Change In Optical Transmission Research Articles

Change of crystallinity and optical transmittance of K2Ni(SO4)2·6H2O single crystal by heat treatment

Potassium nickel sulfate hexahydrate (KNISH) was prepared and grown as single crystal from the supersaturated aqueous solution at 309 K using slow evaporation method. Thermal measurements were achieved for the prepared crystal. The dehydration process, structural phase transitions and melting point of the obtained material were detected. Crystal structure and optical transmittance of KNISH crystal were studied through heat treatment. At 370 K, the dehydration process started to convert KNISH to the anhydrous phase KNIS and the crystallinity decreased gradually until the material became totally amorphous at 383 K. The anhydrous KNIS stayed at the amorphous state from 383 K to 629 K where it transformed again to the crystalline state with different structure. The heat treatment under dehydration temperature did not affect the efficiency of KNISH crystal for using as ultraviolet light filter and sensor. Above dehydration temperature, the obtained anhydrous phase KNIS is not suitable for these applications.

Achieving ultrahigh electrochromic stability of triarylamine-based polymers by the design of five electroactive nitrogen centers

A shortage of long-term stability of electrochromic materials has been hindering their practical application. A series of novel polyamides (PAs) (4) with five electroactive nitrogen atoms within triphenylamine (TPA)-containing structures was synthesized via phosphorylation polyamidation. Polyamide 4b exhibited highly integrated electrochromic performances, including multiple color changes, high contrast of optical transmittance change, and the highest electrochromic stability (only 11.2 and 9.6 % decay of its coloration efficiency (CE) at 450 nm after 50000 and 16000 switching cycles, respectively) compared to all other triarylamine-based polymers to date. This record-high electrochromic cycling is attributed to the enhanced stability of polaron, which was studied through the electron-donating or electron-withdrawing effect of substituents and the resonance effect of electron delocalization over the electroactive nitrogen centers. Importantly, our core design of five electroactive nitrogen centers with electron-donating methoxy groups is the key factor to increase stability of polaron in the resulting polymers 4. More electroactive nitrogen centers are able to create a weaker electronic coupling due to a charge of cation radical dispersed by resonance successfully in-between the different redox states, which is evidenced clearly by the observed longer wavelength absorption in the NIR region. Our research confirms that the key to determining polaron stability is the resonance by the electrons delocalized over all the redox centers, rather than the electronic coupling between the different redox centers. And the resonance leads to increasing electrochromic stability of the polymer.

Auxetic kirigami structure-based self-powered strain sensor with customizable performance using machine learning

Recently, soft material based wearable sensors have discovered numerous applications in healthcare, sports monitoring, and virtual reality/augmented reality (VR/AR) systems. For these sensors, fulfilling user-specified requirements rather than just improving the sensor performance has become an important issue. In this study, a self-powered piezo-transmittance type strain sensor based on auxetic structures was optimized for configurable and user-specified characteristics using a machine-learning surrogate model. The sensor mechanism is based on the optical transmittance change induced by the gap opening of the auxetic kirigami structure. The sensor performance was analyzed according to the geometric design variables, and the optimal design was determined using Bayesian and Gaussian process to maximize the sensor performance for different purposes. The optimally designed geometries were used for self-powered sensors on a structural health monitoring (SHM) system, a human motion monitoring (HMM) system for monitoring sports performance and incorporated into an AR system.

All-photonic artificial synapses based on photochromic perovskites for noncontact neuromorphic visual perception

Recently optoelectronic synapses generating light-driven electrical memories have played a vital role in the neuromorphic computing of visual perception. However, all the optoelectronic synapses demonstrate photoelectric conversion. Peripheral circuits are used for contact photocurrent measurement, leading to significant energy consumption and impeding the evolution of optical wireless communication. It is crucial to develop noncontact neuromorphic visual perception based on light-driven photonic memories. Herein, we report all-photonic artificial synapses based on photochromic perovskites. Triggered by ultraviolet and visible light pulses, cesium lead iodide bromine induces a structural disorder. Optical transmittance changes induced by the disorder last after the pulses are gone. Next, the photonic memories are propagated in the air and processed by a recurrent neural network. The accuracy of binary image recognition is instantly stabilized at 1.0, and accuracy above 0.8 after 7 epochs is achieved in the recognition of digitals from 0 to 9. The all-photonic synapses realize remote perception with zero in-situ energy consumption and enable artificial sensory systems with low-power computation, remote control, and ultrahigh propagation speed.

Investigations on temperature dependent properties of spray deposited tin oxide thin films

The present study reported the temperature dependent properties of tin oxide (SnO2) thin films deposited by using conventional, cost effective and non-vacuum-based spray pyrolysis technique (SPT). The as deposited films were characterized by various characterization techniques such as X ray diffraction (XRD), UV-Vis spectroscopy and Scanning electron microscopy (SEM) to study their structural, optical and morphological properties respectively. XRD analysis revealed tetragonal rutile crystal structure of SnO2 with preferred orientation along (200) plane. The refinement of XRD data was also carried out by Rietveld refinement to obtain the fitting parameters, crystallite size and lattice parameters. UV-Vis study showed considerable change in optical absorbance and transmittance with change in substrate temperature. Effect of substrate temperature on film thickness, refractive index and band gap energy were determined by Swanepoel method and by Tauc’s plot respectively. The Urbach energy was also calculated and were correlated to the defects in SnO2 films. SEM micrograph showed the transformation from granules to nanospheres as a function of substrate temperature. Electrical properties were determined by Hall effect measurements which gives carrier concentration, electrical resistivity and mobility in the order of 1019-1020 /cm3, 10−2-10−3 Ω.cm and 4–23 cm2/Vs respectively.

Improvement of electrical characteristics and wet etching procedures for InGaTiO electrodes in organic light-emitting diodes through hydrogen doping

We investigated the effect of hydrogen doping on characteristics of InGaTiO (IGTO) electrode with high conductivity and transmittance during sputtering process. After hydrogen doping, the 300 nm-thick IGTO:H electrode showed lower sheet resistance of 13.79 Ω/square compared to sheet resistance (69.2 Ω/square) of pure IGTO electrode without change of optical transmittance. In addition, wet etching reaction rate of IGTO:H electrode for patterning process was significantly accelerated after hydrogen doping. Possible explanation for hydrogen doping effect on electrical properties and wet etching process of the IGTO:H electrode was suggested. The doped hydrogen influenced the electrical characteristics through the passivation of dangling bonds and oxygen vacancies. Moreover, it significantly impacts crystalline structure, consequently altering the etching rate. Using patterned IGTO:H electrodes, we fabricated red organic light emitting diodes (OLEDs) to show feasibility of the IGTO:H electrodes. External quantum efficiency and current efficiency of the red OLED with IGTO:H (10%) were higher than IGTO electrode without hydrogen doping, indicating that hydrogen doping is an effective method to improve the film properties and IGTO:H electrode can serve as a prospective transparent anode for both flexible and rigid OLEDs.

Induced blue phase of cholesteric-nematic mixtures under the action of acetone vapors

Liquid crystals can exhibit structural orientational order. The creation of a mixture with the addition of chiral molecules to the nematic liquid crystal induces helical twisting, the axis of which is directed perpendicular to the cell surfaces. When some cholesteric mixtures with a sufficiently short spiral pitch (up to 400-500 nm) are heated to a temperature close to, but still lower than, the temperature of the main transition to the isotropic state, in some cases the so-called blue phases can be formed.
 We carried out a study on the detection of structural manifestations of the blue phase under the action of vapors of chemical substances, in particular acetone. The main dependences of effect of acetone on the liquid crystal mixture depending on the concentration were also revealed. The two-stage phase transformation from cholesteric liquid crystal to the isotropic liquid via the intermediary blue phase could be clearly recorded by changes in optical transmission. Possible applications are discussed.

Dual-mode scramjet control using optical emission sensors.

Closed-loop fueling control of a dual-mode scramjet was successfully demonstrated using optical emission spectroscopy as the sole sensor for controller feedback. The optical emission from species of interest (O H ∗, C H ∗, C2∗) was first characterized throughout the combustor. The relative emission intensity between species pairs was studied over a range of fueling conditions and imaging locations throughout a dual-mode scramjet combustor flow path. The pair of emissive species (C2∗/O H ∗) and imaging location that were the most sensitive to changes in fueling condition were selected for use in the control system. Changes in optical transmission of the observation windows and the impact on fuel control were explored. To our knowledge, this paper is the first demonstration of fueling control of a dual-mode scramjet using only optical emission spectroscopy as feedback.

Combined Displacement and Angle Sensor with Ultra-High Compactness Based on Self-Imaging Effect of Optical Microgratings

In this paper, an ultracompact combined sensor for displacement and angle-synchronous measurement is proposed based on the self-imaging effect of optical microgratings. Using a two-grating structure, linear and angular displacement can be measured by detecting the change of phase and amplitude of the optical transmission, respectively, within one single structure in the meantime. The optically transmitted properties of the two-grating structure are investigated in both theory and simulation. Simulated results indicate that optical transmission changes in a sinusoidal relationship to the input linear displacement. Meanwhile, the amplitude of the curve decreases with an input pitch angle, indicating the ability for synchronous measurement within one single compact structure. The synchronous measurement of the linear displacement and the angle is also demonstrated experimentally. The results show a resolution down to 4 nm for linear displacement measurement and a maximum sensitivity of 0.26 mV/arcsec within a range of ±1° for angle measurement. Benefiting from a simple common-path structure without using optical components, including reflectors and polarizers, the sensor shows ultra-high compactness for multiple-degrees-of-freedom measuring, indicating the great potential for this sensor in fields such as integrated mechanical positioning and semiconductor fabrication.

Monolithic integrated light-emitting-diode/photodetector sensor for photoactive analyte monitoring: design and simulation.

We present the simulation and design optimization of an integrated light-emitting-diode/photodetector (LED-PD) sensor system for monitoring of light absorbance changes developing in analyte-sensitive compounds. The sensor integrates monolithically both components in a single chip, offering advantages such as downsizing, reduced assembly complexity, and lower power consumption. The changes in the optical parameters of the analyte-sensitive ink are detected by monitoring the power transmission from the LED to the PD. Ray tracing and coupled modeling approach (CMA) simulations are employed to investigate the interaction of the emitted light with the ink. In highly absorbing media, CMA predicts more accurate results by considering evanescent waves. Simulations also suggest that an approximately 39% change in optical transmission can be achieved by adjusting the ink-deposited layer thickness and varying the extinction coefficient from 10-4 to 3×10-4.

Label-free optical detection of calcium ion influx in cell-derived nanovesicles using a conical Au/PDMS biosensor.

Ion channels, which are key to physiological regulation and drug discovery, control ion flux across membranes, and their dysregulation leads to various diseases. Ca2+ monitoring is crucial for cellular signaling when performing Ca-based assays in ion channel research; these assays are widely utilized in both academic and pharmaceutical contexts for drug screening and pharmacological profiling. However, existing detection methods are limited by slow detection speeds, low throughput, complex processes, and low analyte viability. In this study, we developed a label-free optical biosensing method using a conical Au/polydimethylsiloxane platform tailored to detect Ca2+ influx in A549-originated nanovesicles facilitated by the transient receptor potential ankyrin 1 (TRPA1) channel. Nanovesicles expressing cellular signaling components mimic TRPA1 signal transduction in cell membranes and improve analyte viability. The conical Au/polydimethylsiloxane sensor converted Ca2+ influx events induced by specific agonist exposure into noticeable changes in relative transmittance under visible light. The optical transmittance change accompanying Ca2+ influx resulted in an enhanced sensing response, high accuracy and reliability, and rapid detection (∼5 s) without immobilization or ligand treatments. In the underlying sensing mechanism, morphological variations in nanovesicles, which depend on Ca2+ influx, induce a considerable light scattering change at an interface between the nanovesicle and Au, revealed by optical simulation. This study provides a foundation for developing biosensors based on light-matter interactions. These sensors are simple and cost-effective with superior performance and diverse functionality.

New PV encapsulants: assessment of change in optical and thermal properties and chemical degradation after UV aging

This work aims to investigate the change in chemical and physical properties of different polymeric materials, potentially usable for photovoltaic modules encapsulation, caused by UV aging. Three classes of polymeric materials have been examined: ethylene-vinyl-acetate (EVA), thermoplastic polyolefins (TPO) and polyolefin elastomers (POE). EVA is currently the most used encapsulant in the photovoltaic field; TPO and POE are new materials, alternative to EVA, which can allow to overcome some of the reliability problems of photovoltaic modules linked to the degradation of EVA properties. Of each of these three material classes, different commercially available encapsulating polymer films, with different chemical formulations, have been examined. Stressful environmental conditions have been simulated in a climatic chamber and the associated changes in optical, thermal and chemical properties of the different encapsulants have been analysed and compared before and after UV aging. The link between the chemical structure, formulation and degradation of the encapsulants with their lifetime under simulated conditions of UV stress has been investigated by the assessment of the changes in thermal stability, optical transmittance, crystallinity, yellowness index and chemical degradation. This study helps to better understand the causes of the module performance reduction due to the degradation of the encapsulant material and is a guide for the selection of encapsulant films with improved characteristics, for the manufacture of more durable PV modules.

Optical effects of graphene addition on adhesives for orthodontic lingual retainers.

The objective of this study was to determine the effects on the colour of adding increasing concentrations of graphene to orthodontic fixed retainer adhesives and to evaluate changes in optical transmission during light curing and the resultant degree of conversion. Two different types of adhesives commonly used for fixed retainers were investigated: A packable composite (Transbond) and a flowable composite (Transbond Supreme). Graphene was added to the adhesives in three different concentrations (0.01, 0.05, and 0.1wt%). Adhesives without graphene addition were set as control groups. A Minolta colourimeter was used to measure the colour and translucency parameters. Irradiance transmitted during curing was quantified using MARC Light Collector. Fourier-transform infrared spectroscopy was used to record degree of conversion. Data were statistically analysed with the Student's t-test and one-way ANOVA with Tukey's tests (α=0.05). The findings showed that incorporating graphene darkened the adhesive colour significantly and reduced translucency. As the graphene concentration reached 0.1wt%, samples became opaque; yet, no adverse effect on degree of conversion was observed. The addition of graphene reduces optical transmission of lingual retainer adhesives; the effect increases with graphene concentration.

Nanomesh‐YOLO: Intelligent Colorimetry E‐Skin Based on Nanomesh and Deep Learning Object Detection Algorithm

AbstractPerspiration is an important physiological process that maintains thermal homeostasis and water–salt balance. However, the collection and analysis of perspiration currently rely on microfluidic technology and colorimetric assays. The complexity and high cost of fabricating microfluidic channels and the insecurity of chemical reagents for color reactions should be optimized. In this work, a colorimetry electronic skin (e‐skin) for intelligent perspiration monitoring has been realized. The colorimetry e‐skin system consists of the polyurethane (PU) nanomesh and the object detection algorithm You Only Look Once version 3 (YOLOv3). Due to the 44% porosity of the PU nanomesh and capillary action, the low‐cost PU nanomesh (<1 cent) can be used as the colorimetric indicator. The volume of the PU nanomesh expands to 362.37% as a result of perspiration being absorbed and changes the optical transmittance (up to 277.78%). A finite element model based on capillary action has been proposed to explain the change in optical transmittance. Finally, a database containing 735 images has been built, and the object detection algorithm YOLOv3 is used to analyze the perspiration absorbed by the PU nanomesh. The detection results can identify the perspiration volume with a high accuracy of 97%. These results show that this work has great potential in healthcare field.

Efficient control of light propagation assisted by photothermal effect in a graphene-integrated all-fiber device

Graphene has arisen as an efficient photothermal (PT) nanomaterial owing to the strong light-matter interaction, ultrafast and nonradiative annihilation of the photoexcited carriers, and high thermal conductivity. Combined with the unique optical properties such as universal absorption coefficient at broadband wavelengths, the PT effect in graphene can be synergistically utilized for all-optical control of light. Here, we report an efficient transmission control of propagating light in graphene-covered side-polished fiber through the PT effect of graphene. When the local heat was generated via PT effect in graphene, a significant change in optical transmission was observed through two different mechanisms. The first one was implemented by the absorption change at the graphene layer via the asymmetrical reshaping of the mode-field distribution, resulting in the optical transmission change of up to 25 dB. The other mechanism was realized by the guiding property switching from the radiation mode to the guided mode of the light, resulting in the all-optical transmission control of over 56 dB at 1550 nm. The proposed method proves that the PT effect assists the broadband and efficient all-optical control with great versatility in graphene-integrated all-fiber devices.

Effect of samarium oxide on the structural and ligand field parameters of iron cations inside sodium borate glass

In this work, we prepared sodium borate glass doped with different amounts of iron (Fe2O3) and samarium oxides (Sm2O3). The effects of replacing Fe2O3 with Sm2O3 on the transparency, ligand field parameters, and structural properties were studied using different techniques such as FTIR, density, optical absorbance and optical transmittance. Further, we explored the effect of sunlight on the optical transmittance at 90 min of irradiation time. Our results showed that, with further additions of Sm2O3, the BO4 units, density values increased, and ligand field splitting increased. In contrast, molar volume values decreased. The transparency of the glass specimens showed increased behavior with further Sm2O3 additives. Moreover, the transmittance of the glass samples showed decreasing values with exposure to sunlight. This behavior was attributed to the creation of structural defects inside the glasses with further sunlight irradiation. Moreover, the percent of change in optical transmittance for all glass samples is insignificant (<10%). This small percentage of change in optical transmittance shows that the glasses are stable when exposed to sunlight. Further, these results make them potential candidates to be used in photovoltaic modules.

Novel composites of nano-metal–organic frameworks (IRMOF-3) and silver nanoparticles for the ultra-sensitive performance of SERS sensing and optical fiber modes

Rapid chemical detection of drugs of abuse in biological fluids such as blood and saliva is a concern within medicine and law enforcement. As an outcome, a label-free detection platform takes biological fluid samples with concentrations ranging from extremely high to very low. We obtained experimentally the limit of detection (LOD) of glycerol concentration, corresponding to a minimum resolvable refractive index of 3.4 × 10−7 RIU (refractive index unit). We applied the microfluidic device sensors to the quantitating concentration dopamine solutions. The experiment was recorded in real-time as the concentration of analyte injected exposed to the fiber core surface resulted in a sensitive change in optical power transmission. The presented sensors also exhibited reasonably good reproducibility and higher sensitivity, providing the LOD as 1.02 × 10−11 M. A relatively simple scheme procedure is proposed for the simultaneous detection and quantitative assessment of rhodamine B using surface-enhanced Raman spectroscopy with a limit of detection of 10−12 M and a relative standard deviation of 5.78% across a detection concentration range mainly from 10−5 M to 10−12 M. The obtained results demonstrate the potential of nano-metal–organic framework materials as large-area, label-free optical fiber sensors and SERS-based platforms for biomedical sensing and environmental applications.

Nanostructured Vanadium Dioxide Materials for Optical Sensing Applications.

Vanadium dioxide (VO2) is one of the strongly correlated materials exhibiting a reversible insulator-metal phase transition accompanied by a structural transition from a low-temperature monoclinic phase to high-temperature rutile phase near room temperature. Due to the dramatic change in electrical resistance and optical transmittance of VO2, it has attracted considerable attention towards the electronic and optical device applications, such as switching devices, memory devices, memristors, smart windows, sensors, actuators, etc. The present review provides an overview of several methods for the synthesis of nanostructured VO2, such as solution-based chemical approaches (sol-gel process and hydrothermal synthesis) and gas or vapor phase synthesis techniques (pulsed laser deposition, sputtering method, and chemical vapor deposition). This review also presents stoichiometry, strain, and doping engineering as modulation strategies of physical properties for nanostructured VO2. In particular, this review describes ultraviolet-visible-near infrared photodetectors, optical switches, and color modulators as optical sensing applications associated with nanostructured VO2 materials. Finally, current research trends and perspectives are also discussed.

Layer‐Dependent Optical Modulation and Field‐Effect‐Transistor in Two‐Dimensional 4H‐SnS2 Layers

AbstractTwo–dimensional (2D) 4H‐polytype tin disulfide (SnS2) flakes are synthesized using the chemical vapor transport technique. The weak Van der Waals force between the 2D SnS2 layers offers an easy exfoliation of flakes down to a bilayer of thickness ≈2.02 (±0.1) nm using a mechanical exfoliation technique. The optical and field effect transistor (FET) characteristics of the exfoliated 2D 4H‐SnS2 layers are studied. The exfoliated layers are used to fabricate the ≈13‐layered SnS2 FET. The 4H‐SnS2 exhibits a high on/off ratio of ≈106 and mobility ≈1–4 cm2 V−1 s−1. The low mobility of the 4H‐SnS2 FET devices shows an insulating state concordant with the 2D Motts variable range hopping mechanism at varying temperatures. Moreover, it is found that the optical bandgap of the 2D SnS2 single‐crystal layers is largely widened for the bilayers and tri‐layers. The optical bandgap energies vary in the range of 2.56–1.99 eV. The significant alteration in bandgap energies of ≈0.57 eV offers downscaling of the 2D nanoscale semiconducting devices. Such layer‐sensitive changes in optical transmittance, absorbance, and bandgap energies are reflected in Commission Internationale de L'Eclairage (CIE) chromaticity, showing the distinct color of transmittance through various 2D 4H‐SnS2 layers.

Wavelength-shift-free racetrack resonator hybrided with phase change material for photonic in-memory computing.

The photonic in-memory computing architecture based on phase change materials (PCMs) is increasingly attracting widespread attention due to its high computational efficiency and low power consumption. However, PCM-based microring resonator photonic computing devices face challenges in terms of resonant wavelength shift (RWS) for large-scale photonic network. Here, we propose a PCM-slot-based 1 × 2 racetrack resonator with free wavelength shift for in-memory computing. The low-loss PCMs such as Sb2Se3 and Sb2S3 are utilized to fill the waveguide slot of the resonator for the low insertion (IL) and high extinction ratio (ER). The Sb2Se3-slot-based racetrack resonator has an IL of 1.3 (0.1) dB and an ER of 35.5 (8.6) dB at the drop (through) port. The corresponding IL of 0.84 (0.27) dB and ER of 18.6 (10.11) dB are obtained for the Sb2S3-slot-based device. The change in optical transmittance of the two devices at the resonant wavelength is more than 80%. No shift of the resonance wavelength can be achieved upon phase change among the multi-level states. Moreover, the device exhibits a high degree of fabrication tolerance. The proposed device demonstrates ultra-low RWS, high transmittance-tuning range, and low IL, which provides a new scheme for realizing an energy-efficient and large-scale in-memory computing network.