Synthesis, characterization and optical spectroscopy of Eu3+ doped titanate nanotubes
Highlights
► Synthesis of Eu3+ doped titania nanotubes was carried out via a hydrothermal method. ► Structural and morphological characterization were done by XRD, Raman and TEM. ► Luminescence properties of Eu3+ ions were analyzed. ► Nanotubes were formed by rolling multilayered titania structure.
Introduction
Since their discovery of two decades ago [1], carbon nanotubes have attracted a lot of interest from the scientific community for their unique properties [2]. The different chemical and physical properties of these materials have been ascribed to their characteristic structural features, that is, high surface-to-volume ratios and size-dependent properties. The controlled manipulation of low-dimensional forms has generated much interest in the literature [3], especially nanotubes generated from TiO2, which have been expected to be applicable such as photocatalysts [4], [5], sensors [6], electrochemical capacitors [7], proton conduction [8] and lithium-inserting and ion-exchange materials [9]. Moreover, several studies revealed that titania is a good candidate to be used as host material for the rare-earth (RE) ions to prepare photoluminescent materials [10], [11], [12], [13].
Through the years, the luminescence properties of RE ions hosted in several crystalline and non-crystalline matrices such as metal oxides and fluorides, organic complexes and a variety of semiconductors materials have been studied due to their many technological applications [14], [15], [16], [17]. As it is known, the luminescence properties of the RE doped host depend critically on their localizations in the host. In this sense, Eu3+ ions are widely used as a crystal field probe to test the ion–ion and ion–host interactions [14], [18], [19], [20]. The main advantages are the simplicity of its energy level structure, the sensitivity shown by the luminescence to the local surroundings and the fact that the 5D0↔7F0 transition occurs between non-degenerate levels.
In this work, Eu3+ doped titania nanotubes were synthesized by a hydrothermal process where the precursor powder was obtained by the sol–gel. The luminescence spectroscopy of nanotubes was measured and compared with the precursor powder at 10 K. The existence of multiple sites for Eu3+ ions was found in the material under investigation.
Section snippets
Synthesis of materials
The preparation method of Eu3+ doped TiO2 nanopowders is similar to the classical sol–gel procedure. First, 0.464 mol of Eu(NO3)3·5 H2O were dissolved in 44.8 ml of 2-propanol and then 6.9 ml of acetylacetone were added. After a few minutes of vigorous stirring 2.3 mol of titanium isopropoxide was added and finally 5 ml of citric acid aqueous solution (1% wt). The resultant solution was maintained under vigorous stirring for 5–6 h and was dried at RT for 24 h. The obtained gel was heated at 500 °C for 24
Structural and morphological characterization
The composition of the Eu3+ doped nanocrystalline titania starting powder used to synthesize the titanate nanotubes was found to be anatase (62%, volume fraction) and rutile (38%, volume fraction) (Fig. 1.a) [22]. The hydrothermal treatment on this powder leads to the formation of titanate nanotubes as evidenced by the comparison between the measured XRPD patterns (Fig. 1.b) and the powder patterns reported previously for titanate nanotubes [8], [23], [24], [25], and by the comparison with the
Conclusions
The synthesis of Eu3+ doped titania nanotubes was carried out successfully via a hydrothermal treatment method from a precursor powder. The differences between the precursor powder and the nanotubes were studied by X-ray powder diffraction, Raman spectroscopy, transmission electron microscope technique and optical spectroscopy. These results showed the formation of Eu3+-doped titanate nanotubes constructed by rolling multilayered titania structure concentrically arranged with a length of up to
Acknowledgments
The authors are grateful to Fondazione Cariverona (Verona, Italy), Comisión Interministerial de Ciencia y Tecnología (MAT2010-21270-C04-02), Malta Consolider Ingenio 2010 (CSD2007-0045) and FPI of Gobierno de Canarias for financial support.
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