Photosensitized charge injection into TiO2 particles as studied by microwave absorption

The fluorescence of rose bengal is quenched with 96% efficiency when this dye is adsorbed on TiO₂ particles. Microwave measurements on suspensions of these dye-coated particles have shown large absorption signals when the suspension is irradiated with pulses of 532 nm light from a laser. The microwave absorption is attributed to mobile charge carriers injected into the TiO₂ from the excited singlet state of the dye. The observed rise time of the signal indicates no intermediate surface state of greater than 2 ns lifetime. Various characteristics of the observed signals are compared with those from TiO₂ single crystals.