Study On The Synthesis And Luminescence Properties Of Halogen Ion Co-doped ZnS Quantum Dots

As a new type of semiconductor luminescent material,zinc sulfide(ZnS)quantum dots have unique optical and electrical properties,and have important application values in many fields.In the field of optoelectronics,improving the luminescence performance of ZnS quantum dots is the primary work of research.In the research on luminescence performance in recent years,doping is one of the simplest and most economical ways to increase luminous intensity.In this thesis,a low-temperature solid-phase reaction synthesis method was used to synthesize ZnS:Cl,X(X=F,Br,I)and ZnS:Br,Y(Y=F,I)co-doped quantum dots,and used X-ray diffractometer(XRD),Transmission Electron Microscope(TEM),Ultraviolet Visible Diffuse Reflectance Spectroscopy(UV-vis),Photoluminescence Spectroscopy(PL)Nitrogen Absorber(BET)and Fourier Infrared Spectroscopy(FTIR)on the shape of quantum dot materials Characterization of appearance,structure,composition,performance,etc.Analyze the influence of doped ions on the optical properties of quantum dots such as the structure and defects,absorption spectrum,reflection spectrum,emission spectrum,dielectric function and refractive index,calculate the energy band structure and electronic density of states,compare their changes,and discuss the matrix lattice.The regular characteristics of energy absorption and transfer between defects and doped ions.The main findings are as follows:1.ZnS:Cl,X(X=F,Br,I)quantum dots preparation and luminescence propertiesZnS:Cl,X(X=F,Br,I)quantum dots were prepared by low-temperature solid-phase method.The material is spherical.The average grain size distribution of XRD analysis is 5.3 nm,4.5 nm,3.6-4.3 nm,2.2-3.0 nm,3.2-3.3 nm correspond to ZnS,ZnS:Cl,ZnS:Cl,X(X=F,Br,I)quantum dots respectively.High-resolution transmission electron microscopy observed that the material was spherical with a grain size of about 5 nm,which corresponds to the value of XRD analysis.In the co-doped samples,when the Cl~-concentration is 7%,the luminous intensity first increases and then decreases with the increase of the F~-,Br~-,and I~-concentrations.The optimal doping concentrations are 5%,3%,and 5%,respectively.The luminous intensity is 4.7,4.9,and 7.2 times higher than that of undoped ZnS.The absorption spectrum shows that it increases with the increase of F~-,Br~-,and I~-concentrations,which means that doping can regulate the band gap of ZnS quantum dots.The band gap of the ZnS:Cl,X(X=F,Br,I)co-doping model calculated by MS software is 2.364eV,2.197 eV,and 2.305 eV,which are all larger than the calculated value 1.956 eV of the pure ZnS band gap.The experiment results have the same trend.And it is found that after co-doping,the energy band of ZnS shifts and transforms to an N-type semiconductor.2.ZnS:Br,Y(Y=F,I)quantum dots preparation and luminescence propertiesZnS:Br,Y(Y=F,I)quantum dots based on Br co-doped were synthesized by low-temperature solid-phase method.XRD analysis results show that the average grain size is between 3.3-3.7 nm and 3.6-4.1 nm,respectively.The high-resolution transmission electron microscope image is consistent with the XRD analysis result.Luminous intensity Due to the introduction of Br~-and F~-,Br~-and I~-,the carrier concentration increases,which increases the luminous intensity by 10.6 and 6.6 times.The band structures of the best luminous intensity are 3.78 eV and 3.80 eV,which have a tendency to increase compared with undoped ZnS,and the theoretical values of2.377 eV and 1.985 eV obtained from the calculation result match the experimental results.3.L-cys/ZnS quantum dot preparation and luminescence propertiesL-cys coated ZnS QDs with a mean diameter of 3.7-5.7 nm were successfully obtained in two-step method.The results displayed that the water-dispersity and PL intensity of ZnS QDs were furthered by modification with L-cys.When the mass ratio of L-cys to ZnS QDs was equal to 0.7:0.5,the emission intensity was 4.5 times as much as that of ZnS sample.The result of First-principles calculations implied that type-I and type-II heterojunction can be formed after L-cys modification,which should reduce the chance of the nonradiative recombination on the surface,and then increase the emission intensity.