Broad-spectrum Light Research Articles

Hydrogen incorporation by plasma treatment gives mesoporous black TiO2 thin films with visible photoelectrochemical water oxidation activity

Neutron reflectometry (NR) is used to investigate the role of hydrogen in the visible light absorption and enhanced photoactivity for water oxidation of mesoporous black titania thin films. The cubic mesoporous frameworks of TiO2 thin films are prepared by a surfactant-templated sol-gel method and subsequently treated with hydrogen plasma, an approach hypothesized to capitalize on the high degree of disorder in the material and the high energy of the plasma species to achieve efficient hydrogen doping. UV-vis absorbance spectra indicate broad-spectrum visible light absorption in H2 plasma-treated black TiO2 films, and XPS indicates the generation of reduced Ti3+ in the treated films. The presence of hydrogen in black mesoporous titania (H-TiO2) films is confirmed by the scattering length density (SLD) profiles obtained from neutron reflectometry measurements. The H-TiO2 shows ca. 28 times and 8 times higher photocurrent for photoelectrochemical water oxidation compared to undoped TiO2 films under UV (365 nm) and blue (455 nm) LED irradiation, respectively. These findings provide direct evidence that the dramatic change in visible light absorbance of H-treated black TiO2 is accompanied by significant hydrogen uptake and not just Ti3+ generation or surface disordering.

Enhancing Photocurrent Generation in Photosynthetic Reaction Center-Based Photoelectrochemical Cells with Biomimetic DNA Antenna.

Three- to four-times higher performance of biohybrid photoelectrochemical cells with photosynthetic reaction centers (RC) has been achieved by using a DNA-based biomimetic antenna. Synthetic dyes Cy3 and Cy5 were chosen and strategically placed in the anntena in such a way that they can collect additional light energy in the visible region of the solar spectrum and transfer it to RC through Förster resonance energy transfer (FRET). The antenna, a DNA templated multiple dye system, is attached to each Rhodobacter sphaeroides RC near the primary donor, P, to facilitate the energy transfer process. Excitation with a broad light spectrum (approximating sunlight) triggers a cascade of excitation energy transfer from Cy3 to Cy5 to P, and also directly from Cy5 to P. This additional excitation energy increases the RC absorbance cross-section in the visible and thus the performance of the photoelectrochemical cells. DNA-based biomimetic antennas offer a tunable, modular light-harvesting system for enhancing RC solar coverage and performance for photoelectrochemical cells.

Noble metal-free near-infrared-driven photocatalyst for hydrogen production based on 2D hybrid of black Phosphorus/WS2

Efficient production of H2 from water using solar energy holds tremendous promise for clean energy. The optimal photocatalysts require earth abundant elements for the cost-effective as well as harvesting broad spectrum of solar light, particularly in the near-infrared (NIR) region. Therefore, pathways leading to NIR-driven H2 production activity on noble metal-free photocatalyst are of high scientific and economic interest. Here we report a binary two dimensional (2D) hybrid of black phosphorus (BP) and WS2 as noble metal-free NIR-driven photocatalyst for H2 production. Under >780nm NIR light irradiation, substantive H2 productions were observed. Compare to pure BP and WS2, the solid enhancement (21 and 50 folds) of photocatalytic activity was achieved in the BP/WS2 hybrid. The mechanism has been investigated by photoelectrochemical measurements, electron reductive reaction analyses, and transient absorption spectroscopy. It is indicated that 2D BP/WS2 hybrid has great potential as a noble metal-free NIR-driven photocatalyst for solar energy conversion.

Novel ternary photocatalyst of single atom-dispersed silver and carbon quantum dots co-loaded with ultrathin g-C3N4 for broad spectrum photocatalytic degradation of naproxen

The development of highly efficient photocatalysts with broad spectrum light response is a primary goal in the photocatalysis domain. Here we report on a novel ternary photocatalyst comprised of single atom-dispersed silver and carbon quantum dots, co-loaded with ultrathin g-C3N4 (SDAg-CQDs/UCN), which exhibited a highly enhanced photoresponse and broad-spectrum (UV, visible, and near-infrared light) photocatalytic activity. The content of 1.0wt% of CQDs and 3.0wt% of Ag resulted in a 10-fold higher reaction rate than that of UCN under visible light irradiation. This improved broad-spectrum photocatalytic performance may be attributed to the surface plasmon resonance effect of Ag, up-converted fluorescent properties of CQDs, narrowed energy gap, as well as the electron separation and transfer capacity of both the Ag and CQDs. An electron spin resonance (ESR) technique, and reactive species (RS) scavenging experiments indicated that 1O2 and O2− were the dominant active species involved in the degradation of naproxen (NPX). Product identification and reaction site prediction revealed that the photocatalytic degradation of NPX included decarboxylation, hydroxylation, as well as the opening of the naphthalene ring. Mineralization experiments indicated that NPX and its degradation products would be finally transformed into CO2 and H2O. Reactions in different water matrices indicated that SDAg-CQDs/UCN can be effectively employed for the degradation of NPX under ambient water conditions. Therefore, SDAg-CQDs/UCN offers a new strategy for the broad-spectrum utilization of solar light and provides a promising method for the remediation of water contamination.

Intense Pulsed Light Processing of Perovskite Thin Films

The manufacturing of solar photovoltaic panels has seen dramatic reductions in costs primarily through business innovations to the extent that the industry is quite large. The industry is dominated by a single technology, crystalline solar cells. The implementation of newer technologies that could further reduce costs are very attractive, especially technologies that can be adapted to continuous printing particularly involving polymer film substrate. The perovskite solar cells offers this; however, most of the processing techniques rely on extended thermal process or very exact solvent control. The Intense Pulsed Light (IPL) technology has been shown to rapidly process perovskite thin films and our recent work explores how the technology can open up the processing window. The Intense Pulsed Light technology is well suited to continuous manufacturing platforms such as roll-to-roll due to its very large processing area and rapid processing time scales. The IPL technique delivers high energy pulses of broad spectrum light (UV-Vis-NIR) in a very short duration (ms) over a large processing area (100 cm2). In the past few years, the method has found a number of applications within the flexible electronics industry as printed structures for wire traces, transparent conductors and RFID and is now gaining traction with more complex materials. The most promising opportunity for the IPL within photovoltaics is the application towards the flexible large area roll-to-roll production offered by the solution phase processed perovskites. In this paper we will discuss our work with the IPL and the extremely rapid processing of perovskite thin films using a number of precursor materials. We have shown the process for both the two-step and the single step deposition producing devices that perform as well as the traditional thermal processing at significantly faster speeds. This paper will also discuss the morphological changes that occur during the IPL with an intent to develop a robust process. Data from X-ray diffraction and scanning electron microscopy is used to describe the changes to the films, and current-voltage and electrochemical impedance spectroscopy is used to probe the devices.

Measurement of the Verdet Constant of Polarization-Maintaining Air-Core Photonic Bandgap Fiber.

We propose a method based on the white-light interference technique for measuring the Verdet constant of a polarization-maintaining air-core photonic bandgap fiber (PM-PBF). The experimental results show that the Verdet constant of the PM-PBF is ~3.3 mrad/T/m for the broadband light with a spectral width of ~38 nm and a mean wavelength of ~1550 nm, which is ~124 times less than that of a conventional stress-induced birefringent fibers called PANDA fibers (~0.41 rad/T/m for the same broad-spectrum light). The results indicate that the nonreciprocal error induced by the Faraday effect in a fiber optic gyroscope (FOG) made of the PM-PBF is theoretically ~25 times less than that of a conventional FOG made of the PANDA fiber when other conditions, such as the fiber twist, fiber coil area, and so on, are the same.

Spectroscopic imaging with spectral domain visible light optical coherence microscopy in Alzheimer's disease brain samples.

A visible light spectral domain optical coherence microscopy system was developed. A high axial resolution of 0.88 μm in tissue was achieved using a broad visible light spectrum (425 – 685 nm). Healthy human brain tissue was imaged to quantify the difference between white (WM) and grey matter (GM) in intensity and attenuation. The high axial resolution enables the investigation of amyloid-beta plaques of various sizes in human brain tissue and animal models of Alzheimer’s disease (AD). By performing a spectroscopic analysis of the OCM data, differences in the characteristics for WM, GM, and neuritic amyloid-beta plaques were found. To gain additional contrast, Congo red stained AD brain tissue was investigated. A first effort was made to investigate optically cleared mouse brain tissue to increase the penetration depth and visualize hyperscattering structures in deeper cortical regions.

Light based technologies for microbial inactivation of liquids, bead surfaces and powdered infant formula

This study evaluates the potential of continuous wave Ultraviolet C light (UV-C) and broad-spectrum intense pulsed light (in this study referred to as High Intensity Light Pulses, HILP) for the inactivation of pathogens of public concern in powdered infant formula (PIF) producers. To achieve this goal a sequential set of experiments were performed, firstly in clear liquid media, secondly on the surface of spherical beads under agitation and, finally in PIF. L. innocua was the most sensitive microorganism to both technologies under all conditions studied with reductions exceeding 4 log10 cycles in PIF. In the clear liquid medium, the maximum tolerance to light was observed for C. sakazakii against UV-C light and for B. subtilis spores against HILP, with a fluence of approximately 17 mJ/cm2 required for a 1 log10 cycle inactivation (D value) of each species. In PIF it was possible to inactivate >99% of the vegetative cell populations by HILP with a fluence of 199 mJ/cm2 and of B. subtilis spores by doubling the fluence. By contrast, for UV-C treatments a fluence of 2853 mJ/cm2 was needed for 99.9% reduction of C. sakazakii, which was the most light-resistant microorganism to UV-C. Results here obtained clearly show the potential for light-based interventions to improve PIF microbiological safety.

Heterojunction p-n-p Cu2O/S-TiO2/CuO: Synthesis and application to photocatalytic conversion of CO2 to methane

Photocatalytic conversion of CO2 to fuel is a topic of great current interest. The problem is a challenging one, requiring a photocorrosion-stable, industrially-scalable, broad-spectrum light absorbing semiconductor, the energy bands of which align with the CO/CO2 and H2O/O2 potentials. Herein we report the synthesis of a unique p-n-p heterojunction material architecture, Cu2O/S-doped TiO2 micro-blocks covered with CuO nanowires, using anodization and annealing processes. The photocatalytic material shows excellent performance in the photocatalytic conversion of CO2 and water vapor to methane under AM 1.5G illumination. The heterojunction material architecture exhibits a methane yield of 2.31μmolm−2h−1, a rate approximately ten times higher than TiO2 nanotube array films synthesized using similar anodization conditions. The improved performance of the heterojunctioned material architecture appears due to improved light absorption and efficient separation of the photogenerated charge.

Multiporous Supramolecular Microspheres for Artificial Photosynthesis.

Artificial photosynthesis shows a promising potential for sustainable supply of nutritional ingredients. While most studies focus on the assembly of the light-sensitive chromophores to 1-D architectures in an artificial photosynthesis system, other supramolecular morphologies, especially bioinspired ones, which may have more efficient light-harvesting properties, have been far less studied. Here, MCpP-FF, a bioinspired building block fabricated by conjugating porphyrin and diphenylalanine, was designed to self-assemble into nanofibers-based multiporous microspheres. The highly organized aromatic moieties result in extensive excitation red-shifts and notable electron transfer, thus leading to a remarkable attenuated fluorescence decay and broad-spectrum light sensitivity of the microspheres. Moreover, the enhanced photoelectron production and transfer capability of the microspheres are demonstrated, making them ideal candidates for sunlight-sensitive antennas in artificial photosynthesis. These properties induce a high turnover frequency of NADH, which can be used to produce bioproducts in biocatalytic reactions. In addition, the direct electron transfer makes external mediators unnecessary, and the insolubility of the microspheres in water allows their easy retrieval for sustainable applications. Our findings demonstrate an alternative to design new platforms for artificial photosynthesis, as well as a new type of bioinspired, supramolecular multiporous materials.

Light- and circadian-controlled genes respond to a broad light spectrum in Puffer Fish-derived Fugu eye cells

Some cell lines retain intrinsic phototransduction pathways to control the expression of light-regulated genes such as the circadian clock gene. Here we investigated the photosensitivity of a Fugu eye, a cell line established from the eye of Takifugu rubripes, to examine whether such a photosensitive nature is present. Microarray analysis identified 15 genes that showed blue light-dependent change at the transcript level. We investigated temporal profiles of the light-induced genes, as well as Cry and Per, under light-dark, constant light (LL), and constant dark (DD) conditions by quantitative RT-PCR. Transcript levels of Per1a and Per3 genes showed circadian rhythmic changes under both LL and DD conditions, while those of Cry genes were controlled by light. All genes examined, including DNA-damage response genes and photolyase genes, were upregulated not only by blue light but also green and red light, implying the contribution of multiple photopigments. The present study is the first to identify a photosensitive clock cell line originating from a marine fish. These findings may help to characterize the molecular mechanisms underlying photic synchronization of the physiological states of fishes to not only daily light-dark cycles but also to various marine environmental cycles such as the lunar or semi-lunar cycle.

Observation of whispering gallery modes through electron beam-induced deposition.

Surprisingly intense spectra of whispering gallery modes were observed in polymer microbeads after illumination with electrons in a scanning electron microscope and subsequent laser illumination and spectral analysis. It will be proposed that whispering gallery mode resonances became visible after local deposition of hydrocarbon material through electron beam-induced deposition. The illumination of deposited material with a near infrared laser generates a broad light spectrum, acting as a local "white light" source that couples, for favorable wavelengths, with the WGM sustained by the sphere. This facilitates a spectroscopic analysis of the WGM and provides the Q-factor and free spectral range for all investigated particles. The analysis by an integrated SEM and Raman micro-spectrometer offers a direct approach to the analysis of WGM resonators as they are, for instance, used in sensing.

UV-visible broad spectrum light emitting device of ZnO/MgO/ITO structure

Xenon gas and mercury vapor based broad spectrum light sources have wide application, however, are hard to compact. On the contrary, LEDs are easy for compaction, but are hard to emit a broad spectrum. In this work, we demonstrate a simple phosphor free LED structure of ZnO/MgO/ITO, of which the spectrum covers the range from 300 to 650nm. The device was fabricated on commercially available ITO substrate, and the ZnO/MgO structure was successively grown by MOCVD method, of which the morphology, crystallinity and optical quality were characterized. A thin MgZnO layer with graded composition is believed to form through the miscibility of MgO and ZnO during the initial growth stage of ZnO. The active region of the device includes the thin MgZnO layer and part of the subsequent grown ZnO layer. The light with wavelength shorter than ~360nm is attributed to the near band edge emission of the MgZnO layer. And the near band edge emission and deep level emissions of ZnO contribute to the spectrum from ~360 to 650nm. The working mechanism of the device is discussed mainly based on the energy band diagram.

Metallic binary alloyed superconductors for photogenerating current from dissociated water molecules using broad light spectra

The production of hydrogen through water splitting via photocatalysis seems to be a promising and appealing pathway for clean energy conversion and storage. Here, we report for the first time that a series of metallic binary alloyed superconductors (MgB2, AlB2, NbB2, and NbSe2) can be used as a photoanode and a cathode in a photocatalyst composite for both hydrogen production and water oxidation reactions. It was found that the highly active ion binary metal-based photocatalyst can be used as a low-cost alternative to Pt for water photolysis. The metallic binary alloyed superconductors exhibit high activity toward both the oxygen and hydrogen evolution reactions in pure distil water and seawater. The combination of the two such photoanode and cathode yields a water splitting photocurrent density of around 1 mA/cm2, corresponding to a solar-to-photocurrent efficiency of 34%. The strong correlation between the superconductive temperature and the photocatalytic water splitting effectivity for investigated diborides has been revealed.

Surface Treatment of Broad-Spectrum Ultraviolet Light Shielding Titania/Zinc Oxide Composites and Their Applications in Sunscreens

Surface Treatment of Broad-Spectrum Ultraviolet Light Shielding Titania/Zinc Oxide Composites and Their Applications in Sunscreens

An RNA-Seq Analysis of Grape Plantlets Grown in vitro Reveals Different Responses to Blue, Green, Red LED Light, and White Fluorescent Light

Using an RNA sequencing (RNA-seq) approach, we analyzed the differentially expressed genes (DEGs) and physiological behaviors of “Manicure Finger” grape plantlets grown in vitro under white, blue, green, and red light. A total of 670, 1601, and 746 DEGs were identified in plants exposed to blue, green, and red light, respectively, compared to the control (white light). By comparing the gene expression patterns with the growth and physiological responses of the grape plantlets, we were able to link the responses of the plants to light of different spectral wavelengths and the expression of particular sets of genes. Exposure to red and green light primarily triggered responses associated with the shade-avoidance syndrome (SAS), such as enhanced elongation of stems, reduced investment in leaf growth, and decreased chlorophyll levels accompanied by the expression of genes encoding histone H3, auxin repressed protein, xyloglucan endotransglycosylase/hydrolase, the ELIP protein, and microtubule proteins. Furthermore, specific light treatments were associated with the expression of a large number of genes, including those involved in the glucan metabolic pathway and the starch and sucrose metabolic pathways; these genes were up/down-regulated in ways that may explain the increase in the starch, sucrose, and total sugar contents in the plants. Moreover, the enhanced root growth and up-regulation of the expression of defense genes accompanied with SAS after exposure to red and green light may be related to the addition of 30 g/L sucrose to the culture medium of plantlets grown in vitro. In contrast, blue light induced the up-regulation of genes related to microtubules, serine carboxypeptidase, chlorophyll synthesis, and sugar degradation and the down-regulation of auxin-repressed protein as well as a large number of resistance-related genes that may promote leaf growth, improve chlorophyll synthesis and chloroplast development, increase the ratio of chlorophyll a (chla)/chlorophyll b (chlb), and decrease the ratio of carbohydrates to proteins in plants. Although exposure to red and green light seems to impose “shade stress” on the plantlets, growth under blue light is comparable to growth observed under white or broad-spectrum light.

Visible-Light-Driven BiOI-Based Janus Micromotor in Pure Water

Light-driven synthetic micro-/nanomotors have attracted considerable attention due to their potential applications and unique performances such as remote motion control and adjustable velocity. Utilizing harmless and renewable visible light to supply energy for micro-/nanomotors in water represents a great challenge. In view of the outstanding photocatalytic performance of bismuth oxyiodide (BiOI), visible-light-driven BiOI-based Janus micromotors have been developed, which can be activated by a broad spectrum of light, including blue and green light. Such BiOI-based Janus micromotors can be propelled by photocatalytic reactions in pure water under environmentally friendly visible light without the addition of any other chemical fuels. The remote control of photocatalytic propulsion by modulating the power of visible light is characterized by velocity and mean-square displacement analysis of optical video recordings. In addition, the self-electrophoresis mechanism has been confirmed for such visible-light-driven BiOI-based Janus micromotors by demonstrating the effects of various coated layers (e.g., Al2O3, Pt, and Au) on the velocity of motors. The successful demonstration of visible-light-driven Janus micromotors holds a great promise for future biomedical and environmental applications.

Pulsed light and antimicrobial combination treatments for surface decontamination of cheese: Favorable and antagonistic effects

Postprocessing cross-contamination of cheese can lead to both food safety issues and significant losses due to spoilage. Pulsed light (PL) treatment, consisting of short, high-energy, broad-spectrum light pulses, has been proven effective in reducing the microbial load on cheese surface. As PL treatment effectiveness is limited by light-cheese interactions, the possibility to improve its effectiveness by combining it with the antimicrobial nisin was explored. The effect of natamycin, which is added to cheeses as an antifungal agent, on PL effectiveness was also investigated. Pseudomonas fluorescens, Escherichia coli ATCC 25922, and Listeria innocua were used as challenge microorganisms. Bacterial cultures in stationary growth phase were diluted to initial inoculum levels of 5 or 7 log cfu per cheese slice. Slices of sharp white Cheddar cheese and white American singles were cut in rectangles of 2.5 × 5 cm. For cheese slices receiving antimicrobial treatment before PL, slices were dipped in natamycin or nisin, spot inoculated with 100 μL of bacterial suspension, and then treated with PL. Cheese slices receiving PL treatment before antimicrobials were spot inoculated, treated with PL, and then treated with antimicrobials. The PL fluence levels from 1.02 to 12.29 J/cm2 were used. Survivors were enumerated by standard plate counting or the most probable number technique, as appropriate. All treatments were performed in triplicate, and the data were analyzed using a general linear model. Treatment with nisin or natamycin before PL decreased the effectiveness of PL for all bacteria tested. For instance, PL reduced P. fluorescens on Cheddar cheese by 2.19 ± 0.27 log after 6.14 J/cm2, whereas combination treatments at the same PL fluence yielded barely 1 log reduction. Inactivation of L. innocua on Cheddar was only 0.78 ± 0.01 log when using PL after nisin, compared with a 1.30 ± 0.76 log reduction by nisin alone. This was attributed to the absorption of UV light by the 2 antimicrobials, which diminished the UV fluence received by the bacteria. Increased inactivation was obtained when antimicrobials were applied after PL. On process cheese, a maximum reduction of 3.73 ± 0.96 log of L. innocua was obtained at 9.22 J/cm2 for PL followed by nisin, compared with 3.01 ± 0.48 by PL alone. This study demonstrates that antimicrobials may increase the antimicrobial effectiveness of PL on cheese surface, but the order of treatments is critical.

Scalable colloidal synthesis of uniform Bi2S3nanorods as sensitive materials for visible-light photodetectors

A facile colloidal chemistry method is reported for synthesis of uniform Bi2S3 nanorods in a mixed solution of oleylamine with other organic amines including n-dodecylamine (C12), n-octylamine (C8), and n-hexylamine (C6). The nanorod length can be tuned through the carbon-chain length of these amines and importantly multigrams of Bi2S3 nanorods can be readily synthesized in a single scaled-up batch. Current–voltage (I–V) measurements showed that the Bi2S3 nanorods, obtained from both the small and large-scale batches or ones with different chain-length amines, exhibit fast light response characteristics (at the sub-second scale) with an obviously enhanced photocurrent (or photoconductivity) under broad-spectrum white light or monochromatic visible light of different wavelengths. The as-obtained nanorods, as determined by time-dependent current (I–t) curves, also exhibit excellent photoresponsive stability and reproducibility with the on–off switch of light. The photoconductivity enhancement in the Bi2S3 nanorods is assigned to the efficient electron–hole pair separation due to a hole-trapping mechanism. These results indicate the promising potential of Bi2S3 nanorods for optoelectronic device applications including photodetection (sensing), optical switch, photocatalysis, and photovoltaics within the visible spectrum range.

Plasmonic W18O49-photosensitized TiO2 nanosheets with wide-range solar light harvesting

Plasmonic TiO2/W18O49 hybrid nanosheets have been synthesized through an in situ solvothermal growth method. This hybrid catalyst exhibits broad spectrum light harvesting and photocatalytic activity under full-spectrum, UV, visible, and NIR light.