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Titanium dioxide photoanodes for hydrogen generation suffer from a profound mismatch between the optical absorption of TiO2 and the solar spectrum. To solve the problem of low solar-to-chemical efficiency, optically active materials are proposed. In this work, TiO2 thin films containing erbium were deposited by radio frequency RF magnetron sputtering under ultrahigh vacuum conditions UHV. Morphology, structural, optical and electronic properties were studied. TiO2:Er thin films are homogenous, with uniform distribution of Er ions and high transparency over the visible VIS range of the light spectrum. However, a profound 0.4 eV blue shift of the fundamental absorption edge with respect to undoped TiO2 was observed, which can be attributed either to the size effect due to amorphization of TiO2 host or to the onset of precipitation of Er2Ti2O7 nanocrystals. Near-infrared NIR to VIS up-conversion is demonstrated upon excitation at 980 nm, while strong green photoluminescence at 525 and 550 nm occurs upon photon absorption at 488 nm.

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The electrical resistivity of thin film metal oxide photoanodes in the photoelectrochemical cells, PEC, for hydrogen generation, the importance of which should not be neglected in the design and construction of water-splitting devices, is found to be affected by the departure from stoichiometric composition and film thickness. Here, we propose to use TiO 2 /ITO photoanodes for photoelectrochemical cells. The TiO 2Àx thin films with x indicating a departure from the stoichiometric composition have been prepared by dc magnetron sputtering with the deposition rate controlled by the optical emission spectroscopy, OES. Photoanode properties were determined by scanning electron microscopy, SEM, atomic force mocroscopy, AFM, Raman spectroscopy, transmittance and reflectance measurements over uv/vis/nir wavelength ranges, impedance spectroscopy, Mott-Schottky plots, and photocurrent versus voltage dependence in the dark and under white light illumination. The contributions of the charge carrier concentration and mobility to the enhanced photocurrent of the PEC have been determined and correlated to the varying film stoichiometry and thickness, respectively.