Ultraviolet Light-emitting Diodes Research Articles

Life Cycle Assessment of Immobilised and Slurry Photocatalytic Systems for Removal of Natural Organic Matter in Water

This study investigates the environmental impacts caused by the scaling up of the photocatalytic purification of drinking water using ultraviolet light-emitting diode technology. The life cycle assessment methodology was utilised to estimate the environmental impacts of two different reactor setups commonly used in lab-scale studies: an immobilised and a suspended TiO2 catalytic system. The functional unit adopted was the treatment of 1 L of water with an initial 7.8 mg/L concentration of natural organic matter, achieving a final 1 mg/L concentration. The use of a suspended photocatalyst was found to have an environmental footprint that was 87% lower than that of the immobilised one. From the sensitivity analysis, the environmental hotspots of the treatment process were the electricity usage and immobilised catalyst production. Therefore, alternative scenarios investigating the use of a renewable electricity mix and recyclable materials were explored to enhance the environmental performance of the photocatalytic treatment process. Using a renewable electricity mix, a decrease of 55% and 15% for the suspended and immobilised catalyst, respectively, was observed. Additionally, the process of recycling the glass used to support the immobilised catalyst achieved a maximum reduction of 22% in the environmental impact from the original scenario, with 100 glass reuses appearing to provide diminishing returns on the environmental impact savings.

Numerical simulation of deep ultraviolet LED, micro-LED, and nano-LED with different emission wavelengths based on FDTD

Numerical simulation of deep ultraviolet LED, micro-LED, and nano-LED with different emission wavelengths based on FDTD

A Review of Light-Emitting Diodes and Ultraviolet Light-Emitting Diodes and Their Applications

A Review of Light-Emitting Diodes and Ultraviolet Light-Emitting Diodes and Their Applications

(Invited) III-Nitride Ultraviolet LEDs and Lasers for Applications in Biology and Medicine

Solid-state ultraviolet (UV) light emitters are being developed for emerging biomedical applications such as surface sterilization, air/water purification, and medical treatments as a replacement for mercury vapor lamps. While these UV emitters offer many advantages over mercury lamps, such as more compact form factors, tunable emission wavelengths, and greatly increased lifetimes, they also suffer from a number of issues which hinder their implementation in many potential applications. UV emitters are based on AlGaN heterostructures which usually have very poor external quantum efficiencies (EQEs) of less than 10%, with EQEs decreasing with emission wavelength. This makes it very challenging to realize high efficiency UV emitters whose high energy photons are capable of inactivating viruses, bacteria, and other pathogens. This work discusses recent developments made by the Zhang Research Group at the Rochester Institute of Technology in improving the efficiencies of UV LEDs and lasers.

Effect of coil diameter on water disinfection efficiency in a helical photoreactor using ultraviolet-C light emitting diodes

ABSTRACT This study investigated the disinfection efficiency of a photoreactor equipped with a helical water flow channel and ultraviolet-C (UV-C) light emitting diodes (LEDs). Theoretical simulations and biodosimetry tests were conducted to investigate the effects of coil diameter and flow rate on the reactor’s performance in inactivating Escherichia coli. The interplay between hydrodynamics and UV radiation was analyzed to determine the UV fluence absorbed by the microbes. The simulations revealed that, primarily due to the specific radiation pattern of the UV LEDs, the coil diameter strongly influenced the distribution of irradiance in the water and the UV fluence received by microbes. The experimental results indicated that the photoreactor achieved the highest inactivation value of 2.8 log when the coil diameter was 48 mm for a flow rate of 40 mL/min; this log value was superior to those for coil diameters of 16, 32, 64, and 80 mm by approximately 1.9, 0.4, 0.5, and 0.7 log units, respectively. This optimal coil diameter leading to the maximal UV irradiance and the highest degree of irradiance uniformity along the flow channel. This study offers design guidelines for constructing a high-efficiency water disinfection reactor with a helical flow channel configuration.

Strategically constructed AlGaN doping barriers for efficient deep ultraviolet light-emitting diodes: erratum

We present an erratum to our Letter [Opt. Lett. 49, 2049 (2024)10.1364/OL.522212]. There is a careless omission of some references because our Letter is longer than the maximum allowed four pages. The missing references and their specific quote location are listed in the following. These corrections do not affect the data plotted in figures, discussion, or conclusion of the original Letter.

An Efficient Indoor Nursery Controlled by IOT and Monitored by Android App.

Gardening is one of the greatest hobbies or mind relaxing activities for all age groups, which kindles them to make nursery management system. Nowadays also most of the nursery owners using a manual system to water and monitor their plants. There are many difficulties or challenges for nursery owners to take care of the plants growth, so that they need to check the moisture of the soil, monitor the air humidity and temperature, and others parameters. This paper offers a solution to combine the Internet of Things (IoT) system and Android apps to monitor the plant's growth with a real-time data monitoring and also provides the system control. In this paper, the sensors are used to sense the moisture of soil, check the air humidity and temperature, discover the light intensity and measure the soil temperature. This system allows nursery owners to monitor and control the irrigation system where they can water their plants using mobile application. The sensor checks the condition of the plant and updates the data in every one hour. Other than that, Indoor nursery often faces the issue of inadequate sunlight. Natural light coming through windows may not be as strong as outdoor sunlight, which is essential for photosynthesis. Therefore, this system offers a solution that allows nursery owners to control a specific light-emitting diode (LED) or UV LED to simulate sunlight. This ensures that plants receive the necessary light for photosynthesis and grow healthy. Growth of Plants contribute towards air purification providing fresher air to breathe.

Using ultrasonic washing combined with UV-LEDs as a novel chemical-free method to disinfect fresh ready-to-eat produce

The consumption of ready-to-eat fresh produce raises the issue of food-borne pathogen infections; thus, disinfecting ready-to-eat produce for commercial use, such as in homes and restaurants, is important to ensure food safety. Chemical sanitizers are typically used for disinfection. Ultraviolet-light emitting diodes (UV-LEDs) are a novel non-thermal disinfection technology that consumes less energy and generates less heat than traditional UV lamps, making them more appealing to consumers. In this study, we combined ultrasonic (US) washing method with UV-LEDs (US-UV-LEDs) to develop a technique for disinfecting fresh produce without using chemical sanitizers and compared its efficacy with three common household sanitizers (“84” (sodium hypochlorite) disinfectant, kettle descaler (citric acid), and vinegar (acetic acid)). In addition, we investigated the efficacy of this method in controlling pathogen numbers in the water used to wash (washing water) the produce to prevent cross-contamination between water and produce. Cherry tomatoes and lettuce were selected as produce models and Salmonella Typhimurium and Escherichia coli O157:H7 were used as the bacterial models. The results showed that US-UV-LEDs reduced the numbers of S. Typhimurium and E. coli O157:H7 on produce by 2.1–2.2 log CFU/g, consistent with the results achieved by the three household sanitizers; however, kettle descaler and vinegar had a limited effect (2.6–3.5 log CFU/mL) on residual pathogens in the washing water. Furthermore, we created washing water with low (754 mg/L) and high (1425 mg/L) chemical oxygen demand (COD) levels and determined the disinfection efficacy of “84” disinfectant and US-UV-LEDs. The results showed that US-UV-LEDs reduced the number of S. Typhimurium and E. coli O157:H7 by 2.0–2.1 and 1.8–2.1 log CFU/g under low and high COD levels, respectively, which was similar a result to that of “84” disinfectant. However, the residual pathogen numbers in the washing water were reduced to 1.4–1.9 log CFU/mL after treatment with US-UV-LED under high COD, whereas the pathogens were undetected in the washing water disinfected with “84” disinfectant. These results suggest that US-UV-LEDs have better application potential than acidic household sanitizers, but chlorine sanitizer remains the most effective disinfecting method.

Application of UV LEDs to inactivate antibiotic resistant bacteria: Kinetics, efficiencies, and reactivations

Unregulated antibiotic use has led to the proliferation of antibiotic-resistant bacteria (ARB) in aquatic environments. Ultraviolet light-emitting diodes (UV LEDs) have evolved as an innovative technology for inactivating microorganisms offering several advantages over traditional mercury lamps. This research concentrated on utilizing UV LEDs with three distinct wavelengths (265 nm, 275 nm, and 285 nm) to inactivate E. coli DH10β encoding the ampicillin-resistant blaTEM-1 gene in its plasmid. Non-linear models, such as Geeraerd's and Weibull, provided more accurate characterization of the inactivation profiles than the traditional log-linear model due to the incorporation of both biological mechanisms and a deterministic approach within non-linear models. The inactivation rates of ARB were higher than antibiotic-sensitive bacteria (ASB) when subjected to UV LEDs. The highest inactivation rates were observed when all microorganisms were exposed to 265 nm. Photoreactivation emerged as the primary mechanism responsible for repairing DNA damage induced by UV LEDs. 285 nm showed the highest reactivation efficiencies for ARB under different fluences. At higher fluences, both 265 and 275 nm displayed similar effectiveness in suppressing reactivation, while at lower fluences, 275 nm exhibited better efficacies in controlling the reactivation. Therefore, the inhibition of reactivation was influenced by the extent of damage incurred by both DNA and enzymes. In nutrient-poor media (0.9 % NaCl), ASB did not exhibit any reactivation potential. However, the addition of Luria-Bertani (LB) broth promoted the reactivation of ASB. Lower fluence rate was more beneficial at 265 nm whereas higher fluence rates were more effective for longer wavelengths. The inactivation of ARB was enhanced by dissolved organic carbon (DOC) at low fluences. However, the removal of ARB was reduced due to the presence of DOC at higher fluences. The highest energy demand for ARB inactivation was reported at 285 nm. Environmental implicationThe excessive and unregulated utilization of antibiotics has emerged as a significant issue for public health. This paper presents a comprehensive analysis of the effectiveness of UV LEDs, an emerging technology, in the inactivation of antibiotic-resistant bacteria (ARB). This research paper explores the kinetics of UV LEDs with different wavelengths to inactivate ARB along with the reactivation efficiencies. This research work also explores the impact and relevant mechanisms of the impact of dissolved organic carbon (DOC) on the inactivation of ARB by UV LEDs.

Metal-modulated epitaxy of Mg-doped Al0.80In0.20N-based layer for application as the electron blocking layer in deep ultraviolet light-emitting diodes

This work reports the growth and characterization of p-AlInN layers doped with Mg by plasma-assisted molecular beam epitaxy (PAMBE). AlInN was grown with an Al molar fraction of 0.80 by metal-modulated epitaxy (MME) with a thickness of 180 nm on Si(111) substrates using AlN as buffer layers. Low substrate temperatures were used to enhance the incorporation of indium atoms into the alloy without clustering, as confirmed by X-ray diffraction (XRD). Cathodoluminescence measurements revealed ultraviolet (UV) range emissions. Meanwhile, Hall effect measurements indicated a maximum hole mobility of 146 cm2/(V∙s), corresponding to a free hole concentration of 1.23 × 1019 cm−3. The samples were analyzed by X-ray photoelectron spectroscopy (XPS) estimating the alloy composition and extracting the Fermi level by valence band analysis. Mg-doped AlInN layers were studied for use as the electron-blocking layer (EBL) in LED structures. We varied the Al composition in the EBL from 0.84 to 0.96 molar fraction to assess its theoretical effects on electroluminescence, carrier concentration, and electric field, using SILVACO Atlas. The results from this study highlight the importance and capability of producing high-quality Mg-doped p-AlInN layers through PAMBE. Our simulations suggest that an Al content of 0.86 is optimal for achieving desired outcomes in electroluminescence, carrier concentration, and electric field.

Enhancing the Hole Injection in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes With Engineered p-AlGaN Hole Supplier Layer

Enhancing the Hole Injection in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes With Engineered p-AlGaN Hole Supplier Layer

The effect of FeGa (0/–) level presence on material properties in dilute AlxGa1−xN layers

AlxGa1−xN epilayers are used as the basis of ultraviolet LEDs and detectors. The trap states produced by defects and impurities can play a key role in the device performance. In this work, conventional deep-level transient spectroscopy, photoluminescence (PL), and secondary ion mass spectrometry have been used to characterize a deep-level trap termed as E3 in dilute AlxGa1−xN (x < 0.063) epilayers grown by metal-organic vapor phase epitaxy (MOVPE) on highly conductive ammono-GaN substrates. The AlxGa1−xN epilayers were doped with silicon to about 3 × 1016 cm−3. The electrical and the optical measurements were conducted on Ni/Au Schottky barrier diodes and virgin samples, respectively. First, we observed a general trend that the E3 (FeGa) electron trap concentration significantly changes along the wafers in AlxGa1−xN layers that is fully consistent with previously reported results for GaN materials grown by the MOVPE technique. Second, we report that the activation energies for electron emission for the E1 and E3 traps in dilute AlxGa1−xN exhibit linear variations with Al content. Moreover, low-temperature PL results show a proportional relation between the intensity of the line with its maximum at 1.299 eV and concentration of residual Fe impurity. Finally, we discuss how the presence of defects resulting from Fe contamination may result in degradation of AlxGa1−xN-based devices.

Design of High-Precision Driving Control System for Charge Management

Due to the interaction of accumulated charges on the surface of a test mass with the surrounding electric and magnetic fields, the performance of inertial sensors is affected, necessitating charge management for the test mass. Discharge technology based on Ultraviolet LEDs is internationally recognized as the optimal solution for charge management. Precision driving of Ultraviolet LEDs is considered a key technology in charge management. This paper presents the driving control system used for Ultraviolet LEDs, achieving precision pulse-width-modulation-type current output with controllable pulse width and amplitude. The system generates the pulse-width-controllable pulse voltage signal via analog pulse-width modulation, and subsequently regulates the amplitude of the PWM signal through range switching. To convert the voltage into the pulse-width-modulation-type driving current, the improved Howland current source is employed. The test results demonstrate that the driving control system can output controllable current in the range of 0.01 mA to 10 mA, with a minimum step of 0.01 mA. The accuracy of the current reaches 1%, the stability within 1 h is better than 1%, and the load regulation is better than 2%. The driving control system provides an important reference for the integration of charge management system and the precision drive control method for LEDs.

TiO2-Coated Meltblown Nonwoven Fabrics Prepared via Atomic Layer Deposition for the Inactivation of E. coli as a Model Photocatalytic Drinking Water Treatment System

The controlled manufacturing of semiconductor photocatalysts is crucial to their development for drinking water treatment. In this study, TiO2-coated meltblown nonwoven fabrics prepared via Atomic Layer Deposition (ALD) are applied for the inactivation of Escherichia coli (E. coli). It is observed that in the presence of an ultraviolet light-emitting diode (UV-LED) light source (255 nm), 1.35 log E. coli inactivation is achieved. However, exposure to catalyst-coated fabrics in addition to the light source resulted in >4 log E. coli inactivation, suggesting a much higher rate of hydroxyl radical formation on the surface, leading to cell death.

Investigation of Ohmic contact to plasma-etched n-Al0.5Ga0.5N by surface treatment

We investigated the optimization effects of KOH solution treatment and SiN x sacrificial layer treatment on the contact characteristics of V/Al/Ni/Au on plasma-etched n-AlGaN. The results showed that the contacts on n-Al0.5Ga0.5N with both surface treatments are truly Ohmic in nature, while the contacts on untreated plasma-etched samples are still rectifying. Surface atomic concentration analysis revealed that both surface treatment methods effectively reduced the nitrogen vacancies on n-AlGaN induced by plasma etching, which mostly act as acceptor-like states, leading to severe compensation and hindering of the formation of Ohmic contact. Moreover, the operating voltage was reduced by 0.9 V at 20 mA for 285 nm ultraviolet light-emitting diodes, demonstrating that the surface treatment could work well for plasma-etched n-AlGaN Ohmic contacts.

Innovative surfactant-free synthesis of core-shell SiO2/ZnO particles: rapid ultrasonication and photocatalytic inhibition.

This study demonstrates the preparation of SiO2/ZnO core-shell nanoparticles with controllable shell size and their optical properties. A facile ultrasonication method was utilized to prepare the core-shell particles in the absence of surfactant materials. The synthesis duration was 75% shorter than that required for the common sol-gel method, which favours its potential applicability in the future for mass production. Tetraethyl orthosilicate (TEOS) was used as the silica source, while the core material was prepared using zinc acetate dihydrate. The outer shell size could easily be controlled by changing the molar ratio of silica from 0.25 to 1.00. The experimental results show that increasing the silica ratio was effective in suppressing the self-agglomeration of ZnO and, further, in obtaining agglomeration-free particles. The investigation of the photoluminescence (PL) properties of nanometre-sized ZnO revealed several emission peaks in the ultraviolet (UV) wavelength range, indicating variations in bandgap energy. This did not appear in the spectrum of micrometre-sized ZnO particles. The core-shell particles produced with higher amounts of silica showed higher UV-A and UV-B absorption. In addition, the presence of silica reduced the photocatalytic activity of ZnO by 65% and reduced the PL intensity. The obtained emission peaks, intensity changes, and spectral characteristics open new avenues for further research on tailoring the properties of SiO2/ZnO core-shell structures for specific technological advancements. These advancements hold promising applications in UV attenuation materials, LED technologies, lenses, and solar cells within the realm of optical devices.

Demonstration of Full AlGaN Tunnel Junction Ultraviolet LED

Demonstration of Full AlGaN Tunnel Junction Ultraviolet LED

Enhanced efficiency of deep ultraviolet light-emitting diodes utilizing full-coverage Al reflector and highly reflective Ni/Rh p-electrode

Increasing the reflection of p-side is an effective way to improve the optoelectronic performance of flip-chip light-emitting diodes (FCLEDs). Here, we propose a full-coverage Al reflector (FAR) and a highly reflective Ni/Rh p-electrode to enhance the performance of deep ultraviolet (DUV) FCLEDs. The physical mechanism for the impact of the FAR and Ni/Rh electrode on the light extraction efficiency (LEE) is discussed theoretically. Simulations demonstrate that the combination of the FAR and Ni/Rh electrode improves the LEEs of transverse electric- and transverse magnetic-polarized light by 13.62% and 27.08%, respectively. At an injection current of 100 mA, the fabricated DUV FCLEDs with FAR and Ni/Rh electrode exhibits an external quantum efficiency of 4.01% and a wall plugging efficiency of 2.92%, which are 16.85% and 13.18% higher than those of conventional DUV FCLEDs, respectively. These results support the promise of the FAR and Ni/Rh electrode for high-power DUV LED applications.

Evaluating the Performance of UV Disinfection across the 222-365 nm Spectrum against Aerosolized Bacteria and Viruses.

Bioaerosols play a significant role in the transmission of many infectious diseases, especially in enclosed indoor environments. Ultraviolet (UV) disinfection has demonstrated a high efficacy in inactivating microorganisms suspended in the air. To develop more effective and efficient UV disinfection protocols, it is necessary to evaluate and optimize the effectiveness of UV disinfection against aerosolized bacteria and viruses across the entire UV spectrum. In this study, we evaluated the performance of UV disinfection across the UV spectrum, ranging from 222 to 365 nm, against aerosolized bacteria and viruses, including Escherichia coli, Staphylococcus epidermidis, Salmonella enterica, MS2, P22, and Phi6. Six commonly available UV sources, including gas discharge tubes and light-emitting diodes with different emission spectra, were utilized, and their performance in terms of inactivation efficacy, action spectrum, and energy efficiency was determined. Among these UV sources, the krypton chloride excilamp emitting at a peak wavelength of 222 nm was the most efficient in inactivating viral bioaerosols. A low-pressure mercury lamp emitting at 254 nm performed well on both inactivation efficacy and energy efficiency. A UV light-emitting diode emitting at 268 nm demonstrated the highest bacterial inactivation efficacy, but required approximately 10 times more energy to achieve an equivalent inactivation level compared with that of the krypton chloride excilamp and low-pressure mercury lamp. This study provides insights into UV inactivation on bioaerosols, which can guide the development of effective wavelength-targeted UV air disinfection technologies and may significantly help reduce bioaerosol transmission in public areas.

Significant conductivity enhancement in Al-rich n-AlGaN by modulation doping

Enhancing the conductivity in Al-rich n-AlGaN is a key issue for realizing AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) with low operating voltage and high wall-plug efficiency, especially in a planar geometry of flip–chip configuration. An approach of modulation doping is herein proposed, where an alternating-layer structure consisting of Si-doped and unintentionally doped AlGaN is assembled to achieve the spatial separation of electron activation and transport. As massive electrons diffuse from the AlGaN:Si layer into the neighboring i-AlGaN ones and then drift, the ionized-donor scattering is effectively weakened, leading to a significant enhancement of mobility as well as conductivity. An impressive electrical property of n-Al0.6Ga0.4N with a lateral conductivity of 201.7 S/cm is realized as a consequence, being 2.1 times of that in the continuously doped one. Furthermore, the operating voltage of 280 nm UV-LEDs is correspondingly reduced by 0.1–0.2 V at 100 mA by adopting modulation-doped n-AlGaN in the n-cladding layer.