The mutual influence of Orange I1 and Rhodamine B on their sensitizing ability for the electron transfer across the interface ZnO/adsorbed species has been studied by an electrochemical cell technique. Besides voltage against current measurements the absorption and fluorescence of the dyes were also determined. It was demonstrated that despite the similarity of the quenching of the fluorescence of Rhodamine B both by Orange I1 and halide ions, they do not follow a similar mechanism. Furthermore, the complexity of the mechanism of the sensitization by binary dye mixtures has been shown by photocurrent measurements in the presence of Morin and Rhodamine B, and Morin and an azo dye, at various pH of the electrolytes.In zinc oxide electrophotography, unsensitized zinc oxide requires U.V. illumination for charge transfer to take place across ZnO interfaces. However, since light sources operating in the visible region are cheaper and more reliable than U.V. xenon high pressure lamps, the application of suitable dyes as spectral sensitizers is useful in order to shift the energy of formation of unoccupied electron states into the visible region; these are the states which can react with trapped electrons in the surface of ZnO produced by a corona discharge process. To avoid the complications which arise with polycrystalline zinc oxide embedded in a resin binder, the sensitization of the charge transfer through the interface ZnO/ambient was studied by means of a zinc oxide single crystal operating as anode in an electrochemical cell with aqueous and non-aqueous electrolytes, e.g., toluene + methanol electrolytes. The justification for the electrochemical cell experiments described below is evidenced by the composition of Electrofax paper * and its use in a copying machine as discussed elsewhere2The following electrochemical cell was employed : ( +) indium I ZnO single crystal + adsorbed dye I electrolyte +dye I Pt (-).Here, the electrolyte can be compared to the salt-containing paper supporting the zinc oxide resin layer. The blocking barrier in the electrochemical cell is localized at the ZnO/electrolyte interface for the electron transfer from the electrolyte into the ZnO crystal. The application of the electrochemical cell technique for the study of the sensitization of the electron transfer across ZnO interfaces was introduced simultaneously by Gerischer and by H a~f f e .~ Recently, the influence of complex formation of sensitizing dyes with zinc ions on their sensitizing ability was investigated particularly for azo dyes which possess either two OH groups or one OH group and a pyridyl nitrogen atom o and 0' to the N=N group.4 To obtain additional information, fluorescence spectra have been recorded which are useful for the study of the influence of the ambient, for example ions and * Registered trademark of R.C.A. for a paper coated with a zinc oxide resin layer.
PLASMA ANODIZATION 51on the exact role of the cathode in the plasma anodization process, rather than the current assumption in the literature that the cathode is needed just to produce the oxygen plasma and that any sputtering of cathode material is an unwanted side effect. ABSTRACTTo study the mechanism of the spectral sensitization with the electrochemical cell ~-In/ZnO-single crystal/dye ~-electrolyte/Pt --measurements of the photocurrent influenced by salt additions to the electrolyte were performed. The ZnO-semiconductor-anode operates as a probe for excited states of dyes acting as sensitizer for the charge transfer through the interface zinc oxide/electrolyte. By addition of Br-, J-, SCN-, and SeCN-ions to the dye-containing electrolyte a significant increase of the sensitized photocurrent was generated. This enhancement can either be attributed to a change of the dye adsorption on zinc oxide or be explained by the fluorescence quenching of the adsorbed sensitizer in the presence of halide ions. With this quenching, radical anions F'--or excited triplet states ~F* of the dyes are produced which are responsible for the increase of the phot Ocurrent. The possible single steps of this reaction are discussed. * Electrochemical Society Active Member. Key words: dye sensitization, photosensitization, ZnO/electrolyte interface, electrochemical cell, reducing fluorescence quenching, dye adsorption. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 147.188.128.74 Downloaded on 2015-05-30 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 147.188.128.74 Downloaded on 2015-05-30 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 147.188.128.74 Downloaded on 2015-05-30 to IP
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