Visible Spectrum Research Articles

Photodetectors Based on ZrS3/MoS2 Heterostructures.

High-performance photodetectors with the detection capability of linearly polarized light have broad applications in both military and civilian fields. Quasi-one-dimensional ZrS3 as an emerging anisotropic two-dimensional material has come under the spotlight owing to its intriguing properties. However, the performance of the ZrS3 photodetector is seriously restricted by its low responsivity. Herein, a novel high-performance photodetector based on the van der Waals ZrS3/MoS2 heterostructure is proposed. Attributed to the charge trapping-assisted photogating effect, interlayer carrier transitions, and fast spatial separation of the photogenerated electron-hole pairs, the device displays superior photoresponse characteristics ranging from the ultraviolet to the visible spectrum in terms of high responsivity up to 212 A/W, an extraordinary external quantum efficiency of 8.5 × 104%, and a prompt rise/decay time of 0.19/0.38 ms. In addition, owing to the profound birefringence and dichroism effects in ZrS3 together with strong light-matter interactions in the heterostructure, profound linear-polarization sensitivity is demonstrated with a dichroic ratio of about 2.8. Overall, this photodetector not only is integrated with the excellent properties of ZrS3 and monolayer MoS2 but also further enhances the advantages through interlayer couplings, which demonstrate the strong potential of the ZrS3-based devices for high-performance, ultrafast, and polarization-sensitive photodetection.

Directional Charge Carrier Management Enabled by Orderly Arranged Perovskite Heterodomain with Defined Size for Self‐Powered Photodetectors

AbstractPerovskite planar heterojunction is reported to promote charge‐carrier separation at the interface due to the introduced built‐in potential, leading to improved charge‐carrier harvesting. However, the possible diffusion of charge carriers along the film lateral will increase their travel distance to respective electrodes, resulting in increased recombination probabilities. Constructing independent transport channels for positive and negative charge carriers individually is an efficient way to optimize the transport in the perovskite layer and thereby to achieve enhanced device performance. Here, a solution‐based strategy is proposed to fabricate lateral bulk heterojunction (BHJ) by arranging methylammonium‐based and formamidinium‐based perovskites alternately in an ordered array with controllable domains. The structure of perovskite heterodomain directs charge carrier transport along the film normal and limits in‐plane charge carrier diffusion. Moreover, the ordered perovskite array is found to greatly increase light harvesting. Consequently, the self‐powered photodetector based on the perovskite heterodomain with a thickness of only 250 nm achieves a specific detectivity exceeding 1 × 1014 Jones for weak light over the whole visible light spectrum. This work provides guidance toward the fabrication of perovskite lateral BHJ using solution processing, meeting the requirements not only for charge‐carrier manipulation but also for light management.

Cellulose-based biomass composite films for plastic replacement: Synergistic UV shielding, antibacterial and antioxidant properties

With the gradual increase in environmental awareness and the growing demand for food safety, sustainable and environmentally friendly cellulose-based materials have become a promising alternative to petroleum-based plastics. However, in practice, packaging materials prepared from cellulose-based materials still have some unsatisfactory properties, such as monofunctionality, low transparency, and lack of UV shielding, antibacterial or antioxidant properties. Herein, a novel synthetic strategy is proposed in this paper, specifically, tannic acid (TA), a green natural extract with antibacterial and antioxidant properties, is used as a plasticizer and cross-linker, and oxidized cellulose nanocellulose (TOCN) modified with folic acid (FA) grafting is blended with TA, and cellulose-based biomass thin films with ultraviolet (UV) shielding, antibacterial, and antioxidant properties have been successfully prepared by using a simple vacuum-assisted filtration. The experimental results showed that the films could completely block ultraviolet light at wavelengths of 200–400 nm while providing 81.47 % transparency in the visible spectrum, while the introduction of TA conferred excellent antibacterial and antioxidant capabilities with antioxidant activity of up to 95 %, and also resulted in films with excellent mechanical properties. Therefore, this work provides ideas for the design and manufacture of competitive biomass green packaging materials, laying the foundation for future applications in food packaging.

Enhancing secret key distribution through advanced color modulation in visible light communication

Visible light communication (VLC) has emerged as a dynamic area of research poised to revolutionize high-speed wireless communication. VLC technology uses light-emitting diodes (LEDs) within existing infrastructure to emit light within the visible spectrum. VLC complements traditional radio frequency (RF) communications, addressing its inherent limitations and drawbacks. To navigate the demands of modern urban environments, VLC systems must prioritize secure data transmission, accessibility, and economic feasibility, particularly within the framework of smart cities. We introduce what is to our knowledge a novel privacy-enhanced VLC system for optical wireless communication. Leveraging color data modulation techniques and the intricacies of a hyperchaotic three-dimensional map, this innovative approach ensures robust security. By employing diverse LED colors for data transmission and exploiting the unpredictable mathematical properties of hyperchaotic maps, enhanced privacy is achieved. The performance of the proposed system was rigorously evaluated through various tests, manipulating initial control parameters of the encryption process with the hyperchaotic map, as well as adjusting message length and content. Tests were conducted over a 1 m connection distance at a symbol transmission rate of 2 baud. Remarkably, the proposed system demonstrated high accuracy in message recovery, achieving a symbol error rate (SER) of only 0.02 at an incident optical power of 22 µW. We highlight the critical importance of precise decryption parameter values in the proposed method, demonstrating the necessity for accuracy within the range of 10−15 for each decryption parameter; it underscores the indispensability of meticulous parameter calibration to ensure the correct decryption of transmitted symbols. These results pave the way for applications where absolute security is imperative, particularly in smart city environments, such as for key distribution purposes.

Effect of hydrogen flow rate on properties of silicon oxycarbide thin films via hot wire chemical vapor deposition

AbstractThis study explores the impact of hydrogen flow as a carrier gas on silicon oxycarbide thin films produced via hot wire chemical vapor deposition (HWCVD) using tetraethyl orthosilicate as a precursor. Systematically varying the hydrogen flow rates, the influence on thin film composition, microstructure, and optical properties is investigated. Employing diverse characterization techniques, such as X‐ray diffraction, field‐emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy, Fourier‐transform infrared (FTIR), X‐ray photoelectron spectroscopy (XPS), ellipsometry, and photoluminescence (PL) spectroscopy, it is revealed that there is a correlation between hydrogen flow rate and thin film elemental composition. Higher hydrogen flow rates result in increased silicon content and reduced contributions of oxygen and carbon. FE‐SEM images show agglomerates with improved homogeneity at higher flow rates. FTIR spectra highlight distinctive vibrational modes, including Si–H bonds. XPS confirms the emergence of Si–H bonds at elevated hydrogen flow rates. Ellipsometry indicates increased thickness and refractive index. PL spectra exhibit a broadband across the visible spectrum, influenced by hydrogen‐related defects and electronic transitions. This study provides findings for optimizing HWCVD parameters to tailor thin films for specific applications, emphasizing the important role of hydrogen flow as a carrier gas.

Novel Octahedral Nickel (II) Complex with Flexible Piperazinyl Moiety Exhibits Potent Cytotoxic Effect Along with Anti-Migratory and Anti-Metastatic Effect on Human Cancer Cells.

Synthesis of non-platinum transition metal complexes with N,O donor chelating ligand for application against cancer with higher efficacy and selectivity is currently an important research field. We assessed The anti-cancer effects of a mixed ligand Ni(II) complex on human breast and lung cancer cell lines in the current investigation. Mononuclear mixed ligand octahedral Ni(II) complex [NiIIL(NO3)(MeOH)] complex(1), with tri-dentate phenol-based ligand 2,4-dichloro-6-((4-methylpiperazin-1-yl)methyl)phenol (HL) along with methanol and nitrate as ancillary ligand was prepared. Piperazine moiety of the ligand exists as boat conformation in this complex as revealed from single crystal X-ray study. UV -visible spectrum of complex (1) exhibits three distinct d-d bands due to spin-allowed 3A2g→3T1g(P), 3A2g→3T1g(F) and 3A2g→3T2g(F) transitions as expected octahedral d8 system. Complex (1) through transactivation of p53 and its pro-apoptotic downstream targets induce apoptotic cell death in mouse and human cancer cells such as mcf-7, A549 and MDA-MB-231 in dose dependent manner. Furthermore, complex (1) was able to slow the migratory rate of MDA-MB-231 cells' in vitro as well as epithelia -mesenchymal transition (EMT), the key step for metastatic transition and malignancy. Over all our results suggest complex (1) as potential agent in anti-tumor treatment regimen both as cytotoxic and anti-metastatic agent against malignant neoplasia.

Synthesis, structure, and mechanism of action of a unique mixed-ligand nickel (II)-complex of tetra-dentate phenol-based ligand with di-aquo co-ligands with significant pro-apoptotic and anti-metastatic effect against malignant human cancer cells

From the discovery of the anticancer activity of “cisplatin”, various type of numerous mononuclear platinum (II) complexes has been evaluated for antitumor activities, though therapeutic use is limited due to side effects and resistance. In this study, A unique mixed ligand mono nuclear octahedral Ni (II) complex [NiL(H2O)2].0·.5H2O (1) [H2L = N,Nʹ-dimethyl-N,Nʹ-bis (2-hydroxy-3,5-di methyl benzyl)-ethylenediamine] with tetra dentate phenol based ligand with N2O2 donor environment along with two labile water molecules was synthesised. The complex (1) is structurally characterized by spectroscopic tools including single-crystal X-ray diffractometer. Complex (1) crystallizes in monoclinic space group P21/n with a = 10.4871(17) Å, b = 20.860 (4) Å and c = 20.955(4) Å. The UV – visible spectra show two peaks around 507 nm and 367 nm due to spin-allowed 1A1g → 1A2g and 1A1g → 1B1g transitions respectively as expected for a square planar d8 system. Mixed ligand octahedral nickel (II) complex with facially coordinating tetra dentate phenol-based ligand (H2L) is in association with two water molecule as ancillary ligand. Two water molecules associated with coordination zone of nickel (II) centre is loosely bound. In this present study, we have evaluated the anti-cancer properties of Complex (1). We found that Complex (1) show potent cancer cell killing activity in case of poorly invasive mice and human cancer cell lines. Complex (1) trigger apoptosis chiefly via p53 dependent pathway. Complex (1) also inhibits cancer cell migration and epithelial to mesenchymal transition in case of metastatic breast cancer cells suggesting potent anti-cancer properties of complex (1).

Ultraviolet-Visible Spectroscopy with All-Dielectric Multi-Foci Dispersive Metalens

Abstract Metasurfaces are a cutting-edge development in optical technology miniaturization, enabling the manipulation of light at a microscopic scale while providing unprecedented control over its intrinsic characteristics, such as amplitude, polarization, and phase. Researchers have been making significant progress in advancing and developing high-efficiency and functionally versatile metasurfaces, aiming to achieve miniaturization and overcoming the technological limitations of conventional components. This article aims to develop a single-layered, highly transmissive all-dielectric multi-foci metalens that serves as a compact spectrometer that can be used for portable investigative measurements within the ultraviolet to the visible spectrum, especially for 290–460 nm band. The proposed metalens can achieve top-notch performance by precisely mapping the wavelength information into subwavelength diffraction-limited focusing spots by accomplishing simultaneous spectral splitting and focusing on the same plane. The proposed metalens consists of an array of intelligently optimized nanoantennas made of a CMOS-compatible silicon nitride material. It exploits a unique phase and wavelength multiplexing strategy to create highly dispersive multi-foci metalens, making it an ideal choice for an ultra
•compact, high-resolution, and dual-band meta-spectrometer. We expect our proposed framework to have numerous applications in the industrial and medical fields, enabling diagnosis, detection, and assessment within a compact platform.

One‐step Synthesis of UV‐Curable CsPbX3 (X = Cl, Br, and I) Nanocrystal Inks for Printing

AbstractMetal halide perovskite nanocrystals (NCs) have garnered significant attention due to their captivating optoelectronic properties. One promising application for these materials is their use as color‐conversion layers (CCLs) in blue micro‐LED technology, enabling the realization of full‐color displays. Nonetheless, a pivotal challenge revolves around producing efficient luminescent perovskite inks and subsequently employing them for inkjet printing finely patterned CCLs. In this study, a straightforward single‐step hot‐injection method is introduced for synthesizing inks comprising CsPbX3 NCs, where X represents Cl, Br, and I, or mixed halide systems such as Cl/Br and Br/I. Through precise composition control, the emission spectra can be effortlessly adjusted across the entire visible spectrum, spanning from 410 to 710 nm. The resulting CsPbX3 NCs exhibit narrow emission line‐widths, ranging from 21 to 39 nm, an expansive color gamut encompassing up to 130% of the National Television Standards Committee color standard, and exceptional quantum yields reaching up to 100%. With their superb optical performance, facile synthesis procedure, and robust stability, these CsPbX3 NCs emerge as highly suitable candidates for their use as CCLs with blue light‐emitting devices deployed as backlights.

Cycloaddition reaction of methylidyne radical with dipyrromethanol: quantum chemical insights into the formation of di(pyridin-2-yl)methanol

Density functional theory was employed to investigate methylidyne radical reaction on to the unsaturation of dipyrromethanol moiety through cycloaddition forming a six membered di(pyridin-2-yl)methanol followed by H-elimination via ring expansion. Time-dependent density functional theory (TD-DFT) simulations were performed to figure out the ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol. Ultraviolet–visible spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that two sharp absorption peaks were obtained at λ max = 161 nm and 206 nm for the reactant dipyrromethanol while a sharp peak was observed for the product di(pyridin-2-yl)methanol at shorter wavelength (λ max = 170 nm). The theoretical IR spectrum of dipyrromethanol and di(pyridin-2-yl)methanol shows that a significant red shift of 129 cm−1 was observed in the case of di(pyridin-2-yl)methanol due to presence of two strong intra-molecular hydrogen bonds, which indicates its higher stability than the dipyrromethanol. HOMO–LUMO energy gap calculations and natural bond orbital (NBO) analysis endorse the type of electronic transition for the desired product di(pyridin-2-yl)methanol is π–π*. The global reactivity analysis shows the electron donor and acceptor nature of dipyrromethanol and methylidyne radical, respectively. A potential energy surface is constructed via methylidyne radical addition, ring expansion, and hydrogen elimination transition states. Thermodynamics study and potential energy surface of the title reaction indicates its highly exothermicity and spontaneous in nature.

Ground- and Space-based Dust Observations of VV 191 Overlapping Galaxy Pair

Ground- and Space-based Dust Observations of VV 191 Overlapping Galaxy Pair

Assessment of the Effect of Surface Modification of Metal Oxides on Silver Nanoparticles: Optical Properties and Potential Toxicity.

Silver nanoparticles (AgNPs) have garnered significant interest due to their distinctive properties and potential applications. Traditional fabrication methods for nanoparticles often involve high-energy physical conditions and the use of toxic solvents. Various green synthesis approaches have been developed to circumvent these issues and produce environmentally benign nanoparticles. Our study focuses on the green synthesis of AgNPs using L-ascorbic acid and explores the modification of their properties to enhance antibacterial and anticancer effects. This is achieved by coating the nanoparticles with Zinc oxide (ZnO) and Silica oxide (SiO2), which alters their optical properties in the visible spectrum. The synthesized formulations-AgNPs, zinc oxide-silver nanoparticles (Ag@ZnO), and silica oxide-silver nanoparticles (Ag@SiO2) core/shell nanoparticles-were characterized using a suite of physicochemical techniques, including Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), Zeta potential measurement, UV-Vis spectroscopy, Refractive Index Measurements, and Optical Anisotropy Assessment. TEM imaging revealed particle sizes of 11 nm for AgNPs, 8 nm for Ag@ZnO, and 400 nm for Ag@SiO2. The Zeta potential values for Ag@ZnO and Ag@SiO2 were measured at -17.0 ± 5 mV and -65.0 ± 8 mV, respectively. UV-Vis absorption spectra were recorded for all formulations in the 320 nm to 600 nm wavelength range. The refractive index of AgNPs at 404.7 nm was 1.34572, with slight shifts observed for Ag@ZnO and Ag@SiO2 to 1.34326 and 1.37378, respectively. The cytotoxicity of the nanocomposites against breast cancer cell lines (MCF-7) was assessed using the MTT assay. The results indicated that AgNPs and Ag@ZnO exhibited potent therapeutic effects, with IC50 values of 494.00 µg/mL and 430.00 µg/mL, respectively, compared to 4247.20 µg/mL for Ag@SiO2. Additionally, the antibacterial efficacy of AgNPs was significantly enhanced under visible light irradiation. Ag@ZnO demonstrated substantial antibacterial activity both with and without light exposure, while the Ag@SiO2 nanocomposites significantly reduced the inherent antibacterial activity of silver. Conversely, the Ag@ZnO nanocomposites displayed pronounced antibacterial and anticancer activities. The findings suggest that silver-based nanocomposites, particularly Ag@ZnO, could be practical tools in water treatment and the pharmaceutical industry due to their enhanced therapeutic properties.

Dual Role of a Novel heteroleptic Cu(I) Complex in Visible-Light-Driven CO2Reduction.

A novel mononuclear Cu(I) complex was synthesized via coordination with a benzoquinoxalin-2'-one-1,2,3-triazole chelating diimine and the bis[(2-diphenylphosphino)phenyl] ether (DPEPhos), to target a new and efficient photosensitizer for photocatalytic CO2 reduction. The Cu(I) complex absorbs in the blue-green region of the visible spectrum, with a broad band having a maximum at 475 nm (ε = 4500 M-1cm-1), which is assigned to the metal-to-ligand charge transfer (MLCT) transition from the Cu(I) to the benzoquinoxalin-2'-one moiety of the diimine. Surprisingly, photo-driven experiments for the CO2 reduction showed that this complex can undergo a photoinduced electron transfer with a sacrificial electron donor and accumulate electrons on the diimine backbone. Photo-driven experiments in a CO2 atmosphere revealed that this complex can not only act as a photosensitizer, when combined with an Fe(III)-porphyrin, but can also selectively produce CO from CO2. Thus, owing to its charge-accumulation properties, the non-innocent benzoquinoxalin-2-one based ligand enabled the development of the first copper(I)-based photocatalyst for CO2 reduction.

Facile hydrothermal synthesis of a multifunctional copper zinc tin sulfide (CZTS) nanoparticle-coated sepiolite fiber composite: structural characterization and photocatalytic properties

This work presents a facile hydrothermal synthesis method for fabricating a multifunctional composite of copper zinc tin sulfide (CZTS) nanoparticles coated onto sepiolite fibers. Morphological analysis confirms the firm attachment of approximately 10 nm CZTS nanoparticles onto the sepiolite surface. Elemental analysis verifies the presence of constituent elements from both CZTS and sepiolite, with a slight deficiency in Cu and an abundance of Zn observed. The compositional formula of CZTS in the composite is estimated as Cu1.93Zn1.05Sn0.98S4.04. Notably, the material exhibits a narrow band gap of 1.5 eV, enabling effective utilization of the entire visible light spectrum, making it promising for photocatalytic applications. BET nitrogen adsorption/desorption measurements reveal a substantial surface area of approximately 85.720 m2 /g, confirming the composite’s versatility and applicability, particularly in photocatalysis and adsorption processes. Additionally, X-ray diffraction analysis indicates reflections consistent with the crystal structures of kasterite CZTS and sepiolite, further confirming the composite’s composition. The multifunctional CZTS/Sepiolite composite demonstrates exceptional potential for simultaneous photocatalytic degradation and adsorption of organic pollutants, presenting a promising avenue for sustainable water treatment applications.

Unveiling the enhanced optical limiting of polyaniline – Fullerene composite investigated by z-scan

The reverse saturable absorption (RSA) and optical limiting (OL) mechanisms of polyaniline (PANI) and fullerene doped PANI (PANI-C60) solutions were investigated by open-aperture z-scan studies, using a nanosecond pulsed Nd:YAG laser operating at 532 nm wavelength as the excitation source. The nonlinear absorption coefficient (β), OL threshold, and imaginary part of nonlinear susceptibility (χi(3)) of PANI and PANI-C60 solutions were determined for three different laser input pulse energies and are found to be in the order of 10−9 cm/W, 106 W/cm2, and 10−10 esu respectively. The results showed enhanced OL efficiency for the PANI-C60 solution, making it a promising candidate for applications in optoelectronics and optical limiting. The transmission electron microscope (TEM) images revealed the uniform distribution of C60 of particle size in the range of 5–10 nm in the PANI matrix. The composite formation of PANI-C60 was confirmed by Fourier transform infrared spectroscopy (FTIR). The presence of C60 and its charge transfer complex (CTC) formation with PANI are responsible for the enhanced OL efficiency. The linear refractive index values were measured using UV–Visible absorption spectra and compared with the theoretical values. The investigation of the OL mechanism and the calculation of its associated NLO parameters for PANI and PANI-C60 solutions are reported for the first time.

Phytosynthesis and characterization of tin-oxide nanoparticles (SnO2-NPs) from Croton macrostachyus leaf extract and its application under visible light photocatalytic activities

Nanotechnology is rapidly becoming more and more important in today's technological world as the need for industry increases with human well-being. In this study, we synthesized SnO2 nanoparticles (NPs) using an environmentally friendly method or green method from Croton macrostachyus leaf extract, leading to the transformation of UV absorbance to visible absorbance by reducing the band gap energy. The products underwent UV, FTIR, XRD, SEM, EDX, XPS, BET, and DLS for characterization. Characterization via UV–Vis spectroscopy confirmed the shift in absorbance towards the visible spectrum, indicating the potential for enhanced photocatalytic activity under visible light irradiation. The energy band gap for as-synthesized nanoparticles was 3.03 eV, 2.71 eV, 2.61 eV, and 2.41 eV for the 1:1, 1:2, 1:3, and 1:4 sample ratios, respectively. The average crystal size of 32.18 nm and very fine flakes with tiny agglomerate structures of nanoparticles was obtained. The photocatalytic activity of the green-synthesized SnO2 nanoparticles was explored under visible light irradiation for the degradation of rhodamine B (RhB) and methylene blue (MB), which were widespread fabric pollutants. It was finally confirmed that the prepared NPs were actively used for photocatalytic degradation. Our results suggest the promising application of these green-synthesized SnO2 NPs as efficient photocatalysts for environmental remediation with low energy consumption compared to other light-driven processes. The radical scavenging experiment proved that hydroxyl radicals (_OH) are the predominant species in the reaction kinetics of both pollutant dyes under visible light degradation.

Recent Progress in Metasurfaces: An Introductory Note from Fundamentals and Design Methods to Applications

Metasurfaces refer to the sub-wavelength nanostructures that are capable of manipulating the amplitude, phase, polarization, and other characteristics of light, to enable diverse applications across the ultraviolet, visible, infrared, and terahertz spectra. In this review paper, we aim to provide an introductory note on metasurfaces, from fundamentals and design methods to applications, such as biosensing, environmental monitoring, metalenses, optical cloaking, electromagnetic scattering, structural color, miniaturized devices, and others. Moreover, we also identify the key challenges and limitations of metasurfaces, such as fabrication, integration, optimization, tuning, signal processing, and analysis, and suggest possible directions and solutions for future research. At last, we envision several emerging and promising trends for metasurfaces, such as new materials and structures, new phenomena and mechanisms, machine learning, and artificial intelligence techniques. The review is expected to inspire future development in this exciting and rapidly evolving field of metasurface devices.

E-beam synthesized fast-switching TiO2/SnO2 type-II heterostructure photodetector

A fast-switching TiO2/SnO2 heterostructure thin-film (TF) photodetector synthesized by electron beam evaporation technique is analyzed in this study. The substrate utilized is n-type silicon (Si), while gold (Au) is employed as the top electrode. To assess sample morphology and confirm elemental composition, field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDS), and chemical mapping were conducted. Structural characteristics were determined using X-ray diffraction (XRD) analysis. The XRD analysis confirmed the presence of various phases of TiO2 (anatase and rutile) and SnO2 (rutile). UV-Vis spectroscopy revealed multiple absorption peaks, at 447 nm, 495 nm, 560 nm, and 673 nm, within the visible spectrum. The device demonstrates high detectivity (D∗) of 1.737×109 Jones and a low noise equivalent power (NEP) of 0.765×10−10W. Evaluation of the device’s switching response through current-time characteristic (I-T) analysis indicates rapid switching with a rise time and fall time of 0.33 s and 0.36 s, respectively.

Screen-Printed Metamaterial Absorber Using Fractal Metal Mesh for Optical Transparency and Flexibility

In stealth applications, there is a growing emphasis on the development of radar-absorbing structures that are efficient, flexible, and optically transparent. This study proposes a screen-printed metamaterial absorber (MMA) on polyethylene terephthalate (PET) substrates using indium tin oxide (ITO) as the grounding layer, which achieves both optical transparency and flexibility. These materials and methods enhance the overall flexibility and transparency of MMA. To address the limited transparency caused by the silver nanoparticle ink for the top pattern, a metal mesh was incorporated to reduce the area ratio of the printed patterns, thereby enhancing transparency. By incrementing the fractal order of the structure, we optimized the operating frequency to target the X-band, which is most commonly used in radar detection. The proposed MMA demonstrates remarkable performance, with a measured absorption of 91.99% at 8.85 GHz and an average optical transmittance of 46.70% across the visible light spectrum (450 to 700 nm), indicating its potential for applications in transparent windows or drone stealth.

Chromatic light therapy for inhibiting myopia progression: human studies

Myopia, a common refractive error, has been associated with various risk factors, with outdoor time emerging as a significant protective factor against its onset. This association is believed to be mediated by the influence of sunlight on dopamine release, a neurotransmitter crucial for regulating eye growth. Recent research explores the specific properties of light to identify potential interventions for myopia control in children. Low-level red light therapy has gained attention, showing promise in inhibiting myopia progression, although with concerns regarding safety and rebound effects. Similarly, blue light stimulation aims to upregulate retinal dopamine activity, yet conclusive evidence supporting its efficacy is lacking. Moreover, researchers explore the use of the entire visible light spectrum by digitally imposing longitudinal chromatic aberration to adjust proper eye growth. Preliminary findings suggest that digitally simulated chromatic aberration could potentially serve as a myopia control strategy, highlighting the need for further investigation into its long-term effects. As research progresses, understanding the efficacy and safety of light-based interventions for myopia control remains crucial for informing clinical practice and optimizing patient outcomes.