Extrinsic Absorption Research Articles

NEAR-ULTRAVIOLET ABSORPTION, CHROMOSPHERIC ACTIVITY, AND STAR-PLANET INTERACTIONS IN THE WASP-12 SYSTEM

We observed the extreme close-in hot Jupiter system WASP-12 with HST. Near-UV transits up to three times deeper than the optical transit of WASP-12b reveal extensive diffuse gas, extending well beyond the Roche lobe. The distribution of absorbing gas varies between visits. The deepest NUV transits are at wavelength ranges with strong photospheric absorption, implying the absorbing gas may have temperature and composition similar to the stellar photosphere. Our spectra reveal significantly enhanced absorption (greater than 3 \sigma below the median) at ~200 wavelengths on each of two HST visits; 65 of these wavelengths are consistent between the two visits, using a strict criterion for velocity matching which excludes matches with velocity shifts exceeding ~20 km/s. Excess transit depths are robustly detected throughout the inner wings of the MgII resonance lines independently on both HST visits. We detected absorption in FeII 2586A, the heaviest species yet detected in an exoplanet transit. The MgII line cores have zero flux, emission cores exhibited by every other observed star of similar age and spectral type are conspicuously absent. WASP-12 probably produces normal MgII profiles, but the inner portions of these strong resonance lines are likely affected by extrinsic absorption. The required Mg+ column is an order of magnitude greater than expected from the ISM, though we cannot completely dismiss that possibility. A more plausible source of absorption is gas lost by WASP-12b. We show that planetary mass loss can produce the required column. Our Visit 2 NUV light curves show evidence for a stellar flare. We show that some of the possible transit detections in resonance lines of rare elements may be due instead to non-resonant transitions in common species. We present optical observations and update the transit ephemeris.

Characterization of afterglow-related spectroscopic effects in vacuum sintered Tb3+, Sr2+ co-doped Lu2O3 ceramics

Persistent luminescence phosphors, Tb3+, Sr2+ co-doped Lu2O3 ceramics were fabricated under vacuum at 1870°C. A strong green color afterglow could be observed after excitation with 254nm UV radiation. The afterglow was found to be roughly doubled in intensity upon stimulation with violet or blue-green photons (∼400–600nm) as well as upon IR radiation (∼800–980nm). Hence, the enhancement of the green afterglow could also be attained by means of natural sunlight. Short wavelength UV radiation was found to induce an extrinsic absorption band below about 600nm and extending into the deep UV. This was mirrored by a simultaneous decrease of the absorption by Tb3+ around 230–320nm. The extrinsic absorption seemed to contain at least two overlapping components which supposedly resulted from a band related to Tb4+/Tb3+-h and a feature resulting from F/F+ centers created upon irradiation with short UV. This absorption was shown to be reversible, as it disappeared after a short heat treatment at about 300°C as well as with continuous irradiation of ∼400nm radiation.

All-fiber chalcogenide-based mid-infrared supercontinuum source

An all-fiber based supercontinuum source with emission covering the wavelength range of 1.9–4.8μm is demonstrated. The laser source is based on a combination of silica commercial off-the shelf components and a chalcogenide-based nonlinear optical fiber. The system provides 10dB spectral flatness from 2.0 to 4.6μm, and −20dBm points from 1.9 to 4.8μm. The output power is 565mW but scalable by scaling the repetition rate. The limit on the long wavelength edge of the system is identified as an extrinsic absorption feature in the fiber used; confirming the system could be scaled to generated a broadband source even further in the infrared.

Electron-Deficient Pyrimidine Adopted in Porphyrin Sensitizers: A Theoretical Interpretation of π-Spacers Leading to Highly Efficient Photo-to-Electric Conversion Performances in Dye-Sensitized Solar Cells

A mass of porphyrin sensitizers have been designed and synthesized for dye-sensitized solar cells in previous works, and almost all of them incorporated an electron-rich system as the π-spacer. We here adopted the electron-deficient pyrimidine as an effective π-spacer and combined a cyanoacrylic acid anchoring group, as such a design yields a more bathochromic shift of the spectral absorption of the dye and results in an improved spectral overlap with the solar spectrum and an enhanced light-harvesting efficiency. The result does tally with the performance of sensitizer adsorbing on a semiconductor. From the electron density difference plots of electron transitions, we found that not all electron transitions could make for the effective electron transfer from donor to acceptor groups, which means the sensitizer performance in dye-sensitized solar cells not only relies on the extrinsic spectral absorption intensity but also depends on the intrinsic character of electron movement related to electron excitation. Moreover, the introduction of electron- deficient pyrimidine could affect the energy levels of excited molecules in solution, further affecting the kinds of electron transfer processes. We presented several novel porphyrin sensitizers for comparison on how the π-spacer and anchoring group influence the optical absorption, electron transfer processes, and regeneration of the oxidized dyes, thereby gaining potential dye-sensitized solar cells with highly efficient photo-to-electric conversion performances.

Structure–property correlations in the SiO2–PbO–Bi2O3 glasses

SiO2–PbO–Bi2O3 glasses having the composition of 35SiO2–xPbO–(65−x)Bi2O3 (where x = 5, 10, 15, 20, 25, 35, 45; in mol%) have been prepared using the conventional melting and annealing method. Density, molar volume and Vickers microhardness of the prepared glasses were measured. Infrared (IR) and UV–visible spectroscopic techniques were used for structural studies of these glasses. Density as well as the microhardness increase systematically and, conversely, the molar volume decreases with increasing the lead oxide content. This behavior can be explained by the correlation with the glass structure. Increasing the lead oxide content (≥20 mol%) increases the network former PbO4 groups which can play an important role in increasing the connectivity and compactness of the glass matrix via increasing the cross-linking with the other constituent silicate and bismuthate structural units. The increased compactness may explain, in turn, the increase of the density and microhardness. IR spectra reinforce the idea that bismuth participates in the glassy network predominantly as BiO6 octahedral structural units. UV–VIS optical absorption spectra revealed UV-charge transfer absorption bands related to the contribution of Pb2+ ions in the region 350–385 nm; in addition to the extrinsic absorption of trace iron impurities in the range 220–290 nm. In the visible region, three optical bands in the ranges 415–435, 605–650 and 880–890 nm were correlated with the contribution of electronic transitions in Bi3+ ions. Calculation of the optical mobility gap and the width of the energy tail of glass from the UV–VIS absorption indicated a slight increase followed by a decrease in their values. The behavior change occurred at the glass in which PbO content is 20 mol% where lead oxide starts to participate into the glassy matrix as a network former. The combination of analytical FTIR and UV–visible spectroscopy provided a consistent picture of structure–property relations in this glass system.

Synthesis and physical properties of glasses in the Sb 2O 3–PbCl 2–MoO 3 system

Lead chloroantimonite glasses form stable binary glasses that may accommodate numerous oxides or halides as a third component. Molybdenum trioxide is a glass progenitor leading to molybdate glasses. Ternary glasses have been synthesized and studied in the Sb 2O 3–PbCl 2–MoO 3 system. Compositional limits of glass formation are reported and two series of glass samples have been prepared corresponding to the general formulas: (90 − x)Sb 2O 3 –xPbCl 2 –10MoO 3 and (90 − x)Sb 2O 3 –xMoO 3 –10PbCl 2. Glass transition temperature is close to 290 °C at high Sb 2O 3 content and decreases as antimony oxide is substituted by MoO 3 or PbCl 2. Position, width and intensity of crystallization peak suggest that devitrification rate is small in some composition ranges. The evolution of density, thermal expansion, refractive index and microhardness has been studied as a function of composition parameter x. Deviations from linearity are observed. They suggest structural changes in the case of the MoO 3/Sb 2O 3 substitution while it appears that molar volume increases linearly versus lead content in the other series of glasses. Refractive index is close to 2.04. Optical transmission ranges from 550 nm in the visible spectrum to 5.5 μm in the infrared. It is limited by extrinsic absorption bands arising from hydroxyls and silicon impurities. Young's, bulk and shear moduli have been measured for the two series of samples.

First-principles calculations on electronic structures of Fe-vacancy-codoped TiO 2 anatase (1 0 1) surface

The electronic structures of Fe-doped TiO 2 anatase (1 0 1) surfaces have been investigated by all spin-polarized density functional theory (DFT) plane-wave pseudopotential method. The general gradient approximation (GGA)+U (Hubbard coefficient) method has been adopted to describe the exchange-correlation effects. Through the density functional calculations for the formation energies of various configurations, the complex of a substitutional Fe plus an O vacancy was found to form easily in the most range of O chemical potential. The calculated density of the states of the system of Fe-doped surface with a surface oxygen vacancy shows a band gap narrowing from 2.8 to 1.9 eV comparing with the pure surface due to the synergistic effects of surface Fe impurities with O vacancies. The system processes high visible light sensitivity and photocatalytic ability by decreasing extrinsic absorption energy. By comparing the partial DOS of some O and Ti atoms lying in the outermost and bottom layers of Fe-doped surfaces, it was found that the influence of Fe impurities on the electronic structure of the system is localized.

Intrinsic and extrinsic x-ray absorption effects in soft x-ray diffraction from the superstructure in magnetite

We studied the ($00\frac{1}{2}$) diffraction peak in the low-temperature phase of magnetite (${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) using resonant soft x-ray diffraction at the $\mathrm{Fe}\ensuremath{-}{L}_{2,3}$ and $\mathrm{O}\ensuremath{-}K$ resonances. We studied both molecular-beam-epitaxy grown thin films and in situ cleaved single crystals. From the comparison, we have been able to determine quantitatively the contribution of intrinsic absorption effects, thereby arriving at a consistent result for the ($00\frac{1}{2}$) diffraction peak spectrum. Our data also allow for the identification of extrinsic effects, e.g., for a detailed modeling of the spectra in case a dead surface layer is present that is only absorbing photons but does not contribute to the scattering signal.

Optical mapping study of blebbistatin-induced chaotic electrical activities in isolated rat atrium preparations

We have studied the spatiotemporal pattern of blebbistatin-induced anomalous electrical activities in isolated rat atrial preparations using the optical mapping of excitation spread. Atrial preparations including the right or left auricle were dissected from adult rat hearts. Each preparation was then stained with a fast merocyanine-rhodanine voltage-sensitive dye (NK2761). Using a multi-element (16 x 16) photodiode array, we assessed the spread of excitation optically by timing the initiation of the action potential-related extrinsic absorption changes. The contraction-related optical signals were suppressed by adding (S)-(-)-blebbistatin (10-100 miocroM) to the bathing solution. Blebbistatin had an effective delay time of about 1.5 h following its application, at which time anomalous electrical activities occurred. These took the form of triggered activities and rhythmical spontaneous excitations. We optically mapped the spatiotemporal patterns of the excitation spread during these anomalous electrical activities. When the triggered activities occurred, the site of ectopic focus, where the triggered action potential first appeared, and the area of excitation spread varied in every event. When the rhythmical spontaneous excitations occurred, the excitation spread from the anomalous pacemaker and, occasionally, their spatial shift was observed. In addition, the combination pattern of the spontaneous excitations and triggered activities was also observed. We suggest that these phenomena are due to the disturbed intracellular calcium dynamics induced by the application of blebbistatin.

A Compact Optical Fibre Based Mid- Infrared Sensor System for Detection of High Level Carbon Dioxide Emissions in Exhaust Automotive Applications

A highly compact optical fibre based sensor system for real-time measurement of CO2 gas emissions in modern automotive exhaust is reported. The sensing principle is based on extrinsic open-path absorption spectroscopy operating in the mid-infrared wavelength range. The sensing system which comprises of low cost and compact mid-infrared components is suitable for applications in the harsh environment of the vehicle exhaust system. It has been shown that the output of developed sensor system correlates closely with the commercial analyser in respond to high concentrations of CO2 gas. The sensor system also demonstrates minimal susceptibility to cross interferences of other gases present in the exhaust system.

Wavelength-dependent photostimulated adsorption of molecular O 2 and H 2 on second generation titania photocatalysts: The case of the visible-light-active N-doped TiO 2 system

The wavelength-dependence of photostimulated adsorption of O 2 and H 2 on visible-light-active N-doped TiO 2 has been examined in the intrinsic (λ < 387 nm) and in the N-doping induced extrinsic absorption range (λ > 387 nm). Rates of photoadsorption scaled linearly with photon flow ρ at 4 Pa at four selected wavelengths from 300 to 550 nm, but were independent of gas pressure and correspond to rates of photogeneration of surface-active centers. The spectral dependence of quantum yields Φ of surface photoprocesses displayed multi-band-like structural features in both the intrinsic and extrinsic regions ascribed to the existence of three (and perhaps four) different types of defect states, confirming the absorption edge red-shift in N-doped TiO 2 to be due to electronic excitation of intragap localized states that leads to the photogeneration of electrons and/or holes.

Optical Mapping Analysis of the Spatiotemporal Pattern of Experimental Tachyarrhythmia in Improved Isolated Rat Atrium Preparation

We have studied the experimental tachyarrhythmia in an improved isolated rat atrial preparation for the optical mapping of excitation spread. The atrial preparation, including the right or left auricle, was dissected from the adult rat heart, and an artificial hole was made in the center of the preparation. The preparation was then stained with a fast merocyanine-rhodanine voltage-sensitive dye (NK2761). Using a multi-element (16 x 16) photodiode array, the spread of excitation was assessed optically by timing the initiation of the action potential-related extrinsic absorption changes. In comparison with the intact isolated right atrial preparation, which we used previously, the mapping of the excitation spread was much easier and more precise because of the simple structure of the preparation. The electrical stimulation applied by a bipolar electrode evoked the sustained excitation with a fast rhythm, which we termed "experimental tachyarrhythmia" (ET). We optically mapped the spatiotemporal patterns of the spread of excitation during the initiation and the maintenance phases of ET. In most cases, a rotation of the excitatory wave around the artificial hole, i.e., a circus movement of the excitatory wave, was observed. These maps suggest that this circus movement resembles the basic mechanism of the tachycardia-like excitation observed in the intact isolated right atrial preparation. On the other hand, the appearance of an ectopic pacemaker with a fast rhythm was also observed. In some examples, two ectopic pacemakers appeared simultaneously. We consider that the experiment using the improved preparation is a superb in vitro model of atrial arrhythmia.

Low-temperature preparation of F-doped TiO 2 film and its photocatalytic activity under solar light

A novel and simple method for preparing F-doped anatase TiO 2 (defined as FTO) film with high photocatalytic activity was developed using titanium- n-butoxide and NH 4F as TiO 2 and fluorine precursors under mild condition, i.e. low temperature (lower than 373 K) and ambient pressure. The prepared samples were characterized by XRD, SEM, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectrum (DRS), photoluminescence spectrum (PL) and TG–DSC analysis. The photocatalytic activity was evaluated by decomposing X-3B under artificial solar light. The results showed that the crystallinity of TiO 2 was improved by F-doping. F − ions can prevent the grain growth, and the transformation of anatase to rutile phase was also inhibited. The doped fluorine atoms existed in two chemical forms, and the ones incorporated into TiO 2 lattice might take a positive role in photocatalysis. Compared with surface fluorination samples, FTO film exhibited better photocatalytic activity. The high photocatalytic activity of FTO may due to extrinsic absorption through the creation of oxygen vacancies rather than the excitation of the intrinsic absorption band of bulk TiO 2. Furthermore, the FTO can be recycled with little photocatalytic activity depression. Without any further treatment besides rinsing, after 6 recycle utilization, the photocatalytic activity of FTO film was still higher than 79%.

Photoinduced Coloration and Photobleaching of Titanium Dioxide in TiO2/Polymer Compositions upon UV- and Visible-Light Excitation of Color Centers' Absorption Bands: Direct Experimental Evidence Negating Band-Gap Narrowing in Anion-/Cation-Doped TiO2s

The present article examines the photocoloration of TiO2/polymer compositions with various polymers and the photobleaching of color centers at selected irradiation wavelengths from the UV region to the near-infrared region. Photoactivation of color centers was examined by irradiating into the absorption bands (ABs) with maxima at 2.90 eV (427 nm, AB1), 2.55 eV (486 nm, AB2), and 2.05 eV (604 nm, AB3). Two principal types of photostimulated absorbance changes were observed: (i) increases in absorbance and (ii) decreases in absorbance. The latter is a direct experimental manifestation of the photobleaching of colored TiO2/polymer compositions, which demonstrates the presence and photoinduced disappearance/destruction of color centers in these TiO2 systems. The spectral results also demonstrate that photobleaching of colored TiO2/polymer compositions originates from intrinsic absorption of light by the TiO2 (at hν > 3.2 eV) and also from extrinsic absorption of light by the color centers at wavelengths corresponding to their absorption spectral bands (i.e., at hν < 3.2 eV). These bands, therefore, are also active in the photodestruction of the color centers. A photochemical mechanism is proposed for the photobleaching process involving oxygen-assisted annihilation of oxygen vacancies. The unambiguous experimental data reported herein confirm an earlier proposal that the absorption of light by the various TiO2 systems in the visible region originates only from color centers and not from a narrowing of the band gap of pristine TiO2. Unlike the color centers, the valence and conduction bands, which some have suggested as being involved in the observed red shifts of the absorption edges in doped visible-light-active TiO2s because of an apparent narrowing of the band gap of TiO2, cannot be photodestroyed. The competitive photoinduced formation and destruction of color centers were modeled by simple considerations, the results of which are in qualitative agreement with experimental observations.

Temporal Evolution of Pair Attenuation Signatures in Gamma‐Ray Burst Spectra

The spectra obtained above 100 MeV by the EGRET experiment aboard the Compton Gamma-Ray Observatory for a handful of gamma-ray bursts has given no indication of any spectral attenuation that might preclude detection of bursts at higher energies. With the discovery of optical afterglows and counterparts to bursts in the last few years, enabling the determination of significant redshifts for these sources, it is anticipated that profound spectral attenuation will arise in the Gamma-Ray Large Area Space Telescope (GLAST) energy band of 30 MeV-300 GeV for many if not most bursts. This paper explores time-dependent expectations for burst spectral properties in the EGRET/GLAST band, focusing on how attenuation of photons by pair creation internal to the source generates distinctive spectral signatures. The energy of spectral breaks and the associated spectral indices provide valuable information that constrains the bulk Lorentz factor of the GRB outflow at a given time. Moreover, the distinct temporal behavior that is present for internal attenuation is easily distinguished from extrinsic absorption due to intervening cosmic background fields. These characteristics define palpable observational goals for both spaced-based hard gamma-ray experiments such as GLAST, and ground-based Cherenkov telescopes, and strongly impact the observability of bursts above 300 MeV.

Development in Laser Induced Extrinsic Absorption DamageMechanism of Dielectric Films

Absorption of host and the temperature-dependence of absorptioncoefficient have been considered in evaluating temperature distributionin films, when laser pulse irradiates on films. Absorption of dielectricmaterials experience three stages with the increase of temperature:multi-photon absorption; single photon absorption; metallic absorption.These different absorption mechanisms correspond to different band gapenergies of materials, which will decrease when the temperature ofmaterials increases. Evaluating results indicate that absorption of hostincreases rapidly when the laser pulse will be over. If absorption ofhost and the temperature-dependence of absorption are considered, themaximal temperatures in films will be increased by a factor of four.

Application of a “Black Body” Like Reactor for Measurements of Quantum Yields of Photochemical Reactions in Heterogeneous Systems

We report for the first time an experimental application of the concept of a "black body" like reactor to measure quantum yields (Phi) of photochemical reactions in liquid-solid heterogeneous systems. A major advantage of this new method is its simplicity since the fractions of reflected and transmitted light are negligible due to reactor geometry and high optical density of the heterogeneous systems. The average quantum yield of a test reaction (phenol photodegradation) over TiO(2) (Degussa P25) as determined by this method was 0.14, identical to the quantum yield measured earlier for this same reaction under similar conditions by Salinaro and Serpone. We also report the quantum yield of phenol photodegradation over N-doped TiO(2) during photoexcitation at the fundamental absorption band (lambda = 365 nm; Phi = 0.12) and at the N-doping induced extrinsic absorption band (lambda = 436 nm; Phi = 0.08) of the photocatalyst.

Photophysical Processes Related to Photoadsorption and Photocatalysis on Wide Band Gap Solids: A Review

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae Leading to a Fully Corrected Hubble Diagram tov&lt; 30,000 km s−1

Photometric (BVI) and redshift data corrected for streaming motions are compiled for 111 Branch-normal, four 1991T-like, seven 1991bg-like, and two unusual supernovae of Type Ia (SNe Ia). Color excesses E(B - V)host of normal SNe Ia, due to the absorption of the host galaxy, are derived by three independent methods, giving excellent agreement leading to the intrinsic colors at maximum of (B - V)00 = -0.024 ± 0.010 and (V - I)00 = -0.265 ± 0.016 if normalized to a common decline rate of Δm15 = 1.1. The strong correlation between redshift absolute magnitudes (based on an arbitrary Hubble constant of H0 = 60 km s-1 Mpc-1), corrected only for the extrinsic Galactic absorption, and the derived E(B - V)host color excesses leads to the well-determined yet abnormal absorption-to-reddening ratios of BVI = 3.65 ± 0.16, 2.65 ± 0.15, and 1.35 ± 0.21. Comparison with the canonical Galactic values of 4.1, 3.1, and 1.8 forces the conclusion that the law of interstellar absorption in the path length to the SN in the host galaxy is different from the local Galactic law, a result consistent with earlier conclusions by others. Improved correlations of the fully corrected absolute magnitudes (on the same arbitrary Hubble constant zero point) with host galaxy morphological type, decline rate, and intrinsic color are derived. We recover the result that SNe Ia in E/S0 galaxies are ~0.3 mag fainter than in spiral galaxies for possible reasons discussed in the text. The new decline rate corrections to absolute magnitudes are smaller than those by some authors for reasons explained in the text. The four spectroscopically peculiar 1991T-type SNe are significantly overluminous as compared to Branch-normal SNe Ia. The overluminosity of the seven 1999aa-like SNe is less pronounced. The seven 1991bg types in the sample constitute a separate class of SNe Ia, averaging in B 2 mag fainter than the normal Ia. New Hubble diagrams in B, V, and I are derived out to ~30,000 km s-1 using the fully corrected magnitudes and velocities, corrected for streaming motions. Nine solutions for the intercept magnitudes in these diagrams show extreme stability at the 0.02 mag level using various subsamples of the data for both low and high extinctions in the sample, proving the validity of the corrections for host galaxy absorption. We shall use the same precepts for fully correcting SN magnitudes for the luminosity recalibration of SNe Ia in the forthcoming final review of our Hubble Space Telescope Cepheid-SN experiment for the Hubble constant.

Photophysical processes related to photoadsorption and photocatalysis on wide band gap solids: A review

During the last two decades, various pathways describing photoexcitation of small molecules’ surface reactions at the wide band gap metal oxides and halides (Eg &gt; 3 eV) have been recognized. Photogeneration of excitons and free charge carriers may occur in bands of: i) fundamental absorption; ii) extrinsic and intrinsic defect absorption, including those related to surface states; and iii) in UV‐induced color centers. Considerable red shifts relative to the fundamental absorption threshold of wide band gap solids have been observed for the spectral limits of surface photoreactions induced in extrinsic absorption bands. This allows thinking about the wide band gap solids as a potential competitors for the relatively narrow band gap photocatalysts. This review discusses the concept of surface photoadsorption (photocatalytic) center while differentiating active and inactive states of the center. Electronically excited defect, surface self‐trapped or bound exciton, and the surface defect with trapped photo carrier are considered as the active states of photoadsorption (photocatalytic) centers of different types. The decay pathway of active state determines the lifetime of a photocatalytic center, and in this connection the Langmuir‐Hinshelwood kinetic approach is discussed.