Visible Light Research Articles

Quasi‐Bound States in the Continuum on Dislocated Bilayer Metal Gratings for Spatiotemporal Vortex Pulse Generation

AbstractSpatiotemporal vortex pulses (STVPs) with transverse orbital angular momentum (OAM) have recently stimulated great interest, influencing wide disciplines from classical to quantum optics. However, generating sophisticated STVPs in high‐efficiency and compact systems remains a challenge. This work outlines an ultra‐compact metasurface approach to efficiently generate STVPs through the coupling of free‐space plane waves with a quasi‐bound state in the continuum (quasi‐BIC). The approach leverages external excitation of the quasi‐BIC at the Γ‐point by slightly dislocating two sub‐layer gratings to break the mirror symmetries. This operation converts the incident wave into a unidirectional surface mode and induces a Fano resonance, resulting in STVPs in the frequency‐momentum domain. The method is demonstrated experimentally with a meta‐grating to produce an electromagnetic (EM) STVP with a topological charge of l = −1 with high fidelity and use the set‐up to unravel the hitherto unexplored diffraction and dispersive properties of near‐field STVPs. The present work can be extended from the microwave to the visible light regime by simply scaling the metasurface, and allowing high‐order OAM generation through cascaded elements, thereby paving a robust way to build up ultra‐compact STVP multiplexing devices for future applications.

Engineering the electron localization of metal sites on nanosheets assembled periodic macropores for CO2 photoreduction

Photocatalytic conversion of CO2 into syngas is highly appealing, yet still suffers from the undesirable product yield due to the sluggish carrier transfer and the uncontrollable affinity between catalytic sites and intermediates. Here we report the fabrication of Co sites with tunable electron localization capability on two dimensional (2D) nanosheets assembled three dimensional (3D) ordered macroporous framework (3DOM-NS). The as-prepared Co-based 3DOM-NS catalysts exhibit attractive photocatalytic performances toward CO2 reduction, among which the cobalt sulfide one (3DOM Co-SNS) shows the highest syngas generation rate up to 347.3 μmol h−1 under the irradiation of visible light and delivers a remarkable catalytic activity (1150.7 μmol h−1) in a flow reaction system under natural sunlight. Mechanism studies reveal that the high electron localization of metal sites in 3DOM Co-SNS strengthens the interaction between Co and HCOO* via the orbital interactions of dyz/dxz-p and s-s, thus facilitating the cleaving process of C-O bond. Additionally, the ordered macroporous framework with nanosheet subunits elevates the transfer efficiency of photoexcited electrons, which contributes to its high activity.

Synergistic Strategy toward Enhancing Photosynthesizing Reactive Oxygen Species of Covalent Organic Frameworks

AbstractPhotocatalytic reactive oxygen species (ROSs) plays an important role in photodynamic therapy and photochemical reactions. However, most reported photocatalysts suffer from insufficient utilization of visible light and low conversion of O2, which requires the development of higher performance catalysts toward practical applications. Herein, a series of porphyrin‐based COFs have been prepared. Comparative experimental and theoretical studies have revealed that the synergistic interaction between the two building blocks can significantly enhance the yields of ROSs by independently accomplishing photon harvesting and oxygen capture with smooth energy transfer between them. Particularly, the 1O2 yield of 3P‐Por‐COF is increased to 1.3 and 3.4 times that of the classical PCN‐224 and porphyrin molecular aggregates. Furthermore, the TOF of 3P‐Por‐COF is as high as 271 h−1 with ≈100% selectivity under red light irradiation in catalyzing thioanisole to methyl phenyl sulfoxide. The conversion and stability of degradation of toluene gas under natural light are also superior to the conventional Fenton catalytic system. The present results should contribute to the design of high‐performance frameworks‐based photocatalysts for ROSs production.

An innovative fabrication of g-C3N4-ZrO2 nanocomposite with enhanced photocatalytic degradation of methylene blue under UV–visible light

An innovative fabrication of g-C3N4-ZrO2 nanocomposite with enhanced photocatalytic degradation of methylene blue under UV–visible light

Sensing of gas mixtures via nonlinear interferometry

Abstract We demonstrate the use of a nonlinear interferometer with bulk lithium niobate crystal for sensing of gas mixtures over broadband mid-infrared (mid-IR) range of wavelengths. Our method utilizes spontaneous parametric down-conversion to generate correlated photon pairs in the visible and mid-IR ranges. We show that by leveraging the phase-matching properties of lithium niobate crystal, it is possible to access the ‘fingerprint’ region of greenhouse gases in the mid-IR range by detection of correlated visible light signal. Our technique enables simultaneous detection of gas mixtures with high spectral resolution and fast readout without the need for specialized mid-IR equipment. The experimental results show its applicability to molecular gas sensing, paving the way for new advancements in environmental monitoring.

Induced Charge Compensation effect for Boosting Photocatalytic Water Splitting in Covalent Organic Frameworks

Imine‐based covalent organic frameworks (COFs) are promising for photocatalytic water splitting, but their performance is often constrained by inefficient charge separation due to the high electron localization nature of polar imine bonds. In this study, we have optimized the electron delocalization across the imine linkage within a COF by implementing a charge compensation effect. This effect is achieved when a strong electron‐donating thieno[3,2‐b]thiophene linker is directly attached to the iminic carbon of a zinc‐porphyrinic COF. This modification significantly reduces the electron binding effect within the imine bonds of the COF, facilitating both in‐plane charge separation and out‐plane charge transfer to the catalytic site. Conversely, the use of strong electron‐withdrawing pyrizine linker aggravates the electron localization at the imine linkage in the ZnP‐Pz variant. Consequently, ZnP‐Tt shows a substantially improved photocatalytic water‐splitting activity under visible light irradiation, with a hydrogen evolution of 44288 ± 2280 μmol g–1 in 4 h, which exceeds the ZnP‐Pz counterpart by a factor of 10. These results offer fresh perspectives for the design of imine‐based COFs to overcome their limitations in charge separation efficiency.

Enhanced Visible-Light Photocatalysis Activity of TiO2/Ag Nanocomposites Prepared by the Ultrasound-Assisted Sol–Gel Method: Characterization and Degradation–Mineralization of Cationic and Anionic Dyes

Coupling TiO2 with various elements could enhance its photocatalytic activity. In this study, an innovative ultrasound-assisted sol–gel method was used to synthesize TiO2/Ag(x%) by varying Ag–support mass (x = 9.3, 17.1, and 23.6%), followed by calcination at 450 °C for 30 min. The aim was to demonstrate that Ag compositing improves photoactivity under visible light (>400 nm). The synthesized photocatalysts were assessed for their effectiveness in the degradation and mineralization of Methylene Blue (MB) and Acid Orange 7 (AO7) using visible lamps emitting in the range of 400–800 nm. Characterization of the prepared photocatalysts was performed by using Raman spectroscopy, SEM/EDS, pHpzc, and UV–visible spectroscopy. Raman spectroscopy confirmed the predominance of the anatase phase in all the photocatalysts. The photodegradation efficiencies of the selected dyes, MB and AO7, reached 99% (pH 6) and 95% (pH 3) after 180 min of irradiation, respectively. The best performance for the degradation of the two dyes was observed with TiO2/Ag9.3%, showing optimal kinetics at this doping concentration. The improved photoactivity of the TiO2/Ag composite is due to a decrease in the recombination rate of electron/hole (e−/h+) and a decrease in the band gap from 3.13 to 2.49 eV. The mineralization rate of both dyes under visible light is about 9.3%, indicating the presence of refractory by-products that resist complete degradation. Under UVA irradiation, complete mineralization is obtained. This study confirms the potential of TiO2/Ag composite as a high-performance and cost-effective photocatalyst for solar environmental remediation, highlighting the role of silver in extending light absorption into the visible region and improving charge separation.

Recent Developments in Applications of G-CuO Nanocomposites for Photocatalytic Dye Removal

Abstract The extensive application of synthetic dyes across industries poses significant environmental challenges, particularly concerning water quality degradation. Regarding the possible solutions, copper oxide (CuO) stands out as a feasible candidate. Being a p-type Nano-heterogeneous semiconductor with a bandgap of 1.2–2.71 eV, CuO is a reasonable choice and widely studied photocatalyst for addressing such challenges. When the wavelength exceeded the UV-visible region, its functionality showed deterioration. At the same time, there are difficulties associated with reproducibility and reusability, as well as rapid electron-hole recombination, which prevent the widespread application of this technology within this spectral range. In an attempt to eliminate this defect, researchers have been investigating strategies to activate CuO under visible light, with one promising approach being carbon nanomaterials such as graphene to form carbon-CuO composites. The unique properties of graphene, i.e., its large surface area and excellent electron mobility, make it a remarkable candidate for the enhancement of CuO photoactivity. This study highlighted the recent progress in the synthesis of graphene-based CuO photocatalysts, with the main characteristic of extending the light absorption capacity of CuO into the visible spectrum. It reveals achievements in material innovations and applications, with a focus on photocatalytic dye degradation. These breakthroughs are a sign that the field is growing in popularity and is evolving.

Chemoselective Anaerobic Dehydrogenation of Alcohols By Using Visible Light and a Positively Charged Deazaflavin Catalyst Regenerated by Acetonitrile Solvent

Three series of novel deazaflavinum salts differing in their substitutions at positions 5 (R = H, phenyl or mesityl), 7 and 8 (R = OMe, Me, H or Cl) were synthesized as potential catalysts of a novel chemoselective visible light–mediated anaerobic oxidation of primary and secondary alcohols to carbonyl compounds. This mild procedure uses acetonitrile as a solvent, which acts simultaneously as a sacrificial electron acceptor (in place of the oxygen usually used in photooxidation reactions) and therefore the reaction does not need any additives. Structural and properties‐versus‐catalytic activity studies identified 5‐mesityl‐7,8‐dimethoxy‐3‐methyldeazaflavinium chloride (3a‐Cl) as the most potent catalyst. 3a‐Cl was effective in non‐deuterated acetonitrile (CH3CN), unlike its original 5‐phenyl analogue 2a‐Cl, which is efficient only in deuterated solvent (CD3CN). This difference arises because the regeneration of the 2a‐Cl catalyst is slower in CH3CN than in CD3CN. Our method using the optimized 3a‐Cl photocatalyst and CH3CN as a sacrificial oxidant and solvent in one is a useful addition to synthetic organic chemistry. Anaerobic conditions prevent side oxygenation reactions and overoxidations that usually occur in air or oxygen. This property makes this method suitable for dehydrogenations of alcohols that possess additional group(s) sensitive to oxygenation.

Low-valence platinum single atoms in sulfur-containing covalent organic frameworks for photocatalytic hydrogen evolution

This study focuses on optimizing catalytic activity in photocatalytic hydrogen evolution reaction by precisely designing and modulating the electronic structure of metal single atoms. The catalyst, denoted as PtSA@S-TFPT, integrates low-valence platinum single atoms into sulfur-containing covalent organic frameworks. The robust asymmetric four-coordination between sulfur and platinum within the framework enables a high platinum loading of 12.1 wt%, resulting in efficient photocatalytic hydrogen production activity of 11.4 mmol g−1 h−1 and stable performance under visible light. These outcomes are attributed to a reduced hydrogen desorption barrier and enhanced photogenerated charge separation, as indicated by density functional theory calculations and dynamic carrier analysis. This work challenges traditional notions and opens an avenue for developing low-valence metal single atom-loaded covalent organic framework catalysts to advance photocatalytic hydrogen evolution.

Photostimulated Ultraviolet Luminescence for Anti‐Counterfeiting in Daylight Conditions

AbstractPhotostimulated luminescence in the ultraviolet (PSL‐UV) holds promise for high‐security anti‐counterfeiting applications, especially in brightly lit environments. Despite its potential, research on PSL‐UV is relatively limited. Here, the PSL‐UV properties of a NaYF4:Gd3+ fluoride‐based phosphor is explored, demonstrating its suitability for advanced anti‐counterfeiting purposes. This phosphor effectively captures excitation energy from X‐rays and subsequently emits UV light at 311 nm when stimulated by visible ambient light. Remarkably, the material exhibits exceptional reliability and durability, maintaining effectual PSL‐UV output even after enduring exposure to 100 cycles of ambient light and subsequent decay. Furthermore, ultraviolet imaging experiments highlight the practicality of PSL‐UV for real‐world implementation, presenting a fresh and robust strategy for enhancing security and authentication processes.

Mn-doped SrTiO3 perovskite: Synthesis and characterisation of a visible light-active semiconductor

This study focuses on the synthesis and characterisation of Mn-doped SrTiO3 using the citric method. As-prepared samples featured a non-porous microstructure with a mean particle size of approximately 5 μm, composed of sintered submicron crystallites. Manganese was successfully incorporated into the perovskite structure as Mn4+, with a homogeneous distribution across the Sr and Ti positions. The doping induced a distinctive dark brown hue, indicating significant visible light absorption. A pronounced band gap shift from 3.32 to 2.92 eV was revealed via Tauc analysis of the Kubelka-Munk function. Both the SrTiO3 and Mn-doped SrTiO3 samples demonstrated a high adsorption capacity exclusively for cationic dye (Methylene Blue) at pH 10, with the Mn-doped sample showing slightly enhanced removal efficiency, reaching a maximum adsorption capacity of 310.7 mg g−1. The selective adsorption at high pH can be attributed to electrostatic interactions between the perovskite surface and MB molecules. This combination of high adsorption capacity and a reduced band gap highlights the material’s potential for photocatalysis applications.

Degradation Pattern of a Biodegradable and Photocurable Sealants Based on Hyaluronic Acid : A Serial Magnetic Resonance Imaging Observational Study in Rat Craniectomy Model.

The aim of this study is evaluating in vivo degradation of photocrosslinkable hyaluronic acid (HA)-based dural sealant (HA photosealant) using magnetic resonance imaging (MRI) and histopathological analysis to assess its biodegradability and effectiveness in preventing cerebrospinal fluid (CSF) leakage. HA photosealants were applied to the incised dura in a rat craniectomy and durotomy. The HA photosealant quickly seal the wound upon low-energy visible light exposure (405 nm, < 5 s, < 1 J/cm2). The degradation of HA photosealants was tracked through serial MRI scans at 1, 2, and 4 weeks post-application. The remaining area of HA photosealants on the dura was measured using image processing program for volumetric analysis. Additionally, histopathological analyses were performed to evaluate the biocompatibility and effectiveness of the dural repair. The MRI and histopathological analyses showed that the HA photosealants achieved progressive degradation while successfully preventing CSF leakage without any adverse tissue reactions. The residual area of HA photosealants measured at 2 weeks ranged from 41.36% to 94.88%, with an average of 66.57%. At 4 weeks, a more distinct degradation pattern was observed compared to 2 weeks, showing a residual area of 10.28% to 56.12%. The HA photosealants maintained structural integrity until dural regeneration was complete. HA photosealant showed gradual degradation in vivo while maintaining mechanical strength until the dura was repaired for preventing CSF leakage without inflammation and toxicity. HA photosealant has great potentials for clinical application for dural repair with biodegradable properties and biocompatibility.

Realization of partially transmitted titanium/glass windows using a nanosecond pulsed laser

Titanium has been widely used in aerospace, ocean exploration, and other extreme fields because of its superior physical and chemical properties. In some specific fields, it is necessary to process titanium films to control the optical properties. In this study, we designed and fabricated four kinds of titanium-coated BK7 glass windows by using a weak 532 nm nanosecond pulsed laser and then analyzed their effective transmittance with a digital image processing approach. Finally, the actual effective transmittances of all processed samples were measured by utilizing a well-designed optical system. The results show that the total transmittance of the titanium-coated glass windows is from 5.70% to 48.72%. The processed four types of samples might be applied in different application scenes for the resistance of cosmic radiation. Such special windows we obtained in the study are thought to effectively shield cosmic rays and transmit some visible light at the same time. Our works may open up a new path for the realization of special windows used in some fields such as airline, outer space, scientific research stations at high altitude, etc.

Visible Light‐Mediated Radical Decarboxylative Strategies for the Synthesis of Heterocyclic Compounds

AbstractHeterocycles are an important structural motif found in many bioactive compounds, natural products and pharmaceuticals. Heterocycles have been synthesised at large employing conventional methods which are usually associated with limitations such as the need for an external oxidant or reductant, harsh reaction conditions, lower selectivity and its unsustainable nature. To circumvent these drawbacks, visible light photocatalysis has emerged as a milder, energetically efficient and environmentally benign tool in organic synthesis. Visible light‐mediated radical decarboxylation of carboxylic acid and its derivatives has been widely explored to affect a wide range of chemical transformation reactions. Redox‐active NHPI derivatives are easily prepared from carboxylic acids which are inexpensive, non‐toxic and stable finding wide applications across various fields. Further, carboxylic acids are one of the most plentiful and renewable feedstock of our planet. Hence, this review brings forth the current developments in the area of visible light‐mediated decarboxylative strategies employing carboxylic acid and its derivatives for the synthesis of heterocyclic compounds.

Mobility Prediction Algorithms for Handover Management in Heterogeneous LiFi and RF Networks: An Ensemble Approach

Light Fidelity (LiFi) is a communication technology that operates in the Visible Light (VL) region, using light as a medium to enable ultra-high-speed communication. The spectrum occupied by LiFi does not overlap with the Radio Frequency (RF) spectrum. Thus, they can be used in a hybrid manner to enhance the Quality of Service (QoS) for users. However, in a heterogeneous LiFi and RF network, users experience constant handovers due to the small coverage area of the LiFi and their frequent movement. This study proposes an intelligent handover scheme, where the network parameters of the users are used to train four machine learning models, namely an Artificial Neural Network (ANN), an Adaptive Neurofuzzy Inference System (ANFIS), a Support Vector Machine (SVM), and a Regression Tree (RT), to predict the mobility of the users, so that the central network can have a priori mobility information to ensure seamless connectivity. Furthermore, the performance of the standalone models was enhanced by integrating ensemble learning techniques such as the Simple Averaging Ensemble (SAE), Weighted Averaging Ensemble (WAE), and a Meta-Learning Ensemble (MLE). The results show that the ensemble algorithms improved prediction performance, with an average error decrease of 44.40%, 53.53%, and 61.03% for SAE, WAE, and MLE, respectively, which further demonstrated the effectiveness and robustness of using ensemble algorithms to predict user mobility.

Highly effective photocatalytic decomposition of tetracycline and reduction of Cr(VI) under visible light using Ag/polyoxometalate composite nanomaterials prepared by a mild grinding method

Highly effective photocatalytic decomposition of tetracycline and reduction of Cr(VI) under visible light using Ag/polyoxometalate composite nanomaterials prepared by a mild grinding method

Novel SiNWs/MnO2/Ni(OH)2 Heterostructure as Photocatalyst for Efficient Degradation of Rhb Under Visible Light

Novel SiNWs/MnO2/Ni(OH)2 Heterostructure as Photocatalyst for Efficient Degradation of Rhb Under Visible Light

Real-time three-dimensional monitoring and analysis of perovskite solar cell using short wavelength infrared digital holography

The quality and crystallization process of all-inorganic perovskite films play a crucial role in the performance of solar cells. However, traditional detection methods lack three-dimensional depth information and real-time capabilities, hindered by strong visible light absorption, posing challenges to research. Here, a simple digital holography technique is proposed that offers real-time, nondestructive, three-dimensional phase imaging with low absorption characteristics in the short-wave infrared range. The use of short-wave infrared reduces the negative impact of visible light and vibrations in the environment on detection accuracy, while being nearly non-absorbing. The proposed method operates at a speed of 15 Hz, combining a lensless vertical structure, holographic reconstruction algorithm, and phase unwrapping algorithm to achieve real-time three-dimensional observation without image distortion and with low noise of the crystallization process of CsPbBr3 perovskite quantum dots (PQDs)/ethylene-vinyl acetate solution, which crystallizes in 39 s. Subsequently, employing minimum bounding rectangle, field stitching, intensity registration, and sub-pixel level calibration algorithms, real-time characterization is performed on the large-sized droplet of polymethyl methacrylate-matrix-encapsulated CsPbBr3 perovskite quantum dots, which has a crystallization time of 1285 s, without being limited by the field of view. Finally, using this system, the surface quality of the film is assessed, revealing fluctuations at the edge and fabrication defects of the perovskite film. Experimental results demonstrate the potential of short-wave infrared digital holography in enhancing the film formation process and quality inspection. By leveraging this technology, advancements in the development of high-performance all-inorganic perovskite solar cells can be fostered, optimizing global energy output.

0-Dimensional/1-dimensional S-scheme Ag2S/BiSI hetero-structured photocatalyst for superb Cr(VI) reduction under full spectrum irradiation

Developing ultraviolet (UV), visible (Vis) and near-infrared (NIR) responsive photocatalysts for Cr(VI) reduction is valuable. Herein, a 0-dimensional/1-dimensional (0D/1D) S-scheme Ag2S/BiSI hetero-structured photocatalyst was successfully synthesized, which displays greatly enhanced Cr(VI) removal activity either under UV, Vis or NIR light irradiation. In-situ characterization technique and theoretical calculation confirm that an internal electric field (IEF), directing from Ag2S to BiSI, exists between the interface, which facilitates the spatial-oriented separation of photoirradiated carriers. Furthermore, the immobilization of Cr2O72− and the transformation from *Cr2O72− to *CrO3H2 on the surface of S-scheme Ag2S/BiSI heterostructure is much more favorable than that on the surface of single Ag2S or BiSI. This work gives a comprehensive insight on the design of full spectrum responsive S-scheme photocatalysts for heavy metal removal.