Vis NIR Region Research Articles

Quantifying the optical and thermoplasmonic properties of some bimetallic alloy nanospheres

The bimetallic alloy NPs are ideal objects for a variety of applications like catalysis, nanofluidics, thermo-voltaic and bio-imaging due to their peculiar and adaptable optical response in UV–visible-NIR region of optical spectra. The heating effect of bimetallic alloys involves surface plasmon resonance (SPR) and takes place when the material is illuminated by light. Instead of pure and alloy NPs of Au & Ag, the opto-thermal properties of Au-Cu, Au-Al, Ag-Cu and Ag-Al bimetallic alloy nanospheres for their different compositions with a size radius of 10 nm to 50 nm immersed in water (n = 1.33) using the Mie theory approach are investigated theoretically. In order to determine the heat generation and the temperature distribution by plasmonic nanoparticles in the host medium (water in this study) we have solved the heat transfer equation analytically for steady-state conditions. The great utility of these bimetallic alloy nanoparticles for thermoplasmonic investigation is accompanied with a large extent of SPR tunability which is rarely found in their pure monometallic counterpart. The SPR of Aux-Cu1-x (214 nm to 548 nm), Aux-Al1-x (213 nm to 493 nm), Agx-Cu1-x (214 nm to 539 nm), and Agx-Al1-x (214 nm to 381 nm) bimetallic alloys with compositions of x = 0.25,0.50 and 0.75 have been observed for different size of the nanospheres. Thus, we anticipate that the results of this work will evoke the curiosity of researchers towards the use of bimetallic alloys in thermoplasmonic applications.

Crystalline AuNP-Decorated Strontium Niobate Thin Films: Strain-Controlled AuNP Morphologies and Optical Properties for Plasmonic Applications.

Gold nanoparticle (AuNP) decoration is a commonly used method to enhance the optical responses in many applications such as photocatalysis, biosensing, solar cells, etc. The morphology and structure of AuNPs are essential factors determining the functionality of the sample. However, tailoring the growth mechanism of AuNPs on an identical surface is not straightforward. In this study, AuNPs were deposited on the surface of a perovskite thin film, strontium niobate (SNO), using pulsed laser deposition (PLD). AuNPs exhibited a dramatic variation in their growth mechanisms, depending on whether they were deposited on SNO thin films grown on magnesium oxide (SNO/MgO) or strontium titanate (SNO/STO) substrates. On SNO/MgO, the Au aggregates form large NPs with an average size of up to 3500 nm2. These AuNPs are triangular with sharp edges and corners. The out-of-plane direction of growth is favored, and the surface coverage ratio by AuNPs is low. When deposited on SNO/STO, the average size of AuNPs is much smaller, i.e., ∼250 nm2. This reduction in the average size is accompanied by an increase in the number density of NPs. AuNPs on SNO/STO have a round shape and high coverage ratio. Such an impact from the substrate selection on the AuNP structure is significant when the sandwiched SNO film is below 80 nm thickness and is weakened for 200 nm of SNO films. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize all samples. Strain analysis was used to explain the growth mechanism of AuNPs. The average height of AuNPs was measured by using atomic force microscopy (AFM). Ellipsometry in the visible-near-infrared (vis-NIR) region was used to characterize the optical response of all samples. AuNP-decorated SNO/MgO and SNO/STO thin films exhibit different optical properties, with only gold-decorated SNO/MgO samples showing a size-dependent epsilon-near-zero behavior of nanoparticles. These results provide an additional route to control the structure of AuNPs. They can be used for various plasmonic applications like the design and development of strain-engineered gold-nanoparticle-decorated devices for surface-enhanced Raman spectroscopy (SERS) and photocatalysis.

W18O49 Nanowire Arrays for Plasmonic Photodetector with Electromediated Broadband Photoresponse

Plasmonic semiconductors offer significant advantages for the development of photodetectors with a tunable wide spectral response. Herein, we developed a plasmonic semiconductor photodetector based on the W18O49 nanowire array (NWA) to achieve a tunable broadband photodetector by adjusting the plasmonic absorption intensity of the W18O49 NWA. The plasmonic absorption intensity could be mediated through adjusting the free electron density of the W18O49 NWA by applying the external voltage on the W18O49 NWA-loaded electrode in HCl electrolyte. When the applied voltage decreased from +2 to −2 V, the plasmonic absorption intensity of the W18O49 NWA gradually enhanced due to the increased electron density. As a result, the responsivity and detectivity of the W18O49 NWA-based photodetector in the visible–NIR region were dramatically increased. Especially, upon 940 nm illumination, the responsivity and detectivity could reach ∼47.2 mA W–1 and ∼8.22 × 109 Jones, respectively, which is much higher than the corresponding values (∼2.9 mA W–1 and ∼4.53 × 109 Jones) obtained by the W18O49 NWA-based photodetector with a low plasmonic absorption. This work proposes a promising strategy to construct broadband-tunable photodetectors by using low-cost nonmetallic plasmonic nanostructures.

On-Chip Optical Waveguide Visible-Light Power Detector Based on Photothermal Effect of PPy/SU-8 Photopolymer

In this work, an all-optical on-chip polymer waveguide visible-light power detector is proposed based on photothermal effect of polypyrrole (PPy) nanoparticles. PPy/SU-8 waveguide material is prepared and the strong optical absorption of the photopolymer in the visible-light region is beneficial for efficient photothermal energy conversion. The photothermal characteristics of PPy/SU-8 are analyzed, and through selective absorption specificity of the PPy/SU-8 photopolymer in Vis-NIR region, the performances of the multimode interference (MMI) waveguide device by thermo-optic (TO) tuning are simulated. The photothermal energy conversion coefficient of the PPy/SU-8 waveguide is obtained as 2.5 K/mW. The actual sensitivity of the on-chip light power detector is measured as 2.3 nm/mW. This technique could be used to achieve ultra-compact on-chip all-optical detectors in future.

Exfoliated Se nanoparticles decorated on MoS2/paper-based heterojunction as a flexible, self-powered and highly responsive photodetector

Self-powered heterostructure based photodetectors are of great research interest owing to their zero-power consumption, enhanced light-matter interaction, and the ability to respond in harsh environmental conditions. Selenium (Se) nanoparticles have been recently explored in photodetectors due to their high absorption coefficient and superior light-sensing ability. However, most reported Selenium based photoconductors utilize sophisticated device fabrication methodology, requiring regulated environmental conditions, elevated temperature and face flexibility issues. This work demonstrates a discrete(localized) heterojunction of exfoliated Selenium decorated on hydrothermally grown MoS2/paper-based high-performance, flexible, and self-powered photodetector. X-ray Diffraction and Raman Spectroscopy studies reveal the presence of hexagonal Se and the SEM image shows the uniformly grown MoS2 on cellulose paper. It also confirms the presence of Se clustered nanoparticles. The hybrid heterostructure device displays broadband response in the Vis-NIR region. Upon light illumination, a built-in field is generated due to the efficient separation of the charge carriers, making the fabricated device to operate at zero bias. The as-fabricated device exhibits superior responsivity of 0.14 A/W and 0.49 A/W and detectivity of 4.55 × 1011 Jones (intensity- 35.8 mW/cm2) and 5.01 × 1010 Jones (intensity- 30.08 mW/cm2) upon Vis and NIR irradiation, respectively, at no bias. This superior performance is asserted to the peak absorption of Se nanoparticles in the NIR region. The device also showed superior resistance to bending stress and retained its original characteristics even after multiple bending cycles (∼1050). Hence, with this facile device fabrication and simple device architecture strategy, this work paves the way for developing high-performance tensile photodetectors.

MXene/d-Mannitol aerogel phase change material composites for medium-temperature energy storage and solar-thermal conversion

Accelerate the development of medium-temperature phase change materials (PCMs) with high enthalpy of phase change and light absorption capability is very important for medium-temperature energy storage and solar thermal utilization. However, low energy conversion capacity and easy leakage limit the practical application of PCMs. To improve these properties of materials, a MXene/DM aerogel composite phase change material was prepared by self-assembly followed by freeze-drying of d-mannitol (DM) and MXene nanosheets using a simple solution blending method. The MXene/DM containing 20 wt% MXene has a high enthalpy (Hm) of phase change (202.7 J/g) with phase change temperature (Tm) of 153.3 °C, and still has good shape stability at 170 °C without leakage. In addition, MXene/DM has strong absorption ability in UV–Vis-NIR regions, with significant solar-thermal conversion efficiency of 88.1 %. The results indicate that the MXene/DM aerogel have comprehensive performance and have promising applications in medium-temperature thermal storage and photothermal conversion.

Chemically sprayed CdO: Cr thin films for formaldehyde gas detection and optoelectronic applications

Chromium (Cr) doped CdO films are chemically sprayed and are characterized by their optical, electrical, structural, and microstructural characteristics. The thickness of the films is determined by spectroscopic ellipsometry. The cubic crystal structure with a superior growth along (111) plane of the spray-deposited films is confirmed from the powder X-ray diffraction (XRD) analysis. XRD studies also suggested that some of the Cd2+ ions were substituted by Cr3+ ions, and the solubility of Cr in CdO is minimal, to be around ∼0.75 wt%. The analysis by atomic force microscopy shows uniform distribution of grains throughout the surface, whose roughness is varied from 33 to 13.9 nm concerning Cr-doping concentration. The microstructures from the field emission scanning electron microscope reveal a smooth surface. The elemental composition is examined using an energy dispersive spectroscope. The micro-Raman studies carried out in room temperature endorse the presence of metal oxide (Cd–O) bond vibrations. Transmittance spectra are obtained using UV–vis–NIR spectrophotometer, and the band gap values are estimated from the absorption coefficient. The films show high optical transmittance (>75%) in vis-NIR region. A maximum optical band gap of 2.35 eV is obtained from 1.0 wt% Cr-doping. The electrical measurement (Hall analysis) confirmed the degeneracy nature and n-type semi-conductivity. The carrier density, carrier mobility, and dc-conductivity are increased for higher Cr-dopant percentage. High mobility (85 cm2V−1s−1) is observed for 0.75 wt% Cr-doping. The 0.75 wt% Cr-doping show a remarkable response to formaldehyde gas (74.39%).

Phenyl-Terminated Coupling Interface Enabled Highly Efficient and Stable Multiwavelength Perovskite Single Crystal/Silicon Integrated Photodetector.

The use of amino-terminated siloxanes as coupling interface for perovskite single crystals (PSCs)/silicon integrated devices has been demonstrated to be an effective method toward CMOS compatible optoelectronics; however, it suffers from the coupling stability against the hydrophilicity of the exposed terminal amino groups. In this work, a phenyl-terminated interfacial molecule, anilino-methyl-triethoxysilane (AMTES), is proposed to achieve the effectively galvanic coupling between PSCs and silicon, which can not only improve the device environmental reliability but also lower the surface energy of the silicon substrate so as to facilitate the epitaxial growth of PSCs. Benefiting from the interfacial coupling of AMTES, the obtained MAPbI3 SC/silicon integrated device possesses highly efficient multiwavelength photodetection properties across the X-ray and NIR range, which exhibits a specific detectivity D* of 3.84 × 1013 cm Hz1/2 W-1 in the visible-NIR region and an X-ray sensitivity of 1.18 × 104 μC Gyair-1 cm-2 with the lowest detection limit of 49.6 nGyair s-1. The ultra wide -3 dB bandwidth of 67,300 Hz and the linear dynamic range (LDR) of 112 dB also prove its impressive dynamic response capabilities. Moreover, the AMTES modified integrated device almost maintains 96% of the initial photodetection performance even after keeping in the atmosphere environment for 28 days. This work opens a new avenue for interfacial engineering toward the development of on-chip PSC integrated silicon optoelectronic devices.

Boosting the Catalytic Performance of AuAg Alloyed Nanoparticles Grafted on MoS2 Nanoflowers through NIR-Induced Light-to-Thermal Energy Conversion.

MoS2 nanoflowers (NFs) obtained through a hydrothermal approach were used as the substrate for the deposition of tiny spherical bimetallic AuAg or monometallic Au nanoparticles (NPs), leading to novel photothermal-assisted catalysts with different hybrid nanostructures and showing improved catalytic performance under NIR laser irradiation. The catalytic reduction of pollutant 4-nitrophenol (4-NF) to the valuable product 4-aminophenol (4-AF) was evaluated. The hydrothermal synthesis of MoS2 NFs provides a material with a broad absorption in the Vis-NIR region of the electromagnetic spectrum. The in situ grafting of alloyed AuAg and Au NPs of very small size (2.0-2.5 nm) was possible through the decomposition of organometallic complexes [Au2Ag2(C6F5)4(OEt2)2]n and [Au(C6F5)(tht)] (tht = tetrahydrothiophene) using triisopropilsilane as reducing agent, leading to nanohybrids 1-4. The new nanohybrid materials display photothermal properties arising from NIR light absorption of the MoS2 NFs component. The AuAg-MoS2 nanohybrid 2 showed excellent photothermal-assisted catalytic activity for the reduction of 4-NF, which is better than that of the monometallic Au-MoS2 nanohybrid 4. The obtained nanohybrids were characterised by transmission electron microscopy (TEM), High Angle Annular Dark Field-Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (HAADF-STEM-EDS), X-ray photoelectron spectroscopy and UV-Vis-NIR spectroscopy.

Tuning of smart cobalt doped borate glasses by electron beam as band-pass filters

CoO (0.2, and 0.7 wt%) doped lithium borate glass samples according to the composition of 84 % B2O3 + 12 % Li2O + 4 % Al2O3 have been prepared by melt quenching technique. Archimedes's method was used to compute the molar volumes of the formed glasses by measuring their density. For the purpose of analyzing the band-pass glass filter and UV-IR cut-off, the optical spectroscopic features of the obtained lithium borate glasses were evaluated over the entire wavelength range from 190 to 1100 nm. The effect of CoO doping ratios (0.2, and 0.7 wt%) on the optical properties of the prepared glass samples (refractive index, optical and electrical conductivity, reflection loss (RL), optical transmission (Toptical), extinction coefficient, permittivity, dielectric constants, electric susceptibility and polarizabilities) were studied. The decrease in ETauc and increase in UV–Visible cutoff range with the increase of CoO content is due to the increase of the non-bridging oxygen concentration. Co2+ ions are detected in both tetrahedral and octahedral positions in the glass matrix, according to the electron paramagnetic resonance EPR spectra. The transmittance data of the glass filters revealed that they have a broad band-pass in the Vis-NIR region. The electron beam irradiation showed an increase in the stopping range of the prepared glasses as band pass filters which makes them available for a wide-range of optical equipment including lenses and laser shields, as well as optoelectronic and photovoltaic apparatus.

Light-colored solar-driven PANI/polyacrylonitrile fiber with low-temperature resistance for wearable heater

High-performance photothermal textiles with favorable low-temperature resistance and washing resistance demonstrate obvious superiority and growing demand. However, most photothermal conversion materials show dark color, restricting their color tunability in wearable heating garments. The light-colored solar-driven polyaniline (PANI)/polyacrylonitrile fiber with high low-temperature resistance and washing resistance is fabricated continuously via the wet-spinning method. The temperature of the solar-driven PANI/polyacrylonitrile fiber (0.5 wt%) rises from room temperature (20.00 °C) to 48.12 °C irradiated at 600 W m−2 for 10 min. Even at −30.01 °C, the equilibrium temperature of the solar-driven PANI/polyacrylonitrile fiber is maintained at 25.42 °C, demonstrating its prominent low-temperature resistance. This phenomenon is attributed to the effective and stable light absorption of PANI particles in the Vis-NIR region. The K/S value of the solar-driven PANI/polyacrylonitrile fiber is 0.08 at 700 nm, indicating the color depth is very light. Besides, the tiny temperature difference is observed after being washed 25 times, demonstrating the solar-driven PANI/polyacrylonitrile fiber possesses high washing resistance. The solar-driven PANI/polyacrylonitrile fiber can be easily woven into a bracelet or sewn into the fabric, suggesting a facile fabrication strategy overcoming the constraints of photothermal fiber color is obtained to promote the development of wearable heater.

Surface/Interface Defect Engineering on Charge Carrier Transport toward Broadband (UV-NIR) Photoresponse in the Heterostructure Array of p-Si NWs/ZnO Photodetector

The surface/interface properties, especially interfacial states, have a key impact on overall carrier generation, recombination/transport, and/or collection proficiency for heterostructure-based photodetectors. This study demonstrates the significant enhancement of ultraviolet–near infrared (UV-NIR) (300–1100 nm) broadband photodetection in the heterostructure array of p-Si NWs/ZnO photodetectors with engineering of surface/interface charge carrier transportation under different processing conditions. In the case of a pulsed laser deposition (PLD)-grown photodetector, coupling of the subsidiary value of the defect state with the interfacial layer (Si–O–Zn) at the p–n junction reduces the charge carrier recombination, resulting in a large enhancement of transient photocurrent in the visible (Vis)–NIR region. However, in the case of a chemical solution deposition (CSD)-grown photodetector, plenty of oxygen vacancies (Vos) become the trap-assisted recombination centers by capturing of photoinduced carriers. The average value of responsivity (R) at 1 V bias for the PLD-grown detector is ∼5.5 A/W in the Vis–NIR (500–1100 nm) region, whereas in the UV region (≤375 nm), the value of R reached ∼8 A/W. The value of R in the PLD-grown detector is enhanced ∼102 folds in the UV region and ∼20 folds in the Vis–NIR region in comparison with the CSD-grown detector. Further, carrier generation, trapping, and transport/recombination processes in the surface/interface are well illustrated to explain the dynamics of the charge carrier contributing to the photoresponse behavior in the UV-NIR broadband region.

Study on Black Spot Disease Detection and Pathogenic Process Visualization on Winter Jujubes Using Hyperspectral Imaging System.

In this work, the potential of a hyperspectral imaging (HSI) system for the detection of black spot disease on winter jujubes infected by Alternaria alternata during postharvest storage was investigated. The HSI images were acquired using two systems in the visible and near-infrared (Vis-NIR, 400-1000 nm) and short-wave infrared (SWIR, 1000-2000 nm) spectral regions. Meanwhile, the change of physical (peel color, weight loss) and chemical parameters (soluble solids content, chlorophyll) and the microstructure of winter jujubes during the pathogenic process were measured. The results showed the spectral reflectance of jujubes in both the Vis-NIR and SWIR wavelength ranges presented an overall downtrend during the infection. Partial least squares discriminant models (PLS-DA) based on the HSI spectra in Vis-NIR and SWIR regions of jujubes both gave satisfactory discrimination accuracy for the disease detection, with classification rates of over 92.31% and 91.03%, respectively. Principal component analysis (PCA) was carried out on the HSI images of jujubes to visualize their infected areas during the pathogenic process. The first principal component of the HSI spectra in the Vis-NIR region could highlight the diseased areas of the infected jujubes. Consequently, Vis-NIR HSI and NIR HSI techniques had the potential to detect the black spot disease on winter jujubes during the postharvest storage, and the Vis-NIR HSI spectral information could visualize the diseased areas of jujubes during the pathogenic process.

Spectroscopic properties of YPO4 crystals activated with Ho3+, Er3+, Tm3+

This paper presents a systematic investigation on the spectroscopic properties of YPO4 crystals activated with Ho3+, Er3+ or Tm3+, carried out in order to obtain preliminary information on the device potentialities of these materials. Relevant information about the radiative properties have been obtained by means of the Judd-Ofelt analysis of the polarized absorption spectra, measured at room temperature in the UV–vis–NIR region. The polarized emission spectra have been measured at 77 and 300 K in the visible and in the NIR upon laser excitation, and the transitions of major interest for application have been identified and characterized. The decay profiles of the main emission manifolds have been measured at room temperature in order to obtain information about the non-radiative processes active in the investigated crystals The stimulated emission cross sections have been estimated for the laser transitions in the NIR, indicating that these compounds can be considered suitable active media for laser operation.

Synthesis, growth, crystal structure analysis, optical characterization, thermal and dielectric studies on 2-amino-5-chloropyridinium phenoxyacetate (2A5CPA): An efficient new organic single crystal for nonlinear optical applications

The new organic 2-amino-5-chloropyridinium phenoxyacetate (2A5CPA) nonlinear optical (NLO) crystal was synthesized and grown from methanol solvent by slow evaporation method successfully. The complete 2A5CPA crystal structure was solved by single crystal XRD analysis and it indicates that the 2A5CPA crystal belongs to the tetragonal crystal system with the space group P41212. From the structure, the possible hydrogen bonding interactions have been analyzed. The presence of distinctive functional peaks in the 2A5CPA crystal was affirmed by FTIR analysis. The optical investigation reveals that the crystal was completely transparent in the UV–Vis–NIR region. The TG-DTA investigation assured that the 2A5CPA compound is thermally stable up to 134°C without any decomposition. The sharp endo thermic peak at 205°C in the DTA trace indicates the melting point of the crystal. The broad emissive band at 382[Formula: see text]nm implies the violet emission characteristics of the 2A5CPA crystal. The dielectric study of the 2A5CPA crystal portrays the normal behavior to that of optical materials. The high work-hardening coefficient of 2.94 indicates the soft material nature of the crystal. The LDT value of the 2A5CPA crystal is estimated as 0.6135[Formula: see text]GW/cm2. The third-order NLO properties of the 2A5CPA crystal were analyzed through Z-Scan experiment.

Structural isomers of di-p-benzidithiaoctaphyrins.

The cis and trans structural isomers of di-p-benzidithiaoctaphyrins were synthesized by adopting two different synthetic routes using readily available precursors under acid-catalyzed conditions, and the isomers were separated using basic alumina column chromatography. 1D and 2D NMR spectroscopy were used to deduce the molecular structures of the macrocycles, which also helps to differentiate the cis isomer from the trans isomer. DFT studies revealed that both the cis and trans isomers adopt figure of eight conformations but exhibit clear differences in their structural features, and the trans isomer is more distorted than the cis isomer. Experimental and theoretical studies revealed that both the cis and trans isomers are nonaromatic stable macrocycles and show subtle differences in their structure, spectral and redox properties. The cis and trans isomers of di-p-benzidithiaoctaphyrin exhibit nonaromatic absorption features in the visible-NIR region, and electrochemical studies revealed their electron-rich nature. TD-DFT studies are in agreement with the experimental observations.

Assessing grapevine water status using Sentinel-2 images

Grapevine water status strongly impacts vine yield and berry quality, hence the importance of a cost- and time-effective methodology to estimate it in commercial vineyards. A two-year experiment was carried out in a rainfed commercial vineyard (cv. ‘Vermentino’ grafted on ‘1103P’) to test the ability of vegetation indices (VIs) derived from Sentinel-2 (S2) multispectral imagery in estimating the stem water potential (Ψstem). The S2 VIs calculated including NIR and SWIR bands (NDMI, MSI and NMSI), performed better (R2 values of 0.66, 0.66 and 0.59, respectively) than those calculated using the bands in the VIS-NIR region (R2 values 0.47, 0.58 and 0.58 for NDVI, GNDVI and NDWI, respectively). The slope between B8a and B11 bands was also significantly affected by grapevine water status. The different weather conditions occurred during the two experimental years also allowed to observe as the S2 VIs performed better in estimating Ψstem under prolonged drought conditions. Moreover, S2 VIs were not able to detect differences in grapevine water status during the onset of water stress condition

The Utility of Airborne Hyperspectral Measurement in Assessment of Soil Fertility

A study was undertaken to evaluate the correlation between hyperspectral data with soil fertility status in the study area of Chinnapalem village Guntur district, Andhra Pradesh. One hudredfifty-three (153) samples were collected at different locations with GPS coordinates by adopting grid method. The hyperspectral data revealed that soil reaction, available Mg, Zn, Fe, Cu and Mn showed positive and significant correlation between VIS-NIR region of electromagnetic spectrum. However, EC and available S were negative and significant throughout VIS and SWIR. From, Stepwise regression approach the poorest fit was observed in all the properties although the highest accuracy (R2=0.467) was found for available zinc, while lowest predictability (R2=0.028) was for sand.

Insights into the Effects of Study Area Size and Soil Sampling Density in the Prediction of Soil Organic Carbon by Vis-NIR Diffuse Reflectance Spectroscopy in Two Forest Areas

Sustainable forest land management requires measuring and monitoring soil organic carbon. Visible and near-infrared diffuse reflectance spectroscopy (Vis-NIR, 350–2500 nm), although it has become an important method for predicting soil organic carbon (SOC), requires further studies and methods of analysis to realize its full potential. This study aimed to determine if the size of the study area and soil sampling density may affect the performance of Vis-NIR diffuse reflectance spectroscopy in the prediction of soil organic carbon. Two forest sites in the Calabria region (southern Italy), which differ in terms of area and soil sampling density, were used. The first one was Bonis catchment area (139 ha) with a cover consisting mainly of Calabrian pine, while the second was Mongiana forest area (33.2 ha) within the “Marchesale” Biogenetic Nature Reserve, which is covered by beech. The two study areas are relatively homogeneous regarding parent material and soil type, while they have very different soil sampling density. In particular, Bonis catchment has a lower sampling density (135 samples out of 139 ha) than Mongiana area (231 samples out of 33.2 ha). Three multivariate calibration methods (principal component regression (PCR), partial least square regression (PLSR), and support vector machine regression (SVMR)) were combined with different pretreatment techniques of diffuse reflectance spectra (absorbance, ABS, standard normal variate, SNV, and Savitzky–Golay filtering with first derivative (SG 1st D). All soil samples (0–20 cm) were analyzed in the laboratory for SOC concentration and for measurements of diffuse reflectance spectra in the Vis-NIR region. The set of samples from each study area was randomly divided into a calibration set (70%) and a validation set (30%). The assessment of the goodness for the different calibration models and the following SOC predictions using the validation sets was based on three parameters: the coefficient of determination (R2), the root mean square error (RMSE), and the interquartile range (RPIQ). The results showed that for the two study areas, different levels of goodness of the prediction models depended both on the type of pretreatment and the multivariate method used. Overall, the prediction models obtained with PLSR and SVMR performed better than those of PCR. The best performance was obtained with the SVMR method combined with ABS + SNV + SG 1st D pretreatment (R2 ≥ 0.77 and RPIQ > 2.30). However, there is no result that can absolutely provide definitive indications of either the effects of the study area size and soil sampling density in the prediction of SOC by vis-NIR spectroscopy, but this study fostered the need for future investigations in areas and datasets of different sizes from those in this study and including also different soil landscapes.

Detection of Alternaria alternata infection in winter jujubes based on optical properties and their correlation with internal quality parameters during storage

In this work, a single integrating sphere system was applied to characterize the optical absorption (μa) and reduced scattering (μs′) properties (550 – 1050 nm) in winter jujube flesh infected by Alternaria alternata during storage at 4 and 20 °C, respectively. Meanwhile, physical (L*, a*, weight loss) and biochemical characteristics (soluble solids content, titratable acids, chlorophyll, total phenolic, and ascorbic acid) of winter jujubes were measured. Among them, chlorophyll, weight loss and ascorbic acid were highly correlated with μa at 680 nm, 690 nm, while chlorophyll and a* had the best correlations with μs′ at 700 – 920 nm. These optimal optical properties were proved efficiently contributed to the disease detection of winter jujubes after 12 days at 4 °C and 3 days at 20 °C during storage, with satisfactory discrimination accuracies (acc > 93.75 %). Consequently, optical properties in Vis-NIR region were available to detect the postharvest disease in winter jujubes.