RESUMO
Undoped and Nd3+ doped lutetium niobate phases have been prepared by a conventional solid state reaction method using lutetium acetate and niobium oxide at 1250 °C for 6 h. X-ray diffraction patterns of the 6 mol% Lu3NbO7 sample exhibited a cubic fluorite single phase. Phase structure exhibited interesting crystallization behaviour depending on increasing Nd3+ concentration which led to a Lu3NbO7 single phase formation during the heat treatment process. SEM investigations were also in agreement with the XRD results. Morphologies of Nd3+ doped lutetium niobate powders exhibited oval like shapes and grain sizes varied between 0.3 and 5 µm. Near-infrared luminescence properties of Nd3+ doped Lu3NbO7 were also studied. 1.06 µm laser transition characteristics of Nd3+ doped lutetium niobate have been observed. Concentration quenching phenomenon was not detected depending on increasing Nd3+ doping concentrations at room temperature.
RESUMO
Pure, Eu(3+) - doped and Eu(3+),B(3+) co-doped CdNb2O6 powders have been prepared by a molten salt synthesis method using Li2SO4/Na2SO4 salt mixture as a flux at a relatively low temperatures as compared to solid state reaction. X-ray diffraction patterns of pure CdNb2O6 samples indicated orthorhombic single phase. Photoluminescence investigations of CdNb2O6 samples showed a strong blue emission band centered at 460 nm. For Eu-doped CdNb2O6 samples, the luminescence of Eu(3+) was observed with the host red emission varying with the Eu-doping concentrations. This PL characteristic of the doped samples may be attributed to the energy transfer between Eu(3+) and niobate groups (NbO6). Boron incorporation has remarkably increased the luminescence of Eu(3+)-doped CdNb2O6.
RESUMO
Pure and 0.5 to 10 mole% Sm(3+) doped TTB (tetragonal tungsten bronze)-type BaTa2O6 ceramic phosphor was produced by the solid state reaction method which performed at 1425 °C for 20 h. XRD and SEM analysis indicated single TTB phase for undoped and 0.5 to 10 mole% Sm(3+) doped BaTa2O6 structures. SEM also showed that the BaTa2O6 grain size decreased with the increasing content of Sm(3+). Optical analysis indicated significant emissions in the visible spectral region as green (λ = 562.7 nm) and orange-reddish (λ = 597.1 nm). The emission intensity increased with the increasing doping concentration up to 2.5 mole%, and then decreased due to the concentration quenching effect.
RESUMO
Pure Nd(3+)- or Eu(3+)-doped CoNb2O6 powders have been prepared by a molten salt synthesis method using a Li2SO4-Na2SO4 or NaCl-KCl salt mixture as a flux at relatively low temperatures as compared to the solid state reaction method. X-ray diffraction patterns of pure CoNb2O6 samples indicated an orthorhombic single phase. For Eu(3+)-doped CoNb2O6 samples, the luminescence of Eu(3+) was observed at 615 nm as red emission while the Nd(3+) doped sample showed a typical emission at 1064 nm varying with the Eu(3+) or Nd(3+) doping concentrations. These luminescence characteristics of the doped samples may be attributed to the energy transfer between rare earth ions and CoO6 octahedral groups in the columbite structure.
RESUMO
Novel mono- and ball-type Co(ii), Zn(ii) and Cu(ii) metallophthalocyanines (MPcs) were synthesized from 1,1'-p-anisylidenbis(2-naphthoxyphthalonitrile). The MPcs have been characterized by elemental analysis, UV/Vis, IR and (1)H-NMR spectroscopy and MALDI-TOF mass spectrometry. The performances of organic field effect transistors (OFETs) of the dinuclear ball-type MPcs have been compared to those of mononuclear counterparts. The ball-type MPc based OFETs showed a p-channel and typical ambipolar transport properties. On the other hand, it was not possible to measure the full transfer characteristics of the mononuclear MPc based devices. The best results were obtained in the case of dinuclear Cu2Pc2. In this case, the mobility value is µ = 4.4 × 10(-2) cm(2) V(-1) s(-1) and the threshold voltage is 27.6 volts. The reduction and oxidation characteristics of the mono-nuclear and ball-type MPcs have been compared by cyclic voltammetry, square wave voltammetry and controlled potential coulometry on platinum in nonaqueous media. The comparison suggested that the ball-type complexes form ring-based and/or metal-based mixed-valence species as a result of the remarkable interaction between the two Pc rings and/or metal centers. The stability of these species was confirmed by the mixed-valence splitting values for the complexes. The electrocatalytic performances of the mononuclear and dinuclear complexes for the oxygen reduction reaction were also studied. The compounds involving Co(ii) at the phthalocyanine core, especially the ball-type one, showed much higher catalytic performances towards oxygen reduction than those of the other ones.
