficiency increased from 5.75%10.71%.Via fluorescence spectrum analysis,the optimum synthesis conditions are as follows:oil bath temperature is 95?,pH=10.5,n?L-Cys?:n(Zn2+):n?HSe-?=1.53:1:0.2,the fluorescence lifetime is 24.27 ns.2)On the basis of preparation of ZnSe quantum dots,ZnSe:Ag quantum dots was prepared successfully via chemical co-precipitation method using L-cysteine as a modifier in aqueous solution.The reaction conditions such as reflux time,the amount of modifier,pH value,the doping concentration of silver ion on the fluorescence properties were investigated.And the illumination time of indoor light was further studied.The structure,morphology,size,component and optical property of ZnSe:Ag quantum dots were investigated via XRD,IR,TEM,PL,EDX and UV-Vis spectrum.It turned out that ZnSe:Ag quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water solubility and biocompatibility.The quantum efficiency increased from 5.75%to 10.07%after doped with Ag+.After illuminated it under the indoor natural light,the quantum efficiency of the ZnSe:Ag quantum dots increased from 10.07%to 15.46%.Via the fluorescence spectrum analysis,the optimum synthesis conditions are as follows:Reflux time for 2 h,pH=9.0,Ag+ doping amount is 1.5%,n?L-Cys?:rn(Zn2+):n?HSe"?=1.53:l:0.2,the fluorescence lifetime is 36.33 ns.Compared with ZnSe quantum dots,the stability of ZnSe:Ag quantum dots enhanced obviously,placing time from 12 days to 35 days in a dark room environment.The quantum efficiency and fluorescence lifetime is also impruved obviously.3)On the basis of preparation of ZnSe:Ag quantum dots,ZnSe:Ag/ZnS quantum dots was prepared successfully via chemical co-precipitation method using L-cysteine as a modifier in aqueous solution.The influence of the shell thickness,reflux time and the illumination time of indoor light on the fluorescence properties were investigated.The structure,morphology,size,component and optical property of ZnSe:Ag/ZnS quantum dots were investigated via XRD,IR,TEM,PL,EDX and UV-Vis spectrum.The results show that ZnSe:Ag/ZnS quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water-soluble and biocompatible.After coated with ZnS shell,the quantum yield of quantum dots increased from 10.07%to 14.73%.After illuminated it under indoor natural light,the quantum efficiency of the ZnSe:Ag/ZnS quantum dots increased from 14.73%to 23.56%.The fluorescence lifetime is 43.41 ns,the best shell and core is n?shell?:n?core?=1:1.Compared with ZnSe:Ag quantum dots,the stability of ZnSe:Ag/ZnS quantum dots enhanced obviously,placing time from 35 days to 66 days in a dark room environment.The quantum efficiency and fluorescence lifetime is also improved obviously. |
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