The Synthesis, Magneto-optic Propetry Study Of Rare-eatrh Doped Yttrium Vanadate Nanocomposites Coated With Iron Oxide

In recent years, bifunctional nanocomposites that exhibit significant magneticmoment and luminescence have attracted much attention because of many potentialapplications in biological fluorescence imaging, drug delivery, and treatment. Innature, materials that exhibit significant magnetic moment and luminescence do notexist. The magnetic material can be used for nanocomposites, including: iron oxide,γ-ferric oxide, magnetic metal particles. The main preparation methods arecoprecipitation, thermal decomposition method, micro-emulsion method andhydrothermal, solvothermal synthesis method. These methods have its owncharacteristics. The preparation of magnetic nano-particle size and dispersion are alsodifferent. The iron oxide is widely used, for the simple preparation method, low cost,strong magnetic. The fluorescent materials include inorganic and organic twocategories. Inorganic fluorescent materials include the lanthanide rare earth ion-dopedcompounds, semiconductor quantum dots; organic fluorescent materials, includeorganic dyes, fluorescent proteins. The design of the composites is used magneticmaterial as the core, the outer layer coated with a fluorescent material, or a mixture oftwo material is coated by another. However, each route selection and application ofthe material have its own advantages and disadvantages, there are many challengesplaced in front of scientists. As the iron oxide particles are photocatalysts, thisnanocomposite must be stored away from daylight. The inorganic light-emittingmaterial ZnS can dissolve in the iron oxide to form zinc ferrite solid solution. Theywill lose the luminescence and magnetic. The problem can be solved by the middlebarrier. Preparation of lanthanide rare-earth doped compounds need high-temperatureprocessing. If it is used as the fluorescent material coated on the magnetic materials,the magnetic material will be destroyed. In this paper, we would like to synthesize a series of bifunctionalnanocomposites with magnetic and luminescent properties. The structure,luminescent and magnetic properties of the nanocomposites were investigated byX-ray diffraction (XRD), transmission electron microscopy (TEM), field emissionscanning electron microscope (FESEM), fluorescence spectroscopy (PL), andvibrating sample magnetometer (VSM). The main contents are as follows:1. We select the lanthanide rare-earth ions doped compounds as fluorescentmaterials, iron oxide synthesized by a hydrothermal method as magnetic materials.We use fluorescent nanoparticles as the core coated with iron oxide to synthesizebifunctional nanocomposites. This strategy, the phosphor coated with iron oxide,could avoid the high-temperature process of the preparation of phosphors, which candestroy the magnetic materials. We used the Sol-gel method to produce the yttriumvanadate doped with europium ion precursor. After high-temperature calcination, weobtained the YVO₄: Eu³⁺nanoparticles. We used them as the nucleus, coated withFe₃O₄which synthesized by the hydrothermal method, then obtained magneto-opticbifunctional nanocomposites. We investigated the bifunctional nanocomposites byXRD, TEM, FESEM to determine their component, struction, and morphology. Wefocused on the luminescent properties of the nanocomposites and the phosphors, andinvestigated by PL. We discussed the impact of iron oxide on the luminescence. Themagnetic properties of the nanocomposites and the iron oxide were investigated byVSM. We also discussed the impact of the different surfactants and solvents, whichused to disperse the phosphors in the synthesis of Fe₃O₄, on the morphology and theluminescent properties of the YVO₄:Eu³⁺_5%@Fe₃O₄bifunctional nanocomposites.2. Based on the previous chapter, we synthesized the YVO₄:Dy³⁺@Fe₃O₄magneto-optic nanocomposites, and studied their luminescent and magneticproperties. We studied the impact of Fe₃O₄on the luminescent properties ofnanocomposites contrast to the pure YVO₄: Dy³⁺nanoparticles. The optimal dopingconcentration of Dy is1%. We also studied the magnetic properties of theYVO₄:Dy³⁺@Fe₃O₄nanocomposites and the pure Fe₃O₄nanoparticles.3. We were successfully prepared a series of different concentrations of Eu³⁺,Dy³⁺codoping YVO₄@Fe₃O₄magnetic phosphors by using two steps route, including Sol-gel and hydrothermal method. We calcined the precursors whichprepared by the Sol-gel method to get the phosphors, then used CTAB to dispersethe phosphors in aqueous solution for coated with the Fe₃O₄which prepared by thehydrothermal method. Finally, we got a series of bifunctional nanocomposites withdifferent optical emission peaks, which excited in the same wavelengths. Wecharacterized the structure of the bifunctional nanocomposites by XRD, TEM. Weused PL to study the luminescent properties of nanocomposites. We also studied theimpact of Fe₃O₄on the luminescent properties of the phosphors, and got plots ofemission peaks intensity variation with various co-doping concentrations. We candesign nanocomposites with the desired emission. We characterized the magneticproperties of the nanocomposites by VSM. Finally, we successfully synthesized aseries of bifunctional nanocomposites with orange emission and orange-redemission. As increasing the co-doping concentration, the color gradually turned tored. Adding the rare-earth single-doped nanocomposites prepared in the previouschapters, we got the bifunctional nanocomposites with different emissions, such asyellow-green, orange, orange-red, red, in the same excitation wavelength.4. In the fifth chapter, we introduced the synthesis process of Fe₃O₄/ZnSmagneto-optic bifunctional composites and the findings of the fluorescent andmagnetic properties of the composites. We synthesized the Co_xFe_1-x/CoFe_3-yO₄composites by using cobalt as a catalyst to disproportion Fe (II) under hydrothermalcondition. We studied the influence of cobalt doping on the structure of thecomposites, and learned that cobalt doping amount can not exceed the Co: Fe=1. Ifit was excess, the hybrid phase would appear. We used these magnetic composites asthe magnetic core, modified with ZnS as luminescent materials, to synthesizebifunctional composites. Because of the magnetic metal in the core, the Ms of thebifunctional composites was high. However the fluorescent intensity of the ZnS wasdecreased affected by the magnetic core. In order to improve the fluorescentintensity of ZnS, we doped with different concentrations of Mn²⁺as an excitationcentre. The optimum is5mol%. We used the Fe₃O₄nanoparticles prepared by thehydrothermal method instead of Co_xFe_1-x/CoFe_3-yO₄composites, in order to reducethe particle size. Because ZnS can be dissolved in Fe₃O₄, we used16nm SiO₂as a barrier to isolate the luminescent material and magnetic material. We got Fe₃O₄@SiO₂@ZnS: Mn_5%nanocomposites with the diameter between550nm⁹00nm, theemission peak at490nm, and the saturation magnetization27.6emu/g.