The Study Of CoFe₂O₄and Y₂O₃: RE³⁺ Nanocomposites With Magnetic And Luminescent Properties

The rare earth luminescent materials and magnetic nanoparticles arerepresentative functional nanomaterials. In biomedical research field, fluorescencelabeling and magnetic separation are the two most commonly used methods. Becauseof the excellent magnetic property and controllability, the magnetic nanomaterials candirectional move under the external magnetic field, so it can be used to separate thespecific component in biological system and drug targeting field. Due to its uniqueproperties, such as marrow line-width emission bands, high quantum yields, andexcellent photostability, the rare earth luminescent materials are most potentialfluorescent biomarker materials. With the rapid development of modern science andtechnology, the single nanomaterials cannot meet people’s demands, such asfluorescence labeling and magnetic separation for the special components at the sametime. The combination of two or more than two single materials to be a highperformance composites is the developing trend of modern science and is also one ofthe themes for the science researchers. Base on the magnetic CoFe2O4nanoparticlesand rare earth Y2O3:RE3+fluorescent materials, we constructed a multifunctionalnanocomposite materials with magnetic and luminescent properties. The magnetic andluminescent properties of the multifunctional nanocomposites were also besystematically studied and compared. Meanwhile, we also constructed the Gd2O3:Eu3+hollow nanomaterials with magnetic and luminescent properties. The main researchcontents of this thesis are as follows:(1) The porous CoFe2O4@Y2O3:Eu3+nanocomposites withe obvious core-shellstructure were prepared through the combination of the coprecipitation process,hydrothermal process, and urea assisted homogeneous precipitation process, followed by calcination process. The compositeion and morphology of the nanocompositeswere charctreizied by the XRD, FT-IR, SEM, TEM and EDX. VSM and fluorescencespectra indicated the ferrimagnetic and red luminescent properties of thenanocomposites. The effects of external magnetic field on the luminescent propertiesof porous CoFe2O4@Y2O3:Eu3+nanocomposites indicated that the nanocompositeshave the weakest luminescent intensity when the composites are under the externalfield for2hours.(2) The CoFe2O4@SiO2@Y2O3:RE3+(RE=Eu, Tb, Dy) nanocomposites withspherical morphology were obtained through the coprecipitation process, St ber andurea assisted homogeneous precipitation process (hydrothermal process), followed bycalcination process. VSM showed that the three kinds of nanocomposites with Eu3+,Tb3+, and Dy3+doping are ferrimagnetic. Fluorescence spectra indicated that the threekinds of nanocomposites with Eu3+, Tb3+, and Dy3+doping show excellent red, green,and yellow, corresponding to electron energy level transition5D0-7F2of Eu3+,5D4-7F5of Tb3+, and4F9/2-6H13/2of Dy3+, respectively. Using the representative Eu3+dopingnanocomposites, we investigated the quenching mechanism of the magnetic core tothe luminescent layer.(3) We compared the properties of the above four kinds of nanocomposites. Thecomparison between the porous CoFe2O4@Y2O3:Eu3+andCoFe2O4@SiO2@Y2O3:Eu3+nanocomposites showed that the existence of SiO2coupling improve the Ms and luminescent intensity of CoFe2O4@SiO2@Y2O3:Eu3+nanocomposites. Then we compared the magnetic and fluorescent properties of theCoFe2O4@SiO2@Y2O3:RE3+(RE=Eu, Tb, Dy) nanocomposites. The three kinds ofnanocomposites displayed ferrimagnetic property. The fluorescent spectra and CIEchromaticity diagram showed that the three kinds of nanocomposites for Eu3+, Tb3+,Dy3+doping displayed the characteristic emission peaks of Eu3+, Tb3+, Dy3+,corresponding red, green and yellow, respectively. The results implied that we canadjusting the Ms and luminescent intensity just by changing the doping rare earth inthe nonocomposites.(4) Based on the CoFe2O4@SiO2@Y2O3:Eu3+nanocomposites, we successfully obtained the CoFe2O4@SiO2@Y2O3:Eu3+nanocomposites with Gd3+doping. VSMindicated that the Co(Fe,Gd)2O4@SiO2@Y2O3:Eu3+andCoFe2O4@SiO2@(Y,Gd)2O3:Eu3+nanocomposites display ferrimagnetic property.With Gd3+doping not only in the magnetic core, but also in luminescent shell, the Msof the nanocomposites decreased and the Hc consisted. The fluorescent spectrashowed that the luminescent intensity of Co(Fe,Gd)2O4@SiO2@Y2O3:Eu3+nanocomposites decrease with increasing the Gd3+doping into the magnetic core. Onthe contrary, the luminescent intensity of CoFe2O4@SiO2@(Y,Gd)2O3:Eu3+nanocomposites was improved as a small amount of Gd3+was introduced into theluminescent shell. With increasing the amount of Gd3+, the luminescent intensitydecreased.(5) Last, we exploringly prepared the Gd2O3:Eu3+hollow nanospheres withmagnetic and luminescent intensities. The thickness of Gd2O3:Eu3+shell is60nm.When the applied magnetic field is20000Oe, the magnetization of the nanospheres isnot saturated, the magnetization is1.90emu/g. The hollow structure of thenanospheres reduced the magnetization of the samples. The fluorescent spectrashowed that the Gd2O3:Eu3+hollow nanospheres display excellent red luminescentproperty, corresponding to5D0-7F2electron energy level transition of Eu3+. Theluminescent intensity of the nanospheres was improved because of the hollowstructure. Moreover, the magnetization, luminescent intensity and emitting colorpurity of the nanospheres are influenced by calcination temperature.