Investigation On The Controllable Synthesis And Luminescent Properties Of Lanthanide Orthophosphate Nanomaterials

Recently, rare earth inorganic compounds have been extensively used as functional materials based on the unique 4f shell structure of their electrons. Among them, lanthanide orthophosphate?REPO4? is an important kind of rare earth compound family due to their great thermal stability and chemical stability. They have wide applications as phosphors, laser hosts and biomedical labels. Inorganic nano-/microcrystals with well-defined morphologies and tunable sizes have stimulated great interest because the properties of a material strongly depend on its crystal phase, morphology and size. Constructing materials with fascinating hierarchical three-dimension?3D?architectures, built from nano-substructures arranged in a particular way, have been of great importance, due to the more interesting optical, magnetic and catalytic properties than 1D architectures. Hydro-/solvothermal method that is simple and easy to be controlled has a mild reaction condition. As a consequence, the simple hydro-/solvothermal method was choosed in this paper to synthesize GdPO₄ and LuPO₄ three-dimensional ordered architectures. In the meanwhile, the phase structure, morphology, size, possible mechanisms and luminescent properties of the products were investigated in detail. The main research contents of this paper are shown as follows:1. We successfully prepared GdPO₄ nano-/microcrystals with solvothermal method. The as-prepared samples have a variety of crystal structures and morphologies, such as monoclinic phase microspheres, nanosheets, nanoparticles and hexagonal nanowires, nanorods structure. We discussed the influence of the solvothermal conditions and organic additive trisodium citrate on crystal phase, morphology, size and crystallinity of final products. In various phosphorus source reaction systems, it is found that the influences of pH value on product properties are different. The above results suggest that the different products have different growth habits under diverse reaction conditions. By substantiating the role of trisodium citrate in the shape control of products, a series of parallel experiments were carried by altering its contents. On the basis of analysis, the addition of an appropriate amount of trisodium citrate has a significant role in the formation of the uniform microspheres. Moreover, the possible formation mechanisms of different pH value and trisodium citrate for products with various phases and morphologies were mainly explained. In addition, we further analyzed the samples with different ratio of ethanol to water. As a result, it can be concluded that the ratio of ethanol to water has an important influence on the morphology and size of the products. Furthermore, the luminescent properties of GdPO₄:Eu³⁺ with different phase structure and morphologies were also investigated. Compared with hexagonal GdPO₄·H2O:Eu³⁺, a small red shift of the strongest excitation peak and increase in the intensity of the emission spectra can be observed for the monoclinic GdPO₄:Eu³⁺. The results indicate that the luminescent properties of products have a strong association with crystal structure, morphology and so on.2. Using the self-sacrificial template method with some modification, we successfully synthesized tetragonal LuPO₄ hollow spheres. By analyzing the Lu?OH?CO₃ precursor and LuPO₄ hollow spheres prepared with different ratio of ethylene glycol to water, it is found that with the increase of the ratio, sizes of the Lu?OH?CO₃ precursor and LuPO₄ hollow spheres gradually decrease. Morphologies also have a slight change. Subsequently, the formation mechanism of hollow spheres and the impact of ratio of ethylene glycol to water on samples are investigated. LuPO₄: Yb³⁺/Er³⁺ shows the green upconversion luminescence properties under laser excitation of 980 nm. Our capability of obtaining LuPO₄ hollow spheres can further expand its application fields.