Synthesis, Luminescent Properties Of Novel Rare Earth Oxide Nanomaterials And Their Application

Rare earth （RE） nanomaterials are the most promising materials for avariety of applications, such as lighting, displays, and biolabels. And asan important branch of the RE fluorescent material, RE oxides havereceived great attention. Over the past decade, a variety of RE oxideswith one-dimensional and two-dimensional nano-/microstructures, suchas rods, wires, tubes, belts and plates, have been synthesized throughhydro-/solvothermal process. And some zero-dimensional RE oxides,such as Gd₂O₃and Y₂O₃spherical phosphors, have been also synthesizedthrough co-precipitation method. As is well known, Eu³⁺-doped Gd₂O₃and Y₂O₃phosphors are the important RE fluorescent materials.Moreover, the compound containing Gd³⁺is a known contrast agent formagnetic resonance imaging （MRI）. Therefore, monodispersed RE dopedGd₂O₃and Y₂O₃nanospheres with size less than100nm in diameter arevery required in biomedical field. However, it is hard to synthesize REoxides with spherical morphology through traditional hydro-/solvothermal process, and the size of the product is much biggerthrough co-precipitation method. An effective synthesis method is neededvery urgently. For bio-applications, water solubility of the nanocrystals（NCs） is also crucial; numerous efforts have been made to transfer theNCs from hydrophobic to hydrophilic. The most popular strategy wassurface hydroxylation. And one approach is to coat the NCs with SiO₂shells, which contain a number of–OH bonds on the surface of thenanoparticles. Up to now, no work has systemically studied how the SiO₂shell affects the photoluminescent properties of RE oxides. Moreover, oneof the important biological applications of RE NCs isfluorescence-labeled drug carrier. The traditional idea is preparing ofcomposite materials, in which the RE NCs is the fluorescence-label partand the drug carrying part is commonly mesoporous materials. Thismethod is more complex, and an easier way to achieve the bifunction ofdrug-load and fluorescent label is needed very urgently. Finally,upconversion phosphors show their potential applications in vivofluorescence imaging and solar spectrum conversion areas. However,there are some bottlenecks in practical applications for the traditional rare earth upconversion materials (e.g. NaYF₄: Yb³⁺, Er³⁺), such as:（1） lowerupconversion efficiency;（2） having only a narrower excitation bandmatching with sun spectrum, and a narrow emission band matching withabsorption of active materials. Yb₂O₃, as the representative of theupconversion white broadband emission system is a new class of highlyefficient upconversion luminescence system and provides a new choice tosolve these problems. But there are still some defects such as the highthreshold power of excitation. To solve the aforementioned problems, wecarry out and complete the following researches:（1） We present a new solvothermal method, and a series of uniform,monodisperse Gd₂O₃:Eu³⁺or Y₂O₃:Eu³⁺nanospheres less than100nm indiameter were successfully synthesized with this method. Iron or silverion was used as catalyst and Dimethylformamide （DMF） as solvent,Cetyltrimethyl Ammonium Bromide （CTAB） and Polyvinylpyrrolidone（PVP） were performed as surfactants.（2） Y₂O₃:Eu³⁺@SiO₂composites with different silica shellthicknesses were systemically synthesized, and how the SiO₂shell affectsthe photoluminescent properties of Y32O3:Eu+was systemically studied. （3） We present the facile synthesis of uniform and monodisperseGdOF: Yb³⁺, Er³⁺hollow nanospheres of about100-nm diameter by acontrolled ion exchange process. Furthermore, hollow nanospheres ofvarious shell thicknesses were obtained by tuning the reaction conditionvia the Kirkendall effect.（4） We designed and fabricated a novel kind of efficient UCnanocomposites, Yb₂O₃/Au, in which the upconversion luminescence（UCL） of Yb₂O₃was a white broad band originated from electron-holerecombination and the excitation bands were expanded at least ranging of770-980nm through the photon-assisted energy transfer （ET） fromanisotropy gold nanoparticles （GNPs） to Yb₂O₃host. At the same time,the excitation threshold was reduced. Exploring Yb₂O₃/Au as theupconverter of a dye-sensitized solar cell （DSSC）, NIR photovoltaicresponse was successfully realized and extended, presenting a novelstrategy to solve spectral matching problem of upconverter with sunlight.