Synthesis Of Multifunctional Nanocomposites And Performance Research

Multifunctional nanocomposites have the surface effect, quantum size effect and small size & macro-quantum tunnel effect of nanomaterials. Meanwhile, by combining different component with various physical and chemical properties organically, the nanocomposites would also have new functions and effects. Therefore, such materials have potential application in optial, magnetic, catalytic and biological fields. In the dissertation, we designed and synthesized some multifunctional nanocomposite materials based on rare-earth doped upconversion materials, noble metal nanoparticles and multiferroic complexed oxide. The detailed results and discussions are shown as follows:1. We designed and synthesized the Au/SiO2/Y2O3:Yb3+,Er3+ (core/spacer/shell) nanocomposite. Because of localized surface plasmon effect, the upconversion luminescence of green emission enhanced when excited at 980 nm and when ～40nm SiO2 shell coated on-30nm Au core, a maximum 9.59-fold enhancement of the green emission was obtained. The plasmon enhances/quenches upconversion luminescence caused by the competition of following factors:a increase of the excitation rate by the local field enhancement(LFE), an enhancement of radiative decay rate by the surface plasmon-coupled emission(SPCE) and quenching that reduces the efficiency caused by the non-radiative energy transferring (NRET) from the upconversion material to the metal surfaces. Effect of the spacer distance on the Au-Y2O3:Yb3+, Er3+ green upconversion mechanism was numerically simulated by 3D-Comsol. In theory for radiative decay and excitation rates, they can be largely enhanced at the spacer thicknesses of less than 70 and 75nm, respectively, and the quenching can be caused by the non-radiative energy transferring at the distance of less than 55 nm.2. In this work, Nd3+-Yb3+ ions co-sensitized Gd2O3:Yb3+,1%Nd3+,Er3+/SiO2/Au multifunctional nanocomposite were synthesized, in which each of the components was assumed to have respective roles, and to work together to achieve multifunctions of magnetic resonance imaging and upconversion luminescence dual-mode imaging and magnetically targeted photothermal therapy under the excitation of a～808 nm laser. Novel use of Nd3+ ions as the co-sensitizer facilitates the energy transfer and photon upconversion of Yb3+-Er3+ ions at a much biocompatible excitation by the 808 nm wavelength, and will then significantly minimize the overheating problem associated with the conventional 980 nm excitation. Incorporation of Au inside the core/spacer/shell structure delivered a 3.7-fold enhancement of the green emission in core Gd2O3:Yb3+,1%Nd3+,Er3+, thanks to the plasmonic resonance effect. Meanwhile, magnetism from Gd ions in Gd2O3:Yb3+,1% Nd3+,Er3+/SiO2/Au nanoparticles was demonstrated by a nearby magnet. All results demonstrate a great potential of using the nanoparticles for magnetic targeting MRI/UCL dual-mode imaging and photothermal therapy.3. By coating SiO2 shell and Nd3+ doping, hexagonal phase Gd2O2CO3:Yb3+,Er3+/SiO2 multifunctional nanocomposite were synthesized successfully through homogeneous precipitation method. When heat treated Gd(OH)CO3·H2O:Yb3+,Er3+,Nd3+ precursor at optimized 600℃, the optical transparent and biocompatible SiO2 shell and Nd3+doping ions can effectively prevent Gd2O2CO3 hexagonal phase from further decomposing into Gd2O3 cubic phase because SiO2 shell limits the diffusion of CO2 gas and Nd3+ doping enhances the decomposition temperature of Gd2O2CO3. Compared with non-layered structure GdVO4:20at%Yb3+,2at%Er3+,4at%Nd3+particles, layer-structured Gd2O2CO3: 20at%Yb3+,2at%Er3+,4at%Nd3+/SiO2 hexagonal phase particles show much stronger upconversion emission. This can be explained as follows:energy transfer from an excited emitter Gd ion to another Gd ion across CO32- layer in Gd2O2CO3/SiO2 particles is inhibited because of the long Gd3-Gd3+ distance, which suppresses the concentration quenching and therein enhance upconversion efficiency. This result further validates that layered-structure host is more beneficial for increasing upconversion efficiency. Besides, paramagnetic properties of Gd2O2CO3:Yb3+, Er3 Nd3+/SiO2 nanoparticles were also demonstrated, suggesting potential application in UCL/MRI dual-mode imaging.4. In this work, Bi6Fe1,9Co0.1Ti3O18 (BFCTO) multifunctional nanocrystals, which are a visible-light active photocatalyst with room temperature ferromagnetism, were successfully synthesized through hydrothermal process. Furthermore, the morphology dependent magnetism and band gap of the BFCTO-1.00/BFCTO-1.50/BFCTO-2.00 nanocrystals are studied by adjusting the NaOH concentration of 1.00M/1.50M/2.00M in the hydrothermal process, respectively. As the{117} facet ratio increases, the intrinsic absorption edge has an obvious red-shift by 32 nm and the corresponding bandgap is shorten from 2.58 to 2.42 eV. Remarkably, the specific surface area normalization of degradation rate of BFCTO-1.50 was considerably higher than those of BFCTO-1.00 and BFCTO-2.00 due to the optimal ratio of{001} and{117} facets.5. In this chapter, A new kind of ferromagnetic/upconversion luminescence/photocatalysis BFCTO/NaGdF4:Yb3+,Er3+(NGF) multifunctional nanocomposites were synthesized based on the previous chapter. The results indicated that the ferromagnetic property, upconversion luminescence intensity and visible-light photodegradation efficiency are dependent on the BFCTO/NGF nanoparticles size and morphology. Meanwhile, such nanocomposite has the potential application in biology.