PHOTOLUMINESCENCE FROM A BULK DEFECT NEAR-THE-SURFACE OF AN N-TIO2 (RUTILE) ELECTRODE IN RELATION TO AN INTERMEDIATE OF PHOTOOXIDATION REACTION OF WATER

A photoluminescence (PL) band peaked at 840 nm is observed for an n-Ti O2 (rutile) electrode in aqueous electrolyte solutions when illuminate d under a slight anodic bias and was previously explained as arising f rom an intermediate of photooxidation reaction of water on the n-TiO2 electrode, The chemical structure and properties of the PL-emitting sp ecies have been investigated in the present work by measurements of ph otocurrent, photoluminescence, electroluminescence, and transient lumi nescence as well as inspection of the electrode surface by transmissio n electron microscopy. It is concluded that the PL hand should be assi gned to an electronic transition from the conduction band to the vacan t level of HO. radicals present in a bulk defect (atomic gaps) near th e n-TiO2 (rutile) surface and that the radicals act as an intermediate of the photooxidation reaction of water. The results give confirmativ e evidence to our previously proposed new mechanism that the surface T i-OH group cannot be oxidized by photogenerated holes, and thus the re action in acidic solutions is initiated by the oxidation of Ti-OH or O H- in the bulk defect near the surface.