Weak Light Intensity Research Articles

Highly Sensitive InSe Nanosheet Ultraviolet Photodetector Realized Via an Asymmetric Fabry–Pérot Structure

AbstractDue to the wavelength‐dependent absorption, narrow bandgap semiconductors show potential application in ultraviolet (UV) photodetection by thinning. However, the limited absorption in the thinner layer retards their application in high‐performance photodetection. In this paper, the fabrication of an asymmetric Fabry–Pérot (F–P) structure is reported by planar stacking of InSe layer, Al2O3 spacer, and Al back reflector. For the selective absorption enhancement in UV region, the Al2O3 thickness is optimized to be 39 nm by finite element method (FEM). The device presents a peak response at 265 nm illumination, showing the photo‐to‐dark current ratio (Ilight/Idark) of 719. Responsivity (R) and photoconductive gain (G) reach 11.7 A W−1 and 54.7 at the weak light intensity of 0.03 mW cm−2, respectively, which are two orders of magnitude higher than those of the device without the asymmetric F–P structure, revealing the remarkably enhanced absorption. This work shows well compatibility with the manufacturing processes for 2D semiconductor‐based photodetectors and provides a simple and versatile strategy for the application of 2D narrow bandgap semiconductors in high‐performance UV photodetectors.

Enhancing Indoor Photovoltaic Performance of Inverted Type Organic Solar Cell by Controlling Photoactive Layer Solution Concentration

With the development of various low-power indoor electronic devices, indoor photovoltaics, particularly organic solar cells (OSCs) have attracted a lot of interest in recent years. Increasing the light absorption and suppressing the leakage current are pivotal to improve the indoor photovoltaic performance of OSCs. In this study, the carbon quantum dots (CQDs)-incorporated photoactive layer solution concentration was varied to improve the photovoltaic performance under 1-sun and indoor white LED illumination. The photoactive layer was composed of (6,6)-phenyl-C61-butyric acid methyl ester) (PCBM) as the acceptor and poly(3-hexylthiophene) (P3HT) as the donor. The ZnO electron transport layer was deposited on fluorine-doped tin oxide (FTO)-coated glass substrates using a spin coating technique. The photoactive layers with different solution concentrations were spin coated on top of the ZnO layer. For device completion, silver anode was thermally evaporated. It is interesting to find that the optimum solution concentration obtained under white LED illumination is larger than that under 1-sun illumination. The maximum power conversion efficiency (PCE) of 0.95% was obtained under 1-sun illumination for device with the solution concentration of 36 mg/mL, whereas, under white LED illumination, the highest PCE of 3.59% was obtained for the device with solution concentration of 48 mg/mL.The discrepancy is ascribed to the higher light absorption of thicker photoactive layer and less significant charge recombination loss under weak light intensity. This study highlights the importance of using different optimization strategies to improve the photovoltaic performance of OSCs for outdoor and indoor applications.

The Crystal Structure, Band Gap, and Optoelectronic Performance of Lead‐free Cs2PdBr4 Metal Halide Single Crystal and its Thin Film

AbstractPd‐based halide materials play an important role in organic synthesis, catalysis, and optoelectronic areas. As a typical metal halide, Pb‐based perovskite materials have the potential to become a newcomer in the field of photodetectors due to their excellent optoelectronic properties. However, the toxicity of lead has led to its unfriendliness to the environment. Herein, we synthesized the lead‐free Cs2PdBr4 metal halide single crystal (SC). The crystal structure of needle‐like Cs2PdBr4 SC is resolved and identified to monoclinic crystal system and C2 space group by X‐ray diffraction. The band gap of Cs2PdBr4 SC is extrapolated to 1.54 eV by absorption and reflection spectra. Cs2PdBr4 thin films (TFs) on ITO Interdigitated electrodes (IEs) were prepared by methods of vacuum evaporation. The photodetectors based on Cs2PdBr4‐ITO IEs exhibit regular responses under 397–564 nm monochromatic light, stable operation at weak light intensity of 1 mW/cm2 (397 nm), a responsivity of 0.27 mA/W and a detectivity of 1.13×106 Jones. This study can arouse interest in catalysis and photodetector.

Effects of Different Light Conditions on Anatomical and Histological Features of Galls in Bacterial Gall Disease of Cerasus × yedoensis.

Cerasus × yedoensis (cherry 'Somei-yoshino' Fujino) is affected by bacterial gall disease caused by Pseudomonas syringae pv. cerasicola (PSC). C. × yedoensis is often infected with PSC under weak light intensity, which indicates that susceptibility of C. × yedoensis to PSC is affected by light. To evaluate the effects of white light intensity and different light qualities, white or blue, on bacterial gall disease development, we quantitatively assessed the anatomical and histological features of bacterial-inoculated sites on branches of 2-year-old potted C. × yedoensis seedlings grown under different light intensities and qualities. The stronger the white light intensity, the less severe the gall symptoms. Gall formation was suppressed more by blue than white light of the same intensity. The validity of a simple gall index for assessing gall development with the naked eye, via quantitative evaluation of gall shape by measuring gall height, width, and volume, showed that the gall index could be used as a practical method for on-site assessments of gall development. The ratio of degeneration area in the gall remained constant, suggesting the presence of some regulatory mechanism preventing PSC from affecting the entire gall within the plant. Microscopy showed that the gall tissue is composed primarily of callus cells and has voids containing gummy material that is exuded from cracks in the gall, and the periderm develops at the gall foot but not at the gall apex, so the cells at the gall apex were necrotic or collapsed.

YOLOv8n-CSE: A Model for Detecting Litchi in Nighttime Environments

The accurate detection of litchi fruit cluster is the key technology of litchi picking robot. In the natural environment during the day, due to the unstable light intensity, uncertain light angle, background clutter and other factors, the identification and positioning accuracy of litchi fruit cluster is greatly affected. Therefore, we proposed a method to detect litchi fruit cluster in the night environment. The use of artificial light source and fixed angle can effectively improve the identification and positioning accuracy of litchi fruit cluster. In view of the weak light intensity and reduced image features in the nighttime environment, we proposed the YOLOv8n-CSE model. The model improves the recognition of litchi clusters in night environment. Specifically, we use YOLOv8n as the initial model, and introduce the CPA-Enhancer module with chain thinking prompt mechanism in the neck part of the model, so that the network can alleviate problems such as image feature degradation in the night environment. In addition, the VoVGSCSP design pattern in Slimneck was adopted for the neck part, which made the model more lightweight. The multi-scale linear attention mechanism and the EfficientViT module, which can be deeply divided, further improved the detection accuracy and detection rate of YOLOv8n-CSE. The experimental results show that the proposed YOLOv8n-CSE model can not only recognize litchi clusters in the night scene, but also has a significant improvement over previous models. In mAP@0.5 and F1, YOLOv8n-CSE achieved 98.86% and 95.54% respectively. Compared with the original YOLOv8n, RT-DETR-l and YOLOv10n, mAP@0.5 is increased by 4.03%, 3.46% and 3.96%, respectively. When the number of parameters is only 4.93 m, F1 scores are increased by 5.47%, 2.96% and 6.24%, respectively. YOLOv8n-CSE achieves an inference time of 36.5ms for the desired detection results. To sum up, the model can satisfy the criteria of the litchi cluster detection system for extremely accurate nighttime environment identification.

Spread spectrum for covert communication in ultra-violet communication system.

In this paper, we propose a covert communication scheme based on a spread spectrum for ultra-violet communication. We first characterize the system model of the communication system, where Warden is adopted to monitor the legitimated user transmission based on the binary hypothesis test and Kolmogorov-Smirnov test. To avoid periodic transmission of the pilot sequence which potentially degrades covertness, we propose a blind synchronization approach, such that the pilot sequence does not need to be transmitted. It is observed from system-level simulation that the spread spectrum-based approach can achieve both low detection bit error rate and covertness under weak light intensity. Moreover, we experimentally evaluate the detection performance and covertness of the proposed approach.

Development of Thin-Film Light-Emitting Devices for Hyper Localized Photodynamic Therapy

In this study, we fabricated a thin-film light-emitting device to apply metronomic photodynamic therapy (PDT) in a weak light emitted by LED chips that showed the PDT effect at the cellular level. Thin-film light-emitting devices can operate an LED chip by the wireless power supply. This device has been developed by exploiting a flexible antenna coil made from Au nanoparticle ink printed on a 5-μm-thick poly(D, L-lactic acid) thin film. The weak light intensity of LED (10∼400 µW/cm2) can direct the cell death regions. Further quantification of mPDT at the cellular level as well as in vivo evaluation, will be carried out.

Reflective nonlinear optical limiter design based on coupled Tamm plasmon polaritons and optical Kerr effect

With the increasing applications of high-power lasers in fields such as laser fabrication, laser measurement, laser therapy and scientific research, there is an increasing demand for high-performance nonlinear optical limiters (NOLs) to protect human eyes and optical sensitive elements. Here we propose a brand-new approach to design a reflective NOL with an ultra-wide stop band based on coupled Tamm plasmon polaritons (TPPs) and optical Kerr effect. The NOL permits the transmission of weak signal light at the desired wavelength while effectively blocking potentially harmful or accidentally intense lasers at the same wavelength to avoid damage to sensitive optical elements or human eyes. The design can be optimized for the desired operating wavelength and threshold intensity by using different dielectric layers. In a proof-of-concept design, taking the 1064 nm laser as an example, we design a NOL capable of dynamically adjusting its transmission in response to laser intensity. The NOL has a high transmission of 85.21 % at weak light (intensity less than 0.20 MW/cm2), and the transmission can be rapidly reduced to 1.39 % when the incident light intensity increases to 60.37 MW/cm2. Furthermore, the broad stop band effectively safeguards the limiter from potential damage caused by intense light at different wavelengths. Our proposed limiter exhibits an exceptionally wide stop band range spanning from 0.5 ∼ 20 µm, nearly 30 times broader than conventional reflective NOLs. The proposed NOL design scheme provides a new promising method to design an excellent reflective NOL at the desired wavelength.

Genome-Wide Identification and Expression Analysis of the Trehalose-6-phosphate Synthase and Trehalose-6-phosphate Phosphatase Gene Families in Rose (Rosa hybrida cv 'Carola') under Different Light Conditions.

Trehalose, trehalose-6-phosphate synthase (TPS),and trehalose-6-phosphatase (TPP) have been reported to play important roles in plant abiotic stress and growth development. However, their functions in the flowering process of Rosa hybrida have not been characterized. In this study we found that, under a short photoperiod or weak light intensity, the content of trehalose in the shoot apical meristem of Rosa hybrida cv 'Carola' significantly decreased, leading to delayed flowering time. A total of nine RhTPSs and seven RhTPPs genes were identified in the genome. Cis-element analysis suggested that RhTPS and RhTPP genes were involved in plant hormones and environmental stress responses. Transcriptome data analysis reveals significant differences in the expression levels of RhTPSs and RhTPPs family genes in different tissues and indicates that RhTPPF and RhTPPJ are potential key genes involved in rose flower bud development under different light environments. The results of quantitative real-time reverse transcription (qRT-PCR) further indicate that under short photoperiod and weak light intensity all RhTPP members were significantly down-regulated. Additionally, RhTPS1a, RhTPS10, and RhTPS11 were up-regulated under a short photoperiod and showed a negative correlation with flowering time and trehalose content decrease. Under weak light intensity, RhTPS11 was up-regulated and negatively regulated flowering, while RhTPS5, RhTPS6, RhTPS7b, RhTPS9, and RhTPS10 were down-regulated and positively regulated flowering. This work lays the foundation for revealing the functions of RhTPS and RhTPP gene families in the regulation of rose trehalose.

Multifunctional solar‐blind ultraviolet photodetectors based on p‐PCDTBT/n‐Ga2O3 heterojunction with high photoresponse

AbstractSolar‐blind ultraviolet (UV) photodetectors based on p‐organic/n‐Ga2O3 hybrid heterojunctions have attracted extensive attention recently. Herein, the multifunctional solar‐blind photodetector based on p‐type poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT)/n‐type amorphous Ga2O3 (a‐Ga2O3) is fabricated and investigated, which can work in the phototransistor mode coupling with self‐powered mode. With the introduction of PCDTBT, the dark current of such the a‐Ga2O3‐based photodetector is decreased to 0.48 pA. Meanwhile, the photoresponse parameters of the a‐Ga2O3‐based photodetector in the phototransistor mode to solar‐blind UV light are further increased, that is, responsivity (R), photo‐detectivity (D*), and external quantum efficiency (EQE) enhanced to 187 A W–1, 1.3 × 1016 Jones and 9.1 × 104 % under the weak light intensity of 11 μW cm–2, respectively. Thanks to the formation of the built‐in field in the p‐PCDTBT/n‐Ga2O3 type‐II heterojunction, the PCDTBT/Ga2O3 multifunctional photodetector shows self‐powered behavior. The responsivity of p‐PCDTBT/n‐Ga2O3 multifunctional photodetector is 57.5 mA W–1 at zero bias. Such multifunctional p‐n hybrid heterojunction‐based photodetectors set the stage for realizing high‐performance amorphous Ga2O3 heterojunction‐based photodetectors.image

Preparation of UiO-66-NH2/Bi2.15WO6 composite with enhanced tetracycline degradation under weak light intensity

Preparation of UiO-66-NH2/Bi2.15WO6 composite with enhanced tetracycline degradation under weak light intensity

The purification performance of S doped g-C3N4 photocatalyst with outstanding reduction efficiency over Cr(VI) under the actual underwater transmission light

Cr(VI) existed in the industrial wastewater which has high biological toxicity has become one of the main pollution sources at present, and it is also difficult to remove from the wastewater because of its chemical stability. In this work, a raspberry-like sulfur doped carbon nitride photocatalyst (SCNx) with significant high reduction performance over Cr(VI) was prepared by solvothermal process. The BET data showed that the specific surface area of SCN4 was 3.75 times that of g-C3N4. Meanwhile, sulfur doping successfully reduce the band gap, which significantly improve the effective photoelectron density on the surface of the material, thus enhance its reduction ability. On this basis, the reduction activity of the SCNx to Cr(VI) in actual underwater environment was further investigated. Results show that SCNx still has good removal performance under weak light intensity and weak UV conditions. At 20 cm depth where ultraviolet spectral is attenuated 86.2%, the removal rate of SCN4 over Cr(VI) can still reach 58.1%. This research demonstrated that through S-doping and morphology control modification, carbon nitride can remain high photoreaction activity in the underwater weak light and weak UV environment, thus realize the efficient reduction treatment of Cr(VI). The research demonstrated the feasibility of heavy metal water treatment, and indicate a possible direction for the future practical application of heavy metal water purification.

Light-enabled coupling of tandem ethane dehydrogenation and CO2 hydrogenation

The integration of electromagnetic energy into a thermal reaction is beneficial in catalytic performance and product distribution. To date, such a photothermal strategy has mainly been applied to relatively low-temperature reactions, such as CO2 hydrogenation, and its application to high-temperature reactions has yet to be explored. Herein, electromagnetic energy is successfully introduced into a tandem ethane dehydrogenation and CO2 hydrogenation system over a Zn-based catalyst. According to the experiments and theoretical simulations, light enables a new reverse water-gas shift reaction, which consumes the produced H2 and thus right shifts the ethane dehydrogenation reaction and enhances the catalytic performance. The resulting ethylene rate could achieve 11.5 mmol g−1 h−1 with a selectivity of 96%, and the estimated external quantum efficiency is up to 18.85% under weak light intensity (2 sun). In the meantime, the ethylene rate could be improved by about 600-fold with higher light intensities.

Self‐Driven Fast‐Speed Photodetector Based on BP/ReS2 van der Waals Heterodiode

AbstractBroadband photodetectors based on 2D layered materials provide great potential applications in night vision, sensing, and communications. However, it remains a challenge for detectors to achieve both high photoresponsivity and fast response. Here, a high‐sensitive photodetector based on ReS2/BP van der Waals (vdW) heterodiode with fast speed, rising time (τr) of 770 ns, and decay time (τd) of 760 ns under a 637 nm laser is reported. The detection range is covered from visible to mid‐wave infrared (MWIR) 0.405–3.753 μm. In the visible range, a high photoresponsivity of 107.1 AW−1, competitive specific detectivity (D*) of 1.89 × 1010 cm Hz1/2 W−1, and a low noise equivalent power of 3.03 × 10−14 W Hz−1/2 are obtained. In the MWIR the D* of 3.26 × 108 cm Hz1/2 W−1 is demonstrated in the photovoltaic model. Notably, the photodiode realizes a high external quantum efficiency of 71.8%, and a high power conversion efficiency of 2.0%. This work provides a way to design broadband response and fast‐speed self‐driven photodetectors with great potential applications in weak light intensity.

Polarization-Sensitive Detector of Two-Dimensional Multilayer Hybrid Perovskite Crystals Showing High Polarization Ratio to Weak Light.

Two-dimensional (2D) hybrid perovskite materials have been widely used for polarization-sensitive photodetection due to their fascinating optical and physical attributes. However, studies on those materials that enable strong polarized-light activities under a weak-light condition remain quite scarce. Here, by tailoring aromatic cation into 3D prototype, we have successfully obtained a new 2D hybrid perovskite, (FPEA)2(MA)Pb2Br7 (1, where FPEA is 4-fluorophenethylammonium and MA is methylammonium). The alternative alignment of inorganic and organic structural components results in significant anisotropy, including optical absorption and electric conductivity. The coupling effect of these anisotropic properties in 1 gives rise to strong dichroic activities toward detecting polarized light. Especially, under weak light intensity (~330 nW/cm2), it can still generate a large polarization ratio up to 1.35, which is even higher than those of some typical 2D materials (i.e., GeSe ~ 1.09). Besides, single crystal-based photodetector of 1 displays fascinating detecting performances, including large photocurrent on/off ratio (~ 104), fast response time (~ 154/182 μs) and excellent antifatigued stability. These findings disclose the potentials of 1 as a robust candidate for detecting weak polarized light, which has practical applications in the field of polarized optoelectronics.

Effects of light size and intensity on photoconductive effect-based optically-induced dielectrophoresis for three-dimensional manipulation

This study aims to study the effect of light size and intensity on photoconductive effect-based optically-induced dielectrophoresis (ODEP) for three-dimensional manipulation of cells. HL-7702 cells and SMMC-7721 cells in sucrose solution were manipulated three-dimensionally by ODEP. We found that the ODEP force generated by the three-dimensional non-uniform electric field will form a three-dimensional space, and the positive ODEP force will attract the cells near the space into it. When the number of cells is large, the three-dimensional stacking phenomenon will occur, that is, the three-dimensional assembly of cells. When the size of the light spot is similar to that of the cell, the projector with weak light intensity can only manipulate a single cell, while the laser with higher light intensity can carry out cell three-dimensional assembly. When the light intensity is similar, the larger size of light can produce larger a three-dimensional assembly space. So the cell three-dimensional manipulation by ODEP is achieved only when the photoconductive effect induced by the light pattern reaches the required intensity. The three-dimensional manipulation of cells by ODEP is from plane to stereo, and its realization is related to the light size and the photoconductive layer resistance determined by light intensity. And the three-dimensional space of assembling cells is related to the light size and intensity, and the larger and stronger the light, the larger the space.

A Novel Multispectral Vessel Recognition Based on RGB-to-Thermal Image Translation

In the last decade, advances in deep learning have led to considerable progress in the field of ship classification in Red Green Blue (RGB) and Infra-Red (IR) images. However, ship classification performs poorly on images acquired in weak visible light intensity. Multispectral imaging constitutes a potential solution to address such difficulty. In this paper, we first propose Convolutional Neural Network (CNN) for ship classification in multi-spectral images (RGB, IR, etc.). The proposed architectures were trained from scratch and fine-tuned to another pre-trained network. Validation was carried out on the publically available RGB-IR pairs ship dataset VAIS. Unfortunately, owing to the small size of the dataset, the obtained classification result was 59,09%, hence not satisfactory for most applications. We, therefore, proposed a new image data augmentation approach for the generation of IR ship images from RGB images. The generation process was carried out through an adaptation of a Generative Adversarial Network (GAN) network and a Pix2Pix model. In fact, VAIS dataset was kept aside for validation purposes and KAIST RGB-IR pairs dataset was used for the training of our translator. The augmented IR dataset yielded more than a 9% increase in the performance of VAIS IR-based ship classification.

Stepwise photoassisted decomposition of carbohydrates to H2

Stepwise photoassisted decomposition of carbohydrates to H2

Underwater environment laser ghost imaging based on Walsh speckle patterns

Underwater imaging is a challenging task because of the effects of scattering and absorption in water. Ghost imaging (GI) has attracted increasing attention because of its simple structure, long range, and achievability under weak light intensity. In an underwater environment, conventional imaging is limited by low sensitivity, resulting in fuzzy images, while ghost imaging can solve this problem. This study proposes underwater laser ghost imaging based on Walsh speckle patterns. According to the simulated and experimental results, noise resistance and a low sampling rate of ghost imaging based on Walsh speckle patterns are proved. As the turbidity of the underwater environment increases, the imaging quality of ghost imaging based on Walsh speckle patterns decreases. However, it remains much better than that of ghost imaging based on random speckle patterns and Hadamard speckle patterns, whereas conventional imaging is no longer distinguishable. Ghost imaging based on Walsh speckle patterns can be performed with a sampling rate lower than 10%, and the peak signal-to-noise ratio and the structural similarity of the results increase by 150.15% and 396.66%, respectively, compared with random speckle pattern ghost imaging. An identifiable image of ghost imaging based on Walsh speckle patterns can be reconstructed with a sampling rate of 6% in a turbid water environment, which is simulated with the concentration of the milk powder not higher than 11.0 g/L. This method promotes the further development of optical imaging technology for underwater targets with a low sampling rate based on ghost imaging.

The Effect of Light Pollution on the Sea Finding Behavior of Green Turtle Hatchlings on Lanyu Island, Taiwan.

octurnal animals use their vision and acute hearing to adapt to the nighttime environment. Light pollution has become a serious problem for nocturnal animals in coastal areas, especially nesting sea turtles and sea turtle hatchlings. Hatchlings use visual clues to find the ocean. However, when the artificial light is stronger than the natural light, hatchlings become either misoriented, disoriented or both. Due to rapid tourism development on Lanyu Island, new sources of light pollution, especially streetlights, pose a serious threat to sea turtle hatchlings. In this study, we used a portable lamp constructed by Liteon Inc. on a circular area of a turtle nesting beach to see how artificial light sources could affect green turtle hatchlings' sea finding behavior. In the experiments, we tested hatchling behavior under different lamp settings (strong or weak light intensity; white or yellow light; lamp shield presence or absence) and moon visibilities (moonlit or moonless). The hatchlings' crawling tracks and locations at the end of the trials were recorded. Results showed that the light intensity had no effect on hatchling sea finding behavior. White light had a stronger impact on hatchling sea finding behavior than yellow light. When the lamp shield was installed on moonlit nights, more hatchings were able to find the sea under both white and yellow lights. Thus, it is recommended that light shields be installed on the streetlights of Lanyu Island in order to protect the sea turtle hatchlings effectively.