Thin Solid Films, Vol.553, 13-16, 2014
Optical properties of rare earth-doped TiO2 anatase and rutile thin films grown by pulsed-laser deposition
Ln(3+) (Ln = Tm, Eu and Yb) doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700 degrees C under 0.1 mbar O-2. By using c-cut (0001) Al2O3 sapphire or (100) LaAlO3 single crystal substrates, TiO2 films doped with Ln(3+) are constituted with either highly oriented (200) rutile or (004) anatase, respectively. Energy transfer from TiO2 to Ln(3+) is studied by photoluminescence spectroscopy with UV excitation (364 nm) under band gap excitation of the oxide matrix. It is demonstrated that Tm3+ dopant is not efficient as sensitizers. On the contrary, energy transfer from TiO2 to Eu3+ and Yb3+ occurs in both matrixes, which make this material suitable for down-shifting purpose. Results obtained for Yb3+ compared with our previous study on Nd3+ show that Nd3+ doped-rutile and Yb3+ doped-anatase are the more efficient combinations to convert UV to NIR photon. Finally, a cooperative conversion mechanism is suggested to explain the higher integrated photoluminescence intensity found in anatase Yb3+ rather than in rutile. (C) 2013 Elsevier B. V. All rights reserved.
Keywords:Titanium oxide;Rare earth;Energy transfer;Photoluminescence;Down shifting;Solar cell;Photovoltaic;Pulsed-laser deposition