Investigations On The Synthesis, Morphology Control And Luminescence Of Rare Earth Ions Doped Fluoride Nano-crystals

We employed a conventional hydrothermal approach to sythesize fluoridenanocrystals. In this thesis, the effects of the synthesis conditions, the dopingconcentration, kinds and the radius of the lanthanide rare earth ions on the phases,sizes and morphology of the nanocrystals were studied. NaLnF4and GdF3nanocrystals with different shape including rod, cube, hexagon and speherial dotwere obtained. Also, the photoluminescence emission spectra of Ln3+doped NaGdF4and GdF3nanocrystals were studied.1. Herein, GdF3and NaGdF4nanocrystals we prepared through a conventionalhydrothermal approach. The sizes, phases and the morphologies of GdF3nanocrystals can be controlled and tuned by changing the synthesis parameters (pHvalues, time, ratio of the Gd to F or the surfactant). Also, the influence of preparationconditions (reaction time, temperature, the stoichiometric ratio and concentration ofthe reactants etc.) on the phases, sizes, the aspect ratio of the NaGdF4nanocrystalswere studied. Temperature is the key factor to control the phases.2. For nanocrystalline materials, doping can stabilize crystallographicphase, modify electronic properties, modulate magnetism and tune emissionproperties. Herein, the influence of doping concentration of the Yb3+on thephases and sizes of the NaGdF4nanocrystals were studied. The resultsindicated that doping played an important role in tuning the phases andmorphologies and sizes of the NaGdF4nanocrystals. With the increase of thedoping concentration of Yb3+ion， the phase of the NaGdF4nanocrystalschanges from pure hexagonal crystal structures into the mixture containingboth cubic and hexagonal phases and then into cubic crystal structurescompletely. When the Er3+ions were replaced by Tb3+ions, the shape of theNaGdF4nanocrystals changed from nanorods into hexagonal shape.3. Monodisperse fluoride colloidal nanocrystals (NCs) including LnF3, NaLnF4, Na5Ln9F32with two crystal phases and varieties of sizes and morphologies have beensynthesized by a conventional hydrothermal approach using oleic acid as surfactant.The as-synthesized NCs were characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM) and high resolution transimission electronmicroscopy (HRTEM), respectively. The results suggest that the as-synthesized NCsconsist of monodisperse nanoparticles with diverse shapes such as sphere, rod, andcubic and have a narrow size distribution.4. The NaGdF4nanocrystals doped with Ho3+/Yb3+, Er3+/Yb3+, Tm3+/Yb3+wereprepared by a hydrothermal method using the oleic acid as the organic suffactant.The XRD results together with the TEM and HRTEM show that the sample obtainedare the poly-phases of cubic and hexagonal crystal structures and have blendmorphologies. The luminescent spectra obtained under the980nm excitation withdifferent powers show that the upconversion luminescence can attributed to theefficient energy transfer from Yb3+to Ln3+(Ho3+, Er3+, Tm3+). Nanocrystals with highmonodispersity and crystallinity, small grain sizes and strong luminescent intensitywere obtained. Therefore, it may find potential applications in the fields such as thebiological imaging and so on.