Xanthene dye molecules form a chelate complex with the titanium species on the titania surface in dye−titania systems. The complex formation causes a fast electron injection into the titania conduction band. In this study, simple spectroscopic and photocurrent measurements of the xanthene dye-doped titania gels prepared by the sol−gel method were conducted in order to clarify the influence of a steam treatment on the dye−titania interaction and electron transfer. The photocurrent quantum efficiency of the fluorescein-doped electrode was remarkably increased by the steam treatment compared to that of the untreated electrode consisting of an amorphous titania gel. The photocurrent action spectrum was red-shifted, and the short circuit photocurrent and open circuit voltage values increased with the steam treatment time. The steam treatment promoted the dye−titania complex formation, a negative shift in the conduction band potential of the titania, and the electron injection from the dye to the titania.

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Thin titania gel films containing well-dispersed fluorescein dye were prepared by the sol−gel method and treated with steam to promote crystal growth of the titania particles. It is known that steam treatment converts the titania structure from amorphousness to crystalline. In the present study, such change is found to increase the rate of the photoinduced electron transfer from and to dispersed fluorescein dye molecules.

Thin sol-gel films including rhodamine B (RB) which were dip-coated using the sol-gel reaction of tetraethyl orthosilicate have been prepared as a function of time after mixing of the reaction systems. The absorption and fluorescence spectra of the individual thin films have been observed as a function of time after the preparation of the individual thin films. The relative contribution of the monomer, H-dimer, and J-dimer of RB existing in the individual thin films to the total absorption and fluorescence spectra of the individual samples was obtained as a function of time. RB molecules were encapsulated in a certain structural region (prestructure of the pores) long before the gelation point. With the progress of the sol-gel reaction, dimerization in the prepared film was gradually prevented, and the monomer RB became the preferential species. On the other hand, dimerization of RB in the thin film was pronounced just after dip-coating until the SiO 2 network was almost formed, and the dimerization was enhanced progressively with the time course of the reaction under a specific reaction condition. Water plays an important role in the dimerization process.