Anatase TiO 2 nanoparticles doped with Al or Fe have been synthesized via a modified Pechini method which allows us to reach high control in size and composition. Microstructural analysis confirms the good crystallinity of the doped anatase nanoparticles with average sizes around 5 nm and dopant cationic concentrations up to 30%. The anatase to rutile transition (ART) has been thermally driven and analyzed as a function of the doping. Thermo-diffraction measurements indicate that the phase transition can be either promoted or inhibited by Fe or Al doping, respectively. The influence of Al and Fe doping on the phase transition has been discussed by means of Raman spectroscopy, photoluminescence and X-ray photoelectron spectroscopy, with special attention paid to the role played by Ti 3+ at the surface. The anatase phase has been stabilized up to temperatures above 900 C by appropriate Al doping.

Rutile TiO2 nanoparticles doped with V, Cr, or Mn ions have been synthesized via a modified Pechini method using polymeric precursors. The final particle sizes range between 20 and 500 nm depending on the selected dopant. The TiO2 rutile phase has been stabilized in the doped nanoparticles at 650 °C. Microstructural analysis shows a good crystallinity and cationic homogeneity of the doped nanoparticles. The cathodoluminescence study of the doped and undoped nanoparticles shows a luminescence signal related to the structural defects of the samples and the presence of dopants. In particular, an intense 1.52 eV emission associated with Ti3+ interstitials dominates the luminescence of undoped nanoparticles, which also exhibit less intense emissions extending from 2 to 3.4 eV. The presence of V, Cr, or Mn in the rutile TiO2 nanoparticles induces variations in the associated cathodoluminescence signal which would be useful in order to achieve a deeper understanding of the doping process and spread future optical applications. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti3+ in the near-surface region of the nanoparticles, the concentration of which decreases when doping. The presence of Ti3+ interstitials related states in the band gap is discussed.

A study of the anatase to rutile transition (ART) induced by laser irradiation in TiO2 nanoparticles synthesized by a modified Pechini method has been carried out in this work, with special attention focused on the effects of doping with Al or Fe on the phase transition. Either promotion or inhibition of ART can be achieved by Fe or Al doping, respectively, as demonstrated by X-ray diffraction, Raman spectroscopy, photoluminescence, X-ray absorption, and transmission electron microscopy results presented in this work. The influence of dopants (Al, Fe) in the kinetics of the ART, the key role played in this process by the surface of the nanoparticles and the presence of oxygen vacancies, and the formation of rutile nucleation points at twinned regions have been discussed in this work. Finally, advantage has been taken of the ART controlled by laser irradiation, and an original laser-induced micropatterning based on spatial phase-controlled titania polymorphs has been developed, which assures significant progress in challenging microdevice design based on titania polymorphs.

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Elongated micro- and nanostructures of Sn doped or Sn and Cr co-doped monoclinic gallium oxide have been grown by a thermal method. The presence of Sn during growth has been shown to strongly influence the morphology of the resulting structures, including Sn doped branched wires, whips, and needles. Subsequent co-doping with Cr is achieved through thermal diffusion for photonic purposes. The formation mechanism of the branched structures has been studied by transmission electron microscopy (TEM). Epitaxial growth has been demonstrated in some cases, revealed by a very high quality interface between the central rod and the branches of the structures, while in other cases, formation of extended defects such as twins has been observed in the interface region. Cathodoluminescence (CL) measurements show a Sn-related complex band in the Sn-doped structures. In the Sn−Cr co-doped samples, the characteristic, very intense Cr3+ red luminescence emission quenches the bands observed in the Sn doped samples. Branched, Sn−Cr co-doped structures were studied with microphotoluminescence imaging and spectroscopy, and waveguiding behavior was observed along the trunks and branches of these structures.