The synthesis of titanium oxide nanoparticles by laser pyrolysis is studied in this work. This original gas phase technique is a versatile method which allows us to obtain a one-step synthesis of nanoparticles of controlled size, chemical composition and crystalline structure.In this study, two approaches have been proposed to synthesize titanium oxides nanoparticles with absorption in the visible range. In the first place, the synthesis of nitrogen doped titanium dioxide (TiO2) and second, the synthesis of less oxidized titanium oxides than TiO2.First, the synthesis of titanium dioxide nanoparticles is achieved through the use of titanium tetraisopropoxide as a precursor. The laser pyrolysis allows us to control the obtained TiO2 phase, anatase or rutile. Then, using ammonia as a dopant, we were able to synthesize nitrogen doped TiO2 anatase, with an absorption in the visible.Second, by changing the synthesis parameters, it was possible to synthesize nanoparticles of Magnéli phases, also having absorption in the visible. It was also possible to obtain under atmospheric pressure the TiO2-II phase, a high-pressure phase of TiO2 by oxidation of one of the Magnéli phases.Third, using the reducing effect of ammonia we were able to synthesize titanium oxynitrides, Ti(O,N). A detailed study by X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, electron energy loss spectroscopy and a study in temperature, allowed us to characterize the structure of this unusual phase. In addition, the optical properties were very interesting, since the material undergoes a transition metal/semiconductor depending on its oxidation and has a very high absorption in the visible region.Finally, the TiO2 nanoparticles and nitrogen doped TiO2 were used for the development of solid state, dye-sensitized solar cells. Initial results show that the morphology of these nanoparticles is suitable for their use for such devices, with yields close to the world state of the art. Secondly, it shows that the nitrogen doping allows to collect a larger amount of photons, through the area of absorption of these nanoparticles and to generate a higher current density.
