Preparation And Characterization Of ZnSe Quantum Dots In Aqueous Solution

Among the II-VI semiconductor quantum dots(QDs),as typical representative of luminescent semiconductor QDs,cadmium based QDs have become the backbone of the light emitting devices.However due to the poor biocompatibility and the intrinsic toxicity of the Cd to the environment,biological cells and the human,which have brought the Cd based QDs into a disadvantageous situation in many practical applications.Therefore,this dissertation focuses on the preparation of non-toxic water-soluble ZnSe QDs by colloidal water phase method,and study the optical properties of the ZnSe QDs.For the poor stability and low fluorescence quantum yield of ZnSe QDs,we prepared ZnSe/ZnS QDs by epitaxial growth method.Then we prepared them as films,and researched the optical properties of the films.The specific content of this dissertation is as follows:(1)In this thesis,the ZnSe QDs were prepared by the cationic-reversed-injection method in aqueous solution,using thioglycolic acid(TGA)as a surfactant,sodium hydrogen selenide(NaHSe)as selenium source and zinc acetate dihydrate and thioglycolic acid complexes(Zn-TGA)as zinc source.Firstly,the highly reactive NaHSe was rapidly injected into a three-necked flask,in which the mixture of TGA and deionized water with the NaOH solution have been injected,and then Zn-TGA solution was slowly injected into the three-necked flask.The experimental results indicate that when the molar ratios of reactants was nzn2+:nHSe-:nTGA =1:0.125:1.2,the precursor solution concentration ratios was set to be CZn2+:CHSe-=1:1,the reaction time was fixed to be 2 h,the temperature and pH value were 90? and 8.5,the as-synthesized ZnSe QDs had strong band edge emission.ZnSe QDs with the full width at half maximum(FWHM)about of 32 nm and average part shows approximately spherical and belongs to the zinc blende structure.ZnSe QDs with the fluorescence quantum yield of 31.8%and fluorescence lifetime of 25.24 ns reveals good crystallinity.(2)Due to the problems of low quantum yield and poor stability of single nucleus ZnSe QDs.In this paper,the surface defects of ZnSe QDs were modified by low temperature growth of wide bandgap ZnS,using thiourea(CH4N2S)as sulfur source,Zn-TGA as zinc source.By studying the optical properties of ZnSe/ZnS QDs,which indicate that when the molar ratios of ZnSe solution to S source was nznSe:ns2-=1:5,the reaction time was 3 h,the temperature and pH value were fixed to be 90 ? and 8.5,the as-acquired ZnSe/ZnS core/shell QDs had better quality.ZnSe/ZnS QDs with the FWHM about of 25 nm and average nm suggests better stability and particle size dispersivity,and belongs to the zinc blende structure.ZnSe/ZnS QDs with the fluorescence quantum yield of 59.5%and fluorescence lifetime of 46.32 ns reveals nearly two times higher than the ZnSe single nucleus,which indicates that the presence of ZnS shell effectively reduces the delocalization of intranuclear excitons and increases the intrinsic recombination probability of excitons.(3)In this dissertation,ZnSe/ZnS QD films were prepared by photolithography and spin coating techniques.The effects of QD solution concentration and the number of spinning to the optical properties of ZnSe/ZnS QD films were discussed.The results indicate that when the concentration ratios was 1:4 and spin coating 4 counts,the as-prepared film with the emission peaks of 408 nm and the FWHM about of 35 nm shows the average transmission rate is 80.76%,fluorescence lifetime is 21.79 ns,and color coordinates is(0.1817,0.1248).After ZnSe/ZnS QD film is excited,it is expected to be used in QDEF and QLED devices due to the change of the luminescent modes.