Shortwave-Infrared Silver Chalcogenide Quantum Dots for Optoelectronic Devices.

Silver chalcogenide (Ag2X, X = S, Se, Te) semiconductor quantum dots (QDs) have been extensively studied owing to their short-wave infrared (SWIR, 900-2500 nm) excitation and emission along with lower solubility product constant and environmentally benign nature. However, their unsatisfactory photoluminescence quantum yields (PLQYs) make it difficult to obtain optoelectronic devices with high performances. To tackle this challenge, researchers have made great efforts to develop valid strategies to improve the PLQYs of SWIR Ag2X QDs by suppressing their nonradiative recombination of excitons. In this Perspective, we summarize the significant approaches of heteroatom doping and surface passivation to enhance the PLQYs of SWIR Ag2X QDs, and we conclude their application in high-efficiency optoelectronic devices. Finally, we examine the future trends and promising opportunities of Ag2X QDs with regard to their optical properties and optoelectronics. We believe that this Perspective will serve as a valuable reference for future advancement in the synthesis and application of SWIR Ag2X QDs.

In vitro early proximal caries detection using trilateral short-wave infrared reflection at 1050 and 1550 nm.

OBJECTIVES: This in vitro study evaluated the diagnostic potential of short-wave infrared reflection (SWIRR) at 1050 and 1550 nm for proximal caries detection from the occlusal, buccal and lingual surfaces of posterior teeth under clinically relevant conditions. Bitewing radiography (BWR) was the alternative index test and micro-computed tomography (µCT) the reference standard. METHODS: 250 proximal surfaces of extracted human teeth were examined using SWIRR at 1050 and 1550 nm and BWR. SWIRR, BWR and µCT findings were evaluated twice by two trained examiners. SWIRR images were evaluated from occlusal and trilateral (occlusal, buccal and lingual combined) views. Sensitivity, specificity and AUC were calculated. Reliability assessment was performed using κ statistics. RESULTS: SWIRR (1050 nm) showed sensitivity of 0.44 for occlusal and 0.55 for trilateral assessment, paired with specificity of 0.96 and 0.90, whereas SWIRR (1550 nm) showed sensitivity of 0.73 and 0.85 paired with specificity of 0.76 and 0.59. Compared to occlusal view, trilateral SWIRR view revealed ≈10% higher sensitivity and lower specificity. BWR revealed lowest sensitivity (0.30) and highest specificity (0.99). Over-and underestimation of caries demonstrated opposite trends: from 1050-1550 nm, overestimation of trilateral SWIRR increased (0.08-0.29), while underestimation decreased (0.15-0.06). CONCLUSION: Trilateral SWIRR has higher sensitivity and lower specificity for proximal caries, than occlusal SWIRR. 1050 nm are more suitable for trilateral SWIRR and 1550 nm for occlusal examinations. A combination of SWIRR at 1050 and 1550 nm may exhibit a balanced sensitivity and specificity for proximal caries.

Innovative strategies for protein content determination in dried laver (Porphyra spp.): Evaluation of preprocessing methods and machine learning algorithms through short-wave infrared imaging.

In this study, we explored the application of Short-Wave Infrared (SWIR) hyperspectral imaging combined with Competitive Adaptive Reweighted Sampling (CARS) and advanced regression models for the non-destructive assessment of protein content in dried laver. Utilizing a spectral range of 900-1700 nm, we aimed to refine the quality control process by selecting informative wavelengths through CARS and applying various preprocessing techniques (standard normal variate [SNV], Savitzky-Golay filtering [SG], Orthogonal Signal Correction [OSC], and StandardScaler [SS]) to enhance the model's accuracy. The SNV-OSC-StandardScaler- Support vector regression (SVR) model trained on CARS-selected wavelengths significantly outperformed the other configurations, achieving a prediction determination coefficient (Rp2) of 0.9673, root mean square error of prediction of 0.4043, and residual predictive deviation of 5.533. These results highlight SWIR hyperspectral imaging's potential as a rapid and precise tool for assessing dried laver quality, aiding food industry quality control and dried laver market growth.

Novel multi-spectral short-wave infrared imaging for assessment of human burn wound depth.

Burn depth determination is critical for patient care but is currently lacking accuracy. Recent animal studies showed that Short Wave Infrared (SWIR) imaging can distinguish between superficial and deep burns. This is a first human study correlating reflectance of multiple SWIR bands using a SWIR assessment tool (SWAT) with burn depth classifications by surgeons and histology. Burns and adjacent normal skin in 11 patients with thermal injuries were imaged with visual and narrow bands centred at 1200, 1650, 1940 and 2250 nm and biopsies were taken from select areas. Reflectance intensities for each band in 273 regions of interest (ROI) were divided by the normal skin reflectance and combined into three Reflectance Indices (RIs). In addition, burns in ROIs and biopsies were classified by five surgeons and three pathologists, respectively, as superficial partial, deep partial, or full thickness. Results show that for burn depth increase classified by the surgeons, reflectance increased at 1200 and 2250, decreased at 1940, and didn't change at 1650 nm. In contrast, all three RIs increase with burn depth and predict the deep and full depths ROIs representing operable regions (Area Under Curve >0.6507, p < 0.0001). Pathologists' classification matched surgeons' classification of burn category only in eight of 21 biopsies (38.1%), but reflectance at all bands and one RI for all deep partial and full thickness biopsies were larger than in non-biopsy normal and superficial partial thickness ROIs (p < 0.0118). In conclusion, multi-spectral imaging with a new SWAT is a promising approach for evaluation of burn wound depth.

A direct comparison of a next generation hyperspectral camera to state-of-the-art.

Hyperspectral camera technology is advancing rapidly, and this paper seeks to compare a state-of-the-art industrial dual-camera setup to a single-camera system employing the latest chip technology (IMX990 from Sony). The hyperspectral cameras are compared over both the Visual and Short-Wave Infrared range (400-1700 nm) of the electromagnet spectrum. The spectral range and resolution, as well as spatial parameters and spectroscopic information are quantified with comparable optics, electronics, and test targets. Generally, enhanced spectral detail and reduced noise were observed for the single-camera compared to its peers. Thus, the IMX990 shows promising performance for the new generation of hyperspectral cameras directly relevant to industrial applications, such as detection, documentation, and sorting.

Synergic Surface Modifications of PbS Quantum Dots by Sodium Acetate in Solid-State Ligand Exchange toward Short-Wave Infrared Photodetectors.

PbS quantum dots (QDs) are promising for short-wave infrared (SWIR) photodetection and imaging. Solid-state ligand exchange (SSLE) is a low-fabrication-threshold QD solid fabrication method. However, QD treatment by SSLE remains challenging in seeking refined surface passivation to achieve the desired device performance. This work investigates using NaAc in the ligand exchange process to enhance the film morphology and electronic coupling configuration of QD solids. By implementing various film and photodetector device characterization studies, we confirm that adding NaAc with a prominent adding ratio of 20 wt % NaAc with tetrabutylammonium iodide (TBAI) in the SSLE leads to an improved film morphology, reduced surface roughness, and decreased trap states in the QD solid films. Moreover, compared to the devices without NaAc treatment, those fabricated with NaAc-treated QD solids exhibit an enhanced performance, including lower dark current density (<100 nA/cm2), faster response speed, higher responsivity, detectivity, and external quantum efficiency (EQE reaching 25%). The discoveries can be insightful in developing efficient, low-cost, and low-fabrication-threshold QD SWIR detection and imager applications.

Water rotational relaxation time measurement by shortwave infrared micro spectroscopy(SWIR) at sub-zero temperatures.

The shortwave infrared spectroscopy (SWIR) is the noble method which allows to evaluate the rotational relaxation time of water (RRTW) in a sample. Because SWIR requires the reference sample of pure water, the measurement temperature is limited only at above 0 °C. In this study, we expanded this temperature limitation of SWIR by using alternative reference solutions with freezing points below 0 °C, including sugar and glycerol solutions. The results showed that some reference sample solutions are useable for evaluating RRTW in samples below 0 °C. It was found that RRTW in solution measured by newly proposed SWIR agrees with RRTW measured by dielectric spectroscopy in 10% accuracy when it is shorter than 100psec.

Short-Wave Infrared Light-Emitting Diodes Using Colloidal CuInS2 Quantum Dots with ZnI2 Dual-Passivation.

Short-wave infrared (SWIR) light-emitting diodes (LEDs) have emerged as promising technologies for diverse applications such as optical communication, biomedical imaging, surveillance, and machine vision. Colloidal quantum dots (QDs) are particularly attractive for SWIR LEDs due to their solution processability, compatibility with flexible substrates, and tunable absorption and luminescence. However, the presence of toxic elements or precious metals in most SWIR-emitting QDs poses health, environmental, and cost challenges. In this context, CuInS2 (CIS) QDs are known for low toxicity, cost-effective fabrication, and SWIR-light emitting capability. However, CIS QDs have not yet been directly utilized to fabricate SWIR LEDs to date, which is due to low particle stability, inefficient charge carrier recombination, and significantly blue-shifted luminescence after integrating into LED devices. To address challenges, we propose a dual-passivation strategy using ZnI2 as a chemical additive to enhance both the optical property of plain CIS QDs and charge carrier recombination upon LED device implementation. The resulting CIS-QD-based LEDs exhibit a stable SWIR electroluminescence (EL) peak (over 1000 nm) with a high EL radiance and a record external quantum efficiency in the SWIR region. Our study represents a significant step forward in SWIR-QLED technology, offering a pathway for the development of high-performance, low-cost, and nontoxic SWIR light sources.

Realize short-wave infrared luminescence in NaScP2O7:Cr3+,Yb3+ phosphor: Spectral and energy transfer.

Short-wave infrared emitting phosphors have extensive applications for spectroscopy technology. The near-infrared phosphor NaScP2O7:Cr3+ that we present in this work has a full width at half maximum (FWHM) of approximately 196 nm, which ranges from 700 to 1200 nm. To achieve efficient short-wave infrared, Yb3+ ions were co-doped. The NaScP2O7:Cr3+,Yb3+ material emitted infrared bands with peaks at 970 and 1003 nm upon excitation at450 nm. Benefitting from energy transfer (ET), the light in the 900-1200 nm from Yb3+ is effectively enhanced. Photoluminescence spectra, thermal quenching, and decay curves of Cr3+/Yb3+ single and codoped NaScP2O7 were investigated. An internal quantum yield of 29.6 % wasdemonstrated by the optimized phosphor NaScP2O7:Cr3+,Yb3+. Furthermore, The final fabrication of the short-wave infrared pc-LED was done through the combination of a blue-emitting chip and NaScP2O7:Cr3+,Yb3+ phosphor, thereby showing great promise for real implementations.

Performance Estimation of a Medium-Resolution Earth Observation Sensor Using Nanosatellite Replica.

In many areas of engineering, the design of a new system usually involves estimating performance-related parameters from early stages of the project to determine whether a given solution will be compliant with the defined requirements. This aspect is particularly relevant during the design of satellite payloads, where the target environment is not easily accessible in most cases. In the context of Earth observation sensors, this problem has been typically solved with the help of a set of complex pseudo-empirical models and/or expensive laboratory equipment. This paper describes a more practical approach: the illumination conditions measured by an in-orbit payload are recreated on ground with the help of a replica of the same payload so the performance of another Earth observation sensor in development can be evaluated. The proposed method is specially relevant in the context of small satellites, as the possibility of having extra units devoted to these tasks becomes greater as costs are reduced. The results obtained using this method in an actual space mission are presented in this paper, giving valuable information that will help in further stages of the project.

Short-Wave Infrared Colloidal QD Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers.

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, nanosecond-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, record 4 ns response time in PbS-based QDPDs that operate at SWIR wavelengths is reported, a result reaching the requirement of SWIR light detection and ranging based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330 nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers. Based on these results, it is estimated that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-nanosecond response time.

Needlestick-Stimulation-Induced Conversion of Short-Wave Infrared-Light Transparency Using a Liquescent Radical Anion.

A liquescent salt consisting of a 7,7,8,8-tetracyanquinodimethane (TCNQ) radical anion and a tetra-n-decylammonium ion, 1+•TCNQ•-, exhibits rapid changes in the short-wave infrared (SWIR) light transparency at 1000-1400 nm upon the application of a one-shot needlestick-stimulus. Radical anion salt 1+•TCNQ•- transforms from a blue solid to a green liquid at 90 °C without decomposition under aerated conditions, and remains in the liquid state upon cooling to 70 °C. After applying pressure with a needlestick on a cover glass at 70 °C, the liquid transforms rapidly into the solid state over a timescale of seconds across a centimeter scale of area. Along with the liquid-solid transition, the SWIR-light transparency at 1200 nm completely switches from the "on" to the "off" states. Experimental results, such as electronic spectra and crystal structure analysis, indicates that the SWIR-light absorption in the solid state is due to the existence of a slipped-stacking π-dimer structure for TCNQ•-. The rapid rearrangement is induced by the formation of the π-dimer structures from the monomers of TCNQ•- and the subsequent generations of the solid-state seed.

InSb/InP Core-Shell Colloidal Quantum Dots for Sensitive and Fast Short-Wave Infrared Photodetectors.

Colloidal quantum dot (CQD) technology is considered the main contender toward a low-cost high-performance optoelectronic technology platform for applications in the short-wave infrared (SWIR) to enable 3D imaging, LIDAR night vision, etc. in the consumer electronics and automotive markets. In order to unleash the full potential of this technology, there is a need for a material that is environmentally friendly, thus RoHS compliant, and possesses adequate optoelectronic properties to deliver high-performance devices. InSb CQDs hold great potential in view of their RoHS-compliant nature and─in principle─facile access to the SWIR. However, to date progress in realizing high-performance optoelectronic devices, including photodetectors (PDs), has been limited. Here, we have developed a synthesis method for producing size-tunable InSb CQDs with distinct excitonic peaks spanning a wide range from 900 to 1750 nm. To passivate the surface defects and enhance the photoluminescence (PL) efficiency of InSb CQDs, we further designed an InSb/InP core-shell structure. By employing the InSb/InP core-shell CQDs in a photodiode device stack, we report on robust InSb CQD SWIR photodetectors that exhibit an external quantum efficiency (EQE) of 25% at 1240 nm, a wide linear dynamic range exceeding 128 dB, a photoresponse time of 70 ns, and a specific detectivity of 4.4 × 1011 jones.

Dicarboxylic Acid-Assisted Surface Oxide Removal and Passivation of Indium Antimonide Colloidal Quantum Dots for Short-Wave Infrared Photodetectors.

Heavy-metal-free III-V colloidal quantum dots (CQDs) are promising materials for solution-processed short-wave infrared (SWIR) photodetectors. Recent progress in the synthesis of indium antimonide (InSb) CQDs with sizes smaller than the Bohr exciton radius enables quantum-size effect tuning of the band gap. However, it has been challenging to achieve uniform InSb CQDs with band gaps below 0.9 eV, as well as to control the surface chemistry of these large-diameter CQDs. This has, to date, limited the development of InSb CQD photodetectors that are sensitive to ≥ ${\ge }$ 1400 nm light. Here we adopt solvent engineering to facilitate a diffusion-limited growth regime, leading to uniform CQDs with a band gap of 0.89 eV. We then develop a CQD surface reconstruction strategy that employs a dicarboxylic acid to selectively remove the native In/Sb oxides, and enables a carboxylate-halide co-passivation with the subsequent halide ligand exchange. We find that this strategy reduces trap density by half compared to controls, and enables electronic coupling among CQDs. Photodetectors made using the tailored CQDs achieve an external quantum efficiency of 25 % at 1400 nm, the highest among III-V CQD photodetectors in this spectral region.

Short-wave Infrared Photoluminescence Lifetime Mapping of Rare-Earth Doped Nanoparticles Using All-Optical Streak Imaging.

The short-wave infrared (SWIR) photoluminescence lifetimes of rare-earth doped nanoparticles (RENPs) have found diverse applications in fundamental and applied research. Despite dazzling progress in the novel design and synthesis of RENPs with attractive optical properties, existing optical systems for SWIR photoluminescence lifetime imaging are still considerably restricted by inefficient photon detection, limited imaging speed, and low sensitivity. To overcome these challenges, SWIR photoluminescence lifetime imaging microscopy using an all-optical streak camera (PLIMASC) is developed. Synergizing scanning optics and a high-sensitivity InGaAs CMOS camera, SWIR-PLIMASC has a 1D imaging speed of up to 138.9 kHz in the spectral range of 900-1700 nm, which quantifies the photoluminescence lifetime of RENPs in a single shot. A 2D photoluminescence lifetime map can be acquired by 1D scanning of the sample. To showcase the power of SWIR-PLIMASC, a series of core-shell RENPs with distinct SWIR photoluminescence lifetimes is synthesized. In particular, using Er3+ -doped RENPs, SWIR-PLIMASC enables multiplexed anti-counterfeiting. Leveraging Ho3+ -doped RENPs as temperature indicators, this system is applied to SWIR photoluminescence lifetime-based thermometry. Opening up a new avenue for efficient SWIR photoluminescence lifetime mapping, this work is envisaged to contribute to advanced materials characterization, information science, and biomedicine.

Temperature-Dependent Modulation of Short-Wave-Infrared Light Transparency Based on Associated Structures of a Liquescent Nickel(III) Complex.

A liquescent bis(malononitriledithiolato)nickel(III) complex with a bis(methoxyethyl)imidazolium cation, 1[Ni(mnt)2 ], exhibits three-stage thermochromic modulation of transparency/absorption in the short-wave-infrared (SWIR) region (1000-2500 nm), driven by associated structural changes. Upon heating, the electronic spectra of 1[Ni(mnt)2 ] in the SWIR region shift to shorter wavelengths accompanying with the solid-liquid phase transition at 76 °C. Further heating to over 109 °C induces a second transition of the electronic spectra, characterized by a blue-shift of the SWIR absorption in the liquid phase. The results of temperature-dependent electronic spectra and magnetic susceptibility indicated that the thermochromic changes can be attributed to the two-step dissociation of the associated structures of [Ni(mnt)2 ]- , occurring during the solid-liquid phase transition and the shift of dimer-monomer equilibrium in the liquid state. These changes can be visualized using an SWIR imaging camera under appropriate SWIR lights.

Colloidal InSb Quantum Dots for 1500 nm SWIR Photodetector with Antioxidation of Surface.

III-V quantum dots (QDs) have emerged as significant alternatives to Cd- and Pb-based QDs, garnering notable attention over the past two decades. However, the understanding of III-V QDs, particularly in the short wave-infrared (SWIR) region, remains limited. InAs QDs are widely recognized as the most prominent SWIR QDs, but their absorption beyond 1400 nm presents various challenges. Consequently, InSb QDs with relatively narrower bandgaps have been investigated; however, research on their device applications is lacking. In this study, InSb QDs are synthesized with absorption ranging from 1000 to 1700 nm by introducing Cl- ions to enhance QD surface stability during synthesis. Additionally, it coated InAs and ZnSe shells onto the InSb QDs to validate photoluminescence in the SWIR region and improve photostability. Subsequently, these QDs are employed in the fabrication of photodetector devices, resulting in photodetection above 1500 nm using Pb-free QDs. The photodetection device exhibited an external quantum efficiency (EQE) of 11.4% at 1370 nm and 6.3% at 1520 nm for InSb core QDs, and 4.6% at 1520 nm for InSb/InAs core/shell QDs, marking the successful implementation of such a device. In detail, the 1520 nm for InSb core device showed a dark current density(JD ) value of: 1.46 × 10-9 A/cm2 , responsivity(R): 0.078 A/W, and specific detectivity based on the shot noise(Dsh *): 3.6 × 1012 Jones at 0 V.

Heavy water coupling gel for short-wave infrared photoacoustic imaging.

Significance: Changes in lipid, water, and collagen (LWC) content in tissue are associated with numerous medical abnormalities (cancer, atherosclerosis, and Alzheimer's disease). Standard imaging modalities are limited in resolution, specificity, and/or penetration for quantifying these changes. Short-wave infrared (SWIR) photoacoustic imaging (PAI) has the potential to overcome these challenges by exploiting the unique optical absorption properties of LWC>1000 nm. Aim: This study's aim is to harness SWIR PAI for mapping LWC changes in tissue. The focus lies in devising a reflection-mode PAI technique that surmounts current limitations related to SWIR light delivery. Approach: To enhance light delivery for reflection-mode SWIR PAI, we designed a deuterium oxide (D2O, "heavy water") gelatin (HWG) interface for opto-acoustic coupling, intended to significantly improve light transmission above 1200 nm. Results: HWG permits light delivery >1 mJ up to 1850 nm, which was not possible with water-based coupling (>1 mJ light delivery up to 1350 nm). PAI using the HWG interface and the Visualsonics Vevo LAZR-X reveals a signal increase up to 24 dB at 1720 nm in lipid-rich regions. Conclusions: By overcoming barriers related to light penetration, the HWG coupling interface enables accurate quantification/monitoring of biomarkers like LWC using reflection-mode PAI. This technological stride offers potential for tracking changes in chronic diseases (in vivo) and evaluating their responses to therapeutic interventions.

One-Pot Colloidal Synthesis Enables Highly Tunable InSb Short-Wave Infrared Quantum Dots Exhibiting Carrier Multiplication.

Colloidal quantum dots (CQDs) are emerging materials for short-wave infrared (SWIR, ≈1100-3000 nm) photodetectors, which are technologically important for a broad array of applications. Unfortunately, the most developed SWIR CQD systems are Pb and Hg chalcogenides; their toxicity and regulated compositions limit their applications. InSb CQD system is a potential environmentally friendly alternative, whose bandgap in theory, is tunable via quantum confinement across the SWIR spectrum. However, InSb CQDs are difficult to exploit, due to their complex syntheses and uncommon reactive precursors, which greatly hinder their application and study. Here, a one-pot synthesis strategy is reported using commercially available precursors to synthesize-under standard colloidal synthesis conditions-high-quality, size-tunable InSb CQDs. With this strategy, the large Bohr exciton radius of InSb can be exploited for tuning the bandgap of the CQDs over a wide range of wavelengths (≈1250-1860 nm) across the SWIR region. Furthermore, by changing the surface ligands of the CQDs from oleic acid (OA) to 1-dodecanthiol (DDT), a ≈20-fold lengthening in the excited-state lifetime, efficient carrier multiplication, and slower carrier annihilation are observed. The work opens a wide range of SWIR applications to a promising class of Pb- and Hg-free CQDs.

Proximal Caries Detection Using Short-Wave Infrared Transillumination at Wavelengths of 1050, 1200 and 1300 nm in Permanent Posterior Human Teeth.

This in vitro study aimed to investigate the diagnostic potential of short-wave infrared transillumination (SWIRT) at 1050, 1200 and 1300 nm for the detection of proximal caries in molars and premolars. It was compared to the diagnostic performance of bitewing radiography (BWR) and micro-computed tomography (µCT) as the reference standard. 250 sound or decayed proximal surfaces of permanent posterior extracted teeth were examined using (1) SWIRT at 1050, 1200 and 1300 nm with two camera systems of different resolutions, (2) BWR and (3) µCT. Thresholds were defined for both test methods and the reference standard for caries in general, enamel caries and dentin caries. All images were assessed by two examiners twice, at an interval of two weeks. SWIRT at wavelengths of 1050, 1200 and 1300 nm achieved sensitivity values more than 2.5 times higher than BWR (enamel caries 3.2-4.4 times; dentin caries 3.25-4.25 times) for the detection of proximal caries. Sensitivity values of SWIRT improved with the higher wavelength. No significant difference was found in diagnostic quality between the two camera systems. SWIRT at 1300 nm imaged proximal enamel caries with the highest accuracy, while the physical optimum for transillumination in dentin was located at a lower wavelength (<1000 nm).