Inhibition of Electron-Hole Recombination in Substitutionally Doped Colloidal Semiconductor Crystallites |
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Authors: | Jacques Moser Michael Grtzel Roland Gallay |
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Institution: | Jacques Moser,Michael Grätzel,Roland Gallay |
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Abstract: | The subtitutional doping of 120-Å- sized TiO2 Particles with Fe( III )ions has a profound effect on the charge carrier recombination time in this colloidal semiconductor. In undoped particles, the mean lifetime of an electronhole pair is ca. 30 ± 15 ns. Doping with 0.5% Fe( III ) drastically augments the charge-carrier lifetime which is extended to minutes or hours. The slow character of the recombination dynamics in Fe( III )-doped colloids was confirmed by laser photolysis using the characteristic optical of electrons in TiO2 to monitor the time course of the reaction. EPR studies showed the Fe( III ) ions to enter the host lattice on Ti( IV ) sites, charge compensation taking place through the formation of oxygen vacancies. Valence-band holes produced under band-gap excitation react with these centers it the bulk forming Fe( IV ), the conduction band electrons being trapped by Ti( IV ) at the particle surface. Presumably, the spatial separation of the trapped electron and hole sites inhibits their recombination. |
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