Extinction Coefficient Values Research Articles

Simulation and application of external quantum efficiency of solar cells based on spectroscopy

In this study, a method for optical simulation of external quantum efficiency (EQE) spectra of solar cells based on spectroscopy is proposed, which is based on the tested transmittance and reflectance spectra. First, to obtain a more accurate information of refractive index and extinction coefficient values, we modified the reported optical constants from the measured reflectance and transmittance spectra. The obtained optical constants of each layer were then collected to simulate the EQE spectra of the device. This method provides a simple, accurate and versatile way to obtain the actual optical constants of different layers. The EQE simulation approach was applied to the flat and textured heterojunctions with intrinsic layers (HIT) solar cells, respectively, which showed a perfect matching between the calculation results and the experimental data. Furthermore, the specific optical losses in different devices were analyzed.

Influences of grain size and microstructure on optical properties of microcrystalline diamond films**Project supported by the Key Project of the National Natural Science Foundation of China (Grant No. U1809210), the National Natural Science Foundation of China (Grant Nos. 50972129 and 50602039), the International Science Technology Cooperation Program of China (Grant No. 2014DFR51160), the National Key Research and Development Program of

Microcrystalline diamond (MCD) films with different grain sizes ranging from 160 nm to 2200 nm are prepared by using a hot filament chemical vapor deposition (HFCVD) system, and the influences of grain size and structural features on optical properties are investigated. The results show that the film with grain size in a range of 160 nm–310 nm exhibits a higher refractive index in a range of (2.77–2.92). With grain size increasing to 620±300 nm, the refractive index shows a value between 2.39 and 2.47, approaching to that of natural diamond (2.37–2.55), and a lower extinction coefficient value between 0.08 and 0.77. When the grain size increases to 2200 nm, the value of refractive index increases to a value between 2.66 and 2.81, and the extinction coefficient increases to a value in a range of 0.22–1.28. Visible Raman spectroscopy measurements show that all samples have distinct diamond peaks located in a range of 1331 cm−1–1333 cm−1, the content of diamond phase increases gradually as grain size increases, and the amount of trans-polyacetylene (TPA) content decreases. Meanwhile, the sp2 carbon clusters content and its full-width-at-half-maximum (FWHM) value are significantly reduced in MCD film with a grain size of 620 nm, which is beneficial to the improvement of the optical properties of the films.

Laser-induced optically modified Se58Ge27Pb15 and Se58Ge24Pb18 thin films

ABSTRACTAmorphous samples of Se58Ge27Pb15 and Se58Ge24Pb18 glasses were prepared using the melt quenching method. Thin films of samples were deposited using the vacuum evaporation method. These films were illuminated with Nd: YAG 532 nm green laser radiation. The samples were structurally characterised using X-ray Diffraction (XRD) and Energy-dispersive X-ray analysis. XRD indicated an increase in the crystallinity of samples on laser irradiation. The samples were optically tested through absorption, reflection and transmission spectra recorded on UV-vis spectrophotometer. The obtained values of energy band gap, refractive index, extinction coefficient and Urbach energy of the films were compared both before and after laser exposure. Furthermore, it was found that sample thickness also changes on laser irradiation. The band gap of the samples was found to decrease laser irradiation in Se58Ge27Pb15thin films, while for Se58Ge24Pb18 thin film samples, an unexpected increase in band gap was observed at a laser irradiation time of 8 min. The variable behaviour of band gap has been explained on the basis of Mott and Davis model and heteropolar bond formation.

Retrieval of Evapotranspiration from Sentinel-2: Comparison of Vegetation Indices, Semi-Empirical Models and SNAP Biophysical Processor Approach

Remote sensing evapotranspiration estimation over agricultural areas is increasingly used for irrigation management during the crop growing cycle. Different methodologies based on remote sensing have emerged for the leaf area index (LAI) and the canopy chlorophyll content (CCC) estimation, essential biophysical parameters for crop evapotranspiration monitoring. Using Sentinel-2 (S2) spectral information, this study performed a comparative analysis of empirical (vegetation indices), semi-empirical (CLAIR model with fixed and calibrated extinction coefficient) and artificial neural network S2 products derived from the Sentinel Application Platform Software (SNAP) biophysical processor (ANN S2 products) approaches for the estimation of LAI and CCC. Four independent in situ collected datasets of LAI and CCC, obtained with standard instruments (LAI-2000, SPAD) and a smartphone application (PocketLAI), were used. The ANN S2 products present good statistics for LAI (R2 > 0.70, root mean square error (RMSE) < 0.86) and CCC (R2 > 0.75, RMSE < 0.68 g/m2) retrievals. The normalized Sentinel-2 LAI index (SeLI) is the index that presents good statistics in each dataset (R2 > 0.71, RMSE < 0.78) and for the CCC, the ratio red-edge chlorophyll index (CIred-edge) (R2 > 0.67, RMSE < 0.62 g/m2). Both indices use bands located in the red-edge zone, highlighting the importance of this region. The LAI CLAIR model with a fixed extinction coefficient value produces a R2 > 0.63 and a RMSE < 1.47 and calibrating this coefficient for each study area only improves the statistics in two areas (RMSE ≈ 0.70). Finally, this study analyzed the influence of the LAI parameter estimated with the different methodologies in the calculation of crop potential evapotranspiration (ETc) with the adapted Penman–Monteith (FAO-56 PM), using a multi-temporal dataset. The results were compared with ETc estimated as the product of the reference evapotranspiration (ETo) and on the crop coefficient (Kc) derived from FAO table values. In the absence of independent reference ET data, the estimated ETc with the LAI in situ values were considered as the proxy of the ground-truth. ETc estimated with the ANN S2 LAI product is the closest to the ETc values calculated with the LAI in situ (R2 > 0.90, RMSE < 0.41 mm/d). Our findings indicate the good validation of ANN S2 LAI and CCC products and their further suitability for the implementation in evapotranspiration retrieval of agricultural areas.

Calculating Resin Functionalization in Solid-Phase Peptide Synthesis Using a Standardized Method based on Fmoc Determination.

Solid-phase synthesis is the method of choice for peptide preparation in both research and industrial settings. The whole synthetic process is governed by the initial functionalization of the resin. Although the literature provides several methods to determine such functionalization, the addition of an Fmoc-amino acid and the posterior spectrophotometric measurement of the dibenzofulvene adduct formed after Fmoc removal is the most widely used for this purpose. However, a range of molar extinction coefficient (ε) values and even wavelengths are currently used in the field, with no standardization of the method. Here, we propose a single-point standardization method that involves a standard solution of the corresponding amino acid to be checked that is prepared freshly at the time of the analysis.

A Combined Conduction–Radiation Model for Analyzing the Role of Radiation on Freezing of a Biological Tissue

AbstractTissue freezing has significant applications in cryopreservation and cryosurgery processes. The freezing rate is an important factor during the cryopreservation process. To improve and make an accurate estimation of the freezing rate, radiation heat transfer plays a major role. To analyze in details, a two-dimensional coupled conduction–radiation model is developed. The tissue is frozen from the left side while the other sides are at the initial temperature. Finite volume method (FVM) is used to discretize both the radiative transfer equation (RTE) and energy equation. The algebraic equation after discretization is solved by the tri-diagonal matrix algorithm. The radiative heat flux is calculated by solving the RTE. The energy equation provides the temperature field. The enthalpy-porosity method is used to update the liquid volume fraction and thus the freezing front is captured. A linearization technique is proposed to linearize the radiative source term in the energy equation to avoid chances of divergence of the solution. The present model is first validated with the results of the existing literature and a good agreement is found. The effects of different parameters such as conduction–radiation parameter, scattering albedo, extinction coefficient and Stefan number on the prediction of temperature field, and the position of the freezing front are studied in details. It is found that a decrease in the values of conduction–radiation parameter, scattering albedo, and increase in the values of extinction coefficient and Stefan number cause more radiative heat loss. Hence, the freezing rate is improved and more frozen region is observed.

Physical properties and ethanol response of sprayed In2S3:Sn films

Tin-doped indium sulfide (In2S3:Sn) thin films were deposited on the glass substrate by varying molar ratio of Sn:In from 0 to 4% using spray pyrolysis. X-ray diffraction analysis showed that the deposited films were polycrystalline and crystallized in a cubic structure. The evaluated crystallite size varied in the range, 14.8–25.5 nm. The root-mean-square (RMS) roughness values decreased from 39 to 17 nm. Raman studies showed different peaks related to In2S3 phase and no additional phase was detected. The optical analysis allowed us to know that In2S3:Sn thin films had a transparency over 65%–70% in the visible region and 75%–90% in the near-infrared region. It displayed a band gap from 2.68 to 2.91 eV for the direct transition. The refractive index (n) values of In2S3:Sn thin films decreased from 2.45 to 2.37. The extinction coefficient (k) values were in the range of 0.01–0.21. Effect of tin doping on ethanol sensing response was also investigated. A slight enhancement in response is shown for In2S3:1%Sn sample.

Synthesis and characterization of some novel Mn(III) glycinato complexes with catalytic applications

Tris(glycinato)Mn(III) and its mixed ligand complexes with azido-, thiocyanato-, chloro- and bromo- groups have been synthesized and characterized by UV–Vis spectrophotometry, IR spectrophotometry, elemental analysis, magnetic susceptibility measurements, thermal analysis, Dart-mass spectrometry, EPR spectral studies, and X-ray powder diffraction studies. The molar extinction coefficient values of the complexes are in the range of spin allowed 5T2g → 5Eg transitions. The magnetic susceptibility measurements of all the complexes confirmed the presence of four unpaired electrons and high spin d4 systems. Room temperature EPR spectrum gives g isotropic value 2.002 indicative of octahedral geometry for the complex. PXRD studies suggest monoclinic system with space group P21/c with a = 9.1382(60) Å, b = 15.5340(11) Å, c = 10.2576(68) Å, and β = 110.598(15)°. The particle size of the complexes lies in the range 26.60–38.79 nm. The tris(glycinato)Mn(III) is an efficient heterogeneous catalyst for decolorization of Xylenol Orange and Methyl Red in the presence of H2O2. It also initiates polymerization of acrylonitrile.

Direct UV photolysis of pharmaceutical compounds: Determination of pH-dependent quantum yield and full-scale performance

When using municipal wastewater as a potable water source, advanced treatment is mandatory for the removal of trace organic contaminants, including pharmaceuticals. UV-radiation (254 nm) is frequently used in combination with hydrogen peroxide at the end of the advanced treatment train for simultaneous disinfection and degradation of trace organic contaminants. In this work, a comprehensive study on the direct UV photolysis of eleven organic compounds (including ten pharmaceuticals and N-Nitrosodimethylamine (NDMA)) was conducted at varying pH of 5–8 using a collimated beam apparatus. Molar extinction coefficient (ε) and quantum yield (QY) values of different ionic forms (cationic, neutral and anionic) for eleven organic compounds were estimated in the tested pH range. Furthermore, direct UV photolysis at a full-scale UV photoreactor with 30 low-pressure UV lamps was performed at pH 6.2 and 7.8 by varying water flow rates (375–2700 L min−1) and UV fluences (400–4000 mJ cm−2). A process model was developed to determine the log reduction of the test compounds. The model combines a Lagrangian fluence model in the photoreactor with a pH-dependent photochemical kinetic model that ulilized the measured molar extinction coefficient and quantum yield values. The observed log reductions matched well with the model predictions for most of the tested compounds.

Physical, chemical and optical properties of CdSe and CdSe:Zn thin films obtained through low cost electrochemical route

Abstract In the present report, thin films of Cadmium Selenide (CdSe) and Zn doped Cadmium Selenide (CdSe:Zn) have been deposited on Fluorine doped tin oxide coated (SnO 2 :F) glass substrate by electrodeposition technique. Structural investigation showed that the prepared films have polycrystalline nature with cadmoseleite structure. Williamson Hall plot analysis has been used to estimate the microstructural parameters. Film composition has been analyzed using Energy dispersive X-ray analysis. UV–Visible spectroscopic measurement has been carried out to find out the parameters such as Band gap, refractive index, extinction coefficient value of the deposited films.

Identification of hardware fault data of particle LiDAR

The hardware fault of the LiDAR will make the quality of the echo data worse. However, there is still a lack of effective identification methods for the error data caused by the hardware failure. Analysis of echo characteristics of atmospheric particulate matter monitoring when LiDAR has hardware failure, according to the echo signal information of the echo shape and intensity of the LiDAR, the fuzzy logic algorithm is used to identify the fault data. The hardware fault data of the atmospheric particulate LiDAR is identified and tested. At the same time, in order to reduce the false positive rate of data without hardware failures, the mean values of extinction coefficient and signal-to-noise ratio (SNR) at the height of 300 meters to 500 meters were compared between the data of hardware failures and the data was misjudged, reduced the false positive rate by setting the signal to noise ratio threshold. The experimental results show that this method is used to identify the hardware fault data of the LiDAR monitoring of the external field, the recognition rate is 94.6%, and the false positive rate is only 1.5%. This method has a good recognition effect on hardware fault data.

A study on the effect of the macrocycle ring size and R-group chain length on the optical properties of the CuPc thin films

Optical properties of spin-coated films of copper phthalocyanine (CuPc) are investigated by using UV–visible spectroscopy. The absorption spectra were recorded in the UV–visible region and showed two absorption bands of the phthalocyanine molecules, namely, the Soret (B) and the Q-band. The UV–visible spectrum is used to calculate the physical parameters of the thin film under investigation such as absorption A, reflectance R, refractive index n, extinction coefficient k, optical conductivity σopt and optical band gap Eg values. The obtained refractive index and the extinction coefficient values vary from 1.5 to 2.5 and from 0.1 to 4.5, respectively. We have observed that the direct allowed gaps have been found to be 1.5 eV and 3 eV for CuPc I; 2.4 eV, 3.2 eV and 3.65 eV for CuPc II. On the other hand, for CuPc III thin films, they have been observed as 1.55 eV, 2.55 eV and 2.9 eV. Differences in optical properties are attributed to different chemical structures of the CuPc molecules in terms of their macrocycle ring size and R-group chain length.

Magnetic and optical properties of electrodeposited nanospherical copper doped nickel oxide thin films

Copper doped nickel oxide (NiO:Cu) thin films were synthesized via electrodeposition technique. X-ray diffraction, Scanning Electron Microscope, UV–visible spectroscopy, Vibrating Sample Magnetometer techniques and electrochemical analysis were utilized for the study of the structural, morphological, optical, magnetic and cyclic voltammogram properties respectively of both undoped and doped NiO thin films. The crystallographic studies of the undoped and doped NiO thin films showed that they are polycrystalline with cubic structure. Surface morphology of both the undoped and doped thin films showed nanocrystalline grains with spherical shaped particles. The optical studies showed a decrease in band gap energy from 3.34 eV to 3.32 eV and finally to 3.20 eV for the undoped, 2% and 3% respectively. The refractive index peaked between 2.60 and 2.65 while the calculated extinction coefficient values of the doped thin films have significant variation in the visible and NIR range. The studies of magnetization saturation values were found to be 1.52E-4 and 2.29E-4 for 2% and 3% doped respectively with low remanence values. Electrochemical studies revealed good cyclic voltammograms of the deposited films. These values indicate that the electrodeposited Cu doped NiO thin films are good candidates for magnetic applications.

Estimating protein quantities from microalgae: protein per biomass percentage, spectroscopic concentration, and lectin content

Protein quantifications can be essential steps in the screening of microalgae strains. The protein per biomass percentage of seven species of Chlorophyceae microalgae was estimated by a procedure that includes a protein precipitation step for removal of interfering substances. Ankistrodesmus fusiformis, Coelastrum microporum and Scenedesmus obliquus presented the highest protein content (22%, 21%, and 25%, respectively), whereas Chlamydocapsa bacillus presented the lowest protein per biomass ratio (11%). Specific values of percent extinction coefficients (E1%) for each strain was used as a strategy for rapid estimations of total protein concentrations from microalgae by absorbance readings at 280 nm. The species found with the highest lectin contents were Kirchneriella lunaris, Pseudokirchneriella subcapitata and C. bacillus, since they rendered the highest specific hemagglutinating activity (SHA) values for their total protein precipitates (5.2, 3.5, and 2.3, respectively), which was defined as the ratio between the hemagglutinating activity titer and the logarithm of its total protein concentration in μg/mL. Because the titer is indirectly associated to the concentration of lectins in a sample before the serial dilution, the SHA is more convenient for screening of different species, as it also includes the protein concentration of the titer.

New 2-methoxy-4,6-bis(4-(4-nitrostyryl)phenyl)nicotinonitrile: Synthesis, characterization and DSSC study

A new 2-methoxy-4,6-bis(4-(4-nitrostyryl)phenyl)nicotinonitrile (W-NO2) has been synthesized and the photovoltaic performances in dye‐sensitized solar cells (DSSCs) are investigated by utilizing it as co-sensitizer dye. From the study, its molar extinction coefficient value is found to be much higher than the N719 and the co-sensitized DSSC device showed a 1.78 times better efficiency than the N719 based devices. Preliminary DSSC results also revealed that the molecular architecture of dye (W-NO2) can be effectively utilized as a co-sensitizer along with the N719 to increase the spectral coverage as well as to achieve improved efficiency.

Reassessment of different antireflection coatings for crystalline silicon solar cell in view of their passive radiative cooling properties

In outdoor condition, the performance of the commercial solar photovoltaic (PV) modules depends on various parameters like (1) amount of direct solar radiation, (2) ambient temperature, (3) the location of installation, (4) wind speed, (6) aerosol, and most of these parameters are uncontrollable. The first two of these parameters increase the solar cell operating temperature which in turn decreases the performance of the solar cell. This simulation-based study presents the development of a passive radiative cooling system for a simple flat crystalline silicon (c-Si) solar cell using a thin film of SiO2, Al2O3, Si3N4, HfO2 or TiO2. Some of these materials are being used as an antireflection coating (ARC) in the commercial solar panel for having a suitable refractive index (n) and very low extinction coefficient (k) values in 300–1200 nm wavelength range. In the 8–13 µm wavelength range, the variation of emissivity of the materials w.r.t. thickness and angle have been calculated. The thickness of ARC, the absorptivity of Silicon, the emissivity of ARC in the atmospheric window was also estimated. Suitable ARC cum emissive layer helps the solar cell in absorptivity improvement as well as keeping its temperature near the ambient temperature. The present study finds that Si3N4 is having a higher emissive power than the other materials and increases (10–161.63 W m−2) with the increase in thickness from 20 to 1000 nm in 8–13 µm wavelength range. Material like SiO2 and Al2O3 have emissivity lower than Si3N4 of comparable thickness.

Investigation on physical properties of CdO thin films affected by Tb doping for optoelectronics

Thin films of Tb-doped CdO were grown on FTO substrates using the sol–gel-spin coater technique. XRD studies confirmed the polycrystalline cubic growth of the films with a (200) preferential orientation. XRD analysis was used to estimate the crystallite sizes, dislocation density, and microstrain values, and found that they are highly dependent on the doping percentage. Homogeneous distributions of the nano-gains were observed from the AFM studies. Energy-dispersive spectroscopy and mapping analyses were used for the uniform elemental composition confirmation. All the films displayed high transmission reaching nearly 80% in the visible spectrum and the effect of Tb doping was very clear by corresponding systematic increase in intensities. The direct band-gap values were estimated from the Tauc plots and are found to be highly tunable based on the doping percentage, which was varying between 2.79 and 2.91 eV. The refractive index and extinction coefficient values are lies between 1.8 and 2.5 and 0.44 to 0.82. The $${\chi ^{(1)}}$$ values are found to be varying between of 0.05 to 0.45 within the range 1–4 eV. This suggests all the linear and nonlinear optical properties of the present samples can be tailored for the various applications by the doping.

Tb3+-doped WO3 thin films: A potential candidate in white light emitting devices

Good crystalline, highly ordered, highly transparent and efficient luminescent Tb3+-doped tungsten oxide (WO3) thin films are fabricated using Radio Frequency (RF) magnetron sputtering technique. XRD analysis shows that the prepared films are in monoclinic phase showing crystal growth along a-axis. Micro-Raman spectra also support the formation of monoclinic crystalline WO3 phase in the prepared thin films. Morphological studies reveal a porous nature for heavily Tb3+-doped WO3 films. Prepared films are very close to the chemical stoichiometry of WO3 and the added impurity Tb exists mainly in +3 oxidation state. The fabricated thin films show better transparency particularly in the visible region. The calculated band gap energy values are in the range of 3.08–3.24 eV. Thickness and optical constants of the prepared films are calculated using spectroscopic ellipsometric measurements. Low values of extinction coefficient also support better transparency of the deposited films in the visible region. Tb3+-doped WO3films exhibit strong blue, green and red emissions under UV excitation which suggest the possibility of using these luminescent films in white light emitting devices. The experimental value of decay time constants corresponds to intense green emission (546 nm) shows a slight increase with increase in Tb3+ concentration.

Effect of pH on the structural and optical properties of polycrystalline ZnSe thin films produced by CBD method

In this study, zinc selenide (ZnSe) thin films were produced on glass substrate by using chemical bath deposition (CBD) method at 80[Formula: see text]C, from aqueous solutions of zinc sulphate and sodium selenosulphide, which were produced using solid selenium as the selenium source. The optical and structural properties of ZnSe thin films were investigated at room-temperature. The pH of the chemical bath, in which ZnSe thin films were immersed, were changed between pH:8–11. Optical properties of the films, including extinction coefficient, refractive index, reflectance, absorbance, transmittance, dielectric constants and optical density values were calculated using absorbance and transmittance measurements determined using a Hach Lange 500 spectrophotometer, in 300–1100 nm wavelength range. Optical bandgap values were obtained from transmittance and absorbance spectra ranged between 2.12 and 2.49 eV. According to XRD results, it was found that the films have polycrystalline structure and they exhibited different film thicknesses depending on phase and pH changes.

Seasonal and vertical distributions of aerosol type extinction coefficients with an emphasis on the impact of dust aerosol on the microphysical properties of cirrus over the Taklimakan Desert in Northwest China

In the present study, the seasonal and vertical distributions of key aerosol types and its extinction coefficient (EC) are investigated with an emphasis on the impact of desert dust aerosols on the microphysical properties of cirrus. For this, we obtained near-simultaneous and collocated datasets retrieved from the CALIPSO (Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations), CloudSat, and MODerate-resolution Imaging Spectroradiometer (MODIS) over the Taklimakan Desert (TMD) area situated in Northwest China during 2006–2011. We found that the main aerosol types prevalent over the TMD region are desert dust (DD), polluted dust (PD), and polluted continental/elevated smoke (PC/SE) which accounted for ∼88.38%, ∼10.81%, and ∼0.47%, respectively. The DD type was the most dominant aerosol type during the total observational period due to the nature of the desert underlying surface, and the frequent dust activities occurred over the region. Further, the concentrations of PD and PC/SE were observed larger in winter compared to the other seasons contributing ∼25.66% and 1.42%, respectively. This is likely attributed to increased burning of fossil fuels used for combustion processes in the cold season over Northwest China. On the other hand, the latitudinal distribution total aerosol loading of EC presented the south-to-north gradient with a declined tendency in all seasons due to enhanced amount of dust aerosols transported from the TMD area. Further, the seasonal mean values of total EC over TMD showed a maximum of 0.021 km−1 appeared in spring, with a minimum (0.017 km−1) in autumn. In addition, we also investigated the impact of dust aerosols on the cirrus microphysical properties namely, ice water content (IWC), ice water path (IWP), ice cloud effective radius (IER), ice number concentration (INC), and ice distribution width (IDW). The results showed that dust aerosol can possibly change the microphysical properties of cirrus over the study domain.