Light Emitting Diode Backlight Research Articles

Mn2+ doped aluminum-rich spinel transparent ceramic phosphor with higher performance for wide color-gamut backlight display

Due to the great potential of narrow-band green-emitting phosphors for wide color-gamut white light-emitting diodes (WLED) backlight displays, there is great interest in finding host materials with the desired luminescent properties and high quantum efficiency. Herein, a series of Mg0.98-xAl2(1+x/3)O4: 0.02Mn2+ (x = 0, 0.125, 0.25) powders were synthesized using high-temperature solid-phase reactions, followed by a combination of pressureless sintering and hot isostatic pressure sintering to fabricate transparent ceramic phosphors. The crystal structure refinement, NMR spectroscopy, and photoluminescence results show tetrahedral coordination of Mn2+ ions and an increase in cation vacancies and disorder with increasing x. These transparent ceramics exhibit narrow-band green emission, which shifts from 523 to 520 nm with increasing x. The Mg0.855Al2.08O4: 0.02Mn2+ ceramic sample has an in-line transmittance of over 80 % above 500 nm and internal quantum efficiencies as high as 96.2 %. The luminous intensity of the Mg0.855Al2.08O4: 0.02Mn2+ ceramic remains above 88.6 % at 425 K compared to room temperature, with a thermal conductivity of 12.4 W·m−1·K−1. A WLED device fabricated using the Mg0.855Al2.08O4: 0.02Mn2+ ceramic, K2SiF6:Mn4+ phosphors, and a blue chip show a wide color gamut of 126 % National Television System Committee standard. The results show that Mn2+-doped aluminum-rich spinel transparent ceramics have great potential for application in wide color gamut WLED backlight devices.

Exploring an InGaN Micro-LED structure for optimum IQE operating on low current condition through simulation study

Light-emitting diodes (LEDs) are key components in display applications. The quantum efficiency of GaN/InGaN LEDs has been enhanced, leading to advancements in indoor and outdoor RGB LED display applications. White LED backlights are commonly used in displays due to the increased efficiency of InGaN LEDs. Despite efficiency, lifespan and image retention issues, OLED displays are utilized in high-end mobile phones to meet market expectations for screen response time and color saturation. Micro-LED RGB full-color displays have the potential to dominate the next-generation display market, driven by the increasing demands for resolution, power consumption and response time. Micro-LEDs are becoming smaller, reaching sizes of 50[Formula: see text][Formula: see text]m or even smaller, to meet the high-resolution requirements of displays. They offer higher contrast, brightness and faster response speeds. This research utilizes numerical simulations to develop a model for radiative and nonradiative recombination in InGaN semiconductor materials. The aim is to investigate the internal quantum efficiency (IQE) of various chip sizes, quantum well counts, well thicknesses and electron block layers under low current densities. The research reveals that the optimal structure is a single quantum well with an electron block layer (EBL), which can increase IQE from 53.85% to 80.9% at 0.01[Formula: see text]A/cm2 under low current density conditions, with a decrease in the number of quantum wells to one. The IQE efficiency improvement is 27.05%.

Foldable low-cost point-of-care device for testing blood coagulation using smartphones

Cardiovascular diseases (CVDs) caused by thrombotic events are a significant global health concern, affecting millions of people worldwide. The international normalized ratio (INR) is the most widely used measure of coagulation status, and frequent testing is required to adjust blood-thinning drug dosage, requiring hospital visits and experts to perform the test. Here we present a low-cost and portable smartphone-based device for screening INR levels from whole blood samples at the point of care. Our device uses a 3D printed platform and light-emitting diode backlight modules to create a uniform optical environment, and its foldable design allows for easy transport. Our device also features an algorithm that allows users to acquire and process video of sample flow in a microfluidic channel on their smartphone, providing a cost-effective and convenient option for blood coagulation monitoring at the point of care. We tested the performance of our smartphone-based INR device using both commercially available control samples and clinical human blood samples, demonstrating high accuracy and reliability. Our device has the potential to improve patient outcomes by enabling more frequent monitoring and, as appropriate, dosage adjustments of blood-thinning drugs, providing an affordable and portable option for screening INR levels at the point of care.

Optimized Design with Artificial Intelligence Quantum Dot White Mini LED Backlight Module Development

This study delves into the innovation of mini light-emitting diode (mini-LED) backlight module designs, a significant advancement in display technology. The module comprises a substrate, a receiving plane, and an LED structure, which uses a blue light with specific spectral characteristics. When combined with a red-green quantum dot (QD) film, it produces white light. For improved illumination uniformity, the Mini-LED structure was optimized with a focus on the thickness and concentration of layers, especially the TiO2 diffusion layer. A comprehensive design methodology using LightTools (8.6.0) optical simulation software was employed, linked with MATLAB (R2022a) for varied parameters and using the double deep Q-network (DDQN) algorithm via Python as a reinforcement learning agent. This approach facilitated optimal architecture design based on illumination uniformity. Also, the bidirectional scattering distribution function (BSDF) was employed to calculate the scattering properties of the backlight module’s surface, providing accurate simulation results. The DDQN algorithm enhanced the learning design, reducing simulation runs by 76.7% compared to traditional methods. The optimized solution achieved an impressive illumination uniformity of 83.8%, underscoring the benefits of integrating advanced algorithms into display technology optimization.

Nanostructure Control of GaN by Electrochemical Etching for Enhanced Perovskite Quantum Dot LED Backlighting.

Upgraded technology has realized miniaturization and promoted transformation in each field. Miniaturized light-emitting diode (LED) chips enable higher resolution and create a full sense of immersion in displays. Porous GaN is a structure that can reduce excitation light leakage and enhance the light conversion efficiency. Perovskite quantum dots with the highest optical density as candidate materials for loading in pores can significantly decrease the aggregation phenomenon and increase the path of light absorption. Here, the porous tunability is explored by electrochemical etching under a range of voltages, concentrations, and etching times with acid and base electrolytes, such as oxalic acid and potassium hydroxide. Based on scanning electron microscopy images, the distribution of the pores and the morphology of pore channels can be distinguished under acid and base etching. Larger pore sizes and distorted channels (∼680 nm) are presented on the oxalic acid-etched GaN chip. In contrast, smaller pore sizes and straight-deeper channels (∼5650 nm) are demonstrated on the GaN by potassium hydroxide etching. Therefore, the hybrid nanostructure is etched by oxalic acid and potassium hydroxide, separately. The green and red light conversion efficiencies of perovskite quantum dots pumped by a blue LED can be improved by 3 and 10 times, respectively, resulting in a color gamut of approximately 124%.

Design of a superb Eu2+–Mn2+ co‐doped narrow‐band green phosphor via nearly 100% energy transfer efficiency

AbstractThe excellent narrow‐band emitters, especially the green ones, are regarded as a pivotal research direction for light‐emitting diodes (LED) backlights in liquid‐crystal displays (LCDs). A nearly single‐peak green emission centered at 513 nm with a full width at half maximum of 28 nm is reached in KAl11O17:0.1Eu2+, 0.15Mn2+ phosphor via nearly 100% energy transfer (ET) efficiency, and the extended X‐ray absorption fine structure analysis elucidates its mechanism, which is that Eu2+ and Mn2+ are constrained to form Eu2+–Mn2+ pairs with a small distance 3.7 Å caused by the local environment relaxation inducement. Meanwhile, by creating an unhindered energy flow between Eu2+, Mn2+ and K+/O2− defect levels through ET and multilevel electron trapped and recombination process, the KAO:Eu2+, Mn2+ phosphors perform superb photoluminescence property with a high color purity of 83%, an excellent thermal stability (94%@200°C), and unexceptionable internal and external quantum efficiencies of 91.7% and 66.4%, which all are superior to characteristics of commercial β‐SiAlON:Eu2+ phosphor. Moreover, the white LED fabricated using KAO:Eu2+, Mn2+ to provide green component shows a wide color gamut of 105% National Television System Committee. These results indicate a potential for an application of our material in LCD–LED backlights, and the design of such local relaxation‐induced structure provides a significative reference to develop the new narrow‐band emitters.

Development of a quasi-collimated UV LED backlight for producing uniform and smooth 3D printing objects.

3D printing techniques have great potential in the direct fabrication of microfluidic and many kinds of molds, such as dental and jewelry models. However, the resolution, surface roughness, and critical dimension uniformity of 3D printing objects are still a challenge for improvement. In this article, we proposed a 405nm light emitting diode (LED) backlight module based on stacks of structured films, and the full width half maximum (FWHM) of the angular distribution of this module is reduced to less than ± 15°. Compared with the commercial lens array optical module, the ten points intensity uniformity of an 8.9" build area is improved from 56% to 80%. Moreover, we found that the surface roughness and the sharpness of the edge of the printing objects are also obviously improved by our novel quasi-collimated LED backlight module. These features give us a promising way for the application of microfluidics and micro-optics components in the future.

Improving Mini-LED Pattern Quality by Using Distributed Bragg Reflector and Digital Twin Technology

Fine-pitch backlight technology is rapidly evolving along with display technology, and chips are increasingly designed for direct integration with modules. This study used a distributed Bragg reflector (DBR) for mini light-emitting diode (mini-LED) backlights with high dynamic contrast and developed a digital twin design by using a light-emitting diode (LED) and a distributed Bragg reflector (DBR).

Thin mini-LED backlight using reflective mirror dots with high luminance uniformity for mobile LCDs.

A new mini light-emitting diode (mini-LED) backlight with reflective dots is proposed for high luminance uniformity, high contrast ratio, and low power consumption for use in mobile liquid crystal displays. The proposed backlight, comprising a small number of mini-LEDs, was verified as having high luminance uniformity and high light use efficiency, due to the optimized reflective dots, backlight thickness and light distribution of the mini-LEDs. Moreover, the light leakage to adjacent segments was reduced by cutting a slit between each segment, improving the light use efficiency per segment and suppressing halo artifacts.

A novel Mn4+-activated layered oxide-fluoride perovskite-type KNaMoO2F4 red phosphor for wide gamut warm white light-emitting diode backlights.

Mn4+-activated oxide-fluoride phosphors are attractive for application in a wide range of solid-state lighting devices because of their distinct red emission at about 630 nm and the abundant storage of Mn ions. However, the zero-phonon line (ZPL) of Mn4+ ions is too weak to be detected in most host materials due to the magnetic dipole nature. In this article, we introduce a co-precipitation method for synthesizing a Mn4+-doped oxyfluoride perovskite KNaMoO2F4 phosphor containing [MoO2F4]2- building units. The electron paramagnetic resonance (EPR) spectra are consistent with the presence of a MnF62- species at g = 1.991. The KNaMoO2F4:0.01Mn4+ phosphor exhibits strong absorption under blue light and an internal quantum yield (IQE) of 65.8%. Attributed to the distorted octahedral environment of the Mn4+ ions, visible ZPL emission was detected at 625 nm. Based on theoretical calculations, the Mn4+ ions in the KNaMoO2F4 host exist in a strong crystal field with a high Dq/B value of ∼3.86. A series of photoluminescence-dependent low-temperature spectra indicates that the Mn4+ emissive state experiences weak electron-phonon interactions upon calculating the Huang-Rhys factor. Benefiting from the ZPL, a warm white-light-emitting diode is achieved using YAG:Ce3+ and KNaMoO2F4:Mn4+ as color converters, in which the color rendering index was Ra = 83.5 and CCT = 4490 K.

Perovskite Multiple Quantum Wells on Layered Materials toward Narrow-Band Green Emission for Backlight Display Applications.

Quasi-two-dimensional perovskite multiple quantum wells (MQWs) have garnered attention on account of their good stability in comparison with three-dimensional analogs for light-emitting diode (LED) applications, but they exhibit a declined photoluminescence quantum yield (PLQY) for the backlight display technology. Herein, we report an in situ process by introducing layered materials as substrates to prepare the perovskite MQW powder and utilize hexagonal boron nitride (h-BN) as an example to investigate the luminescence characteristics and mechanism of h-BN@(PMA)2MAn-1PbnBr3n+1 (h-BN@PMPB). Remarkably, the deposition strategy enables an enhanced PLQY from 2.6 to 32.4%. A synergetic effect of low reabsorption, low defect concentration, and high absorptivity leads to high-efficiency cascade energy transfer and also an improvement in stability. Moreover, the h-BN@PMPB composite powder shows a narrow-band green emission band peaking at 532 nm with a full width at half maximum of 32 nm, and the white LED backlight reaches a wide color gamut 106.1% of the National Television Standards Committee (NTSC). This work reveals a general synthesis method for preparing perovskite powder and paves the way to achieve new solid-state luminescent materials with controlled size and morphology for backlight display applications.

Experimental study on multiphase flow in fracture-vug medium using 3D printing technology and visualization techniques

Strong heterogeneity and anisotropy exist in fractured-vuggy reservoirs, resulting in complex flow and relatively low oil recovery. Therefore, the mechanism of water flooding and gas injection displacement in fracture-vug medium constitutes a key issue in oil production. In this study, based on similarity criteria, physical models of fracture-vug medium are designed and constructed through 3D printing technology. Then, by combining the LED (light-emitting diode) backlight visualization method (BVM) and the particle image velocimetry (PIV) technique, experiments of multiphase flow (i.e., oil-water and gas-oil) through the printed fracture-vug medium are carried out. During the experiments, the morphological changes of the fluid interfaces are captured with BVM, and the velocity field and streamlines of the fluid in the system are determined by the PIV technique. In addition, we also investigate various factors affecting the recovery efficiency of fracture-vug medium, such as injection velocity, gravity, outlet position, and shape factors. Results show that oil recovery in fracture-vug medium varies with injection velocity (or Reynolds number), shape of the vug, and fracture-vug structure. Specifically, distribution of the remaining oil is affected by the shape of the vug. Gravity also exerts a great influence on the morphology of bubbles in the case of gas injection. The present study leads to a better understanding of multiphase flow in fracture-vug medium and a valuable experimental dataset.

P‐52: Novel LED Boost Architecture Enables Higher Efficiency and Thinner Display Panels

The light‐emitting diode (LED) backlight has been the biggest energy consumer in liquid crystal display (LCD) panels. As screen resolution and luminance requirements increase, the energy consumed by the LED backlight increases as well. Efficiency performance is limited with existing conventional LED boost drivers on the market, and a new type of LED boost driver architecture is needed for an efficiency performance breakthrough. This paper discusses a new LED boost architecture with breakthrough performance and its advantage over conventional LED boost drivers.

Effects of the Emitted Light Spectrum of Liquid Crystal Displays on Light-Induced Retinal Photoreceptor Cell Damage.

Liquid crystal displays (LCDs) are used as screens in consumer electronics and are indispensable in the modern era of computing. LCDs utilize light-emitting diodes (LEDs) as backlight modules and emit high levels of blue light, which may cause retinal photoreceptor cell damage. However, traditional blue light filters may decrease the luminance of light and reduce visual quality. We adjusted the emitted light spectrum of LED backlight modules in LCDs and reduced the energy emission but maintained the luminance. The 661W photoreceptor cell line was used as the model system. We established a formula of the ocular energy exposure index (OEEI), which could be used as the indicator of LCD energy emission. Cell viability decreased and apoptosis increased significantly after exposure to LCDs with higher emitted energy. Cell damage occurred through the induction of oxidative stress and mitochondrial dysfunction. The molecular mechanisms included activation of the NF-κB pathway and upregulation of the expression of proteins associated with inflammation and apoptosis. The effect was correlated with OEEI intensity. We demonstrated that LCD exposure-induced photoreceptor damage was correlated with LCD energy emission. LCDs with lower energy emission may, therefore, serve as suitable screens to prevent light-induced retinal damage and protect consumers’ eye health.

Vertical Self-Assembly of Polarized Phage Nanostructure for Energy Harvesting.

Controlling the shape, geometry, density, and orientation of nanomaterials is critical to fabricate functional devices. However, there is limited control over the morphological and directional characteristics of presynthesized nanomaterials, which makes them unsuitable for developing devices for practical applications. Here, we address this challenge by demonstrating vertically aligned and polarized piezoelectric nanostructures from presynthesized biological piezoelectric nanofibers, M13 phage, with control over the orientation, polarization direction, microstructure morphology, and density using genetic engineering and template-assisted self-assembly process. The resulting vertically ordered structures exhibit strong unidirectional polarization with three times higher piezoelectric constant values than that of in-plane aligned structures, supported by second harmonic generation and piezoelectric force microscopy measurements. The resulting vertically self-assembled phage-based piezoelectric energy harvester (PEH) produces up to 2.8 V of potential, 120 nA of current, and 236 nW of power upon 17 N of force. In addition, five phage-based PEH integrated devices produce an output voltage of 12 V and an output current of 300 nA, simply by pressing with a finger. The resulting device can operate light-emitting diode backlights on a liquid crystal display. Our approach will be useful for assembling many other presynthesized nanomaterials into high-performance devices for various applications.

PWM Dimming Method for Capacitor-Clamped Current-Sharing Circuit in LED Backlight System

When multichannel light-emitting diode (LED) strings are applied in display backlight application, it’s necessary to keep the brightness identical and adjustable. This paper deals with the capability of pulsewidth modulation dimming control method for capacitor-clamped current sharing circuit. By detecting the rising-edge of dimming pulse and turn on the switches of current sharing circuit in rotation, this method can achieve current sharing at any dimming frequency and dimming ratio. What is more, to improve the dynamic response of LED current and achieve a high dimming ratio, a control method based on the output voltage feedforward is proposed, which can decrease the rising time of the LED forward current significantly. The operational principle and parameter design are analyzed in detail. Based on this analysis, a three-string current sharing circuit driven by Buck converter is fabricated and tasted in the laboratory. Experimental waveforms demonstrate the validity.

Next‐Generation Narrow‐Band Green‐Emitting RbLi(Li3SiO4)2:Eu2+ Phosphor for Backlight Display Application

The discovery of high efficiency narrow-band green-emitting phosphors is a major challenge in backlighting light-emitting diodes (LEDs). Benefitting from highly condensed and rigid framework structure of UCr4 C4 -type compounds, a next-generation narrow green emitter, RbLi(Li3 SiO4 )2 :Eu2+ (RLSO:Eu2+ ), has emerged in the oxide-based family with superior luminescence properties. RLSO:Eu2+ phosphor can be efficiently excited by GaN-based blue LEDs, and shows green emission at 530 nm with a narrow full width at half maximum of 42 nm, and very low thermal quenching (103%@150 °C of the integrated emission intensity at 20 °C), however its chemical stability needs to be improved later. The white LED backlight using optimized RLSO:8%Eu2+ phosphor demonstrates a high luminous efficacy of 97.28 lm W-1 and a wide color gamut (107% National Television System Committee standard (NTSC) in Commission Internationale de L'Eclairage (CIE) 1931 color space), suggesting its great potential for industrial applications as liquid crystal display (LCD) backlighting.

High-Efficiency Resonant LED Backlight Driver With Passive Current Balancing and Dimming

A novel high-efficiency resonant light emitting diode (LED) backlight driver with passive current balancing and dimming is proposed and analyzed in this paper. The proposed LED driver achieves uniform brightness of each LED string by the charge balance of the resonant capacitor, which benefits from high efficiency. By controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of resonant capacitors, which makes its control simple. The proposed LED driver uses only one active switch, which decreases circuit volume and simplifies the control. Furthermore, a wide load range can be achieved by controlling the turn-on duty ratio of the single power switch of the LED driver with a fixed frequency. Finally, a prototype of a high-dimming-ratio small-size three-string LED driver is provided to verify the studied results.

Performance Improvement of a Boost LED Driver With High Voltage Gain for Edge-Lit LED Backlights

This brief proposes a new method for improving the performance of a dc/dc boost converter used as a light-emitting diode (LED) driver for edge-lit LED backlights. The proposed method uses a passive snubber circuit that consists of two capacitors, two diodes, and an inductor; it improves the power efficiency of the dc/dc boost converter at the high duty ratio of the main switch by providing zero-current switching turn on and charge pumping operations. To verify the effectiveness of the proposed method, a new boost LED driver with the proposed passive snubber was built and tested at the various output power levels dissipated by LED backlights. The power conversion efficiency of a boost LED driver with an input voltage of 24 V and an output voltage of 114 V was measured as 94.80%, 94.15%, and 92.82% for output power of 40, 70, and 100 W, respectively; these values are 6.08%, 4.47%, and 3.67% higher than conventional values.

Color‐by‐Blue QD‐Emissive LCD Enabled by Replacing RGB Color Filters with Narrow‐Band GR InP/ZnSeS/ZnS QD Films

AbstractColor‐by‐blue quantum dot (QD)‐emissive liquid‐crystal displays (LCDs) with eco‐friendly, green, red (GR) InP/ZnSeS/ZnS QD films are introduced to overcome the disadvantages of conventional color‐by‐white color filter (CF)‐assisted LCDs, such as a narrow viewing angle, low external device efficiency of these types of LCDs, and a restricted color gamut. In this study, the color‐by‐blue InP‐based QD‐emissive LCD consists of a blue (B) light‐emitting diode (LED) and GR InP‐based QD films sandwiched between a light recycling filter and a long‐wavelength pass dichroic filter. The GR InP‐based QDs are synthesized with a high photoluminescence quantum yield (>77%) and narrow bandwidth (<40 nm), which are suitable for display applications. The overall enhancement of InP‐based QD‐emissive LCDs, in this case by the enhanced efficiency of a blue LED backlight transmitted through the LC shutter compared to a white LED backlight and the improved efficiency of the enlarged color gamut, is 2.42 times that of a conventional red, green, and blue (RGB) CF‐LCD with a GR phosphor‐converted (pc)‐LED (a B LED + R K2SiF6:Mn + G β‐SiAlON:Eu phosphor) backlight. Therefore, this considerable enhancement of the external efficiency of a QD‐emissive LCD makes it more feasible as a replacement for conventional RGB CF‐assisted LCDs.