Integrated Absorption Coefficient Research Articles

Evolution of sample optical pathlength during diffuse reflectance FT-IR analyses

In situ and operando diffuse reflectance FT-IR (DRIFTS) studies are often carried out over samples that may undergo changes in optical properties due to stronger absorptivity (darkening), for instance when coking or being reduced. The variation of IR optical pathlength of two Fe and Co-based Fischer-Tropsch catalysts treated at different temperatures was investigated through the use of an internal standard CaCO3 that was physically mixed with the catalyst. The CaCO3 overtone band at 1795 cm-1 was used, exhibiting an integral molar absorption coefficient ε = 2.68 × 105 cm mol-1. The IR penetration depth was negligible over the iron oxide sample once reduced above 400 °C, due to the formation of a strongly absorbing material. A reduction of the cobalt sample up to 350 °C revealed large changes of optical pathlength (dropping four-fold from 66 to 16 µm), likely related to the onset of cobalt oxide deep reduction. These data indicate that changes in optical pathlength should be considered when attempting quantitative DRIFTS analyses and that mixing a small concentration of CaCO3, e.g. 2 wt%, is a suitable way of doing so.

First principle study of optical and electronic response of Ca-based novel chalcopyrite compounds

A series of Ca-based novel chalcopyrite compounds have been studied by means of the full-potential linearized augmented plane wave method. In this work, we have used one of the utmost precise exchange and correlation functional of Tran-Blaha modified Becke Johnson (TB-mBJ) for the investigation of electronic as well as optical properties of Ca based chalcopyrite compounds namely, CaXY2 (X = Ge, Sn; Y = N, P, As). The computed energy bands and density of states reveals the semiconducting nature of all these studied compounds. The bandgap of CaXY2 (X = Ge, Sn; Y = N, P, As) compounds are found within the energy range 1.60–3.74 eV. The frequency dependent optical properties are investigated here, to understand the probable usage of these Ca-based chalcopyrite’s in optoelectronic applications. The imaginary dielectric tensors are presented and explained in terms of inter-band transitions. The integrated absorption coefficients are calculated to interpret the absorption spectra of all studied compounds.

Investigation of the optoelectronic properties of cubic metal halide perovskite compound RbSiCl3

Lead free halide metal perovskite compounds have been exploring more since last decades due to their wide potential applications as well as their environmental friendly nature. Presented work agreements with the density functional investigation of the material properties (optoelectronic) of lead free halide metal perovskite compound RbSiCl3 by using WIEN2k code that is rely on FP-LAPW: full potential-linearized augmented plane wave method. The optoelectronic response are well explored by the Perdew Burke Ernzergof GGA exchange correlation functional. The computed energy band gap of this compound is 0.96 eV and results reveal that it is direct band gap semiconductor material. In addition, the integrated absorption coefficient also computed through absorption spectra, which gives the value 123.39 (×104 eV/cm). All computation proves the utility of the compound for photovoltaic and optoelectronic applications.

Radiation stability of optical properties of Wollastonite powder with SiO2 nanoparticle addition

We studied the phase composition, diffuse reflectance spectra (ρλ), and integral absorption coefficient (аs) and their variations after a 30 keV electron irradiation of wollastonite powder with added silicon dioxide nanoparticles.It was found that after heating and nanoparticle addition, the reflectivity of wollastonite decreases in the UV and visible ranges, and increases in the near-IR range. The addition of 0.5 and 1 wt% SiO2 nanoparticles increases the radiation stability of the wollastonite powder by 255 and 233%, respectively.Such nanoparticle-micro powder systems can be used in high-performance spacecraft thermal control coatings and other applications where optical properties should be resistant to radiation.

Study of photobiosynthesis efficiency of Arthrospira (Spirulina) platensis batch culture

The dynamics of the integral coefficient of light absorption and photobiosynthesis efficiency of dense cultures of microalgae is researched. A batch cyanoprokaryotic culture of Arthrospira (Spirulina) platensis (Nordst.) Gomont was grown under light-limiting conditions. The choice of the light-limiting region is due to the low rates of photobiosynthesis, which, from a methodological point of view, simplifies the determination of the dynamics of biomass concentration and its main biochemical components. An express method for determining the concentration of chlorophyll a from true absorption spectra compensated for scattering is proposed. The production characteristics of culture were calculated (maximum specific growth rate – 0.02 h-1, productivity 0.17 g·l-1·d-1, percentage of Chl a – 1.5%). It is shown their relationship with the surface irradiation of the. It is revealed the dependence of the integral light absorption coefficient on the surface concentration of Chl a is described with high accuracy (R2 = 0.99) by the Bouguer-Lambert-Beer law. The specific absorption rate was 0.02 m2·mg-1, which is 2 times higher than that calculated for green algae. The efficiency of light energy utilization decreased at the exponential growth phase and stabilized at the linear one at the level of 4.9%. The obtained results can be used to predict the production of biologically valuable components in laboratory and semi-industrial conditions.

Dependence of Judd-Ofelt parameters on integrated absorption coefficient or cross-section of an individual transition of Er3+

Dependences of two factors on Judd-Ofelt (JO) intensity parameters Ω t (t = 2,4,6) have been studied theoretically by exemplifying the widely studied Er 3+ ion, which is doped into Gd 3 Ga 5 O 12 , LiNbO 3 and SrGdGa 3 O 7 bulk single-crystals and β-NaYF 4 powder. The two factors include 1) selection of induced electric-dipole transitions for JO calculation and 2) integrated absorption coefficient (IAC) or integrated absorption cross-section (IACS) of individual electric-dipole transition of Er 3+ . Absolute and relative root-mean-square methods were considered in the JO fits and consistent results were obtained. Ω t depends mainly on strong and medium-intensity transitions. These transitions must be all included in the fit. The exclusion of an individual transition from the fit leads to deviation of Ω t . From the matrix elements [ U (t) ] 2 values, it is possible to rate how the inclusion or not of a transition affects the Ω t . The study also shows that the Ω t changes almost linearly with the IAC or IACS of an individual transition, and the relevant linear slope may have a positive or negative sign, depending on the [ U (t) ] 2 value. Moreover, the larger the [ U (t) ] 2 value is, the larger the corresponding Ω t value is. In addition, the Ω 2 , Ω 4 and Ω 6 are dependent of each other because it is the summation ∑ t Ω t [ U ( t ) ] 2 instead of its component term Ω t [ U ( t ) ] 2 that has a linear relationship to the IAC or IACS.

Optical properties degradation of wollastonite powders under the electron irradiation in vacuum

The study on grain size distribution, phase composition, diffuse-reflectance spectra (ρλ), and integral absorption coefficient has been provided. In addition, the properties of wollastonite powders were examined after the irradiation with 30 keV electrons with recording ρλ spectra before and after each irradiation period in vacuum at the irradiation site (in situ). High powder reflectance has been determined, which provides a small value of absorption coefficient (аs = 0.11). It has been shown that optical properties degradation is determined mainly by UV radiation absorbing defects, the most probable among them being anionic vacancies. ρλ spectra are modified to a smaller extent while irradiating in the visible spectrum. The powder under analysis exceeds titanium dioxide powders, which are widely used as pigments for dyes and spacecraft reflective coatings, by the value of initial optical properties and their post-irradiation changes.

Coupled hydrogen and fluorine incorporation in garnet: New constraints from FTIR, ERDA, SIMS, and EPMA

Abstract It is well known that some garnet compositions can incorporate hydrogen and/or fluorine at levels up to several wt%. However, accurate measurement of these elements can be difficult at trace to minor concentration levels, so they are frequently ignored in routine chemical analysis. Furthermore, the mechanisms of H incorporation are still under debate, and only one mechanism for F substitution is commonly considered. We employed infrared spectroscopy (FTIR), elastic recoil detection analysis (ERDA), secondary ion mass spectrometry (SIMS), and electron probe microanalysis (EPMA) to measure H and F concentrations and constrain incorporation mechanisms in ten grossular garnets. We also present SIMS data for 11 spessartine and two andradite garnets. Three grossular garnets were measured with ERDA to obtain an infrared integral molar absorption coefficient (εi) for H2O of 13 470 L/(mol·cm2). Grossular H2O and F concentrations range from 0.017 to 0.133 wt% and 0.012 to 0.248 wt%, respectively. Correlations between 16OH and 19F and interpretation of FTIR spectra prompt us to consider various coupled substitutions of H and F for Si, which can explain some high-frequency IR absorption bands that have been attributed previously to “hydrogrossular clusters” (variably sized clusters in which 4H substitute for Si) or to inclusions of hydrous minerals. A strong correlation between 16OH and 19F in spessartine and similar high-frequency IR bands implies a similar role for H-F substitution. Coupled H-F substitution is also probably relevant to some andradite-rich garnets, rare pyrope from the Dora Maira massif, and some synthetic garnets. Improvements in analytical methods for trace to minor H and F open up more possibilities for using these elements to calculate the activities of H2O and F-species in fluids that were in equilibrium with garnet-bearing phase assemblages, as well as constraining the recycling of these elements into the mantle via study of xenoliths.

Effect of atmosphere on recovery of diffuse reflection spectra of ZnO powder modified with nanoparticles upon irradiation in vacuum

Abstract The changes of diffuse reflection spectra (ρλ) in the range 0.2–2.2 μm and the integral absorption coefficient of solar radiation (as) of ZnO powder modified with SiO2 nanoparticles were studied. These changes were recorded in vacuum at the site of irradiation of the samples (in situ) after irradiation (30 keV electrons, 5 keV protons, and solar spectrum quanta (SSQ)), as well as upon exposure the samples to the atmosphere. It was found that for all types of irradiation, a significant recovery of the ρλ spectra in the near-IR region in the atmosphere is recorded. The recovery is 1.5 times for the samples irradiated with electrons and solar spectrum quanta, and 1.1 times for the sample irradiated with protons. In the visible region, absorption is due to the intrinsic point defects of ZnO, the reflection coefficient is not only not restored in the atmosphere, but it even decreases (1–3%). Mechanism of formation of photo- and radiation defects under these types and parameters of irradiation is explained; the processes of restoration of the ρλ spectra of the modified ZnO powder are considered.

Structural, electronic and optical modeling of perovskite solar materials ASnX3 (A = Rb, K; X = Cl, Br): First principle investigations

In this paper, we present structural, electronic and optical response for inorganic lead-free tin halide perovskites ASnX3 (A = Rb, K; X = Cl, Br) compounds, to examine their possible utilization as future photovoltaic materials. The structural optimization, energy band structure, density of states and exhaustive optical spectra for these perovskite compounds are delved using the Tran-Blaha modified Becke-Johnson exchange and correlation potential as implemented in Wien2k code. Optical performance of the compounds is accomplished through the investigation of real & imaginary dielectric tensor components, optical absorption, reflectivity and refractivity spectra. Direct band gap for RbSnCl3 (RbSnBr3) and KSnCl3 (KSnBr3) compounds is obtained as 1.46 (0.98) eV and 1.48 (0.93) eV, respectively which lies within standard photo-voltaic range. Results obtained in present computations are in decent agreement with earlier reported data, which firmly endorse the accuracy of present calculations. In addition, band gap reduction is perceived while switching from X = ‘Cl’ to ‘Br’ which has also revealed the enhancement in integrated absorption coefficient. Promising electronic and optical properties obtained for these perovskite compounds affirms their potential utilization in photo-voltaic and other opto-electronic applications.

Effect of Al2O3 nanoparticle modification on increase in reflectivity of BaSO4 pigment

The effect of modification with Al2O3 nanoparticles (1–10 wt%) on the reflection spectra of BaSO4 powders in the range of 0.2–2.2 μm and integral absorption coefficient of solar radiation (as) was studied. With a lower reflectivity of Al2O3 nanoparticles in comparison with BaSO4 powder, its increase in the entire range of the solar spectrum in the modified powder was obtained. The modification efficiency, determined by the ratio of the absorption coefficient as of the unmodified and modified powders, is 1.77 times at the optimum concentration of nanoparticles equals 5 wt%. The determining factor of such increase was experimentally established – that is the change in the size and concentration of grains and granules of BaSO4 powder during modification. The obtained results were compared with the results of BaSO4 powder modification by SiO2 nanoparticles.The achieved effect is a significant result for spacecraft, in which BaSO4 powders can be used as a pigment for thermal control coatings of the “optical solar reflectors” class.

Linear absorption tomography with velocimetry (LATV) for multiparameter measurements in high-speed flows.

We present a linear model for absorption tomography with velocimetry (LATV) to reconstruct 2D distributions of partial pressure, temperature, and streamwise velocity in a high-speed flow. Synthetic measurements are generated by multi-beam tunable diode laser absorption spectroscopy (TDLAS). The measurement plane is tilted relative to the streamwise direction and absorbance spectra are Doppler-shifted by the gas flow. Reconstruction comprises two stages. First, the thermodynamic state is obtained by reconstructing two or more integrated absorption coefficients and evaluating local Boltzmann plots. Second, the velocity field is directly reconstructed from absorbance-weighted linecenters. Absorbance data are inferred by Voigt fitting and reconstructions are quickly computed by matrix-vector multiplication. Nonlinear parameter combinations, such as the mass flow, are more accurate when computed by LATV than estimates obtained by assuming uniform gas properties along each beam.

Synergistic effects in the change in optical properties of ZnO powder modified with SiO2 nanoparticles upon sequential irradiation with electrons and solar quanta

The change in the diffuse reflection spectra and the integral absorption coefficient of solar radiation after sequential irradiation with 30 keV electrons and solar spectrum quanta of the of ZnO powder modified by SiO2 nanoparticles were studied. It was established that irradiation with quanta of a wide energy range (0.5–6 eV) after electron exposure does not result in an anneal of the defects induced by electron irradiation – an increase in the intensity of the net absorption band, caused by intrinsic defects and free electrons, is recorded.

Synergistic Effects in a ZnO Powder-Based Coating Sequentially Irradiated with Protons, Electrons, and Solar Spectrum Quanta

The authors investigated the changes in diffuse reflectance spectra (ρλ) within 0.32–2.1 μm and integral absorption coefficient (as) of solar irradiation for a zinc oxide powder-based coating. The latter was consequently irradiated with protons (E = 3 keV, F ≤ 1 × 1016 cm−2), solar spectrum quanta (5 eq. of solar irradiation, 1 h), electrons (E = 30 keV, F = 1 × 1016 cm−2), and—repetitively—solar spectrum quanta (5 eq. of solar irradiation, 1 h). Following the irradiation procedure, the decrease in absorption coefficient varied from 0.044 to 0.036 and from 0.062 to 0.04, respectively. Additionally, it was shown that the solar spectrum quanta did not significantly affect the coating pre-irradiated with protons or electrons and did not change the value of induced absorption in the visible region (the latter being caused by the absorption of intrinsic point defects of the zinc oxide crystal lattice). The absorption coefficient degradation decreased under solar spectrum quanta irradiation, which was determined by the decrease in the concentration of free electrons that absorbed in the near-infrared (near-IR) region. ρλ spectra were measured in high vacuum in situ. A post-irradiation transfer of a coating into the atmosphere leads not only to the complete recovery of its reflectance, but also to partial translucence in comparison with the non-irradiated state.

Changing optical properties of ZnO powder upon separate and sequential irradiation by electrons and protons with an energy of 100 keV

The authors examined synergistic effects during sequential irradiation of zinc oxide powders by electrons and protons with an energy of 100 keV. Two modes were employed: 1) electrons followed by protons; 2) protons followed by electrons. It was found that the additive coefficient, when determined by the change in the integral absorption coefficient of solar radiation and calculated via diffuse reflectance spectra within 0.3–2.1 μm, depends on the irradiation mode and on the type of radiation-induced defects (i.e., intrinsic point defects or free electrons).

Theoretical analysis of Sn-doped ZnS for optoelectronic applications

The wide band gap semiconductors like ZnS have gained tremendous response in the optoelectronic applications claiming their significant role in device operability at varied compositions and temperature. We have performed a detailed study of pure and Sn doped ZnS using Perdew-Burkhe-Ernzerhof (PBE) exchange correlation as embodied in Wien2k code. The doping of 6.25% Sn at Zn site, in ZnS has reduced the band gap (Eg) to 1.70 eV from 2.15 eV (Eg for bulk ZnS) thus making it more suitable for the applications of solar cell. Various properties such as band structure, density of states and integrated absorption coefficient depicting their electronic and optical nature are examined. The spectra of absorption curve states the possibility of material to be solar if it lies in the visible spectra range of 0-5 eV.

FTS measurements of O2 collision-induced absorption in the 565–700 nm region using a high pressure gas absorption cell

The collision-induced absorption (CIA) spectra of oxygen and dry air have been measured in the near-infrared and visible regions, covering the O2(B) band at 687 nm and double transitions in the 630 nm and 577 nm regions. A custom-design 1 m path length high-pressure cell was developed and configured to a Bruker 125HR Fourier transform spectrometer at the Jet Propulsion Laboratory. A super-luminous Laser Driven Light Source (LDLS) was also used to improve the photon flux incident upon the spectrometer. A series of spectra of pure O2 and dry air were obtained at various high pressures up to 131 bars at room temperature. For the measurement of O2–O2 CIA in the B band region, the monomer resonance absorption contribution has been subtracted from the observed spectra by simulating the O2(B) band absorption with a speed-dependent Voigt line shape profile with line mixing effects taken into account. The remaining absorption component was regarded as the CIA in the region. The integrated absorption coefficient was measured to be 3.2(6) × 10−6 cm−2/Amagat2 for the O2(B) band region, which is significantly lower than literature values. For the two double transition bands in the 630 and 577 nm regions, the integrated CIA bands from the present work were measured to be 2.50(14) and 3.26(18) × 10−4 cm−2/Amagat2, respectively. The present measurements are significantly higher than prior measurements for the 630 nm band region, while they are slightly lower than prior measurements for the 577 nm band region. For dry air, the integrated CIA bands were measured to be 0.10(2) and 0.15(2) × 10−4 cm−2/Amagat2, respectively, for the 630 and 577 nm regions, no appreciable contribution from O2–N2 pairs was observed. The results are compiled in electronic supplements.

Aliphatic hydrocarbon content of interstellar dust

AbstractThe mid-IR spectrum of the interstellar medium contains both aromatic and aliphatic hydrocarbon features. These are generally attributed to carbonaceous dust. The aliphatic component is of particular interest because it produces a significant 3.4 μm absorption feature. The optical depth of this feature is related to the number and type of aliphatic carbon C–H bonds in the line of sight. It is possible to estimate the column density of aliphatic carbon from quantitative analysis of the 3.4 μm interstellar feature, providing that the absorption coefficient of interstellar aliphatic hydrocarbon is known. We produced interstellar dust analogues with spectra closely matching astronomical observations. Using a combination of FTIR and 13C NMR spectroscopy, we determined an integrated absorption coefficient of the aliphatic component. The results thus obtained permit direct calibration of astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the ISM.

Extinction spectra in the fundamental region of hexafluoroethane at different condensed phases

RAIR spectra of liquid and crystalline hexafluoroethane were recorded in the temperature range 100–200 K. The ν5 and ν10 reflection bands had been normalized and used to obtain their extinction profiles. New normalizing method outlined in this paper. The integral absorption coefficients had been determined at each phase and compared with literature data. The contours obtained have asymmetrical and broad profiles with enhanced low frequency branch (TO-branch). The structures of these contours were explained in framework of resonance dipole-dipole (RDD) interaction. The mathematical apparatus of spectral moments were used to describe profiles of the bands studied.

Absorption of light by a particulate monolayer: Effect of ordering, concentration, and size of particles

Absorption of light by a free standing monolayer of monodisperse crystalline silicon (c-Si) spherical particles is investigated using the quasicrystalline approximation (QCA) of the theory of multiple scattering of waves. The simulation results for the partially ordered monolayer and the highly ordered monolayer with imperfect triangular lattice are presented in the ranges of particle diameters from 0.05 µm to 1 µm, monolayer filling factors from 0.1 to 0.7, and wavelengths of incident light from 0.3 µm to 1.12 µm. The spatial pattern of a monolayer affects the absorption coefficient most strongly when the particle sizes are comparable with the wavelength. The spatial-order-induced peaks in the absorption spectra of a highly ordered monolayer are studied. The spectral absorption by such a monolayer can be more than 30 times greater than that of the partially ordered monolayer in the narrow wavelength intervals. The integrated over the terrestrial solar spectral irradiance “Global tilt” ASTM G173-03 absorption coefficient is analyzed. In the wavelength range of 0.3 µm ≤ λ ≤ 1.12 µm the integral absorption can be almost twice as large as that for the partially ordered monolayer. In the wavelength range of small absorption index of c-Si (0.8 µm ≤ λ ≤ 1.12 µm) the integral absorption coefficient of highly ordered monolayer can be more than 10 times greater than for the partially ordered monolayer.