PHOTOINDUCED ELECTRON-TRANSFER OF DYE ON THE SURFACE OF SEMICONDUCTORS

Free radicals generated during illumination of ZnO, TiO2, and AgCl pow der with adsorbed dye sulphopropyl-5,5'-diphenyl-9-ethyl-oxacarbocyani ne hydroxide) were investigated by ESR spin trapping. An ESR spectrum having superfine structure was observed. It was attributed to the supe roxide anion radical adduct of DMPO. This indicates that the electron can be transfered from excited dye molecules to the conduction band of the semiconductors. Subsequently it reacts with oxygen to form the su peroxide anion radical. The observed results illustrate that oxygen de creases the efficiency of spectral sensitization and provides decisive evidence for the electron transfer theory of the spectral sensitizati on of semiconductors.