Optically Active TiO(2):Er Thin Films Deposited by Magnetron Sputtering

Titanium dioxide photoanodes for hydrogen generation suffer from a profound mismatch between the optical absorption of TiO(2) and the solar spectrum. To solve the problem of low solar-to-chemical efficiency, optically active materials are proposed. In this work, TiO(2) 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. TiO(2):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 TiO(2) was observed, which can be attributed either to the size effect due to amorphization of TiO(2) host or to the onset of precipitation of Er(2)Ti(2)O(7) 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.