Light Absorption Coefficient Research Articles

Contrasting mass absorption efficiency of carbonaceous aerosols between PM1 and PM2.5 in urban Beijing

Carbonaceous aerosol, mainly comprising elemental carbon (EC) and organic carbon (OC), plays an important role in aerosol–climate interaction owing to its light-absorbing feature. The radiative forcing of carbonaceous aerosol is largely determined by its mass absorption efficiency (MAE). To depict the MAE of carbonaceous aerosol and its variations with aerosol size and chemical composition, light absorption coefficients and the main chemical composition of PM1 and PM2.5 were comparably measured in a winter field campaign in urban Beijing. On average, aerosol absorption by PM1 at 880 nm wavelength contributes to approximately half of aerosol absorption by PM2.5, mainly because aerosol absorption at this wavelength was dominated by EC and nearly half of the total EC mass in PM2.5 existed in PM1. The average MAE of EC at 880 nm (MAEEC,880nm) was 3.9 ± 0.7 m2 g−1 for PM2.5, lower than that for PM1 (4.4 ± 0.8 m2 g−1) likely because of the larger EC cores and lower coating degrees of EC particles in PM1–2.5. Variation in MAEEC,880nm was related to the bulk mass fractions of nitrate in PM1 and PM2.5, implying the important impact of secondary nitrate formation on the modification of EC mixing states and enhancing EC absorption efficiency in Beijing. Absorption by OC took up about 40% of the absorption coefficients for PM1 and PM2.5 at 370 nm. The mean MAE of OC at 370 nm (MAEOC,370nm) was 2.4 ± 0.9 m2 g−1 for PM1, higher than that of for PM2.5 (1.9 ± 0.6 m2 g−1). The high value of MAEOC,370nm might be associated with regionally transported aerosols during clean and polluted periods. Enlarged particle sizes might have considerably weakened MAEOC,370nm for PM2.5 while exerting negligible impact on MAEOC,370nm for PM1.

The spontaneous polarization of In-doped κ-Ga2O3 by first-principles calculation

The crystal structure, band structure, density of states, and optical properties of κ-(Ga1−xInx)2O3 (x = 0, 0.125, 0.25, 0.5) were studied using the first-principles calculation based on the density functional theory. With the increase of In content x, the bandgap of κ-(Ga1−xInx)2O3 decreases, while the light absorption coefficient increases. The spontaneous polarization of κ-(Ga1−xInx)2O3 was calculated qualitatively using the Born effective charge. The results suggested that κ-(Ga1−xInx)2O3 is also a material with spontaneous polarization properties. The spontaneous polarization in the extended c-axis has increased 1.27 times, from 27.31 to 34.58 μC/cm2, with the increase of In content from 0 to 0.5. This work paves the way for modulating spontaneous polarization of wide bandgap semiconductors. It provides a theoretical basis for the potential application of κ-(Ga1−xInx)2O3 in high electron mobility transistors, quantum well-infrared photodetectors, and photovoltaic materials.

Effect of Solution and Dry Processing Techniques on the Optical and Transport Properties of Inorganic CsPbBr3 Perovskite Films

Cesium-based inorganic CsPbBr3 perovskite material possesses remarkable optoelectronic properties, such as high light absorption coefficient, high carrier mobility, and long diffusion length, and hence has promising applications in solar cells, photo-detectors, and high-energy radiation detectors, among others. Because of its simplicity, low cost, and high efficiency, spin-coating deposition for the CsPbBr3 perovskite layer for such diverse applications has been widely used. However, the spin-coating technique has technological constraints when it comes to uniformly deposit large-area films. Thermal evaporation, on the other hand, is inexpensive and produces a uniform and repeatable thin film. In this study, the stability, energy band alignment, surface morphologies, and light absorption of a CsPbBr3 perovskite layer produced by spin coating and thermal evaporation are investigated and discussed.

A metallic CP3 monolayer with very high absorption coefficients for visible light and as the CO2 absorbent

In this paper, we predicted a metallic CP3 monolayer and investigated its formation possibilities. The CP3 monolayer exhibits obvious optical anisotropy and very high absorption coefficient (∼24 %) at the visible light range. In addition, CO2 molecule can be stably adsorbed on the surface of CP3 monolayer with the adsorption energy as −2.466 eV aimed to lower the greenhouse effect. Therefore, the CP3 monolayer should be a novel and potential two-dimensional material for applications in optoelectronic, electronic, photovoltaic devices and as the CO2 absorbent.

Using machine learning to quantify sources of light-absorbing water-soluble humic-like substances (HULISws) in Northeast China

Water-soluble humic-like substances (HULISws) are a group of heterogeneous organic compounds in the atmosphere, greatly impacting climate change and human health. As the most significant biomass burning (BB) and fossil fuel burning polluted area in China, Northeast China Plain could generate more light absorbing HULISws to the atmosphere. In this work, daily fine particle (PM2.5) samples were collected in Changchun, located in Northeast China Plain, from October 17th to November 29th, 2016, to investigate the potential sources of optical properties of HULISws. Here, the whole sampling period was divided into three sub-periods using the density of fire spots and the timeline of the central heating: the non-heating (October 17th to October 24th), early heating (October 25th to November 13th), and normal heating (November 14th to November 29th) periods. The mean mass concentrations of HULISws were 4.2 ± 1.2, 8.6 ± 3.6, and 2.4 ± 1.3 μg m−3 during the non-heating, early heating, and normal heating periods, respectively. The positive matrix factorization (PMF) model results suggested that the contribution of primary BB, secondary BB, and fossil fuel burning emissions were 46%, 24%, and 19% during the non-heating period, 22%, 29%, and 17% during the early heating period, and 13%, 16%, and 50% during the normal heating period, respectively. Combining the PMF results with the random forest (RF) algorithm, the contribution of each source to the optical properties was quantified. Here, BB still dominated the optical properties of HULISws in Northeast China. During the study period, the primary BB and secondary BB contributed 25% and 34% in the light absorption coefficient (Abs), 22% and 33% in the mass absorption exponent (MAE), and 17% and 33% in the absorption Ångström exponent (AAE), respectively. Other sources like cooking and fossil combustion contributed 25% and 35% in Abs, 35% and 26% in MAE, and 16% and 33% in AAE, respectively.

Structural, elastic, phononic, optical and electronic properties investigation of two-dimensional XIS (X=Al, Ga, In) for photocatalytic water splitting

Two-dimensional (2D) materials have been widely developed due to their attractive properties. Here, by using density functional theory (DFT) calculations, for the first time, we explore potential applications of the novel XIS (X = Al, Ga, In) monolayer 2D materials on photocatalytic water splitting. A series of simulations were carried out to predict and study the structural, elastic, phononic, optical and electronic properties of 2D XIS materials. The results show that GaIS and InIS demonstrate low thermal conductivity. For optical properties, AlIS shows strong light absorption coefficients and refractive index only under ultraviolet (UV) light, while GaIS and InIS show stronger performance under both visible light and UV light with the band edge positions spanned the redox potential of water. The reasonable band positions and bandgaps make them promising photocatalysts for water splitting. This work reveals the potential applications of monolayer 2D XIS in thermal, electronic, and photocatalytic water splitting.

Optical properties and potential sources of water-soluble and methanol-soluble organic aerosols in Taipei, Taiwan

The optical properties and sources of brown carbon (BrC) have been poorly constrained in climate models due to the variability of spatiotemporal characteristics, impeding the accurate understanding of its impact on air quality and climate. In this study, daily PM2.5 samples, which were collected from January to November 2021 in urban Taipei, Taiwan, and seasonal variations of optical properties of water-soluble and methanol-soluble organic carbon (WSOC and MSOC) were evaluated. The light absorption coefficients at 365 nm (Abs365) of both extracts, which strongly correlated with WSOC and MSOC mass concentrations, displayed distinct seasonal variations with the highest in winter and the lowest in summer. The Absorption Ångström Exponent of WSOC and MSOC ranged from 4.16 to 7.75 and 4.03–6.83, with averages of 6.05 ± 0.56 and 5.29 ± 0.61, respectively. The mass absorption efficiency (MAE365), which normalizes the Abs365 of both extracts to the mass of WSOC and MSOC, showed significant seasonal difference with the high MAE365, WSOC of 0.96 ± 0.29 m2 g−1 in winter and the lowest in summer of 0.49 ± 0.07 m2 g−1, whereas contrasting with the largest MAE365, MSOC of 0.99 ± 0.46 m2 g−1 in summer and the lowest in winter of 0.66 ± 0.28 m2 g−1, respectively. Fossil fuel combustion, such as traffic emission, and biomass burning, such as crematorium, were identified to be important contributors to light-absorbing substances. The estimated fractional radiative forcing by WSOC and MSOC to elemental carbon was most significant during winter (8.15 ± 3.77%) and spring (13.90 ± 4.38%), respectively, which may greatly affect the atmospheric photochemistry and climate. This study suggests that the impact of BrC in Taiwan on the local and regional air quality and climate is non-negligible.

Quasi-Planar tetracoordiante carbon Networks with tunable electronic properties combined with Ultra-High carrier mobility and optical absorption Coefficient: Two-dimensional Be2C

Tunable electronic structure, high carrier mobility and high optical absorption coefficient are three key properties for the application of two-dimensional (2D) semiconductors in nanoelectronic and optoelectronic devices. Based on first-principles calculations, we have designed a novel 2D quasi-planar material, Be2C monolayer, which contains tetracoordiante carbon structure formed by the metal bonding between carbon and four surrounding beryllium atoms. The monolayer Be2C has a wide indirect band gap of 2.33 eV (calculated by HSE06 functional), which can be regulated into a direct band gap by applying strain and changing the number of Be2C layers, leading to a change of the band gap from 0 to 2.62 eV. In addition, the monolayer Be2C has ultra-high electron mobility of 1.44 × 104 cm2V-1s−1 and light absorption coefficient of 1.12 × 106 cm−1, which are comparable to graphene and perovskite materials in solar cell. These excellent properties provide a very bright prospect for the monolayer Be2C in the applications of microelectronic and optoelectronic devices.

A novel two-dimensional transition metal dichalcogenide as water splitting photocatalyst with excellent performances.

With the rising demand for renewable energy, photocatalysts are considered the most promising solution to harness solar energy, and the search for photocatalysts with excellent performances remains an urgent task. Here, based on density functional theory (DFT), the photocatalytic properties of MoWS4 are systematically investigated. The MoWS4 monolayer and bilayer are demonstrated as semiconductors with indirect band gaps of 2.01 and 1.48 eV. Moreover, they exhibit high and anisotropic light absorption coefficients of up to ∼105 cm−1 in the visible-ultraviolet region. The intrinsic band edge positions could fully satisfy the redox potentials of water without any external adjustment. The electron mobility of MoWS4 monolayer is 557 cm2 V−1s−1, which is seven times higher than MoS2 monolayer. Hence, MoWS4 can be regarded as a promising 2D photocatalyst candidate for water splitting.

Development of 2nd Generation Thin Film Photovoltaics Based on CZTS Absorber Layer and ZnS Window Layer

Among the second-generation solar cells, thin-film solar cells based on CIGS, CZTS and CdTe are well known due to their higher efficiencies, low cost and simple fabrication techniques. In this proposed work, we are committed to developing CZTS and ZnS thin films for second-generation thin-film photovoltaics. CZTS and ZnS have energy band gap of 1.4-1.5 eV and 3.6 eV, while their light absorption coefficients are 104 cm-1 and 3.3×104 cm-1 respectively. In thin film solar cells, absorber layer consists of photovoltaic material that should have optimal bandgap close to 1.34 eV. Moreover, a wide band gap window layer acts as p-n junction with absorber layer. In this work, we are reporting the synthesis of CZTS and ZnS thin films via wet chemistry route using spin coating method. Deposition of thin films on SLG substrate were carried out at specific process parameters such as spinning speed, concentration of precursors and annealing temperature to get the optimized thin film suitable for photovoltaic applications. Surface morphology and elemental compositional analysis investigated through SEM and EDX spectroscopy respectively. Electrical and optical properties were examined via Hall effect measurements and UV-VIS NIR spectrophotometry respectively. In addition micro-chemical and functional group analysis were conducted by FRIT spectroscopy. Keywords: Thin film PV, wet-chemistry, CZTS, ZnS

Tetrazolium-Based Visually Indicating Bacteria Sensor for Colorimetric Detection of Point of Contamination.

Protective equipment for detecting bacterial contamination has been in high demand with increasing interest in public health and hygiene. Herein, a fiber-based visually indicating bacteria sensor (VIBS) embedded with iodonitrotetrazolium chloride is developed for the general purpose of detecting live bacteria, and its chromogenic effectiveness is investigated for Gram-negative Escherichia coli and Gram-positive Micrococcus luteus. The developed color intensity is measured by the light absorption coefficient to the scattering coefficient (K/S) based on the Kubelka-Munk equation, and the colorimetric sensitivities of different membranes are examined by calculating the limit of detection (LOD) and the limit of quantification (LOQ). The results demonstrate that the interactions between VIBS and bacteria depend on the wetting properties of membranes. A hydrophobic membrane shows excessive interactions at high concentrations of Gram-negative E. coli bacteria, whose cell membrane is lipophilic. The membrane blended with hydrophobic and hydrophilic polymers displays linear colorimetric responses for both Gram-negative and Gram-positive bacteria strains, demonstrating a reliable sensing capability in the range of the tested bacteria concentration. This study is significant in that explorative experimentations are performed to conceive a proof of concept of a fiber-based bacteria sensor, which is readily applicable in various fields where bacteria pose a threat.

Comparison of black carbon, primary and secondary brown carbon light absorption and direct solar absorption at the foothill and summit of Mt. Hua, China

Atmospheric black carbon (BC), primary and secondary brown carbon (BrCpri and BrCsec) are the light-absorbing carbonaceous aerosol components. The vertical changes in the BC and BrC distributions are not generally known. Here, we presented a study of the spectral light absorption properties, direct solar absorption, and potential source areas of BC and BrC at the foothill (375 m a.s.l.) and summit (2060 m a.s.l.) of Mt. Hua, China. More than tripled BC and BrC light absorption coefficient were observed at the foothill compared to the summit. The dominant carbonaceous light-absorbing was attributed to BC with the percentages of 77 % (foothill) and 79 % (summit), respectively. The light absorption coefficient and direct solar absorption of BrCpri were much higher than those of BrCsec at foothill, especially in winter. The enhancing contributions of BrCsec light absorption coefficient and direct solar absorption were observed with high RH and visibility at the summit. The light absorption properties of BC, BrCpri, and BrCsec may be attributed to the emissions, meteorological conditions, and photochemical oxidation. The inferred potential source spatial distributions of BC and BrCpri showed different patterns at the foothill and summit. The results underlined the primary emission effects (including BC and BrCpri) at the foothill and the importance of BrCsec at the summit, respectively.

First-principles study of two-dimensional HfS2/GaS van der Waals heterostructure for photocatalytic action

Exploring excellent performance of photocatalysts for hydrogen/oxygen evolution reactions is an effective way for solar energy applications. In this work, a HfS 2 /GaS van der Waals heterostructure (vdwH) has been designed to achieve efficient and spontaneous water decomposition. Through first-principles calculation, HfS 2 /GaS vdwH has been proved to be a stable and promising photocatalyst with the following obvious advantages: both water reduction and oxidation potentials are located in the band gap of HfS 2 /GaS vdwH (2.04 eV), ensuring that water splitting can occur. The type-Ⅱ band structure and built-in electric field ensure the effective separation of photoelectron-hole, and the high mobility of electrons and holes can also predict high photocatalytic activity . By calculating the free energy of the oxygen evolution reaction on the surface of GaS and the hydrogen evolution reaction on the surface of HfS 2 of the heterostructure , it's found that the water decomposition reaction can occur spontaneously under light. Furthermore, after 1–6% in-plane biaxial tensile strain was applied, the redox reaction of photocatalytic decomposition water can still occur on the HfS 2 /GaS vdwH, and the application of strain can effectively regulate the optical and electronic properties. Therefore, HfS 2 /GaS vdwH could be a promising candidate material for the photocatalytic decomposition of water. • The spatial separation of photogenerated carriers is realized in type-II HfS 2 /GaS heterostructure. • The electron mobility can be as high as 10 3 cm 2 V −1 s −2 . • Free energy calculation shows that the water decomposition reaction can occur spontaneously under light. • HfS 2 /GaS heterostructure reach high light absorption coefficients of 3.6 × 10 5 cm −1 .

Investigation on photocatalytic property of SiH/GaSe and SiH/InSe heterojunctions for photocatalytic water splitting

The structural stability, electronic structure and optical property of the monolayers SiH, GaSe and InSe as well as constructed SiH/GaSe and SiH/InSe heterojunctions are investigated based on first principles calculations. The band alignment and the charge transfer of SiH/GaSe and SiH/InSe heterojunctions as well as their solar-to-hydrogen production efficiency during photocatalytic process for water splitting are analyzed systematically. The effect of applied electric field or biaxial strain taking on the electronic structure of heterojunctions is also included. The results indicated that the absorption range and intensity of SiH/GaSe and SiH/InSe heterojunctions are significantly improved. Both SiH/GaSe and SiH/InSe heterojunctions have the relatively higher light absorption coefficient in the visible and ultraviolet range. These light absorption capacities are conducive to improve the solar-to-hydrogen production efficiency. Compared with the monolayers SiH, GaSe and InSe, the SiH/GaSe and SiH/InSe heterojunctions have the property of type-II band alignment. This band alignment is also in favor of improving the efficiency of photocatalytic activity. The band gap and band edge structure of SiH/GaSe and SiH/InSe heterojunctions can also be adjusted effectively by applied electric field or biaxial strain, which provides a method for improving the photocatalysis performance.

Synthesis of Azo Disperse Dyes with High Absorption for Efficient Polyethylene Terephthalate Dyeing Performances in Supercritical Carbon Dioxide.

Supercritical carbon dioxide dyeing (SCDD) not only enables strong dyeing performance for a versatile range of polymer material but is also regarded as a green chemical media due to its low environmental impact as well as low risk of product denaturation. Over the decades, azo disperse dyes have been revealed to be efficient dyes and represent the wide majority of dyeing material. Azo dyes possess a wide variety of functional groups to optimize dye synthesis and tune the light absorption properties. Using SCDD, end-chain of different lengths, and functional group exhibiting various electronic affinity, six disperse red azo dyes were synthesized to investigate dyeing performances as woven fabric type, color strain, and color fastness after dyeing are discussed. Dye structure synthesized through a coupling reaction was confirmed by 1H NMR and mass spectroscopy. We found that the light absorption wavelength and absorption coefficient value variation are associated to the nature of the functional group. From the color strength values of the polyethylene terephthalate woven after dyeing, we find that the fiber host and dye dopant chemical structure greatly influence the dyeing process by providing enhanced woven, color strain, and color fastness. In comparison with commercial products, our approach not only improves the dyeing process but also guarantees a strong resistance of the dyed product against water, detergent, perspiration, abrasion, and friction.

Photo-electro-striction in halide perovskite semiconductors

MAPbI3, MAPbBr3, and CsPbBr3 are excellent halide perovskite semiconductors with super long carrier diffusion length, long minority carrier lifetime, and large light absorption coefficient. Compared with the small intrinsic electrostriction, photocarriers induce a large photostriction in the surface layer. Furthermore, an electric field can efficiently separate the light excited electron–hole pairs, enhance photocarriers diffusion, and finally increase the crystal expansion, i.e., photo-electro-striction. For each crystal under 30 V/mm and in light with 450 nm wavelength and 840 mW/cm2, the photo-electro-striction is over four times of the pure electrostriction and is larger than the sum of photostriction and electrostriction. Most importantly, MAPbI3 single crystal shows a large photostriction of ∼0.35% and the photo-electro-striction of ∼0.64%. This work proves a very large photo-electro-striction as a result of the strong coupling among photocarriers, electric fields, and crystal lattices, which is important to develop semiconductor devices.

Biaxial strain engineering of the electronic and optical properties of Ge2SeS monolayer: Promising for optoelectronic applications

Biaxial strain effects on the electronic and optical properties of the Ge2SeS monolayer were studied using the first-principles calculations in the present work. The band gap calculations show that the G2eSeS monolayer is a semiconductor at equilibrium state with an indirect band gap of 1.47 eV calculated by generalized gradient approximation (GGA) of Perdew Burke Ernzerhof (PBE) functional, which can be modulated by applying the biaxial strain changing from −6% to +6%. The optical properties such as dielectric constant, reflectivity, extinction coefficient, and absorption coefficient rise with the compression strain and reduce with tensile strain. Interestingly, it's confirmed that biaxial compression strain results in a high absorption coefficient in visible light. The anticipated results could make the Ge2SeS monolayer a candidate for optoelectronic applications.

Sublingual microcirculation: comparison between the 415nm blue light and 520nm green light of sidestream dark field videomicroscopes.

Green light with a wavelength of 520nm is commonly used in sidestream dark field (SDF) video microscopes for sublingual microcirculation assessment in clinical practice. However, blue light could obtain a clearer microcirculatory image due to a higher light absorption coefficient of hemoglobin. The aim of this study was to compare the sublingual microcirculatory image quality acquisition and related microcirculatory parameters between 520nm green light and 415nm blue light probes in the SDF device named MicroSee V100. Sublingual microcirculation films from twenty-one healthy volunteers were prospectively collected by blue light and green light probes, and only one video of each wavelength was recorded and analyzed in each volunteer. Moreover, 200 sublingual microcirculation films (100 by blue light probe and 100 by green light probe) of ICU patients were retrospectively scored for microcirculation image quality. Compared to green light, an increase in the perfused vessel density (paired t test, increased by 4.6 ± 4.7mm/mm2, P < 0.0001) and total vessel density (paired t test, increased by 5.1 ± 4.6mm/mm2, P < 0.0001) was observed by blue light in the healthy volunteers. The blue light probe had a significantly lower rate of unacceptable films than the green light probe in the 200 films of ICU patients (10/100 vs. 39/100, P < 0.0001). Blue light provides a higher microcirculatory vessel density and image quality than the existing SDF probe using green light.

Secondary Organic Aerosol (SOA) from Photo-Oxidation of Toluene: 1 Influence of Reactive Nitrogen, Acidity and Water Vapours on Optical Properties

Many climate models treat the light-absorbing SOA component called “brown carbon” (BrC) as non-light absorbing because its formation and transformations are poorly understood. We therefore investigated the influence of reactive nitrogen (NOx, NH3)-, acidity (H2SO4)-, and water-mediated chemistry on SOA formed by the photo-oxidation of toluene, the subsequent formation and transformation of BrC, and its optical properties. We discovered that nitrogen-poor (NP) SOA is formed when the molar ratio of NOx to reacted toluene (henceforth, [NOx/ΔHC]) is 0.15 or less, whereas nitrogen-rich (NR) SOA is formed when [NOx/ΔHC] &gt; 0.15. NR and NP SOA have markedly different characteristics. The light absorption coefficient (Babs) and mass absorption cross-section (MAC) of the SOA increased with [NOx/ΔHC] under both the NP and NR regimes. For NP SOA, the MAC increased with [NOx/ΔHC] independently of the relative humidity (RH). However, the MAC of NR SOA was RH-dependent. Under both NP and NR regimes, acidity promoted SOA browning while NH3 increased Babs and MAC at 80% RH. The highest MAC was observed at the lowest RH (20%) for acidic NR SOA, and it was postulated that the MAC of SOA depends mainly on the pH and the [H+]free/[SOA mass] ratio of the aqueous SOA phase.

Quantitative Regularities of Growth of Arthrospira platensis Batch Culture

The work focuses on the modeling the light-dependent growth of Arthrospira platensis. During the experimental study, we obtained a batch curve, which characterizes the presence of a long linear phase. We showed that the constant culture productivity is determined by the light conditions in which cells are located. The simplest model of the light-dependent growth of a batch culture is proposed. The model is based on the assumption that the specific growth rate is determined by the surface irradiation, the light absorption coefficient, and the concentration of chlorophyll a. Verification of the obtained equations indicates that the constant productivity is observed only in the case of a hyperbolic decrease chlorophyll a content and other structural compounds of microalgal biomass. A method for rapid assessment of the concentration of photosynthetic pigments in the A. platensis culture by its absorption spectrum using the sum of Gaussian curves is proposed. Mathematical decomposition of the absorption spectrum of A. platensis was carried out, all Gaussian parameters were calculated. For the red part of the spectrum, a simple expression is presented that allows one to estimate the concentration of chlorophyll a and phycobiliproteins. The native extinction coefficient of chlorophyll a at 678 nm was calculated to be 65 l·g-1·cm-1. We proposed an algorithm for determining the concentration of photosynthetic pigments directly from the true absorption spectrum of the A. platensis culture without interfering with its growth processes.