Apparent Two-Dimensional Behavior of TiO2 Nanotubes Revealed by Light Absorption and Luminescence.

Optical absorption and photoluminescence (PL) properties of colloidal TiO2 nanotubes, produced by the alkali hydrothermal method, were studied at room temperature in the range 300-700 nm. Nanotubes having an internal diameter in the range 2.5-5 nm have very similar optical properties, in contrast to the expected behavior for quasi-1-D systems. This is explained by the complete thermal smearing of all 1-D effects, due to the large effective mass of charge carriers in TiO2, resulting in an apparent 2-D behavior of TiO2 nanotubes.