High-brightness Light-emitting Diodes Research Articles

From interface effect to bulk effect: Probing the capacitive coupling enhancement mechanism to achieve high performance DC droplet-based nanogenerator

The DC droplet-based nanogenerator (DNG) technology has opened up a new avenue for high-entropy water energy harvesting. However, the conventional DC DNG relies on the interface effect to generate a limited surface charge density, which severely restricts its electrical performance. Here, inspired by the MOS transistors, a novel total current DNG (TC-DNG) platform with back-gate modulation structure is developed, successfully realizing the transform from interface effect to bulk effect. By using the rationally patterned DNG as triboelectric probe, an intriguing capacitive coupling enhancement mechanism is discovered. With such a mechanism, the nanogenerator could employ both the capacitive coupling effect of the back-gate electrode and the self-exciting effect of droplet charge-shuttles to achieve a significantly enhanced performance in both charge transfer and voltage output. As a result, this TC-DNG provides a transferred charge of 30 nC per droplet and an output voltage of 800 V and is capable of illuminating 480 high-brightness LEDs without using any power management circuit. In addition, this TC-DNG could easily adapt to a wide range of application scenarios owing to the interchangeability of the back-gate material. This work could inspire further innovations in energy transfer mechanism and harvesting technology at the liquid-solid interface.

Wafer-Scale Characterization of 1692-Pixel-Per-Inch Blue Micro-LED Arrays with an Optimized ITO Layer.

Wafer-scale blue micro-light-emitting diode (micro-LED) arrays were fabricated with a pixel size of 12 μm, a pixel pitch of 15 μm, and a pixel density of 1692 pixels per inch, achieved by optimizing the properties of e-beam-deposited and sputter-deposited indium tin oxide (ITO). Although the sputter-deposited ITO (S-ITO) films exhibited a densely packed morphology and lower resistivity compared to the e-beam-deposited ITO (E-ITO) films, the forward voltage (VF) values of a micro-LED with the S-ITO films were higher than those with the E-ITO films. The VF values for a single pixel and for four pixels with E-ITO films were 2.82 V and 2.83 V, respectively, while the corresponding values for S-ITO films were 3.50 V and 3.52 V. This was attributed to ion bombardment damage and nitrogen vacancies in the p-GaN layer. Surprisingly, the VF variations of a single pixel and of four pixels with the optimized E-ITO spreading layer from five different regions were only 0.09 V and 0.10 V, respectively. This extremely uniform VF variation is suitable for creating micro-LED displays to be used in AR and VR applications, circumventing the bottleneck in the development of long-lifespan and high-brightness organic LED devices for industrial mass production.

Spectrum regulation of LuAG:Ce phosphor ceramic with Gd doping for high-brightness and high-power yellow-emitting LEDs applications

To realize the high-brightness of yellow light-emitting diodes (LEDs), the yellow-emitting phosphor ceramics with high luminous efficiency (LE) are urgently explored. Based on the idea of spectrum regulation, the Lu3-x-yGdyAl5O12:xCe3+ (LuGdAG:Ce) phosphor ceramics were prepared via vacuum solid-state sintering. The effect of Gd3+ and Ce3+ content on the structure, luminescence and thermal properties of LuAG:Ce ceramics were investigated. The distortion ratio (D) of CeO8 and bandgap were effectively modified via Gd3+ doping, resulting in massive red-shifting of Ce3+ emission (513→561 nm). The LEDs lighting encapsulated by LuGdAG:Ce ceramics changes from green to yellow. Importantly, the yellow LEDs with a LE up to 139.0 lm/W@180 W and a warm correlated color temperature (CCT) of 3620 K were achieved based ceramic Ce07Gd9. The LuGdAG:Ce phosphor ceramic has the best of luminescence performance in phosphor-converted yellow LEDs lighting so far, which is considered to be the highly promising color converter.

The Zn1−xMgxO electron transport layer for charge balance in high-brightness inverted quantum-dot light-emitting diodes

The Zn1−xMgxO electron transport layer for charge balance in high-brightness inverted quantum-dot light-emitting diodes

Effect of segment structure of monotrimethoxysilylethyl-terminated asymmetric polysiloxanes on the thermal management performance of AlN-filled silicone pastes

Three kinds of α-triethylsiloxyl-ω-trimethoxysilyethyl-terminated oligomers (TES-PDMS-TMOS, TES-PTFPMS-TMOS, and TES-PDES-TMOS) were synthesized through an anion catalyzed non-equilibrium ring-opening polymerization reaction of cyclotrisiloxanes and subsequent hydrosilylation reaction with vinyltrimethoxysilane. As the in situ surface modification agent for mixed-size AlN inorganic fillers (1, 20 and 50 μm blended in a mass ratio of 3:5:9), these oligomers have been mixed with Vi-PDMS in a mass ratio of 1:2. Relative to that of silicone pastes using Vi-PDMS as the polymer matrix, the thermal conductivity of silicone pastes made from AlN particles treated with these oligomers is enhanced, while their thermal resistances decreased. With the change of the repeating unit structure in the oligomers, the silicone pastes prepared from these oligomer-treated AlN fillers differ significantly in filler content, thermal conductivity, and thermal resistance. When TES-PTFPMS-TMOS is used and filled with 800 parts (70.3 vol%) of hybrid AlN powders, a silicone paste with a thermal conductivity of 4.56 W/(m. K) could be achieved, which was 37.8% higher than that silicone paste using pure Vi-PDMS as the matrix. When TES-PDES-TMOS is used and filled with 900 parts (72.7 vol%) of hybrid AlN powders, the thermal conductivity of the silicone paste reaches 4.13 W/(m. K). Despite its thermal conductivity being only 3.5% higher relative to the silicone paste using only Vi-PDMS as the polymer matrix, its thermal resistance decreased by 20.3%. When TES-PDMS-TMOS is used and filled with 1200 parts (78.0 vol%) of hybrid AlN powders, the thermal conductivity of the silicone paste could reach up to 4.59 W/(m. K), together with a thermal resistance 29.6% lower than that of silicone paste where 1000 parts (74.7 vol%) of hybrid AlN particles filled in the Vi-PDMS. The heat dissipation of the 30 W high-brightness LED chip also illustrated the excellent thermal conductivities of these silicone pastes. The effect of another terminal group on the monotrimethoxysilylethyl-terminated asymmetric polysiloxanes on the thermal resistance of thermal interface materials was also discussed in detail.

Design of a high-power collimating optical system based on Fresnel lenses.

In light-emitting diode (LED) illumination (e.g., LED maritime lighting for ships), creating a uniform light environment for optical systems is an important challenge. In this study, we present a high-power collimating system based on Fresnel lenses, which allows high-brightness LED illumination in the earlier-mentioned remote distance. The work presented in this article focuses on improving the power, compacting the optical structure, and promoting the brightness of the spot. To prove the claims, the system with a total power of 1 kW is designed. The system consists of a 27 W LED array, a freeform surface lens array, and a confocal Fresnel lens array. In comparison with the traditional optical system, the optical structure shortens from 390 to 120 mm, and the divergent angle decreases from 3° to 2 . Meanwhile, the illuminance of the system is obtained as high as 230 lx at the near field of 200 m and 3.0lx at the far field of 1.5 nautical miles. This new method provides a practical and effective way to solve the problem of low power, insufficient illuminance, and long optical structure for LED array illumination, which is suitable for remote illumination and guidance of ships.

LED-based Fourier transform spectroscopy of 14N216O in the 9750-12050 cm−1 region

The five bands of the nitrous oxide molecule (ν1+4ν3,ν1+4ν20+3ν3, 3ν1+3ν3, ν1+5ν3 and 6ν1+2ν3) were studied in the 9750–12,050 cm−1 region using a Bruker IFS-125 M Fourier Transform Spectrometer. High brightness LEDs used as the light sources, which have provided a high signal-to-noise ratio and made it possible to record weak lines with intensities of the order of 1 × 10−26 cm/molecule at 296 K. Each spectrum was obtained by averaging over 33,120 scans. The line parameters (centers and intensities) were recovered from the observed spectra. The spectroscopic constants of the upper vibrational states together with the vibrational transition dipole moments were fitted to the measured line positions and intensities, respectively. It was found that the ν1+5ν3 band is in an interpolyad resonance anharmonic interaction with the 6ν1+2ν3 band.

Highly Monochromatic Ultraviolet LED Based on the SnO2 Microwire Heterojunction Beyond Dipole-Forbidden Band-Gap Transition.

SnO2 has been extensively applied in the fields of optoelectronic devices because of its large band gap, high exciton binding energy, and outstanding optical/electrical properties. However, its applications in ultraviolet light-emitting diodes (LEDs) are still hindered by the dipole-forbidden rule. Herein, the dipole-forbidden rule can be conquered by synthesizing Sb-incorporated SnO2 microwires (SnO2:Sb MWs), which are examined by ultraviolet photoluminescence emitting at 363.2 nm and a line width of 11.3 nm. Subsequently, a highly monochromatic ultraviolet light-emitting diode (LED) based on a SnO2:Sb MW heterojunction was constructed with a p-GaN film serving as the hole supplier. In the LED, the presence of a MgO intermediate layer can modulate carrier transport and recombination path, thus achieving band-edge optical transition in the SnO2:Sb MW. As the LED is modified using Ag nanowires, electrical properties, especially for the hole injection efficiency, were dramatically boosted, contributing significantly to the device high brightness. The LED emits at 365.9 nm and a line width of 12.4 nm. Therefore, we have realized a high-brightness and narrow-band ultraviolet LED with the shortest peak wavelength never seen in previously reported SnO2 LEDs. This work will promote the potential applications of low-dimensional SnO2 optoelectronic devices and provide an effective exemplification to overcome the dipole-forbidden rule in metal-oxide materials with "forbidden" energy gaps.

Highly Sensitive Detection of DNA Fragments by an Inexpensive and Simple Method Fabricated In-House Blue LED Transilluminator

Agarose gel electrophoresis is a routinely employed experimental technique for visualizing nucleic acids, typically combined with ethidium bromide or some other molecular dye staining and a UV transilluminator. However, the utilization of a UV transilluminator is restricted due to high cost and safety considerations. In this study, an inexpensive and simple in-house blue Light Emitting Diode (LED) transilluminator was developed using a high-brightness blue LED, carbon resistor, and smartphone charging cable. Its sensitivity for DNA detection was compared with conventional methods. A detection limit of 4 ng/band was confirmed by observing a 100 bp DNA fragment, which is comparable to ethidium bromide staining and UV transilluminator. Additionally, the in-house blue LED transilluminator can be attached to existing electrophoresis chambers, allowing real-time observation of electrophoresis and offering a superior alternative to conventional methods. In conclusion, the developed in-house blue LED transilluminator demonstrates high sensitivity in detecting DNA fragments and holds potential for advancing low-cost research facilities.

A Nonisolated Wide-Range Resonant Converter for LED Driver Applications

In this article, a non-isolated resonant light-emitting diode (LED) driver based on the LCLC resonant network is presented. The adopted LCLC network can provide load-independent current for LED string, also, the soft switching range and the semiconductor devices RMS current can be optimized within the entire range of the input and output voltage using the LCLC network parameters. A single auxiliary switch is employed for regulating the output current within a wide input voltage range using PWM control. In addition, the employed auxiliary switch can provide PWM dimming and open-load protection features. Detailed theoretical analysis including the operating modes and soft switching conditions of the proposed LED driver is presented, and the impact of the auxiliary switch snubber capacitor on the load-independent output current characteristic is analyzed. To verify the analysis and effectiveness of the proposed topology operation, a 40 W laboratory prototype with the input voltage range of 80 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 230 V is designed and implemented which delivers 0.5 A current to a high-brightness light-emitting diode (HB-LED) string.

Inspection of improved ghost imaging for hight-light LED with different factory quality

High brightness and high reflective properties are two important challenges for machine vision inspection. We propose a new method for nonlinear feature extraction and inspection of visual weak signals from highlight-emitting rather than “interference” bright objects. Based on the ghost image principle, the highlight characteristics of the light source become a useful characteristic. Under the guidance of ghost image theory, optimized design of ghost lens group, visual inspection of bright objects for the purpose of obtaining ghost images with high signal-to-noise ratio. We improved the high-brightness LED appearance quality inspection experiment of ghost image. Results show that the inspection method of improved ghost image of highlighted objects combined with deep learning has a good detection result. The method has an accuracy rate of 90.1%. In the early stages of the visual inspection process, there is great potential in applying the theory and method of ghost image to detect objects with high brightness and high reflective properties.

Red Electroluminescence from Light Emitting Diodes Based on Eu-Doped ZnO Embedded in p-GaN/Al2O3/n-ZnO Heterostructures

Heterojunction p-GaN/n-ZnO light emitting diode (LED) structure using Eu-doped ZnO (ZnO:Eu) as an active component is demonstrated in order to realize low-cost and environmentally-friendly red LEDs with sharp linewidth and temperature stability against surrounding environment including operating temperature and injection current. Chemically stable Al2O3 is inserted as an electron blocking layer between p-GaN and ZnO:Eu/n-ZnO in order to facilitate the injection of carriers into the ZnO:Eu active layer. Al2O3 insertion with a moderate thickness (∼10 nm) facilitates the carrier recombination at the ZnO layer with comparatively low resistivity. Device characteristics of the p-GaN/Al2O3/ZnO:Eu/n-ZnO LED structures show red luminescence under current injection with reversed bias voltage originated from Eu3+ ions in the ZnO host. Detailed optical characteristics of the ZnO:Eu layer in the LED structures utilizing the combined excitation emission spectroscopy measurement enable the identification of the luminescence centers contributing to Eu luminescence under both indirect excitation and collisional excitation. The luminescence center contributing to Eu luminescence under indirect excitation via the ZnO host is different from that under collisional excitation, which would pave the way to understand the Eu luminescence mechanism in ZnO:Eu, and hence realize high-brightness LED structures based on rare-Earth doped ZnO as an active component.

Quantum Shell in a Shell: Engineering Colloidal Nanocrystals for a High-Intensity Excitation Regime.

Many optoelectronic processes in colloidal semiconductor nanocrystals (NCs) suffer an efficiency decline under high-intensity excitation. This issue is caused by Auger recombination of multiple excitons, which converts the NC energy into excess heat, reducing the efficiency and life span of NC-based devices, including photodetectors, X-ray scintillators, lasers, and high-brightness light-emitting diodes (LEDs). Recently, semiconductor quantum shells (QSs) have emerged as a promising NC geometry for the suppression of Auger decay; however, their optoelectronic performance has been hindered by surface-related carrier losses. Here, we address this issue by introducing quantum shells with a CdS-CdSe-CdS-ZnS core-shell-shell-shell multilayer structure. The ZnS barrier inhibits the surface carrier decay, which increases the photoluminescence (PL) quantum yield (QY) to 90% while retaining a high biexciton emission QY of 79%. The improved QS morphology allows demonstrating one of the longest Auger lifetimes reported for colloidal NCs to date. The reduction of nonradiative losses in QSs also leads to suppressed blinking in single nanoparticles and low-threshold amplified spontaneous emission. We expect that ZnS-encapsulated quantum shells will benefit many applications exploiting high-power optical or electrical excitation regimes.

Multiple Shapes Micro‐LEDs with Defect Free Sidewalls and Simple Liftoff and Transfer Using Selective Area Growth on Hexagonal Boron Nitride Template

AbstractSeveral technological challenges have prevented GaN‐based micro‐LEDs from finding application in mass market displays, despite their unique properties such as very high brightness and the very fast response time of GaN‐based materials. The primary challenges are the cost and complexity of lift‐off and transfer of LEDs from sapphire substrates to suitable supports as well as the lowered performance of tiny micro‐LEDs caused by chemical etching that defines individual LEDs. Herein, this work reports demonstration of a complete process that solves these challenges with epitaxy and cleanroom technologies that are commercially available. The process begins with van der Waals epitaxy of 2D h‐BN on silica masks with square, triangular and hexagonal patterns on sapphire substrates which define the micro‐LED regions. Then selective area growth of MQW LED heterostructures, with ultra smooth crystalline sidewalls, down to ultra tiny size of 1.4 µm is performed. Because of the lack of vertical chemical bonds in the h‐BN layer, simple mechanical lift‐off and transfer is performed on an array of LEDs heterostructures down to size of 8 µm. Finally, transparent ITO p‐contacts are deposited on LEDs with uniform lift‐off, resulting in high brightness LEDs.

A Novel Version of the Ripple-Modulation Technique for Enabling the Use of Single-Phase Buck Converters in VLC Applications

Visible light communication (VLC) has recently emerged as a promising technology for alleviating the saturation of the radio frequency (RF) spectrum. VLC uses high-brightness light-emitting diodes (HB-LEDs) both for lighting and communication. In particular, the information transmission is carried out by performing fast changes of the light intensity emitted by the HB-LEDs. The conventional VLC driver includes a linear power amplifier (LPA) for reproducing the communication signal. Unfortunately, this approach penalizes the efficiency. During the last years, a wide variety of VLC drivers fully based on the use of switching-mode power converters (SMPCs) have been proposed to overcome the efficiency limitation. One of the most promising approaches is the ripple-modulation (RM) technique, which consists in using the output voltage ripple of an SMPC to reproduce the communication signal. However, the conventional RM technique has a major drawback: it can only be applied to multiphase buck converters. This work is focused on overcoming that limitation by introducing a novel version of the RM technique that enables the use of a single-phase buck converter. In this way, the work aims to reduce the required power-stage complexity, which is a critical parameter of HB-LED bulbs. Moreover, a novel output filter structure is proposed to reduce the total harmonic distortion of the reproduced signal. A ripple-modulated buck converter prototype was built with an output power and a switching frequency of 8 W and 2 MHz, respectively. Moreover, the reproduced passband modulation scheme provides a bit rate of up to 1.25 Mb/s with a communication range of 100 cm and a peak efficiency of 94%.

Optimization of heat-dissipated structures with cuprous oxide deposits to improve thermal management of high-brightness LED arrays

This project reports on improving the thermal performance of light-emitting diode (LED) packages based on an optimized thermal structure with a sprayed cuprous oxide coating. Eighteen orthogonal arrays of LED aluminum plates were used and the influence of the parameters of thermal dissipation structure on the LED junction temperature was established. The junction temperature of the LED assembly is developed by various heat dissipation structures based on Taguchi methods. The experimental results show that by measuring the temperature of the 12W LED module, the best results were compared with the lowest values in the overall experiment, where the junction temperature dropped from 67°C to 51°C Also, the contribution of the error to the total variance is about 0.8%, indicating that the experiment is quite successful and robust results. It was found that lower junction temperature values were obtained with optimized heat sink structures with Cu2O-coated Al substrates, and the thermal performance of the LEDs was further improved.

Efficient Synthetic Aperture for Phaseless Fourier Ptychographic Microscopy with Hybrid Coherent and Incoherent Illumination (Laser Photonics Rev. 17(3)/2023)

Efficient Synthetic Aperture for Phaseless Fourier Ptychographic Microscopy In article number 2200201, Qian Chen, Chao Zuo, and co-workers introduce an efficient synthetic aperture for phaseless Fourier ptychographic microscopy (ESA-FPM), which employs both coherent and incoherent illuminations to maximize the efficiency of data and achieve high spatial-bandwidth product reconstruction with few acquisitions. Furthermore, a customized miniaturized ESA-FPM system with a high-numerical-aperture, low-magnification objective lens, and a high-brightness LED array is built, demonstrating its potential for biomedical and pathological applications.

LED Systems Applications and LED Driver Topologies: A Review

High-power light-emitting diodes (LEDs) and high-brightness LEDs have revolutionized the lighting industry. The availability of cost-effective LEDs with high luminous flux, efficacy, and reliability has expanded their application to replace incandescent and fluorescent light sources. They have also enabled many new applications that were considered infeasible before, due to the inherent limitations of traditional sources of light. This survey provides a comprehensive overview of ac- and dc-supplied LED lighting systems and their applications, corresponding specifications and their similarities to/differences from regular power supplies. Restrictions imposed by LEDs characteristics, safety considerations, and dimmers are discussed. Also, LED driving approaches are categorized and their suitability for different applications is provided.

Quantum shells versus quantum dots: suppressing Auger recombination in colloidal semiconductors.

Colloidal semiconductor nanocrystals (NCs) have attracted a great deal of attention in recent decades. The quantum efficiency of many optoelectronic processes based on these nanomaterials, however, declines with increasing optical or electrical excitation intensity. This issue is caused by Auger recombination of multiple excitons, which converts the NC energy into excess heat, whereby reducing the efficiency and lifespan of NC-based devices, including lasers, photodetectors, X-ray scintillators, and high-brightness LEDs. Recently, semiconductor quantum shells (QSs) have emerged as a viable nanoscale architecture for the suppression of Auger decay. The spherical-shell geometry of these nanostructures leads to a significant reduction of Auger decay rates, while exhibiting a near unity photoluminescence quantum yield. Here, we compare the optoelectronic properties of quantum shells against other low-dimensional semiconductors and discuss their emerging opportunities in solid-state lighting and energy-harvesting applications.

Formation of multiple aerial LED signs in multiple lanes formed with AIRR by use of two beam splitters

We propose multiple aerial imaging system by use of two beam splitters in the optical system of aerial imaging by retro-reflection (AIRR). The AIRR optical system consists of a light source, a beam splitter, and a retro-reflector. Use of two-layered beam splitters enables us to show multiple aerial signs to drivers in multiple driving lanes. The purpose of this paper is to confirm feasibility that an aerial display by use of AIRR for a novel traffic information provision. First, we explain an optical configuration to show aerial images to multiple road lanes, a driving lane and an overtaking lane with AIRR by use of two beam splitters. Next, we have developed a prototype optical system by use of two large beam splitters and a large high-brightness LED sign that is designed to be used for actual road displays. The light source was an LED display with a height of 450 mm and a width of 390 mm, which shows a character. We observed aerial images by naked eyes as experiments. And we discuss the issues for practical application that the experiments have revealed.