Dependent Absorption Research Articles

Analysis of the radiative corrections and dynamic extensions to the local field in the effective refractive index of particle suspensions

We analyze the predictions of two recently developed effective-medium approximations for the effective refractive index of a system of either transparent or plasmonic spherical particles, dispersed randomly in a transparent liquid matrix, as a function of their geometrical and physical parameters. The importance and significance of these approximations is that besides the radiative corrections to the optical response of the particles, they include full dynamic corrections to the field exciting any given particle. We perform this analysis by comparing the values obtained using them with the ones obtained from three well-known and widely used effective-medium approximations: Maxwell Garnett, Maxwell Garnett-Mie and van de Hulst. We provide plots of the real and imaginary parts of the effective index of refraction, for the five approximations considered, for polystyrene and gold nanoparticles of different sizes, as a function of the filling fraction and wavelength, pointing out the relevance of the new predictions, as well as the actual physical processes behind the so-called dependent scattering and what we now call dependent absorption.

Localized surface plasmon resonance induced nonlinear absorption and optical limiting activity of gold decorated graphene/MoS2 hybrid

The synergistic supremacy of a hybrid nanocomposite made of reduced graphene oxide (rGO), molybdenum disulfide (MoS2) and gold nanoparticles (Au) for Q-switching and optical limiting applications is investigated. Hydrothermally synthesized Au-rGO-MoS2 hybrid with varying concentrations of Au (2.5, 5, 7.5 and 10 wt%) was subjected to interact with Q-switched Nd:YAG nanosecond green laser pulses. The intensity dependent nonlinear absorption studies revealed a switch over in the nonlinear behaviour from saturable absorption (SA) to reverse saturable absorption (RSA) behaviour. SA occurs due to ground state bleaching at comparatively lower laser irradiances serving the need for Q-switching and optical communications. The RSA trait at higher laser irradiance is attributed to sequential two-photon absorption which serves as the platform for optical limiting behaviour prompting laser safety and effective photothermal therapy applications. The strong mid-visible and UV absorption promotes the availability of multiple energy bands for energy transitions of excited state absorption (ESA). Enhanced local fields due to localized surface plasmon resonance effect, structural defects, hierarchical morphology, increased absorption cross-section and plasmon induced energy transfer promotes robust ESA process. These tunable nonlinear optical properties make Au-rGO-MoS2 hybrid promising futuristic candidates for applications in nonlinear photonic devices, ultrafast optical switches and all-optical signal processing systems.

Hard x-ray magnetic circular dichroism under high magnetic field

We describe high-field X-ray magnetic circular dichroism (XMCD) setup developed at the European Synchrotron Radiation Facility beamline ID12, which is dedicated to polarization dependent X-ray absorption spectroscopy in the soft and hard X-ray range from 2 to 15 keV. The static magnetic field up to 17 T is generated by a superconducting solenoid. Performance of the setup is illustrated with three representative studies: metamagnetic transitions in PrCo2Ge2 single crystal, Pauli paramagnetism in uranium monocarbide, and induced magnetism on gold atoms in different environment: MnAu4, UAu4 and a pure gold metal.

Opto-electronic responses of large area WSe2 layers synthesized by chemical conversion of WO3 thin films

Atomically thin tungsten diselenide (WSe2) has drawn much interest due to its remarkable optical properties and potential applications in next-generation optoelectronics and energy harvesting devices. High-quality, wafer-scale synthesis of such two-dimensional (2D) semiconductors is necessary for their practical applications. Chemical vapor deposition (CVD) is a promising method for synthesizing large-area thin films of 2D materials where the constituent elements are of widely different vapor pressure. Herein, we demonstrate large-area synthesis of the 2H phase of WSe2 with a precise control over the 2D film thickness. The first step of this process is the deposition of tungsten trioxide (WO3) films of a well-defined thickness by thermal evaporation over large areas. The subsequent selenization of these films in an atmospheric pressure CVD reactor, yields high-quality uniform films of WSe2. The quality of these films is ascertained by measuring their characteristic Raman active vibrational modes and layer thickness dependent optical absorption and photoluminescence. The photoconductivity (PC) of these films has been measured with 405, 532 and 915 nm laser excitation. We note an increase in the PC of the films with their thickness. The best photoresponsivity and detectivity obtained are 11.3 mA/W and 1.42 × 108 Jones respectively. These results are promising to create photo-transistor arrays over large areas using such WO3 processed films.

Exploring the denaturations in cancer and non-cancer DNA molecules by optical absorption, thermal, and electric measurements: A case study

In this article, we carried out the temperature dependent UV-Visible (UV-Vis) spectroscopy, differential scanning calorimetry (DSC), and electrical studies for normal and cancerous (glioma) DNA samples of single patient. Based on this method, we were able to monitor the denaturation process and thermal stability in these molecules. From the temperature dependent optical absorption data, we calculated various optical parameters for these two types of samples. The optical band gap of these samples were also estimated and discussed as per the experimental conditions. The various optical parameters calculated indicate that mutated (tumor) DNA is less stable than the normal one. From the DSC data, clear melting peaks were observed for the tumor and normal samples. Also various thermodynamic parameters like change in enthalpy (ΔH), entropy (ΔS), and specific heat (Cp) were estimated. From the thermal study, it seems that the tumor DNA is less stable. Further from the electrical or current-voltage (I-V) characteristics data, the resistance for normal DNA decreases with temperature. But for tumor sample, it show anomalous behavior (like decreasing and then increasing trend) with temperature. For electrical transport, small polaron hopping could be the possible transport mechanism in the current sample. Here from these studies, the tumor sample seems more disordered, and structural fluctuations due to the speculated structure could be the best reason for this behavior. If such kind of molecular (at nano scale range) studied are done more vividly, then these calculated parameters of the molecule could be explored for further confirmation/diagnostics of the diseases in addition to clinical investigations.

Comparing Molecular Weight Dependent Absorption Rates of Collagen in Oral Mucosal and Epidermis/dermis Tissue Models

Comparing Molecular Weight Dependent Absorption Rates of Collagen in Oral Mucosal and Epidermis/dermis Tissue Models

Solvatochromism mechanism of perylene diimide radicals stabilized by low barrier hydrogen bond and detection of formaldehyde in real food samples

Formaldehyde (FA) is widely used for food preservation and whitening because of its preservative and bleaching effects. Excessive FA seriously endangers human health, so monitoring FA-treated food is of great significance for food safety. In this paper, perylene diimide radicals with the chirality (BTFPDI) and water-solubility (TFPDI-bPEI) were designed respectively based on our previous studies. Property of solvatochromism induced by these perylene diimide radicals aggregation was demonstrated by the concentration and temperature dependent absorption spectrum and the circular dichroism spectrum. Further the colorimetric monitoring of trace FA in gaseous and liquid was realized by the condensation reaction of FA with amine to induce TFPDI-bPEI aggregation. After the addition of FA, TFPDI-bPEI molecule aggregated in aqueous solution due to the specific reaction of a large number of –NH2 groups with FA, resulting in a blue-shift of the maximum absorption peak from 780 nm to 561 nm, and the detection limit as low as 0.86 μM to FA and the response time of only 20 s. This method could further detect FA in food with good recoveries and detect FA in contaminated food samples.

Application Of Two Dye Two-Color Laser-Induced Fluorescence Spectroscopy On Droplets Of Green Solvent Mixtures Containing Water And Ethanol

In order to reach a higher sustainability, the utilization of green solvents is decisive in many technical applications. Water and ethanol substitute more complex solvents, showing advantages like ecological manufacturing, reusability or biodegradation. Both liquids are found in various industrial areas, ranging from a use as additives in biofuels, coolants or solvents for extraction in pharmaceutical, medical or food industries. Regarding these industrial processes, important variables are the liquid phase temperature and the composition in binary fluids. The focus of this work is two dye two-color laser induced fluorescence (2c-LIF) measurements in ethanol, water and their mixtures. Liquid phase thermometry via 2c LIF requires a selection of suitable fluorescence dyes regarding solubility, temperature sensitivity and the interaction among the dyes themselves. A mixture of a temperature sensitive and a temperature insensitive dye is used in order to reach a large change in signal ratio for thermometry. In this work, two dyes – fluorescein disodium (FL) and sulforhodamine 101 (SRh), as proposed by Chaze et al. (Chaze et al. 2016) – are analyzed regarding their absorption and emission behavior in various ethanol/water mixtures, which are examples of "green solvents". The absorption spectra of the dissolved dye mixture are measured with a spectrophotometer at temperatures from 293 K to 343 K. Information on the temperature dependent absorption of the single dyes and reabsorption effects in ethanol/water mixtures is obtained. Additionally, the fluorescence of the mixtures is analyzed spectrally and by an imaging system. Therefore, a fiber coupled spectrometer and a system with two sCMOS cameras equipped with a long distance (LD) microscope are applied for simultaneous detection of the signal of tempered solutions a monodisperse droplet chain. A study of small droplets with sizes below 50 μm are evaluated and the limit of the spectral detection system is determined and discussed. The application of the measurement technique to several solvent mixtures is investigated. Additionally, an application for composition investigations of binary water/ethanol droplets via 3c-LIF is proposed.

Study on temperature-sensitive factors relevant to thermographic features of Tb3+-doped phosphate glasses

Intensities of the 5D4 luminescence with the 5D3 level populated by GSA and ESA transitions of Tb3+ in ternary phosphate glass were measured at different temperature between 300 K and 675 K. Acquired 5D4 luminescence intensities related to GSA and ESA excitation transitions from thermally coupled 7F6 and 7F5 levels were treated to assess luminescence intensity ratios (LIR) as a function of temperature and resulting values of relative sensitivity SR. To understand origin of marked dissimilarity of SR values observed in some few Tb3+-doped hosts reported thus far an in-depth analysis of the excitation energy flow in systems under study is made. Spectra of absorption cross section and temperature dependent absorption coefficient for ESA transition were evaluated. Rates of temperature dependent cross relaxation process governing energy transfer between 5D3 and 5D4 were calculated. It was supposed that temperature-dependent absorption of colour centres in the blue region may affect adversely relative thermal sensitivity.

Quinoline based viologen as a multifunctional organic material – From crystal structures to photophysical and electrochemical properties, and application in DNA sensing and bioimaging

Developing new multifunctional organic materials is one of the current themes of research in organic materials chemistry. The class of N,N'-dialkylated bis-pyridinium compounds, namely, the viologens have been proven to offer such multifunctional materials. Herein, syntheses and crystal structure elucidation of trans-1,2-bis(4-quinolinyl)ethylene (BQE) and analogous N,N-dimethylated trans-1,2-bis(4′-quinolinium)ethylene (M2BQE) are discussed with their multifaceted materials properties. Two different crystal structures with significantly different molecular structures, namely, BQE and BQE⋅2H2O were obtained by tuning the solvent of crystallization. M2BQE showed a bathochromic shift both in its absorption by ∼ 3300 cm−1 and in emission by ∼2900 cm−1 in compared to BQE, which is the effect of quaternization. Large Stokes shifts were observed for both the BQE (∼8500 cm−1) and M2BQE (∼8050 cm−1). Both compounds showed two-step reduction events in cyclic voltammetry, of which the first steps were reversible. The pH dependent absorption and emission properties of BQE have been explored which revealed the stronger effect by methylation than protonation. M2BQE exhibited selective binding to ct-DNA, as confirmed by selective quenching of emission intensity, over AMP and ATP. Furthermore, both the BQE and M2BQE displayed very intriguing features in bioimaging by intracellular co-localization in HeLa cells. While BQE is predominantly localizes in lysosomes over mitochondria, M2BQE dication, on the other hand, explicitly localizes in mitochondria.

High Electronic Coupling between Cu Complexes and Oxidized Dyes Confirmed by Measurements of Driving Force Dependent Regeneration Kinetics in Minimal Electrolyte System.

We confirm fast regeneration kinetics between copper complexes and oxidized organic dyes and the major contribution of electronic coupling (HDA). The highest efficiency of dye-sensitized TiO2 solar cells has been shown by employing Cu complex redox couples. Various groups have reported a fast regeneration rate of oxidized dyes by Cu complexes giving a low driving force attributed to low reorganization energy (λ), but the effect of HDA has not been evaluated. The values of HDA and λ can be derived from driving force dependent transient absorption (TA) measurements. However, analyzing TA decay using Cu complexes is not trivial because accelerated recombination by the presence of Cu2+ complexes and biphasic TA decay often complicates the analysis. Here we employ 16 Cu1+ and Co2+ complexes and two dyes. To simplify the system, i.e., making a minimal electrolyte system, Cu2+ and Co3+ complexes and a common additive of 4-tert-butylpyridine are not used. From the driving force dependent TA decays of oxidized dyes by both Cu1+ and Co2+ complexes, λ for the combination of the Cu complexes and dyes is found to be about 0.15 eV lower than that of Co complexes. Approximately 3 to 5 times higher HDA values of Cu complexes than those of Co complexes are obtained, which is the dominant factor for faster rates. The values vary with the structure of the molecules, showing the possibility of increasing the HDA values further. The higher HDA values of a Cu complex than that of a Co complex are also reproduced by quantum chemical calculations.

Coumarin Derivative and Gold Nanoparticle Conjugate as a Selective Fluorescent Sensor for Mercury Ion in Real Sample.

A biphenyl based coumarin fluorescent molecule, N,N'-bis(7-diethylamino-2-oxo-2H-chromen-3-yl)methylene)biphenyl-2-2'-dicarbohydrazide (molecule 1) has been synthesized and characterised. Photophysical studies of 1 exhibit solvent polarity dependent absorption and emission maxima. Citrate capped gold nanoparticles (AuNPs) have been mixed with molecule 1 for the preparation of AuNPs/1 conjugate. The association constant of the AuNPs/1 conjugate has been calculated to 4.54 × 104 M- 1. The AuNPs/1 conjugate has been found to detect Hg2+ ion selectively by fluorescence enhancement. While addition of molecule 1 into the solution of AuNPs, fluorescence intensity of 1 quenched. On addition of several monovalent, divalent and trivalent metal ion into the solution of AuNPs/1 conjugate separately, there was no change in fluorescence intensity of 1 has been observed. However, upon addition of Hg2+ ion into the solution of AuNPs/1 conjugate, the fluorescence intensity enhancement occurred, indicating released of 1 from the surface of AuNPs and probably aggregation of AuNPs took place in presence of Hg2+ ion. The AuNPs/1 conjugate has been found to have a detection limit of 2.3 × 10- 9 M for Hg2+ ion in aqueous solvent. Meanwhile, the AuNPs/1 conjugate have also been successfully applied for the determination of Hg2+ in real water samples.

Contribution of black carbon and desert dust to aerosol absorption in the atmosphere of the Eastern Arabian Peninsula

Discriminating the absorption coefficients of aerosol mineral dust and black carbon (BC) in different aerosol size fractions is a challenge because of BC's large mass absorption cross-section compared to dust. Ambient aerosol wavelength dependent absorption coefficients (babs) in supermicron and submicron size fractions were determined with a high time resolution. The measurements were performed simultaneously using identical systems at an urban and a regional background site in Qatar. At each site, measurements were taken by co-located Aethalometers, one with a virtual impactor (VI) and the other with a PM1 cyclone to respectively collect super-micron-enhanced and submicron fractions. The combined measurement of aerosol absorption and scattering coefficients enabled the particles to be classified based on their optical properties' wavelength dependence. The classification reveals the presence of BC internally/externally mixed with different aerosols. Helium ion microscopy images provided information concerning the extent of mineral dust in the submicron fraction. The determination of absorption coefficients during dust storms and non-dust periods was used to establish the absorption Ångström exponent for dust and BC. Non-parametric wind regression, potential source contribution function and back-trajectory analysis reveal major regional sources of desert dust associated with north-westerly winds and a minor local dust contribution. In contrast, major BC sources found locally were associated with south-westerly winds with a smaller contribution made by offshore emissions transported by north-easterly and easterly winds. The use of a pair of Aethalometers with VI and PM1 inlets separates contributions of BC and dust to the aerosol absorption coefficient.

Influence of temperature on bandgap shifts, optical properties and photovoltaic parameters of GaAs/AlAs and GaAs/AlSb p–n heterojunctions: insights from ab-initio DFT + NEGF studies

The III–V group semiconductors are highly promising absorbers for heterojunctions based solar cell devices due to their high conversion efficiency. In this work, we explore the solar cell properties and the role of electron–phonon coupling (EPC) on the solar cell parameters of GaAs/AlSb and GaAs/AlAs p–n heterojunctions using non-equilibrium Green function method (NEGF) in combination of ab-initio density functional theory (DFT). In addition, the band offsets at the heterointerfaces, optical absorption and bandgap shifts (BGSs) due to temperature are estimated using DFT + NEGF approach. The interface band gaps in heterostructures are found to be lower than bulk band gaps leading to a shift in optical absorption coefficient towards lower energy side that results in stronger photocurrent. The temperature dependent electronic BGS is significantly influenced by the phonon density and phonon energy via EPC. The phonon influenced BGS is found to change the optical absorption, photocurrent density and open-circuit voltage. In case of GaAs/AlSb junction, the interface phonons are found to have significantly higher energies as compared to the bulk phonons and thereby may have important implications for photovoltaic (PV) properties. Overall, the present study reveals the influence of EPC on the optical absorption and PV properties of GaAs/AlSb and GaAs/AlSb p–n heterojunctions. Furthermore, the study shows that the DFT + NEGF method can be successfully used to obtain the reasonable quantitative estimates of temperature dependent BGSs, optical absorption and PV properties of p–n heterojunctions.

Tuning charge transport by manipulating concentration dependent single-molecule absorption configurations

Understanding and tuning charge transport in molecular junctions is pivotal for crafting molecular devices with tailored functionalities. Here, we report a novel approach to manipulate the absorption configuration within a 4,4'-bipyridine (4,4'-BPY) molecular junction, utilizing the scanning tunneling microscope break junction technique in a concentration-dependent manner. Single-molecule conductance measurements demonstrate that the molecular junctions exhibit a significant concentration dependence, with a transition from high conductance (HC) to low conductance (LC) states as the concentration decreases. Moreover, we identified an additional conductance state in the molecular junctions besides already known HC and LC states. Flicker noise analysis and theoretical calculations provided valuable insights into the underlying charge transport mechanisms and single-molecule absorption configurations concerning varying concentrations. These findings contribute to a fundamental comprehension of charge transport in concentration-dependent molecular junctions. Furthermore, they offer promising prospects for controlling single-molecule adsorption configurations, thereby paving the way for future molecular devices.

Temperature-dependent tuning of band gap of Fe3O4 nanoparticles for optoelectronic applications

We have investigated structural, morphological and temperature dependent absorption characteristics of Fe3O4 nanoparticles. X-ray diffraction pattern exhibited six diffraction peaks belonging to the cubic phase structure with lattice parameter of a = 8.1602 Å. Spectral variation of absorption coefficient were utilized to achieve Tauc and spectral derivative analyses providing the band gap of the Fe3O4 at varying temperature. The band gap of Fe3O4 nanoparticles was found around 2.08 eV at 300 K and around 2.14 eV at 10 K. The band gap variation with applied temperatures between 10 and 300 K were also investigated using Varshni relation.

Spatially varying optical characteristics in quantum-dot molecules through interdot tunneling

In this paper, we investigate the spatially dependent absorption characteristics in structurally asymmetric quantum-dot molecules (QDMs), characterized by four energy levels interacting with position-dependent beams and varying system parameters. We explore the effects of detuning, standing wave intensity, and the relative phase of applied fields on the absorption patterns within the medium. A diverse array of patterns emerges, including cross-like structures, ring-like formations, and localized absorption maxima, illustrating the intricate interplay between these parameters and the spatial distribution of absorption features. The introduction of a vortex-shaped control field adds a new dimension to the study, revealing azimuthal dependence and providing a novel perspective for manipulating absorption and gain properties based on the orbital angular momentum of the control field. This work contributes to a comprehensive understanding of the intricate dynamics governing spatially dependent absorption in QDMs, offering valuable insights for controlled manipulation and practical applications in quantum systems.

The sound absorption of air permeable structures produced by 3D printing using PLA material

The aim of the contribution is comparison of noise absorption properties of two designs of acoustic dampening air permeable structures. A circular test samples with a diameter of 89 mm and three different thicknesses of samples were produced using of 3D printing process. In addition to the thickness, the internal structure of the samples was also changed. The prepared samples were tested using an impedance tube. The acoustic properties of the test samples were investigated in accordance with the standards ASTM E1050-19, E2611-17 and ISO 10534-2. A two-microphone method based on the calculation of transfer function method was used to determine the absorption coefficient of the designed structures. The Brüel&Kjær PULSE system was used to estimate the frequency dependence of sound absorption coefficient of test samples. In the paper are presented the experimentally obtained values of the sound absorption coefficient for different structure design and thicknesses of samples produced by 3D printing technology. The measurements were evaluated in the range of working frequencies of the impedance tube.

The investigation of diesel soot emission using instrument combination of multi-wavelength photoacoustic spectroscopy and scanning mobility particle sizer

The parallel measurements of wavelength dependent optical absorption, particle number size distribution have made by a multi wavelength photoacoustic spectrometer (4λ-PAS) and scanning mobility particle sizer (SMPS) respectively at different modes of a diesel engine using two different types of fuel. The thermal evolution of the emission was also investigated using posterior temperature treatment of emission. The bimodal size distribution of emitted particles at a set reference temperature has been observed regardless of the applied fuel at idle. However, the emitted particulate assembly had lognormal size distribution falls into the accumulation mode at all other defined engine modes and both fuel types. The total number- and volume concentration (TNC and TVC) showed retrograde tendency with the increasing torque and rpm independently of the applied fuel types. The TNC values decreased up to 50% for both fuels with engine operation changes from idle engine mode(em#1) to low engine mode(em#2). With further increase in torque and rpm of engine, the change in TNC is negligible. On the other hand, the TVC remains more or less the same for idle to low engine mode transition and increased more than 60% for high mode (em#3) transition. The Optical Absorption Coefficient (OAC) values measured at the operational wavelengths of the 4λ-PAS instrument decreased at all wavelengths with increasing rpm and torque. The wavelength dependency quantified by Aerosol Ängström Exponent (AAE) was applied here for qualitative analysis of the carbonaceous emission and showed decreased values towards the higher engine speed and torque output of the engine. The proposed technique can be used as real-time, precise and accurate measurement of light absorption by DPM aerosols, which opens up novel possibilities for the volatility and thermal evolution investigation of diesel emissions.

Impact of Sn-doping on the optoelectronic properties of zinc oxide crystal: DFT approach.

This study aims to provide a concise overview of the behavior exhibited by Sn-doped ZnO crystals using a computational technique known as density functional theory (DFT). The influence of Sn doping on the electronic, structural, and optical properties of ZnO have been explored. Specifically, the wavelength dependent refractive index, extinction coefficient, reflectance, and absorption coefficient, along with electronic band gap structure of the Sn doped ZnO has been examined and analyzed. In addition, X-ray diffraction (XRD) patterns have been obtained to investigate the structural characteristics of Sn-doped ZnO crystals with varying concentrations of Sn dopant atoms. The incorporation of tin (Sn) into zinc oxide (ZnO) has been observed to significantly impact the opto-electronic properties of the material. This effect can be attributed to the improved electronic band structure and optical characteristics resulting from the tin doping. Furthermore, the controllable structural and optical characteristics of tin-doped zinc oxide will facilitate the development of various light-sensitive devices. Moreover, the impact of Sn doping on the optoelectronic properties of ZnO is thoroughly investigated and documented.