| In order to improve the luminous efficiency of rare-earth luminescence materials, researchers have proposed a variety of solutions, for example, ion co-doping, core-shell structure building, and metal nanostructures intervening, etc. With the development of nanotechnology, core-shell type composite construction nanomaterials have been received more and more attention. Based on summarizing and analyzing of a vast amount literatures, through constructing core-shell composite structure nanomaterials can realize effective control of fluorescence. Core-shell type composite nanomaterials have many excellent properties, and have potential application value in physics, chemistry and biology medicine and other fields. In this paper we prepared a unified morphology LaF3:Eu3+@LaF3/CeF3/Si02 active-core/inert-shell and LaF3:Er3+@LaF3:Yb3+ active-core/active-shell composite nanostructure materials respectively. And we studied the down/up conversion fluorescence characteristics and luminescence mechanism of two types of core-shell composite nanostructure materials. This thesis mainly includes the following:(1) Through the improved hydrothermal method, we successfully prepared the following samples:LaF3:Ln3+(Ln=Eu, Er) fluorescent core, LaF3:Eu3+@LaF3/CeF3 active-core/inert-shell nanoparticles, LaF3:Er3+@LaF3:Yb3+active-core/active-shell nanoparticles; And we prepared LaF3:Eu3+@Si02 nanoparticles by the modified Stober method. The morphology, phase, composition, and the fluorescent properties of the as-synthesized samples were well characterized by means of transmission electron microscopy, scanning electron microscopy, X-ray diffraction, fourier transform infrared spectroscopy, energy dispersive X-ray detector, X-ray photoelectron spectra, photoluminescence spectra, respectively.(2) Based on the LaF3:Eu3+fluorescence core, we prepared homogeneous cladding LaF3:Eu3+@LaF3 and heterogeneous cladding LaF3:Eu3+@Si02 active-core/inert-shell nanoparticles, and measured the fluorescence spectra of them, respectively. The surface properties of LaF3:Eu3+particles was successfully modified by coating LaF3 and SiO2 shell onto the surface of the particles, which resulted in the change of the surface property and luminescence emission spectra of LaF3:Eu3+. It was found that the surface quenchers were decreased and thus the nonradiative pathways were reduced with core/shell structure, which not only enhanced the yellow (5D0-7F1) emission of the samples, but also changed the intensity ratio of the yellow to orange emission. The dependence of the shell property and shell thickness on the luminescence emission spectra were investigated systematically. It indicates that a very suitable shell thickness of SiO2 and LaF3 (5.5 nm and 10.0 nm respectively) ensures luminous intensity of the samples reached its maximum. Based on the effective control of such compounds, it provide the possibility of the application in biological imaging, detection, sensing and other aspects.(3) We prepared LaF3:Er3+@LaF3:Yb3+ active-core/active-shell hybrid nanostructure by using the localized partition design concept. LaF3:Er3+@LaF3:Yb3+ active-core/active-shell nanoparticles has stronger green and red emission with the near-infrared excited laser beam, which could be used as carriers of targeted drugs for bioapplications. Compared with LaF3:Er3+@LaF3 active-core/inert-shell nanoparticles, the luminescent intensity of LaF3:Er3+@LaF3:Yb3+active-core/active-shell nanoparticles enhances the intensity of green emission (4S3/2-4I15/2) up to 11.1 times and red emission (4F9/2-4I15/2) up to 10.3 times when Yb ions doping concentration of shell was 1.5%. These results indicates that the synthetic method is feasible since it allows tailoring of the upconversion emission properties of the material simply by varying the concentration of Yb ions. The current investigation can provide useful information for developing applications in vivo imaging, drug delivery, photodynamic therapy, etc. |
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