SPECTROSCOPIC AND EXCITED-STATE PROPERTIES OF TITANIUM-DIOXIDE GELS

The optical and excited-state properties of sol-gel processed monolith ic titanium dioxide (TiO2) gels are reported. An important conclusion of this study is that amorphous polymeric TiO2 gels display a band str ucture similar to crystalline materials rich in defect sites. This ban d structure manifests itself in a fundamental absorption edge, band-ed ge photoluminescence, and excited-state redox chemistry from the valen ce and conduction bands. The generation of long-lived electrons by ult raviolet light excitation proceeds with a quantum efficiency of 1%. Ro om-temperature absorption and electron paramagnetic resonance measurem ents indicate that the electrons are trapped at Ti(IV) sites. The elec trons can be freed from the solid through interfacial electron transfe r to acceptors located within the gel intrapore space producing mobile electron shuttles capable of doing external work.