Sol-Gel Template Synthesis and Photoluminescence Properties of (Pb_0.5Sr_0.5)TiO₃ Nanotube Arrays

Lead strontium titanate (Pb_0.5Sr_0.5)TiO₃ (PST) nanotube arrays are prepared by a sol-gel and spin-coating process using an anodic aluminium oxide template. The structure and morphology of the as-prepared sample are characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the as-prepared PST sample possesses a perovskite structure with a relatively uniform diameter of about 200 nm. Photoluminescence (PL) spectrum of the sample shows emission bands centered at about 2.87 eV at room temperature, which consists of three intense emission sub-bands at 3.02, 2.87 and 2.76 eV, respectively. The energy corresponding to the central PL peak is lower than the band-gap energy (3.2 eV) of PST bulk materials, which may originate from the size effect of the PST nanotube arrays. The multi-peaks in the PL spectrum may be attributed to the radiative recombination of trapped electrons and holes in tail and gap states induced by local defect and oxygen vacancies. The Raman scattering spectrum of the PST nanotube arrays, which are obviously broadened in comparison with the bulk materials, show that their phonon modes are in agreement with those allowed in the tetragonal phase.