The Preparation, Magnetic And Luminescent Properties Of Iron Oxide/Rare-Earth Doped Yttrium Vanadate Composites

In recent years, fluorescent-magnetic bifunctional composites have attracted a lotof attentions of more and more scientists. It is because that the bifunctional materialspossess the rapid separation of magnetic particles and the excellent fluorescencecharacteristics of the phosphor. They have a wide range of applications in thebiological, chemical, medical and wastewater treatment and so on. The purpose of thispaper is to prepare a series of magnetic and fluorescent bifunctional composites withthe core-shell structure and the Fe₃O₄as core and doped rare earth YVO₄phosphor asshell. In addition, we also study magnetic and fluorescent properties of thebifunctional materials. And we selected the carbon layer as the interface betweenFe₃O₄and YVO₄phosphor shell. The carbon interlayer was introduced as a key rolethat it separated lanthanide based luminescent component from the magnetite; moreimportantly, it effectively protected iron oxide from being oxided during the wholepreparation process. Finally, we have also successfully prepared flower-like structure,magnetic, fluorescent, mesoporous multifunctional composites. The compositesexhibit excellent magnetic and fluorescence properties and have a large specificsurface area. Therefore, we take the methylene blue as the example and study theadsorption capacity of the organic dyes in the wastewater. Specific work conentfollows:We have prepared Fe₃O₄@C@YVO₄:Eu³⁺, Fe₃O₄@C@YVO₄:Dy³⁺andFe₃O₄@C@YVO₄:Sm³⁺three magnetic-fluorescent bifunctional composites bycombining solvothermal method with sol-gel method. The samples were characterizedby XRD, Raman，XPS, SEM，TEMå'ŒHRTEM to study the structure and morphologyof the composites. We take the Fe₃O₄@C@YVO₄:Eu³⁺as the example and explore the optimal synthesis conditions through a series of experiments.The emission and excitation spectra of Fe₃O₄@C@YVO₄:Eu³⁺were studied bythe fluorescent spectra. In the emission spectra obtained by the excitation at320nm, itexhibits the characteristic of emission peaks of Eu³⁺. The samples emit redfluorescence and digital photos under UV-light also prove this point. Compared withYVO₄:Eu³⁺, the intensity of emission spectra of composites decreases about70%. It isdue to the fluorescence quenching effect of Fe₃O₄. The magnetic properties ofcomposite were studied by VSM. The result shows that the composites have the goodmagnetic properties. But the magnetism of composites reduce a lot compared to puredue to Fe₃O₄, which is due to coating the carbon layer and fluorescent shell on thesurface of the magnetic core. Finally, we also discussed the effects of the magneticfield on the luminescence intensity of Fe₃O₄@C@YVO₄:Eu³⁺and gave the possibleexplanation. When the duration reached3h, the intensity of emission spectra ofcomposites is the strongest, it is due to the excited valence electron of the phosphorsreached the maximum. This provides a good basis for our study about the interactionbetween the magnetic and fluorescent in the future.For the Fe₃O₄@C@YVO₄:Dy³⁺and Fe₃O₄@C@YVO₄:Sm³⁺composites, westudied their fluorescent properties systematically through the emission and excitationspectra. We studied fluorescence properties of complexes doped with differentconcentrations of Dy³⁺and Sm³⁺. We determine the optimal doping concentration ofDy³⁺complexes is1%through the comparison of luminous intensity and the intensityof emission spectra reduced more than1%. Likewise, the optimal dopingconcentration of Sm³⁺also is1%. The intensity of emission spectra of the twocomposites decreases about60%compared to YVO₄:Dy³⁺and YVO₄:Sm³⁺. It is alsodue to the fluorescence quenching effect of Fe₃O₄. The results of VSM show that boththe composites have the good magnetic properties. In addition, we studied theluminescent and magnetic properties of the two composites with the different massratio of core/shell. The results indicated they showed excellent luminescent andmagnetic properties the mass ratio of core/shell is1:3.We also focus on the comparative study on the structure and properties of three bifunctional composites. The results indicate their structure and morphology areanalogous. We also studied the fluorescence properties and luminous colors byfluorescence spectroscopy and CIE color coordinates. The three complexes dopedEu³⁺, Dy³⁺and Sm³⁺showed characteristic emission peaks of Eu³⁺, Dy³⁺and Sm³⁺,respectively and they loacted in red, yellow-green and orange-red light-emittingregion in the color coordinates.We also prepared multifunctional composites Fe₃O₄/YVO₄:Eu³⁺-SiO₂andFe₃O₄@SiO₂@YP0.1V0.9O₄:Dy³⁺taking SiO₂as interface. For theFe₃O₄/YVO₄:Eu³⁺-SiO₂composites, the as-obtained products were characterized byXRD, SEM, TEM, XPS and N2adsorption/desorption. The fluorescent properties ofthe composites were studied by fluorescence spectroscopy. In the emission spectraobtained by the excitation at292nm, it exhibits the characteristic of emission peaksof Eu³⁺. The samples emit red fluorescence. The magnetic properties of compositewere studied by VSM. The result shows that the composites have the good magneticproperties, which indicated the composites can be manipulated by an externalmagnetic field. We also discuss the effects of magnetic field on the luminescentintensity of multifunctional composites and gave the possible explanation. In theprocess, Fe₃O₄captures the excited state electron of Eu³⁺and the intensity of emissionspectra of complexes decreases. When the duration reached3h, the intensity ofemission reaches the minimum value. And then the capturing effect disappears withthe time extend, leaving the fluorescence intensity of the complexes is also enhanced.Finally, we take the methylene blue as the example and study the adsorption capacityof the organic dyes in the wastewater. The results indicate that the multifunctionalcomposites are powerful adsorbents for the remo val of methylene blue from waterwith maximum adsorption efficiency of98%. For Fe₃O₄@SiO₂@YP0.1V0.9O₄:Dy³⁺, Ithas good fluorescent and magnetic properties.