Near-infrared Light-emitting Diodes Research Articles

Estimating Leaf Chlorophyll Content of Buffaloberry Using Normalized Difference Vegetation Index Sensors

Commercial optical chlorophyll meters estimate relative chlorophyll content using the ratio of transmitted red light and near-infrared (NIR) light emitted from a red light-emitting diode (LED) and an NIR LED. Normalized difference vegetation index (NDVI) sensors have red and NIR light detectors and may be used to estimate chlorophyll content by detecting the transmitted red and NIR light through leaves. In this study, leaf chlorophyll content of ‘Torrey’ buffaloberry (Shepherdia ×utahensis) plants treated with 0 mm [zero nitrogen (N)], 2 mm (medium N), or 4 mm (ample N) ammonium nitrate for 3 weeks were evaluated using two commercial chlorophyll meters and NDVI sensors. The absolute chlorophyll content was determined using chlorophyll extraction. Our results showed that plants receiving ample N and medium N had decreased transmitted red light (i.e., greater absorption in red light). Measurements of optical chlorophyll meters, NDVI sensors, and chlorophyll extraction similarly showed that plants receiving medium N and ample N had greater leaf chlorophyll content than those receiving zero N. Relative leaf chlorophyll content estimated using NDVI sensors correlated positively with those from the chlorophyll meters (P < 0.0001; r2 range, 0.56–0.82). Therefore, our results indicate that NDVI measurements are sensitive to leaf chlorophyll content. These NDVI sensors, or specialized sensors developed using similar principles, can be used to estimate the relative chlorophyll content of nursery crops and help growers adjust fertilization to improve plant growth and nutrient status.

Facile Synthesis of Unimodal Polymethacrylates with Narrow Dispersity via NIR LED Light-Controlled Bromine-Iodine Transformation Reversible-Deactivation Radical Polymerization.

A facile and clean strategy for synthesizing unimodal polymethacrylates with narrow dispersity (Đ <1.10) is successfully developed by a near-infrared (NIR) light-emitting diode (LED) light (λmax = 740nm)-controlled in situ bromine-iodine transformation reversible-deactivation radical polymerization system without the use of NIR dyes and expensive catalysts. In this system, alkyl iodide ethyl α-iodophenylacetate (EIPA) initiator is generated in situ by the nucleophilic substitution reaction between an alkyl bromide compound ethyl α-bromophenylacetate and sodium iodide (NaI). At the same time, excessive NaI is also acted as a highly active catalyst by forming halogen bonds with terminal iodine of the polymer chains in this system to make it capable of precisely synthesizing polymethacrylates with narrow dispersities (Đ = 1.03-1.10). In addition, the strong penetration ability of NIR LED light is illustrated by the successful polymerization even through 11 pieces of A4 paper.

Development of a Smartphone-Based Optical Device to Measure Hemoglobin Concentration Changes for Remote Monitoring of Wounds.

Telemedicine (TM) can revolutionize the impact of diabetic wound care management, along with tools for remote patient monitoring (RPM). There are no low-cost mobile RPM devices for TM technology to provide comprehensive (visual and physiological) clinical assessments. Here, a novel low-cost smartphone-based optical imaging device has been developed to provide physiological measurements of tissues in terms of hemoglobin concentration maps. The device (SmartPhone Oxygenation Tool—SPOT) constitutes an add-on optical module, a smartphone, and a custom app to automate data acquisition while syncing a multi-wavelength near-infrared light-emitting diode (LED) light source (690, 810, 830 nm). The optimal imaging conditions of the SPOT device were determined from signal-to-noise maps. A standard vascular occlusion test was performed in three control subjects to observe changes in hemoglobin concentration maps between rest, occlusion, and release time points on the dorsal of the hand. Hemoglobin concentration maps were compared with and without applying an image de-noising algorithm, single value decomposition. Statistical analysis demonstrated that the hemoglobin concentrations changed significantly across the three-time stamps. Ongoing efforts are in imaging diabetic foot ulcers using the SPOT device to assess its potential as a smart health device for physiological monitoring of wounds remotely.

Two-dimensional perovskites with alternating cations in the interlayer space for stable light-emitting diodes.

Lead halide perovskites have attracted tremendous attention in photovoltaics due to their impressive optoelectronic properties. However, the poor stability of perovskite-based devices remains a bottleneck for further commercial development. Two-dimensional perovskites have great potential in optoelectronic devices, as they are much more stable than their three-dimensional counterparts and rapidly catching up in performance. Herein, we demonstrate high-quality two-dimensional novel perovskite thin films with alternating cations in the interlayer space. This innovative perovskite provides highly stable semiconductor thin films for efficient near-infrared light-emitting diodes (LEDs). Highly efficient LEDs with tunable emission wavelengths from 680 to 770nm along with excellent operational stability are demonstrated by varying the thickness of the interlayer spacer cation. Furthermore, the best-performing device exhibits an external quantum efficiency of 3.4% at a high current density (J)of 249mA/cm2 and remains above 2.5% for a J up to 720mAcm-2, leading to a high radiance of 77.5W/Srm2 when driven at 6V. The same device also shows impressive operational stability, retaining almost 80% of its initial performance after operating at 20mA/cm2 for 350min. This work provides fundamental evidence that this novel alternating interlayer cation 2D perovskite can be a promising and stable photonic emitter.

Low Roll-Off and High Stable Electroluminescence in Three-Dimensional FAPbI3 Perovskites with Bifunctional-Molecule Additives

Three-dimensional (3D) perovskites have been demonstrated as an effective strategy to achieve efficient light-emitting diodes (LEDs) at high brightness. However, most 3D perovskite LEDs still suffer from serious efficiency roll-off. Here, using FAPbI3 as a model system, we find that the main reason for efficiency droop and degradation in 3D perovskite LEDs is defects and the ion migration under electrical stress. By introducing bifunctional-molecule 3-chlorobenzylamine additive into the perovskite precursor solution, the detrimental effects can be significantly suppressed through the growth of high crystalline perovskites and defect passivation. This approach leads to bright near-infrared perovskite LEDs with a peak external quantum efficiency of 16.6%, which sustains 80% of its peak value at a high current density of 460 mA cm-2, corresponding to a high brightness of 300 W sr-1 m-2. Moreover, the device exhibits a record half-lifetime of 49 h under a constant current density of 100 mA cm-2.

Noninvasive Hemoglobin Level Prediction in a Mobile Phone Environment: State of the Art Review and Recommendations.

BackgroundThere is worldwide demand for an affordable hemoglobin measurement solution, which is a particularly urgent need in developing countries. The smartphone, which is the most penetrated device in both rich and resource-constrained areas, would be a suitable choice to build this solution. Consideration of a smartphone-based hemoglobin measurement tool is compelling because of the possibilities for an affordable, portable, and reliable point-of-care tool by leveraging the camera capacity, computing power, and lighting sources of the smartphone. However, several smartphone-based hemoglobin measurement techniques have encountered significant challenges with respect to data collection methods, sensor selection, signal analysis processes, and machine-learning algorithms. Therefore, a comprehensive analysis of invasive, minimally invasive, and noninvasive methods is required to recommend a hemoglobin measurement process using a smartphone device.ObjectiveIn this study, we analyzed existing invasive, minimally invasive, and noninvasive approaches for blood hemoglobin level measurement with the goal of recommending data collection techniques, signal extraction processes, feature calculation strategies, theoretical foundation, and machine-learning algorithms for developing a noninvasive hemoglobin level estimation point-of-care tool using a smartphone.MethodsWe explored research papers related to invasive, minimally invasive, and noninvasive hemoglobin level measurement processes. We investigated the challenges and opportunities of each technique. We compared the variation in data collection sites, biosignal processing techniques, theoretical foundations, photoplethysmogram (PPG) signal and features extraction process, machine-learning algorithms, and prediction models to calculate hemoglobin levels. This analysis was then used to recommend realistic approaches to build a smartphone-based point-of-care tool for hemoglobin measurement in a noninvasive manner.ResultsThe fingertip area is one of the best data collection sites from the body, followed by the lower eye conjunctival area. Near-infrared (NIR) light-emitting diode (LED) light with wavelengths of 850 nm, 940 nm, and 1070 nm were identified as potential light sources to receive a hemoglobin response from living tissue. PPG signals from fingertip videos, captured under various light sources, can provide critical physiological clues. The features of PPG signals captured under 1070 nm and 850 nm NIR LED are considered to be the best signal combinations following a dual-wavelength theoretical foundation. For error metrics presentation, we recommend the mean absolute percentage error, mean squared error, correlation coefficient, and Bland-Altman plot.ConclusionsWe addressed the challenges of developing an affordable, portable, and reliable point-of-care tool for hemoglobin measurement using a smartphone. Leveraging the smartphone’s camera capacity, computing power, and lighting sources, we define specific recommendations for practical point-of-care solution development. We further provide recommendations to resolve several long-standing research questions, including how to capture a signal using a smartphone camera, select the best body site for signal collection, and overcome noise issues in the smartphone-captured signal. We also describe the process of extracting a signal’s features after capturing the signal based on fundamental theory. The list of machine-learning algorithms provided will be useful for processing PPG features. These recommendations should be valuable for future investigators seeking to build a reliable and affordable hemoglobin prediction model using a smartphone.

Non-Invasive Measurement of Glucose Concentration Using Red and Near-Infrared Light-Emitting Diodes

Many diabetic mellitus patients envision a non-invasive method of blood glucose measurement since they require periodic monitoring of their blood glucose levels to ensure that it is stable and within the normal range. In this study, we detected glucose concentration using commercial light emitting diodes (LEDs) with a wavelength of 700–1600 nm. Light of long wavelengths (e.g. NIR) infiltrate human skin and reach the blood vessel lining, thereby aiding in the non-invasive measurement of blood glucose concentration. To demonstrate this, the concentration of glucose solutions was measured using red and NIR-LEDs in a non-invasive manner. The sensitivity of glucose detection was greater when light of wavelength below 1000 nm was used, owing to the absorption of wavelengths above 1000 nm by water. Furthermore, we controlled the input current of the red and NIR-LEDs to confirm the light intensity deviation with increasing glucose concentrations and suggested the optimum wavelength of light using this in-vitro system. Among various LEDs, the 700 nm LED showed higher light intensity deviation with change in injection current compared to LEDs with the other wavelengths. In particular, compared to other LEDs, a stark difference was observed in the light intensity of the 700 nm LED while measuring glucose concentrations in the range of 50–100 mg/dl.

A highly efficient and thermally stable broadband Cr3+-activated double borate phosphor for near-infrared light-emitting diodes

GdAl3(BO3)4:Cr3+is used to fabricate a NIR-pc-LED that shows promise for plant lighting and applications in the nondestructive analysis of agricultural products.

Real-Time Optical Monitoring of Endotracheal Tube Displacement.

Proper ventilation of a patient with an endotracheal tube (ETT) requires proper placement of the ETT. We present a sensitive, noninvasive, operator-free, and cost-effective optical sensor, called Opt-ETT, for the real-time assessment of ETT placement and alerting of the clinical care team should the ETT become displaced. The Opt-ETT uses a side-firing optical fiber, a near-infrared light-emitting diode, two photodetectors with an integrated amplifier, an Arduino board, and a computer loaded with a custom LabVIEW program to monitor the position of the endotracheal tube inside the windpipe. The Opt-ETT generates a visual and audible warning if the tube moves over a distance set by the operator. Displacement prediction is made using a second-order polynomial fit to the voltages measured from each detector. The system is tested on ex vivo porcine tissues, and the accuracy is determined to be better than 1.0 mm. In vivo experiments with a pig are conducted to test the performance and usability of the system.

Parameterization of the Dielectric Function of GaAsSb Alloy Films

The GaAsxSb1−x; alloys are particularly promising materials for near-infrared light-emitting diode and detector devices. The optical properties, such as the dielectric function, complex refractive index, and absorption coefficient, are needed to properly design and understand semiconductor devices. Here, we report a method to obtain the optical properties of GaAsxSb1−x for the energy range from 1.5 to 6 eV and for an As composition from 0 to 1 at arbitrary wavelengths and compositions. The parameterization of the dielectric function of GaAsxSb1−x for specific compositions at x = 0, 0.183, 0.397, 0.528, 0.8, and 1 were realized by using the dielectric function parametric model.

Multi-Site Cation Control of Ultra-Broadband Near-Infrared Phosphors for Application in Light-Emitting Diodes.

Near-infrared (NIR) phosphors are fascinating materials that have numerous applications in diverse fields. In this study, a series of La3Ga5GeO14:Cr3+ phosphors, which was incorporated with Sn4+, Ba2+, and Sc3+, was successfully synthesized using solid-state reaction to explore every cationic site comprehensively. The crystal structures were well resolved by combining synchrotron X-ray diffraction and neutron powder diffraction through joint Rietveld refinements. The trapping of free electrons induced by charge unbalances and lattice vacancies changes the magnetic properties, which was well explained by a Dyson curve in electron paramagnetic resonance. Temperature and pressure-dependent photoluminescence spectra reveal various luminescent properties between strong and weak fields in different dopant centers. The phosphor-converted NIR light-emitting diode (pc-NIR LED) package demonstrates a superior broadband emission that covers the near-infrared (NIR) region of 650-1050 nm. This study can provide researchers with new insight into the control mechanism of multiple-cation-site phosphors and reveal a potential phosphor candidate for practical NIR LED application.

Synthesis of highly transparent titanium-indium-tin oxide conductive film at low temperatures for application in near-infrared devices

In this study, we investigated the development of titanium-indium-tin oxide (TITO) film for low-temperature near-infrared light-emitting diodes (NIR-LEDs) and studied their transmittance and conductivity characteristics. To fabricate the TITO structure, a 2 nm-thick titanium barrier, which exhibits high transparency in the visible-light region, was inserted between the ITO film and the top layer of the LED structure. The inclusion of Ti activated crystallization in the ITO films and improved their optical characteristics. Spectrometric analysis indicated outstanding transparency (nearly 93%) for 300 nm- and 450 nm-thick TITO films annealed at 550 °C in the NIR range (>700 nm). Furthermore, IR-LEDs with TITO films exhibited a 150% higher light output power than IR-LEDs with conventional ITO films. Therefore, we posit that using titanium as an activation barrier delivers effective crystalline ITO films for application in NIR devices.

Content-Aware Eye Tracking for Autostereoscopic 3D Display.

This study develops an eye tracking method for autostereoscopic three-dimensional (3D) display systems for use in various environments. The eye tracking-based autostereoscopic 3D display provides low crosstalk and high-resolution 3D image experience seamlessly without 3D eyeglasses by overcoming the viewing position restriction. However, accurate and fast eye position detection and tracking are still challenging, owing to the various light conditions, camera control, thick eyeglasses, eyeglass sunlight reflection, and limited system resources. This study presents a robust, automated algorithm and relevant systems for accurate and fast detection and tracking of eye pupil centers in 3D with a single visual camera and near-infrared (NIR) light emitting diodes (LEDs). Our proposed eye tracker consists of eye–nose detection, eye–nose shape keypoint alignment, a tracker checker, and tracking with NIR LED on/off control. Eye–nose detection generates facial subregion boxes, including the eyes and nose, which utilize an Error-Based Learning (EBL) method for the selection of the best learnt database (DB). After detection, the eye–nose shape alignment is processed by the Supervised Descent Method (SDM) with Scale-invariant Feature Transform (SIFT). The aligner is content-aware in the sense that corresponding designated aligners are applied based on image content classification, such as the various light conditions and wearing eyeglasses. The conducted experiments on real image DBs yield promising eye detection and tracking outcomes, even in the presence of challenging conditions.

Abnormal Bi3+-Activated NIR Emission in Highly Symmetric XAl12O19 (X = Ba, Sr, Ca) by Selective Sites Occupation

Near-infrared light-emitting diodes (NIR-LEDs) have been a potential candidate in food composition analysis, tempera-ture and security monitoring, biometrics, and medical applications. To realize t...

Rearranging Low-Dimensional Phase Distribution of Quasi-2D Perovskites for Efficient Sky-Blue Perovskite Light-Emitting Diodes.

Metal halide perovskites have received much attention for their application in light-emitting diodes (LEDs) in the past several years. Rapid progress has been made in efficient green, red, and near-infrared perovskite LEDs. However, the development of blue perovskite LEDs is still lagging far behind. Here, we report efficient sky-blue perovskite LEDs by rearranging low-dimensional phase distribution in quasi-2D perovskites. We incorporated sodium ions into the mixed-Cl/Br quasi-2D perovskites with phenylethylammonium as the organic spacer and cesium lead halide as the inorganic framework. The inclusion of the sodium ion was found to significantly reduce the formation of the n = 1 phase, which was dominated by nonradiative transition, and increase the formation of other small-n phases for efficient exciton energy transfer. By managing the phase distribution, a maximum external quantum efficiency (EQE) of 11.7% was achieved in the sky-blue perovskite LED, with a stable emission peak at 488 nm. Further optimizing the phase distribution and film morphology with Pb content, we demonstrated the sky-blue devices with the average EQE approaching 10%. This strategy of engineering phase distribution of quasi-2D perovskites with a sodium ion could provide a useful way for the fabrication of high-performance blue perovskite LEDs.

Near-infrared NIR irradiation and sodium hypochlorite: An efficacious association to counteract the Enterococcus faecalis biofilm in endodontic infections

New strategies are necessary for the prevention of endodontic infections caused by Enterococcus faecalis, a common resistant pathogen and biofilm producer. Aim of the present study was to compare the effects of Near-Infrared (NIR) Light-Emitting Diode (LED) irradiation and different concentrations of sodium hypochlorite (NaOCl) alone or combined to each other on the E. faecalis biofilm, on artificial and human dentin surfaces.E. faecalis ATCC 29212 preformed biofilms, on polystyrene wells and on dentin discs, were treated with 880 nm NIR irradiation and NaOCl at 4%, 2.5%, 1% and 0.5% alone and combined to each other (NIR irradiation plus NaOCl 1% or 0.5%) at 5 and 10 min. Treated biofilms were compared to the controls for (i) biofilm biomass evaluation, (ii) CFU count for the quantification of cultivable cells and (iii) cells viability.All the detected experimental conditions displayed a significant reduction of biofilm biomass (p < 0.001) and CFUs/mL (p < 0.01) in respect to the controls on both tested surfaces. The effects on the E. faecalis biomass, colony count and cell viability were not time-dependent except for NaOCl 2.5% and 1% in the biofilm biomass reductions on human dentin discs. NIR-LED irradiation alone showed a reduction of E. faecalis aggregates without interfering with cell viability whereas NaOCl alone expressed a killing effect in a concentration dependent way. The combination of NIR-LED irradiation with NaOCl 1% and 0.5% displayed a double effect of cluster disaggregation and cell killing.In particular, NIR-LED irradiation combined with NaOCl 0.5% displayed an anti-biofilm activity major than those expressed by NaOCl 0.5% alone (p = 0.001) with a reduction of biomass 93% vs 71% and 97% vs 25% after 10 min, on polystyrene wells and human dentin discs, respectively.The innovative use of NIR-LED irradiation combined at short times with low concentration of NaOCl (1% and 0.5%) is capable to reach a significant effect on E. faecalis biofilm, especially on human dentin discs.

Power density dependent upconversion properties of NaYbF4: Er3+@NaYbF4: Tm3+@NaYF4 nanoparticles and their application in white-light emission LED

White light sources play a vital role in our daily lives, which were usually generated by optimizing the proportions of individual emitters with different colors. Benefiting from the abundant energy levels of rare earth ions (Re3+), Re3+ doped upconversion nanoparticles (UCNPs) with multicolor luminescence output in one fixed structure have attracted broad attention. Here, we constructed a NaYbF4: Er3+@NaYbF4: Tm3+@NaYF4 core-shell-shell structure with Er3+ and Tm3+ in different layers to avoid the cross-relaxation. In the structure, red and green emissions were originated from Er3+, and blue emission was generated by Tm3+ through the upconversion process. The simultaneous red, green and blue emissions in the designed structure made it possible to realize white light emission. More importantly, the NaYbF4 host leads to three photons upconversion pathway and result in tunable color output under moderate varying power density. The results showed that warm white color was achieved at the excitation power of 20.9 W/cm2, meanwhile, tunable output colors were also realized by changing the external excited power density. Finally, the high luminescence intensity of NaYbF4: Er3+@NaYbF4: Tm3+@NaYF4 makes it possible to be excited by a near infrared-light emitting diode (NIR-LED), and a white emission LED was prepared by encapsulating the prepared UCNPs on a NIR chip.

Design and control of the luminescence in Cr3+-doped NIR phosphors via crystal field engineering

Near-infrared (NIR) light-emitting diodes (LEDs) have currently attracted increasing attention owing to high efficiency and longevity. Accordingly, NIR phosphor, as the indispensable role in NIR LEDs, needs to be enriched to meet widespread applications worldwide. Benefitting from structural tunability of LaSc3B4O12(LSB), a sequence of broadband phosphors, with continuous-tunable luminescence toward longer wavelength, can be designed by regulating the crystal field environment of the Cr3+ via substituting the Sc3+ by Y3+ in LSB host. The correlations among structural evolution, crystal field environment, and luminescence properties of LaSc3-xYxB4O12(LSYB): Cr3+ (0 ≤ x ≤ 1.3) have been discussed in detail. Furthermore, substitution Y3+ for Sc3+ in LSB causes band gap variation of host lattice, demonstrated by the diffuse reflectance spectra, consequently resulting in improved quantum yield (QY), and mitigated thermal quenching behavior of LSYB: Cr3+ compared to that of Y3+-free sample. The above results demonstrate the superiority of crystal field engineering in exploring broadband NIR phosphors with modified luminescence performance for potential application in NIR pc-LEDs.

Low cost blood vein detection system based on near-infrared LEDs and image-processing techniques

Abstract Drawing blood and injecting drugs are common medical procedures, for which accurate identification of veins is needed to avoid causing unnecessary pain. In this paper, we propose a low-cost system for the detection of veins. The system emits near-infrared radiation from four light-emitting diodes (LEDs), with a charge-coupled device (CCD) camera located in the middle of the LEDs. The camera captures an image of the palm of the hand. A series of digital image-processing techniques, ranging from image enhancement and increased contrast to isolation using a threshold limit based on statistical properties, are applied to effectively isolate the veins from the rest of the image.

Highly Efficient Near-Infrared Light-Emitting Diodes Based on Chloride Treated CdTe/CdSe Type-II Quantum Dots.

Quantum dot light-emitting diodes (QLEDs) have been considered as the most promising candidate of light sources for the new generation display and solid-state lighting applications. Especially, the performance of visible QLEDs based on II-VI quantum dots (QDs) has satisfied the requirements of the above applications. However, the optoelectronic properties of the corresponding near-infrared (NIR) QLEDs still lag far behind the visible ones. Here, we demonstrated the highly efficient NIR QLEDs based on chloride treated CdTe/CdSe type-II QDs. The maximum radiant emittance and peak external quantum efficiency (EQE) increased by 24.5 and 26.3%, up to 66 mW/cm2 and 7.2% for the corresponding devices based on the chloride treated CdTe/CdSe QDs with the PL peak located at 788 nm, respectively, compared with those of devices before chloride treatment. Remarkably, the EQE of > 5% can be sustained at the current density of 0.3–250 mA/cm2 after the chloride treatment. Compared with NIR LEDs based on transition metal complex, the efficiency roll-off has been suppressed to some extent for chloride treated CdTe/CdSe based NIR QLEDs. Based on the optimized conditions, the peak EQE of 7.4, 5.0, and 1.8% can be obtained for other devices based on chloride treated CdTe/CdSe with PL peak of 744, 852, and 910 nm, respectively. This improved performance can be mainly attributed to the chloride surface ligand that not only increases the carrier mobility and reduces the carrier accumulation, but also increases the probability of electron-hole radiative efficiency within QD layers.