Increase In Extinction Coefficient Research Articles

Scattering Effect of Iron Metallic Particles on the Extinction Coefficient of CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 Glasses

The extinction coefficient of the CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 glasses has been studied using a FT-IR and a UV-visible spectrometer in the range of 0.5-5 μm to investigate thermal radiation through glassy flux film during continuous casting of steels. In present investigations, iron oxide has been reduced to metallic iron droplets by reaction with graphite crucible during melting, which brings considerable increase of the extinction coefficient due to the scattering. To analyze the scattering effect of these droplets on the extinction coefficient, the number density and size parameter of metallic particles have been measured using an automated scanning electron microscope. The number of metallic particles is intensively proportional to boron contents due to the transition of molar structure, BO4 to BO3, with increasing boron oxide. It is found that calculated scattering coefficients based on Mie scattering theory are in good agreement with measured ones. As the increased scattering coefficient of glassy film would not cause any serious side effects on casting operations, utilization of scattering effects is believed to be significantly essential for the future design of commercial mold fluxes.

Methoxy supported, deep red emitting mono, bis and tris triphenylamine-isophorone based styryl colorants: Synthesis, photophysical properties, ICT, TICT emission and viscosity sensitivity

A novel strategy for the synthesis of triphenylamine based and methoxy supported deep red emitting push-pull chromophores is developed. The methoxy groups though not in conjugation with the acceptor exhibited a red shifted absorption and emissions (670 nm) as compared to the unsubstituted analogues due to the improved donating ability of triphenylamine. The dyes show high molar extinction coefficients (1, 65,800 M−1 cm−1) and as the number of withdrawing groups increases the molar extinction coefficient and emission intensity increase. Positive solvatochromism (96 nm) was observed which is well supported by linear and multi-linear regression. The mono styryl dyes showed enhancement of fluorescence while the di and tri-styryl dyes show quenching of fluorescence in polar solvents, which is correlated with the intramolecular charge transfer and twisted intramolecular charge transfer. Viscosity induced emission enhancement has also been observed. The experimental findings were correlated theoretically by using Density Functional theory computations.

Efficient and robust method for simultaneous reconstruction of the temperature distribution and radiative properties in absorbing, emitting, and scattering media

A rapid computational method called generalized sourced multi-flux method (GSMFM) was developed to simulate outgoing radiative intensities in arbitrary directions at the boundary surfaces of absorbing, emitting, and scattering media which were served as input for the inverse analysis. A hybrid least-square QR decomposition–stochastic particle swarm optimization (LSQR–SPSO) algorithm based on the forward GSMFM solution was developed to simultaneously reconstruct multi-dimensional temperature distribution and absorption and scattering coefficients of the cylindrical participating media. The retrieval results for axisymmetric temperature distribution and non-axisymmetric temperature distribution indicated that the temperature distribution and scattering and absorption coefficients could be retrieved accurately using the LSQR–SPSO algorithm even with noisy data. Moreover, the influences of extinction coefficient and scattering albedo on the accuracy of the estimation were investigated, and the results suggested that the reconstruction accuracy decreased with the increase of extinction coefficient and the scattering albedo. Finally, a non-contact measurement platform of flame temperature field based on the light field imaging was set up to validate the reconstruction model experimentally.

Effects of cloud and humidity on atmospheric extinction coefficient derived from visual range observations in Iranian major airports

ABSTRACTVisibility impairment, one of the restricting phenomena for aviation, results from light scattering and absorption. In this study, the historical visibility database for the period of 1981–2010 is used to obtain extinction coefficient according to the Koschmieder theory in the four busiest airports in Iran, including Tehran‐Mehrabad, Mashhad, Shiraz and Isfahan. The long‐term trend of extinction coefficient and its seasonal variations are investigated using 10th and 90th percentiles of extinction data to show the visual range in each airport. Correlation of the long‐term visibility trend with relative humidity (RH) and cloudiness is also examined. The comparison of seasonal mean extinctions shows the noticeable effect of local climate. The highest extinction coefficient value in each airport is seen during winter, while the lowest value occurs in summer. The seasonal mean extinction coefficient level in winter is about 0.1 km−1 higher than those of the other seasons. This is likely due to pollutants trapped by the stagnant cold air that partly obstruct visibility and increase the extinction in wintertime. There is not an outstanding variation of the tenth percentile of the extinction coefficient in the four airports. The low variation may relate to the definition of the upper threshold in visibility. Analysis shows that there is a positive correlation between extinction and humidity in all the airports that indicates the increase of scattering by hygroscopic particles with increasing humidity, such effect would be accentuated in high RH. The same result is seen for different percentages of cloudiness. To minimize the effects of humidity and cloudiness on the long‐term visibility trend, the days with the relative humidity values more than 70% and cloudiness of more than 5/8 of the sky are removed from the visibility trend analysis. The trends of the screened days are nearly parallel to the trends of raw data, but with a slight difference in each airport. The overall filtered long‐term trends show the increase of extinction coefficient at all the airports that emphasize the effect of pollution on the trend of light extinction within the whole period of this study. Eliminating the meteorological factors from the raw data does not change the overall increasing trend of extinction at Tehran and Isfahan airports. It suggests that the changes in air quality are responsible for the long‐term visibility degradation at these two stations that are located in the two most highly industrialized and polluted cities in Iran.

Assessment of satellite-based aerosol optical depth using continuous lidar observation

Due to a reliance on solar radiation, the aerosol optical depth (AOD) is observed only during the day by passive satellite-based instruments such as the MODerate resolution Imaging Spectroradiometer (MODIS). Research on urban air quality, atmospheric turbidity, and evolution of aerosols in the atmospheric boundary layer, however, requires 24-h measurement of aerosols. A lidar system is capable of detecting the vertical distribution of the aerosol extinction coefficient and calculating the AOD throughout the day, but routinely lidar observation is still quite limited and the results from MODIS and lidar sometimes are contradictory in China. In this study, long-term lidar observations from 2005 to 2009 over Hong Kong were analyzed with a focus on identification of the reasons for different seasonal variation in the AOD data obtained from MODIS and lidar. The lidar-retrieved AOD shows the lowest average level, but has the most significant diurnal variation during the summer. When considering only a 5-h period between 10:00 a.m. and 3:00 p.m. local time to match satellite passages, the average of the lidar-retrieved AOD doubles during the summer and exceeds that during the winter. This finding is consistent with the MODIS observation of a higher AOD during the summer and a lower AOD during the winter. The increase in the aerosol extinction coefficient in the upper level of the mixing layer makes the greatest contribution to the increase in the AOD at midday during the summer. These assessments suggest that large over-estimation may occur when long-term averages of AOD are estimated from passive satellite observations.

Synthesis and photophysical properties of a new BODIPY-based siloxane dye

A fluorescent dye comprising four BODIPY derivatives conjugated to a cyclotetrasiloxane core was synthesized by consecutive hydrosilylation and esterification reactions. Photophysical properties of the dye in various organic solvents were investigated. It was shown that due to a fourfold extinction coefficient increase and a moderate quantum yield decrease the brightness of the tetra-BODIPY dye in low-polarity solvents, calculated per molecule, increased 3 times when compared to mono-BODIPY. By contrast, in polar solvents there was a dramatic drop in brightness apparently associated with intramolecular interactions of the low-polar BODIPY chromophores.

Anthraphen: A Salphen‐Like Non‐Innocent Tetradentate Anthraquinone Imine Dye – Coordination and Electrochemistry

AbstractA new, highly redox‐active chromophore ligand, H2(anthraphen) (1), containing two o‐phenylenediamine‐linked anthraquinone imine units has been synthesized in a three‐step synthesis and fully characterized by X‐ray crystallography, UV/Vis spectroscopy, and cyclic voltammetry. The dark‐red dye 1 shows molar extinction coefficients of up to 47000 L mol–1 cm–1 and four reversible reduction processes. This dianionic N2O2 ligand, with a significantly extended π system, offers a salphen‐like binding cavity for metal coordination, as has been demonstrated by the synthesis of [K2(anthraphen)] (2) and the transition‐metal complexes of TiIV (3), VIV (4), FeII (5), FeIII (6), CoII (7), NiII (8), CuII (9), PdII (10), PtII (11), and ZnII (12). These metal chromophores have colors ranging from dark‐red, violet, green to black. Their optical and electrochemical properties were investigated and compared with those of the diprotic ligand. Coordination led to an increase in the molar extinction coefficients up to 66400 L mol–1 cm–1 in the case of [V(anthraphen)O] (4), broadening of the absorption bands in the visible‐light region as well as a redshift of the lowest‐energy absorption band. The lowest‐energy absorption observed for these complexes to date is for [Ni(anthraphen)] (8) at 784 nm. The metal chromophores exhibit up to five fully reversible oxidation and reduction processes.

Studies on phase change Ge15Se77Sb8 thin films by laser irradiation

Ge15Se77Sb8 chalcogenide thin films having thickness 300 nm were grown on glass/Si wafer by vacuum evaporation technique and induced by Transverse Electrical Excitation (TEA) laser for 10, 20 and 30 min. The synthesized Ge15Se77Sb8 chalcogenide exhibited the glassy as well as amorphous nature, as evidenced in differential scanning calorimetry measurements. TEA laser irradiation on Ge15Se77Sb8 thin films showed the polycrystalline nature while the as-prepared thin films were in amorphous nature. The optical band gap of as-prepared and laser irradiated films were determined by measuring the optical absorbance with photon energy. An increase in absorption coefficient and extinction coefficient was observed while the decrease in optical band gaps with laser irradiation time was demonstrated.

π-Extension of a 4-ethoxy-1,3-thiazole via aryl alkyne cross coupling: synthesis and exploration of the electronic structure

A series of four donor aryl alkynyl substituted thiazole derivatives 3a-d and three similar aryl donor-acceptor systems 6a-c have been synthesized. All compounds bear different electron-donating groups in the 5-position of the thiazole core. The influence of both electron donor strength and the additional phenylethynyl unit on photophysical properties, i.e. UV/Vis absorption, fluorescence emission and fluorescence lifetime, has been evaluated. Additionally, theoretical calculations have been performed at the CAM-B3LYP/6-31+G(d,p) level and good agreement with the experimental data has been achieved. The new derivatives synthesized via palladium catalyzed cross coupling are characterised by moderately strong emission between 474 and 538 nm (ΦF = 0.35-0.39) and Stokes' shifts ranging from 0.54 to 0.79 eV (4392-6351 cm(-1)). The smaller chromophores of type 6 exhibit modest to high fluorescence emission (ΦF = 0.45-0.76) between 470 and 529 nm and their Stokes' shifts range from 0.59 to 0.65 eV (4765-5251 cm(-1)).

Vertical structure and optical properties of Titan’s aerosols from radiance measurements made inside and outside the atmosphere

Prompted by the detection of stratospheric cloud layers by Cassini’s Composite Infrared Spectrometer (CIRS; see Anderson, C.M., Samuelson, R.E. [2011]. Icarus 212, 762–778), we have re-examined the observations made by the Descent Imager/Spectral Radiometer (DISR) in the atmosphere of Titan together with two constraints from measurements made outside the atmosphere. No evidence of thin layers (<1km) in the DISR image data sets is seen beyond the three previously reported layers at 21km, 11km, and 7km by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M.G. [2009]. Icarus 199, 442–448). On the other hand, there is evidence of a thicker layer centered at about 55km. A rise in radiance gradients in the Downward-Looking Visible Spectrometer (DLVS) data below 55km indicates an increase in the volume extinction coefficient near this altitude. To fit the geometric albedo measured from outside the atmosphere the decrease in the single scattering albedo of Titan’s aerosols at high altitudes, noted in earlier studies of DISR data, must continue to much higher altitudes. The altitude of Titan’s limb as a function of wavelength requires that the scale height of the aerosols decrease with altitude from the 65km value seen in the DISR observations below 140km to the 45km value at higher altitudes. We compared the variation of radiance with nadir angle observed in the DISR images to improve our aerosol model. Our new aerosol model fits the altitude and wavelength variations of the observations at small and intermediate nadir angles but not for large nadir angles, indicating an effect that is not reproduced by our radiative transfer model. The volume extinction profiles are modeled by continuous functions except near the enhancement level near 55km altitude. The wavelength dependence of the extinction optical depth is similar to earlier results at wavelengths from 500 to 700nm, but is smaller at shorter wavelengths and larger toward longer wavelengths. A Hapke-like model is used for the ground reflectivity, and the variation of the Hapke single scattering albedo with wavelength is given. Fits to the visible spectrometers looking upward and downward are achieved except in the methane bands longward of 720nm. This is possibly due to uncertainties in extrapolation of laboratory measurements from 1km-am paths to much longer paths at lower pressures. It could also be due to changes in the single scattering phase functions at low altitudes, which strongly affect the path length through methane that the photons travel. We demonstrate the effects on the model fits by varying each model parameter individually in order to illustrate the sensitivity of our determination of each model parameter.

Tuning the absorption of ultraviolet spectra and optical parameters of aluminum doped PVA based solid polymer composites

In this research work PVA:xAl (0.01 ≤ x ≤ 0.05) based solid polymer composites have been prepared by solution cast technique. The transmittances of the samples are decreased with increasing Al powder concentration. The absorption spectra of the samples are shifted to higher wavelengths which indicate their importance for shielding. The increase of absorption intensity in UV region was observed. The clear shift of absorption edge upon the addition of Al powder content indicated the decrease of energy band gap. The increase of extinction coefficient at high wavelengths for the samples containing Al powder revealed the loss of photon energy. The refractive indexes of the doped samples are increased compared to that of pure PVA. The linear relationship between the refractive index and volume fraction indicates a good dispersion of Al powder in PVA host polymer. The direct optical band gap measured from the plot of (αhυ)2 versus photon energy (hυ) showed a decreasing trend with increase of Al content. The Urbach energy was found to increase with increasing aluminum concentration. The complex optical dielectric functions were used to determine the type of electron transition.

Electronic and optical properties of O-doped MgF2: First-principles calculations and experiments

The electronic and optical properties of O-doped MgF2 are studied by first-principles calculations and experiments. As for the calculations, geometric structures, electronic structures and optical properties of O-doped MgF2 are systematically investigated using the first-principles calculations. The calculation results show that the band gap of MgF2 is narrowed by doping O, but with further increase of O level, the band gap changes a bit. Besides, both the refractive index and the extinction coefficient increase with the raise of O-doping level, and a new absorption peak can be found after doping. In term of experiments, magnetron sputtering deposited films are investigated by X-ray photoelectron spectroscopy and spectroscopic ellipsometer. The experimental results indicate that the MgF2 films with different O-doping levels have similar band gap values, while the film with larger amount of O possesses higher refractive index and extinction coefficient.

Heat generation and conduction in PDMS-carbon nanoparticle membranes irradiated with optical fibers

Carbon based materials have recently been used to fabricate highly photo-absorbing surfaces for heat generation purposes. In this report we present experimental measurements of the temperature increments ΔT in polymer (PDMS)-carbon nanopowder membranes irradiated by a light source via an optical fiber. In particular, we analyze experimentally the effects of the optical depth, τλ=βL, on the transient and steady state temperature profiles. In order to analyze the experimental data under the heat conduction theory, we also constructed a 2D axi-symmetric heat transfer solution for a semi-transparent finite membrane using Green's functions. With this approach we obtained two analytical expressions: one for the axial unsteady profile and another for the steady ΔT profile in the r−z plane using the delta function approximation. We found a linear relationship between the experimental ΔT steady values and the optical intensity Io; this linear relationship was maintained until incandescence at the membrane surface appeared. We also found that the steady ΔT values had little dependance on the membrane thickness L; conversely, the transient ΔT values exhibited a clear dependance on L, as expected. The theoretical solution fitted the experimental data only for a thermal diffusivity smaller than that of pristine PDMS. Our analysis suggests that such heat transfer retardation may be due to the nonlinear scattering behavior of the composite or due to additional interfacial resistances imposed by the experiment. Finally, experiments and theory showed that the L−ΔT curves have a maximum point (maximum temperature) at an optimal membrane thickness Lop; this optimal point in turn decreases as the extinction coefficient increases. Additional analysis of the results were also conducted regarding the area of the membranes, and both, experiments and theory, suggest that the heat generation induced by irradiating a surface with optical fibers is indeed highly localized.

Multi-thiophene-substituted NIR boron-dibenzopyrromethene dyes: synthesis and their spectral properties

Thiophene-substituted boron-dibenzopyrromethene dyes has been synthesized and characterized. We found that the optical properties of dithienyl-substituted dibenzo-BODIPYs depend on the substituted pattern. Namely, thiophene substitutions at the 5,5′-positions of the isoindole rings (5-2T) led to a bathochromic shift of 37 nm and an increase in the molar extinction coefficient (ε), whereas the replacement of the phenyl rings with thiophene rings at the 3,3′-positions (3-2T) resulted in a significant decrease of the ε value, despite a large bathochromic shift of 65 nm. The emission properties were also characterized; the replacement of phenyl units with thiophene units at the 3,3′-positions led to a larger Stokes shift than that of thiphene-free dibenzo-BODIPY 0T, which was rationalized to occur through geometry relaxation upon photoexcitation. Newly synthesized dendritic oligothiophene‒dibenzo-BODIPY conjugates have emitted near-infrared light at 766 nm when excited with UV light, through fluorescence resonance energy transfer (FRET) from the thiophene dendron unit to the dibenzo-BODIPY core.

Investigation of structural and optical properties of 100 MeV F7+ ion irradiated Ga10Se90-xAlx thin films

Present work focuses on the effect of swift heavy ion (SHI) irradiation of 100 MeV F7+ ions by varying the fluencies in the range of 1 × 1012 to 1 × 1013 ions/cm2 on the morphological, structural and optical properties of polycrystalline thin films of Ga10Se90-xAlx (x = 0, 5). Thin films of ~300 nm thickness were deposited on cleaned Al2O3 substrates by thermal evaporation technique. X-ray diffraction pattern of investigated thin films shows the crystallite growth occurs in hexagonal phase structure for Ga10Se90 and tetragonal phase structure for Ga10Se85Al5. The further structural analysis carried out by Raman spectroscopy and scanning electron microscopy verifies the defects or disorder of the investigated material increases after SHI irradiation. The optical parameters absorption coefficient (α), extinction coefficient (K), optical band gap (Eg) and Urbach’s energy (EU) are determined from optical absorption spectra data measured from spectrophotometry in the wavelength range 200–1100 nm. It was found that the values of absorption coefficient and extinction coefficient increase while the value of optical band gap decreases with the increase in ion fluence. This post irradiation change in the optical parameters was interpreted in terms of bond distribution model.

Visible‐Light‐Triggered Molecular Photoswitch Based on Reversible E/Z Isomerization of a 1,2‐Dicyanoethene Derivative

AbstractA designed bis(dithienyl) dicyanoethene‐based, strictly E/Z photoswitch (4TCE) operates through state‐selective (E and Z isomer) photoactivation with visible light. The E and Z isomers of 4TCE exhibit remarkably different spectroscopic characteristics, including a large separation (70 nm) in their absorption maxima (λmax) and a 2.5‐fold increase in molar extinction coefficient from cis to trans. The energetically stable trans form can be completely converted to the cis form within minutes when exposed to white light, whereas the reverse isomerization occurs readily upon irradiation by blue light (λ&lt;480 nm) or completely by thermal conversion at elevated temperatures. These features together with excellent thermal stability and photostability of both isomers make this new E/Z photoswitch a promising building block for photoswitchable materials that operate without the need for UV light.

Visible-light-triggered molecular photoswitch based on reversible E/Z isomerization of a 1,2-dicyanoethene derivative.

A designed bis(dithienyl) dicyanoethene-based, strictly E/Z photoswitch (4TCE) operates through state-selective (E and Z isomer) photoactivation with visible light. The E and Z isomers of 4TCE exhibit remarkably different spectroscopic characteristics, including a large separation (70 nm) in their absorption maxima (λ(max)) and a 2.5-fold increase in molar extinction coefficient from cis to trans. The energetically stable trans form can be completely converted to the cis form within minutes when exposed to white light, whereas the reverse isomerization occurs readily upon irradiation by blue light (λ<480 nm) or completely by thermal conversion at elevated temperatures. These features together with excellent thermal stability and photostability of both isomers make this new E/Z photoswitch a promising building block for photoswitchable materials that operate without the need for UV light.

Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Thin Films Prepared by Spray Pyrolysis Technique and Study the Annealing on its Optical Properties

Fe2O3 thin films that doped by NiO were obtained on glass substrates by the chemical spray pyrolysis technique, and annealed at 450 °C and 500 °C. The effect of annealing on optical properties was studied by recording the absorbance spectra using UV-Visible spectrophotometer. The refractive index decreases with increasing annealing temperature, such as an optical band gap that decreases from 2.68 eV before annealing to 2.58 eV after annealing of 500 °C. Absorption coefficient and extinction coefficient increase with increasing annealing temperature.

Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Thin Films Prepared by Spray Pyrolysis Technique and Study the Annealing on its Optical Properties

Fe2O3 thin films that doped by NiO were obtained on glass substrates by the chemical spray pyrolysis technique, and annealed at 450 °C and 500 °C. The effect of annealing on optical properties was studied by recording the absorbance spectra using UV-Visible spectrophotometer. The refractive index decreases with increasing annealing temperature, such as an optical band gap that decreases from 2.68 eV before annealing to 2.58 eV after annealing of 500 °C. Absorption coefficient and extinction coefficient increase with increasing annealing temperature.

Effect of thermal annealing on the structure and properties of plasma enhanced chemical vapor deposited SiCOH film

The development of high-performance integrated circuit chips and the shrinkage of feature sizes according to Moore’s law bring forward continuously the requirements for low dielectric constant (low-k) materials with various excellent properties in the back-end-of-the-line (BEOL) interconnect. Porous SiCOH films prepared by plasma enhanced chemical vapor deposition (PECVD) through a porogen approach are widely applied to industry and extensively studied. Thermal annealing is an important process for fabricating the porous low-k films, which has a great influence on film structure as well as properties. SiCOH films are deposited by PECVD using tetraethoxysilane and limonene as precursors, and annealed at 450 ℃ for 1.5 h under nitrogen atmosphere. The evolutions of film structure and properties during thermal annealing are revealed, and the reaction mechanism for structure change is also proposed. Fourier transform inferred spectroscopy and solid state nuclear magnetic resonance results show that the as-deposited film is an organic-inorganic hybrid film composed of various kinds of Si-O-Si, -CHx, Si-O-CH2CH3, etc. The organic component is removed almost completely during thermal annealing, making a porous film with a Si-O-Si inorganic skeleton. The skeleton is also rearranged at the same time. Deconvolution of the Si-O-Si absorption band of the FTIR spectrum reveals that the cage-like Si-O-Si occupies the major part for both as-deposited and annealed films, while the amount of silicon suboxide Si-O-Si decreases and that of network Si-O-Si increases during thermal annealing, making the film more robust. More C=C and Si-C are formed through chemical reactions between Si-H, -CHx and Si-O-CH2-CH3, and crosslinking is further enhanced. Nitrogen adsorption/desorption isothermal measurement reveals that a large number of micropores with diameter less than 2-3 nm are created during thermal annealing, which is consistent with the removal of organic groups and the existence of cage-like Si-O-Si. As a result, both the refractive index and dielectric constant decrease significantly from 1.476 (λ =630 nm) and 3.45 to 1.365 and 2.60, respectively. Because of the increase of C=C after annealing, extinction coefficient and leakage current density increase. Although there is a shrinkage of 14.7% in film thickness and a reduction of mechanical properties after annealing, the Young’s modulus is still larger than 4 GPa. Considering all kinds of properties, the obtained film appears to be a competitive candidate as inter layer dielectrics in the BEOL interconnect of integrated circuits.