Near-infrared Region Research Articles

Separating Shrub Cover From Green Vegetation in Grasslands Using Hyperspectral Vegetation Indices

Shrub cover is a key parameter for monitoring woody plant encroachment (WPE) in the background of global grassland degradation. At the critical early encroachment stage, many shrub species are small, and it is impossible to be detected through height parameters. Hyperspectral vegetation indices (HVIs) are valuable tools to estimate vegetation cover, while the effect of shrubs of different cover levels (e.g., low: <35%, moderate: 36–55%, high: >56%) on the spectrum of mixed grassland is still unclear. In this study, narrowband HVIs were created for shrub cover estimation using field hyperspectral data collected in Cypress Hills Interprovincial Park, SK. Published HVIs and newly developed HVIs were examined for the relationship between green shrub cover and total green vegetation (GV) cover. Averaging normalized difference vegetation index (NDVI) was also used to minimize in the variation of shrub cover and GV in each quadrat. Results showed that HVIs SR [600, 800] and NDVI [705, 750] had the highest R2 with green shrub and GV cover (R2 = 0.34 and R2 = 0.30, p-value < 0.05). Blue bands (449 and 489 nm) and SWIR bands (1619 and 1739 nm) combination exhibited the highest accuracy for shrub and GV covers estimation (R2 = 0.60 and 0.40, p-value < 0.05). Averaging NDVI positively correlated with green shrub cover below 30% or above 70%. Three separability metrics (JM, TD, and M) results also showed the red and NIR region may promise to distinguish different shrub cover levels.

Linewidth reduced cascaded Raman fiber lasers and their harmonic conversion for visible laser sources

Cascaded Raman Fiber Lasers (CRFLs) are wavelength versatile sources that can provide power at any wavelength in the Near-Infrared (NIR) region. Conventional CRFLs with broadband feedback are widely wavelength tunable but have broad line widths. A feedback mechanism must be used to reduce the broadening of the linewidth without compromising the wavelength tunability. Here, we propose to use a dual feedback mechanism that combines broadband feedback at all wavelengths, using a flat cleave, with filtered feedback at a desired wavelength due to a grating filter. This allows substantial linewidth reduction of CRFLs up to the 6th Raman shifts, from 1100 nm to 1500 nm, and can be extended further. Significantly reduced linewidth with multi-watt in-band output power is achieved with fine wavelength tuning within each Raman Stokes band using a fixed wavelength pump. As an application of linewidth narrowed output, we performed frequency doubling of CRFL output to generate over 100 mW of wavelength tunable yellow-green and yellow output with enhanced efficiency.

A theoretical analysis to reveal the prospects of MoS2 as a back surface field layer in TiS3-based near infrared photodetector

In this article, a photodetector based on TiS3 absorber material, featuring a narrow direct bandgap of 1 eV, has been simulated. Throughout this research, the J-V (current–voltage) curves and spectral responses have been explored by systematically varying the thickness, doping concentration, and defect density of specific layers. The JSC (short circuit current) and VOC (open circuit voltage) of the heterostructure photodetector are found to be 45.77 mA cm−2 and 0.693 V respectively. Also, the responsivity (R) and detectivity (D*) are 0.81 A W−1 and 2.19 × 1014 Jones at a light wavelength of 1100 nm. The spectral response exhibits significantly elevated values within the wavelength range of 800 nm to 1200 nm, indicating the device’s ability to detect light in the near-infrared (NIR) region effectively. The novel research offers valuable insights, emphasizing the material’s suitability for photodetector (PD) applications and signaling a promising direction for further research interest in photodetector development.

Coordination assembly and NIR photothermal conversion of Metal-organic framework based on 5-(2-cyanophenoxy) isophthalic acid

The development of new photothermal conversion materials in the field of metal-organic frameworks (MOFs) shows broad prospects, but their design synthesis and proper mechanism analysis are still full of huge challenge. Here, four novel MOFs were constructed with 5-(2-cyanophenoxy) isophthalic acid, {Ni(2-CB-IPA)(bpp)(H2O)}n (1), {Ni2(2-CB-IPA)2(bpa)2(H2O)2}n (2), {Co(2-CB-IPA)(bpp)}n (3), {Mn2(2-CB-IPA)2 (bpp)(H2O)2}n (4). (Where 2-CB-IPA = 5-(2-cyanophenoxy) isophthalic acid, bpa = 1,2-bis(4-pyridine)-ethane; and bpp = 1,3-bis(4-pyridyl)propane). The absorption peak at 730 nm in the near-infrared region indicates that different charge transfer interactions affect the photothermal conversion ability. Under laser irradiation (730 nm, 0.45 W cm−2), such compounds exhibit different and distinct warming processes (1 from 20.8 to 91.8 °C; 2 from 20.1 °C to 86.2 °C; 3 from 20.6 to 77.1 °C) except for compound 4. The excellent crystallinity of these materials after irradiation demonstrates excellent thermal stability and cycling durability. Subsequently, further research on the structure-activity relationship revealed that strong π - π interactions are also the reason for the excellent performance of NIR photothermal conversion of 1 under the premise of high NIR absorption. This work provides a visual platform for the photothermal phenomena of crystalline materials.

Facile synthesis of hierarchical W18O49 microspheres by solvothermal method and their optical absorption properties

In this study, a simple route for the synthesis of hierarchical W18O49 assembled by nanowires is reported. The morphologies and formation of W18O49 single-crystal could be controlled by changing the concentration of WCl6-ethanol solution. This synthesis strategy has the advantages that the hierarchical W18O49 microspheres could be economic synthesized at 180 °C without adding additives. Furthermore, efficient optical absorption properties in ultraviolet, visible and near-infrared region were obtained for the hierarchical W18O49 microspheres comparing with nanowires. These results will further promote the research of tungsten-based oxide nanomaterials.Graphical abstract

Ab initio calculation of electronic and optical properties of vdWHs HfX2/BSb(X = Se,S) using density functional theory

Recently, another series of two-dimensional (2D) materials called van der Waals heterostructures (vdWhs) have attracted a lot of attention due to their outstanding properties and wide application in electronic and optical devices. Based on density functional theory (DFT) calculations, the properties of heterostructures were investigated with two different vertical arrangements, formed by two isolated sheets of HfX2(X = Se,S) and Boron antimonide(BSb) monolayer. In particular, vdW interactions are present in all these heterostructures rather than covalent bonding. All thevdWHsare semiconductor with indirect k-M band gap, for which the HSE06 functional exhibit a larger gap, but the electronic gap of all heterostructures is smaller than the electronic gap of their constituent sheets. In addition, all vdWHs show excellent optical absorption in the visible, near-infrared, and ultraviolet regions in the x direction, while the absorption peaks for all vdWHs are higher in the z direction. By fabricating heterostructures from isolated plates, their absorption power increases. The present review demonstrates an effective method for the design of novel vdWHs, and it explores their applications for photocatalytic, photovoltaic, and optical devices.

Using Optimized Spectral Indices and Machine Learning Algorithms to Assess Soil Copper Concentration in Mining Areas

Soil copper (Cu) contamination in mining areas poses a serious threat to the surrounding environment and human health. Timely determination of Cu concentrations is crucial for the ecological protection of mining areas. Hyperspectral remote sensing technology, with its non-destructive monitoring advantages, is essential for monitoring soil Cu pollution and achieving sustainable agricultural development. Using the hyperspectral technique for assessing soil Cu concentration, four machine learning models (support vector regression (SVR), random forest (RF), partial least squares regression (PLSR), and artificial neural network (ANN)), combined with three types of input variables (the full-band, sensitive bands, and optimized spectral indices (Opt-TBIs)) were employed. The hyperspectral reflectance of 647 soil samples from an abandoned tailings mine in western Inner Mongolia, China was collected. The sensitive bands were extracted using the successive projections algorithms (SPA), and 12 Opt-TBIs were selected. Results showed that the regions with higher soil Cu concentration extracted by SPA and Opt-TBIs were concentrated in the red edge and near-infrared regions. Compared with the full spectrum and SPA-sensitive bands, models based on Opt-TBIs successfully predicted soil Cu concentrations. The Opt-TBIs-RF model provided higher accuracy in estimating soil Cu among the four models. Using only four Opt-TBIs as input variables, the model maintained a stable performance in estimating Cu concentrations in different mining areas (R2Val = 0.72, RPDVal = 1.90). In conclusion, Opt-TBIs as input variables demonstrate good predictive capabilities for soil Cu concentrations in the study area, providing a basis for the formulation of sustainable strategies for soil reclamation and environmental protection in Inner Mongolia.

Enhanced Near-infrared Phosphorescent Emission Modulated by Clipping of Metallotweezers in Aqueous Media.

Near-infrared phosphorescent materials have received significant attention due to their potential applications in bioimaging and diagnostics. Although, many types of organic phosphors with near-infrared emission have been developed, the low phosphorescence efficiency in aqueous solution hampers their practical applications in biological systems. Hence, there is an urgent need to develop near-infrared phosphorescent materials with high emission efficiency in aqueous media. Metallotweezers, based on d8 transition metal complexes, emerge as the potential candidates for realizing this objective. Specifically, metallotweezers, featuring two positively charged platinum(II) terpyridine and neutral gold(III) diphenylpyridine pincers on diphenylpyridine spacer, have been designed and synthesized, respectively. The pre-organization effect, rendered by the rigid spacer, enables the resulting metallotweezers to complex with each other, resulting in the formation of clipping complex. The synergistic rigidifying and shielding effects of clipping structure results in enhanced phosphorescent emission intensity. Concurrently, due to phase segregation between the clipping units and the polyethylene glycol tail, the clipping complex undergoes self-assembly in aqueous solution, resulting in phosphorescent emission in the near-infrared region. Overall, non-covalent clipping of metallotweezers illustrated in this study presents a new and effective approach toward near-infrared phosphorescent materials.

Unlocking dual-band electrochromism with stacked structure of amorphous tungsten oxide and Prussian blue

Dual-band electrochromic smart windows can selectively regulate the transmittance of visible and near-infrared (NIR) light, thereby significantly reducing energy consumption in buildings. However, the selective regulation for visible and NIR regions often relies on the integration of multiple components, together with meticulous design and fabrication. Herein, we propose the stacking of amorphous tungsten oxide (a-WO3) on the surface of Prussian blue (PB) through a straightforward magnetron sputtering deposition. Benefiting from the numerous voids-containing structures in the microstructure of a-WO3 films, the stacking structures are conducive to the insertion and transport of electrolyte ions, ensuring the electrochemical activity and electrochromic performance of the inner PB layer. The prepared PB/WO3 bilayer thin film can achieve three functionality modes in dual-band electrochromism: “bright”, “warm”, and “dark”, with high optical modulation of 74.9 % at 700 nm and 80.3 % at 1300 nm, respectively. Additionally, they demonstrate fast coloring/bleaching response (2.9/7.6 s at 700 nm and 6.0/6.2 s at 1300 nm) and satisfying cycling stability (retaining 95.3 % of its initial modulation after 500 cycles). The bilayer thin films based on amorphous electrochromic materials with an intrinsic abundance of voids-containing structures introduce a novel approach to the independent dual-band modulation for demanded light/thermal control.

Extension of nature's NIR-I chromophore into the NIR-II region.

The development of chromophores that absorb in the near-infrared (NIR) region beyond 1000 nm underpins numerous applications in medical and energy sciences, yet also presents substantial challenges to molecular design and chemical synthesis. Here, the core bacteriochlorin chromophore of nature's NIR absorbers, bacteriochlorophylls, has been adapted and tailored by annulation in an effort to achieve absorption in the NIR-II region. The resulting bacteriochlorin, Phen2,1-BC, contains two annulated naphthalene groups spanning meso,β-positions of the bacteriochlorin and the 1,2-positions of the naphthalene. Phen2,1-BC was prepared via a new synthetic route. Phen2,1-BC is an isomer of previously examined Phen-BC, which differs only in attachment via the 1,8-positions of the naphthalene. Despite identical π-systems, the two bacteriochlorins have distinct spectroscopic and photophysical features. Phen-BC has long-wavelength absorption maximum (912 nm), oscillator strength (1.0), and S1 excited-state lifetime (150 ps) much different than Phen2,1-BC (1292 nm, 0.23, and 0.4 ps, respectively). These two molecules and an analogue with intermediate characteristics bearing annulated phenyl rings have unexpected properties relative to those of non-annulated counterparts. Understanding the distinctions requires extending concepts beyond the four-orbital-model description of tetrapyrrole spectroscopic features. In particular, a reduction in symmetry resulting from annulation results in electronic mixing of x- and y-polarized transitions/states, as well as vibronic coupling that together reduce oscillator strength of the long-wavelength absorption manifold and shorten the S1 excited-state lifetime. Collectively, the results suggest a heuristic for the molecular design of tetrapyrrole chromophores for deep penetration into the relatively unutilized NIR-II region.

Comparison of machine learning and deep learning models for the assessment of rondo wine grape quality with a hyperspectral camera

Hyperspectral images provide rich spectral/spatial data and have shown remarkable performance in precision viticulture. Standardized data-processing methods are necessary to reduce the dimensionality and to identify powerful wavelengths. Toward this goal, we evaluated and compared the performance and novel-wavelength-identification ability of five renowned machine learning models: the linear models Ridge and LASSO, a 1D + 2D convolutional neural network (1D +2D CNN) non-linear model, a gradient boosting decision tree (GBDT) using XGBoost as an ensemble model, and an explainable boosting machine (EBM) followed by support vector regression (SVR) as a hybrid model. The model evaluations were conducted using leave-one-out cross-validation (LOOCV) as we sought to clarify the best-fitted machine learning model. Our results demonstrated that Ridge, LASSO, showed better performance with relatively high accuracy but were weak as a wavelength identifier. GDBT-XGBoost showed considerable prediction power and wavelength identification. EBM-SVM emerged as the most powerful model, demonstrating exceptional stability and clear wavelength classification even for destructive measurements under varying environmental stresses across Rondo's growth stages. The combined approach of 1D + 2D CNN algorithms was advantageous to handle the dynamic shapes of spectral curve and horizontal shift of the wavelengths obtained from outdoor data acquisition, and notably, it showed the highest accuracy to predict the brix and pH of wine grapes for both indoor and outdoor sensings. But the combined effects of 1D and 2D CNN algorithms were difficult to clarify the importance of spectral features for the brix and pH prediction. The integrated machine learning models with dimensionality reduction, and proper image acquisition can increase the model's accuracy. The common absorption peaks were observed in the near-infrared region of 700 nm and 900 nm. Those wavelengths should be considered for the development of low-cost sensing platforms with fewer bands. Wavelengths over 900 nm are also important to develop outdoor sensing platforms.

Hydroxyl-Bonded Co Single Atom Site on Boroncarbonitride Surface Realizes Non-sacrificial H2O2 Synthesis in the Near-Infrared Region.

Photocatalytic synthesis of hydrogen peroxide (H2O2) from O2 and H2O under near-infrared light is a sustainable renewable energy production strategy, but challenging reaction. The bottleneck of this reaction lies in the regulation of O2 reduction path by photocatalyst. Herein, we construct the center of the one-step two-electron reduction (OSR) pathway of O2 for H2O2 evolution via the formation of the hydroxyl-bonded Co single-atom sites on boroncarbonitride surface (BCN-OH2/Co1). Our experimental and theoretical prediction results confirm that the hydroxyl group on the surface and the electronic band structure of BCN-OH2/Co1 are the key factor in regulating the O2 reduction pathway. In addition, the hydroxyl-bonded Co single-atom sites can further enrich O2 molecules with more electrons, which can avoid the one-electron reduction of O2 to •O2 -, thus promoting the direct two-electron activation hydrogenation of O2. Consequently, BCN-OH2/Co1 exhibited a high H2O2 evolution apparent quantum efficiency of 0.8% at 850nm, better than most of the previously reported photocatalysts. This study reveals an important reaction pathway for the generation of H2O2, emphasizing that precise control of the active site structure of the photocatalyst is essential for achieving efficient conversion of solar-to-chemical. This article is protected by copyright. All rights reserved.

Photoinduced carrier transfer dynamics in a monolayer MoS2/PbS quantum dots heterostructure

Two-dimensional molybdenum disulfide (MoS2) has been proven to be a candidate in photodetectors, and MoS2/lead sulfide (PbS) quantum dots (QDs) heterostructure has been used to expand the optical response wavelength of MoS2. Time-resolved pump-probe transient absorption measurements are performed to clarify the carrier transfer dynamics in the MoS2/PbS heterostructure. By comparing the carrier dynamics in MoS2 and MoS2/PbS under different pump wavelengths, we found that the excited electrons in PbS QDs can transfer rapidly (&lt;100 fs) to MoS2, inducing its optical response in the near-infrared region, although the pump light energy is lower than the bandgap of MoS2. Besides, interfacial excitons can be formed in the heterostructure, prolonging the lifetime of the excited carriers, which could be beneficial for the extraction of the carriers in devices.

Near-Infrared Absorbing Aza-BODIPY Dyes for Optoelectronic Applications.

Organic dyes that absorb light in the visible to near-infrared region have garnered significant interest, owing to their extensive utility in organic photovoltaics and various biomedical applications. Aza-boron-dipyrromethene (Aza-BODIPY) dyes are a class of chromophores with impressive photophysical properties such as tunable absorption from the visible region towards near infrared (NIR) region, high molar absorptivity, and fluorescence quantum yield. In this review, we discuss the developments in the aza-BODIPYs, related to their synthetic routes, photophysical properties and their applications. Their design strategies, modifications in chemical structures, mode/position of attachment, and their impact on photo-physical properties are reviewed. The potential applications of aza-BODIPY derivatives such as organic solar cells, photodynamic therapy, boron-neutron capture therapy, fluorescence sensors, photo-redox catalysis, photoacoustic probes and optoelectronic devices are explained.

Design and comparative analysis of aluminum-BiFeO3-based plasmonic device in the near-infrared region

Design and comparative analysis of aluminum-BiFeO3-based plasmonic device in the near-infrared region

Advancing Detectivity and Stability of Near-Infrared Organic Photodetectors via a Facile and Efficient Cathode Interlayer.

Near-infrared (NIR) organic photodetectors (OPDs) are pivotal in numerous technological applications due to their excellent responsivity within the NIR region. Polyethylenimine ethoxylated (PEIE) has conventionally been employed as an electron transport layer (hole-blocking layer) to suppress dark current (JD) and enhance charge transport. However, the limitations of PEIE in chemical stability, processing conditions, environmental impact, and absorption range have spurred the development of alternative materials. In this study, we introduced a novel solution: a hybrid of sol-gel zinc oxide (ZnO) and N,N'-bis(N,N-dimethylpropan-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide (PDINO) as the electron transport layer for NIR-OPDs. Our fabricated OPD exhibited significantly improved responsivity, reduced internal traps, and enhanced charge transfer efficiency. The detectivity, spanning from 400 to 1100 nm, surpassed ∼5 × 1012 Jones, reaching ∼1.1 × 1012 Jones at 1000 nm, accompanied by an increased responsivity of 0.47 A/W. Also, the unpackaged OPD remarkedly demonstrated stable JD and external quantum efficiency (EQE) over 1000 h under dark storage conditions. This innovative approach not only addresses the drawbacks of conventional PEIE-based OPDs but also offers promising avenues for the development of high-performance OPDs in the future.

Graphene and ZnO NPs-enhanced photodetectors based on SiO NWs: Synthesis, characterization, and applications

In this study, we successfully synthesized and characterized silicon oxide nanowires/graphene/zinc oxide nanoparticles (SiO NWs/Graphene and ZnO NPs) hybrid nanostructures using pulsed laser deposition (PLD) technique. The characterization of the crystalline phase, morphology, and optical properties of the synthesized hybrid nanostructure systems revealed that the addition of graphene and ZnO NPs led to increased roughness values and changes in the surface topography of the films. The optical properties showed that the addition of graphene and zinc oxide enhanced the reflectivity in specific regions, including the UV and visible ranges, and improved the collection of charge carriers. The SiO NWs/Graphene and ZnO NPs was assessed as a photodetector and exhibited excellent performance, with high quantum efficiency, detectivity, and responsivity in the visible and near-infrared regions, making it a promising platform for the development of next-generation optoelectronic devices in various fields, including security, environmental monitoring, and medical diagnostics.

Oxide Based Pentachromatic‐Vision Inspired Optoelectronic Synaptic Transistor with Large Conduction States Over 512

AbstractOptoelectronic neuromorphic devices based on oxide semiconductors have been potentially investigated to mimic the functions of human visual synapses. However, the challenge comes from the wide bandgap characteristics of numerous oxide semiconductors, which restricts the response range of the device under ultra‐violet (UV) region. Strategies for widening the response range are mostly focused on artificially generating the defect states, however, most of them results in mimicking the tetrachromatic visual system from UV to visible light range. To be used for industries such as robotics, or autonomous vehicles, mimicking the tetrachromatic vision system should be overcome up to near‐infrared (NIR) region. Here, a facile solution processed indium‐gallium‐zinc‐oxide and silver oxide structured optoelectronic synaptic transistor is fabricated not only to mimic the function of human synapses, but to overcome the tetrachromatic human visual system up to the NIR region. The device not only showed photoresponse characteristics under the entire 405 to 830 nm wavelength region, but also showed significant synaptic behaviors with over 512 conduction states under a reasonable incident light power density of 4.5 mW cm−2. The results will offer a useful facile method for fabricating optoelectronic synaptic transistors that can overcome the tetrachromatic vision systems.

Emission Spectra of Uranium Particulates at High Temperature.

The emission spectrum of micron-scale uranium particulates at high temperatures in the ultraviolet, visible, and near-infrared spectral regions is investigated using a heterogeneous shock tube. Temperatures from 3000 to 9000 K are characterized in an inert argon environment and with incremental amounts of added oxygen. Atomic line spectra do not emerge above the continuum emission spectrum until between 4500 and 5000 K in pure argon, and 6100 and 6600 K in 1% oxygen. For 5% oxygen, however, the threshold for atomic emission drops below 3800 K. Uranium monoxide molecular emission in the strongest visible band at 595.4 nm is not observed at any condition. Uncertainties in particle temperature determination in high-temperature shock tube environments are discussed, and limitations to such measurements are presented, such as those from experimental factors such as the powder loading method and expected detection limits of uranium species in relevant conditions.

Detection of Fusarium spp. infection in potato (Solanum tuberosum L.) during postharvest storage through visible–near-infrared and shortwave–near-infrared reflectance spectroscopy

Abstract Pathogen infection can damage agricultural products, thereby reducing their economic value. Fusarium spp. is a fungal pathogen that infects potatoes (Solanum tuberosum L.) and causes dry rot. In this study, we utilized visible–near-infrared (Vis–NIR) and shortwave–near-infrared (SW–NIR) spectroscopy for the early detection of Fusarium spp. infection in potato tubers. The spectrometer used in this study analyzed the Vis–NIR (400–1,000 nm) and SW–NIR (970–1,700 nm) regions. A total of 183 potato (G2 “Granola L.” variety) samples were used. Among these, 93 samples were artificially inoculated with Fusarium solani mycelia, while 90 samples were left uninfected and considered the control group. The potato samples were stored at two different temperatures (12 and 25°C). Vis–NIR and SW–NIR spectra were analyzed by a chemometric method, namely principal component analysis with linear discriminant analysis (PCA–LDA), to differentiate healthy and infected potatoes. The PCA–LDA model based on Vis–NIR spectra exhibited a calibration accuracy of 80.26% and a reliability of 65%. Meanwhile, the PCA–LDA model based on SW–NIR spectra exhibited a calibration accuracy of 100% and a reliability of 97.30%. Overall, both methods demonstrated their suitability for differentiating potato tubers with Fusarium spp. fungal infection and healthy ones; however, the results suggest that SW–NIR spectroscopy is more effective than Vis–NIR spectroscopy.