Upconverting materials are currently explored in the field of solar energy conversion in order to extend the light harvesting properties of semiconductors to the near-infrared (NIR) region, their absorption being generally limited to the visible region of the solar spectrum. Here, we propose to photosensitize nanostructured films of tungsten oxide (WO3), a semiconductor widely investigated in photoelectrochemistry, photocatalysis and electrochromics, with NaGdF4:Er3+, Yb3+ upconverting nanoparticles (UCNPs). In order to do so, we fabricate nanocomposite films of WO3 and NaGdF4: Er3+, Yb3+ UCNPs (indicated as UCNP/WO3 films). Current-time measurements show that, under irradiation at lambda = 980 nm, a relative increase in current of about 3% with respect to the dark current is observed in the UCNP/WO3 films. The UCNP/WO3 mol% ratio and the temperature of the thermal treatment of the nanocomposite films are both critical to simultaneously achieve photosensitization and charge carrier transport in the UCNP/WO3 films.
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