Pol. J. Chem. Tech., Vol. 14, No. 3, 2012 1 Polish Journal of Chemical Technology, 14, 3, 1 — 7, 10.2478/v10026-012-0077-2 Photocatalytic properties of transparent TiO 2 coatings doped with neo- dymium Damian Wojcieszak 1* , Danuta Kaczmarek 1 , Jarosław Domaradzki 1 , Michał Mazur 1 , Antoni W. Morawski 2 , Magdalena Janus 2 , Eugeniusz Prociów 1 , Pietro Gemmellaro 3 1 Wroclaw University of Technology, Faculty of Microsystem Electronics and Photonics, Janiszewskiego 11/17, 50-372 Wrocław, Poland 2 Szczecin University of Technology, Institute of Chemical and Environment Engineering, Piastow 42, 71-065 Szczecin, Poland 3 University of Catania, Department of Chemical Science, V. le Andrea Doria 6, 95125 Catania, Italy * Corresponding author: damian.wojcieszak@pwr.wroc.pl In this work photocatalytic properties of TiO 2 thin films doped with 8.51 at. % of Nd were described. The self-cleaning phenomenon of thin films was discussed together with the structural, optical and surface properties of prepared thin films. Transparent coatings based on titanium dioxide were manufactured by high-energy reactive magnetron sputtering process. Incorporation of Nd during sputtering process results in amorphous behavior, without a significant influence on transparency and colour as compared to the undoped TiO 2 -rutile matrix. Nevertheless, doping with neodymium doubles the photocatalytic activity of the matrix due to higher quantity of photo-generated charge carriers and more efficient mechanism of energy transfer. Keywords: TiO 2 , neodymium, photocatalysis, wettability, surface properties. INTRODUCTION Transparent thin films based on titanium dioxide are widely applied in coating industry, because TiO 2 is being used for preparation of hydrophobic or hydrophilic films, self-cleaning coatings, optical filters or protective films 1–5 . The properties of TiO 2 can be modified by selection of deposition parameters, doping with different elements or post-process treatment (i.e. annealing) 1–6 . By doping with rare earth elements thin films, which exhibit photo- luminescence or have high photocatalytic activity can be manufactured 7–9 . Neodymium is often applied dopant for TiO 2 due to its photoluminescence properties in near-IR range 10 . Moreover, it is also an important material in the field of lasers technology. Nd 3+ -doped materials are one of the most versatile laser host materials 11 . Similarly like Eu 3+ or Tb 3+ , incorporation of Nd 3+ ions results in the increase of TiO 2 photocatalytic activity due to a higher number of energy levels which can take part in energy transfer mechanism. Our previous works have shown that incorporation of RE-dopant into nanocrystalline TiO 2 thin film increases their photocatalytic activity more than two times, without a meaningful decrease of its high transparency 12 . In this work the influence of neodymium on photo- catalytic properties of TiO 2 thin films are discussed. A self-cleaning phenomenon of thin films based on TiO 2 is a consequence of photo-generation of electron – hole pairs under UV-Vis light exposure. The induced charge carriers are transferred to different positions on the sur- face to react with donors or acceptors 13 . Electrons, which have a strong reducing power, are easily trapped by O 2 (acceptors) in order to produce superoxides O 2 - (radical anions). The holes are trapped by organic pollutants (do- nors) and oxidize them. The phenomena of separation, recombination, capture and transfer of photo-induced carriers are conditioning the photocatalytic activity of thin film 13 . Incorporation of the equivalent amount of the dopant, especially from rare earth (RE) group, results in receiving coatings with high photocatalytic activity and exhibit other phenomena. Doping TiO 2 thin films with Eu, Tb or Nd results in structure modification (receiving of different phase, densification), increases the temperature of phase transformation, retains high transparency of the matrix, increases photocatalytic properties and may cause photoluminescence effect 10, 14 . A significant effect of RE-doping on the properties of TiO 2 matrix is due to a participation in energy transfer of photo-induced charge carriers 15 . In the present paper the results of photocatalytic experiment together with structural, optical and sur- face properties (adsorption, wettability) of transparent TiO 2 :Nd thin films are discussed. EXPERIMENTAL Thin films were manufactured by a high energy reactive magnetron sputtering process 16 . For deposition metallic Ti and Ti-Nd targets were sputtered under the low oxygen pressure (0.1 Pa). Thin films were deposited on SiO 2 and Si substrates. The thickness of the films was about 400 nm. The atomic concentration of Nd-dopant in the film was determined by Energy Dispersive Spectroscopy. The results have shown that in TiO 2 :Nd thin film was 8.51 at. % of neodymium. The structure (crystalline form and crystallites size) of as-deposited films was determined by X-Ray Diffraction (XRD). For measurements Dron-2 powder diffractom- eter was used. The average size of crystallites (D) was calculated based on XRD patterns according to the Scherrer formula 17 . The structural characterization was extended by surface diversification analysis obtained from atomic force microscope (AFM). The topography was investigated in contact mode, in an ambient air by Veeco PicoForce microscope. WSxM ver. 4.0 software was used to transform the received data points into the images of the surface 18 . Distribution of titanium, oxygen and neodymium in as-deposited films was investigated by Secondary Ion Mass Spectroscopy (SIMS). The applied SIMS system Unauthenticated Download Date | 3/20/17 11:10 PM