Light-emitting Diodes Research Articles

Direct band gap white light emission from charge carrier diffusion induced nanowire light-emitting diodes

Light-emitting diodes (LEDs) have been investigated during the past decades, for which a major challenge is total internal reflection that limits the light extraction efficiency. ‘Nanotree’ LEDs elegantly solve this bottleneck. Lower band gap nanowire branches are grown on higher band gap core wires. Charge carriers diffuse into the branches and recombine there. Total internal reflection is impeded since the branch diameter is much smaller than the wavelength of light emitted from the material. Our ‘nanotree’ LEDs show direct band gap emission with color corresponding to the semiconductor materials composition. By stronger biasing of the core wires, we provoke white light emission without down-converting phosphors. The concept of nanoscale-enhanced charge carrier diffusion LEDs may be a game changer for industrial LED design.

Feasibilty of UVC-LED/H2O2 Advanced Oxidation Processes as a Hybrid Water Treatment System Uniting Secondary Battery and Microbial Fuel Cell

An innovative hybrid water treatment system consisting of an ultraviolet C light-emitting diode sequentially connected to a secondary battery and microbial fuel cells was developed and systematically optimized via an electrochemical performance test. According to standardized bio-dosimetry, the generated ultraviolet intensity powered by a pre-charged battery was determined to be 2.3×10-1 μW cm-2. The quantified UV intensity was used in calculating the fundamental kinetic parameters for the inactivation of microbial entities and the degradation of organic pollutants during UVC-LED and UVC-LED/H2O2 treatment processes. The fluence-based first-order rate constants were 1.07 and 2.43 cm2/mJ for Escherichia coli and 0.10 and 0.18 cm2/mJ for MS-2 bacteriophage, respectively. The study detected 2.76–8.00×10−16 M hydroxyl radicals at steady-state during UVC-LED/H2O2 treatment with 0.3–1mM H2O2. The second-order rate constant for atrazine during UVC-LED/H2O2 treatment was 1.90×109M−1 s−1 according to linear regression analysis of atrazine elimination over •OH exposure. This comprehensive investigation expands the application of microbial electrochemical systems in water treatment, providing a fundamental kinetic dataset for quantifying and predicting the microbial and (persistent) organic pollutants abatement.

Blue-emission crystalline OLED doped with DMAC-DPS TADF material.

Doping thermally activated delayed fluorescence (TADF) materials with high exciton utilization into crystalline hosts with high carrier mobility is an effective approach for developing novel OLEDs. This approach harnesses the strengths of both materials to realize high-performance blue light-emitting crystalline organic light-emitting diodes (C-OLEDs). Nevertheless, the high triplet energy levels of blue emitting TADF materials may facilitate the outflow of triplet excitons through Dexter energy transfer to the lower energy levels within the crystalline host, thus leading to efficiency losses in the device. In this study, we present a pioneering strategy designed to improve the exciton utilization efficiency of TADF materials in C-OLED by leveraging the up-conversion capability of TTA materials to reclaim triplet excitons. With a well-designed energy level structure, this device achieves a maximum EQE of 5.6% and a low turn-on voltage of 2.7 V. The benefits of the crystalline host allowed for fast turn-on, and a rapid increase in brightness and current density, leading to significantly improved blue photon output and a lower series resistance Joule heat loss ratio. This work introduces a novel approach to employ TADF materials in crystalline hosts and manage excitons within the emissive layer of devices, aiming to develop high-performance C-OLEDs.

Reducing Total Plate Count of Bacteria through Dark Sealed Storage for Plant Factory Nutrient Solution Sterilization

Plant factories are efficient systems for vegetable production under a clean and controlled environment. To improve the sterilization efficiency of nutrient solutions (NS) in plant factories, this study examined the changes in the number and composition of colonies from in-use and post-use stored NS. The sterilization effect under ultraviolet (UV) light-emitting diode light was also investigated. The results indicated that the total plate count of bacteria (TPC) of newly prepared NS was 3.99 lg CFU/mL (9870 CFU/mL); within 7 days of cultivation, this number sharply increased ∼7.8 times to 4.88 lg CFU/mL (76,000 CFU/mL), then remained stable. After dark sealed storage (DSS) of post-use NS, TPC dramatically decreased by 82.8% and reached its lowest point at 4.29 lg CFU/mL (19,566 CFU/mL) on day 3, equivalent to a log survival ratio of −0.76, then rapidly rebounded by 235.6% to 4.82 lg CFU/mL (65,666 CFU/mL) on day 4. During storage, bacterial community composition was also remarkably changed, and the relative abundance of heterotrophic bacteria such as Variovorax paradoxus and Pararhizobium giardinii and photosynthetic bacteria such as Pseudo-Nitzschia multiseries were greatly decreased. The log survival ratio for in-use and post-use stored NS under UV sterilization were −1.29 and −1.30, respectively, and was not significantly different. Coupled with the dramatic decrease in TPC during DSS, the overall log survival ratio of post-use NS UV sterilization was −2.06 and was the most effectively form of sterilization in our study. In short, TPC of in-use NS remained high for a long period, and DSS may serve as a low-cost NS sterilization method in plant factories.

Achieving efficient and stable deep-blue tandem organic light-emitting diodes with high color purity via novel charge generator layer

Efficient and stable deep blue OLEDs with high color purity are desirable for OLEDs based displays. However, the development of deep blue OLEDs is lagging far behind green and red OLEDs for lots of years due to their higher-energy exciton, which reduces the final device performance and increases the consumption of electrical energy. Here, we designed a novel charge generator layer (CGL): Liq/Al/MoO3/SimCP2 with improved charge injection capability than traditional CGL. Based on this CGL, we successfully fabricated tandem deep blue OLEDs using thermally actively delayed fluorescence materials SYBN as guest and triplet–triplet annihilation material NPADN as host, which exhibits high external quantum efficiency of 17.7 %, current efficiency of 13.3 cd/A, power efficiency of 7.1 lm/W and stable LT95 device lifetime over 1200 h at initial luminescence of 1000 cd/m2. Simultaneously, it’s convenient to adjust the micro-cavity effect through increasing Spiro-BFA-2 thickness to reduce the full width at half maximum (FWHM) of EL spectra from 26 nm to 21 nm, realizing small CIEy value of 0.061 at a mild emission wavelength of 461 nm while maintaining a low driving voltage of 8.6 V at 1000 cd/m2. We believe that this work is significant to promote the development of deep blue OLEDs.

Dy doped calcium silicates synthesized using agro-food wastes and conventional chemicals as resources: a comparative study

Based on an earlier study, a mimic composition 38SiO2-60CaO-0.5Dy2O3-0.2Na2O-1MgO-0.1Al2O3-0.1TiO2-0.1Fe2O3 (wt.%) are synthesized by solid-state reaction method. The structural, morphological, and optical properties of the synthesized sample presented in this study are compared with the corresponding properties of a similar sample derived from rice husk ash and eggshell powder as resources. The conventional chemicals derived sample are multi-phasic, containing β−Ca2SiO4, γ−Ca2SiO4, Ca3Si2O7, and CaFeO3 phases, and the CaO/SiO2 ratio was believed to be affecting the room temperature stabilization of the β phase. Field emission scanning electron microscopy images showed that twinned particles, cracks, and edge dislocations were present in the synthesized sample. The presence of precipitates in the micrographs indicated that Dy ions were segregated on the surface of the sample. The optical bandgap of the samples was 3.7 eV, as calculated by diffuse reflectance spectroscopy. The photoluminescence emission spectrum contained characteristic emission peaks of the Dy3+ ions. Apart from these, additional peaks were observed due to the titanium ions present in the sample. Understanding the properties of calcium silicates containing multiple dopant ions is important to develop a white light-emitting diode. The properties of the mineral-derived sample are compared to those of the agro-food waste-derived similar sample.

Tuning of bandgap for warm white light emissions in indium-doped cesium metal halide perovskites by solvothermal method

Cesium-based perovskites, particularly Cs3Bi2Br9, doped with indium, have emerged as promising materials for energy-efficient lighting, notably in white light-emitting diodes (WLEDs). This study aimed to address environmental concerns associated with lighting technology by employing solvothermal synthesis to fabricate these materials. Comprehensive characterization techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL), were applied to assess their properties. XRD analysis confirmed the formation of Cs3Bi2Br9 with a trigonal crystal structure and indium doping induced significant changes in the material’s color and crystal lattice. TEM imaging, even after six months, revealed the presence of stable nanocrystals, indicating the material’s durability in practical applications. UV–Vis absorption and photoluminescence spectroscopy showed variable bandgaps and efficient photon emission. Notably, as the indium doping concentration increased, the emitted light shifted from blue to bluish-white, making these materials highly suitable for the synthesis of WLEDs. This research offers a promising prospect to address environmental issues associated with lighting technology while advancing energy-efficient illumination solutions.

Role of LED (Light Emitting Diode) Light Illumination on the Growth of Plants in Greenhouse Farming-Hydroponics: IOT Technology

This review paper of literature highlights role of Light Emitting Diode (LED) on the growth of plants under controlled conditions of greenhouse farming particularly hydroponics. “Internet of Things (IOT)” is a system of interconnected computing devices, sensors, objects, microcontrollers, and cloud servers that can transmit data across a network and control other devices remotely without human intervention. Light Emitting Diode (LED) is a more efficient, versatile, lasts longer, highly energy-efficient, directional, narrow light spectrum, low power consumption, and little heat production. Common LED colors include amber, red, green, and blue. Hydroponic grow lights are designed to mimic the natural light that plants need for photosynthesis. Plants can only use the spectrum of visible light to produce photosynthesis, and this narrow spectrum (400 to 700 nanometer) is recognized as the Photosynthetically Active Radiation (PAR). The development and growth of diverse plant species can be influenced differently by a variety of colored LED lights. LED illumination provides an efficient way to improve yield and modify plant properties. Therefore, LED systems plays an important role in controlling morphological, genetic, physiological, chemical properties, increasing the synthesis of a variety of beneficial secondary metabolites, and optobiological interactions of plants in greenhouse farming. In general, red and blue light is essential for maximizing the photosynthesis process due to their strong absorption by the plant chlorophyll molecules. LED illumination sources are increasingly being utilized to enhance the growth rate of vegetables and herbs cultivated in greenhouses worldwide. LED illumination spectrum manipulation could enable significant morphological adaptations, and identification of the wavelength ranges is required to increase the plant photosynthesis process.

Performance-optimized and phase purity-improved high-n quasi-two-dimensional perovskite for green light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskite has the advantage of enlarging exciton binding energy and is more suitable for efficient perovskite light-emitting diodes (PeLEDs). However, the quasi-2D perovskite films deposited with solution methods are usually mixtures of multiple phases with different inorganic layer numbers (n), unfavorable to obtaining high emission efficiency. In this study, we selected formamidinium lead bromide (FAPbBr3) as the light emitter and (2-phenylethyl)ammonium cation (PEA+) as the long-chain organic spacer cation to prepare high-n (n = 9) quasi-2D perovskite films with improved phase purity. Based on the multiple cations mixed engineering, the quality of these films improved obviously by partly replacing FA+ with minute quantities of cesium cation (Cs+). The improvement focused on remarkably enhanced photoluminescence, few low-n phases, and decreased grain sizes. The green PeLED based on the performance-optimized and phase purity-improved high-n quasi-2D perovskite reached a high brightness of 28 960 cd/m2 together with a maximum current efficiency of 44.8 cd/A and a maximum external quantum efficiency of 9.99%.

Organic Circularly Polarized Room-Temperature Phosphorescence: Strategies, Applications and Challenges.

Organic circularly polarized luminescence (CPL) plays crucial roles in chemistry and biology for the potential in chiral recognition, asymmetric catalysis, 3D displays, and biological probes. The long-lived luminescence, large Stokes shift, and unique chiroptical properties make organic circularly polarized room-temperature phosphorescence (CPP) a new research hotspot in recent years. Nevertheless, achieving high-performance organic CPP is still challenging due to the sensitivity and complexity of integrating triplet excitons and polarization within organic materials. This review summarizes the latest advances in organic CPP, ranging from design strategies and photophysical properties to underlying luminescence mechanisms and potential applications. Specifically, the design strategies for generating CPP are systemically categorized and discussed according to the interactions between chiral units and chromophores. The applications of organic CPP in organic light-emitting diodes, sensing, chiral recognition, afterglow displays, and information encryption are also illustrated. In addition, we present the current challenges and perspectives on developing organic CPP. We expect this review to provide some instructive design principles to fabricate high-performance organic CPP materials, offering an in-depth understanding of the luminescence mechanism and paving the way toward diverse practical applications.

Targeted elimination of tetravalent-Sn-induced defects for enhanced efficiency and stability in lead-free NIR-II perovskite LEDs.

Eco-friendly Sn-based perovskites show significant potential for high-performance second near-infrared window light-emitting diodes (900 nm - 1700 nm). Nevertheless, achieving efficient and stable Sn-based perovskite second near-infrared window light-emitting diodes remains challenging due to the propensity of Sn2+ to oxidize, resulting in detrimental Sn4+-induced defects and compromised device performance. Here, we present a targeted strategy to eliminate Sn4+-induced defects through moisture-triggered hydrolysis of tin tetrahalide, without degrading Sn2+ in the CsSnI3 film. During the moisture treatment, tin tetrahalide is selectively hydrolyzed to Sn(OH)4, which provides sustained protection. As a result, we successfully fabricate second near-infrared window light-emitting diodes emitting at 945 nm, achieving a performance breakthrough with an external quantum efficiency of 7.6% and an operational lifetime reaching 82.6 h.

Interfacial Metal Chlorides as a Tool to Enhance Charge Carrier Dynamics, Electroluminescence, and Overall Efficiency of Organic Optoelectronic Devices.

Interface engineering is the key to optimizing optoelectronic device performance, addressing challenges like reducing potential barriers, passivating interface traps, and controlling recombination of charges. Metal fluorides such as lithium fluoride are employed in interface modification within organic devices due to their strong dipole characteristics but carry health risks, high processing costs, and minimal impact on interface traps in organic electronics. Hence, this study investigates alternative metal chloride (MC) nanocrystals (sodium, cesium, rubidium, and potassium chlorides) that exhibit a strong dipole moment and are readily processable with the aim of reducing the influence of interface traps. Interfacial properties are assessed via various techniques, including electron paramagnetic resonance, X-ray/ultraviolet photoelectron spectroscopy, capacitance-voltage measurements, and density functional theory calculations. In organic light-emitting diodes (OLEDs), the influence of MC on charge transfer, trap density, and light emission properties is evaluated. MCs in ZnO:PEIE nanocomposites (NCs) show improved charge transport, accelerated trapping/detrapping in ZnO:PEIE NCs, and a 50% reduction in active traps in NaCl-based devices versus the reference without MCs. RbCl-, CsCl-, and NaCl-based OLEDs exhibit substantial reductions in the potential barrier between the electron injection layer and the metal contact (Al) from 4.43 to 2.93, 3.02, and 4 eV, respectively, accompanied by enhancements of 35, 27, and 25% in electroluminescence intensity.

Recent Advances in Light Outcoupling from Quantum-Dot Light-Emitting Diodes

Recent Advances in Light Outcoupling from Quantum-Dot Light-Emitting Diodes

Efficient Organic Light-Emitting Diodes Obtained by Introducing Gadolinium (Gd) Complexes Based on Pyrazolone Derivative Ligands as Hole Trappers.

The utilization of lanthanide (Ln) complexes in the realm of organic light-emitting diodes (OLEDs) has garnered extensive interest, particularly in their role as luminescent materials or electron trappers. A series of gadolinium (Gd) complexes with energy levels of high HOMO/LUMO and different triplet state energies were designed and synthesized by introducing substituents with different electronic effects onto the pyrazolone derivative ligands. Subsequently, these complexes were precisely purified by vacuum sublimation and codoped into the light-emitting layer (EML) of the OLEDs. This process was facilitated through the well-matched HOMO/LUMO levels and triplet energies among various functional materials. Consequently, the maximum external quantum efficiencies of blue, red, and green OLEDs were simultaneously enhanced with the ratios of 119%, 28%, and 71%, respectively. This improvement can be credited to the introduction of Gd(III) complex molecules within EMLs, which helps to capture excess holes and improve carriers' balance.

Replication advancements review in ultraviolet GaN/AlGaN quantum well light emitting diodes: engineering, simulation and validation

Abstract This paper presents a comprehensive study on the replication of ultraviolet (UV) GaN quantum well light emitting diodes (LEDs) based on Han et al.’s experimental work. The replication structures of the electroluminescence emission at 353.6 nm with a narrow 5.8 nm linewidth validated the reliability of the simulation model. However, during the simulation run, a surprising and significant peak shift was observed, resulting in an emission peak at 358.6 nm, which deviated from the reported value. This discrepancy necessitates further investigations to understand the factors responsible for this unexpected change. Nonetheless, this correlation remains crucial as a benchmark for evaluating potential quantum well and device performance enhancements by following the existing structure and composition. Ultimately, it improves learning progress in scientific studies to the quantum level. Remarkably, the optimized devices exhibited exceptional stability at high current densities and demonstrated the efficacy of Drift-diffusion Charge Control (DDCC) solver simulation, which advances UV-LED technology, tallying with the literature claims and indirectly paving the way for high-performance applications.

Human-centric lighting asset management for LED bulbs: a context-driven approach on prognostics and maintenance strategy development in public libraries

ABSTRACT Traditional asset management of lighting systems typically focuses on functionality, cost, and lifespan. In contrast, a human-centric approach prioritizes social sustainability and user well-being by ensuring lighting assets “provide the right light at the right time” for diverse activities. Light-emitting diode (LED) bulbs, known for energy efficiency and longevity, have become a preferred choice, yet public libraries often struggle to manage these assets sustainably, remaining in a reactive “fix/replace when it breaks” stage. Current predictive methods, such as artificial intelligence and machine learning, rely on laboratory data that often overlook real-world contexts, leading to performance gaps. This paper presents a context-driven, human-centric methodology for LED prognosis and maintenance strategies in public libraries, employing limited degradation data from LED testing. Advanced analytical techniques, including Markov Chain Monte Carlo (MCMC) and Deviance Information Criterion (DIC), support a shift from function-based to performance-based reliability assessment. By incorporating Mean Time of Exposure (MTOE) and Critical Integrated Levels (CILs), the approach defines optimal maintenance inspection intervals. This research enhances sustainable LED lighting management in public libraries, offering a framework adaptable to broader applications and aligned with human-centric goals..

Two-Step Chemical Vapor Deposition for Fabrication of FAPbI3 Single-Crystal Microsheets with High Exciton Binding Energy.

Hybrid perovskites exhibit highly efficient optoelectronic properties and find widespread applications in areas such as solar cells, light-emitting diodes, photodetectors, and lasers. Here, we report the innovative synthesis of formamidinium lead iodide (FAPbI3) single-crystal microsheets via a two-step chemical vapor deposition (CVD) method. The microsheets exhibit hexagonal and trapezoidal shapes, with hexagonal FAPbI3 growing parallel to the substrate and trapezoidal FAPbI3 growing perpendicular to the substrate. The dominant role of single-exciton recombination in the photoluminescence (PL) of these microsheets is observed, especially pronounced at low temperatures, attributed to the relatively large exciton binding energies of the samples. Calculations reveal exciton binding energies as high as 110.8 meV for hexagonal and 133.3 meV for trapezoidal FAPbI3 single-crystal microsheets, attributed to reduced rotational freedom of the formamidinium (FA) ions. Further investigation into low-temperature phase transitions indicates lower transition temperatures (around 100 K) for these microsheets, suggesting reduced FA ion rotational freedom and consequently higher exciton binding energies.

Atomic Layer Deposition of ZnO on CsPbBr3 Perovskite Nanocrystals: Surface-Dependent Mechanistic Insights.

In this study, we investigate the atomic layer deposition (ALD) process on all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) to introduce an inorganic electron transport layer (ETL) in light-emitting diode (LED) devices. Two types of CsPbBr3 PNCs were synthesized with oleate (OA) and oleylammonium (OLA) ligands on the surface. We found that CsPbBr3 PNCs with Cs oleate surfaces experienced severe photoluminescence (PL) quenching after the ALD process, while those with oleylammonium bromide surfaces did not show any significant PL drop. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed that significant Pb metal formation and Ruddlesden-Popper planar faults, linked to uncoordinated Pb2+ ion defects, were generated in CsPbBr3 PNCs terminated with Cs oleate after ALD ZnO. Finally, we fabricated LEDs using PNCs with an ALD ZnO process to introduce inorganic ZnMgO nanoparticles as the ETL. The devices processed with ALD exhibited superior luminance and external quantum efficiency compared to those without the ALD process. This research provides crucial insights into the surface-dependent chemistry of PNCs and the surface-dependent performance of perovskite-based optoelectronic devices.

Plasticizer Design Principle of "Like Dissolves Like": Semiconductor Fluid Plasticized Stretchable Fully π-Conjugated Polymers Films for Uniform Large-Area and Flexible Deep-Blue Polymer Light-Emitting Diodes.

Physical blending of fully π-conjugated polymers (FπCPs) is an effective strategy to achieve intrinsically stretchable films for the fabrication of flexible optoelectronic devices, but easily causes phase separation, nonuniform morphology and uncontrollable photo-electronic processing. This may cause low efficiency, unstable and nonuniform emission, and poor color purity, which are undesirable for deep-blue flexible polymer light-emitting diodes (FPLEDs). Herein, a "Like Dissolves Like" design principle to prepare semiconductor fluid plasticizers (SFPs) is established and intrinsically stretchable FπCPs films via external plasticization for high-performance deep-blue FPLEDs are developed. Three fundamental requirements are proposed, "similar conjugated skeleton, similar molecular polarity, and similar electronic structures," to prepare model-matched nonpolar M1 and polar M2 plasticizers for poly(9,9-dioctylfluorene) (PFO). Large-area plasticized PFO films exhibit an efficient, narrowband, and stable ultra-deep-blue electroluminescence (FWHM < 40nm, CIE: 0.12, 0.04), uniform morphology, and excellent intrinsic stretchability (fracture strain >20% and crack-onset strain >120%). Efficient and uniform deep-blue FPLEDs based on stretchable PFO films are fabricated with a high brightness of ≈3000cd cm-2. Finally, blended PFO films exhibit outstanding stretch-deformation cycling stability of their deep-blue electroluminescent behavior, confirming the effectiveness of the "Like Dissolves Like" principle to design matched SFPs for stretchable FπCP films in flexible electronics.

Long-Lived Room-Temperature Phosphorescence from Silica Nanoparticles with In Situ Generated Carbonaceous Defects for Blue Organic Light-Emitting Diodes.

In this study, in situ formed silica nanoparticles (SNPs) emitting second-level phosphorescence at room temperature without a phosphorescent dopant have been achieved for the first time. This phosphorescence is achieved through the simple in situ formation of carbonaceous defects (CDs) within the SNPs, followed by passivation of the CDs by a robust silica matrix. The CD in the SNPs, termed CD@SNPs, are synthesized by cross-linking tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES), and these cross-linked components create a porous structure within the silica matrix. Upon calcination, the carbon-related structures within the pores deform, leading to the formation of CDs. Confined within a robust silica matrix, the molecular motion of the CD is restricted, facilitating the generation of a stable triplet state and suppressing nonradiative decay. Moreover, the robust silica matrix passivates the CD confined in the SNPs at a nanoscale. These comprehensive effects enable prolonged phosphorescence emission from the SNPs. In addition, these phosphorescence-emitting SNPs have been applied as dopants in the emissive layer of organic light-emitting diodes to realize blue light emission. This feature suggests the possibility of utilizing luminescent SNPs as light emitters in display technologies.