Optical properties of rare earth-doped TiO2 anatase and rutile thin films grown by pulsed-laser deposition

Abstract Ln 3 + (Ln = Tm, Eu and Yb) doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700 °C under 0.1 mbar O 2 . By using c-cut (0001) Al 2 O 3 sapphire or (100) LaAlO 3 single crystal substrates, TiO 2 films doped with Ln 3 + are constituted with either highly oriented (200) rutile or (004) anatase, respectively. Energy transfer from TiO 2 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 Tm 3 + dopant is not efficient as sensitizers. On the contrary, energy transfer from TiO 2 to Eu 3 + and Yb 3 + occurs in both matrixes, which make this material suitable for down-shifting purpose. Results obtained for Yb 3 + compared with our previous study on Nd 3 + show that Nd 3 + doped-rutile and Yb 3 + 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 Yb 3 + rather than in rutile.