Study On Synthesis And Luminescence Properties Of Zinc Sulfide Quantum Dots Co-Doped By Europium With Halogen And Oxygen With Bromine

As a new kind of luminescent material,ZnS quantum dots（QDs）have been becoming a research hot topic due to its unique optical properties and wide application prospect in many fields.The photoelectric performance of QDs improved obviously by proper doping so as to expand their application potential.In order to further improve the luminescent properties of ZnS QDs administered,Eu³⁺with halogen ions and O^2-with Br^-co-doped ZnS QDs were synthesized by solid-state reaction method at low temperature,and their properties were characterized by X-ray powder diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,transmission electron microscope（TEM）,diffuse reflection spectroscope and photoluminescence（PL）spectroscopy.At the same time,according to the first-principles,energy structure and density of electronic states of ZnS,ZnS:3.125%O,ZnS:3.125%Br and ZnS:3.125%Br:3.125%O are calculated by MS simulation.Main research results are as following:1.Preparation and luminescence properties of Eu³⁺and halogen ions co-doped ZnS QDsZnS,ZnS_0.99Eu_0.01.01 and Zn_0.99S_1-xEu_0.01M_x（M=F,Cl,Br,I）QDs with cubic zinc blende structure,quasi-sphere,and the average grain size of 4.5,5.2,3.5⁴.3,4.2⁴.8,3.6⁴.2 and 3.7⁴.0nm were synthesized.The lattice constant and the particle size of ZnS QDs were increased after doping Eu³⁺,and the dispersibility of the QDs was obviously improved.The lattice constant and grain size of Zn_0.99SEu_0.01.01 QDs was changed by doping halogens.The average particle diameter of ZnS_0.99Eu_0.01.01 was decreased halogen doping,and the dispersibility was improved.In addition,Eu³⁺doped into ZnS QDs will form a new impurity level,and the impurity level will capture free carriers to form the luminescence center.As a result,the luminescence intensity of ZnS QDs was enhanced by 2.7 times by doping Eu.Higher PL was observed after doping halogen in Zn_0.99SEu_0.01.01 QDs compared to Zn_0.99SEu_0.01.01 QDs.The strongest luminescence was obtained when x=0.02,0.04,0.06 and 0.03 for Cl^-,I^-,F^-and Br^-,respectively.And it was about 9,7.2,6.3 and 5.8 times higher than that of ZnS QDs（Cl>I>Br>F）,and about 2.4,1.9,1.7,1.6 times of Zn_0.99SEu_0.01.And the corresponding bandgap widths were 3.704,3.665,3.706 and 3.700eV respectively.2.Synthesis and luminescence properties of O^2-and Br^-co-doped ZnS QDsZnS_0.96-xO_0.04Br_x（0≤x≤0.07）QDs were synthesized by solid-state reaction method at low temperature.The results showed that all of the samples with the average grain size of 3.3⁴.5nm were cubic zinc blende structure.The dispersibility of the samples was improved significantly by co-doping O^2-and Br^-.The luminescence intensity of the QDs reached the maximum when the doping concentration of Br^-was 3mol%,and it was about 9 and 2.5 times of ZnS and ZnS_0.96O_0.04.04 QDs,respectively.The band gap of ZnS and ZnS_0.93O_0.04Br_0.03.03 was about3.64 and 3.76eV respectively,it was consistent with the theoretical values calculated.The results of theoretical calculation showed that the O^2-and Br^-co-doped ZnS QDs were direct band-gap semiconductor,and the density of electron carriers was increased effectively,thus the luminescence intensity of the samples was strengthened.