Light-emitting Diode Industry Research Articles

Performance Improvement Based on Latitude Classification of Perovskite Light-Emitting Diodes

The Perovskite Light-emitting Diode (PeLED) can effectively convert light energy and electrical energy, and the study of Light-Emitting Diode (LED) is conducive to the efficient use of energy. Starting from the dimension classification of perovskite light-emitting diodes, this paper introduces the advantages of perovskite in different dimensions and the methods to improve the performance of perovskite light-emitting diodes. It is expected to realize the preparation of low-cost and high-performance perovskite light-emitting diodes. Light-emitting diodes or electroluminescent devices have many excellent properties such as high brightness, wide colour gamut, low power consumption, long life and environmental protection. They have been widely used in the field of display and lighting, and have become one of the most competitive products in the optoelectronic industry. With the development of the LED industry and the higher requirements for LED display in the new era, scientific researchers exploration of new electroluminescent materials has also been gradually strengthened. Among them, organic molecules and new low-dimensional halogenated perovskite have attracted much attention because of their many advantages. The performance of LED depends on the type of light-emitting material and device structure. It is also important to understand the light-emitting mechanism of such devices and their internal carrier transport mechanism. Studying the light-emitting mechanism and carrier transport mechanism of LEDs based on different light-emitting materials is not only of scientific significance, but also can provide a reliable theoretical basis for further improving their performance.

Energy Conversion and Transfer in the Luminescence of CeSc3(BO3)4:Cr3+ Phosphor.

Novel near-infrared (NIR) phosphors are in demand for light-emitting diode (LED) devices to extend their suitability for new applications and, in turn, support the sustainable and healthy development of the LED industry. The Cr3+ has been used as an activator in the development of new NIR phosphors. However, one main obstacle for the Cr3+-activated phosphors is the low luminescence efficiency due to the spin-forbidden d-d transition of Cr3+. The rare-earth (RE) huntite minerals that crystallize in the form of REM3(BO3)4 (M = Al, Sc, Cr, Fe, Ga) have a large family of members, including the rare-earth scandium borates of RESc3(BO3)4. Interestingly, in our research, we found that the luminescence efficiency of Cr3+ in the CeSc3(BO3)4 host, whose quantum yield was measured at 56%, is several times higher than that in GdSc3(BO3)4, TbSc3(BO3)4, and LuSc3(BO3)4 hosts. Hereby, the energy conversion and transfer in the luminescence of CeSc3(BO3)4:Cr3+ phosphor were examined. The Stokes shift of electron energy conversion within the Cr3+ 4T2g level for the emission at 818 nm and excitation at 625 nm in CeSc3(BO3)4 host was evaluated to be 3775.1 cm-1, and the super-large splitting energy of the 2F5/2 and 2F72 sub-states of the Ce3+ 4f1 state, about 3000 cm-1, was found in CeSc3(BO3)4 host. The typical electronic thermal vibration peaks were observed in the excitation spectra of CeSc3(BO3)4:Cr3+. On this basis, the smallest phonon energy, around 347.7 cm-1, of the CeSc3(BO3)4 host was estimated. Finally, the energy transfer that is responsible for the far higher photoluminescence of Cr3+ in CeSc3(BO3)4 than in other hosts was proven through the way of Ce3+ emission and Cr3+ reabsorption.

A Review of Moldflow and Finite Element Analysis Simulation of Chip Scale Packaging (CSP) for Light Emitting Diode (LED)

LED technology has been evolving aggressively in recent years from incandescent bulb during older days to as small as chip scale package. There is tremendous pressure to stay competitive in the market by optimizing products to next level of performance and reliability with shortest time to market. This changes the conventional way of product design and development to virtual prototyping by means of Computer Aided Engineering (CAE). The objective of the paper is to review challenges in chip scale packaging application in LED technology. The first part of the paper covered the literature survey of Chip Scale Packaging (CSP) in Light Emitting Diodes (LED), CSP architecture challenges, molding process and material for CSP. The findings of literature found that very few researchers had study silicone encapsulations process in CSP for LED in term of material characterization, mold process and simulation. Findings also shows that deployment Computational Fluid Dynamic (CFD) and integration of virtual prototyping using Finite Element Analysis (FEA) in product development in CSP for semiconductor industry had greatly reduced the time to market. However, there are very few papers discuss the application for CSP technology in LED industry. Second objective of the papers is discussion of methodolology in molding material characterization and simulation methodology. CFD helps to simulate the flow pattern of molding material as a function of different temperature, molding parameters settings for voids and displacement. FEA also help to evaluate the deformation of silicone in panel form and enable designer to predict the displacement of devices with different silicone.

Mean Differential Continuous Pulse Method for Accurate Optical Measurements of Light-Emitting Diodes and Laser Diodes.

Limited sources exist for the application of germicidal ultraviolet (GUV) radiation. Ultraviolet light-emitting diodes (UV-LEDs) have significantly improved in efficiency and are becoming another viable source for GUV. We have developed a mean differential continuous pulse method (M-DCP method) for optical measurements of light-emitting diodes (LEDs) and laser diodes (LDs). The new M-DCP method provides an improvement on measurement uncertainty by one order of magnitude compared to the unpublished differential continuous pulse method (DCP method). The DCP method was already a significant improvement of the continuous pulse method (CP method) commonly used in the LED industry. The new M-DCP method also makes it possible to measure UV-LEDs with high accuracy. Here, we present the DCP method, discuss the potential systematic error sources in it, and present the M-DCP method along with its reduced systematic errors. This paper also presents the results of validation measurement of LEDs using the M-DCP method and common test instruments.

Development of an adaptive template for fast detection of lithographic patterns of light-emitting diode chips

With the expansion in light-emitting diode (LED) lighting market and technology, control of product quality has become the focus of LED development. To achieve high online production capacity, automated quality detection with object image has been employed for comparison using mostly the standard templates. However, the resulting poor fitting causes misjudgment of the detection system. This study proposes an adaptive template method to improve the system fitting, reduce the system misjudgment, and enhance the detection efficiency. The severely damaged LED chips were screened out based on their grayscale entropy indices and related coefficient indices, which enhanced the reliability of the adaptive template system and accelerated the overall system detection process. To overcome the displacement and scale changes of the lithographic patterns, the scale-invariant feature transform (SIFT) and Harris–Laplace methods were used for comparison. The scale-invariant feature transform (SIFT) and Harris–Laplace methods were used to search and compare the feature points of the chip patterns, with the aim to overcome the displacement and scale changes of the lithographic patterns and establish the adaptive template in real conditions. The fast correlation coefficient comparison method was compared with the adaptive template comparison method proposed in this study. The results showed that the detection accuracy of the new method was 98.36%, which is 15.79% more accurate than the fast correlation coefficient comparison method. In terms of time performance, the method proposed in this study took 0.08 s less to complete the partition defect template. Moreover, the average detection time per chip was reduced by another 1.4 s, which improved the efficiency by 30.43%. The adaptive template proposed in this study exclusively establish itself based on different lithographic patterns, thus improving the detection efficiency and accuracy of the LED industry, and raising its market competitiveness in the industry.

Efficient Blue Light Emitting Diodes Based On Europium Halide Perovskites.

Flat panel displays enjoy 100 billion-dollar markets with significant penetration in daily life, which require efficient, color-saturated blue, green, and red light-emitting diodes (LEDs). The recently emerged halide perovskites have demonstrated low-cost and outstanding performance for potential LED applications. However, the performance of blue perovskite LEDs (PeLEDs) lags far behind red and green cousins, particularly for color coordinates approaching (0.131, 0.046) that fulfill the Rec. 2020 specification for blue emitters. Here, a high-efficiency, lead-free perovskite, CsEuBr3 , is reported that exhibits bright blue exciton emission centered at 448nm with a color coordinates of (0.15, 0.04), contributed from Eu-5d→Eu-4f/Br-4p transition with an optical band gap of 2.85eV. Further optical characterizations reveal its short excited-state lifetime of 151ns, excellent exciton diffusion diffusivity of 0.0227 cm2 s-1 , and high quantum yield of ≈69%. Inspired by these findings, deep-blue PeLEDs based on all-vacuum processing methods, which have been demonstrated as the most successful approach for the organic LED industry, are constructed. The devices show a maximum external quantum efficiency of 6.5% with an operating half-lifetime of 50 mins at an initial brightness of 15.9cd m-2 . It is anticipated that this work will inspire further research on lanthanide-based perovskites for next-generation LED applications.

Critical charge transport networks in doped organic semiconductors

Intrinsic organic small molecule and polymer materials are insulators. The discovery that polymers can be made highly conductive by doping has therefore sparked strong interest in this novel class of conductors. More recently, efficient doping of small molecule materials has also been achieved and is now a key technology in the multi-billion dollar organic light emitting diode industry. Nevertheless, a comprehensive description of charge transport in the presence of doping is still missing for organic semiconductors with localized electronic states. Here, we present a theoretical and computational approach based on percolation theory and quantitatively predict experimental results from the literature for the archetype small molecule materials ZnPc, F8ZnPc and C60. We show that transport in the complex potential landscape that emerges from the presence of localized charges can be aptly analyzed by focusing on the network properties of transport paths instead of just the critical resistance. Specifically, we compute the activation energy of conductivity and the Seebeck energy and yield excellent agreement with experimental data. The previously unexplained increase of the activation energy at high doping concentrations can be clarified by our approach.

Improved Light Extraction of Nitride-Based Light-Emitting Diodes by Al2O3-Doped UV-Curing Encapsulant

Silicone-based UV curing has recently been developed as a novel kind of encapsulation technology, which is time-saving and cost-effective for the package of light-emitting diodes (LEDs). In this work, to improve the light output power (LOP) and device reliability of LEDs packaged by UV curing, Al2O3 nanoparticles (NPs) are doped into silicone. Different compositions of Al2O3 NPs are used and the optimal composition is found to be 0.3%. Compared with LEDs packaged by UV curing without Al2O3 doping (256.3 mW) and by traditional thermal-curing (264.1 mW) encapsulants, the LOP is increased to 272.9 mW for LED with Al2O3-NP-doped encapsulant. The enhancement of LOP is attributed to both the increased refractive index and light scattering effect of the Al2O3 NPs, which improves the light extraction efficiency (LEE) of the encapsulant. Furthermore, the improvement of LEE also suppresses the heat generation and thus improving the long-term reliability of the devices. These results indicate that using high refractive index materials as doping, UV curing could be an excellent choice as a novel package technology for the LED industry.

Sr[Mg3SiN4]Eu2+ phosphor: solution for enhancing the optical properties of the 5600K remote-packaging WLEDs

In the last decade, light-emitting diodes (LEDs), which based on spontaneous light emission in semiconductors can be considered as the main light sources for civil and industrial purposes. In this paper, we presented and investigated the effect of the Sr[Mg 3 SiN 4 ]Eu 2+ concentration on the optical properties of the 5600K remote-packaging WLEDs (RP-WLEDs). We use the Mat Lab and the LightTool software to investigate the effect of the Sr[Mg 3 SiN 4 ]Eu 2+ concentration on the CRI, CQS, D-CCT and LO of the 5600K RP-WLEDs. From the result, we can state that the concentration of the Sr[Mg 3 SiN 4 ]Eu 2+ influenced on the CRI, CQS, D-CCT and LO of the RP-WLEDs. The red Sr[Mg 3 SiN 4 ]Eu 2+ phosphor can be considered as the novel recommendation for LEDs industry.

LED Lighting Systems for Horticulture: Business Growth and Global Distribution

In recent years, research on light emitting diodes (LEDs) has highlighted their great potential as a lighting system for plant growth, development and metabolism control. The suitability of LED devices for plant cultivation has turned the technology into a main component in controlled or closed plant-growing environments, experiencing an extremely fast development of horticulture LED metrics. In this context, the present study aims to provide an insight into the current global horticulture LED industry and the present features and potentialities for LEDs’ applications. An updated review of this industry has been integrated through a database compilation of 301 manufacturers and 1473 LED lighting systems for plant growth. The research identifies Europe (40%) and North America (29%) as the main regions for production. Additionally, the current LED luminaires’ lifespans show 10 and 30% losses of light output after 45,000 and 60,000 working hours on average, respectively, while the vast majority of worldwide LED lighting systems present efficacy values ranging from 2 to 3 μmol J−1 (70%). Thus, an update on the status of the horticultural LED sector, LEDs’ applications and metrics, and the intense innovation are described and discussed.

Enhancement of the luminous efficiency of a ceramic phosphor plate by post-annealing for high-power LED applications

Currently, phosphor-converted white light-emitting diodes offer low energy consumption, good environmental stability, and a long lifetime. Hence, they are widely utilized in high-power light-emitting diode (LED) applications such as those in the automotive headlamp industries. However, obtaining high luminous efficiency of such diodes is challenging because of their internal structural properties such as micropores. Herein, we developed phosphor-in-glass (PiG) plates by mixing a blue LED chip and yellow phosphor to create high-power white LEDs (w-LEDs). In addition, the influence of post-annealing on the prepared PiG plates at different temperatures (350°C-550 °C) was investigated. Post-annealing, a treatment that facilitates the mobility of the ceramic matrix encapsulating the phosphor powder, decreases an LED's porosity, thereby enhancing its overall luminous efficiency. Results show that PiG plates post-annealed at 450 °C exhibit superior optical performance and effective color properties than PiG plates that were non-annealed or post-annealed at 350 °C, 400 °C, 500 °C, and 550 °C. Therefore, post-annealed PiG plates are more suitable potential materials for application in the high-power LED industry.

Fast UV-Curing Encapsulation for GaN-Based Light-Emitting Diodes

Due to the high refractive index of nitrides, encapsulation is necessary to improve the light extraction efficiency for GaN-based light-emitting diodes (LEDs). Traditional thermal-curing encapsulant needs to be heated for several minutes to form a dome-shaped lens, which is time-consuming. In this paper, we have developed a novel kind of silicon-based ultraviolet (UV)-curing encapsulant, for which only 20 s of near-UV (NUV) light radiation at room temperature is needed. The composition of the encapsulants is optimized to enhance light extraction ability. For 392-nm NUV LEDs packaged by this UV-curing encapsulant, the light output power is enhanced by 10.0%. Moreover, the LEDs packaged by UV-curing and thermal-curing encapsulant presented similar stability and reliability after 480 h of the aging test under a high driving current of 200 mA. This paper demonstrates the potential of silicon-based UV-curing encapsulants for the package of NUV, blue and white LEDs, which is time- and cost-effective for the LED industry.

Developing Multiobjective Equilibrium Optimization Method for Sustainable Uncertain Supply Chain Planning Problems

This paper proposes a new multiobjective two-stage equilibrium optimization method for a supply chain planning problem with uncertain demand. To handle the ambiguity in the distribution of demand, the probability and possibility distributions are integrated to characterize the uncertain demand. As a result, the decision process in our equilibrium optimization problem is divided into two stages. In the first stage, decision variables should be taken before knowing the realizations of uncertain demand; while the second-stage decision variables must be taken after knowing the outcome of subjective uncertainty embedded in demand. On the basis of the proposed dynamic decision scheme, the objectives in the first-stage are constructed via credibilistic optimization methods. The objective and constraints in the second-stage are built via stochastic optimization methods. More specifically, three objectives in the first-stage are constructed based on the expected value operator and conditional value-at-risk of fuzzy variable, and the second-stage optimization model is built as a stochastic expected value model under a probabilistic constraint. When the random parameters follow normal distributions, the proposed equilibrium optimization model is equivalent to a triobjective two-stage credibilistic optimization model. To solve this model, we first employ a sequence of discrete possibility distributions to approximate continuous possibility distributions. Then, we design a new archive-guided multiobjective particle swarm optimization based on decomposition to solve the obtained approximate optimization model. Finally, numerical experiments via a light emitting diode industry problem are conducted to demonstrate the feasibility and effectiveness of the proposed optimization method and new heuristic algorithm.

Recycling the GaN Waste from LED Industry by Pressurized Leaching Method

In recent years, with the increasing research and development of the light-emitting diode (LED) industry, which contains gallium nitride (GaN), it is expected that there will be a large amount of related wastes in the future. Gallium has an extremely high economic value, therefore, it is necessary to establish a recycling system for the GaN waste. However, GaN is a direct-gap semiconductor and with its high energy gap, high hardness, and high melting point, these make it difficult to recycle. Therefore, this study will analyze the physical characteristics of LED wastes containing GaN and carry out various leaching methods to leach the valuable metals from the waste optimally. Different acids are used to find out the best reagent for gallium leaching. Different experimental parameters are discussed, such as the effect of the different acid agents, concentration, pressure, liquid-solid mass ratio, temperature and time, which influence the leaching efficiency of gallium. Finally, acid leaching under high pressure is preferred to leach the GaN waste, and hydrochloric acid is used as the leaching solution because of its better leaching efficiency of gallium. Optimally, the leaching efficiency of gallium can reach 98%.

Fast Growth of Strain-Free AlN on Graphene-Buffered Sapphire.

We study the roles of graphene acting as a buffer layer for growth of an AlN film on a sapphire substrate. Graphene can reduce the density of AlN nuclei but increase the growth rate for an individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AlN and sapphire and accommodates their large mismatch in the lattice and thermal expansion coefficients; thus, the compressive strain in AlN and the tensile strain in sapphire are largely relaxed. The effective relaxation of strain further leads to a low density of defects in the AlN films. These findings reveal the roles of graphene in III-nitride growth and offer valuable insights into the efficient applications of graphene in the light-emitting diode industry.

LED Industrial Spatial Structure and its Evolution Trend in Hangzhou Bay Area, China

The numbers of spatial scale structural dimensions and associated structural dimensions in the light emitting diode (LED) industry in Hangzhou Bay Area, China since 2002 were estimated through the fractal method for the prediction of the future evolution trend of the industry. We found that the spatial structure of the LED industry in that area is of strong monopoly but tends to be generally optimal and stable. The morphology in which the main enterprises concentrate in a linear space contributes to the interactions among the enterprises; future spatial structure of LED industry in Hangzhou Bay Area will be a stable state. Changes in external environments and the interaction between internal industrial factors constitute the basic dynamic mechanism for the formation and evolution of LED industrial spatial structure in the Hangzhou Bay Area.

Stable White Light‐Emitting Biocomposite Films

AbstractThe demonstration of reliable and stable white light‐emitting diodes (LEDs) is one of the main technological challenges of the LED industry. This is usually accomplished by incorporation of light‐emitting rare‐earth elements (REEs) compounds within an external polymeric coating of a blue LED allowing the generation of white light. However, due to both environmental and cost issues, the development of low‐cost REE‐free coatings, which exhibit competitive performance compared to conventional white LED is of great importance. In this work, the formation of an REE‐free white LED coating is demonstrated. This biocomposite material, composed of biological (crystalline nanocellulose and porcine gastric mucin) and organic (light‐emitting dyes) compounds, exhibits excellent optical and mechanical properties as well as resistance to heat, humidity, and UV radiation. The coating is further used to demonstrate a working white LED by incorporating it within a commercial blue LED.

A review on discoloration and high accelerated testing of optical materials in LED based-products

Reduction of intensity of light output is one of the most common degradation modes in light-emitting diode (LED) systems. It starts from the failure of the various components in the system, including the chip, the driver, and optical components (i.e. phosphorous layer). The kinetics of degradation in real life applications is relatively slow and in most cases it takes several years to see an obvious deterioration of optical properties. Highly Accelerated Stress Testing (HAST) set-up and a methodology to extrapolate the results to real time applications are therefore needed to test the reliability of LED packages and lens materials. Using HAST concept in LED industry is inevitable due to the necessity of assessing the reliability of new products in a short period of time. This paper aims at briefly clarifying the degradation mechanisms of optical components in LED packages and explaining how they contribute to the depreciation of light output of the LED systems. The concept of HAST and the way the reliability of LED packages can be evaluated will also be discussed.

Green Suppliers Performance Evaluation in Belt and Road Using Fuzzy Weighted Average with Social Media Information

A decision model for selecting a suitable supplier is a key to reducing the environmental impact in green supply chain management for high-tech companies. Traditional fuzzy weight average (FWA) adopts linguistic variable to determine weight by experts. However, the weights of FWA have not considered the public voice, meaning the viewpoints of consumers in green supply chain management. This paper focuses on developing a novel decision model for green supplier selection in the One Belt and One Road (OBOR) initiative through a fuzzy weighted average approach with social media. The proposed decision model uses the membership grade of the criteria and sub-criteria and its relative weights, which consider the volume of social media, to establish an analysis matrix of green supplier selection. Then, the proposed fuzzy weighted average approach is considered as an aggregating tool to calculate a synthetic score for each green supplier in the Belt and Road initiative. The final score of the green supplier is ordered by a non-fuzzy performance value ranking method to help the consumer make a decision. A case of green supplier selection in the light-emitting diode (LED) industry is used to demonstrate the proposed decision model. The findings demonstrate (1) the consumer’s main concerns are the “Quality” and “Green products” in LED industry, hence, the ranking of suitable supplier in FWA with social media information model obtained the difference result with tradition FWA; (2) OBOR in the LED industry is not fervently discussed in searches of Google and Twitter; and (3) the FWA with social media information could objectively analyze the green supplier selection because the novel model considers the viewpoints of the consumer.

Network characteristics and patent value-Evidence from the Light-Emitting Diode industry.

This study proposes a different angle to social network analysis that evaluates patent value and explores its influencing factors using the network centrality and network position. This study utilizes a logistic regression model to explore the relationships in the LED industry between patent value and network centrality as measured from out-degree centrality, in-degree centrality, in-closeness centrality, and network position, which is measured from effect size. The empirical result shows that out-degree centrality and in-degree centrality have significant positive effects on patent value and that effect size has a significant negative effect on patent value.