| Lanthanide oxy-salts micro/nano assemblies have received considerable attention in the past decade owing to their novel optical, electronic and magnetic properties, which enable them to widely apply to display devices, optical communication, solid-state lasers, catalysis and biological labeling, etc. Lanthanide-based phosphors exhibit relatively intense fluorescence, a large Stokes shift, high mono-chromaticity, a long life-time and high resistance to photo-bleaching in comparison with traditional organic dyes and quantum dots. The current demand for high screen-resolution, density and brightness in displays has promoted intensive exploration of ultrafine and mono-disperse phosphors. Micro/nanoscale lanthanide phosphors are of particular interest, since they can offer higher packing density, lower light scattering and brighter luminescent performance in contrast to their bulk counterparts.Practical implementation of nanostructures in a specific application system relies not only on the intrinsic properties that may be affected by their size and shape, but also on the interactions between individual nanostructures when they are in various arrangement patterns. Assembly of nanocrystals has become an important subject in nanoscience in addition to size and shape control, it allows one to finely tune their chemical and their physical properties with great versatility in many cases. Therefore, the development of well defined lanthanide oxy-salts self-assemblies with strong and tunable photoluminescence is of great importance to both scientific research and industrial applications.In this thesis, our interest is to study the rare earth oxy-salt micro/nano-structures, and to explore the synthesis, self-assembly and fluorescence properties of these rare earth borates and tungstate nanomaterials. Firstly, we developed a facile method for synthesizing GdBO3assemblies with a spindle-like profile which consist of small GdBO3nanorods. Investigation of the formation mechanism suggests that these interesting nano structures are formed accompanied with a spontaneous pH change in solution during synthesis. Single-crystal GdBO3micro-disks have been also obtained by aging procedure in solution through Ostwald ripening. The lanthanide ions doped GdBO3assemblies and micro-disks can display various emissions originated form down-shifting, up-conversion or down-conversion mechanism. It is anticipated that the developed nano-/micro-GdBO3crystals not only possess potential in traditional luminescence applications but might be implemented in biomedical engineering and the solar cell industry.Secondly, we present a solution-phase synthesis to selectively produce Gd2(WO4)3micro-scale belts, stars and flowers by hydrothermal treatment. Different micro-structures have been controllably obtained by adjusting the reaction temperature or adding surfactants. The phases and morphologies of the products have been well characterized by X-Ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Possible formation mechanisms of the different Gd2(WO4)3micro-structures have been proposed based on the investigation of the growing process of these micro structures. After doping Eu3+and Tb3+inside these Gd2(WO4)3microstructures, strong light emission with multiple visiable colors has observed. Notably, tunable emissions and a warm-white color have been achieved from these products co-doped with Eu3+and Tb3+ions. These performed micro-structures are expected to be a broad range of applications in future color displays and lightemitting devices. |
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