Abnormal photoluminescence of TiO₂ nanocrystals (nanoparticles and nanotube arrays)

In this paper we report new abnormal photoluminescence results of TiO₂ nanocrystal particles and nanotube arrays. Photoluminescence spectra were recorded for TiO₂ nanocrystal particles and nanotube arrays that were synthesized by a wet chemical route and the electrochemical anodization, respectively. It was found that the TiO₂ nanocrystal with small size of 5-8 nm no emitted when excited by a laser beam of 325 nm, in contrary it emitted when excited by laser beam of 442 nm. The TiO₂ nanotube arrays exhibit a similar emission behavior. The nanotube arrays weakly emitted when excited by a laser beam of 325 nm and more strongly emitted when excited by a laser beam of 442 nm. The obtained results have been explained by a two-step exciting model and supposed to be related with the size effect of nanocrystal and it is an experimental evidence to believe that the TiO₂ nanoparticles and nanotube arrays are applicable for photo-catalysis under sun light. (author)