Thulium and Ytterbium-Doped Titanium Oxide Thin Films Deposited by Ultrasonic Spray Pyrolysis
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e´bastien Forissier, Herve´ Roussel, Patrick Chaudouet, Antonio Pereira, Jean-Luc Deschanvres, and Bernard Moine (Submitted April 5, 2012; in revised form July 25, 2012) Thin films of thulium and ytterbium-doped titanium oxide were grown by metal-organic spray pyrolysis deposition from titanium(IV)oxide bis(acetylacetonate), thulium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate) and ytterbium(III) tris(acetylacetonate). Deposition temperatures have been investigated from 300 to 600 °C. Films have been studied regarding their crystallinity and doping quality. Structural and composition characterisations of TiO2:Tm,Yb were performed by electron microprobe, x-ray diffraction, and Fourier transform infrared spectroscopy. The deposition rate can reach 0.8 lm/h. The anatase phase of TiO2 was obtained after synthesis at 400 °C or higher. Organic contamination at low deposition temperature is eliminated by annealing treatments.
Keywords
CVD, thulium, ytterbium
thin
film,
titanium
oxide,
1. Introduction Over the last decades, titanium dioxide has been attracting great interest due to its relevance for a variety of applications. For example, TiO2 has been investigated for use in photocatalysis (Ref 1-3), protective coatings (Ref 4), and gas sensing applications (Ref 5). TiO2 is also interesting for photovoltaic applications (Ref 6). TiO2 thin films have been the most commonly used antireflective (AR) coating in the photovoltaic industry. Owing to its excellent optical properties, mechanical properties, and good chemical resistance, TiO2 still remains attractive for such application. The physical and chemical properties of an oxide matrix can be tuned by doping it with rare-earth (RE) elements. For example, the incorporation of RE ions into the oxide matrix received great attention for applications in photovoltaic devices (Ref 7-9). Indeed, one solution to reduce the energy losses in the UV region due to thermalization of the charge carriers is to adapt the solar spectrum to better match the bandgap of solar cells. This approach, which involves energy transfer between RE
Se´bastien Forissier, Laboratoire des Mate´riaux et du Ge´nie Physique, CNRS, Grenoble, France; and Laboratoire de Physico-Chimie des Mate´riaux Luminescents, Lyon, France; Herve´ Roussel, Patrick Chaudouet, and Jean-Luc Deschanvres, Laboratoire des Mate´riaux et du Ge´nie Physique, CNRS, Grenoble, France; and Antonio Pereira and Bernard Moine, Laboratoire de Physico-Chimie des Mate´riaux Luminescents, Lyon, France. Contact e-mail: sebastien.forissier@ grenoble-inp.fr.
Journal of Thermal Spray Technology
ions, is well known for lighting issues (Ref 7, 10) and has been recently proposed for photovoltaic applications (Ref 11). Depending on both the host matrix and the RE ions used, down-shifting or quantum-cutting can be observed. In this context, RE-doped titanium dioxide can be a potential low-cost material for the down-conversion. The use of titanium dioxide being well established in the photovoltaics industry, added functionality with RE could be
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