Study On The Composition And Assembly Of Rare Earth Complexes

Rare earth complexes have potential applications in the fields of optical display, laser materials, optoelectronic conversion because of their excellent properties such as high fluorescence efficiencies, wide spectral region, excellent fluorescence monochromaticity and large Stokes shift. Along with the widely application of functional materials in modern society, the development of rare earth complexes will face great chances and challenges. The composition of rare earth complexes and other functional materials are expected, because such materials will possess the advantages of each component, moreover the optical, electrical and magnetic properties of each component will also be improved. At the same time, continuous development of nanotechniques bring infinite vital force to the scientific researches on rare earth complexes. The band structures and fluorescent properties of nano-scaled rare earth complexes are new completely new fields waiting for researchers to explore. Furthermore, fluorescent rare earth complex nanomaterials will no doubt play important roles in the fields of optoelectronic devices and fluorescent labeling, etc. How to combine the properties of rare earth complexes with other functional materials and how to prepare and assemble of rare earth complex nanomaterials are the most important two subjects in recent years. Attention is paid on rare earth complexes in this thesis that the preparation of different rare earth complex nanomaterials, and the compositon and assembly of rare earth complexes with other functional marerials are investigated in detail.In chapter 2, in order to realize the combination of rare earth complex with TiO₂ nanoparticles in polymer matrix, rare earth complex/TiO₂ nanoparticles/polymer composite materials are synthesized through the radical polymerization of Ti(MA)2.86(OBu)1.14, Eu(MA)3 and methacrylic acid monomers and followed by a in-situ hydrolization method. Anatase TiO₂ nanoparticles with average diameters about 2 nm are produced in this process. Compared with traditional methods which are used to prepare TiO₂ nanoparticles, in-situ hydrolyzation method has advantages in producing small sized and well-dispersed TiO₂ nanoparticles; moreover, TiO₂ with anatase structure can be obtained at relatively low temperature. The prepared rare earth complex/TiO₂ nanoparticles/polymer composite materials exhibit multifunctional properties. For one thing, rare earth complex bring the composite materials excellent fluorescence properties, which make it possible to use theses composites as optical materials. For another, thanks to the anatase TiO₂ nannoparticles, these composite materials also have the ability of decomposition of orgnic pollutants. Moreover, because of the sensitizing effect of Eu3+ ions to TiO₂ nanoparticles, the photocatalytic degradation properties of TiO₂ nanoparticles are greatly improved.In chapter 3, we describe the preparation of rare earth complex nanoparticles in aqueous solution. In the preparation process, Eu3+ was selected as metal center; DBM and polycation PEI were selected as ligand and stabilizer respectively. PEI molecules in the reaction system act as stabilizer to coat complex nanoparticles as soon as they formed, that limit their growth and prevented them from aggregation. Furthermore, since the amino groups of PEI can replace the H2O molecules and combine with the Eu3+ as the second ligand, fluorescence quenching can be effectively reduced. The polycation modified positive charges on the surfaces of PED nanoparticles, which not only can prevent PED naniparticles from aggregation by electrostatic repulsion, but also favor the assembly of PED nanoparticles. Luminescent composite films containing PED nanoparticles are fabricated through LBL self-assembly technique. Experimental data confirm that the films are uniformly assembled by the LBL method and the amount of PED nanoparticles are basically the same in each layer, therefore it is possible to precisely control the amount of deposited materials simply by controlling the layer number. Besides planar supports, we also assemble the PED nanoparticels on the surface of microspheres, achieving the purpose of modifying the surface of nano-scaled objects. We believe that the method described here is universal, which can be used to prepare and assemble many rare earth complex nanoparticels.In chapter 4, Eu(MA)3 nanowires are synthesized from the precursor of irregularly shaped Eu(MA)3 powder through the self-assembly of Eu(MA)3 molecules in ethanol. The nanowires have diameters of 100-300 nm and lengths ranging from tens to hundred of micrometers, and their cross sections are regular hexagon. Under UV light excitation, strong red fluorescence can be clearly seen throughout the whole wires. The precursor powder and the nanowires are detailed characterizaed by NMR, FTIR and XRD experiments. It is found that the Eu(MA)3 nanowires and precursor powder have the same chemical composition, their different morphologies are attributed to the change of crystal structures. The as-synthesized rare earth complex nanowires should provide a useful source for 1D rare earth oxide materials, as the europium ions are distributed uniformly in the Eu(MA)3 nanowires. Through calcinations, the Eu(MA)3 nanowires are successfully converted into Eu2O3 nanotubes. A plausible mechanism responsible for the formation of Eu2O3 nanotubes is presented. This approach could also be extended to methacrylates containing other metal ions (such as Pb2+, Co2+, Zn2+, Ca2+). Solvent plays an important role in the process of formation of the namowires. Moreover, the metal complexes exhibit different assembly actions when changing the solvents. For example, two dimensional layered Pb(MA)2 materials can be obtained in aqueous solution. Furthermore, through the combination ofγ-ray irradiated polymerization and gas/solid reaction, these Pb(MA)2 layers are transformed into near infrared luminescent PbS nanoparticles/ layered polymer composite materials, which can found applications in the fields of optoelectronic devices and communication materials, etc.