Light-emitting Diodes Research Articles

Inducing Multicolour emission in MEH-PPV/TiO2 nanocomposites

Fluorescence-based polymers have a wide variety of applications such as light-emitting diodes, optoelectronics, and biosensors. The present study endeavors towards the effect of TiO2 nanoparticles (calcined at various temperature) on the emission of Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) and to induce multicolor emission. The TiO2 nanoparticles synthesized by sol-gel method were calcined at 400°C and 600°C. In situ polymerization was adopted to synthesize MEH-PPV / TiO2 nanocomposites and the structural characteristics of the nanocomposites were studied using Fourier transformed Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The photo-physical characteristics of the nanocomposites were investigated using UV-Visible spectroscopy, Photoluminescence spectroscopy, and Fluorescence microscopy. TiO2 nanoparticles calcined at 400°C demonstrates anatase phase, whereas the particles calcined at 700°C exhibits mixed phase of rutile and anatase. The study reveal that calcination temperature has a strong impact on the morphology of the synthesized nanoparticles. The photoluminescence spectra reveal that the incorporation of TiO2 nanoparticles enhances the red orange emission intensity of MEH-PPV, additionally exhibits emission at multiple wavelengths. Fluorescence microscopy evidences multiple colour emission from MEH-PPV/TiO2 nanocomposites. The multiple emission in the polymer nanocomposite is arised from the oxygen vacancies present in anatase and rutile phases of TiO2 nanoparticle.

Only incandescent light significantly decreases feeding of Anopheles funestus s.s. (Diptera: Culicidae) mosquitoes under laboratory conditions

Recent work has demonstrated that exposure to artificial light at night (ALAN) may alter mosquito feeding behavior and so must be considered a moderator of vector-borne disease transfer. Anopheles funestus mosquitoes are a primary malaria vector in sub-Saharan Africa, but no study to date has tested the impact of ALAN on their feeding behavior. Here we test if the exposure to commonly used household lights (compact fluorescent lights, light-emitting diodes, and incandescent lights) alters Anopheles funestus feeding. Mated, unfed female mosquitoes were exposed to a light treatment, at the onset of darkness, followed by a blood-feeding assay. The light treatments consisted of a 30-min light pulse of one of the three household lights, each in individual experimental containers, versus controls. All three household lights resulted in a reduction in the percentage of females taking a blood meal, but only mosquitoes exposed to incandescent light showed a statistically significant reduction in feeding of 19.6% relative to controls which showed a 42.8% feeding rate. Our results suggest that exposure to some household lights during the night may have an immediate inhibitory effect on Anopheles funestus feeding. By helping identify which light types lead to a suppression of feeding, the findings of this study could provide insight necessary to design household lights that can help minimize mosquito feeding on humans.

Two decades of progressive cost reduction: A paradigm for distributed solar photovoltaics and energy efficiency

The increasing deployment of renewable energy resources has led to massive energy cost effectivity worldwide in the past decade. The emergence of this cost revolution led electricity consumers to increasingly adopt distributed renewable energy resources to decrease dependence on traditional power grids. This paper applies the integrated resource planning framework, the objective of which is to design a least-cost electricity system by looking at renewable energy resources, efficient appliances, and demand response management strategies to reduce electricity bills. The results show that the commercial entity can save its electricity bill by $0.16 if it installs 6 MW solar PV over the lifetime of the solar PV plants. Besides, it was observed that wind turbines were not economically feasible to install at the site because of low wind resources. Biogas power plant is too expensive mainly because of the cost of fuel (waste). It also shows that by retrofitting 2000 compact fluorescent lamps (CFLs) with light-emitting diodes (LEDs), the company can save $0.15 million. By shifting between 0.5 MW and 1.4 MW of heating and cooling demand to periods of low tariff costs, the company can save $0.013 million annually. The climate transition plan for this company relies on PV, efficiency interventions and demand response. The study also demonstrates that an integrated resource planning framework can be used to plan a mini-grid.

High-yield Micro-LED laser transfer accomplished using an ablation-type release material

Micro light-emitting diode (Micro-LED) is a highly promising technology in the field of new displays, with the mass transfer process involved in its manufacturing process widely regarded as a major barrier to their further development. This study adopts laser transfer technology as the primary solution, using ablation-type transfer release materials that improve chip utilization rates over blister-type release materials. In addition, measurement of the laser transfer parameters, inspection, and laser repair technology are combined to achieve a transfer yield of about 100% to the carrier substrate and a cumulative transfer displacement of less than 1 µm in the Micro-LED inverted chip array. Furthermore, cleaning agents were used to remove adhesive residue from the receiving substrate after transfer, improving the bonding yield between the chip and the thin film transistor driver circuit board. This study provides a feasible solution for Micro-LED mass transfer, which could boost its further development toward commercial application.

Insights into the pressure-dependent physical properties of cubic Ca3MF3 (M = As and Sb): First-principles calculations

Here, first-principles calculations have been employed to make a comparative study on structural, mechanical, electronic, and optical properties of new Ca3MF3 (M = As and Sb) photovoltaic compounds under pressure. The findings disclose that these two systems possess a direct band gap, showcasing a large tunable range under pressure, effectively encompassing the visible light spectrum. Adjusting various levels of hydrostatic pressure has effectively tuned both the band alignment and the effective masses of electrons and holes. Both compounds were initially identified as brittle materials at 0 GPa pressure; however, as the pressure increases, they transform, becoming highly anisotropic and ductile. Due to the material's mechanical robustness and enhanced ductility, as evidenced by its stress-induced mechanical properties, the Ca3MF3 (M = As and Sb) material shows potential for use in solar energy applications. Furthermore, as the influence of external pressure increases, the absorption edge seems to move slightly towards lower energy region. Optical properties show that the materials studied might be used from several optoelectronic devices in the visible and ultraviolet range area. Our findings show that pressure considerably influences the physicochemical properties of Ca3MF3 (M = As and Sb) compounds, which is a promising feature that can be useful for optoelectronic and photonic applications, for instance, light-emitting diodes, photodetectors, and solar cells.

Dual-Functional Cs3Bi2Br9 for stable all-solid-state photo-rechargeable batteries

In light of the immense potential solid-state photo-rechargeable batteries hold in the efficient utilization of renewable solar energy, there is a rapidly growing demand for materials that possess both energy harvesting and storage capabilities. In this study, a solid-state photo-rechargeable battery has been designed based on the FTO(Fluorine-doped SnO2 transparent conductive glass)/TiO2/Cs3Bi2Br9/Pt/FTO system, which achieves dual functions of photoelectric conversion and energy storage. The inorganic bismuth-based material employed in these batteries exhibits commendable cyclic stability. Under photo-rechargeable conditions, a single cell can maintain an open-circuit voltage as high as 0.45 V in the absence of illumination. By connecting multiple cells in series, we succeed in powering an LED (Light-emitting diode) continuously for 1 min without light exposure. The findings of this research open new avenues for the design and development of novel materials that could enable highly efficient solid-state photo-rechargeable batteries.

Plant Factory Speed Breeding Significantly Shortens Rice Generation Time and Enhances Metabolic Diversity

Rice (Oryza sativa L.) plays a pivotal role in global food security, yet its breeding is constrained by its long generation time and seasonality. To enhance rice breeding efficiency and meet future food demands, we have developed a vertical hydroponic breeding system integrated with light-emitting diodes (LEDs) lighting in a closed plant factory (PF), which significantly accelerates rice growth and generation advancement. The results show that indica rice can be harvested as early as after 63 days of cultivation, a 50% reduction compared with field cultivation, enabling the annual harvesting of 5–6 generations within the PF. A hyperspectral imaging system (HSI) and attenuated total reflectance infrared (ATR-IR) spectroscopy were further employed to characterize the chemical composition of the PF- and field-cultivated rice. Metabolomics analysis with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and gas chromatography-mass spectrometry (GC-MS) revealed that, compared with the field-cultivated rice, the PF-cultivated rice exhibited an up-regulation of total phenolic acids along with 68 non-volatile and 19 volatile metabolites, such as isovitexin, succinic acid, and methylillicinone F. Overall, this study reveals the unique metabolic profile of PF-cultivated rice and highlights the potential of PFs to accelerate the breeding of crops such as rice, offering an innovative agricultural strategy to support food security in the face of global population growth and climate change.

SIMULATING THE IMPACT OF CLIMATE CHANGE ON ENERGY CONSUMPTION AND YIELD IN CANADIAN GREENHOUSE HORTICULTURE

Greenhouse horticulture is a very energy-intensive industry in cold regions such as Canada due to heating and lighting needs. It is still largely unknown how climate change will impact the energy profile and productivity of this vital industry. In this work, a greenhouse producing tomatoes has been simulated in eight Canadian cities under current and 2080 climates based on climatic trajectory RCP8.5, in order to determine how the energy consumption and tomato yield would be affected. Results show that, on average, energy consumption decreases by 11% due to a reduction of the heating needs, whereas yield decreases by 17% due to a higher canopy temperature. The use of light-emitting diodes (LED) resulted in a lower energy consumption than that of high-pressure sodium (HPS) lighting in both current and future weather conditions. This work suggests that the greenhouse industry is likely to require some adaptations to climate change and that reaching a balance between energy consumption and productivity will be a challenge. As an example, the addition of a mechanical cooling and dehumidification system was simulated and allowed to increase the yield compared to the current situation, even in the 2080 climate change scenario, at the expense of higher energy consumption. However, a more in-depth analysis is required to identify the best adaptative strategies for mitigating the impacts of climate change on greenhouse production.

High correlated color temperature white light-emitting diodes disrupt refractive development in guinea pigs

Ubiquitous white light-emitting diodes (LEDs) possess optical properties that differ from those of natural light. This difference can impact visual perception and biological functions, thus potentially affecting eye health. Myopia, which leads to visual impairments and potentially irreversible vision loss or blindness, is the most prevalent refractive error worldwide. Ambient light has been found to be a significant factor in refractive development. The overlap between the commonly utilized of white LEDs and the rapid increase in the prevalence of myopia raises suspicions that white LEDs may represent hidden visual cues. To clarify the potential effects of white LEDs on refractive development, we exposed guinea pigs to different forms of artificial lighting over a period of eight weeks. We found that exposure to white LEDs with a high correlated color temperature (CCT) of approximately 5000 K can induce significant myopic shifts in guinea pigs, along with a decrease in collagen accumulation in the sclera. Additionally, this exposure was found to significantly reduce choroidal tissue thickness in guinea pigs. Our study findings indicate that high CCT white LEDs disrupt refractive development in guinea pigs. These results suggest that high CCT white LEDs might similarly affect refractive development in humans, highlighting the need for further clinical investigation.

Effect of Dopant Concentration on Luminescence Properties of Na3Ca2(SO4)3F: RE (RE = Eu3+, Dy3+) Phosphor for Solid-State Lighting.

A fluoride material phosphor doped with rare earth ions Eu3+ and Dy3+ was studied for its photoluminescence (PL) properties. The material was synthesized using a combustion method and characterized using X-ray diffraction (XRD) and PL techniques. The Na3Ca2(SO4)3F: Eu3+ phosphor exhibits two distinct peaks at 593 nm (orange) and 615 nm (red) at an excitation wavelength of 395 nm. The PL excitation spectrum of the Na3Ca2(SO4)3F: Dy3+ phosphor showed series of peaks, corresponding to the 4f → 4f transitions of Dy3+ ions. Under 350-nm excitation, the PL emission spectrum revealed two prominent bands one at 483 nm (blue region) due to the 4F₉/₂ → 6H₁₅/₂ transition, and another at 573 nm (yellow region) resulting from the 4F₉/₂ → 6H₁₃/₂ transition. These blue and yellow emissions suggest potential applications in solid-state lighting, particularly for mercury-free excitation sources. Rare earth-doped Eu3+/Dy3+ materials exhibit highly efficient PL properties, making them suitable candidates for white light-emitting diodes (LEDs) or other solid-state lighting phosphors.

Major regulatory factors for reproductive performances of female chickens

The reproductive performance of female chickens is critical for determining the efficiency of production and productivity and thus profitability. Studies have shown that the reproductive performance of female chickens is mainly regulated by the feed, hormones, genes, and light conditions. Herein, we review the major factors regulating female chicken reproductive performance and assess the reproductive organs and their functions. In the current review, we highlight how the interconnections of hormones, candidate genes, and photo-stimulation regulate female chicken reproductive hormones and thus regulate the reproductive organ performance. In this regard, the roles of main hormones [gonadotropinreleasing hormone (GnRH) and genes (GnRH-I)] in regulating sexual maturation and ovarian development and maintenance by influencing the survival and function of follicular granulosa cells were also reviewed. In addition, the current review also highlights how feeding female chickens with diets and artificial light-emitting diodes (LEDs) support the effective functioning of their reproductive capacity through the stimulation of sexual maturity at an appropriate age and regeneration of aged reproductive organs.

Start-up phase performance evaluation of a pilot-scale sequential anaerobic-aerobic hybrid algal-bacterial suspended growth reactor for the domestic wastewater treatment

This study evaluated the start-up phase performance of an 80-cubic-meter pilot-scale anaerobic-aerobic hybrid algal-bacterial reactor treating real domestic wastewater operated at 24 h hydraulic retention time. The aerobic chambers of the reactor were inoculated with heterotrophic bacterial biomass and mixed microalgal culture. Blue light-emitting-diode (LED) lights were provided in the aerobic chambers to facilitate algal photosynthesis. The influent chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (P) values were 241 ± 45 mg/L, 26.8 ± 4.2 mg/L, and 6.7 ± 0.9 mg/L, respectively. After thirty days of operation, the effluent COD, TN, and P values were observed to be 26.7 ± 6.5 mg/L, 15.6 ± 0.73 mg/L, and 4.45 ± 0.16 mg/L, respectively. The sludge volume index of the mixed liquor was 43 mL/g, indicating high settleability. During the operation, an increase in the chlorophyll to biomass ratio was observed, which implies that the algal-bacterial symbiosis might have played a role in simultaneous carbon and nitrogen removal from the domestic wastewater.

Machine Learning-Driven precise design of stable OLED Materials: Predicting and enhancing Multi-State C-N bond dissociation energies

The intrinsic stability of organic light-emitting diode (OLED) materials critically hinges on the bond dissociation energies (BDEs) of fragile bonds, particularly C-N bonds. Despite the necessity of considering BDEs in multiple electronic states due to the complex working conditions of organic materials in OLED devices, comprehensive exploration remains challenging. Herein, we constructed a high-quality dataset, CNBDE-24, comprising nearly 1500 data points for BDEs across multiple electronic states, obtained through an active learning-guided density functional theory (DFT) calculation strategy. Machine learning models trained on the CNBDE-24 dataset exhibit excellent accuracy in predicting BDEs for OLED materials in neutral, triplet excited (T1), and anionic states, achieving an adjusted coefficient of determination exceeding 0.90 on the test set and bypassing the need for high-cost calculation. Moreover, utilizing neutral state BDEs as pre-training data significantly reduces model error and provides deeper insights into the relationships between different BDEs. We find that BDEs in neutral are influenced by the electronic properties of the nitrogen atom, as indicated by descriptors such as Gasteiger charges. Incorporating C-N bonds into aromatic systems and slightly dispersing N atom charges can inherently increase multi-state BDEs without altering luminescent properties. Additionally, anionic BDEs are determined by the extent of charge transfer during bond cleavage and can be regulated by modifying the C-side fragment. High-throughput virtual screening reveals a new stable purple emitter with a dominant 0–0 transition at 360 nm, which was validated through DFT and excited-state property evaluations. Strategies for enhancing BDEs in multiple resonance thermally activated delayed fluorescence materials without altering excited-state properties are also demonstrated.

Structure development and photoluminescence properties of high-purity greenish-yellow emitting LaGaO3:Dy3+ phosphors

This study investigates the structure development and photoluminescence properties of high-purity greenish-yellow emitting LaGaO3 phosphors doped with dysprosium ions Dy3+. The phosphors were synthesized using a high-temperature solid-state reaction method. X-ray diffraction (XRD) confirmed the formation of a single-phase LaGaO3:Dy3+ structure and scanning electron microscopy (SEM) revealed uniform particle size and morphology. The phosphor exhibits the capability of being efficiently excited by ultraviolet 350 nm exhibiting the characteristic greenish-yellow emission with two strong peaks at 478 nm (cyan) and 572 nm (yellow), ascribing to the transitions of 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. The electronic transition mechanism is direct exchange interaction between activators, contributing to the concentration quenching. The phosphor was able to retain 67 % of its intensity without significant color change at an elevated temperature up to 25 °C to 150 °C. The CIE chromaticity coordinates of the emitted light were calculated and found in the desired greenish-yellow region. The electroluminescence performance of the LaGaO3:0.06Dy3+ phosphor was investigated using 365 nm LED chips to check their applicability in the field of white light-emitting diodes (WLEDs). The synthesized phosphors demonstrated high thermal stability, making them suitable for white-LED applications. The study highlights the potential of LaGaO3:Dy3+ phosphors in enhancing white-LEDs' color quality and efficiency.

Unveiling the potential: Gallium-doped zinc oxide/silver-nanoparticles/glass structure for superior anode performance in polymer light-emitting diodes

This study examines the effectiveness of gallium-doped zinc oxide (GZO) combined with silver nanoparticles (Ag-NPs) on glass substrates as anodes for polymer light-emitting diodes (PLEDs). The proposed GZO/Ag-NPs/glass structure achieved superior electrical and optical properties, with a peak luminance of 5834 cd/m2 and an average current efficiency of 1.91 cd/A, significantly outperforming the conventional GZO/Ag-NPs/GZO/glass anode. The GZO/Ag-NPs/glass anode enhanced electroluminescence intensity by 379 % compared to the GZO/glass anode, while the GZO/Ag-NPs/GZO/glass anode showed a 196 % enhancement. This highlights the potential for improved PLED performance through enhanced anode conductivity and localized surface plasmon resonance effects.

InGaN quantum dots for micro-LEDs

Micro-scale light-emitting diodes (micro-LEDs) have received widespread attention in recent years for applications in display and optical communication. Compared with conventional quantum well active regions, quantum dots (QDs) can increase the carrier concentration at the same current density, which is beneficial for improving the efficiency and bandwidth of LEDs at low current densities. This is exactly what micro-LEDs need for display and communication applications. In this Perspective, we give a general introduction to InGaN QDs and provide an overview of the growth of InGaN QDs by metal-organic chemical vapor deposition. We then discuss the advances in green and red micro-LEDs based on InGaN QDs for display applications. This is followed by recent progress on high-speed blue micro-LEDs, which have great potential for use in chip-to-chip optical interconnections. Finally, we address the remaining challenges for a further improvement in InGaN QD-based micro-LEDs.

Full-angle Light Out-coupling Enhancement of Quantum Dot Light-emitting Diodes by Mie-scattering Micro-lens Arrays

High efficiency, high brightness, and long-life quantum dot light-emitting diodes (QLEDs) are crucial for realizing integrated display and lighting applications. However, about 80% of the light is confined inside the device with substrate mode, waveguide mode, and plasma mode, which greatly weakens the brightness, efficiency and lifetime of the device. Here, a quasi-periodic concave template with large area was fabricated through the spontaneous condensation of droplets on the substrate surface. Based on the quasi-periodic template, SiO2 micro-lens arrays (SiO2-MLAs) Mie scattering composite structures were fabricated by nanoimprinted on SiO2-nanosphere thin film, which significantly improved light out-coupling at full angle with optimized quasi-Lambert luminescence characteristics. In comparison to the planar QLED with state-of-the-art, the external quantum efficiency (EQE) demonstrated a qualitative improvement (> 20%). Accordingly, the EQE, brightness (L), T50 lifetime (reduce to half brightness) of the green QLEDs with SiO2-MLAs structure have been optimized by 22%, 28%, 31%, and up to 24.21%, 381962.6 cd/m2, 111335 hours, respectively. This strategy provides valuable insights into mass-producing and utilizing SiO2-MLA Mie scattering composite structures to boost QLED performance in high-efficiency display and lighting applications.

Deep Traps in AlN Hydride Vapor Phase Epitaxy Film on Low-Temperature AlN/Sapphire

Deep trap states were examined in c-plane, Al-polar AlN epilayers, deposited via metal organic chemical vapor deposition on 270 nm thick AlN buffer layers on sapphire substrates. Contacts were created using e-beam deposited Ni through a shadow mask, with I-V characteristics revealing a trapped limited current (TLC) regime and voltage-dependent hysteresis upon light-emitting diode illumination. Thermally stimulated current and photothermal ionization current spectroscopy measurements demonstrated a prominent trap activation energy of approximately 0.75 eV and additional trap energies of 0.6, 0.4, 0.25, 1.05, and 1.1 eV. The observed differences in photocurrent responses between forward and reverse biases suggest that forward bias induces electron trapping at deeper levels, influencing the TLC behavior. Comparisons with bulk n-type AlN crystals from previous studies show similarities in deep trap spectra, suggesting commonality in trap characteristics across different AlN samples.

Enhanced Emitting Dipole Orientation Based on Asymmetric Iridium(III) Complexes for Efficient Saturated-Blue Phosphorescent OLEDs.

Three novel asymmetric Ir(III) complexes have been rationally designed to optimize their emitting dipole orientations (EDO) and enhance light outcoupling in blue phosphorescent organic light-emitting diodes (OLEDs), thereby boosting their external quantum efficiency (EQE). Bulky electron-donating groups (EDGs), namely: carbazole (Cz), di-tert-butyl carbazole (tBuCz), and phenoxazine (Pxz) are incorporated into the tridentate dicarbene pincer chelate to induce high degree of packing anisotropy, simultaneously enhancing their photophysical properties. Angle-dependent photoluminescence (ADPL) measurements indicate increased horizontal transition dipole ratios of 0.89 and 0.90 for the Ir(III) complexes Cz-dfppy-CN and tBuCz-dfppy-CN, respectively. Analysis of the single crystal structure and density functional theory (DFT) calculation results revealed an inherent correlation between molecular aspect ratio and EDO. Utilizing the newly obtained emitters, the blue OLED devices demonstrated exceptional performance, achieving a maximum EQE of 30.7% at a Commission International de l'Eclairage (CIE) coordinate of (0.140, 0.148). Optical transfer matrix-based simulations confirmed a maximum outcoupling efficiency of 35% due to improved EDO. Finally, the tandem OLED and hyper-OLED devices exhibited a maximumEQE of 44.2% and 31.6%, respectively, together with good device stability. This rational molecular design provides straightforward guidelines to reach highly efficient and stable saturated blue emission.

An efficient thermally activated delayed fluorophore featuring an oxygen-locked azaryl ketone acceptor

Thermally activated delayed fluorescence (TADF) dyes are promising for applications like bioimaging, sensing, and optoelectronic devices due to their efficient exciton utilization without noble metals, making them ideal for organic light-emitting diodes (OLEDs). In this contribution, we introduce a new TADF emitter, 3-(9,9-dimethylacridin-10(9H)-yl)-12H-chromeno[2,3-b]quinolin-12-one (CQLO-DMAC), which incorporates an intramolecular oxygen-locked azaryl ketone acceptor, CQLO. This design enhances molecular rigidity and electron-accepting strength. The CQLO-DMAC compound, featuring a bulky donor, shows significant intramolecular charge transfer and TADF emission. Comprehensive analyses, including spectroscopic studies and theoretical calculations, reveal high luminescence efficiency and reduced non-radiative losses. Utilizing CQLO-DMAC in OLEDs, we achieved a green-yellow emission peak at 548 nm and a maximum external quantum efficiency of 17.4%. The findings highlight the potential of CQLQ as a highly effective acceptor in designing of TADF electroluminescent dyes.