Study On Preparation And Property Of Water-Soluble ZnSe:Co?ZnSe:Co/ZnS And ZnSe:Co/ZnSe Fluorescent Quantum Dots

Semiconductor quantum dots are zero-dimensional advanced materials because their sizes can be designed to suit specific applications,exhibit many interesting optical and physical properties,is ideal for a variety of optoelectronic devices,photocatalysis,biomedical analysis of promising nanomaterials.Higher fluorescence efficiency such as CdS,CdTe and CdSe have been used as versatilefluorescent probes at present,but the toxicity limited the application in biological analysis.The toxicity of the zinc chalcogenide can be significantly reduced,especially ZnSe 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 quantumdots.In addition,a suitable modifier may make the quantum dots more water soluble,biocompatible and the ability to couple with biological macromole-cules.Therefore,the paper focuses on synthesize water-soluble L-cysteine-modified doped ZnSe core/shell quantum dots with low toxicity,high quantum yield,good stability and biocompatibility in aqueous solution,and results are listed as following:1)Water-soluble ZnSe:Coquantum dots have been synthesized successfully using L-cysteine as a modifiervia chemical co-precipitation method.The influence of reaction conditionson the fluorescence properties were investigated.X-ray power diffraction(XRD),energy dispersive X-ray analysis(EDX),transmission electron microscope(TEM),infrared spectrum(IR),UV-Vis absorptionspectrum(UV-Vis),photoluminescence spectrum(PL)were applied to characterize the structure,component,morphology,size and optical property of the quantum dots.The results showed that ZnSe:Co quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water-soluble and biocompatible and the fluorescence lifetime is 32.53ns.The optimum synthesis conditions of quantum dots are obtained by fluorescence spectrum analysis:n(L-Cys):n(Zn2+):n(HSe-)= 1.6:1:0.15,pH=10,reaction temperature is 95?,Co2+ doping amount is 2%.The quantum yieldincreased from 4.93%to 13.19%after doped with Co2+,the quantum yield increased from 13.19%to 19.32%after illuminated with indoor natural light.Compared with ZnSe quantum dots,the stability of ZnSe:Co quantum dots enhanced obviously,placing time from 20 days to 45 days.2)Water-soluble ZnSe:Co/ZnSquantum dots have been synthesized successfully by coating the ZnS shell on the surface of ZnSe:Co core quantum dots using L-cysteine as a modifier.The influence of the shell thickness and reflux time on the fluorescence properties were investigated.XRD,EDX,TEM,IR,UV-Vis and PL spectrum were applied to characterize the structure,morphology,size,component and optical property of the quantum dots.The results showed that ZnSe:Co/ZnS quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water-soluble and biocompatible.The quantum yield of quantum dots increased from 13.19%to 25.19%after ZnS shell formed,the quantum yield incresed from 25.19%to 32.44%after illuminated with indoor natural light,n(shell):n(core)=1.5:1 is the best,compared with ZnSe:Co quantum dots,the stability of ZnSe:Co/ZnS quantum dots enhanced obviously,placing time increases from 45 days to 60 days,the fluorescence lifetime increases from 32.53ns to 37.69ns.3)Water-soluble ZnSe:Co/ZnSequantum dots have been synthesized successfully by coating the ZnSeshell on the surface of ZnSe:Co core quantum dots using L-cysteine as a modifier.The influence of the shell thickness and reflux time were investigated.XRD,EDX,TEM,IR,UV-Vis and PL spectrum were applied to characterize the structure,morphology,size,component and optical property of the quantum dots.The results showed that ZnSe:Co/ZnSe quantum dots belong to the cubic zinc blende structure,morphology of the spherical,own good monodispersity,water-soluble and biocompatible.Compared with ZnSe:Co quantum dots,the quantum yield increased from 13.19%to 29.94%,the optimum n(shell):n(core)=0.4:1,the fluorescence lifetime increases from 32.53ns to39.95ns.