Narrowband Near-infrared Research Articles

A Near-Infrared Retinomorphic Device with High Dimensionality Reservoir Expression.

Physical reservoir-based reservoir computing (RC) systems for intelligent perception have recently gained attention because they require fewer computing resources. However, the system remains limited in infrared (IR) machine vision, including materials and physical reservoir expression power. Inspired by biological visual perception systems, the study proposes a near-infrared (NIR) retinomorphic device that simultaneously perceives and encodes narrow IR spectral information (at ≈980nm). The proposed device, featuring core-shell upconversion nanoparticle/poly (3-hexylthiophene) (P3HT) nanocomposite channels, enables the absorption and conversion of NIR into high-energy photons to excite more photo carriers in P3HT. The photon-electron-coupled dynamics under the synergy of photovoltaic and photogating effects influence the nonlinearity and high dimensionality of the RC system under narrow-band NIR irradiation. The device also exhibits multilevel data storage capability (≥8 levels), excellent stability (≥2000 s), and durability (≥100 cycles). The system accurately identifies NIR static and dynamic handwritten digit images, achieving recognition accuracies of 91.13% and 90.07%, respectively. Thus, the device tackles intricate computations like solving second-order nonlinear dynamic equations with minimal errors (normalized mean squared errorof 1.06 × 10⁻3 during prediction).

Wavelength‐Selective Near‐Infrared Organic Upconversion Detectors for Miniaturized Light Detection and Visualization

AbstractUpconversion detectors monolithically combining a detection unit and a light emitting unit, enables light detection and visualization in a compact structure, promising great advances in miniaturized multifunctional optoelectronics. The detection range of upconversion detectors usually covers a broadband spectrum, limiting their use in spectroscopic fields. This work investigates two wavelength‐selective upconversion detectors made with organic semiconductors to realize narrowband near‐infrared (NIR) light detection and visualization dual function. Two non‐fullerene‐based NIR‐sensitive bulk‐heterojunctions (BHJs) are exploited to make wavelength‐selective upconversion detectors, achieving peak sensitivity at 860 and 890 nm, with full width at half maximum of 125 and 170 nm, respectively. Each NIR‐sensitive BHJ comprises a donor polymer and a non‐fullerene acceptor, both of which are selectively sensitive to NIR light. The cumulative analysis of the optical properties of the absorber and current–voltage characteristics of the device indicates that the wavelength selectivity stems mainly from the wavelength‐dependent absorption. In particular, the upconversion detectors exhibit wavelength‐selective electronic and optical dual‐readouts, which are appealing for miniaturized spectroscopic applications, including health monitoring, optical communication, and microbead imaging, paving the way for practical applications.

Low-donor content approach to achieve sensitive narrowband organic photodetectors

Narrowband near-infrared (NIR) detectors are key components for various modern biomedical, agricultural, astronomical sensing as well as monitoring applications. Typically, a narrowband organic photodetector (OPD) requires thick junctions or additional optical elements, which are either tedious or cost-ineffective. Here, we adopt the low-donor content strategy in our thin-film device to realize narrowband spectral features. The much-mitigated aggregation drastically improves shunt resistance and dark current while maintaining decent photocurrent. Upon further dilution, a thinner electron transporting layer can effectively shorten the transient response to reach fast speed. n-i-p and p-i-n device configurations are also compared, which exhibits drastic changes for low-donor content OPDs. The 5 wt% D:A thin-film bulk-heterojunction OPD presents an external quantum efficiency of 49.3% at 770 nm with zero bias, and a high thermal-noise calculated specific detectivity (D*) of 1.0 × 1013 Jones (7.1 × 1012 Jones based on noise spectral density) at 0 V. Such narrowband OPD also shows a fast NIR response of 530 ns/840 ns (rise/fall) when operated at 10 kHz. The results reveal the potential for low-donor-content blend in realizing narrowband photodetection.

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications.

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability, and adjustable optical properties. NIR-emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) of over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, are summarized, and their recent advancement is assessed. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. Also, the various applications of NIR-emitting metal halides are highlighted and an outlook for the field is provided.

Investigation of Narrow-band NIR LED Spectral Response Towards a Non-invasive Glucose Sensor.

Spectroscopy is utilised extensively in medical sensing technology. Typically, hand-held spectroscopy equipment uses miniature narrow-band light emitting diodes (LEDs) and photodiodes to emit and detect light, respectively. Photodiodes typically absorb light across a wide spectra so measurements can be corrupted by surrounding light. LEDs in the visible spectrum have a narrower spectral response and can be used in place of a traditional photodiode. However, the absorption characteristics of near infrared (NIR) spectrum LEDs is unknown. A discrete, low-cost spectrophotometer was designed to assess spectral response for 8 narrow band NIR LEDs. The normalised and raw spectral response determined the optimum detector for 1050 nm - 1300 nm is the 1450 nm LED, and the optimum detector for 1450 nm - 1650 nm emissions is the 1650 nm LED.Clinical relevance - Understanding the spectral response of narrow-band LEDs in the NIR spectrum will aid development of NIR hand-held spectroscopy medical devices.

NIRPed: A Novel Benchmark for Nighttime Pedestrian and Its Distance Joint Detection

In nighttime driving scenes, due to insufficient and uneven lighting, and the scarcity of high-quality datasets, the miss rate of nighttime pedestrian detection (PD) is much higher than that of daytime. Vision-based distance detection (DD) has the advantages of low cost and good interpretability, but the existing methods have low precision, poor robustness, and the DD is mostly performed independently of PD. A narrowband near-infrared (NIR) camera and an NIR lamp to relieve the impact of noisy visible light (VIS) and improve imaging quality have been selected; a LiDAR to obtain distance information has been embedded in the system; a nighttime driving scene pedestrian and its distance joint detection dataset NIRPed has been built. The NIRPed includes 146k pedestrian annotations, which is 3 times that of NightOwls, the largest VIS nighttime pedestrian dataset. Based on Faster-RCNN, a joint PD and DD method using monocular imaging has been proposed. The propo-sed method realizes the joint detection of pedestrian and its distance on the NIRPed dataset with the PD log-average miss rate and DD mean absolute error rate of 6.5% and 5.5%, respectively. For comparison, the joint detection method was implemented on other large-scale VIS pedestrian datasets as well. Moreover, compared with the existing vision-based DD methods, the proposed method is less affected by pedestrian distance and height, exhibits higher accuracy and robustness, and satisfied the ISO requirements for intelligent transportation systems (absolute error rate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 15%).

Aligned Plasmonic Antenna and Upconversion Nanoparticles toward Polarization-Sensitive Narrowband Photodetection and Imaging at 1550 nm.

Lanthanide-doped upconversion nanoparticles (UCNPs) are rising as prospect nanomaterials for constructing polarization-sensitive narrowband near-infrared (NIR) photodetectors (PDs), which have attracted significant interest in astronomy, object identification, and remote sensing. However, polarized narrowband NIR photodetection and imaging based on UCNPs have yet to be realized. Herein, we demonstrate that NIR photodetection and imaging are capable of sensing polarized light as well as affording wavelength-selective detection at 1550 nm by integrating directional-Au@Ag nanorods (D-Au@Ag NRs) with NaYF4:Er3+@NaYF4 UCNPs. Monolayer and large-area D-Au@Ag NRs polarization-sensitive plasmonic antenna films are obtained, and the center of their localized surface plasmon resonance (LSPR) peak is located at around 1550 nm. Experimental and theoretical results reveal that D-Au@Ag NRs have a sharp localized LSPR peak with a dominant scattering cross section. The UCNPs coupled with D-Au@Ag NRs exhibit significantly enhanced and strongly polarization-dependent luminescence with a high degree of polarization (DOP) of 0.72. The first polarization-resolved UC narrowband PD at 1550 nm is achieved, which delivers a DOP of 0.63, a detectivity of 1.69 × 1010 Jones, and a responsivity of 0.32 A/W. Finally, we develop a polarized imaging system for 1550 nm with visual photoelectric detection based on the aforementioned PDs. Our work opens up possibilities for manipulating UC and developing next-generation polarization-sensitive narrowband infrared photodetection and imaging technology.

Transverse-pumping approach for a powerful single-mode Ti:sapphire laser for near infrared lidar applications.

We present a design of a transversely pumped and powerful Ti:sapphire laser, suitable for laser remote sensing in the near infrared (NIR) spectrum. Examining multiple pump configurations revealed that transversal pumping of Ti:sapphire crystals with a Nd:YAG laser (532 nm) from one or two sides yields maximum output power. Together with an optimized bow-tie resonator setup, we were able to extract up to 3 W (30 mJ, 100 Hz) of narrowband NIR laser emission from a cuboid 50 mm long Ti:sapphire crystal. Beam quality and divergence were determined as Mx2=1.1, My2=1.7, φx=0.5mrad, and φy=0.8mrad. The spectral purity (seeded, Pseed≥170µW) was better than 99.8%. Additionally, we show a two-wavelength setup applicable to atmospheric water vapor lidar. The principle performance of this theory of operation suggests a good chance of scalability towards significantly enhanced power of future Ti:sapphire lasers.

Narrowband Near-Infrared Perovskite/Organic Photodetector: TCAD Numerical Simulation

Narrowband photodetectors (PD) established in the near-infrared (NIR) wavelength range are highly required in a variety of applications including high-quality bioimaging. In this simulation study, we propose a filter-less narrowband PD based on the architecture of perovskite/organic heterojunction. The most decisive part of the photodetector is the hierarchical configuration of a larger bandgap perovskite material with a thicker film followed by a lower bandgap organic material with a narrower layer. The design of the structure is carried out by TCAD numerical simulations. Our structure is based on an experimentally validated wideband organic PD, which is modified by invoking an additional perovskite layer having a tunable bandgap. The main detector device comprises of ITO/perovskite (CsyFA1−yPb(IxBr1−x)3)/organic blend (PBDTTT-c:C60-PCBM)/PEDOT:PSS/Al. The simulation results show that the proposed heterojunction PD achieves satisfactory performance when the thickness of perovskite and organic layers are 2.5 µm and 500 nm, respectively. The designed photodetector achieves a narrow spectral response at 730 nm with a full width at half-maximum (FWHM) of 33 nm in the detector, while having a responsivity of about 0.12 A/W at zero bias. The presented heterojunction perovskite/organic PD can efficiently detect light in the wavelength range of 700 to 900 nm. These simulation results can be employed to drive the development of filter-less narrowband NIR heterojunction PD.

Matrix Isolation Study of Fumaric and Maleic Acids in Solid Nitrogen.

Fumaric and maleic acids ((E)- and (Z)-HOOC-CH═CH-COOH, FA and MA) were studied experimentally by infrared spectroscopy in nitrogen matrixes and theoretically by quantum chemical calculations. The calculations, carried out at the DFT(B3LYP) and MP2 levels of theory, predicted the existence of at least 5 conformers of maleic acid and 10 conformers of fumaric acid. After the deposition of the matrixes, two conformers of maleic acid (I and II) and three conformers (I-III) of fumaric acid were observed and characterized vibrationally. Selective narrowband near-infrared (NIR) excitation of the first OH stretching overtones of the different conformers of maleic and fumaric acids initially present in the matrixes allowed the generation of higher-energy forms, never before observed experimentally. In the case of maleic acid, conformers I (a cis-trans form, where cis and trans designate the conformation of the carboxylic groups of the molecule) and II (cis-cis) were found to generate the novel conformers VI (trans-trans) and VII (cis-trans), respectively. The conversion of conformer II into the most stable conformer I was also observed. For fumaric acid, the cis-cis conformers I-III were found to give rise to the new cis-trans conformers IV-VII, respectively. The tunneling decay of the new conformers produced upon NIR excitation of the lowest-energy conformers initially trapped in the matrixes was observed, and their lifetimes in solid N2 were determined. The increased stability of all of the observed high-energy conformers of the studied acids in the N2 matrix, compared to the argon matrix, where they could not be observed experimentally, demonstrates the stabilizing effect of the interaction between the OH groups of the acids with the matrix N2 molecules, in line with previous observations for other carboxylic acids. In addition, the photochemistry of matrix-isolated maleic and fumaric acids upon broad-band UV irradiation (λ > 235 nm) was also investigated. UV-induced isomerization of both acids around the C═C double bond was observed, together with their decarboxylation to acrylic acid.

Selecting nitride host for Yb3+ toward near-infrared emission with low-energy charge transfer band

Yb3+-doped phosphors have characteristic near-infrared (NIR) emissions, but their applications in phosphor-converted light-emitting-diodes (pc-LEDs) and Si solar cells are limited due to their mismatching excitation spectra. Here, we selected nitride La3Si6N11 (LSN) as host material to achieve Yb3+ NIR emission upon low-energy charge transfer (CT) excitation. The obtained phosphor LSN:Yb3+ has a broad CT excitation band ranging from 250 to 500 nm and narrowband NIR emissions ranging from 950 to 1100 nm centered at 983 nm. On the basis of spectral data, the vacuum referred binding energies (VRBE) schemes are constructed to locate energy levels of all lanthanide ions in LSN. We also fabricated NIR pc-LED device using 395 nm LED chip to demonstrate the potential applications of LSN:Yb3+ phosphors.

Narrowband Near‐Infrared Photodetector Enabled by Dual Functional Internal‐Filter‐Induced Selective Charge Collection

AbstractThe spectral selective detection of the near‐infrared (NIR) signals is important for biological sensing, healthy monitoring, and intelligent communication. Herein, a new method to fabricate a visible‐blind NIR‐sensitive narrowband photodetector (NPD) with excellent comprehensive performances is reported. The organic bulk heterojunction (OBHJ) thin film, based on an NIR‐sensitive organic acceptor, is employed to provide fast photoresponse, with adjustable cutoff edge. The key strategy of introducing a solution‐processable optical/electric bifunctional internal filter (CH3NH3PbI3 (MAPbI3)/CuSCN) realizes the selective collection of the NIR‐induced charge carriers. Further combined with the suitable energy level and high mobility of the MAPbI3/CuSCN layer, the extraction of NIR‐light‐induced charges from OBHJ is promoted efficiently. The NPD with optimized structure exhibits narrowband NIR response (full width at half maximum (FWHM) &lt; 100 nm) with maximum external quantum efficiency value up to 74.26% and detection limit down to 3.6 pW cm−2, both of which are the best values among the ever reported NIR NPDs. The highest responsivity reaches 0.485 A W−1 in the NIR region, with a large linear dynamic range of 162 dB. The specific detectivity is close to 1013 Jones, enabling the device to detect weak NIR signals.

Narrowband Near-Infrared Perovskite/Polymer Hybrid Photodetectors

The distinct visible-blind narrowband near-infrared (NIR) photodetection behaviors in the perovskite/polymer hybrid photodetectors (PDs) have been investigated. The narrowband NIR response in the hybrid PDs is realized through the buildup of the space charges at the perovskite/polymer interface. The semiconducting perovskite layer acts as an internal NIR bandpass due to its high absorption to the visible light and high transparency to the NIR light. It also acts as an excellent hole-transporting layer, facilitating the efficient extraction of the holes generated in the low band gap NIR light-absorbing polymer blend layer. The hybrid PDs thus demonstrated have a -3 dB cutoff frequency of 300 kHz, providing an exciting option for a plethora of applications in bioimaging, environmental detection, and security monitoring.

Flexible double narrowband near-infrared photodetector based on PMMA/core–shell upconversion nanoparticle composites

Flexible narrowband near infrared (NIR) photodetectors (PDs) are urgently in demand in the fast-developing era of flexible electronics, due to their crucial roles in various innovative applications. Hence, we designed and synthesized the core–shell structured NaYF4:Yb3+,Er3+@NaYF4:Nd3+ upconversion nanoparticles (UCNPs), which can be pumped by the 808 and 980 nm lights. The upconversion luminescence (UCL) are significantly enhanced after being assembled with the opal photonic crystals (OPCs) due to the photonic crystal effect, with 55 and 48 folds of enhancement factors under illuminations of 808 and 980 nm lights, respectively. Based on this hybrid, the flexible narrowband PDs were successfully fabricated on the PET substrate with the structure of OPCs/NaYF4:Yb3+,Er3+@Nd3+/MAPbI3, which displays excellent detection performance to double narrowband NIR light (808 and 980 nm) benefiting from the amplified UCL, with responsivity of 8.79 and 7.39 A/W, detectivity of 3.01 × 1011 and 2.68 × 1011 cm⋅Hz1/2/W for 808 and 980 nm lights detection respectively, along with short response time in the range of 120–160 ms. Furthermore, the OPCs/NaYF4:Yb3+,Er3+@NaYF4:Nd3+/MAPbI3 double narrowband PDs display low photodetection power threshold (0.05 W/cm2), outstanding flexibility, prominent moisture resistance, and good long-time stability. This work displays a new concept of narrowband NIR PDs, which open a new field for specific NIR light detections.

Near-Infrared Imaging Photoplethysmography During Driving

Imaging photoplethysmography (iPPG) could greatly improve driver safety systems by enabling capabilities ranging from identifying driver fatigue to unobtrusive early heart failure detection. Unfortunately, the driving context poses unique challenges to iPPG, including illumination and motion. First, drastic illumination variations present during driving can overwhelm the small intensity-based iPPG signals. Second, significant driver head motion during driving, as well as camera motion (e.g., vibration) make it challenging to recover iPPG signals. To address these two challenges, we present two innovations. First, we demonstrate that we can reduce most outside light variations using narrow-band near-infrared (NIR) video recordings and obtain reliable heart rate estimates. Second, we present a novel optimization algorithm, which we call AutoSparsePPG, that leverages the quasi-periodicity of iPPG signals and achieves better performance than the state-of-the-art methods. In addition, we release the first publicly available driving dataset that contains both NIR and RGB video recordings of a passenger’s face with simultaneous ground truth pulse oximeter recordings.

Vibrationally Induced Conformational Isomerization and Tunneling in Pyrrole-2-Carboxylic Acid

The conformational behavior of carboxylic acids has attracted considerable attention, as it can be used as a gateway for the study of more complex phenomena. Here, we present an experimental and computational study of pyrrole-2-carboxylic acid (PCA) conformational space and the vibrational characterization of the compound by infrared spectroscopy. The possibility of promoting conformational transformations using selective vibrational excitation of the 2ν(OH) and 2ν(NH) stretching overtones is explored. Two conformers, exhibiting the cis configuration of the COOH group (O═C-O-H dihedral angle near 0°) and differing by the orientation of the carboxylic group with respect to the pyrrole ring (i.e., showing either a cis or a trans NCC═O arrangement), were found to coexist initially for the compound isolated in a cryogenic nitrogen matrix, in an 86:14 ratio, and were characterized by infrared spectroscopy. A third conformer, with the COOH group in the trans configuration, was produced, in situ, by narrowband near-infrared (NIR) excitation of the most stable PCA form (with a cis NCC═O moiety). The photogenerated PCA conformer was found to decay back to the most stable PCA form, by H-atom quantum mechanical tunneling, with a characteristic half-life time of ∼10 min in the nitrogen matrix at 10 K. Tunneling rates were theoretically estimated and compared for the observed isomerization of pyrrole-2-carboxylic acid and for the structurally similar furan-2-carboxylic acid. This comparison showcases the effect of small modifications in the potential energy surface and the implications of quantum tunneling for the stability of short-living species.

Identification and Reactivity of s-cis,s-cis-Dihydroxycarbene, a New [CH2O2] Intermediate.

We report the first preparation of the s-cis,s-cis conformer of dihydroxycarbene (1cc) by means of pyrolysis of oxalic acid, isolation of the lower-energy s-trans,s-trans (1tt) and s-cis,s-trans (1ct) product conformers at cryogenic temperatures in a N2 matrix, and subsequent narrow-band near-infrared (NIR) laser excitation to give 1cc. Carbene 1cc converts quickly to 1ct via quantum-mechanical tunneling with an effective half-life of 22 min at 3 K. The potential energy surface features around 1 were pinpointed by convergent focal point analysis targeting the AE-CCSDT(Q)/CBS level of electronic structure theory. Computations of the tunneling kinetics confirm the time scale of the 1cc → 1ct rotamerization and suggest that direct 1cc → H2 + CO2 decomposition may also be a minor pathway. The intriguing latter possibility cannot be confirmed spectroscopically, but hints of it may be present in the measured kinetic profiles.

Modified RGB Cameras for Infrared Remote-PPG.

Multi-wavelength cameras play an essential role in remote photoplethysmography (PPG). Whereas these are readily available for visible light, this is not the case for near infrared (NIR). We propose to modify existing RGB cameras to make them suited for NIR-PPG. In particular, we exploit the spectral leakage of the RGB channels in infrared in combination with a narrow dual-band optical filter. Such camera modification is simple, cost-effective, easy to implement, and it is shown to attain a pulse-rate extraction performance comparable to that of multiple narrow-band NIR cameras.

Towards high performance visible-blind narrowband near-infrared photodetectors with integrated perovskite light filter

Narrowband near-infrared (NIR) light detection is essential for optical imaging, machine vision, and spectroscopy. In this work, we demonstrate a strategy towards visible-blind narrowband NIR organic photodetectors by integrating perovskite thin film as the light filter. Lead phthalocyanine (PbPc):Fullerene (C60) bulk heterojunction which demonstrates high efficiency in photoexciton dissociation is used as the photosensitive layer due to excellent absorption of PbPc in NIR light region. Perovskite layer which has a strong absorption in the visible region but a weak absorption in the NIR region serves as a light filtering layer. More importantly, we have further improved the device performance by inserting copper phthalocyanine (CuPc) electron blocking layer between the ITO anode and PbPc:C60 bulk heterojunction. A high photoresponsivity (R) of 1.09 A/W, an external quantum efficiency (EQE) of 167%, and a narrow spectral response with the full width of half maximum of ~60 nm for NIR light of 808 nm wavelength is obtained.

A BODIPY-Based Donor/Donor-Acceptor System: Towards Highly Efficient Long-Wavelength-Excitable Near-IR Polymer Dots with Narrow and Strong Absorption Features.

Bright long-wavelength-excitable semiconducting polymer dots (LWE-Pdots) are highly desirable for in vivo imaging and multiplexed in vitro bioassays. LWE-Pdots have been obtained by incorporating a near-infrared (NIR) emitter into the backbone of a polymer host to develop a binary donor-acceptor (D-A) system. However, they usually suffer from severe concentration quenching and a trade-off between fluorescence quantum yield (Φf ) and absorption cross-section (σ). Herein, we describe a ternary component (D1 /D2 -A) strategy to achieve ultrabright, green laser-excitable Pdots with narrow-band NIR emission by introducing a BODIPY-based assistant polymer donor as D1 . The D1 /D2 -A Pdots possess improved Φf and σ compared to corresponding binary D2 -A Pdots. Their Φf is as high as 40.2 %, one of the most efficient NIR Pdots reported. The D1 /D2 -A Pdots show ultrahigh single-particle brightness, 83-fold brighter than Qdot 705 when excited by a 532 nm laser. When injected into mice, higher contrast in vivo tumor imaging was achieved using the ternary Pdots versus the binary D-A Pdots.