Showing papers on "Absorption spectroscopy published in 2022"

Tunable Diode Laser Absorption Spectroscopy Based Temperature Measurement with a Single Diode Laser Near 1.4 μm

Abstract: The rapidly changing and wide dynamic range of combustion temperature in scramjet engines presents a major challenge to existing test techniques. Tunable diode laser absorption spectroscopy (TDLAS) based temperature measurement has the advantages of high sensitivity, fast response, and compact structure. In this invited paper, a temperature measurement method based on the TDLAS technique with a single diode laser was demonstrated. A continuous-wave (CW), distributed feedback (DFB) diode laser with an emission wavelength near 1.4 μm was used for temperature measurement, which could cover two water vapor (H2O) absorption lines located at 7153.749 cm−1 and 7154.354 cm−1 simultaneously. The output wavelength of the diode laser was calibrated according to the two absorption peaks in the time domain. Using this strategy, the TDLAS system has the advantageous of immunization to laser wavelength shift, simple system structure, reduced cost, and increased system robustness. The line intensity of the two target absorption lines under room temperature was about one-thousandth of that under high temperature, which avoided the measuring error caused by H2O in the environment. The system was tested on a McKenna flat flame burner and a scramjet model engine, respectively. It was found that, compared to the results measured by CARS technique and theoretical calculation, this TDLAS system had less than 4% temperature error when the McKenna flat flame burner was used. When a scramjet model engine was adopted, the measured results showed that such TDLAS system had an excellent dynamic range and fast response. The TDLAS system reported here could be used in real engine in the future.

Single-atomic-site iron on N-doped carbon for chemoselective reduction of nitroarenes

Abstract: A facile, gram-scale and sustainable approach has been established for the synthesis of single-atomic-site iron on N-doped carbon (FeSA@NC-20A) via the pyrolysis of aniline modified FeZn-ZIFs, in which the synthesis of zeolitic imidazolate frameworks (ZIFs) can be accomplished in water at room temperature, and no acid etching is required. The as-synthesized catalyst exhibits better performance on the chemoselective hydrogenation of nitroarenes with a broad substrate scope (turnover frequency (TOF) up to 1,727 h−1, 23 examples) than most of previously reported works. Based on high-angle annular dark field scanning transmission microscopy (HAADF-STEM) images in combination with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron spin resonance (ESR), and Mossbauer spectroscopy, Fe is dispersed as single atoms via forming FeNx (x = 4–6). This work not only determines the active sites of FeSA@NC-20A for hydrogenation (FeN4), but also proposes tentative pathways for both N-H activation of hydrazine and the reduction of nitroarene on FeN4 site, both of which are the key steps for the hydrogenation of nitroarenes. In addition, this catalyst shows excellent stability, and no significant activity degradation is observed when recycling for 10 times or restoring in air for 2 months.

Time‐Resolved Potential‐Induced Changes in Fe/N/C‐Catalysts Studied by In Situ Modulation Excitation X‐Ray Absorption Spectroscopy

Abstract: To advance the widespread implementation of electrochemical energy storage and conversion technologies, the development of inexpensive electrocatalysts is imperative. In this context, Fe/N/C‐materials represent a promising alternative to the costly noble metals currently used to catalyze the oxygen reduction reaction (ORR), and also display encouraging activities for the reduction of CO2. Nevertheless, the application of these materials in commercial devices requires further improvements in their performance and stability that are currently hindered by a lack of understanding of the nature of their active sites and the associated catalytic mechanisms. With this motivation, herein the authors exploit the high sensitivity of modulation excitation X‐ray absorption spectroscopy toward species undergoing potential‐induced changes to elucidate the operando local geometry of the active sites in two sorts of Fe/N/C‐catalysts. While the ligand environment of a part of both materials’ sites appears to change from six‐/five‐ to fourfold coordination upon potential decrease, they differ substantially when it comes to the geometry of the coordination sphere, with the more ORR‐active material undergoing more pronounced restructuring. Furthermore, these time‐resolved spectroscopic measurements yield unprecedented insights into the kinetics of Fe‐based molecular sites’ structural reorganization, identifying the oxidation of iron as a rate‐limiting process for the less ORR‐active catalyst.

Optical thermometry and broad infrared luminescence in highly sensitized TBO glass

Abstract: This work mainly reports the optical thermometry based on frequency upconversion and the infrared luminescence of Er3+-Yb3+ codoped TeO2-B2O3 (TBO) glasses prepared via melt-quenching technique. The amorphous nature of the prepared glass samples has been confirmed from the XRD analysis. FTIR analysis of the prepared glasses shows the existence of possible bands along with the phonon energy ∼670 cm−1. Judd-Ofelt analysis has been performed on the basis of absorption spectra and various radiative parameters calculated. The order of the intensity parameters (Ω6 > Ω2 > Ω4) indicates ionic nature of the Er-O bond which is further confirmed by the naphelauxetic ratio, covalency and bonding parameter. The enhancement of about 155 times and 327 times in the green and red UC emission intensity of the codoped glass as compared to the Er3+ doped TBO glass has been reported. The absorption cross-section around 980 nm in the codoped glass is found to be ∼43 times larger as compared to the 4I15/2 → 4I11/2 absorption transition in the Er3+ doped glass. The temperature sensing study of the codoped glass with high ‘Ω6’ value has been performed and low value of the absolute sensitivity has been explained on the basis of Judd-Ofelt parameters. The figure of merit for gain bandwidth (9216.81 × 10−27 cm3) & maximum gain coefficient (2.27 cm−1) corresponding to the infrared luminescence peaking at ∼1.5 μm and spectroscopic quality factor (0.28) have been evaluated.

Substituent-dependent absorption and fluorescence properties of perylene bisimide radical anions and dianions.

Abstract: Perylene-3,4:9,10-bis(dicarboximides) (PBIs) rank among the most important functional dyes and organic semiconductors, but only recently have their radical anions and dianions attracted interest for a variety of applications. Here, we systematically elucidate the functional properties (redox, absorption, and emission) of five PBI anions and dianions bearing different bay-substituents attached to the chromophore core. Cyclic voltammetry measurements reveal the influence of the substituents ranging from electron-withdrawing cyano to electron-donating phenoxy groups on the oxidation and reduction potentials that relate to the HOMO and LUMO levels ranging from −7.07 eV to −6.05 eV and −5.01 eV to −4.05 eV, respectively. Spectroelectrochemical studies reveal a significant number of intense absorption bands in the NIR-spectral range (750–1400 nm) for the radical anions, whereas the dianionic species are characterized by similar spectra to those for the neutral dyes, however being bathochromically shifted and with increased molar extinction coefficients of approximately 100 000 M−1 cm−1. The increase of the transition dipole moment is up to 56% and accompanied by an almost cyanine-like red-shifted (by 300 nm) absorption spectrum for the most electron-poor tetracyanotetrachloro PBI. Whilst the outstanding fluorescence properties of the neutral PBIs are lost for the radical anions, an appreciable near-infrared (NIR) fluorescence with a quantum yield of up to 18% is revealed for the dianions by utilizing a custom-built flow-cell spectroelectrochemistry setup. Time-dependent density functional theory calculations help to assign the absorption bands to the respective electronic transitions.

Physical and spectroscopic characteristics of lithium-aluminium-borate glass: Effects of varying Nd2O3 doping contents

Abstract: The influence of different Nd2O3 doping contents on the physical and optical properties of the glasses was evaluated. XRD patterns of the as-quenched samples confirmed their glassy nature. Density, ion concentration and field strength increases with the addition of Nd2O3 content, respectively. The absorption spectrum of the glasses exhibit intense peaks at approximately 580, 744 and 800 nm corresponding to the electronic transitions in Nd3+. With increasing Nd2O3 contents, the refractive indices of the glasses were increased from 2.363 to 2.415. FTIR spectra revealed the presence of BO4 and BO3 structural units in the glasses. Emission spectrum of glasses (at 300 nm excitation) displayed four prominent peaks at 368, 421, 483 and 514 nm due to the electronic transition in Nd3+from 4I9/2 to 4P3/2, 2P11/2, 2G11/2, 2G9/2, 4G11/2, and 4G9/2, respectively. The proposed glass system were highly sensitive to the Nd2O3 contents changes.

Photophysical properties and optical nonlinearity of cyclo[18]carbon (C18) precursors, C18-(CO)n (n = 2, 4, and 6): focusing on the effect of the carbonyl groups.

Abstract: The electronic spectra and (hyper)polarizability of C18-(CO)n (n = 2, 4, and 6) are studied using theoretical calculations to reveal the effect of introducing carbonyl (-CO) groups on the molecular optical properties. Successive introduction of -CO groups is observed to cause a red-shift in the absorption spectrum, but maximum absorption of all molecules is mainly due to the charge redistribution within the C18 moiety. The (hyper)polarizabilities of the cyclocarbon oxides present an ascending trend with the -CO groups in the molecule, and the higher-order response properties are more sensitive. With (hyper)polarizability density analysis and (hyper)polarizability contribution decomposition, the fundamental reasons for the difference of (hyper)polarizability of different molecules are systematically discussed from the perspective of physical and structural origins, respectively. Significant optical resonances under the frequency-dependent fields are found for the (hyper)polarizabilities of the cyclocarbon oxides, which is in contrast to the insignificant influence on their polarizability.

Impact of Cr³⁺ substitution on the nephelauxetic ratio and Racah parameter of Cr-Mn-Zn nanoferrites

Abstract: Abstract For the first time, we present the ligand field splitting (10Dq) nephelauxetic ratio ( β ), Racah parameter (B) and stability of Cr 3+ within Mn–Zn nanoferrite which synthesized using the citrate route. These parameters were determined via optical absorption spectra. The obtained bands in the significance range of optical absorption spectra are wide as well as asymmetric; therefore the deconvolution process becomes a necessary task. The values of 10Dq and B have been estimated from the produced bands. The values of 10 Dq are observed to increase from 16366.61 to 16447.37 cm −1 whereas, B values are observed to decrease from 829.81 to 760.80 cm −1 with additional Cr 3+ substitution. The increasing 10Dq and decreasing B values, evidence for bonds between Cr 3+ ions with their environments became a further covalent (less ionic). Moreover, the values of β are observed to decrease for further Cr 3+ substitution. This decrease of β produces less stability between Cr 3+ and its ligand. Furthermore, Dq / B values declare that Cr 3+ centers are in the low-field sites by a slight tendency towards the high-field sites with further Cr/Fe substitution process. Therefore, it was suggested that Cr 3+ substituted Mn–Zn nanoferrites are excellent candidates for diverse optical applications such as a tunable laser.

Theoretical design of new carbazole based organic dyes for DSSCs applications. A DFT/TD-DFT insight

Abstract: New series of organic dyes Mi (i = 2–10) derived from M1 have been investigated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods, to find out the effect of different internal acceptor groups on their efficiency in DSSCs. The geometries, electronic structures, absorption spectra, dipole moments, and molecular electrostatic potential of these isolated dyes and dye-(TiO2)6 systems were investigated and discussed. Besides, some quantify parameters influencing the power conversion efficiency (PCE) such as light-harvesting efficiency (LHE), electron injection driving force (ΔGinject) and regeneration driving force (ΔGreg) were also calculated to examine the most appropriate organic dyes for DSSC applications. Theoretical results indicated that all designed dyes exhibit a significant decrease in the gap energy with increasing dipole moments, and red-shifted absorption spectra (except that M2 is blue shifted) compared to M1 (reference dye), which revealed that these designed dyes are promising candidates for DSSC applications. Accordingly, the introduction of new internal acceptor group in D-A-π-A structure may be the best strategy for improving the photovoltaic performances.

Synthesis of ZnO and CuO nanoparticles via Sol gel method and its characterization by using various technique

Abstract: Abstract Nanotechnology is a completely unique branch of technology that offers with substances in a very small size between (1–100 nm) with various crystal shapes. Metals have ability to produce large number of oxides. These metal oxides play a major role in many areas of chemistry, physics, material science and food science. In this research, Zinc Oxide (ZnO) and Copper (II) oxide nanoparticles were synthesized via sol–gel process using zinc nitrate and copper (II) nitrate as precursor respectively. The characterization of CuO and ZnO nanoparticles was done by using various techniques. X-ray Diffraction (XRD) indicates the crystallinity and crystal size of CuO and ZnO nanoparticle. Fourier transform infrared spectroscopy (FT-IR) was used to get the infrared spectrum of the sample indicating composition of the sample which contains various functional groups. XRD result shows the particle size of CuO at highest peak 29.4014 0 was 61.25 nm and the particle size of ZnO at highest peak 36.2476° was 21.82 nm. FT-IR spectra peak at 594.56 cm- 1 indicated characteristic absorption bands of ZnO nanoparticles and the broad band peak at 3506.9 cm −1 can be attributed to the characteristic absorption of O–H group. The analysis of FT-IR spectrum of CuO shows peaks at 602.09, 678.39, and 730.19 cm −1 which refer to the formation of CuO. SEMimages indicate the morphology of CuO and ZnO nanoparticles. Result of EDX characterization indicates that the both synthesized nanoparticles have good purity with very less amount of impurities. EDX data indicates that Cu content was 54.56%, oxygen content was 33.75% in CuO nanoparticles and Zn determined by EDX was 40.77 and O was 45.82 in ZnO. Graphical Abstract

Design of Single-Atom Catalysts and Tracking Their Fate Using Operando and Advanced X-ray Spectroscopic Tools

Abstract: The potential of operando X-ray techniques for following the structure, fate, and active site of single-atom catalysts (SACs) is highlighted with emphasis on a synergetic approach of both topics. X-ray absorption spectroscopy (XAS) and related X-ray techniques have become fascinating tools to characterize solids and they can be applied to almost all the transition metals deriving information about the symmetry, oxidation state, local coordination, and many more structural and electronic properties. SACs, a newly coined concept, recently gained much attention in the field of heterogeneous catalysis. In this way, one can achieve a minimum use of the metal, theoretically highest efficiency, and the design of only one active site-so-called single site catalysts. While single sites are not easy to characterize especially under operating conditions, XAS as local probe together with complementary methods (infrared spectroscopy, electron microscopy) is ideal in this research area to prove the structure of these sites and the dynamic changes during reaction. In this review, starting from their fundamentals, various techniques related to conventional XAS and X-ray photon in/out techniques applied to single sites are discussed with detailed mechanistic and in situ/operando studies. We systematically summarize the design strategies of SACs and outline their exploration with XAS supported by density functional theory (DFT) calculations and recent machine learning tools.

Self-referenced method for the Judd–Ofelt parametrisation of the Eu3+ excitation spectrum

Abstract: Judd-Ofelt theory is a cornerstone of lanthanides' spectroscopy given that it describes 4fn emissions and absorptions of lanthanide ions using only three intensity parameters. A self-referenced technique for computing Judd-Ofelt intensity parameters from the excitation spectra of Eu3+-activated luminescent materials is presented in this study along with an explanation of the parametrisation procedure and free user-friendly web application. It uses the integrated intensities of the 7F0 → 5D2, 7F0 → 5D4, and 7F0 → 5L6 transitions in the excitation spectrum for estimation and the integrated intensity of the 7F0 → 5D1 magnetic dipole transition for calibration. This approach facilitates an effortless derivation of the Ω6 intensity parameter, which is challenging to compute precisely by Krupke's parametrisation of the emission spectrum and, therefore, often omitted in published research papers. Compared to the parametrisation of absorption spectra, the described method is more accurate, can be applied to any material form, and requires a single excitation spectrum.

Optical, Structural, and Mechanical Properties of Gd3Ga5O12 Single Crystals Irradiated with 84Kr+ Ions

Abstract: Herein, the optical absorption, X‐ray diffraction (XRD) analysis data, and mechanical properties along the ion path are analyzed for gadolinium gallium garnet (Gd3Ga5O12 or GGG) single crystals irradiated with fast 84Kr ions to fluences of 1013–1014 ion cm−2. It is found that the optical absorption spectra of Czochralski‐grown unirradiated GGG crystal consist of relatively narrow lines in the UV spectral range associated with the 4f–4f transitions in Gd3+ ions. Transitions from the 6S7/2 ground state to the 6P, 6J, and 6D states in the Gd3+ cation are visible. An additional absorption band is also observed at 350 nm, which is associated with an uncontrolled Ca impurity. In irradiated GGG single crystals, a shift of the fundamental absorption edge by ≈30 nm to the long‐wavelength part of the spectrum is observed. The observed changes are caused by structural disturbances caused by depletion of the surface layer and an increase in the number of displaced atoms accompanied by an increase in the crystal lattice parameter. XRD analysis shows the presence of size effects and deformation of interplanar distances due to the displacement of atoms from the sites of the crystal lattice with subsequent migration. Hardness measurements show ion‐induced softening, which may be due to ion‐induced amorphization.

Characterization of Energy Materials with X-ray Absorption Spectroscopy─Advantages, Challenges, and Opportunities

Abstract: X-ray absorption spectroscopy (XAS) plays a critical role in the characterization of energy materials, including thin-film electrocatalysts and battery materials. XAS is well-suited for this purpose because it is element-specific and can target distinct chemical environments within a material, even in a mixed or complicated matrix. Even so, some key energy materials are far from “ideal” XAS samples. This means that both sample preparation and experimental conditions need to be considered when collecting and interpreting data to ensure that conclusions are correct. This review outlines some of the key questions that an XAS experiment is well-suited to answering, including speciation of amorphous materials, understanding how multi-metal systems interact, and the different ways that we may observe single atoms. In addition, we show how XAS can be highly complementary to other analytical techniques in developing a full picture of a material over different scale bars. Importantly, we also examine instances where the sample matrix can distort XAS data, show an example where bond-length disorder can be confused with a change in the coordination number, and discuss some of the advantages and challenges of in situ electrocatalysis. Finally, we examine the future role that XAS will play in innovations in energy materials.

Fluorescence intensity ratio technique and its reliability

Abstract: The present article reports the optical absorption and upconversion (UC) studies of 1.0 mol% Er3+/2.0 mol% Yb3+ doped/codoped glasses prepared by melt-quenching technique. The elements present and the composition of the prepared glass have been confirmed from XPS and XRF analysis respectively. Judd-Ofelt intensity parameters have been calculated using the absorption spectrum which is further utilized to predict the nature of Er_O bond, the transition probabilities, branching ratios and radiative lifetimes. The CIE study shows non-colour tunable and highly pure green emission (94.2%). The temperature-dependent UC emission spectra of the 2.0 mol% Yb3+ sensitized glass have been recorded at three different pump power densities to establish a reliable FIR based temperature scale. Furthermore, the Arrhenius fitting of the temperature-dependent spectra reveals low thermal quenching of green luminescence in the codoped glass.