Inhomogeneous broadening, luminescence origin and optical amplification in bismuth-doped glass

Absorption and luminescence spectra and optical amplification in bismuth-doped germanate silicate glass were investigated. Two kinds of bismuth ion valence states could exist in the glass. One is Bi2+, which has shown red luminescence, another might be Bi+, which is the active center for infrared luminescence. The infrared luminescence excited at 700, 800, and 980 nm should be ascribed to the electronic transition P-3(1) --> P-3(0) of Bi+ ions in three distinct sites. The shifting, broadening, and multiple configuration of the luminescence could be due to the randomly disorder of local environment and multiple sites of the active centers. In this glass, obvious optical amplification was realized at 1300 nm wavelength when excited at 808 and 980 nm, respectively.

Luminescence properties of bismuth-doped lime silicate glasses

Luminescences from bismuth-doped lime silicate glasses were investigated. Luminescences centered at about 400, 650, and 1300 nm were observed, excited at 280, 532 and 808 nm, respectively. These three luminescence bands arise from three different kinds of bismuth ions in the glasses. The visible luminescences centered at 400 and 650 nm arise from Bi3+, and Bi2+, respectively. The infrared luminescences cover the wavelength range from 1000 to 1600 nm when exited by an 808 nm laser diode. The full width at half maximum (FWHM) of the infrared luminescences is more than 205 urn. The intensity of the infrared luminescence decreases with the increment in CaO content. We suggest that the infrared luminescences might arise from Bi+. Such broadband luminescences indicate that the glasses may be potential candidate material for broadband fiber amplifiers and tunable lasers. (C) 2007 Elsevier B.V. All rights reserved.

Ex Situ Scanning Electrochemical Microscopy (SECM) Investigation of Bismuth- and Bismuth/Lead Alloy Film-Modified Gold Electrodes in Alkaline Medium

Scanning electrochemical microscopy (SECM) in feedback mode was employed to characterise the reactivity and microscopic peculiarities of bismuth and bismuth/lead alloys plated onto gold disk substrates in 0.1 molL(-1) NaOH solutions. Methyl viologen was used as redox mediator, while a platinum microelectrode was employed as the SECM tip. The metal films were electrodeposited ex situ from NaOH solutions containing either bismuth ions only or both bismuth and lead ions. Approach curves and SECM images indicated that the metal films were conductive and locally reactive with oxygen to provide Bi(3+) and Pb(2+) ions. The occurrence of the latter chemical reactions was verified by local anodic stripping voltammetry (ASV) at the substrate solution interface by using a mercury-coated platinum SECM tip. The latter types of measurements allowed also verifying that lead was not uniformly distributed onto the bismuth film electrode substrate. These findings were confirmed by scanning electron microscopy images. The surface heterogeneity produced during the metal deposition process, however, did not affect the analytical performance of the bismuth coated gold electrode in anodic stripping voltammetry for the determination of lead in alkaline media, even in aerated aqueous solutions. Under the latter conditions, stripping peak currents proportional to lead concentration with a satisfactory reproducibility (within 5% RSD) were obtained.

Structure effect on the oxygen permeation properties of barium bismuth iron oxide membranes

In this work, we investigated the oxygen permeation properties of barium bismuth iron oxide within the family of [Ba_2−3xBi_3x−1][Fe_2xBi_1−2x]O_2+3x/2 for x = 0.17–0.60. The structure changed progressively from cubic to tetragonal and then to hexagonal as function of x in accordance with the different relative amounts of bismuth on A-site and B-site of ABO_3−δ perovskite lattices. We found that the oxygen flux and electrical conductivity correlated strongly, and it was prevalent for the cubic structure (x = 0.33–0.40) which conferred the highest oxygen flux of 0.59 ml min⁻¹ cm⁻² at 950 °C for a disk membrane x = 0.33 with a thickness of 1.2 mm. By reducing the thickness of the disk membrane to 0.8 mm, the oxygen flux increased to 0.77 ml min⁻¹ cm⁻², suggesting both surface kinetics and ion diffusion controlled oxygen flux, though the former was more prominent at higher temperatures. For disk membranes x = 0.45–0.60, the perovskite structure changed to tetragonal and hexagonal, and the oxygen flux was insignificant below 900 °C, clearly indicating electron conduction properties only. However, for two compositions with relatively high bismuth content, e.g. x = 0.55 and 0.60, there was a sudden and significant rise of oxygen permeability above 900 °C, by more than one order of magnitude. These materials changed conduction behavior from metallic to semiconductor at around 900 °C. These results suggest the advent of mixed ionic electronic conducting properties caused by the structure transition as bismuth ions changed their valence states to compensate for the oxygen vacancies formed within the perovskite lattices.

Development of a direct evaporation bismuth Hall thruster

Hall thrusters have been under active development around the world since the 1960’s. Thrusters using traditional propellants such as xenon have been flown on a variety of satellite orbit raising and maintenance missions with an excellent record. To expand the mission envelope, it is necessary to lower the specific impulse of the thrusters but xenon and krypton are poor performers at specific impulses below 1,200 seconds. To enhance low specific impulse performance, this dissertation examines the development of a Hall-effect thruster which uses bismuth as a propellant. Bismuth, the heaviest non-radioactive element, holds many advantages over noble gas propellants from an energetics as well as a practical economic standpoint. Low ionization energy, large electron-impact crosssection and high atomic mass make bismuth ideal for low-specific impulse applications. The primary disadvantage lies in the high temperatures which are required to generate the bismuth vapors. Previous efforts carried out in the Soviet Union relied upon the complete bismuth vaporization and gas phase delivery to the anode. While this proved successful, the power required to vaporize and maintain gas phase throughout the mass flow system quickly removed many of the efficiency gains expected from using bismuth. To solve these problems, a unique method of delivering liquid bismuth to the anode has been developed. Bismuth is contained within a hollow anode reservoir that is capped by a porous metallic disc. By utilizing the inherent waste heat generated in a Hall thruster, liquid bismuth is evaporated and the vapors pass through the porous disc into the discharge chamber. Due to the high temperatures and material compatibility requirements, the anode was fabricated out of pure molybdenum. The porous vaporizer was not available commercially so a method of creating a refractory porous plate with 40-50% open porosity was developed. Molybdenum also does not respond well to most forms of welding so a diffusion bonding process was also developed to join the molybdenum porous disc to the molybdenum anode. Operation of the direct evaporation bismuth Hall thruster revealed interesting phenomenon. By utilizing constant current mode on a discharge power supply, the discharge voltage settles out to a stable operating point which is a function of discharge current, anode face area and average pore size on the vaporizer. Oscillations with a 40 second period were also observed. Preliminary performance data suggests that the direct evaporation bismuth Hall thruster performs similar to xenon and krypton Hall thrusters. Plume interrogation with a Retarding Potential Analyzer confirmed that bismuth ions were being efficiently accelerated while Faraday probe data gave a view of the ion density in the exhausted plume.

Effect of oxygen substitution by halide ions on structure, thermal stability and upconversion fluorescence in Er3(+)/Yb3(+)-codoped germanium-bismuth glasses

For the first time. effect of halide ions (F-, Cl-, Br-, and I-) introduction on structure, thermal stability, and upconversion fluorescence in Er3+/Yb3+-codoped oxide-halide germanium-bismuth glasses has been systematically investigated. The results show that halide ions modified germanium-bismuth glasses have lower maximum phonon energy and phonon density, worse thermal stability. longer measured lifetimes of I-4(l1/2) level, and stronger upconversion emission than germanium-bismuth glass. All these results indicate that halide ions play an important role in the formation of glass network, and have an important influence on the upconversion luminescence. The possible upconversion mechanisms of Er3+ ion are also evaluated. © 2005 Elsevier Ltd. All rights reserved.

Effect of chloride ions' introduction on structural, thermal stability, and spectroscopic properties in Yb3+Er3+-codoped germanate-bismuth-lead glasses

Yb3+Er3+-codoped chloride-modified germanate-bismuth-lead glasses have been synthesized by the conventional melting and quenching method. Structural and thermal stability properties have been obtained on the basis of the Raman spectra and differential thermal analysis, which indicate that the PbCl2 addition has an important influence on the phonon density of states, maximum phonon energy, and thermal stability of host glasses. The Judd-Ofelt intensity parameters and quantum efficiencies were calculated on the basis of the Judd-Ofelt theory and lifetime measurements. For the 1.53 mu m emission band, the full widths at the half-maximum increase and peak wavelengths are blueshifted with increasing PbCl2 content. Moreover, the effect of the PbCl2 addition on the phonon density of states, OH- content, and upconversion luminescence has been discussed and evaluated. Our results reveal that, with increasing PbCl2 content, the decrease of phonon density and OH- content contributes more to the enhanced upconversion emissions than that of maximum phonon energy. (c) 2005 Optical Society of America

Optical transitions of Er3+ and Yb3+ ions in novel oxyfluoride bismuth-germanium glass: Observation of up-conversion

Er3+/Yb3+-codoped novel oxyfluoride bismuth-germanium glass was prepared and its up-conversion fluorescence property under 975 nm excitation has been studied. Intense green and weak red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), and F-4(9/2) -> I-4(15/2), respectively, were observed at room temperature. The possible up-conversion mechanism was also evaluated. The optimal Yb3+-Er3+ concentration ratio is found based on the direct lifetime measurements of excited levels for Er3+ ion. The structure of this novel oxyfluoride bismuth-germanium glass has been investigated by peak-deconvolution of FT-Raman spectrum, and the structural information was obtained from the peak wavenumbers. This novel oxyfluoride bismuth-germanium glass with relatively lower maximum phonon energy (similar to 731 cm(-1)) can be used as potential host material for up-conversion lasers. (c) 2005 Elsevier B.V. All rights reserved.

Ternary bismuth oxides Bi26â-xMxO40ay (M = Mg, Al, Co and Ni) related to α - Bi2O3

Reaction of Bi2O3 with MgO, NiO, Co3O4 and Al2O3 gives rise to the corresponding ternary bismuth oxides, Bi18Mg8O36, Bi18Ni8O36, Bi20Co6O39 and Bi24Al2O39. These oxides have the general formula Bi26�xMxO40�y and exhibit BCC structures related to α - Bi2O3. In the first three solids, the metal ions, M, replace bismuth randomly at the octahedral 24r sites (space group 123); in the last case, aluminium ions occupy the tetrahedral 2a sites, the phase being isostructural with Bi24Ge2O40. Starting from Bi2O3 and NiO, orthorhombic Bi2Ni2O5 has also been obtained.

Impurity diffusion in bismuth single-crystals

Measurements of impurity diffusion of 86Rb, 90Sr, 133Ba, and 137Cs in single crystal Bi were carried out. Diffusion samples were prepared from single crystal Bi by ion implantation. About 1012-1013 ions were implanted, resulting in surface activities approx =104 cpm. After implantation, specimens were annealed for specified times at 220-265 deg C, and tracer penetration profiles were determined by an electrolytic method. A typical penetration profile for 137Cs in Bi showed a linear relationship for log C vs x in with Fick's law for volume diffusion. Laws of grain boundary diffusion were not obeyed and the order of magnitude of the penetration distances was much less than on a grain boundary mechanism. Results were interpreted in terms of a modified Fischer analysis using a kinetic trapping term. Effective half lengths for trapping at a twin boundary were determined for each impurity.

Preparation and characterization of nanocrystalline powders of bismuth vanadate

The influence of mechanical activation on the formation of Bi2VO5.5 bismuth vanadate (BiV) phase, was investigated by ball-milling a stoichiometric mixture of bismuth oxide and vanadium pentoxide. The structural evolution of the desired BN phase, via an intermediate BiVO4,phase, was investigated using X-ray powder diffraction; (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). Milling for 54h. yielded monophasic gamma-BiV powders with an average crystallite size of 30 nm. The electron paramagnetic resonance (EPR) peaks associated with the V4+ ions are stronger and broader in nanocrystalline (n) BN than in the conventionally prepared microcrystalline (m) BN, suggesting theta significant portion of V5+ has been transformed to V4+ during milling. The optical bandgap of n-BiV was found to be higher than that of m-BiV. High density (97% of the theoretical density), fine-grained (average grain-size of 2 tun) ceramics with uniform grain-size distribution could be fabricated using n-BiV powders. These fine-grained ceramics exhibit improved dielectric, pyre and ferroelectric properties. (C) 1999 Elsevier Science S.A. All rights reserved.

Infrared luminescence properties of bismuth-doped barium silicate glasses

Infrared (IR) luminescence covering 1.1 to similar to 1.6 mu m wavelength region was observed from bismuth-doped barium silicate glasses, excited by a laser diode at 808 nm wavelength region, at room temperature. The peak of the IR luminescence appears at 1325 nm. A full width half-maximum (FWHM) and the lifetime of the fluorescence is more than 200 nm and 400 mu s, respectively. The fluorescence intensity increases with Al2O3 content, but decreases with BaO content. We suggest that the IR luminescence should be ascribed to the low valence state of bismuth Bi2+ or Bi+, and Al3+ ions play an indirect dispersing role for the infrared luminescent centers.

Improved fluorescence from Tm3+/Er3+/Ce3+ triply doped bismuth-silicate glasses for S+C-bands amplifiers

Fluorescence of Tm3+/Er3+ codoped bismuth-silica (BS) glasses and the sensitization of Ce3+ are investigated. It shows that Ce3+ codoping with Tm3+/Er3+ in BS glasses results in a quenching of Tm3+ ion emission from F-3(4) to the H-3(6) level. Consequently, the 1.47 mu m emission occurs after the population inversion between the H-3(4) and F-3(4) levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum (FWHM) up to about 119nm, as it combines 1.55 mu m emission band of Er3+ with 1.47 mu m emission band of Tm3+ under 800nm excitation.

Optical spectroscopy and energy transfer of Er3+/Ce3+ in B2O3-doped bismuth-silicate glasses

Ce3+ and B2O3 are introduced into erbium-doped Bi2O3-SiO2 glass to enhance the luminescence emission and optic spectra characters of Er3+. The energy transfer from Er3+ to Ce3+ will obviously be improved with the phonon energy increasing by the addition of B2O3. Here, the nonradiative rate, the lifetime of the I-4(11/2) -> I-4(3/2) transition, and the emission intensity and bandwidth of the 1.5 mu m luminescence with the I-4(13/2) -> I-4(5/2) transition of Er3+ are discussed in detail. The results show that the optical parameters of Er3+ in this bismuth-borate-silicate glass are nearly as good as that in tellurite glass, and the physical properties are similar to those in silicate glass. With the Judd-Ofelt and nonradiative theory analyses, the multiphonon decay and phonon-assisted energy-transfer (PAT) rates are calculated for the Er3+/Ce3+ codoped glasses. For the PAT process, an optimum value of the glass phonon energy is obtained after B2O3 is introduced into the Er3+/Ce3+ codoped bismuth-silicate glasses, and it much improves the energy-transfer rate between Er3+ I-4(11/2)-I-4(13/2) and Ce3+ F-2(5/2) -> F-2(7/2), although there is an energy mismatch. (c) 2007 Optical Society of America.