Absorption Coefficient Spectra Research Articles

Electronic and optical properties of eccentric two dimensional quantum rings subjected to transverse tilted magnetic field

ABSTRACT Within the effective mass approximation framework, the electronic and optical properties of GaAs-based two-dimensional eccentric quantum rings subjected to a transverse magnetic field with an inclination θ-angle to the x-axis are investigated using a two-dimensional diagonalisation method. The results show that the electron energy spectra in concentric quantum rings reveal transparency to the action of magnetic field orientation, contrary to their optical properties, which turn out to be anisotropic with this later. In addition, the eccentricity preserves the absorption coefficient spectra for y-polarisation for all orientations of the magnetic field qualitatively, while those of x-polarisation are significantly modified by eccentricity and magnetic field. Specific peak transitions occurring at specific magnetic field values and θ-angle can be used as a signature of magnetic field orientation and eccentricity.

Temperature-Dependent Optical Properties of Oxidized Graphenes.

In this study, we investigate how changing important synthesis-related parameters can affect and control the optical characteristics of graphene oxide (GO) and reduced graphene oxide (rGO). These parameters include drying time and reduction time at two different temperatures. We obtain an understanding of their impact on optical transitions, optical bandgap, absorption coefficient, and absorbance spectrum width by analyzing these factors. Accordingly, GO has an optical bandgap of about 4 eV, which is decreased by the reduction process to 1.9 eV. Both GO and rGO display greater absorption in the visible spectrum, which improves photon capture and boosts efficiency in energy conversion applications. Additionally, our results show that GO and rGO have higher absorption coefficients than those previously reported for dispersions of exfoliated graphene. Defects in GO and rGO, as well as the presence of functional oxygen groups, are the main contributors to this increased absorption. Several measurements are carried out, including spectroscopic and morphological studies, to further support our findings.

A Method of Evaluating NV centers Concentration by UV–Vis Transmittance Spectra

The ultraviolet-visible (UV-Vis) spectrum was not generally considered an available method for measuring the concentration of negatively charged nitrogen-vacancy (NV-, NV center). In this study, we propose the idea of evaluating the concentration of NV center by the slope of the UV-Vis spectrum. To establish this new method we synthesized diamonds with different NV center concentrations by the chemical vapor deposition (CVD) method. We then measured the zero-phonon line (ZPL) intensity of PL spectra at 637 nm and estimated the concentration of the NV centers as a baseline for comparison to our new UV-Vis method. The UV-Vis transmission spectra were then measured and transformed to relative absorption coefficient spectra. Slopes of the transformed UV-Vis spectra between 400 nm and 800 nm were calculated and compared with the ZPL intensities. The results show a strong positive correlation between the slopes of the absorption spectra and the ZPL intensities of PL spectra at 637 nm. Therefore, this paper demonstrates the feasibility of estimating the concentration of the NV centers from measuring the transmission UV-Vis spectrum.

An operational model for separating the absorption of optically active constituents from SeaWiFS measurements

ABSTRACT To analytically or semi-analytically convert satellite-measured remote sensing reflectance (R rs) to widely used biogeochemical variables from the global oceans, it is common to first determine the total absorption coefficient from satellite R rs data and then separate the total absorption coefficient into the absorption coefficients of phytoplankton (a ph ) and non-phytoplankton (a dg ) pigments. While still considering the spectral characteristics of a ph and a dg , we developed an operational model to improve the accuracy of estimating a ph and a dg products from satellite R rs data. Our results show that our model effectively separates a ph and a dg from the total absorption coefficient spectrum, which decreases the uncertainty by 6.81% to 17.52% compared to a widely used quasi-analytical algorithm. Moreover, after applying the new model to SeaWiFS satellite images, we present the spatial and temporal variations of a ph (443) and a dg (443) for the global oceans from 1997 to 2010, further confirming that coastal zones exhibited higher a ph (443) and a dg (443) than the open oceans during that time. In addition, a ph (443) and a dg (443) declined in the tropical Indian Ocean Gyre over those 13 years. Our results improve our knowledge of the spatiotemporal variations of optical properties of the global oceans, and also demonstrate the potential of our model in separating the total absorption.

Investigating structural, electronic and optical properties of Sc2CF2@Fe MXene: A first principle study

In this work, the structural, electronic and optical properties of novel 2D Sc2CF2 MXene alloyed with Fe are studied by first-principles calculations. The computational method is based on the density functional theory (DFT) and generalized gradient approximation (GGA) considering non-spin–orbit and spin–orbit coupling (SOC). By analyzing the behavior of spin-polarized band structure and density of states (DOS), metallic behavior for all alloy compositions has been predicted. In addition, for all alloy compositions except for c=0.5, the ferromagnetic property has been discovered. Moreover, the optical properties like real and imaginary parts of dielectric and energy loss functions, optical conductivity, absorption coefficient, and reflectivity spectrum have been studied. The results of the absorption coefficient and reflectivity spectrum as a function of photon energy predict that the compounds can be sound absorbers at both visible-light and ultraviolet wavelength regions.

Exploring the structural properties and the optoelectronic features of RbPbX3 (X [formula omitted] Cl, F) perovskite crystals for solar cells solicitations: Showcasing the DFT predictions.

A comprehensive study of the structural, optical, and electronic properties of RbPbX3 (where X is Cl or F) perovskite crystals is reported herein. The calculations of the different physical properties of these two distinguishable RbPbCl3 and RbPbF3 perovskite crystals have been carried within the framework of the Density Functional Theory (DFT) approach for the cubic temperature-dependent phase. The study is motivated by the exploration of innovative perovskites materials for solar cells application due to the marvelous augmentation in power conversion efficiency (PCE) obtained by perovskite crystals (≈ 25% up to date). The investigation were undertaken for determining the perceivable role of the X element in their band gap energy features as well as the band structure proprieties. The simulations were commenced by determining the optimal lattice constants and the lowest total energy of both perovskite crystals. The exploration of the electronic properties of RbPbCl3 and RbPbF3 perovskite crystals have been studied by estimating their variation upon employing spin–orbit-coupling (SOC) and without taking into consideration the SOC interaction by means of LDA-pz and GGA-PBE exchange potentials within the framework of projector augmented wave method (PAW) and the Perdew–Burke–Ernzerh of LDA and (PBE) variant of the generalized gradient approximation (GGA). The integrated suite quantum-ESPRESSO is used for materials modeling, structure calculations, and electronic properties of the studied RbPbCl3 and RbPbF3 perovskite crystals. The thermo_pw driver is employed for the determination of the elastic properties whereas the optical properties were elucidated by aid of Yambo code through solving the many-body perturbation theory (MBPT) approach as introduced in the open-source code. The optical band gap of cubic RbPbCl3 and RbPbCF3 within LDA and PBE, were observed at (2.18, 2.2) eV and (2.4, 2.5) eV respectively. Compared and contrasted with those revealed by the electronic band gap energy of the systems, these obtained values are very consistent with the experimental. The two maximum peaks for the absorption coefficients are found to be within the visible range rending the two perovskite crystals in promising candidate for solar cell applications. Despite some quantitative differences, the material’s enhancement potential is well demonstrated by the absorption coefficient spectrum, refractive index, and conductivity. The study holds promise for solar cell applications and may pave the way for consideration of the RbPbCl3 and RbPbF3 as well as their doped analogs for perovskites-based solar cells as the next generation in the photovoltaic industry.

Numerical Simulation of a Light Field Structure in an Integrating Sphere via the Monte Carlo Method

The integrated cavity absorption meter is designed to measure the seawater absorption coefficient spectra which are necessary for studying ocean productivity and heat balance. The performed numerical simulations of a light field structure made it possible to improve the measurement technique. Its results showed that the use of the Lambertian model allows to reduce the calculation time by two orders of magnitude with an acceptable loss of accuracy for these calculations. It is shown that in the case of an integrating sphere made of fluorilon, the use of different volume scattering functions does not affect the calculation result, which is not true in the case of using a sphere with a mirror coating. The effect of an air layer between quartz and fluorilon is considered, and the applicability of the diffusion approximation is verified. Examples of field measurements of the seawater absorption coefficient and its components performed in different water areas of the World Ocean in 2020–2022 are presented.

Extracting Optical Parameters of Cu–Mn–Fe Spinel Oxide Nanoparticles for Optimizing Air-Stable, High-Efficiency Solar Selective Coatings

High-temperature Cu–Mn–Fe spinel-oxide nanoparticle solar selective absorber coatings are investigated experimentally and theoretically. A general realistic approach to evaluate absorption coefficient spectra from the optical measurements of the nanoparticle-pigmented coatings is developed by solving the inverse problem of the four-flux-radiative transfer model. The derived absorption properties are utilized to elucidate the direct and indirect bandgap transitions in the visible spectral regime as well as the sub-bandgap absorption in the infrared range. Furthermore, the optical properties of NP materials can be directly applied to optimize the solar selective coating design and analyze thermal degradation mechanisms. The analysis reveals that the Cu–Mn–Fe spinel oxides are semiconductors with an indirect bandgap ranging from 1.7 to 2.1 eV, while iron-free CuMn2O4 is a direct bandgap material with Eg = 1.84 eV. With the same coating thickness and nanoparticle load, the solar absorptance ranks in the order of Mn2O3 < MnFe2O4 < CuFe2O4 < CuFeMnO4 < CuMn2O4. The optimized spray-coated iron-free CuMn2O4 NP-pigmented coating demonstrates a high solar absorptance of 97%, a low emittance of 55%, a high optical-to-thermal energy conversion efficiency of ∼93.5% under 1000× solar concentration at 750 °C, and long-term endurance upon thermal cycling between 750 °C and room temperature in air. The optical parameter analysis approach can be easily extended to other material systems to facilitate the search and optimization of high-temperature nanoparticle-pigmented solar selective coatings.

Terahertz Spectroscopy Characterization and Prediction of the Aging Degree of Polyethylene Pipes Based on PLS.

Polyethylene (PE) is widely used in pipeline transportation owing to its excellent corrosion resistance, good stability, and ease of processing. As organic polymer materials, PE pipes inevitably undergo different degrees of aging during long-term use. In this study, terahertz time-domain spectroscopy was used to study the spectral characteristics of PE pipes with different degrees of photothermal aging, and the variation in the absorption coefficient with aging time was obtained. The absorption coefficient spectrum was extracted using uninformative variable elimination (UVE), successive projections algorithm (SPA), competitive adaptive reweighted sampling (CARS), and random frog RF spectral screening algorithms, and the spectral slope characteristics of the aging-sensitive band were selected as the evaluation indices of the degree of PE aging. Based on this, a partial least squares aging characterization model was established to predict white PE80, white PE100 and black PE100 pipes with different aging degrees. The results showed that the prediction accuracy of the absorption coefficient spectral slope feature prediction model for the aging degree of different types of pipes was greater than 93.16% and the verification set error was within 13.5 h.

Exploring the candidacy of Mo[formula omitted] A[formula omitted] X2 (A = [Cr, Ta], X = S) for photodetection solicitations: Showcasing the DFT predictions of the structural, elastic, and optoelectronic properties

Previously, most of the theoretical/computational density functional theory (DFT) simulations of transition metal dichalcogenides (TMDs) were used to gain insight into their non-doped structural, elastic, and optoelectronic properties. Although it was shown that most of the TMDs proprieties are relevant giving thereby rise to much more attention due to their promising features with vast potential in many technological applications, it was not clear concerning the stability of these interesting and timely materials. In general, for TMDs the substitutional doping method, which consists of carrier doping by substituting chalcogen or metal sites with impurity atoms, is key for tailoring their physical properties and enabling outstanding stability. In this study, a particular focus will be dedicated to elucidating the stability and the physical properties of Cr and Ta-doped Molybdenum-based TMDs. Since the stability of TMDs depend on the formation energy and occurs on very long timescales, all-DTF and simulations of the physical properties of TMDs are prohibitively costly. However, the inclusion of Cr and Ta in the monolayer MoS2 matrix may pave the way for obtaining excellent stability of TMDs materials and reasonably reduce the computational cost. In this investigation, an illustration of the effect of the Cr and Ta impurities on the overall performance of the monolayer MoS2 matrix will be elucidated. Interestingly, an investigation of Mo(1−x)A(x)X2(A = [Cr, Ta], X = [S]) will be performed starting from the elucidation of the structural properties. It is found that the doped materials are semiconductors within the infrared region, with particular values of the energy gaps. The optical properties findings reveal that Ta–Cr-doped materials are more transparent than those counterparts of Cr and Ta-doped materials. The absorption coefficient spectra, refractive index, reflectivity, and conductivity all reveal good enhancement capability of the doped materials. The computational approach used herein is expected to open the way towards a comprehensive understanding of an efficient application of TMDs doped materials in many ranges of optical applications such as those involved in photodetection technology.

Comparative performance analysis of Cs2TiX6 (X = Br-, Cl-, I-) lead-free perovskite solar cells incorporating single, double and triple layer halides by SCAPS −1D

Halide perovskites have risen in popularity as appealing light absorber materials, owing primarily to their wide range of applications in solar cells, lasers, photodetectors. However, lead-containing perovskites have the potential to cause substantial environmental damage. As a result, there is a significant need to produce environmentally acceptable lead-free perovskites. In this work, we studied the single, double and triple halides perovskite by numerical simulator SCAPS-1D for maximum performance. We have optimized the absorber layer thickness, NA/ND/Nt and interface defect density, back contact electrodes, and temperature effects in a single absorber layer structure. Further, we have optimized the double and triple-layer absorbers for perovskite solar cell structures. The maximum efficiency achieved in the double halide perovskite solar cell is VOC = 1.54 V, JSC = 24.04 mA/cm2, FF = 82.72%, and PCE = 30.06%. Such performance is due to the absorption coefficient spectrum with a wide range of energy band gaps. This has proved its suitability for photovoltaic devices. Overall, our findings reveal that Cs2TiX6 (X = Br, Cl, I) Pb-free perovskites have promising and potential features for device performance.

Electronic structure and optical properties of Br- and Cl-doped rutile TiO2 for application in self-cleaning and photovoltaic panel's coatings: first-principle calculations.

Development of novel self-cleaning technologies, especially those based on semiconductor photocatalysis system, is one of the most important research problems in environmental cleanup. Titanium dioxide (TiO2) is a well-known semiconductor photocatalyst that has a strong photocatalytic activity in the ultra-violet part of the spectrum while its photocatalytic efficiency is very limited within the visible range due to its large band gap. In the field of photocatalytic materials, doping is an efficient method to increase the spectral response and promote charge separation. However, the type of dopant is not the only important factor, but also its position in the material lattice. In the present study, we have carried out first-principle calculations based on density functional theory to explore how particular doping configuration, such as Br or Cl doping at an O site, may influence the electronic structure and the charge density distribution within rutile TiO2. Furthermore, optical properties such as the absorption coefficient, the transmittance, and reflectance spectra have also been derived from the calculated complex dielectric function and examined to see whether this doping configuration has any effect on the use of the material as a self-cleaning coating on photovoltaic panels.

Photoferroic prospective of multiferroic HoMnO3 compound, evaluated on the base of the DFT study of its magnetic, electronic, and optical properties

In this work, non-collinear spin density functional theory based all-electron full-potential linearized augmented plane wave electronic structure method have been employed to study magnetic, electronic, and optical properties of multiferroic HoMnO3 compound in order to evaluate its potential to be used in photovoltaic applications. Exchange and correlation effects of the Ho 4f- and Mn 3d-electrons were treated on the base of the local spin density approximation including effective Hubbard (Ueff) correction. We concluded that the ground state magnetic structure should be described by Γ3 irreducible representation of the P63cm space group, for both the Mn and the Ho magnetic sub-lattices. The calculated indirect and direct band gaps, corresponding to the transition from the O 2p-to the Mn 3d-states, are found to be 1.25 eV and 1.4 eV, respectively, in very good agreement with the experimental findings. Calculated dielectric tensor spectra are found to be in satisfactory agreement with the experiment as well. On the base of these results, we investigated photoferroic properties of the HoMnO3 by calculating its absorption coefficient spectrum and the effective mass tensor of the photogenerated electrons and holes. By comparing results with those of isostructural LuMnO3 and the YMnO3 multiferroics, we concluded that the HoMnO3 exhibits similar photoferroic properties, a fact that classifies it as a material suitable for photovoltaic applications.

Audio-frequency surface wave characteristics above porous and comb-like surfaces

Part of the solution for the sound field due to a point source in air over a porous boundary has the form of an airborne surface wave. Analytical expressions for the surface wave characteristics are reviewed and corresponding analytical expressions for group speed are obtained from a thin air layer approximation for the impedance of a comb-like surface, from two approximate models for the acoustical properties of porous media and from a model for identical slanted slit pores. Predictions of absorption coefficient spectra for a hard-backed porous layer with flow resistivity sufficiently low that there is extended reaction are made using two of the approximate models and compared with those of a relatively exact slanted slit pore model. The model derived specifically to predict the acoustical properties of porous asphalt is found to be the least satisfactory. The various models are used to obtain analytic expressions for the surface wave group speed. Predictions of surface wave characteristics including group velocity are compared with data obtained over arrays of parallel aluminium strips.

Validation and modification of a semi-empirical model for sound absorption by perforated liners in the absence of flow based on comparisons with data from full scale measurements

There is much current interest in improving the efficiency gas turbines used in aircraft engines and thereby reducing their carbon emissions. The perforated combustor liners in gas turbine silencers absorb the sound associated with thermo-acoustic instabilities and thereby reduce them. A semi-empirical model has been developed to predict the absorption of perforated liners in the absence of bias flow as a function of frequency in terms of liner characteristic such as orifice diameter, thickness, spacing, orientation and perforation ratio and liner configuration which requires an additional model for the impedance of the cavity behind the liner. The expression used for impedance includes a cavity factor which corrects for the change in combustor liner diameter. Predictions of energy absorption coefficient spectrum are compared with data from measurements on several configurations of full-scale liners. It is found that predictions using the standard tangent term in the cavity impedance do not agree with data at frequencies below 500 Hz as well as predictions that use a cosine term instead. The resulting model, which is validated by the data comparisons, should be useful in optimising liner characteristics for manufacture.

Structural, electronic and optical properties of monolayer InGeX3 (X = S, Se, Te) by first-principles calculations

Recently, two-dimensional materials have attracted enormous attentions for electronic and optoelectronic applications owing to their unique surface structures and excellent physicochemical properties. Herein, the structural, electronic and optical properties of a series of novel monolayer InGeX3 (X = S, Se, Te) materials are investigated systematically by means of comprehensive first-principles calculations. All these three materials exhibit hexagonal symmetries and dynamical stabilities with no imaginary phonon mode. For monolayer InGeX3 (X = S, Se, Te), there exist obvious In–X ionic bonds and the partially covalent interactions of Ge–Ge and Ge–X. By using the HSE06 method, the band gaps of monolayer InGeX3 are predicted to 2.61, 2.24 and 1.80 eV, respectively. Meanwhile, the p-s orbital hybridizations are happened between X and In atoms in the conduction band regions and their interactions become smaller with the increase of X atomic number. In addition, the dielectric function, absorption coefficient and reflectivity spectra of monolayer InGeS3, InGeSe3 and InGeTe3 show the strong optical peaks along the in-plane direction in the UV light region. The definite bandgaps and optical properties make monolayer InGeX3 (X = S, Se, Te) materials viable candidates for future electronic and optoelectronic applications.

Tuning structural, optical, and dispersion functions of polystyrene via addition of meso-tetraphenylporphine manganese (III) chloride towards optoelectronic applications

Using a standard casting procedure, a polymeric composite of polystyrene (PS) and 5,10,15,20-tetraphenyl-21H,23H-porphine manganese (III) chloride (MnTPPCl) has been created. The structural alteration in the PS matrix brought on by MnTPPCl filling is confirmed by X-ray diffraction (XRD). According to vibrational groups that defined the prepared samples, the main distinctive peaks were found using Fourier transform infrared (FTIR). After filling, the majority of these absorption intensities have randomly varied from their values in the virgin polymer. Furthermore, new peaks at 1230 and 3642 cm−1 appeared and steadily increased with the increase in MnTPPCl content. Changes in the main vibrational bands in the FTIR spectra indicated the interaction of the composite components. The optical properties of the PS/MnTPPCl composite were investigated utilizing measurements of transmittance and reflectance. The absorption coefficient spectra demonstrate the emergence of new peaks (372–618 nm) after filling, which can be related to π→π* orbital transition of MnTPPCl. The optical energy gaps for the indirect and direct allowed transition were found to decrease with increasing MnTPPCl contents. A normal dispersion was found in the wavelength range of 830–2500 nm and an anomalous dispersion in the wavelength range of 190–830 nm, according to an analysis of the refractive index n. Calculations were made for the oscillator parameters, including oscillator and dispersion energies. The possibility of their employment in optoelectronic devices is implied by the reduction of the optical energy gap and the rise in refractive index caused by the addition of MnTPPCl.

Temperature measurement of aqueous solution in miniature sample chamber in microscopic system based on near-infrared spectrum.

Measurement of the sample temperature in biophysics research is challenging, as the samples are commonly placed in a miniature sample chamber under a microscope. In this study, we proposed a method to measure the temperature of an aqueous solution in miniature sample chambers in a microscopic system. Existing studies show that the absorption coefficient spectrum of water shifts with temperature, especially in the near-infrared (NIR) band. We measured the absorption spectra of water with different temperatures and analyzed them, to build a mathematical model relating the temperature and the spectrum. A setup for temperature measurement in a microscopic system was designed and implemented by coupling a spectrometer and a light source to a microscope. The temperature could be calculated by the spectral data and the mathematical model while simultaneously observing the micro-image of the sample. A series of liquid samples at different temperatures were tested using the setup, and the root mean square error of the calculated temperature is less than 0.5 °C. The results demonstrate that the method based on the NIR spectrum can be used for noncontact and quick measurement of the liquid sample temperature in a microscopic system.

Area-Independence of the Biexciton Oscillator Strength in CdSe Colloidal Nanoplatelets.

Colloidal CdSe nanoplatelets (NPLs) are unique systems to study two-dimensional excitons and excitonic complexes. However, while absorption and emission of photons through exciton formation and recombination have been extensively quantified, few studies have addressed the exciton-biexciton transition. Here, we use cross-polarized pump-probe spectroscopy to measure the absorption coefficient spectrum of this transition and determine the biexciton oscillator strength (fBX). We show that fBX is independent of the NPL area and that the concomitant biexciton area (SBX) agrees with predictions of a short-range interaction model. Moreover, we show that fBX is comparable to the oscillator strength of forming localized excitons at room temperature while being unaffected itself by center-of-mass localization. These results confirm the relevance of biexcitons for light-matter interaction in NPLs. Moreover, the quantification of the exciton-biexciton transition introduced here will enable researchers to rank 2D materials by the strength of this transition and to compare experimental results with theoretical predictions.

Terahertz spectroscopic detection of antifatigue illegal additives in health care product matrices.

Tadalafil is an illegal additive in antifatigue supplements. It is often misused in various plant dietary supplements (BDS), resulting in serious health risks. In this paper, terahertz spectroscopy combined with chemometrics is used to quantitatively analyze the content of tadalafil in nutritional and health products. The absorption coefficient spectrum of tadalafil in the range of 0.1-2.5THz was obtained, and an obvious characteristic absorption peak appeared at 1.7THz. To verify the accuracy of this characteristic absorption peak theoretically, tadalafil was simulated by density functional theory, and the calculated terahertz vibration spectrum matched well with the experimental spectrum. Then, the pure fatigue-based nutraceutical matrix and pure tadalafil were mixed in different proportions, and the terahertz absorption coefficient spectra of the mixtures were obtained. Finally, a quantitative analysis model of the tadalafil mixture was developed based on the support vector regression (SVR) algorithm, and the SVR model was optimized using particle swarm optimization (PSO) and genetic algorithm (GA), respectively. Compared with the SVR model, both PSO-SVR and GA-SVR enabled some improvement in their prediction accuracy, but the PSO-SVR model ran faster at 4.85s, whereas the GA-SVR model had a higher prediction accuracy with a prediction set correlation coefficient (R P) of 0.9996 and a root mean square error (RMSEP) of 0.011. In summary, this study used terahertz time-domain spectroscopy for the identification and quantification of tadalafil in health product matrices. This study provides a new solution for the nondestructive detection of illegally added tadalafil in antifatigue health products, which is pivotal to the quality control of the health product industry.