Synthesis And Luminescent Properties Of Rare Earths Doped Titanium Oxide Nanomaterials With Special Morphologies

With the development of the society, people’s physical requirements are alsogetting higher and higher. Lighting materials have been already developed from thepast kerosene lamp era to today’s resplendent with variegated coloration of highperformance electric lighting Era. It was required that the lighting materials shouldalso be developed with the demand of the people. Therefore, the researchers increasedthe luminescent materials research investment, and found much more luminescentmaterials. TiO₂, as a kind of good matrix, has shown a good application prospect inluminescent materials. In this work, TiO₂was used as matrix, and Eu³⁺-doped TiO₂nanorods, nanobelts and spindle-shaped nanoparticles were prepared by hydrothermalmethod. In addition, Eu³⁺ions doped3-dimensional flower-like TiO₂nanoparticleswere fabricated by micro-emulsion method. To study the effects of the morphology onthe luminescent properties, modern analysis techniques including SEM, TEM, XRD,FT-IR and PL were used to investigate the characteristics of these materials. The mainresults of the research work are as follows：1. Titanate nanotubes and nanobelts were successfully synthesized via a simplehydrothermal process. The TiO₂nanoparticles are grown to nanosheets, finally turnedinto nanotubes structure under the driving force in this process. Nanobelts were alsoformed from the TiO₂nanoparticles under certain experimental conditions. Smallnanobelts were formed, and the small nanobelts bind together to form the finalnanobelt structure. The crystallization rate has great influence on the formation ofmorphology. If the crystallization rate is large enough so that the growth of thenanosheets can be more than the general value, and then they will overlap each other,become hard and difficult to curl, resulting in the formation of nanobelt instead of nanotubes.2. TiO₂:Eu³⁺nanobelts have been successfully prepared using the hydrothermalmethod. The XRD results show that anatase-phase TiO₂can be formed attemperatures above300oC, and the optimal calcination temperature is500oC. Underthe UV excitation, TiO₂:Eu³⁺nanobelts exhibit red emission. The calcinationtemperature has a great influence not only on the crystal structure and morphology,but also on the luminescence properties. It is expected that TiO₂:Eu³⁺nanobelts can bea potential candidate as the novel semiconductor fluorescence materials.3. The controllable synthesis of TiO₂:Eu³⁺nanorods have been successfullyachieved through a simple hydrothermal process followed by the calcination process.The as-obtained precursors have the structure of titanate. The morphology of thenanotubes changed to nanorods after calcination process. The final TiO₂:Eu³⁺nanorods showed a strong red emission under ultraviolet excitation.4. Highly uniform TiO₂:Eu³⁺spindle-shaped nanoparticles were synthesized bytwo-step hydrothermal processes. The width of the nanobelt precursor is about50–200nm and the lengths are about several micrometers. The diameters of the TiO₂:Eu³⁺spindle shaped nanoparticles are about50–200nm and the lengths about200-1000nm.The phase transformation among the anatase structure, sodium titanate and titanateand the possible formation mechanism were also investigated in detail. The finalproducts of the TiO₂:Eu³⁺spindle shaped nanoparticles show strong red emissionintensity under ultraviolet excitation, which is due to the lack of inversion symmetryat the Eu³⁺ions site and depends strongly on the site symmetry in a host crystal. It canbe anticipated that the as-prepared product is a potential candidate as the novelsemiconductor luminescent materials.5. TiO₂:Eu³⁺nanorods and spindle-shaped nanoparticles have been synthesized through simple calcination and two-step hydrothermal processes using titanate as theprecursors. Not only the morphologies of the precursors have been changed fromnanotubes to nanorods and spindle-shaped nanoparticles, but also the structures of theprecursors have been transformed into anatase nanostructure. Under UV lightexcitation, the TiO₂:Eu³⁺nanorods and spindle-shaped nanoparticles exhibit the strongred emission corresponding to the5D0-7F2transition of the Eu³⁺ions. In addition, theluminescence intensity of the TiO₂:Eu³⁺nanorods is stronger than that of spindle-shaped nanoparticles, which is due to the defects on the surface of the samples.6. We have demonstrated a facile route to synthesize3-dimensional flower-likeTiO₂using commercial CTAB as the reacting surfactant and template in the acidsurrounding. The PL spectrums show that the3-dimensional flower-like TiO₂:Eu³⁺exhibited emission peak centered at around614nm when the excitation wavelength is393nm. However, It was found that the emission intensity of the3-dimensionalflower-like TiO₂:Eu³⁺is lower than that of the other morphologies TiO₂, which is dueto the matrix can not transfer their energy to rare earth ions, and rare earth ion returnto the excited state by itself. The synthesis of3-dimensional flower like TiO₂:Eu³⁺crystals in the acid surrounding will provide a new route to other compounds withcontrolled shapes and sizes.