We report on the interaction of light with a particular class of media—wet gels, which in contrast to sols of nanoparticles possess a macroscopic bulk structure, and which differ from conventional solids by the existence of the internal liquid-solid interface. We show, taking an absorption cross section of trapped electrons from Safrany, Gao, and Rabani [J. Phys. Chem. B 104, 5848 (2000)], that a separation of charges with quantum efficiency as high as 46% appears under the band-gap irradiation of titanium oxide gels: electrons are stored in the gel network as ${\mathrm{Ti}}^{3+}$ centers, whereas holes are stored in the liquid phase. Under a prolonged UV-laser irradiation, more than 14% of ${\mathrm{Ti}}^{4+}$ centers can be converted into ${\mathrm{Ti}}^{3+}$. Their lifetime can be extremely long and exceeds months at room temperature. The trapped electrons are responsible for a “dark” absorption continuum covering the spectral range from $350\mathrm{nm}\text{to}2.5\mu \mathrm{m}$.

• Received 9 August 2004

DOI:https://doi.org/10.1103/PhysRevE.71.021403