| Fluorescent semiconductor nanocrystals or quantum dots have been widely used in photovoltaics,biomedical labeling,sensors and light-emitting diodes.Because quantum dots exhibit quantum confinement effects and their unique physical and chemical properties.So far,the cadmium chalcogenide such CdTe,CdS and CdSe,etc.have been extensively studied and synthesized and used as versatile fluorescent bioprobes for imaging and sensing applications.However,the biotoxicity of the cadmium chalcogenide will limit their further application.ZnSe,a kind of ideal blue-ray semiconductor materials,has a broadband gap and less toxic.But ZnSe has low quantum efficiency,doped with metal ions and coated with inorganic shell on core 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 water-soluble,and has the ability to couple with biological macromolecules.Therefore,the main research content of L-water-soluble cysteine-modified doped ZnSe core/shell quantum dots,and the results are listed as following:1)Water-soluble ZnSe/ZnS quantum dots were synthesized successfully in aqueous solution via epitaxial growth procedure using L-cysteine as a modifier.Adapting the reaction time,the ZnSe/ZnS quantum dots with different shell thickness can be achieved.The core/shell structure was token by X-ray power diffraction(XRD),energy dispersive X-ray analysis(EDX),transmission electron microscope(TEM),fourier transform infrared spectrum(IR),UV-Vis absorption spectrum(UV-Vis),photoluminescence spectrum(PL)to characterize the structure,component,morphology,size and optical property of the quantum dots.The results show that ZnSe/ZnS quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water-soluble,biocompatible and good stability.The fluorescence quantum yield of quantum dots increased from 15.29%to 26.84%after illuminated with indoor natural light.The optimum synthesis conditions are as follows:reaction time is 1.5h,n(shell/core)=1:1 the fluorescence lifetime is 17.57ns.2)The L-cysteine modified water-soluble ZnSe:Fe quantum dots were synthesized by chemical co-precipitation method in aqueous solution.XRD,EDX,TEM,IR,UV-Vis and PL spectrum were applied to investigate the structure,morphology,size,component and optical properties of the quantum dots.The influences(such as the amount of NaHSe and L-cysteine,reaction time,oil temperature)on the luminescence properties of ZnSe:Fe quantum dots were investigated.The results show that ZnSe:Fe quantum dots have the cubic zinc blende structure,morphology of the spherical,good monodispersity,water-soluble and biocompatible.The quantum yield of quantum dots increased from 12.37%to 19.02%after illuminated with indoor natural light.Via fluorescence spectrum analysis,the optimum synthesis conditions are as follows:Reflux time for 2 h,pH=10.5,n(L-Cys):n(Zn2+):(HSe-)=1.5:1:0.15,the fluorescence lifetime is 29.37ns.3)On the basis of preparation of ZnSe:Fe/ZnS,water-soluble ZnSe:Fe/ZnS quantum dots have been synthesized successfully in aqueous solution via chemical co-precipitation method using L-cysteine as a modifier.XRD,EDX,TEM,IR,UV-Vis and PL spectrum were applied to investigate the structure,size,component and optical properties of the quantum dots.The preparation conditions(such as reaction time and the ratio of the shell/core)of the quantum dots were investigated by PL spectrum.The results show that ZnSe:Fe/ZnS quantum dots were the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water-soluble,biocompatible and good stablity.Compared with the ZnSe:Fe core nanocrystals,the ZnSe:Fe/ZnS core/shell nanocrystals PL intensity increased,and the fluorescence quantum yield of quantum dots was up to 37.65%after illuminated with indoor natural light.The fluorescence lifetime is 53.06ns,n(shell):n(core)=1.5:1. |
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