Thulium and ytterbium-doped titanium oxide thin films deposited by ultrasonic spray pyrolysis

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{\deg}C to 600{\deg}C. Films have been studied regarding their crystallity 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 \mum/h. The anatase phase of TiO2 was obtained after synthesis at 400{\deg}C or higher. Organic contamination at low deposition temperature is eliminated by annealing treatments.Comment: 6 pages, 6 figure

Thulium and ytterbium-doped titania thin films deposited by MOCVD

In this study we synthesized thin films of titanium oxide doped with thulium and/or ytterbium to modify the incident spectrum on the solar cells. This could be achieved either by photoluminescence up-converting devices, or down-converting devices. As down-converter thin films our work deals with thulium and ytterbium-doped titanium dioxide. Thulium and ytterbium will act as sensitizer and emitter, respectively. The rare-earth doped thin films are deposited by aerosol-assisted MOCVD using organo-metallic precursors such as titanium dioxide acetylacetonate, thulium and ytterbium tetramethylheptanedionate solved in different solvents. These films have been deposited on silicon substrates under different deposition conditions (temperature and dopant concentrations for example). Adherent films have been obtained for deposition temperatures ranging from 300{\deg}C to 600{\deg}C. The deposition rate varies from 0.1 to 1 \mu m/h. The anatase phase is obtained at substrate temperature above 400{\deg}C. Further annealing is required to exhibit luminescence and eliminate organic remnants of the precursors. The physicochemical and luminescent properties of the deposited films were analyzed versus the different deposition parameters and annealing conditions. We showed that absorbed light in the near-UV blue range is re-emitted by the ytterbium at 980 nm and by a thulium band around 800 nm.Comment: 4 pages, 6 figures, proceedin

Study of the Physico-Chemical Properties of Sol-Gel (Er, Yb) Doped TiO2 Nanoparticles Prepared with a Novel Protocol

This paper describes the systematic preparation of doped and undoped TiO2 with Er and/or Yb nanoparticles by hydrothermal-assisted sol-gel method using supercritical drying of ethanol followed by systematic calcination steps at 500°C, 800°C and 1000°C for 2/h. The structural study of these powders with XRD reveals that our samples are crystalline with a tetragonal structure and anatase phase, which is well crystallized at 500°C. The annealing at 800°C reveals a transformation of the anatase phase to the rutile phase, which is well crystallized at 1000°C. The XRD analysis clearly indicates that the dopants are incorporated into the TiO2 network without any phase segregation-taking place in these nanoparticles. The study of the grain sizes has shown that they are nanometric in size of around 8-12 nm and that their sizes decrease with Er and/or Yb doping. The elemental analyses with micro-EDX using SEM confirmed the presence of chemical elements of TiO2 nanoparticles with expected atomic ratios. The analysis of the SEM images confirmed the XRD observations. In addition, they attest that the nanoparticles are spherical in shape. The optical analysis with excitation at 488 nm shows the presence of three emission bands in the green zone and the red zone. The heat treatment improves the optical, structural and spectroscopic properties and eliminates the contaminations that are due to the preparation conditions

On the magnetism of Ln{2/3}Cu{3}Ti{4}O{12} (Ln = lanthanide)

The magnetic and thermodynamic properties of the complete Ln$_{2/3}$Cu$_3$Ti$_4$O$_{12}$ series were investigated. Here $Ln$ stands for the lanthanides La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. %Most of the compounds were prepared as single phase polycrystalline powder %without any traces of impurities. Marginal amounts of %impurities $(< 2$ were detected $Ln=$ Gd, Er, and Tm. %Significant amounts of impurity phases were found for $Ln=$ Ce and Yb. All the samples investigated crystallize in the space group $Im\bar{3}$ with lattice constants that follow the lanthanide contraction. The lattice constant of the Ce compound reveals the presence of Ce$^{4+}$ leading to the composition Ce$_{1/2}$Cu$_3$Ti$_4$O$_{12}$. From magnetic susceptibility and electron-spin resonance experiments it can be concluded that the copper ions always carry a spin $S=1/2$ and order antiferromagnetically close to 25\,K. The Curie-Weiss temperatures can approximately be calculated assuming a two-sublattice model corresponding to the copper and lanthanide ions, respectively. It seems that the magnetic moments of the heavy rare earths are weakly coupled to the copper spins, while for the light lanthanides no such coupling was found. The $4f$ moments remain paramagnetic down to the lowest temperatures, with the exception of the Tm compound, which indicates enhanced Van-Vleck magnetism due to a non-magnetic singlet ground state of the crystal-field split $4f$ manifold. From specific-heat measurements we accurately determined the antiferromagnetic ordering temperature and obtained information on the crystal-field states of the rare-earth ions. The heat-capacity results also revealed the presence of a small fraction of Ce$^{3+}$ in a magnetic $4f^1$ state.Comment: 10 pages, 10 figure

Spectres vibrationnels des silicates et germanates renfermant des anneaux, M3O9 (M Si, Ge)-I. Attribution des fréquences caractéristiques de l'anneau M3O9, dans les composés de type bénitoïte, wadéite et tétragermanate

A number of cyclo-silicates and germanates with the benitoïte, wadeite or tetra-germanate structure have been investigated by i.r. and Raman spectroscopy, so as to evidence the essential spectroscopic features of the Si3O9 and Ge3O9 rings and to show how these features are modified under the influence of a change of structure, with or without modification of the local symmetry of the ring. One band in the i.r. spectrum and two bands in the Raman spectrum have been found to be highly specific of the ring structure. The two Raman bands are observed in the 600-500 cm-1 region for the silicates, and 550-450 cm-1 region for the germanates; they correspond to bending motions of the ring, involving a predominant displacement of the ring oxygens, and no large displacement of the cations, as evidenced by the small 28Si-30Si isotopic shift. The characteristic i.r. band is observed in the 760-700 cm-1 region for the silicates, and the 550-500 cm-1 region for the germanates, with a large (14 cm-1) 28Si-30Si isotopic shift. This important mass effect of the cation is also reflected in the large frequency ratio ν(silicate) ν(germanate). This band is unique as long as the ring has the local C3h symmetry, irrespective of the crystal structure (benitoïte or wadeite); but it is split into a multiplet for distorted rings. It is thus a sensitive means of detecting the local symmetry of the ring. © 1975

Deposition conditions for the growth of textured ZnO thin films by aerosol CVD process

The crystalline orientation of ZnO thin films deposited by an aerosol CVD process is studied with regard to the experimental conditions. The quality of the C-axis oriented growth depended on the substrate temperature, on the deposition rate and also on the hygrometric degree of the carrier gas. The quality of the gold sublayer influenced also the quality of the ZnO textured growth. Under a dry gas mixture N2-O2 at 495°C and with a deposition rate of 35Å/mn, the texture ratio was less than -3.5 and the misorientation σ002 was less than 1.6°

Elaboration par le procédé pyrosol de couches minces texturées de ZnO pour la réalisation de microcapteurs

The crystalline orientation of ZnO thin films deposited by an aerosol CVD process is studied with regard to the experimental conditions. The quality of the $C$-axis oriented growth depended on the substrate temperature, on the deposition rate and also on the hygrometric degree of the carrier gas. The quality of the gold sublayer influenced also the quality of the ZnO textured growth. Under a dry gas mixture N$_2$-O$_2$ at 495 $^{\circ}$C and with a deposition rate of 35 Å/mn, the texture ratio was less than -3.5 and the misorientation of the 002 line was less than 1.6$^{\circ}$.L'orientation cristalline de couches minces de ZnO élaborées par le procédé pyrosol est étudiée en fonction des conditions de dépôt. La qualité de la texture selon l'axe $C$ dépend de la température du substrat, de la vitesse de dépôt, du degré d'hygrométrie du gaz vecteur et également de la qualité de la sous-couche chrome/or. Pour des dépôts réalisés avec un mélange pur et sec d'azote et d'oxygène à 495 $^{\circ}$C et pour une vitesse de dépôt de 35 Å/mn, le rapport de texture est inférieur à -3,5 et la désorientation de la raie 002 est inférieure à 1,6$^{\circ}$