Preparation And Optical Properties Of Transition Metal Chalcogenide Quantum Dots

In recent years,two-dimensional materials represented by graphene,which have unique and excellent photoelectric properties,have become the focus of scientific and industrial circles.However,graphene,as a zero-band gap layered material,is expensive,which restricts the application of marketization to a certain extent.At present,scientists have found that transition metal chalcogenide（TMDs）not only have similar characteristics to graphene structures,but also have appropriate band gaps,showing unique physical and chemical properties.At the same time,nanomaterials,which generally depend on the preparation method of materials and the properties such as size,morphology and phase structure of constituent elements,especially the controllable preparation of transition metal chalcogenide quantum dots（TMD QDs）materials with lower dimensions,exhibit more novel photoelectric properties,which is an important direction for researchers at home and abroad to solve.At present,the research on TMD QDs materials is mostly focused on MoS₂QDs and PbS QDs,while the research on other materials is relatively small.Moreover,the reported preparation methods of nano-materials are mostly harsh in conditions and complicated in steps,and are mostly in the laboratory stage,which cannot realize large-scale commercial application.Although recent studies have reported that TMD QDs has broad application prospects in catalysis,batteries,electrodes and other fields,the application research in the optical field is still very limited.Therefore,it has practical research value to try to prepare small-sized TMD QDs materials by a controllable,green and safe method that can be applied in large-scale industrialization.By using ultrasonic stripping technology,this paper takes two-dimensional MS₂（M=Ta,Ti,Re,Zr）as the research object,prepares TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂ QDs materials through grinding,ultrasonic and centrifugation,and analyzes the structure（TEM,XRD）,morphology（TEM,SEM,AFM）,phase（Raman,FTIR,EDS,XPS）and optical properties（UV-Vis,PL&PLE）of the materials,focusing on the morphology,structure,size,fluorescence quantum yield and optical band gap of the materials,so as to lay a foundation for expanding the application of TaS₂,TiS₂,ReS₂ and ZrS₂ materials in the optical field.The main consequence of this paper are as follows:1.TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂ QDs with good dispersivity have been successfully prepared through AFM,TEM and SEM morphology characterization tests,all of which are 1T phase,the grain size is about 3 nm and presents a hexagonal structure with uniform distribution;2.XRD,Raman,FTIR,XPS and EDS elemental composition characterization have all confirmed that TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂ QDs can still maintain the excellent characteristics and unique quantum dot properties of bulk materials,in which S atoms and corresponding Ta,Ti,Re and Zr atoms can be detected,and the atomic percentages all show²:1;3.We have systematically studied the optical performance characterization of UV-Vis and PL&PLE,and obtained that TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂QDs all have characteristic absorption peaks in the ultraviolet band.In addition,we have also studied the optical band gaps of TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂QDs,which are 3.69 eV,3.18 eV,1.57 eV and 3.15 eV respectively,and the fluorescence quantum yields are 45.6%,80.7%,55.6%and 53.3%respectively;4.Stokes displacement effect is significant.stokes displacements of TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂ QDs are about 71 nm,150 nm,107 nm and 139 nm respectively.In a word,the purpose of this thesis is to study the preparation methods and optical properties of TMD QDs materials.It is found that two-dimensional layered materials have abundant electronic structure states,such as insulating state,semiconductor state and semi-metallic state,which have their respective excellent properties and disadvantages,and the thickness and size of the layers have corresponding effects on the application of TMDs in the optical field.We successfully prepared TaS₂ QDs,TiS₂ QDs,ReS₂ QDs and ZrS₂ QDs with better optical properties than bulk materials by ultrasonic method:their Stokes shift effect is remarkable,the fluorescence quantum yield is excellent,polychromatic luminescence and photochromic phenomenon are obvious,and the preparation method also provides certain theoretical support for the preparation of high-quality quantum dots of other layered materials.