Synthesis And Luminescent Properties Of Rare Earth Vanadate/Phosphate/Zirconate Nano-/Micro-Materials

Due to their unique electronic, optical, magnetic, and catalytic properties, novel nano-/micro-sized materials have high potential appications in nanodevices and functional materials. The properties of those materials are sensitively dependent on their compositions, struetures, morphologies, and sizes. Therefore, the problem how to fabricate nano-/micro-sized materials with the controllable structures, shapes and sizes has been an important research in the field of material science. In this thesis, the rare-earth vanadate/phosphate/zirconate with high chemical stability were regarded as the research objects. Nano-/micro-sized materials with regular shapes were synthesized by different methods. The inflences of synthesis conditions on the strucures and morphologies of the as-obtained products were studied. And their formation mechanism and luminescence properties were also investigated in detail. The thesis was mainly focused on:1. The phosphors of Eu3+-doped YVO4were prepared by solid state reaction and hydrothermal process. XRD, TEM, SEM, and PL were employed to characterize the strucures, morphologies and luminescent properties of the products. The results indicate that the products have the structure of tetragonal zircon. The rod-like YVO4:Eu3+phosphor was obtained by solid state method using Na2CO3as the fluxing agent. And the microrods with an average diameter of0.20μm and length of1.16μm. Moreover, the YVO4:Eu3+with tree coral structure was synthesized by a urea-assisted hydrothermal process. The possible formation mechanism for the as-formed YVO4:Eu3+was put forward. Both the products with two different structures exhibit a characteristic red emission of Eu3+ions under the excitation of ultraviolet at395nm.2. With EDTA as the surface-functionalizing agent, the YPO4:Eu3+obtained at180℃for24h are microflakes with a length of0.7-3.1μm and a width of0.2-2.5μm. The possible formation mechanism of YPO4:Eu3+microflakes was put forward, it can be attributed to the self-aggregation and Ostwald ripening of nanoparticles. The influences on the sizes and morphologies of the synthesized products were put forward on the basis of different EDTA amount-morphology experiments. By changing the amount of EDTA from0.5g to0.75g, the YPO4:Eu3+phosphors still appear as particles with flake-like morphology, however, the centrality thickness had grown. With the further increase in the amount of EDTA (1.0g), the as-synthesized samples YPO4·0.8H2O:Eu3+exhibited bundle-like shape, which were comprised of many long and narrow rectangular microflakes and the microflakes were tightly binded together to form microbundles. The results show that the amount of EDTA has a great impact on the compositions and morphologies of the products. The PL properties of the YPO4·nH2O:Eu3+(n=0,0.8) with different morphologies were measured, all samples can be effectively excited by396nm UV lights, and exhibit a characteristic red emission peak of Eu3+ions. The different luminescence intensities of all samples are closed related to morphologies, structures and crystal field symmetry.3. The GdPO4-H2O:Tb3+nanorods were prepared by a glycine-assisted hydrothermal process. With the pH value increasing from2to5then to8, the nanorods become ever shorter and smaller. Similarly, samples prepared at pH=2without glycine are also nanorod. When the pH value increased from7to10without glycine, the GdPO4·H2O:Tb3+phosphors still appear as particles with rod-like morphology, however, the nanorods gradually aggregated together to form nanobundles. According to the results, both the introduction of glycine and the pH value of the mixture solution have a significant influence on the product morphology. The as-obtained products can be effectively excited by369nm UV light, and exhibit strong green emission around545nm, attributed to the5D4→7F5transition of Tb3+.4. The Eu3+-doped La2Zr2O7nanorods were synthesized by hydrothermal method after conventional solid state reaction with La2O3, EU2O3, ZrOCl2·8H2O as the starting materials, and with Li2CO3used as flux. The compositions and structures of the samples were investigated in detail by XRD and TEM techniques. The possible formation mechanism of nanorods was put forward. Under blue excitation with a wavelength of466nm, the emission spectrum is composed of seven bands originated from the excited5D1→7FJ (J=0,1,2) and5D0→7FJ (J=1,2,3,4) transitions of Eu3+ions, among which the5D0→7F2transition is especially sensitive to surrounding and the5D0→7F1,5D0→7F2as well as5D0→7F4transitions split. It was found to be associated with the composition, coordination environment and crystal field symmetry.