Measured Absorption Spectra Research Articles

Development of new gas analytical technique for infrared spectroscopy combined with differential pressure measurements.

A new gas analytical technique for infrared laser spectroscopy combined with differential pressure measurement (IR-DP) is developed. The basic idea of this technique is that the absorption process of molecules by laser irradiation is monitored as the pressure enhancement in a gas cell by use of a differential pressure gauge. The system is composed of a tunable IR laser system, sample cell, differential pressure gauge, and data accumulation system. Using this system, the measurements of the IR absorption spectra for cyclohexane (50 ppm) and ammonia (100 ppm) are demonstrated. By comparison of the current IR-DP spectra with conventional Fourier-transform infrared spectra, the spectral resolution is found to be about 3cm-1, reflecting the laser resolution. Furthermore, the estimated pressure enhancement based on a simple model is consistent with the experimental results. These results suggest that the newly developed IR-DP technique is one of a powerful tool for trace gas detection.

Influence of GeO2/TeO2 ratio on thermal, structure and spectroscopic properties of Dy3+-doped tellurite-germanate glass

Dy2O3-doped tellurite-germanate glasses with an increase of GeO2/TeO2 ratio (TGZ) were synthesized and characterized through X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman, absorption, and emission spectra measurements. XRD spectra of Dy3+-doped TGZ glass confirmed the amorphous structure. The TGZ glass possess the higher anti-crystallization abilities than that of the pure tellurite glass. Raman spectroscopy showed that the amount of [TeO3] and [TeO3+1] units in the glass network were gradually decreased by increasing the ratio of GeO2 to TeO2. The result was further supported by the optical band gap energy of the TGZ glass. The luminescence intensity of the sample increased with an increase in GeO2 content and reached a maximum value at 10 mol%. The chromaticity coordinates of CIE 1931 were in the warm white light range, and the corresponding color temperature range was 3400 K–3600 K. The results showed that the addition of GeO2 to Dy3+-doped tellurite glass can improve the thermal stability and luminescence performance of the white light-emitting band.

Fabry-Perot Effect Suppression in Gas Cells Used in THz Absorption Spectrometers. Experimental Verification.

A standard measuring gas cell used in absorption spectrometers is a cylinder enclosed by two transparent windows. The Fabry-Perot effects caused by multiple reflections of terahertz waves between these windows produce significant variations in the transmitted radiation intensity. Therefore, the Fabry-Perot effects should be taken into account to correctly measure absorption spectra in Bouguer law-based absorption spectroscopy. One approach to reducing the Fabry-Perot effects is based on inserting an additional external movable window with the standard measuring gas cell. This was proposed and numerically analyzed in our previous work. This paper is aimed at the experimental validation of this method when using amplitude modulation (AM) spectroscopy. Also, a comparison of the efficiency of reducing the Fabry-Perot effects using this method is experimentally compared to frequency modulation spectroscopy. The latter was shown to effectively reduce the Fabry-Perot effects compared to AM spectroscopy with the standard measuring gas cell, and the use of the external movable window was shown to further improve the elimination of Fabry-Perot effects.

Thermal, Optical, and Emission Traits of SM3+-Ion-Doped Fluoride/Chloride/Oxide Glass for Red/Orange Laser Fiber Applications

This study examined spectroscopic, thermal, and other qualities, such as the lasing parameters, of Sm3+-doped glass with the composition 40P2O5–30ZnO–20LiCl–10BaF2. The ellipsometric data were used in a Sellmeier dispersion relation to estimate the refractive index values of the glasses investigated. The measured absorption spectra of the doped glass reveal the presence of various absorption bands assigned to transitions from the 6H5/2 ground state attributed to Sm3+-ion-excited states. We studied the decay of the 4G5/2 level of the Sm3+ ions in the doped glass by analyzing its absorption and emission fluorescence spectra. The Judd–Ofelt hypothesis allowed us to determine that the quantum efficiency of the 4G5/2–6H7/2 transition is high: 96% and 97% for glass doped with 4.05 × 1019 ions/cm−3 and 11 × 1019 ions/cm−3, respectively. Furthermore, this glass exhibits efficient red/orange enhanced spontaneous emission that matches the excitation band of the photosensitizer material used in medical applications.

Ensuring the stability of spectrophotometric measurement results during analysis of mixtures composition

Spectrophotometric methods for studying the composition of mixtures are considered. The need to increase the stability and accuracy of the results of spectrophotometric measurements when analyzing substances with low absorption coefficients or a low concentration of the determined substance is shown. A spectrophotometric complex with a thermostated cell is described, which enables to study gaseous and liquid mixtures. Results of study at this complex of absorption spectra of isomers of liquid xylene and their mixtures are given. Methods of increasing the stability of spectrophotometric measurement results, hardware and data processing methods necessary for this are considered. It has been shown that thermostating of not only vaporous, but also liquid samples is one of the necessary conditions for ensuring the stability of measurement results. The procedure for performing experiments and processing the results of spectrophotometric measurements is presented. A differential method has been developed to reduce the impact of spectrophotometer signal instabilities on the accuracy of determining the composition of mixtures. The method consists in using as input data for multiple linear regression not the absorption spectrum, but its wavelength derivative. An analysis of the composition of mixtures of two xylene isomers showed that the use of this method can reduce RMS of determining the composition of mixtures by about 1.6 times. It is noted that additional filtering (smoothing) of the measured absorption spectrum derivative may be required to reduce errors in determining the composition of mixtures. The developed method of reducing the influence of the spectrophotometer signal instabilities on the results of the mixture composition analysis is of the greatest interest for the analysis of substances with low absorption coefficients or in the case of low concentrations of the studied substances and can be used to solve environmental monitoring problems, for example, when determining hydrocarbon contaminants in the atmosphere.

Facilitating Absorption Spectroscopy of Strongly Absorbing Fluids: A High-Throughput Approach.

Measuring absorption spectra of strongly absorbing solutions is usually only possible by diluting the solution. However, the absorption spectra can be heavily influenced by concentration-dependent interactions, so dilution leads to misleading results. To enable reliable absorption measurements of concentrated solutions, we introduce in this work thinning fluid film spectroscopy (TFFS), a simple and highly automatable method. We present three exemplary measurement modes of TFFS suitable for many different applications and validate the TFFS measurements with control data obtained in specialized, low optical path length cuvettes. Additionally, we compare the suitability of the different measurement modes over a broad concentration range and demonstrate the automation possibilities with a spectroscopy robot. Beyond this automated approach for highly efficient and high-throughput lab work, we also show the possibility of direct integration into production systems with an in-line setup, which can be incorporated into a variety of pipe systems. The TFFS method is not limited to samples from material science but can be transferred to a broad variety of research and industry fields, including proteins, food, and pharmaceuticals or also agriculture and forensics.

Temperature Changes in Luminescence of Mixed Complexes of Terbium and Samarium with Organic Ligands Based on 2,2-bipyridyldicarboxamides

Solutions in acetonitrile of three mixed complexes of rare earth elements (terbium and samarium) with organic ligands with various pyridine substituents were studied in this work. The ratios of ligands and metals in the resulting complexes were determined, and the stability constants of samarium complexes were calculated using the spectrophotometric titration method. Measurements of absorption, emission and excitation spectra of luminescence, luminescence kinetics of solutions of mixed complexes of rare earth elements with an excess of metal relative to the ligand were carried out at various temperatures in the range 298–328 K. An increase of luminescence intensity of a samarium ion in complex upon heating has been discovered for the first time. The dependences of the luminescence quantum yield and lifetime of mixed complexes on temperature were obtained. A thermometric parameter — the ratio of the integral luminescence intensities of samarium and terbium ions — was proposed, and the temperature sensitivity coefficient of this parameter was determined for different complexes.

Sound absorbers from walnut shell waste: measurement and models

Waste walnut shells have been cleaned, dried, chopped, glued, pressed, and molded to form porous cylinders for measurement of normal incidence sound absorption coefficient spectra in an impedance tube. Porosities and flow resistivities have been measured non-acoustically. Field Emission Scanning Electron Microscopy images, used to obtain fragment size for determining shell density, reveal that the fragment surfaces are rough, which may influence acoustical performance. Measured absorption spectra have been compared with predictions of two analytical models for acoustical properties of rigid porous media, which assume microstructures of identical uniform parallel slanted slits (SS) and non-uniform cylindrical pores with a log normal radius distribution (NUPSD) respectively. Measured values of flow resistivity and porosity are used in the models but tortuosity is adjusted to give best agreement with the quarter wavelength resonance in the measured absorption coefficient spectra. Predictions agree best with data for samples made from the smallest shell fragments. These samples have the highest values of tortuosity, flow resistivity and offer good absorption at speech frequencies which suggests that recyclable and sustainable sound absorbers made from walnut shell wastes could be useful for controlling indoor reverberation..

Broadened and enhanced MIR emission in Yb3+/Er3+/Dy3+ triply-doped CaYAlO4 crystal

Yb3+/Er3+/Dy3+ triply-doped CaYAlO4 single crystal was successfully grown to obtain the broadened and enhanced 3 μm MIR emission. The structure characters were studied by XRD measurement. The optical properties and energy transfer mechanism between Yb3+, Er3+, and Dy3+ were investigated according to the measured absorption spectra, emission spectra, and fluorescence decay curves. The absorption spectra show that the triply-doped crystal could be effective pumped by 980 nm due to the introduced of Yb3+ and Er3+. In comparison with Dy3+ singly-doped CaYAlO4 crystal, a broadened and enhanced ∼3 μm MIR emission with a full width at half maximum (FWHM) of 286 nm was obtained due to the fact that there exists effective energy transfer process from Yb3+ and Er3+ to Dy3+. For Yb3+, it serves as an effective sensitized ion. For Er3+, it could be not only used as an effective sensitized ion, but also as a 2.7 μm MIR emission center. For Dy3+, it serves as a deactivating ion to solve the self-termination “bottleneck” effect of Er3+, and more importantly, as an emission center to achieve 3 μm emission. The comprehensive effect is to obtain enhanced and broadened MIR emission in the triply-doped crystal. In addition, the corresponding energy transfer efficiency from Yb3+: 2F5/2 to Dy3+: 6H5/2 is as high as 90 %. Hence, the Yb3+/Er3+/Dy3+: CaYAlO4 crystal could be used as promising medium for MIR broadband tunable laser applications.

Modeling and optimizing a broadband sound absorber consisting of a granular activated carbon stack backed by a poro-elastic layer

High surface area particles, like granular activated carbon (GAC), have shown advantages in absorbing low-frequency sound, both by themselves and when combined with other treatments. In this article, a novel sound absorption treatment is described: i.e., a GAC stack supported by a soft, porous layer. At first, it was experimentally observed from impedance tube measurements that the low-frequency absorption performance of GAC stacks can be significantly enhanced by inserting a melamine foam between the stack and a rigid backing. To enable an analytical model of this type of absorber, the interfaces between GAC stacks and other materials were first characterized. Further, both 1-D layered transfer-matrix and 2-D axi-symmetric finite-difference approaches were implemented to predict the measured absorption spectra. Because of the constraint of the stack at the impedance tube wall, the 2-D model leads to more accurate absorption spectrum predictions. However, the difference between the two model predictions becomes negligible for large-area treatments. Therefore, amore efficient 1-D theory was incorporated in the multi-objective optimization to design broadband GAC-foam absorbers. Two optimization objectives were defined to balance the overall absorption performance: i.e., one associated with absorption at low frequencies, and the other with absorption at higher frequencies. It was found that a minimum thickness broadband GAC-foam absorber favors a thin, soft foam. In conclusion, this article presented a framework for the development of general broadband sound absorbers, and by combining both granular and porous materials, it may be possible to design practical sound-absorbing metamaterials that perform well at low frequencies.

Multi-component Freon gas detection based on infrared tunable Fabry-Perot detector

A multi-component Freon gas sensing system was developed based on the non-dispersive infrared (NDIR) spectroscopy, which had the advantages of simple structure and low cost. This system mainly consisted of a broadband infrared light source, a tunable Fabry-Perot (FP) detector and a small brass absorption cell. In order to improve the utilization rate of infrared light source, the absorption cell was optimized. H1301, R134a and R410A were simultaneously detected through the measurement of gas absorption spectrum. The spectral range of the FP detector was from 8.0 to 10.5 μm, and the entire spectrum was recorded by wavelength scanning. The area of measured absorbance was directly proportional to the concentration of the target gas, which was used to calibrate the sensing system. The temperature and frequency response characteristics of the system were tested. The experimental results showed that the higher the temperature, the lower the responsiveness. In addition, the system had the best signal-to-noise ratio (SNR) at 10 Hz. The minimum detection limits of H1301, R134a and R410A were achieved to be 2.5 ppm, 5.3 ppm and 4.8 ppm, respectively. The cross-interference among the gases was suppressed by using BP neural network.

Manipulation and applications of ultrafast all-optical switching based on transient absorption and dispersion in KTN crystals.

Potassium tantalate niobate (KTN) represents a noteworthy category of optical crystals known for their superior nonlinear optical properties. In this study, we conducted measurements of femtosecond time-resolved transient absorption (TA) spectra in KTa0.57Nb0.43O3 crystals. Notably, a rapid and pronounced "plateau" phase, ∼1.5 ps in duration, was detected at the onset of the TA kinetics and succeeded by two distinct decay components, exhibiting lifetimes of ∼140 ps and over 10 ns, respectively. We attribute these observations to a decay process involving two-photon absorption, dispersion characteristics, and excited state absorption. Based on this unique TA characteristic of KTN crystals, an all-optical switching strategy was proposed and utilized to measure the ultrafast lasing dynamics of single-crystal CH3NH3PbBr3 nanowires. This polarization-independent TA gate approach offers an adjustable gate width combining ps and ns time scales and introduces a versatile tool for advanced optical applications.

Terahertz Frequency-Domain Spectroscopy with a Method for Suppressing Water Vapor Absorption Peaks for Analysis of Pharmaceutical Hydrate Samples

Measurements of terahertz absorption spectra of pharmaceutical hydrate samples are achieved under a normal humidity condition by combining terahertz frequency-domain spectroscopy with a newly proposed method for suppressing absorption peaks caused by water vapor. In this method, only simple mathematical operations such as subtraction, thresholding, interpolation, and smoothing are applied to extinction (or absorbance) data obtained by locating samples under a normal humidity condition. By considering the difference in spectral line width between narrow absorption peaks caused by water vapor and the relatively wide absorption peaks caused by active pharmaceutical ingredients (APIs) in solid forms, the absorption peaks caused by water vapor can be effectively suppressed without affecting the absorption peaks of the APIs in the samples. In the present study, levofloxacin hydrates were used as samples to investigate the performance of the proposed method. Spectra were obtained under both dry and normal humidity conditions. The temperature of the samples was raised from 300 to 363 K to dehydrate them and brought back to 313 K to observe hydration under the normal humidity condition. Spectra obtained under the normal humidity condition were processed with the proposed method. The spectra of the hydrates obtained under the dry condition were slightly different from those obtained under the normal humidity condition and processed by our method. Dehydration during the measurements under the dry condition was suggested. Stable and reliable results are expected by measuring spectra under normal humidity conditions and applying the proposed method to suppress absorption peaks by water vapor.

VUV absorption spectra of water and nitrous oxide by a double-duty differentially pumped gas filter.

The differentially pumped rare-gas filter at the end of the VUV beamline of the Swiss Light Source has been adapted to house a windowless absorption cell for gases. Absorption spectra can be recorded from 7 eV to up to 21 eV photon energies routinely, as shown by a new water and nitrous oxide absorption spectrum. By and large, the spectra agree with previously published ones both in terms of resonance energies and absorption cross sections, but that of N2O exhibits a small shift in the {\tilde{\bf D}} band and tentative fine structures that have not yet been fully described. This setup will facilitate the measurement of absorption spectra in the VUV above the absorption edge of LiF and MgF2 windows. It will also allow us to carry out condensed-phase measurements on thin liquid sheets and solid films. Further development options are discussed, including the recording of temperature-dependent absorption spectra, a stationary gas cell for calibration measurements, and the improvement of the photon energy resolution.

Exploring the Photophysics and Photocatalytic Activity of Heteroleptic Rh(III) Transition-Metal Complexes Using High-Throughput Experimentation.

High-throughput synthesis and screening (HTSS) methods were used to investigate the photophysical properties of 576 heteroleptic Rh(III) transition-metal complexes through measurement of the UV-visible absorption spectra, deaerated excited-state lifetime, and phosphorescent emission spectra. While 4d transition-metal photophysics are often highly influenced by deleterious metal-centered deactivation channels, the HTSS of structurally diverse cyclometalating and ancillary ligands attached to the metal center facilitated the discovery of photoactive complexes exhibiting long-lived charge-transfer phosphorescence (0.15-0.95 μs) spanning a substantial portion of the visible region (546-620 nm) at room temperature. Further photophysical and electrochemical investigations were then carried out on select complexes with favorable photophysics to understand the underlying features controlling these superior properties. Heteroleptic Ir(III) complexes with identical ligand morphology were also synthesized to compare these features to this family of well understood chromophores. A number of these Rh(III) complexes contained the requisite properties for photocatalytic activity and were consequently tested as photocatalysts (PCs) in a water reduction system using a Pd water reduction cocatalyst. Under certain conditions, the activity of the Rh(III) PC actually surpassed that of the Ir(III) PC, uncovering the potential of this often-overlooked class of transition metals as both efficient photoactive chromophores and PCs.

Modeling a low-frequency sound absorber consisting of a granular activated carbon stack backed by a poro-elastic layer

High surface area particles, like granular activated carbon (GAC), have shown advantages in absorbing low-frequency sounds by themselves and when combined with other treatments. In this article, a novel sound absorption treatment consisting of a high surface area particle stack supported by a soft, porous layer is described. It was first experimentally observed from impedance tube measurements that the low-frequency absorption performance of GAC stacks can be significantly enhanced by inserting a melamine foam between the stack and a rigid backing. To analytically model this type of sound absorbing treatment, the interfaces between particle stacks and other materials were characterized. Further, a 1-D layered transfer-matrix approach and a 2-D axi-symmetric finite-difference approach were implemented to predict the measured absorption spectra. Because of the constraint of the stack at the impedance tube wall, the 2-D axi-symmetric model leads to more accurate absorption spectrum predictions, particularly at low frequencies. However, the difference between the two model predictions becomes negligible when applied to large-area treatments. Thus, the simpler and faster 1-D theory can be valuable for optimizing large-area sound packages. In addition, by combining both granular and porous materials, it may be possible to design sound-absorbing metamaterials that perform well at low frequencies.

Exploring the structural, optical and photoluminescence of novel terbium-doped barium borosilicate glasses for high-performance technologies

The production process involved the use of the melt-quenching approach to produce a series of barium borosilicate glasses with the specific chemical formula 55B2O3+(26-x)BaO+12SiO2+7Na2O + xTb4O7, where x = 0, 0.5, 1, 2, and 3 mol%. X-ray diffraction (XRD), Raman spectroscopy, optical absorption, and photoluminescence spectra measurement were used to examine the prepared samples. X-ray diffraction revealed the non-crystalline character of the assembled samples. The Raman spectroscopy revealed that the incorporation of Tb4O7 into borosilicate glasses induced alterations in their structure. As the doping of Tb3+ ions increases, the density and molar volume of the glasses under investigation increase. Furthermore, the ion concentration and field strength increase while the polaron radius and inter-ionic distance decrease. The glass optical absorption spectra showed five peaks in the wavelength range from 300 nm to 2000 nm: 5L10, 5D3, 5D4, 7F(0, 1, 2), and 7F3, attributed to Tb3+ ion electronic transitions. In addition, optical parameters like optical energy gap, Urbach energy, refractive index, molar refractive index, reflection loss, electronic polarizability, and optical transmission coefficient were computed. Terbium-doped borosilicate glasses had a decreased optical energy gap and an improved refractive index. Photoluminescence spectra were excited at 325 nm and showed five peaks in the range of 400–750 nm. Photoluminescence (PL) emission spectra exhibit distinct peaks in the visible range.

Modulating Electronic States of Cu in Metal-Organic Frameworks for Emerging Controllable CH4/C2H4 Selectivity in CO2 Electroreduction.

The intensive study of electrochemical CO2 reduction reaction (CO2RR) has resulted in numerous highly selective catalysts, however, most of these still exhibit uncontrollable selectivity. Here, it is reported for the first time the controllable CH4/C2H4 selectivity by modulating the electronic states of Cu incorporated in metal-organic frameworks with different functional ligands, achieving a Faradaic efficiency of 58% for CH4 on Cu-incorporated UiO-66-H (Ce) composite catalysts,Cu/UiO-66-H (Ce) and that of 44% for C2H4 on Cu/UiO-66-F (Ce). In situ measurements of Raman and X-ray absorption spectra revealed that the electron-withdrawing ability of the ligand side group controls the product selectivity on MOFs through the modulation of the electronic states of Cu. This work opens new prospects for the development of MOFs as a platform for the tailored tuning of selectivity in CO2RR.

High-average-power 216 MHz Kerr lens mode-locked Yb:KGW ring laser oscillator for application to laser spectroscopy

We report the development of a ring Yb:KGW laser oscillator with an average power of 4.22 W, a pulse duration of 312 fs at a repetition rate of 216 MHz. The ring laser oscillator is purely Kerr lens mode-locked (KLM) taking advantage of the high nonlinear refractive index of the laser crystal in spite of being pumped by a multimode laser diode. To the best of our knowledge, this is the highest average power obtained from a KLM ring Yb:KGW laser oscillator. Monitoring the repetition rate fluctuations after initial warm-up of the laser cavity, a peak to valley of only 354.28 Hz during 30 min of free-running operation has been achieved. This could make a free-running ring cavity a suitable light source for application to laser spectroscopy. Using the ring laser oscillator, we have measured the absorption of the second overtone of the ν1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _1$$\\end{document} mode of NH3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}. We have also measured absorption spectra of the Yb:KGW crystal to evaluate the quality of the crystal affected by the doped impurities.

Influence of electron irradiation on the band gap and microhardness of TlInS2, TlInSSe and TlIn0.99Cr0.01S2 single crystals

ABSTRACT This work investigated the effect of partial replacement of sulphur atoms with selenium atoms (TlInSSe) and indium atoms with chromium atoms (TlIn0.99Cr0.01S2) on the band gap and microhardness of TlInS2 single crystals irradiated with electrons with energy of 2 MeV and a fluence of up to 1.5 × 1017 el/cm2. The band gap from the measured absorption spectra was determined using the Tauc method. It has been established that this irradiation leads to a decrease in the band gap in TlInS2, TlInSSe and TlIn0.99Cr0.01S2 crystals. It has been shown that after electron irradiation the microhardness of these crystals increased due to an increase in the size of crystallites on their surface.