Layered TiO2-based nanostructures have attracted much attention due to a broad spectrum of potential photochemical and electrochemical applications including photocatalysis, solar cell technology and gas sensing devices [1]. The photochemical activity of these materials depends on the branching ratio between essentially three pathways photoexcited states can undergo: they can either recombine under photoluminescence emission or generation of heat, or become persistently trapped [2] or undergo interfacial charge transfer at the particle surface. Some of these competitive processes can be tracked by means of electron paramagnetic resonance and photoluminescence spectroscopy.
We synthesized titanate nanowires and -tubes by TiO2 anatase powder treatment in aqueous alkaline solutions. The resulting structures are composed of layered sheets which consist of edge-sharing [TiO6] octahedra [3]. A specific photoluminescence process which originates from the deactivation of exciton states trapped in [TiO6] units was observed. It was found that exchange of intercalated ions provides means to adjust the branching ratio between radiative exciton deactivation, on one hand, and charge separation, on the other. Thus, chemical control over the photoelectronic properties of layered oxide structures has become feasible and the role of various ions in between the layered sheets will be discussed [4].
[1] Mor, G. K.; Shankar, K.; Paulose, M.; Varghese, O. K.; Grimes, C. A. Nano Lett. 2006, 6, 215
[2] Berger, T.; Sterrer, M.; Diwald, O.; Knözinger, E.; Panayotov, D.; Thompson, T. L.; Yates, Jr, J.T. J. Phys. Chem. B 2005, 109, 6061
[3] Orzali, T.; Casarin, M.; Granozzi, G.; Sambi, M.; Vittadini, A. Phys.Rev.Lett. 2006, 97, 156101
[4] Riss, A.; Berger, T.; Grothe, H.; Bernardi, J.; Diwald, O.; Knözinger, E. Nano Lett. 2007, 7, 433
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