Phase, Morphology And Luminescence Properties Of Lanthanide Doped Nanostructural Materials

In this thesis, rare earth ions(Eu3+, Tb3+ and Ce3+) doped nanostructural materials have been synthesized by solution method. The phase structures, morphologies and luminescence properties of the as-synthesized samples were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), photoluminescence(PL) spectrum and lifetime. The effect of the synthesis conditions such as p H values, starting materials, the variety and amount of additives, and doping concentration of rare earth ions on the phase, morphology, luminescence properties of the as-synthesized samples were researched systematically. The obtained main results were as follows:Lanthanide doped Zn O mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared Zn O: Ln3+(Ln = Tb, Eu) samples have hexagonal phase structure and possess mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 μm, and the diameters of pileus and stipe are about 0.8 μm and 0.4 μm, respectively. It is found that the flow of N2 atmosphere is the key parameter for the formation of the novel Zn O structure and the addition of(NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by a number of radial Zn O: Ln3+ nanorods, while the stipe is composed of over layered Zn O: Ln3+ nanosheets. Lanthanide doped Zn O samples can exhibit red or green emission under the excitation of UV light.Ln3+(Ln = Tb, Eu) doped zinc phosphate tetrahydrate(ZPT: Ln3+) and ammonium zinc phosphate(AZP: Ln3+) nano-/micro-structured materials were synthesized in aqueous solution without the addition of any structure-directing agent. It indicates that the different phosphate sources MnH(3-n)PO4(M = NH4+ or Na+, n = 1, 2, 3) can lead to the altering of morphology from nanosheet to microflower, but have IV no significant effect on the phase structure of the samples. The microlump, nanosheet, and microflower(constructed by the primary microlumps or nanosheets) of orthorhombic ZPT: Ln3+ could be selectively prepared by adjusting the p H value from 3.5 to 7.0. The mixture of orthorhombic ZPT: Ln3+ and monoclinic AZP: Ln3+ with microflower morphology was obtained when the p H value is adjusted to 8.0. Monoclinic AZP: Ln3+ microplate, microcube and nanoparticle were obtained at the p H value of 8.5, 9.0 and 11.0 respectively. The phase transformation and growth mechanism of the diverse morphologies were proposed, and ZPT: Ln3+(Ln3+ = Eu or Tb) samples exhibit red or green emission under the excitation of UV light.Uniform Eu3+ doped Cd WO4 nanorods were prepared via a simple hydrothermal method. The results indicate that the obtained Eu3+ doped Cd WO4 nanorods have monoclinic phase structure, and the phase structure can be retained at Eu3+ doping concentrations of 0.4%~4.0%. The diameter of nanorods decreases from 27 to 15 nm with an increase in the doping concentrations, and the morphology becomes irregular at the Eu3+ doping concentration of 6.5%. Under the excitation of ultraviolet light, the relative intensities of blue-green emission ascribed to WO42- and red emission from Eu3+ can be tuned through doping Eu3+ ions into the Cd WO4 nanorods and thus altering the energy transfer between WO42- and Eu3+. Hence, the multicolor luminescence in a same host under single excited wavelength can be realized simply by altering the doping concentration of Eu3+.Hollow semi-sphere Sr WO4 and rare earth ions(Tb3+, Eu3+) doped Sr WO4 microspheres were synthesized by hydrothermal treatment. The results indicate that the undoped Sr WO4 has hollow semi-sphere morphology, with a tetragonal phase structure. The phase structure of Sr WO4 doped with Tb3+ or Eu3+ is similar to that of the undoped Sr WO4, but the morphology transforms from hollow semi-sphere to microsphere. With the increasing of Tb3+ doping concentration, the morphology of Sr WO4:Tb3+ changes from microsphere to micro-flower composed of many nanorods. The increasing of Eu3+ doping concentration leads to the presence of monoclinic phase Eu2WO6 and the morphology change of Sr WO4: Eu3+. Under the excitation of UV light, the emission spectra of Sr WO4: Tb3+ and Sr WO4: Eu3+ are mainly attributed to the characteristic emission of Tb3+(5D4-7FJ transitions, J = 6, 5, 4, 3) and Eu3+(5D0-7FJ transitions, J = 1, 2, 3, 4), respectively. The optimal doping concentrations are 3 mol% for Tb3+ and 25 mol% for Eu3+ in Sr WO4.