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

• Oriented anatase or rutile TiO2 films doped with 1%at. Tm, Eu, Yb or Nd are grown.
• The rare-earth-doped TiO2 films are transparent in the visible range.
• Anatase doped with Yb3 + and rutile doped with Nd3 +, are promising for UV to NIR conversion.

Ln3 + (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 O2. By using c-cut (0001) Al2O3 sapphire or (100) LaAlO3 single crystal substrates, TiO2 films doped with Ln3 + are constituted with either highly oriented (200) rutile or (004) anatase, respectively. Energy transfer from TiO2 to Ln3 + 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.