Structural and optical characteristic of single crystal rutile-titania nanowire arrays prepared in alumina membranes

Abstract

In this paper, the structural and optical characteristics of single crystal rutile-titania nanowires and the possible mechanism of photoluminescence are discussed. A template-assisted liquid phase deposition (LPD) method was employed to prepare the nanowire arrays. This approach produced a large quantity of nanowires at relatively high purity and good controllability. The samples were characterized by field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, selected area electron diffraction (SAED), X-ray diffraction (XRD), Raman spectroscopy, UV–vis and photoluminescence spectroscopy. The results revealed that the obtained nanowire arrays were single crystal rutile-titania with the uniform diameter of 50-80 nm over their entire length. The UV-vis absorption spectroscopy displayed that rutile-titania nanowires possessed indirect optical allowed transition with the band gap of 3.06 eV. From the photoluminescence spectrum, it was found that rutile-titania had three strong luminescence bands at 410 (3.02 eV), 418 (2.97 eV), 422 nm (2.64 eV), which could be ascribed to the self-trapped excitons, defects and oxygen vacancies. The broad emission band centered at about 472 nm (2.63 eV) was associated to the charge transfer from Ti3+ to oxygen anion in a complex associated with oxygen vacancies at the surface of nanowires. We believe that this photoluminescence behavior of the prepared titania nanowire arrays could be attributed to bound excitons emission, resulting in the trapping of free excitons by TiO6 octahedra near defects such as oxygen vacancies.