Optical Diffuse Reflectance Spectroscopy Research Articles

Magnetic characteristics of Guangshan loess from northern piedmont of Dabie Mountains, east-central China

SUMMARY The loess from the northern piedmont of the Dabie Mountains is in a transition area between loess from the Chinese Loess Plateau, the Quaternary red soils of southern China and the Xiashu loess. Despite its significant location, the study has been inadequate. In this study, the Guangshan section in the northern piedmont of the Dabie Mountains was selected for investigation. Environmental magnetism, geochemistry, colour reflectance and optical diffuse reflection spectroscopy analyses were applied to detect the magnetic variations in the loess. The results showed that (1) the magnetic minerals consisted mainly of magnetite, maghemite, hematite and goethite, which are the same as those in the Quaternary loess from the Chinese Loess Plateau, the Xiashu loess and the Quaternary red soils of southern China. The average magnetic particles were in the pseudo-single domain, like those of the Chinese Loess Plateau loess. (2) Unit III of the Guangshan section (2.4–4 m), with high chemical index of alteration and low Ba-index, was demonstrated as the most strongly developed palaeosol in the whole section, in agreement with field observations (more Fe-Mn films and weakly vermiculated development). However, it exhibited minimal susceptibility values and the lowest concentration of fine ferrimagnetic minerals. Simultaneously, the unit had low hematite to goethite ratio (Hm/Gt), suggesting that the pedogenic environment was humid; and it also had high values of b* and Gt%, implying that there was more goethite. Therefore, we can conclude that excessive soil moisture and intensive pedogenesis dissolved the fine ferrimagnetic minerals originally produced by pedogenesis and transformed them into goethite. These results could help to trace the palaeoclimatic evolution of the study area and clarify the magnetic variations of loess in different climates throughout China.

Hexamolybdenum Clusters Supported on Exfoliated h-BN Nanosheets for Photocatalytic Water Purification.

Nowadays, the development of new effective photocatalytic materials for the purification of real wastewaters and model systems containing organic molecules constitutes an important challenge. Here we present a preparation strategy for composite materials based on hexamolybdenum cluster complexes and exfoliated hexagonal boron nitride (h-BN) nanosheets. Cluster deposition on the nanosheet surface was achieved by impregnation of the matrix by a (Bu4N)2[{Mo6I8}(NO3)6]/acetone solution. Successful cluster immobilization and chemical composition of the samples were verified by inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy with elemental mapping (TEM/EDS), X-ray photoelectron spectroscopy (XPS), and optical diffuse-reflectance spectroscopy. A small amount of water in acetone initiates the hydrolysis of a molybdenum cluster precursor with labile NO3- ligands, which are absent in the final composite, according to the XPS data. Intermediate hydrolyzed cluster forms anchor to the surface of h-BN nanosheets and promote growth of the insoluble compound [{Mo6I8}(H2O)2(OH)4]·yH2O as the final hydrolysis product. TEM/EDS proves that the cluster exists at the nanosheet surface in the form of an X-ray diffraction amorphous thin film. The samples obtained show high photocatalytic activity in the degradation of a model pollutant rhodamine B under UV- and visible-light irradiation. The materials retain their initial photocatalytic efficacy during at least six cycles without the need for recovery.

Discrimination of Coniferous and Deciduous Leaves of Trees and Shrubs from Decorative and Artificial Materials by Optical Diffuse Reflectance Spectroscopy

The diffuse reflectance spectra from green coniferous and deciduous leaves of trees and shrubs growing in Krasnodar region are compared with the diffuse reflectance spectra from green synthetic decorative and artificial leaves and various camouflage materials. It is proposed to use vegetation indices of “greenness” for the discrimination of coniferous and deciduous leaves of trees and shrubs from decorative and artificial materials by optical diffuse reflectance spectroscopy.

Дискриминация хвойных и лиственных листьев деревьев и кустарников от декоративно-искусственных материалов методом оптической спектроскопии диффузного отражения света

The article was the first time investigation the spectra of diffuse light reflection from coniferous and deciduous green leaves of trees and shrubs that growing in the Krasnodar region territory. The obtained spectral data were compared with the spectra of diffuse light reflection from green synthetic decorative and artificial leaves and various camouflage materials. The use of vegetation indices of "greenness" to discriminate coniferous and deciduous leaves of trees and shrubs from decorative and artificial materials by optical diffuse reflectance spectroscopy was proposed.

A Ferroelectric-Photovoltaic Effect in SbSI Nanowires

A ferroelectric-photovoltaic effect in nanowires of antimony sulfoiodide (SbSI) is presented for the first time. Sonochemically prepared SbSI nanowires have been characterized using high-resolution transmission electron microscopy (HRTEM) and optical diffuse reflection spectroscopy (DRS). The temperature dependences of electrical properties of the fabricated SbSI nanowires have been investigated too. The indirect forbidden energy gap EgIf = 1.862 (1) eV and Curie temperature TC = 291 (2) K of SbSI nanowires have been determined. Aligned SbSI nanowires have been deposited in an electric field between Pt electrodes on alumina substrate. The photoelectrical response of such a prepared ferroelectric-photovoltaic (FE-PV) device can be switched using a poling electric field and depends on light intensity. The photovoltage, generated under λ = 488 nm illumination of Popt = 127 mW/cm2 optical power density, has reached UOC = 0.119 (2) V. The presented SbSI FE-PV device is promising for solar energy harvesting as well as for application in non-volatile memories based on the photovoltaic effect.

Improving In-Situ Estimation of Soil Profile Properties Using a Multi-Sensor Probe.

Optical diffuse reflectance spectroscopy (DRS) has been used for estimating soil physical and chemical properties in the laboratory. In-situ DRS measurements offer the potential for rapid, reliable, non-destructive, and low cost measurement of soil properties in the field. In this study, conducted on two central Missouri fields in 2016, a commercial soil profile instrument, the Veris P4000, acquired visible and near-infrared (VNIR) spectra (343–2222 nm), apparent electrical conductivity (ECa), cone index (CI) penetrometer readings, and depth data, simultaneously to a 1 m depth using a vertical probe. Simultaneously, soil core samples were obtained and soil properties were measured in the laboratory. Soil properties were estimated using VNIR spectra alone and in combination with depth, ECa, and CI (DECS). Estimated soil properties included soil organic carbon (SOC), total nitrogen (TN), moisture, soil texture (clay, silt, and sand), cation exchange capacity (CEC), calcium (Ca), magnesium (Mg), potassium (K), and pH. Multiple preprocessing techniques and calibration methods were applied to the spectral data and evaluated. Calibration methods included partial least squares regression (PLSR), neural networks, regression trees, and random forests. For most soil properties, the best model performance was obtained with the combination of preprocessing with a Gaussian smoothing filter and analysis by PLSR. In addition, DECS improved estimation of silt, sand, CEC, Ca, and Mg over VNIR spectra alone; however, the improvement was more than 5% only for Ca. Finally, differences in estimation accuracy were observed between the two fields despite them having similar soils, with one field demonstrating better results for all soil properties except silt. Overall, this study demonstrates the potential for in-situ estimation of profile soil properties using a multi-sensor approach, and provides suggestions regarding the best combination of sensors, preprocessing, and modeling techniques for in-situ estimation of profile soil properties.

Crystal Chemistry, Optical Spectroscopy and Crystal Field Calculations of Co3TeO6 and Solid Solutions Co3–xZnxTeO6

Solid solutions Co3–xZnxTeO6 (x = 0–3) were prepared both in polycrystalline and single‐crystalline form using solid state reactions and chemical vapour transport reactions, respectively. Miscibility between the isotypic end members was established over the complete range (C2/c, Z = 12, a ≈ 14.85, b ≈ 8.83, c ≈ 10.34 Å, β ≈ 93°). Crystal structure determinations, performed on basis of single crystal laboratory X‐ray (at 295 K) and synchrotron (at 10 and 100 K) data of Co3TeO6 and selected solid solutions, revealed no structural phase transition and allowed a detailed insight into the Co → Zn substitution mechanism. The coordination polyhedra of the five crystallographically independent M2+ cations are distorted octahedra (for three cations), one distorted tetrahedron and one distorted square pyramid. With increasing Zn content the polyhedral distortions increase, and the preference of the Zn2+ cation for the tetrahedral coordination becomes distinctive. Optical absorption and diffuse reflectance spectroscopy reveal extraordinary strong crystal field absorption effects, over wide x ranges predominantly governed by Co2+ in the single tetrahedral and one strongly acentric distorted octahedral site. Superposition Model crystal field calculations yield intrinsic and power‐law exponent parameters in general agreement with previous data for Co2+. The five cation sites show comparatively high crystal field strengths at generally very low interelectronic repulsion parameters, indicating prominent covalent contribution to Co–O bonding in Co3–xZnxTeO6 solid solutions.

Improving the electrochemical response of nanostructured MoO3 electrodes by Co doping: Synthesis and characterization

CoxMo1-xO3 (x = 0, 0.03, 0.06, and 0.09) thin films were deposited on indium-doped tin oxide–coated and glass substrates by a sol-gel method. All the samples crystallized in the stable orthorhombic phase as revealed by X-ray diffraction patterns, with a granular shaped surface confirmed by field emission scanning electron microscopy. The optical band gaps of the samples were obtained by two different optical methods; namely, optical transmittance spectroscopy and diffuse reflectance spectroscopy. There was considerable agreement between the band gaps determined by the two methods. The experimental band gaps were compared with theoretically computed values obtained by density functional theory calculation of the density of states for x = 0 and x = 0.06. The theoretical band gaps served as qualitative confirmation for experimental ones. It was also revealed that the presence of Co as an impurity in MoO3 with an optimized incorporation amount of x = 0.06 refined the morphology and layered structure with an orthorhombic phase, which resulted in improvement of the electrochemical performance in both 1 M KOH electrolyte and LiClO4/propylene carbonate electrolyte.

Approaches for Detecting Madder Lake in Multi-Layered Coating Systems of Historical Bowed String Instruments

Musical instrument coatings are generally made by multi-layered systems of organic and inorganic materials, applied on the wood substrate by the violin makers during the finishing process. This coating has paramount relevance for several aspects: protection from sweat and dirt, increase of specific acoustic features, and especially aesthetic effects. In fact, the colour of historical bowed string instruments represents a very peculiar characteristic of each workshop. Among the various colourants, lakes are the most challenging to detect because of their sensibility to the alteration processes. In this work, non-invasive and micro-invasive procedures were applied to a set of mock-ups mimicking historical coatings systems prior and after artificial ageing, in order to highlight the overall information that can be recovered for the detection of madder lake in historical bowed instruments. A set of techniques, including colourimetry, visible and UV-light imaging, stereomicroscopy, Fibre Optics Diffuse Reflectance spectroscopy (FORS), X-ray Fluorescence spectroscopy (XRF), Scanning Electron Microscopy coupled with Energy-Dispersive X-ray microprobe (SEM-EDX), and Fourier-Transform Infrared spectroscopy (FTIR) were used in order to evaluate the pros and cons in the detection of organic and inorganic component of madder lake at low concentration levels.

Intra-class variability in diffuse reflectance spectroscopy: application to porcine adipose tissue.

Optical diffuse reflectance spectroscopy (DRS) has great potential in the study, diagnosis, and discrimination of biological tissues. Discrimination is based on massive measurements that conform training sets. These sets are then used to classify tissues according to the biomedical application. Classification accuracy depends strongly on the training dataset, which typically comes from different samples of the same class, and from different points of the same sample. The variability of these measurements is not usually considered and is assumed to be purely random, although it could greatly influence the results. In this work, spectral variations within and between samples of different animals of ex-vivo porcine adipose tissue are evaluated. Algorithms for normalization, dimensionality reduction by principal component analysis, and variability control are applied. The PC analysis shows the dataset variability, even when a variability removal algorithm is applied. The projected data appear grouped by animal in the PC space. Mahalanobis distance is calculated for every group, and an ANOVA test is performed in order to estimate the variability. The results confirm that the variability is not random and is dependent at least on the anatomical location and the specific animal. The variability magnitude is significant, particularly if the classification accuracy is needed to be high. As a consequence, it should be taken generally into account in classification problems.

Exploring the Surfactant–Thermal Synthesis of Crystalline Functional Thioarsenates

Two new crystalline thioarsenate compounds, formulated as [pipH2][Mn2As2S6] (1) and [TMDPH2][As4S6] (2) (pip = piperazine, TMDP = 1,3-bis(4-piperidyl)propane), have been surfactant–thermally synthesized with the utilization of octylamine and PEG-400 as the solvents. The crystal structure of 1 features [Mn2As2S6]n2n– anionic layers which are separated by doubly protonated [pipH2]2+ cations, while that of compound 2 is made of discrete [As4S6]2– clusters and doubly protonated [TMDPH2]2+ cations. Both compounds were characterized by powder X-ray diffraction analyses, solid-state optical diffuse reflectance spectroscopy, and thermogravimetric analyses. As estimated from the adsorption spectra, the band gaps of 1 and 2 are 2.32 and 2.49 eV, respectively. The electronic structure calculations based on density functional theory method confirm the indirect band gap of 2. In addition, the magnetic investigation of 1 suggests antiferromagnetic behavior. Since compound 2 crystallizes in the space group Imm2, the non...

Four Novel Zn (II) Coordination Polymers Based on 4'-Ferrocenyl-3,2':6',3''-Terpyridine: Engineering a Switch from 1D Helical Polymer Chain to 2D Network by Coordination Anion Modulation.

Four novel ZnII coordination polymers, [(ZnCl2)2(L)2]n (1), [(ZnBr2)2(L)2]n (2), and [(ZnI2)2(L)2]n (3) and {[Zn(SCN)2]1.5(L)3}n (4), have been synthesized based on 4′-ferrocenyl-3,2′:6′,3′′-terpyridine with ZnII ions and different coordination anions under similar ambient conditions. Their structures have been confirmed using single crystal X-ray diffraction analysis, showing that complexes 1–3 are one-dimensional (1D) double-stranded metal ion helical polymer chains and complex 4 is of a two-dimensional (2D) network. The structural transformations of them from a 1D polymer chain to a 2D network under the influence of the coordination anions has been systematic investigated. Furthermore, the optical band gaps have been measured by optical diffuse reflectance spectroscopy, revealing that the ligand and the complexes should have semiconductor properties.

Phase identification and structure investigation of novel quaternary rare-earth substituted titanates

Novel quaternary lanthanide-substituted oxides of stoichiometry LnxY2−xTi2O7 (where Ln is lanthanum, neodymium, samarium, gadolinium, or ytterbium) were prepared by traditional high-temperature, solid-state techniques and characterized by X-ray powder diffraction. Samples with nominal values of x up to 1.0 were attempted. The well-studied ternary cubic pyrochlore compound yttrium titanium oxide (Y2Ti2O7, space group Fd-3m, Z = 8), served as a parent structural framework in which Ln3+ cations were substituted on the Y3+ site. Laboratory-grade X-ray powder diffraction data revealed pure quaternary pyrochlore phases for LnxY2−xTi2O7 with x ≤ 0.2. Pyrochlore phase purity was verified by Rietveld analysis using high-resolution synchrotron X-ray powder diffraction data when x ≤ 0.2, however, for La3+ substitution specifically, pure quaternary pyrochlore formed at x<0.1. Band gap energies on selected samples were determined using optical diffuse reflectance spectroscopy and showed that these materials can be classified as electrical insulators with indirect band gap energies around 3.7eV.

Semi-empirical model for diffuse reflectance from homogeneous spherical turbid media measured via small diameter detectors

The application of optical diffuse reflectance spectroscopy is impeded by the lack of exact analytical solution. Based on the results of the Monte Carlo simulation, a semi-empirical analytical expression is developed for diffuse reflectance from homogeneous spherical turbid media measured via small diameter detectors. It is valid over the typical optical property ranges for low absorption biological tissues. This solution is characterized by its simplicity and accuracy. The inversion of optical parameters of turbid media is performed using this solution. The reduced scattering coefficient can be inversely deduced from the diffuse reflectance measured via probes with various radii.

Hydrogenation tuned the created ferromagnetic properties of Ni-doped nano-ZnO

Zn1−x Ni x O solid solution nanopowders were synthesised by thermal co-decomposition of Zn and Ni organic complexes method. The samples were characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD), and optical diffuse reflection spectroscopy. The XRD confirmed the formation of single phase of ZnO structure. The host unit-cell volume (V cell) slightly decreased with Ni doping referring to the total doping of Ni ions. The hydrogenation increased the V cell of Ni-doped ZnO. The redshift of the bandgap of Ni-doped ZnO under hydrogenation is attributed to the formation of lattice strain defects through the creation of structural O-vacancies, which plays principle role of enhancing the room-temperature ferromagnetic (FM) properties. Therefore, the major objective of the present study is to investigate the significant effect of hydrogenation on the magnetic properties of Ni-doped ZnO. The appealing combined effect of doping and hydrogenation was discussed based on the Bound Magnetic Polarons (BMP) theory, as the O-vacancies are believed to be responsible for the enhancement of RT-FM properties with the presence of H–H interstitials (Hydrogenation). Therefore, hydrogenated Ni-doped ZnO nanopowders, owning these amazingly tunable magnetic manners, can be considered as a potential candidate for many applications such as optoelectronics and dilute magnetic semiconductors.

S.S. Annunziata Church (L’Aquila, Italy) unveiled by non- and micro-destructive testing techniques

The present research work explores the potential of an integrated inspection methodology, combining Non-destructive testing and micro-destructive analytical techniques, for both the structural assessment of the S.S. Annunziata Church located in Roio Colle (L’Aquila, Italy) and the characterization of its wall paintings’ pigments. The study started by applying passive thermal imaging for the structural monitoring of the church before and after the application of a consolidation treatment, while active thermal imaging was further used for assessing this consolidation procedure. After the earthquake of 2009, which seriously damaged the city of L’Aquila and its surroundings, part of the internal plaster fell off revealing the presence of an ancient mural painting that was subsequently investigated by means of a combined analytical approach involving portable VIS–NIR fiber optics diffuse reflectance spectroscopy (FORS) and laboratory methods, such as environmental scanning electron microscopy (ESEM) coupled with energy dispersive X-ray analysis (EDX), and attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR). The results obtained from the thermographic analysis provided information concerning the two different constrictive phases of the Church, enabled the assessment of the consolidation treatment, and contributed to the detection of localized problems mainly related to the rising damp phenomenon and to biological attack. In addition, the results obtained from the combined analytical approach allowed the identification of the wall painting pigments (red and yellow ochre, green earth, and smalt) and provided information on the binding media and the painting technique possibly applied by the artist. From the results of the present study, it is possible to conclude that the joint use of the above stated methods into an integrated methodology can produce the complete set of useful information required for the planning of the Church’s restoration phase.

Influence of rare earth (RE=Nd, Y, Pr and Er) doping on the microstructural and optical properties of ceria nanostructures

Nanopowders of Ce0.9RE0.1O1.95 (RE=Nd, Y, Pr and Er) were synthesized by nitrate-fuel combustion method and calcinated at 700°C for 2h to obtain completely crystalline structures. The effect of RE dopants on the crystalline nature, lattice parameters, and microstructural parameters such as microstrain, stress, and deformation energy density of ceria was evaluated through uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM) by using the X-ray diffraction (XRD) data. The results revealed that the microstructural parameters were considerably altered with respect to the dopants. The transmission electron microscope (TEM) graphs and their corresponding selected area diffraction (SAED) patterns of ceria nanoparticles confirmed that all doped ceria powders are crystalline with the wide range of particle size distributions aligned in all the directions. The optical diffuse reflectance spectroscopy (DRS) measurements showed a band at around 340nm attributed to the transitions of charge-transfer between O 2p and Ce 4f orbitals in cerium oxide and RE doped CeO2 exhibited the reflectance band in the visible regions due to the transition of 4f energy levels of RE ions. Photoluminescence (PL) spectra of RE doped ceria showed the blue-green emission bands.

Profile Soil Property Estimation Using a VIS-NIR-EC-Force Probe

Abstract. Combining data collected in-field from multiple soil sensors has the potential to improve the efficiency and accuracy of soil property estimates. Optical diffuse reflectance spectroscopy (DRS) has been used to estimate many important soil properties, such as soil carbon, water content, and texture. Other common soil sensors include penetrometers that measure soil strength and apparent electrical conductivity (ECa) sensors. Previous field research has related these sensor measurements to soil properties such as bulk density, water content, and texture. A commercial instrument that can simultaneously collect reflectance spectra, ECa, and soil strength data is now available. The objective of this research was to relate laboratory-measured soil properties, including bulk density (BD), total organic carbon (TOC), water content (WC), and texture fractions to sensor data from this instrument. At four field sites in mid-Missouri, profile sensor measurements were obtained to 0.9 m depth, followed by collection of soil cores at each site for laboratory measurements. Using only DRS data, BD, TOC, and WC were not well-estimated (R2 = 0.32, 0.67, and 0.40, respectively). Adding ECa and soil strength data provided only a slight improvement in WC estimation (R2 = 0.47) and little to no improvement in BD and TOC estimation. When data were analyzed separately by major land resource area (MLRA), fusion of data from all sensors improved soil texture fraction estimates. The largest improvement compared to reflectance alone was for MLRA 115B, where estimation errors for the various soil properties were reduced by approximately 14% to 26%. This study showed promise for in-field sensor measurement of some soil properties. Additional field data collection and model development are needed for those soil properties for which a combination of data from multiple sensors is required. Keywords: NIR spectroscopy, Precision agriculture, Reflectance spectra, Soil properties, Soil sensing.

Comparison of Field and Laboratory VNIR Spectroscopy for Profile Soil Property Estimation

Abstract. In-field, in-situ data collection with soil sensors has potential to improve the efficiency and accuracy of soil property estimates. Optical diffuse reflectance spectroscopy (DRS) has been used to estimate important soil properties, such as soil carbon, nitrogen, water content, and texture. Most previous work has focused on laboratory-based visible and near-infrared (VNIR) spectroscopy using dried soil. The objective of this research was to compare estimates of laboratory-measured soil properties from a laboratory DRS spectrometer and an in-situ profile DRS spectrometer. Soil cores were obtained to approximately 1 m depth from treatment blocks representing variability in topsoil depth located at the South Farm Research Center of the University of Missouri. Soil cores were split by horizon, and samples were scanned with the laboratory DRS spectrometer in both field-moist and oven-dried conditions. In-situ profile DRS spectrometer scans were obtained at the same sampling locations. Soil properties measured in the laboratory from the cores were bulk density, total organic carbon (TOC), total nitrogen (TN), particulate organic matter carbon and nitrogen (POM-C and POM-N), water content, and texture fractions. The best estimates of TOC, TN, and bulk density were from the laboratory DRS spectra on dry soil (R2 = 0.94, 0.91, and 0.71, respectively). Estimation errors with the field DRS system were at most 25% higher for these soil properties. For POM-C and POM-N, the field system provided estimates of similar accuracy to the best (dry soil) laboratory measurements. Clay and silt texture fraction estimates were most accurate from laboratory DRS spectra on field-moist soil (R2 = 0.91 and 0.93, respectively). Estimation errors for clay and silt were almost doubled with the field DRS system. Considering the efficiency advantages, in-field, in-situ DRS appears to be a viable alternative to laboratory DRS for TOC, TN, POM-C, POM-N, and bulk density estimates, but perhaps not for soil texture estimates. Keywords: In-situ sensing, Precision agriculture, Reflectance spectra, Soil properties, Soil spectroscopy.

The photocatalytic performance of silver halides – Silver carbonate heterostructures

Abstract The synthesized rod-like Ag2CO3 particles (2–4 × 0.3–0.6 μm, length × diameter) served as a precursor for preparation of the AgX/Ag2CO3 (X = Cl, I) composites by ion exchange method. The various microstructural (X-ray diffraction analysis, transmission electron microscopy, nitrogen adsorption-desorption isotherms) and optical (diffuse reflection spectroscopy) techniques were used for thorough characterization of obtained heterostructures. The enhanced photocatalytic performance of AgX/Ag2CO3 heterostructures in comparison to Ag2CO3 nanorods (NRs) was evidenced using degradation of organic dye methylene blue as a test reaction. Also, the formation of composites improved their stability under long run illumination conditions. The effect of AgX content on photocatalytic activity of the composites were also investigated. The possible photocatalytic mechanism that facilitates efficient separation of photo-formed charge carriers in heterostructures was discussed in terms of the relative energetic of valence and conduction bands.