2,741 research outputs found
Super-enhancement of 1.54 mu m emission from erbium codoped with oxygen in silicon-on-insulator
No full textWe acknowledge the European Research Council for financial support under the FP7 for the award of the ERC Advanced Investigator Grant SILAMPS 226470 and the Royal Society UK for the award of the 2015 Brian Mercer Award for Innovation
A comparison of the phenomena of photoluminescence and carrier-type reversal in Bi- and Pb-doped glasses
No full textWe present evidence connecting the phenomena of carrier type reversal and photoluminescence (PL), which are observed in certain Bi- and Pb-doped glasses. We also report PL from Bi- and Pb-implanted glass, and that the order of the reaction which generates optically active Bi centers varies significantly between different glass hosts.Comparing contour plots of PL spectra at various excitation wavelengths of Bi-doped chalcogenide, Bi-doped germanate and Pb-doped germanate glasses, indicates that five absorption/PL bands are in approximately the same position. This suggests that very similar active centers are present in Bi- and Pb-doped oxide and chalcogenide glasses. In 4% and 10% PbO doped germanate glass, one and two crystallization temperatures, respectively, can be observed. This could be seen as being analogous to the phase separation observed in Bi-doped GeS glasses displaying carrier-type reversal when the Bi content is increased past 11 mol%. When excited at 782 nm, Bi- and Pb- implanted gallium-lanthanum-sulphide-oxide (GaLaSO) glass thin films display PL bands centered at 820 nm and 860 nm, respectively. The intensity (I) of the 820 nm PL band has a power law dependence on Bi dose (d) of d1.4; a similar power-law dependence occurs in a Bi melt-doped oxide glass. When excited at 514 nm, Bi-implanted GaLaSO thin films display a PL band at 700 nm, which is not present in a Bi melt-doped chalcogenide glass having a similar composition to the implanted glass. This indicates that new Bi centers are formed through implantation, which are absent in the melt-doped glasses. This has important implications for Bi-doped glass lasers, in which the control of Bi centers is critical for improving performance. We report Bi-related red PL bands in Bi-implanted bulk Ge33S67 and Ga5Ge25S70 glasses, and NIR PL bands in Ge23Ga12S64Bi1 glass; all of which have very similar compositions to those in which carrier-type reversal has been observed. This indicates that Bi-related PL and carrier-type reversal may be caused by the same Bi centers.We determined the reaction order for the generation of Bi centers in various oxide glass hosts by extracting absorption data from previously published work, and measuring the gradient (equivalent to the power-law factor) of a double-logarithmic plot of Bi-related absorption coefficient against Bi2O3 doping concentration. The reaction order in Bi-doped oxide glasses decreased with increasing optical basicity of the glass host. A sequential redox reaction involving the decomposition of Bi2O3 into BiO, then Bin clusters, can explain a reaction order dependence on optical basicity. We suggest that red and NIR PL bands result from Bi2+ and Bin clusters, respectively, and these centers are also related to carrier type reversal
Optical and electronic properties of bismuth-implanted glasses
No full textPhotoluminescence (PL) and excitation spectra of Bi melt doped oxide and chalcogenide glasses are very similar, indicating the same Bi center is present. When implanted with Bi, chalcogenide, phosphate and silica glass, and BaF2 crystal all display characteristically different PL spectra to when Bi is incorporated by melt-doping. This indicates that ion implantation is able to generate Bi centers which are not present in samples whose dopants are introduced during melting. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi2+ and Bi clusters
Optical filters utilizing ion implanted Bragg gratings in SOI waveguides
No full textThe refractive index modulation associated with the implantation of oxygen or silicon into waveguides formed in silicon-on-insulator (SOI) has been investigated to determine the feasibility of producing planar, implantation induced Bragg grating optical filters. A two-dimensional coupled mode theory-based simulation suggests that relatively short grating lengths, on the order of a thousand microns, can exhibit sufficient wavelength suppression, of >10 dB, using the implantation technique. Fabricated planar implanted slab-guided SOI waveguides demonstrated an extinction of -10 dB for TE modes and -6 dB for TM modes for the case of oxygen implantation. Extinctions of -5dB and -2 dB have been demonstrated with silicon implantation
R.M. Simmons presentation, Rena Smart book review
No full textR.M. Simmons of the Gospel Music Workshop of America gives a presentation on the African influence in the African American religious experience. He explains how African slaves brought to America their concept of music (utilitarian concept of music). Simmons further discusses the fusion between the utilitarian concept and the Western concept of religion resulting in spirituals. He also describes hymn categories in early forms of formal African American worship experiences. Simmons takes questions from the audience among which is Dr. Riggins Earl Jr. Video concludes with a book review on Christian Theology and Ethics by Rena Smart.The Atlanta University Center Robert W. Woodruff Library acknowledges the generous support of the National Endowment for Humanities - Humanities Collections and Reference Resources Implementation Project Grant in supporting the processing and digitization of a number of its major archival collections as part of the project: Spreading the Word: Expanding Access to African American Religious Archival Collections at the Atlanta University Center Robert W. Woodruff Library.</em
Non-equilibrium doping of amorphous chalcogenides
No full textThe doping of amorphous chalcogenides to control their electronic properties, and specifically change the dominant charge carrier type from holes to electrons, has been a major research challenge for many years. Generally attempts to achieve this through doping during the glass forming phase have been frustrated by autocompensation effects mediated via charged defects resulting in Fermi level pinning. To date progress in this area has remained limited to Bi and Pb-doped GeX (X = S, Se, Te) systems where high doping levels (6-11%) have shown carrier type reversal (CTR) from p-type to n-type.We have readdressed the issue of CTR in amorphous chalcogenides by exploring the concept of non-equilibrium doping, corresponding to the introduction of dopants into the glass matrix following the formation of the network. To achieve this we utilize ion-implantation thereby enabling doping with a wide choice of ion species into any solid chalcogenide system. A number of amorphous chalcogenides systems have been studied including GeX, Ge2Sb2Te5 and GaLaS-based glasses deposited onto substrates via sputtering to form thin films. The structural, electrical and optical properties of the doped systems have been studied in detail revealing their significant modification and aiding understanding of the effect of non-equilibrium doping on these various systems. In particular a series of fabricated chalcogenide/n(p)-type Si devices enable detailed examination of the role of trap states in determining the electrical properties.We demonstrate the success of our non-equilibrium doping approach through achieving CTR in the GeX systems as lower doping concentrations than previously shown possible using conventional approaches. Furthermore, we demonstrate CTR for the first time in a non-GeX system, demonstrating the fabrication of pn-junction devices which are characterized for their electronic and optical behavior
Velocity-Gradient Probability Distribution Functions in a Lagrangian Model of Turbulence
No full textThe Recent Fluid Deformation Closure (RFDC) model of lagrangian turbulence is recast in path-integral language within the framework of the Martin-Siggia-Rose functional formalism. In order to derive analytical expressions for the velocity-gradient probability distribution functions (vgPDFs), we carry out noise renormalization in the low-frequency regime and find approximate extrema for the Martin-Siggia-Rose effective action. We verify, with the help of Monte Carlo simulations, that the vgPDFs so obtained yield a close description of the single-point statistical features implied by the original RFDC stochastic differential equations
Former UD classmates (1908) meet
No full textThis is a negative of former UD classmates (1908), who met in Albany, New York, when Colonel Stuart R. Carswell (left) retired and Colonel Mark R.M. Gwilliam (right) took command of District No. 2. They smile at each other as they shake hands. They are standing in an office with an organizational chart hanging on the wall behind them. An American flag stands in the left-hand corner
Former UD classmates (1908) meet
No full textThis is a negative of former UD classmates (1908), who met in Albany, New York, when Colonel Stuart R. Carswell (left) retired and Colonel Mark R.M. Gwilliam (right) took command of District No. 2. They smile at each other as they shake hands. They are standing in an office with an organizational chart hanging on the wall behind them. An American flag stands in the left-hand corner
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