Ultraviolet Light Source Research Articles

LED TECHNOLOGY FOR DRINKING WATER PURIFICATION

Water supply systems are one of the most important life support systems of society. The existing methods of water purification and disinfection are not able to meet modern requirements for the quality of drinking water and do not fully meet the requirements for energy efficiency due to the use of ineffective equipment and technologies. The purpose of this paper is to find effective ways to reduce the effect of harmful organisms in the water on humans by disinfecting it, using light radiation of a certain intensity and spectrum of radiation. The task of the paper is to assess the effect of LED sources of ultraviolet light on harmful organisms in the water and to determine the radiation spectrum that will have the greatest impact on them. According to the results of the study, a mathematical model of the process of radiation exposure to harmful organisms in the water, and the identification of the conditions for the effective use of disinfecting installations were developed. The practical value of the obtained results lies in the possibility of the practical application of LED ultraviolet light emitters for the purification of drinking water at any stage of water preparation and at various levels of water supply.

Design and Application of a Nitrate Measurement System Based on a Narrowband Tunable Ultraviolet Light Source

The nitrate concentration in seawater is an important parameter for marine environment monitoring, which is of great significance for the analysis of seawater ecosystems. In this paper, a novel nitrate measurement system based on a narrowband tunable ultraviolet light source and SVM-based algorithm is proposed and demonstrated. The system is composed of a tunable light source module, an optical fiber splitter, a temperature control module, a spectrometer and a data processing module. By controlling the motorized rotation stage and motorized filter wheel, a continuous and automatic narrowband tunable deep ultraviolet (DUV) light source module is developed. Different seawater samples from Aoshan Bay (Qingdao, China), the Western Pacific, Sanggou Bay (Weihai, China) and the South China Sea with nitrate concentrations from 0 to 102 μmol/L are measured by this system based on a narrowband tunable DUV light source and the results are compared with a broadband DUV light source system. The calculation model is established based on the support vector machine (SVM) algorithm with/without temperature and salinity correction (TSC), and the prediction results are compared with those of the in situ ultraviolet spectrophotometry (ISUS) algorithm. The results show that the method based on a narrowband tunable light source system and the TSC-SVM algorithm has the best performance in predicting the nitrate concentration, with the root mean squared error (RMSE) reduced by 29.16% (from 1.20 to 0.85 μmol/L) compared with the results of the broadband light source system, and the error range is from -3.01 to 2.99 μmol/L. The method proposed in this paper has the potential to provide more accurate measurements in marine environment monitoring.

Enhanced photovoltaic effect in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface

Since high-mobility electron gas, which is also called two-dimensional electron gas, was discovered at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> (LAO/STO) interface, SrTiO<sub>3</sub>-based heterostructures and nanostructures have become an attractive platform for novel nanoelectronic devices. Exploring the novel physical properties of LAO/STO interface and the mechanisms of interface effect is the key to designing and fabricating the new photoelectric devices. The LAO/STO sample is prepared on an STO (001) substrate by pulsed laser deposition. In order to study the influence of interface effect on photovoltaic effect in the LAO/STO sample, a KrF pulse laser with a wavelength of 248 nm and an energy density of 50 mJ/cm<sup>2</sup> is chosen as an ultraviolet light source, a sampling oscilloscope of 350 MHz is used to measure the photovoltages, and a precision adjustable slit is adopted to control the size of irradiation area. The photovoltaic effect is studied under the condition of applied electric field at ambient temperature. The experimental results prove that the photovolatge of irradiating on the side of sample (LAO/STO interface) is higher than on the front of sample (film surface) under the same area of irradiation. Lateral photovoltaic effect is discovered in the LAO/STO sample. Irradiating on the side of sample (LAO/STO interface) can further improve the lateral photovoltaic effect in the LAO/STO sample. The open-circuit photovoltage depends linearly on the illuminated position, and the sensitivity reaches 36.8 mV/mm. The sensitivity of the lateral photovoltaic effect can be modified by the bias voltage. The experimental results not only contributes to better understanding the interface effect in LAO/STO interface, but also provides a basis for designing and using photoelectric devices for position-sensitive detection.

Helium-oxygen mixture bag, a novel way for extubation of COVID-19 patients: Simulation and proof of concept

Background: Coronavirus disease 2019 (COVID-19) has been a worldwide pandemic in 2020; necessitating significant changes in patient-care procedures. Because of the risk of transmission to health care workers (HCWs) and the shortage of personal protective devices worldwide, novel protective barriers during aerosol-generating procedures have been developed. The intubation box has been proposed and gained popularity. A safe way for extubating patients with COVID-19 in critical care settings does not exist. This report discusses the development and assessment of the efficacy of using a Helium-Oxygen mixture (Heliox) filled bag during the extubation phase for the protection of HCW. Study Design and Methods: This methodology was developed at two tertiary care hospitals in Riyadh, Saudi Arabia and Toronto, Canada. We describe a novel way using a bag filled with Heliox bag. We performed extubation of an intubated manikin with and without using the Heliox bag. The cough during extubation was simulated using a fluorescent dye-filled balloon, which was inflated with a hidden oxygen tube until it bursts. We used an ultraviolet (UV) light source to assess the aerosols generated during extubation. Results: During extubation using the Heliox bag, droplets of the fluorescent dye were all contained within the Heliox bag and only found on the manikin chest. While during extubation without using Heliox bag, using the UV light, we found droplets of the fluorescent dye on the HCW mask and hand, the bed, the floor, and wall of the room. Conclusion: In our simulated experiment, we found that the Heliox bag is an easy and reproducible way for extubating patients with COVID-19 and any other airborne disease. We also found that the Heliox bag is an effective way to protect HCW.

Growth of ZnO nanorods array on PCB for enhanced UV photosensors

Ultraviolet (UV) photosensitive device is fabricated using ZnO nanorods array on commercially available printed circuit board (PCB). Facile open aqueous solution deposition (OASD) method is used to deposit ZnO nanorods array in a trenched region between closely spaced Cu-electrodes. X-ray diffraction (XRD) patterns confirm the wurtzite phase of ZnO nanorods arrays and scanning electron microscopy (SEM) characterizes the multidimensional growth of ZnO nanorods across the trenched part of PCB. The current-voltage (I-V) characteristics of the device in dark is analogous to the back-to-back diode behaviour. However, the device exhibits an excellent photoresponsivity wherein the photocurrent value increases by two orders of magnitude at 2 V bias under the illumination ultraviolet (UV wavelength  ~ 254 nm) light source. The enhancement in photocurrent is mainly due to formation of multiple contacts between neighbouring grain-boundaries of the nanorods arrays extending to the Cu-electrodes. The prototype optoelectronic device displays almost four-times increment in the UV photocurrent at 5 V external bias potential.

Upconverting Phosphor-based Ultraviolet Light Source

Upconverting Phosphor-based Ultraviolet Light Source

A novel kind of nonlinear kicker for the Hefei Advanced Light Facility

The Hefei Advanced Light Facility (HALF) is a vacuum ultraviolet (VUV) and X-ray diffraction-limited storage ring light source. Because of its extremely small dynamic aperture, an injection scheme with a nonlinear kicker (NLK) was considered for the HALF. This magnet was designed with ferrite cores to achieve a higher excitation efficiency and a small gap shield in the central area for a flat magnetic field. In this paper, the design parameters, calculations and measurements of the kicker are described, and further optimization of the magnet structure is discussed.

A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser.

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280–320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320–400 nm) to UVC (<280 nm).

Kaleidoscopic fluorescent arrays for machine-learning-based point-of-care chemical sensing

Multiplexed analysis allows simultaneous measurements of multiple targets, improving the detection sensitivity and accuracy. However, highly multiplexed analysis has been challenging for point-of-care (POC) sensing, which requires a simple, portable, robust, and affordable detection system. In this work, we developed paper-based POC sensing arrays consisting of kaleidoscopic fluorescent compounds. Using an indolizine structure as a fluorescent core skeleton, named Kaleidolizine (KIz), a library of 75 different fluorescent KIz derivatives were designed and synthesized. These KIz derivatives are simultaneously excited by a single ultraviolet (UV) light source and emit diverse fluorescence colors and intensities. For multiplexed POC sensing system, fluorescent compounds array on cellulose paper was prepared and the pattern of fluorescence changes of KIz on array were specific to target chemicals adsorbed on that paper. Furthermore, we developed a machine-learning algorithm for automated, rapid analysis of color and intensity changes of individual sensing arrays. We showed that the paper sensor arrays could differentiate 35 different volatile organic compounds using a smartphone-based handheld detection system. Powered by the custom-developed machine-learning algorithm, we achieved the detection accuracy of 97 % in the VOC detection. The highly multiplexed paper sensor could have favorable applications for monitoring a broad-range of environmental toxins, heavy metals, explosives, pathogens.

High-Flux MHz Vacuum Ultraviolet Light Source

An ideal vacuum ultraviolet light source for applications in angle-resolved photoemission spectroscopy and photoionization mass spectrometry would have a high flux, a MHz repetition rate, a photon energy range from the UV to at least 15 eV, and variable energy and time resolution. This year, we reported a highly cascaded harmonic generation technique that addresses this challenge.

Effects of ultraviolet-light emitting diodes (UV-LEDs) on microbial inactivation and quality attributes of mixed beverage made from blend of carrot, carob, ginger, grape and lemon juice

Efficacy of ultraviolet light-emitting diodes (UV-LEDs) with peak and coupled emissions at 280, 365 and 280/365 nm on inactivation of E. coli K12 in mixed beverage (MB) was investigated. MB comprised of 31.6% carrot, 44.3% carob, 8.7% grape, 10.2% ginger, and 5.2% lemon juice. The impact of UV-LEDs on some physicochemical and phytochemical properties of MB was compared to that of heat treatment (70 °C, 120 s). While, UV-LED irradiation using coupled 280/365 nm for 40 min resulted in the highest inactivation of E. coli K12 (>4 log) out of tested wavelengths, the number of mesophilic bacteria (TAC), and yeast and molds (YM) in mixed beverage were reduced by 2.59 log CFU/mL (from 5.69 log CFU/mL of initial load), and 0.17 log CFU/mL (from 3.28 log CFU/mL of the initial load), respectively. Although, the color parameters slightly changed after irradiation, the color of MB did not show visual difference (ΔE = 0.94) compared to untreated samples. UV-LED treatment caused a significant increase in total phenolic compound (1.75-fold) and antioxidant capacity (4.60 fold) compared to heat-treated samples (p < 0.05). UV-LED treatment caused a decrease in carotenoid content (71.3%) lower than that of heat-treated samples (88.9%), indicating that UV-LED irradiation preserved the total carotenoid content better than the heat treatment. Industrial relevanceLight-emitting diodes (LEDs) are new sources of ultraviolet light utilized for non-thermal processing of foods. In this study, a static bench top unit was designed to investigate the efficacy of UV-LEDs with different treatment times and peak emissions by considering the inactivation of E. coli K12 in newly formulated mixed drink (MB). UV-LED irradiation of MB using coupled 280/365 nm for 40 min provided the highest microbial inactivation and preserved bioactive compounds better than the heat treatment. It can be proposed as an effective method for the processing of fruit juices which is rich in bioactive constituents.

Study on influencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete

Abstract In this study, a high-energy ball mill was used to composite nano-TiO2 and CdS, and three kinds of nanocomposite photocatalysts TiO2, CdS/TiO2-R400, and CdS/TiO2-R600 were prepared, which can respond to visible light. The photocatalytic concrete test block was prepared by mixing the nanocomposite photocatalyst and other masses with cement by incorporation method. To study the effect of the photocatalyst content on the photocatalytic performance of nanoconcrete, a total of four catalyst contents (0, 2%, 5%, and 8%) were set. The effects of high-temperature treatment (400°C) and different light sources (ultraviolet and visible light) on photocatalytic efficiency were also considered. The results show that the catalytic efficiency of CdS/TiO2-R400 under two light sources is higher than that of the other two photocatalysts. Compared to ultraviolet light sources, the photocatalytic efficiency of CdS/TiO2 nanocomposite concrete under visible light is lower, and the efficiency is below 9%. The optimal amounts of CdS/TiO2 nanocomposite photocatalyst under ultraviolet and visible light are 2% and 5%, respectively. The high-temperature treatment can improve the photocatalytic performance of CdS/TiO2 nanocomposite photocatalyst by 2% to 3%.

Sec-Eliminating the SARS-CoV-2 by AlGaN Based High Power Deep Ultraviolet Light Source.

The world‐wide spreading of coronavirus disease (COVID‐19) has greatly shaken human society, thus effective and fast‐speed methods of non‐daily‐life‐disturbance sterilization have become extremely significant. In this work, by fully benefitting from high‐quality AlN template (with threading dislocation density as low as ≈6×108 cm−2) as well as outstanding deep ultraviolet (UVC‐less than 280 nm) light‐emitting diodes (LEDs) structure design and epitaxy optimization, high power UVC LEDs and ultra‐high‐power sterilization irradiation source are achieved. Moreover, for the first time, a result in which a fast and complete elimination of SARS‐CoV‐2 (the virus causes COVID‐19) within only 1 s is achieved by the nearly whole industry‐chain‐covered product. These results advance the promising potential in UVC‐LED disinfection particularly in the shadow of COVID‐19.

Improved Optical Properties of Nonpolar AlGaN-Based Multiple Quantum Wells Emitting at 280 nm

The optical properties of nonpolar AlGaN multiple quantum wells (MQWs) emitting at 280 nm were investigated intensively using temperature-dependent and time-resolved photoluminescence spectra associated with the characterization of structural properties. The densities of superficial pits and basal-plane stacking faults (BSFs) were reduced by 33.8% and 35.9%, respectively, for nonpolar AlGaN MQWs due to the carefully optimized dual nitridation. It was found that the nonpolar MQWs emission can be significantly improved by reducing the BSFs density as the BSFs emission was the main competing channels. Moreover, an internal quantum efficiency of 39% for nonpolar Al0.43Ga0.57N MQWs at emission wavelength of 279 nm was achieved even the full width at half maximum values of X-ray rocking curves were 0.565° for c-direction and 0.797° for m-direction. This fact means that a highly efficient deep ultraviolet light sources can be expected by means of nonpolar AlGaN due to the elimination of quantum confined Stark effect induced the decrease in radiative lifetime.

Tailoring p-type conductivity of aluminum nitride via transition metal and fluorine doping

Aluminum nitride (AlN), as a new-generation ultraviolet light source, has drawn tremendous interest recently. However, one of the urgent problems is to improve its p-type conductivity. In this work, we propose that Zn and F co-doping is an effective strategy to achieve excellent p-type AlN through first-principles calculations. Nine transition metal (TM) elements from group 10–12 are selected to explore the potential dopants. ZnAl shows the lowest defect formation energy and transition level among the considered TMs. Interestingly, there is a closely relation between the strength of p-d hybridization and defect formation energy in the considered TM dopants. On the other hand, Zn and F co-doping (FN-3ZnAl) further decreases the defect formation energy and transition level, remarkably enhancing the solubility of Zn acceptor and carrier concentration (i.e. excellent p-type conductivity). These results are rationalized through the analysis of the projected density of states of doped systems.

Fabrication of three-dimensional high-aspect-ratio structures by oblique-incidence Talbot lithography.

Developing a suitable production method for three-dimensional periodic nanostructures with high aspect ratios is a subject of growing interest. For mass production, Talbot lithography offers many advantages. However, one disadvantage is that the minimum period of the light intensity distribution is limited by the period of the diffraction grating used. To enhance the aspect ratio of fabricated nanostructures, in the present study we focus on multiple wave interference between diffracted waves created using the Talbot effect. We propose a unique exposure method to generate multiple wave interference between adjacent diffraction orders by controlling the angle of incidence of an ultraviolet (UV) light source. Using finite-difference time-domain simulations, we obtain fringe patterns with a sub-wavelength period using a one-dimensional periodic grating mask. Moreover, we demonstrate the practical application of this approach by using UV lithography to fabricate sub-wavelength periodic photopolymer-based structures with an aspect ratio of 30 in millimeter-scale areas, indicating its suitability for mass production.

Comparative study on the molecular beam epitaxial growth and characterization of AlGaN nanowire structures on AlN buffer layer and on Si

AlGaN in the form of nanowires is an important platform for semiconductor ultraviolet light sources on Si. In the past, significant efforts have been devoted to improving the quality of AlGaN nanowires. In this context, we present a comparative study on the molecular beam epitaxial growth and characterization of AlGaN nanowire structures on the AlN buffer layer on Si and on Si directly. It is found that AlGaN nanowires grown on the AlN buffer layer shows an improved internal quantum efficiency, compared with the nanowires grown on Si directly. This improvement is attributed to the reduced nanowire coalescence due to the improved vertical alignment of the nanowires grown on the AlN buffer layer.

A revised manuscript submitted to sensors and actuators B: Chemical illumination modification from an LED to a laser to improve the spatial resolution of IGZO thin film light-addressable potentiometric sensors in pH detections

Indium Gallium Zinc Oxide (IGZO) on Indium Tin Oxide (ITO) glass has been applied as the semiconductor substrate of a light-addressable potentiometric sensor (LAPS) with the advantages of immunity to room light inference and high photocurrent. For the first time, investigations into this IGZO LAPS including two-dimensional (2D) chemical imaging and reduction of the potential biorelative damage induced by the requirement of an ultraviolet (UV) light source are presented in this study. For the spatial resolution, a smaller aperture for the light spot provided by a light emitting diode (LED) makes the photocurrent decrease. To overcome this natural limitation, the type of AC modulation of light source is changed from a sine wave to a square wave with different duty cycles. The photocurrent and power consumption of a 365 nm LED with square wave and a duty cycle of 40 % are 42.2 % higher and 16.2 % lower than those of the conventional setup of a sine wave, respectively. The pH sensitivity, linearity, hysteresis and drift are comparable. The illumination wavelengths of 365, 405 and 435 nm are studied for photoresponse. 405 nm illumination with acceptable pH sensing performance can be suggested for IGZO LAPS for less bio damage concern. Additionally, a laser with a wavelength of 405 nm with spot size of 25 μm and scanning step of 2 μm is proven to have a clear pattern recognition down to 50 μm in 2D image. Further optimization of the spot size of the laser, thickness and composition of IGZO are suggested for better spatial resolution.

Optically excited threshold switching synapse characteristics on nitrogen-doped graphene oxide quantum dots (N-GOQDs)

Carbon-based organic material such as nitrogen-doped graphene oxide quantum dots (N-GOQDs) is a new-class material with unique biocompatible, high chemical inertness, and elevated photoluminescence properties. Two-terminal diffusive memristors can faithfully replicate biological synapse function via mutual similarities of in-/out-diffusion of Ag+ ions with biological Ca2+ migration dynamics for neural network applications. Inspired by hetero-plasticity phenomenon, in which Ca2+ dynamics can also be tuned by the 3rd counterpart – neuromodulatory axon, in this study, using an ultra-violet light source, we develop N-GOQDs based diffusive memristor that performs light-modulated synaptic behaviors. Specifically, photo-sensitive N-GOQDs ionic conductor shows n-π∗ electron transitions under UV excitation; yet, nitrogen-doping further facilitates the electron transitions, giving out additional conductance induced by light. Further, we demonstrate endurable threshold resistive switching (TS) behavior based on Ag+ ions migration and its variety of facilitations via assisted UV illumination. The enhancement of post-synaptic current under assisted UV light, as well as the light stimulated transition from short-to long-term memory potentiation have been achieved. These findings are believed to be a step forward for the realization of higher bandwidth synapse modulation as future hardware-based neural network applications.

UV LED Assisted Printing Platform for Fabrication of Micro-Scale Polymer Pillars

Ultraviolet (UV) assisted printing has emerged as a promising additive manufacturing (AM) technology, which puts UV light sources with focused emission in high demand. Unfortunately, current ultraviolet light-emitting diodes (UV LEDs) are not able to provide adequately focused UV emission required for printing. Thus, a UV LED package with focused UV emission was proposed and fabricated using microelectromechanical system (MEMS) technology in this study. An optical model of the UV LED package with focused UV emission was developed. Based on the designed model, a silicon reflector stacked on another was achieved. By assembling the stacked silicon reflector and hemispherical quartz lenses, the UV LED package with focused UV emission was successfully achieved. A narrow beam with a beam angle of 16° between half maximum intensity was achieved, while the intensity at 0° was greater than 1000 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the focal point. The UV LED curing system using two focused UV LED packages was successfully developed based on the optical simulation results. Polymer pillars were fabricated by instantaneous UV curing process with synchronized UV curable polymer jetting process in one shot, and micro-scale polymer pillars with a diameter of 20 μm were achieved. Thanks to the high intensity and focused UV emission, polymer pillars can be formed in as little as 100 ms. 13600 polymer pillars were printed on a silicon wafer with uniform diameter and geometry in a single dispensing cycle. The UV LED assisted printing platform was successfully demonstrated for fabrication of micro-scale 3D structures in a fast speed with smooth printing process.