Preparation and Optical Properties of Two-dimensional Gallium-based Spinel Oxide Nanomaterials
Author:Yang Wen Jin
Supervisor:jiang xin liu bao dan
The gallium-based spinel oxide nanomaterials are featured with unique structure,electronic configuration and rich valence states,which make them have many excellent optoelectronic properties,photocatalytic and electrocatalytic abilities.Thus,they show promising application in various fields,such as catalyst,energy conversion/storage,environment,lighting,and so forth.2D nanosheets also have attracted great attention due to their unique morphologies,structures,and electronic configurations,exhibiting some unique physical and chemical properties.Therefore,the synthesis of 2D gallium-based spinel oxide nanosheets is of great value and significance not only in basic research fields,but also in practical applications.However,due to the difficulty in the preparation of 2D gallium-based spinel oxide nanosheets,the unclear growth mechanism and the shallow research on its optical properties,it hinders their further research and application.In this thesis,2D MGa2O4(γ-Ga2O3,ZnGa2O4 and MnGa2O4)nanosheets were prepared via a hydrothermal method,and the growth mechanism was studied.Moreover,the CL luminescence of nanosheets was also studied,and the luminescence mechanism was revealed.The relationship between the structure and luminescent properties of two-dimensional gallium-based spinel oxide nanosheets was described.In addition,this paper also studied the preparation of GaN nanosheets by template method.(1)Firstly,the effects of solvent ratio,growth time and reaction temperature for the growth of y-Ga2O3 nanosheets were systematically studied.It was found that the volume ratio of H2O/ethylenediamine would directly affect the morphology,phase composition and structure of the final products.The reaction process research revealed that the GaOOH microrods were formed at a low concentration of ethylenediamine.While at the high concentration of ethylenediamine,the products were y-Ga2O3 nanosheets.The structural analysis confirmed that the as-obtained y-Ga2O3 nanosheets had a(111)surface and a thickness of 8-9 nm.(2)Exploring the universal growth of ternary MGa2O4 nanosheets,2D ZnGa2O4 nanosheets and MnGa2O4 nanosheets were prepared.The morphology,composition and phase of nanometers at different growth stages were studied.It was found that in the initial stage,y-Ga2O3 nanosheets or M2+-doped y-Ga2O3 nanosheets were formed firstly.Then,M2+ ions entered into the lattice of y-Ga2O3 or M2+-doped y-Ga2O3 and replaced part of Ga3+.The growth process of nanosheets confirmed that the essence of hydrothermal ly prepared MGa2O4 nanosheets was a "competition" between M2+ and the two-coordinated and tetracoordihated Ga3+ for the tetrahedral sites.The CL measurement shown that the γ-Ga2O3,ZnGa2O4 and MnGa2O4 nanosheets had the CL emissions centered at 445 nm,460 nm and 530 nm,respectively.And the luminescence mechanism were donor-acceptor pair transition,self-excitation of Ga-O in[GaO6]and d-d transition of Mn2+ in[MnO4],respectively.(3)The luminescence tailoring of ZnGa2O4 nanosheets was then explored due totheir excellent luminescence properties.Using a defect engineering strategy,different types of defects were created in the ZnGa2O4 lattice,and multi-color luminescence was achieved.CL measurement revealed that after annealing at 1000℃,ZnGa2O4 nanosheets had CL emissions centered at 358 nm,505 nm and 705 nm,respectively.Moreover,the luminescence intensity of each color was controlable.Through analyzing the structure change of ZnGa2O4 nanosheets before and after annealing treatment,it was confirmed that the distorted[GaO6],[GaO4]and oxygen vacancies are the reasons for UV,green and red emission of ZnGa2O4 nanosheets,respectively.(4)2D GaN nanosheets were prepared using y-Ga2O3 nanosheets as templates.Thegrowth process could be described as two steps:one is the activated N which decomposed from NH3 diffused into the y-Ga2O3 crystal and replaced the lattice O.Another is the Ga and O evaporated and reacted with N on the surface to form nano pyramids.UV-vis spectra measurement indicated GaN nanosheets had a strong absorption in the range of 300～500 nm,corresponding to a band gap of 3.3 eV,which is smaller than the theoretical calculation value and the band gap value of bulk GaN.