Morphology Controlled Synthesis, Characterzation And Iuminescent Properties Investigation Of Several Compounds Micro/nanostructures

Owing to their shape and size dependent properties, the controllable syntheis of micro/nanostructures has been intensively studied in recent years. Rare earth materials have attracted intensive research interest because of their novel electronic, optical, and chemical characteristics resulting from the 4f electrons. ZnO and CdS are important classical semiconductors with wide band gap, which have been widely applied and received intense attention. In this thesis, the controllable synthesis of several important rare earth compounds, ZnO and CdS have been ivestigaged and their optical properties have been studied. Porous flower-like La2O3, unrchin-like and flower-like La(OH)3, apple-like LaCO3OH, bundle-like ZnO, and CdS with various micro-/nanostructures have been prepared successfuly via various methods such as hydro/solvothermal methods, microwave treatment. The as-obtained products were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy disperse spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL). The formation mechanism and optitca properties of the products were briefly discussed. The main contents are listed as following:1.3D Porous Flower-like Nanostructures of Lanthanum Oxide:Solvothermal Synthesis, and CharacterizationIn this part, flower-like La2O3 precursors were prepared in EG using Lanthanum chloride heptahydrate and hexamethylenetetramine as precursors by a facile solvothermal reaction at 190℃for 72 h. The as-synthesized products were characterized by XRD, SEM, EDS, PL. SEM results demonstrate that the as-prepared flower-like La2O3 precursor is in the diameter of ca.5-7μm and a single microflower is composed of numerous nanoplates with a thickness of about 100 run. Porous flowerlike La2O3 nanostructures were obtained after calcinations of La2O3 precursors at 800℃for 4 h. BET of porous flowerlike La2O3 nanostructures is 9.8 g/m2. Eu3+ doped flowerlike La2O3 porous nanostructures were also prepared using the same preparation process. The flowerlike La2O3:Eu3+ nanostructures show a strong red emission corresponding to 5D0-7F2 transition (625 nm) of Eu3+ under ultraviolet excitation (267 nm). The possible formation mechanism for the 3D flowerlike lanthanum oxide precursor nanostructures was proposed.2.Self-assembled 3D La(OH)3 and La2O3 nanostructures:Fast microwave synthesis and characterizationSelf-assembled three-dimensional (3D) urchin-like and flower-like La(OH)3 nanostructures were successfully prepared for the first time via a facile and fast microwave-assisted solution-phase chemical method. The obtained products were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). SEM results reveal that the urchin-like and flower-like La(OH)3 nanostructures ca.3μm and 6μm in diameter, respectively. The urchin-like La(OH)3 nanostructures are constructed by nanorods with diameters of about 300 nm and lengths of about 500 nm. The flower-like La(OH)3 nanostructures are built from nanopetals about 100 nm thick. The possible formation mechanism of the 3D La(OH)3 nanostructures was preliminarily discussed. We thinked that the unchin-like La(OH)3 nanostructures crystallizes through a nonclassical crystallization and the flower-like La(OH)3 nanostructures crystallizes via an Ostwald ripening route, which is the classical view on crystal growth. Urchin-like and flower-like La2O3:Eu3+ nanostructures were also prepared and their photoluminescence properties were investigated. By comparison, it clearly reveals that the emission intensity of urchin-like La2O3:Eu3+ nanostructures is stronger than that of the flower-like La2O3:Eu3+ nanostructures.3.Gelatin-mediated hydrothermal synthesis and characterization of apple-like LaCOaOH superstructuresUniform apple-like LaCO3OH architectures have been prepared successfully using a facile hydrothermal route in present of a small quantity of gelatin. The as-obtained products are characterized by XRD, SEM, and TEM. Results show that the gelatin plays a vital role of the growth of apple-like LaCO3OH nanostructures. XRD results indicate the crystal phase of apple-like LaCO3OH transform from orthorhombic phase to hexagonal phase with the increasing of reaction time. The apple-like LaCO3OH with diameters in 3μm are consisted of numerous nanorods with a diameter of 6 nm and length of 40 nm. The PL result shows apple-like LaCO3OH have has only one broad band centered on 444 nm with the 365 nm excitation. Interestingly, near white emission was realized in the the Tb3+ doped LaCO3OH apple-like nanostructures when activated by 277 nm, which may bring some new applications. Based on above results, a possible formation mechanism of the apple-like LaCO3OH has been proposed. In the reaction system, the corresponding orthorhombic subcarbonates were obtained when light rare earth elements were used as lanthanide sources; however, when heavy rare earth elements were used lanthanide sources, we only obtained the corresponding oxide precursors.4. controlled synthesis and characterization of ZnO micro-/nanostructuresSeveral nano/microscale structures of ZnO including nanospindles, microbundles, microrods, and nanoflowers have been prepared via a facile hydrothermal method mediated with ammonium molybdate. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and spectrofluorometer (FL) were used to characterize the products. It is found that the morphology of ZnO could be readily tailored by simple variation of the concentration of ammonium molybdate. Based on above results, a possible formation mechanism of various ZnO has been proposed. Results reveal that the photoluminescence (PL) properties of the as-prepared ZnO are strongly dependent on their morphologies.5. Mixed-solvothermal synthesis and characterization of CdS microstructuresSeveral micro/nanostructures of cadmium sulfide, including cauliflower-like microsphere, football-like microspheres, tower-like microrods, and dendrites were controllably prepared with an oxalic acid-assisted mixed-solvothermal route. The as-prepared products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM) and UV/Vis spectrophotometer (UV). CdS microstructures can be selectively obtained by varying the concentration of EG, oxalic acid, and sulfur source. UV results show that the obvious red-shifted was realized in our work compared with that of bulk CdS. The possible formation mechanism of the CdS micro/nanostructures was tentatively proposed.