Glass-to-Vitroceramic Transition in the Yttrium Aluminoborate System: Structural Studies by Solid-State NMR

The crystallization of laser glasses in the system (B(2)O(3))(0.6){(Al(2)O(3))(0.4-y)(Y(2)O(3))(y)} (0.1 <= y <= 0.25) doped with different levels of ytterbium oxide has been investigated by X-ray powder diffraction, differential thermal analysis, and various solid-state NMR techniques. The homogeneous glasses undergo major phase segregation processes resulting in crystalline YBO(3), crystalline YAI(3)(BO(3))(4), and residual glassy B(2)O(3) as the major products. This process can be analyzed in a quantitative fashion by solid-state (11)B, (27)Al, and (89)Y NMR spectroscopies as well as (11)B{(27)Al} rotational echo double resonance (REDOR) experiments. The Yb dopants end up in both of the crystalline components, producing increased line widths of the corresponding (11)B, (27)Al, and (89)Y NMR resonances that depend linearly on the Yb/Y substitution ratio. A preliminary analysis of the composition dependence suggests that the Yb(3+) dopant is not perfectly equipartitioned between both crystalline phases, suggesting a moderate preference of Yb to substitute in the crystalline YBO(3) component.

Efficient UV-visible upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate vitroceramic

Cooperative energy-transfer upconversion luminescence in Tb 3+/Yb 3+-codoped PbGeO 3-PbF 2-CdF 2 vitroceramic and its precursor glass under resonant and off-resonance infrared excitation, is investigated. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm, identified as due to the 5D 3( 5G 6 → 7F J(J=6,5,4) and 5D 4 → 7F J(J=6,5,4,3) transitions, respectively, were readily observed. The results indicate that cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The comparison of the upconversion process in a vitroceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.

Estudo da viabilidade do sistema LZAS para uso como selante de PaCOS

Cells the solid oxide fuel are systems capable to directly convert energy of a chemical reaction into electric energy in clean, quiet way and if its components in the solid state differentiate of excessively the techniques for having all. Its more common geometric configurations are: the tubular one and to glide. Geometry to glide beyond the usual components (anode, cathode and electrolyte) needs interconnect and sealant. E the search for materials adjusted for these components is currently the biggest challenge found for the production of the cells. The sealants need to present chemical stability in high temperatures, to provoke electric isolation, to have coefficient of compatible thermal expansion with the excessively component ones. For presenting these characteristics the glass-ceramics materials are recommended for the application. In this work the study of the partial substitution of the ZrO2 for the Al2O3 in system LZS became it aiming at the formation of system LZAS, this with the addition of natural spodumene with 10, 20 and 30% in mass. The compositions had been casting to a temperature of 1500°C and later quickly cooled with the objective to continue amorphous. Each composition was worn out for attainment of a dust with average diameter of approximately 3μm and characterized by the techniques of DRX, FRX, MEV, dilatometric analysis and particle size analysis. Later the samples had been conformed and treated thermally with temperatures in the interval between 700-1000 °C, with platform of 10 minutes and 1 hour. The analyses for the treated samples had been: dilatometric analysis, DRX, FRX, electrical conductivity and tack. The results point with respect to the viability of the use of system LZAS for use as sealant a time that had presented good results as isolating electric, they had adhered to a material with similar α of the components of a SOFC and had presented steady crystalline phases

Intense red upconversion emission in infrared excited holmium-doped PbGeO3-PbF2-CdF2 transparent glass ceramic

Intense red upconversion emission around 650 nm in PbGeO3-PbF2-CdF2 transparent glass ceramic containing beta-PbF2:Ho3+ nanocrystals, is presented. The holmium-doped vitroceramic samples were excited by a 980 nm diode laser source. The 650 nm upconversion signal was assigned to the F-5(5) --> I-5(8) transition of holmium ions. Very low intensity signals around 490 and 540 nm corresponding to the F-5(2,3) --> I-5(8) and S-4(2), F-5(4) --> I-5(8) transitions, respectively, were also detected. The upconversion excitation mechanism was achieved through a combination of stepwise phonon-assisted multiphoton absorption, cross-relaxation processes involving pairs of holmium ions, and excited-state absorption. Using a diode laser pump source around 850 nm green upconversion emission around 540 nm was the observed predominant signal. (C) 2004 Elsevier B.V. All rights reserved.

Infrared-to-visible frequency upconversion in transparent glass ceramics containing trivalent-rare-earth-doped nanocrystals

In this work we report on visible upconversion emission in Er 3+-, and Ho3+-doped PbGeO3-PbF 2-CdF2-based transparent glass ceramics under 980 nm infrared excitation. In erbium-doped vitroceramic samples, blue(410 ran), green(530, and 550 nm) and red(660 nm) emission signals were generated, which were identified as due to the 2H9/2, 2H 11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground-state, respectively. Intense red(650 nm) upconversion emission corresponding to the 5F5 - 5I8 transition and very small blue(490 nm) and green(540 nm) signals assigned to the 5F 2,3 - 5I8 and 4S2, 5F4 - 5I8 transitions, respectively, were observed in the holmium-doped samples. The 540 nm is the dominant upconversion signal in Ho3+-doped vitroceramics under 850 nm excitation. The dependence of the upconversion processes upon pump power and doping concentration are also investigated, and the main routes for the upconversion excitation processes are also identified. The comparison of the upconversion process in transparent glass ceramics and the precursor glass was also examined and the results revealed that the former present higher upconversion efficiencies.

Estudo da viabilidade do sistema LZAS para uso como selante de PaCOS

Cells the solid oxide fuel are systems capable to directly convert energy of a chemical reaction into electric energy in clean, quiet way and if its components in the solid state differentiate of excessively the techniques for having all. Its more common geometric configurations are: the tubular one and to glide. Geometry to glide beyond the usual components (anode, cathode and electrolyte) needs interconnect and sealant. E the search for materials adjusted for these components is currently the biggest challenge found for the production of the cells. The sealants need to present chemical stability in high temperatures, to provoke electric isolation, to have coefficient of compatible thermal expansion with the excessively component ones. For presenting these characteristics the glass-ceramics materials are recommended for the application. In this work the study of the partial substitution of the ZrO2 for the Al2O3 in system LZS became it aiming at the formation of system LZAS, this with the addition of natural spodumene with 10, 20 and 30% in mass. The compositions had been casting to a temperature of 1500°C and later quickly cooled with the objective to continue amorphous. Each composition was worn out for attainment of a dust with average diameter of approximately 3μm and characterized by the techniques of DRX, FRX, MEV, dilatometric analysis and particle size analysis. Later the samples had been conformed and treated thermally with temperatures in the interval between 700-1000 °C, with platform of 10 minutes and 1 hour. The analyses for the treated samples had been: dilatometric analysis, DRX, FRX, electrical conductivity and tack. The results point with respect to the viability of the use of system LZAS for use as sealant a time that had presented good results as isolating electric, they had adhered to a material with similar α of the components of a SOFC and had presented steady crystalline phases