Controllable Synthesis,Theoretical Caculation And Luminescent Properties Of Scandium-Based Micro/Nanomaterials

Rare earth is the treasure-house of luminescent materials,rare earth luminescent material is a kind of luminescent materials with excellent properties and broad application.Searching for new rare earth luminescent materials with novel properties has been the research focus of luminescent materials.Scandium as a rare earth element with the minimum radius and seats at a unique postion of the element table,the top of IIIB and the beginning of transition metal,which endows Sc and its compounds with special chemical and physical properties.In recent years,with the deeper investigation of rare earth elements and better understand of their special property,the study of Sc has been intensive and diverse.Scandium-based luminescent materials received more and more attention from researchers.Though there are many reports on scandium-based materials,the structure of this kind of materials and their relation with property is not clear.Besides,the theoretical calculation on property has been seldomly studied.As is well known,nano/micro materials always demonstrate different properties from their bulk materials.The control of size and morphology has been one of the important topics of rare earth luminescent materials.Based on the research progress at home and abroad,scandium-based materials with unique property were selected and their micro/nanostructures with controlled size and morphology were prepared by different methods.A series of excellent Sc-based luminescent materials with red,green,blue and white emission were obtained by doping with rare earth ions.After that,their temperature-dependent properties were investigated and calculated and some roles were found,which provided theoretical guidance and experimental suggestion for the design and preparation of functional luminescent materials.The main research contents of this thesis are as follows:（1）Preparation,electronic structure and luminescent properties of ScF₃:Eu³⁺nano/submicroparticlesNegative thermal expansion（NTE）ScF₃ nano/submicroparticles were prepared and selected as host material.Various Eu³⁺concentrations（0.05–50%）doped in the ScF₃ particles were obtained and their temperature-dependent photoluminescence（PL）properties were studied.The phase confirmation and morphology of the as-prepared ScF₃ particles were investigated by X-ray powder diffraction（XRD）and scanning electron microscopy（SEM）.The XRD results reveal that when the doping concentration reaches 3%,EuF₃ phase begins to form.The size of the ScF₃ cubic particles ranges from 300 nm to 800 nm.The temperature-dependent luminescence results of ScF₃:0.01Eu³⁺reveal that the luminescence intensity increases with the decrease in temperature in the range from 80 K to 450 K.Moreover,the decay time increases with a decrease in temperature.The crystal structure,electronic properties,dielectric functions,and absorption spectra have been systematically investigated for pure ScF₃ and Eu³⁺-doped ScF₃.First principles calculations were used to support and explain our experimental observations.（2）Facile microwave synthesis of ScPO₄·2H₂O flowerlike superstructures:morphology control,electronic structure and luminescent propertiesA fast and facile microwave method is employeed to prepare monoclinic ScPO₄·2H₂O flower like superstructures constructed by well-aligned nanorods without the use of any template or surfactant.By varying the preparation parameters including reactant ratio,microwave power and reaction time,various morphologies such as flower-like,nanospheres,cubes and walnut-like particles were obtained.The growth process of the flower-like microstructure was also investigated.The formation mechnism reveal that this supersture undergo a nanorod growth and self-assembling process within the reaction time of 30 min.After calcining the monoclinic ScPO₄·2H₂O at 800^°C,tetragonal ScPO₄ with similar morphology was obtained.Tb³⁺,Eu³⁺,Dy³⁺,Tb³⁺/Eu³⁺and Eu³⁺/Dy³⁺doped ScPO₄·2H₂O were also prepared and their photoluminescent properties were well investigated.By adjusting the relative doping concentration,multicolor tunable emission of green,red and blue could be realized and the decay time results reveal that energy transfer occurs.More significantly,white light could be achieved in a 3%Eu³⁺and 2%Dy³⁺co-doped ScPO₄·2H₂O.The energy transfer of Tb³⁺/Eu³⁺and Eu³⁺/Dy³⁺was discussed based on their luminescent properties.（3）Scandium molybdate with tunable phase and morphology:surface energy and temperature dependent photoluminescence properties.Scandium molybdate microstructures have been prepared via microwave heating method.By controlling the experimental parameters such as molar ratio of reagent and reaction time,scandium molybdate with tunable phase and diverse morphologies,including snowflakes,microflowers,microsheets and branched spindles were obtained.The products were characterized by XRD,SEM,EDS,UV-Vis,etc.Results demonstrated that the molar ratio of Sc/Mo had great effect on the crystal phase and morphology of the product.Diffuse reflection spectra（DRS）revealed the E-gap can be readily tuned from 3.69 to 4.16 eV.The electronic band structures,density of states and surface energies of Sc₂Mo₃O₁₂ were primarily studied from first principles calculations for the first time.An indirect band gap of 3.56 eV was observed for crystalline Sc₂Mo₃O₁₂,and the surface energies of various facets were determined to be 0.21⁰.96 J/m^-2,which is in accordance with the theoretical result.The photoluminescence（PL）properties of Eu³⁺-doped Sc₂Mo₃O₁₂2 were discussed.（4）Sc-based coordination polymer concaved octahedron:preparation,conversion and properties.Well-formed Sc-based coordination polymer（ScCP）octahedrons with diameter of about 5μm have been fabricated by a facile solvothermal method.The ScCP octahedrons are constructed by numerous nanoparticles with size of 10 nm via a self-assembly process.Interestingly,the octahedrons are concaved.The products were well characterized by SEM,TG,FT-IR,et al.After calcination at high temperature,Sc₂O₃/C with similar morphology was obtained.Yb³⁺/Er³⁺doped ScCP polyhedrons were also prepared and their photoluminescent and electrochemical properties were investigated.