Emission Spectra and Lifetimes of R6G Dye on Silica-Coated Titania Powder

Many molecular species adsorbed on semiconductor surfaces show photochemical reactivity. These photosensitization processes attract a lot of attention from a practical point of view for uses such as solar energy conversion.1-3 The organic molecule is excited by light and injects an electron into the conduction band of the semiconductor. This allows conversion from visible light to electric current. The inverse process, that is, electrons at the semiconductor surface are scavenged by the ubiquitously present molecular oxygen, results in the degradation of the dye.4 Since the electron transfer rate ismuchfaster than the radiative lifetime, the fluorescence efficiency for emission is strongly reduced to a few percent. If a high fluorescence efficiency close to a semiconductor surface is required, the dye or the host solid must be shielded, for instance, by coating the semiconductor, such as titania (TiO2) in the form of photonic crystals, with an insulating layer.