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• RB LED promoted the number of shoots and leaves of in vitro Kaempferia parviflora plants, while red LED improved the length of the shoots,. • The production of photosynthetic pigments was increased under white, blue and RGB light,. • Red LED induced the accumulation of carbohydrates, while RB LED increased the production of proteins, with the highest antioxidant activity of Kaempferia parviflora observed under white LED. Black ginger (Kaempferia parviflora) is a popular plant in Thailand and Malaysia that is valued for its medicinal properties, especially its aphrodisiac qualities. Light-emitting diodes (LEDs) have successfully induced regeneration and various growth responses of black ginger plants in vitro. This study aims to investigate LED-induced photomorphogenesis of black ginger and to evaluate its physiology state. Shoot explants were grown in vitro under irradiation of white (400–750 nm), red (660 nm), blue (460 nm), RB (440 nm; 660 nm), and RGB (400 – 660 nm) to determine the vegetative responses of black ginger plants under the influence of light quality after six weeks. Biochemical analyses such as photosynthetic pigments, total carbohydrate content, protein estimation and free radical scavenging activity were also performed. The highest percentage of shoots was obtained at 96.67 % under blue light, but the maximum number of shoots and leaves were produced under RB LED with 3.21 ± 0.25 and 3.92 ± 0.28, respectively. The red light significantly promoted shoot length with an average length of 3.07 ± 0.21 cm. Rooting was spontaneously induced in all light treatments, with the highest number of roots recorded under RGB lighting at 11.80 ± 1.30. In general, RGB light significantly promoted the synthesis of photosynthetic pigments such as total chlorophyll content, carotenoids and porphyrins with 0.68 ± 0.02 µg/ml, 248.67 ± 3.38 µg/g and 3.94 ± 0.11 µg/g, respectively. The highest carbohydrate and protein contents were obtained with red and RB lights at 80.07 ± 9.15 mg/g and 309.33 ± 0.58 µg/ml, respectively. The control plants with white LED light showed the highest DPPH radical scavenging activity 94.34 ± 0.04%. Our results indicate that different light qualities induce photomorphogenesis of in vitro black ginger plants. The spectral combination with green light significantly improved the morphology and physiology of the plants. Therefore, the green spectrum should be considered as an important light source to promote plant growth in controlled environment agriculture. [ABSTRACT FROM AUTHOR]

Solar simulators are instruments used for controllable measurements of the properties of solar cells in indoor environments. The purpose of this paper is to examine the peculiarities of the photoresponses of CdTe/CdSeTe and microcrystalline Si solar cells and to reveal the pathways to reduction of spectrum mismatch effects when using light-emitting diode (LED)-based or hybrid LED and halogen lamp-based solar simulators of an A+-class spectrum with a small number of sources. While only four different LED types are needed to achieve an A+-class spectrum under updated IEC 60904-9:2020 standard requirements, as demonstrated by our results, additional ultraviolet LEDs are necessary to reduce the spectrum mismatch. For hybrid solar simulator configurations, the combination of cool white LED arrays and halogen emitters can serve as a main light source. Optimized for both solar cell types, hybrid simulators have a lower spectral deviation and better spectrum coverage compared to LED-only simulators with the same number of distinct source types. In addition, our results predict lower spectral mismatch errors for optimized simulators when compared with conventional Xe lamp-based simulators. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m−2, and a maximum EQE of 12.2% by incorporating the double‐sided ethane‐1,2‐diammonium bromide (EDBr2) ligand salt along with the long‐chain ligand methylphenylammonium chloride (MeCl). The EDBr2 successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr2) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr2 successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr2 improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi‐2D blue PeLEDs. [ABSTRACT FROM AUTHOR]

• The establishment of micropropagation protocol for Cameron Highlands White Strawberry. • High multiplication rate in full-strength MS medium + 8 µM TDZ. • No damage to the cellular arrangement was observed on the treated in vitro plants in any of the light treatments using scanning electron microscopy (SEM). • Maximum acclimatization efficiency in hydroponic solution (100% survival rate). White strawberry is botanically a member of the Fragaria genus, which is a part of the Rosaceae family, which is primarily found in Japan, where it is a well-known premium fruit. Experiments were conducted to develop a micropropagation method for Cameron Highlands white strawberries (Fragaria x Ananassa). Freshly extracted achenes were surface sterilised with 30 and 40% Clorox®. Achenes germination was studied in vitro under various light spectra [cool white LED (17.0 μ mol/s), red LED (29.30 μ mol/s), blue LED (15.70 μ mol/s), red + blue LEDs (44.80 μ mol/s)] to study how light and different LED spectra affected shoot, root, and leaf growths of seedlings in the culture. Because both treatments have a 0% contamination rate and the same germination rate which is 78.77%, the 30% Clorox® treatment was chosen as the best surface sterilisation protocol for white strawberry achene germination. Scanning electron microscopy (SEM) studies of seedlings germinated under various light treatments demonstrated that no damage to the cellular arrangement was observed in any of the light treatments. However, the stomata of seedlings treated with blue LED were found to be damaged and exhibit uneven structures. Shoot multiplication in the culture was determined by testing various concentrations of 6- benzylaminopurine (BAP) and thidiazuron (TDZ) using shoot tips (0.5 to 0.8 cm) from the 5-leaf stage of the in vitro plants. The highest mean number (6.50 ± 1.05) of shoots differentiated on MS medium with 8 µM TDZ. The regenerated plantlets were rooted on MS medium with indole-3-butyric acid (IBA) and 1-Naphthaleneacetic acid (NAA) at 0 (control), 1, 2, 3, and 5 µM. Rooting (50%) was the highest success with 1 µM IBA. All the rooted plantlets were successfully acclimatized using hydroponics and field transfer. [ABSTRACT FROM AUTHOR]

Microgreens are environmentally friendly and have health benefits in addition to their basic nutritional contents. The effect of white (W), white–blue (W + B), and white–red (W + R) light on the bioactive compounds, nutrient composition, and antioxidant potential of red and white cabbage microgreens were investigated using light-emitting diodes (LEDs). The results showed that protein, fat, ash, chlorophylls, and carotenoids were the highest in microgreens under W light, while phenolic compounds were highest in microgreens under W + B light. Supplementation with white light, as well as red or blue light, resulted in higher levels of sugars and total fiber in both white and red microgreens. Twenty-six and thirty-three phenolic compounds were identified in white and red cabbage microgreens, respectively. The identified phenolics belonged to three classes, including phenolic acids, flavonols, and anthocyanins. The antioxidant potential of both cabbage microgreens was determined by four methods (ABTS, DPPH, ORAC, and FRAP). It was found that the highest antioxidant potential was observed in microgreens grown under the W + B light combination. On the other hand, the W + R light combination increased the content of β-sitosterol and campesterol. The results may be helpful in the selection of the type of LED lighting that determines the high nutritional and health-promoting potential of white and red cabbage microgreens. [ABSTRACT FROM AUTHOR]

Light is a determining factor in plant morphophysiology, as it influences the growth and development of agricultural crops. Thus, the objective was to investigate the effects of light sources on the growth and development of "biquinho" pepper cultivars. The experiment was performed in two stages (Exp1 and Exp2), evaluating two cultivars (BRS Moema;Airetama biquinho) in five light sources (white LEDs, red LEDs, blue LEDs, red/blue LEDs, and fluorescent lamps). In Exp1 theplants were kept in a controlled condition, with a completely randomized design, in a 2x5 factorial scheme (cultivars x light sources) until 76 days after emergence (DAE), in which growth variables and photosynthetic pigments were evaluated. In Exp2, the plants were removed from the above conditions and transplanted in pots, being kept in greenhouse for more76 DAE. At 152 DAE, the same variables as Exp1 were evaluated, as well as gain of shoot fresh and dry mass, and gain of root fresh and dry mass. In both experiments, growth variables were affected by cultivar and the light sources, however, the behavior did not follow the same trend for all variables, indicating that the light quality influences the growthof the crops, and impacting during greenhouse conditions. [ABSTRACT FROM AUTHOR]

• The highest Fv/Fo was obtained in R LED light under foliar glycine exposure to 80 mg.l−1. • Glycine-exposed plants under light treatments exhibited higher fluorescence yield at F0, Fm, and Fv compared to normal light conditions. • Plants exposed to control light under foliar glycine treatment at 80 mg. l−1 resulted in higher Vj and Vi than those of different lighting conditions. • Under B LED light conditions, ∆b*, ∆E*, ∆C* and ∆h* were increased in comparison with normal light conditions. • Plants under B LED light upon exposure to glycine treatment at 40 mg. l−1 revealed the highest stomatal conductance. Light quality plays an important role in all growth and development stages particularly in photosynthesis properties of plant species. The light-emitting diodes (LEDs) present maximum efficiency on biological processes among artificial lighting systems. The current study was aimed to investigate different LED light color (Blue, Red and White) and glycine concentrations (0, 40 and 80 mg L−1) on photosynthetic efficiency of black henbane (Hyoscyamus niger L.) plant in a completely randomized design (CRD) with three to five replications. Results showed that the maxiumu quantum yield of PSII (0.839) was obtained in R LED light spectrum exposed plants upon glycine treatment at 80 mg. L−1, howevre, the lowest Fv/Fm (0.659) was detected in plants subjected to W LED spectrum. The highest Fv/Fo was obtained in plants grown under R LED lighting with glycine treatment at 80 mg. L−1; however, C (normal light conditions) showed the lowest Fv/Fo among the light treatments. Under B LED light conditions, ∆b*, ∆E*, ∆C* and ∆h* were increased in comparison with normal light condition. Results showed that changing trends of these traits were consistent with those of chlorophylls and carotenoids contents under different LED-based light regimes. Moreover, compared with chlorophylls content under B LED light spectrum with glycine, the carotenoids content under W LED light source was found to be a dominant pigment in black henbane plants. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are commercially used as a light source to improve plant growth and antioxidants accumulation. Growth and antioxidant system in Chinese kale microgreens illuminated with blue, red and white LEDs and sunlight, as a control, with the same duration of illumination were investigated. The red LED with low light intensity significantly enhanced hypocotyl length and fresh weight of microgreens, while blue and white LEDs and sunlight showed fairly comparable effects. The synergistic effect of blue, green and red LEDs, as white LED was the most effective in enhancing the accumulation of secondary metabolites, namely, total glucosinolates, phenolic compounds and total ascorbic acid. Microgreens grown with blue and white LEDs showed higher DPPH (1,1-diphenyl-1-picrylhydrazyl) radical scavenging activity and ferric reducing antioxidant power, whereas ABTS [2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)] radical cation (ABTS) fared better under sunlight and blue LEDs. Overall, microgreens treated with red LED significantly reduced H2O2 and lipid peroxidation by only secondary metabolites. While blue and white LEDs treated samples utilised secondary metabolites, as well as, catalase and ascorbate peroxidase when compared to less effective superoxide dismutase in the control samples. The results suggest that light wavelength was a majority factor in enhancement antioxidant accumulation. [ABSTRACT FROM AUTHOR]

This work reports an optomechanical, electronic system consisting of LEDs emitting light in the near-infrared region. The 147 light-emitting diodes were distributed in a semi-spherical dome so that each focused light upon the center of the radius. The LEDs received electrical polarization so that the optical power of each provided 16 ± 0.36 mW for a total of 2.4 W. The developed system allows multifunctional applications in phototherapy, making it possible to perform this clinical technique for the treatment of skin lesions and contusions at the musculoskeletal level. The geometry of the developed system also allows the use of phototherapy in the treatment of neurological pathologies. In terms of instrumentation, the three-dimensional light intensity distribution and the thermographic images were obtained using three working distances from the system to the target. Three-dimensional light intensity distributions were obtained considering each working distance. These were inserted in the thermographic images as indications of the emitted temperature distributions. This work verified that the optomechanical and electronic system developed with LEDs may be used for multiple applications in phototherapy. [ABSTRACT FROM AUTHOR]

Alternative therapeutic approaches to mental, neurological and physiological diseases present cures and treatments based on light-emitting electromagnetic radiation. Low-level laser therapy was introduced half a century ago in various medical fields. Nowadays, in the search for cheaper and less absorbed light doses with which the same therapeutic results can be achieved, light-emitting diodes enter boldly into medical practice. Light-emitting diodes have gained popularity though there is no sufficient evidence on the response of various neuromodulators to electromagnetic radiation at a molecular level. This study was intended to clarify the effect of light-emitting diode red and laser near-infrared light on smooth muscles' reactivity to 5-hydroxytryptamine. The smooth muscle tissues were in vitro irradiated in a self-designed system named wet organ bath, and the specific mechanograms were depicted. Our results demonstrate that in both irradiation cases (light-emitting diode red or laser near-infrared light), smooth muscle contractility is potentiated, which is mediated by the activation of 5-hydroxytryptamine. [ABSTRACT FROM AUTHOR]

Caper seeds present difficulties in their germination, which has been studied by several research teams. It is known that light can release dormancy in some seeds, but its effect on caper seed germination has not yet been deeply studied. The main aim of this study was to analyze the response of caper seeds germination to light exposure. The study analyzed the germination response of seeds to lighting with different wavelengths (white, red, blue, red + blue and darkness) and to the He-Ne laser light, using both dry seeds and seeds that had been previously soaked in water. Overall, it could be stated that caper seeds are insensitive to light during the germination process. Thus, germination could be carried out in lightness or darkness, so germination in nurseries could be carried out in the darkness, leading to substantial energy savings. Caper seed irradiation with a He-Ne laser during short exposure times improved the germination percentage for the seeds previously soaked in water, germinating all viable seeds. However, applying a solution of gibberellic acid was always required in all the cases studied. [ABSTRACT FROM AUTHOR]

A colloidal quantum dot (CQD) package with convex-surface solder reflectors of various diameters exhibited more favorable thermal characteristics and optical reliability performance than did the traditional in-chip package. The results indicated that solder balls provided a direct cooling path on the top of the LED chip to accelerate heat dissipation, and blue photons were reflected by the ball surfaces to enhance their recycling. The areal temperature results decreased from 88.4 °C (in-chip) to < 70 °C (solder ball) at a current of 180 mA. By contrast, continuous aging tests indicated that the devices with metal structures exhibited lifetimes four to six times longer than that of the in-chip device. The metal embedded structures not only provided a relatively low operating temperature but also extended the operating time of the packaged CQDs. This study pushes the envelope in the endeavor to integrate high-thermal-conductivity components into quantum dot photonic devices. [ABSTRACT FROM AUTHOR]

The recent progress in III-nitride tunnel junction (TJ) contacts for optoelectronic devices is summarized in this review paper. Due to the rapid developments of various III-nitride based optoelectronic devices for different emerging applications, TJs are of interest for these devices to achieve more efficient device performance. This review paper first briefly describes the working principles of TJs and the advantages of employing TJs in optoelectronic devices. The significant advancements in III-nitride TJs realized by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) are addressed, as well as their TJ device performances. Lastly, the critical challenges for employing III-nitride TJs in wide bandgap ultraviolet (UV) light emitters are discussed for future investigations. [ABSTRACT FROM AUTHOR]

Pinus pseudostrobus Lindl. is a species endemic to Mexico and is widely used in reforestation programmes, as it is highly adapted to poor, shallow, limestone soils and has high commercial importance. However, it is necessary to preserve this genetic material since it is in trouble due to high rates of deforestation, land use change, and forest fires, so it is necessary to have effective strategies to obtain good quality seedlings. Due to the properties of LED (light emitting diode) lamps used for illumination in the production of in vitro plants, the effects of two different lighting systems (LED and fluorescent) on an in vitro culture were analysed for the morphological characteristics of the growth and photosynthetic pigment content in P. pseudostrobus seedlings. The length and root size of the seedlings were affected by the type of illumination, where a red LED light was the most effective at 30 days of evaluation. However, a blue LED light was equally effective as a red LED light at 60 days of seedling development. On the other hand, the fluorescent light was better in terms of the number of needles in the first stage, but we found the blue LED light to be better in the second stage. For the photosynthetic pigment content, the highest values were found with the blue LED light. The results showed that the LED lighting system favours the growth, development, and photosynthetic pigment content of the species under study. [ABSTRACT FROM AUTHOR]

Light-emitting-diodes (LEDs) are a lighting source useful for the precise evaluation of light quality effect on biological systems. Despite the importance of light spectra on the regeneration of land plant protoplasts ("naked cells"), this factor has not been tested yet on protoplasts from multicellular algae. This study reports on the effects of pure primary colors (red, blue, and green), dichromatic (red plus blue, RB, 1: 2) and white LEDs on protoplast regeneration from male and female Undaria pinnatifida gametophytes. We also evaluated the effect of different light spectra on pigment composition (chlorophyll a, chlorophyll c, and fucoxanthine), and the light intensities under the best condition on the regeneration process. In the early stages, blue or RB LEDs increased the percentage of dividing female protoplasts, whereas red, blue, and RB LEDs enhanced that of dividing male protoplasts. In the later stages, RB LEDs showed a positive effect only on the percentage of multiple rhizoid-like protrusions (male gametophyte). They also increased the final area of both regenerated gametophytes. The LEDs did not affect pigment composition in female gametophytes. In male gametophytes, in contrast, they reduced chlorophyll c, while blue, RB, and green LEDs decreased fucoxanthin. Under RB LEDs, the optimal light intensity was 80 µmol photons m-2 s-1 for female gametophytes and 40 to 60 µmol photons m-2 s-1 for male gametophytes. Our results suggest that dichromatic LED illumination (red-blue) improves regeneration of U. pinnatifida gametophyte-isolated protoplasts. Thus, dichromatic LEDs might a suitable light source for enhancing protoplast regeneration in brown seaweeds. [ABSTRACT FROM AUTHOR]

A high-speed c-plane InGaN/GaN blue micro-scale light-emitting diodes (Micro-LEDs) with a pixel diameter of $60~\mu \text{m}$ , and a high −3 dB modulation bandwidth of 1.53 GHz at the current density of 5996 A/cm2 were demonstrated. The ultra-thin quantum well (QW) structure with InGaN layer of 1 nm was designed, and optimized variable temperature growth processes were adopted to increase In incorporation and localization effect in the quantum wells, which greatly reduce the polarization field and increase the overlap of electron-hole wave functions. The differential carrier lifetime was effectively shortened, increasing the modulation bandwidth of the Micro-LED. And a data rate of 5.27 Gbps with a bit error rate (BER) of $3.1\times 10^{-{3}}$ was demonstrated with orthogonal frequency-division multiplexing (OFDM) signal for a 1 m free space real-time visible light communication (VLC) based on such high-speed micro-LED. Promising results in this work may support a great development of high-speed VLC applications. [ABSTRACT FROM AUTHOR]

Die-bonding materials are essential packaging materials for high-power light-emitting diodes (LEDs), which affects their heat dissipation and reliability. In this work, a die-bonding structure with high strength and low thermal resistance was proposed for high-power LEDs. A Cu-foam/Sn composite preform was prepared as the die-bonding material in this die-bonding structure. The composite preform is composed of high-melting-point Cu skeleton and low-melting-point Sn. The Cu-skeleton structure accelerates the bonding process and forms intermetallic compounds (IMCs) with high remelting point. Consequently, the die-bonding structure displays robust joints from the transient-liquid-phase (TLP) interconnection layer and high thermal conductivity from the Cu skeleton. The effects of bonding temperature on the mechanical and thermal properties of LEDs were investigated. After bonded with the Cu-foam/Sn composite preform, the LED achieves a low thermal resistance of 6.75 K/W, a low junction temperature change of 6.5 °C, and a high shear strength of 37.8 MPa. Moreover, the proposed die-bonding structure has a lower thermal resistance and higher light output power, which are 27.2% lower and 7.2% higher than the traditional die-bonding structure, respectively. [ABSTRACT FROM AUTHOR]

It has recently been proposed that back‐contacted III–V light‐emitting diodes (LEDs) could offer improved current spreading as compared to conventional mesa or double side contacted structures. This has inspired also experimental efforts to realize such structures, but fabrication methods for them have not yet been fully established. Herein, the use of unintentionally doped and partially carrier‐selective contacts (SC) is studied to realize back‐contacted indium gallium nitride (InGaN) LEDs. The sharp electroluminescence peak at 439 nm from the multiquantum well stack demonstrates that the approach allows fabricating back‐contacted InGaN LEDs without intentionally doped n‐GaN layers and without inflicting damage in the active region, often observed in alternative approaches relying on lateral doping and the use of high energy particles during fabrication. The samples are fabricated on a finger configuration with several finger widths between 1 and 20 μm. It is observed that the emission spreads most uniformly throughout the structure for fingers with the width of 5 μm. As shown by the simulations, with improved contact resistances, the structures reported herein could enable fabricating back‐contacted LEDs with unity injection efficiency and improved current spreading, offering a path toward large‐area LEDs without contact shading even in materials where n‐doping is elusive. [ABSTRACT FROM AUTHOR]

An electrothermal LED model for the design and simulation of light-emitting diode (LED) drivers based on the concept of the equivalent resistance is proposed in this article. The main contribution of this work is the integration of the temperature variables as the encapsulation temperature, heatsink temperature, and the ambient temperature in an electrical model based on the equivalent resistance of power LEDs. Therefore, an improved model is achieved by including these temperatures. This is because the LED temperatures are critical variables in the LED performance that could reduce the useful life of the LEDs or may even destroy them. Therefore, these temperatures must be considered in the design of LED drivers. The “equivalent resistance” concept has been previously used in the electrical modeling of power LEDs without considering the temperature variables, and this model was used to achieve fast simulations in LED-driver systems. The proposed model is oriented to the area of electronic engineering and it is recommended for the design and simulation of LED-converter systems. Experimental and simulation results are obtained that demonstrate the performance of the proposed model. [ABSTRACT FROM AUTHOR]

Natural light is imperative for the growth and development of plants. Nevertheless, spectrum of natural light is inadequate to meet the requirement of crops. Artificial lighting system by use of Light Emitting Diodes (LEDs) could be adopted in horticulture in closed chambers, in greenhouses, in open fields, before pre-harvest until post-harvest storage in controlled environment. Various beneficial and physical properties of LEDs make it convenient for revolutionizing crop cultivation even in earth and on space. Selection of appropriate LED light could boost crop production, improve colour in ornamental plants, enhance phytochemical and nutrient contents, regulate flowering, induce or delay ripening, delay senescence, reduce microbial growth and tremendously improve crop production and preservation in the non-chemical way safe for consumption. LED light in combination with different colours and alteration of wavelength could lead to revolution of horticulture technology in producing super food microgreens and other vegetables possessing desired qualitative and quantitative traits. This innovative and futuristic advancement can be exploited to feed salubrious horticultural crops to the burgeoning population on land and off land. Monochromatic light and combination of LED lights can be employed in cold storage for preventing crop spoilage while enhancing various qualitative traits. Though previous researches have reported numerous benefits of LEDs still there is a vast scope for breakthrough novel inventions which could ameliorate LED lighting to an enormous extend. [ABSTRACT FROM AUTHOR]

A white light-emitting diode (WLED) with chip-scale packaging (CSP) has wide applications due to its high power density, small size, and high process integration. The phosphor converter of the CSP WLED needs to endure huge heat shock from LED chips and phosphor conversion. In this work, we proposed a phosphor-in-glass (PiG)-based CSP for high-power WLEDs. A wafer PiG was prepared by printing and sintering a phosphor glass film on a glass plate and then cut into a chip-scale PiG for the fabrication of PiG-CSP WLEDs. The optical performances of PiG-CSP WLEDs were optimized by adjusting the film thickness of PiG. Consequently, the PiG-CSP WLED emits a cool white light with optimal light performances at a film thickness of 88 $\mu \text{m}$. The related luminous efficiency (LE), correlated color temperature (CCT), and chromaticity coordinate are 108.8 lm/W, 5796 K, and (0.3256 and 0.3467), respectively. The down-PiG-CSP structure achieves higher LE and lower CCT than the up-PiG-CSP structure. Compared with the traditional phosphor-in-silicone (PiS)-CSP WLED, the PiG-CSP WLED avoids the carbonization of the converter and displays excellent thermal stability under high input current. The results determine that the PiG-CSP is a reliable and efficient packaging technology for high-power WLEDs. [ABSTRACT FROM AUTHOR]

In this study, quantum dot light-emitting diodes with a side-pumping structure were designed for efficient heat management. The COMSOL Multiphysics software suite was used to conduct numerical evaluations. The electrical and optical field distributions and the heat distribution capability of the aforementioned structure were investigated. The side-pumping package was found to be capable of effectively dissipating heat and significantly reducing the areal temperature from 32.1 °C (in-chip) to 28.9 °C with an operating current of 35 mA. The integrated intensities of the perovskite quantum dot photons of the in-chip and side-pumping devices were approximately identical (1.23:1). However, the side-pumping device required 58.3% less filling material than the in-chip device. Optical and thermal modeling and measurements indicated that the side-pumping architecture can not only enhance thermal dissipation but also reduce the usage of quantum dot material. The findings of this study provide useful information for the incorporation of quantum dots in photonic devices. [ABSTRACT FROM AUTHOR]

Background: Nowadays, light-emitting diodes (LEDs) as a new lighting technology, have been emerged as an alternative source of light for plants due to their wavelength specificity, the narrow width of their bands, small size, solid structure, long lifetime, and low heat generation. Here we investigated the effect of different LED light sources on the essential oil components and antioxidant activity of Melissa officinalis. Two genotypes of lemon balm (Ilam and Isfahan) were subjected to four artificial light treatments, including white, red, blue, red + blue LEDs, and greenhouse light as natural lighting. Results: The LED lights significantly increased shoot fresh and dry weights and leaf number in the two genotypes as compared to greenhouse condition. The results showed that the content and composition of essential oil in the two genotypes were variable under different light treatments and the total amount of compounds in the Ilam genotype was higher than the other genotype. The results of analysis of the essential oil by GC/MS indicated that the highest amount of monoterpenes in the genotypes was related to citronellal under red + blue LED lamps (15.3 and 17.2% in Ilam and Isfahan genotypes, respectively) but blue, white, and greenhouse condition had the most effect on sesquiterpenes content in both genotypes. The results showed that the observed variation between the two genotypes in the essentials oil composition was related to the relative percentage of the constituents and not to the appearance or lack of a specific component. Red + blue lighting also provided the highest radical scavenging activity in both genotypes (80.77 and 82.09% for Ilam and Isfahan genotypes, respectively). Based on principal component analyses (PCA), three main groups were identified regarding genotypes and all light treatments. Conclusions: Overall, results indicated that the essentials oil composition of two genotypes of lemon balm was affected both qualitatively and quantitatively by different LED light sources; hence, LED lights might be used to improve monoterpenes, sesquiterpenes, and antioxidant activity in the selected genotypes. [ABSTRACT FROM AUTHOR]

The correlated color temperature (CCT) variation of the phosphor-converted light-emitting diodes (LEDs) after curing is a common phenomenon. In the past, it was believed that the phenomenon was caused by the sedimentation of phosphor particles. However, not only sedimentation, but these particles can also flow with the natural convection of silicone because of nonuniform heating during curing. The convective flow of the phosphor particles during curing was studied in detail in this work. The CCT variation and phosphor particles flow in the LED device cup with different depths and wall inclination angles were studied. The results show that the CCT increases after curing when the depth of the device cup is shallow. The case is the opposite when the depth of the device cup is deep. The convective flow behaviors of the silicone were revealed in the simulation. The large-angle inclined wall can increase the silicone flow path length and inhibit the particles flow downward caused by the flow to a certain extent. It is envisioned that the findings will strengthen the understanding of the CCT variation phenomenon and guide the encapsulation structure design of LEDs for better color quality. [ABSTRACT FROM AUTHOR]

[Display omitted] • A tunable spectrum, high-power LED-based solar simulator with 19 different type LEDs has been designed. • Main aspects of design procedure including, LEDs arrangement, intensity control, thermal management and secondary optics were addressed. • Spectrum of solar simulator in UV region extended to 250nm. • Spectral match and irradiance non-uniformity of the solar simulator were investigated. • Proposed solar simulator achieved the Class A requirement in both category of spectral match and irradiance non-uniformity. This article describes the design of a tunable, versatile, light emitting diode (LED) based solar simulator that employs 19 different wavelengths controlled independently by high power LEDs, covering 250–1000 nm standard solar spectrum of AM1.5Global. The main aspects of design procedure were addressed, including the LEDs spatial arrangement, intensity control, thermal management and secondary optics. According to International Electrotechnical Commission (IEC) and American Society for Testing and Materials (ASTM) standards on solar simulators rating, spectral match, irradiance non-uniformity and temporal instability of the solar simulator were investigated. The proposed solar simulator meets the Class AAA specifications in the all three categories for the test plane of 2.3 × 2.3 cm at a distance of 8.7 cm from the LEDs. The spectral tunability and extended spectrum of this solar simulator make it a useful tool in research studies of different fields, especially for testing of newly photovoltaic technologies with extended spectral responsivity in UV region such as ultraviolet responsive solar cells. [ABSTRACT FROM AUTHOR]

Though the acoustoelectric and acoustooptic interactions have been widely studied on III–V semiconductors, most studies were conducted at low temperature to avoid the influence of lattice scattering. Here, we demonstrate larger-than-1-GHz optical oscillation and acoustic charge transport at room temperature from a nitride-based LED (light-emitting diode) by acoustic wave excitation. The optical oscillation is generated by the harmonics of acoustic waves, while the acoustic transport of carriers was observed from the LED light output at different acoustic excitation frequencies. Furthermore, with the change of bias voltage, the frequency response of light output varies correspondingly due to the thermal disturbance that affects the lattice vibration and acoustic wave propagation. The results also suggest that we are able to achieve a tunable optical resonant frequency by varying bias voltages without changing the LED structure. [ABSTRACT FROM AUTHOR]

High-power white light-emitting diodes (LEDs) have demonstrated superior efficiency and reliability compared to traditional white light sources. However, ensuring maximum performance for a prolonged lifetime use presents a significant challenge for manufacturers and end users, especially in safety–critical applications. Thus, identifying functional anomalies and predicting the remaining useful lifetime (RUL) is of enormous importance in the operational longevity of the device. To address such challenges, this study proposes a combination of distance-based Mahalanobis distance (MD), entropy generation rate (EGR), and deep learning models for improved anomaly detection and RUL prediction accuracy. Unlike conventional health indicators based on luminous flux data that are challenging to monitor relevant optical performance, the MD and EGR methods are employed to extract in-situ monitored thermal and electrical data as new health indicators. Long short-term memory recurrent neural networks (LSTM-RNN) and convolutional neural networks (CNN) are established to detect anomalies and predict the RUL. The accelerated degradation tests of 3 W high-power white LED have been conducted, and the online and offline collected experimental data are deployed for model development and performance evaluation. The performance of the proposed methods is compared against the Illuminating Engineering Society of North America (IESNA) TM-21 method. The results indicate that LSTM-RNN, when combined with either MD or EGR, can detect anomalies with significantly fewer data (70 %) than is typically required. Furthermore, a significant improvement in prediction accuracy in RUL prediction based on MD and EGR-constructed time series health indicators and employed with the LSTM-RNN model demonstrates the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate a 3-in-1 mini-light emitting diodes (LEDs) with 160 × 65 μm2 mini-LED subpixel chip size. Blue mini-LEDs are combining with red and green quantum dots (QDs) by using ink-jet printing technique to achieve a full-color and high-quality mini-LEDs array in the form of a monolithic chip. Subsequently, low-temperature passivated by atomic layer deposition (ALD) at 50 °C is used to effectively avoid the photo-oxidation and maintain the color purity, 99.5% National Television Standards Committee (NTSC) and 89.6% of Rec. 2020 color gamut of red as well as green QDs (GQDs) during 300 h reliability test under 50 °C/50% relative humidity (RH) condition. The environment stability L50 of both samples is 6761 and 5889 h for red and green QDs. Finally, we advocate the potential of the demonstrated highly stable full-color QD mini-LEDs to be applied in the display technology. This research also meets the requirement for a simple QD deposition method which is expected to achieve a breakthrough. [ABSTRACT FROM AUTHOR]

Ultraviolet light-emitting diodes (UVLEDs) used as excitation sources for quantum dots (QDs) are promising candidates for the display field. To eliminate the residual excitation light, the conventional method is simply increasing the optical density of QDs for packaging, which would significantly reduce the luminous efficiency of QD-light-emitting diode (LED) devices owing to reabsorption loss. In this study, the combination strategy of a boron nitride (BN) reflective coating and an ultraviolet-reflection filter (UV-R filter) for QD-LED devices is proposed. By managing the recycle of UV light to excite more QDs and reducing the reabsorption effect of QDs carefully, their green emission intensity of LED using such a strategy is 82.0% higher than that of a conventional device with a similar QD light energy proportion of ~99.0% (almost no residual UV excitation light). This strategy is also effective for red QD-LED devices while eliminating residual UV excitation light and enhancing the red emission intensity. Therefore, this study provides an effective way to develop QD-LED devices with high QD emission intensity and low UV light leakage for display. [ABSTRACT FROM AUTHOR]

BACKGROUND Light‐emitting diodes (LEDs) are widely used in closed‐type plant production systems to improve biomass and accumulate bioactive compounds in plants. Perilla has been commonly used as herbal medicine because of its health‐promoting effects. This study aimed to investigate the physiological and biochemical responses of green and red perilla under various visible‐light spectra. RESULTS: Results showed that red (R) LEDs improved fresh weights of shoots and roots, plant height, internode length, node number and leaf area, as well as photosynthetic rate of green and red perilla plants compared to blue (B) LEDs and RB combined LEDs. Meanwhile, B resulted in higher stomatal conductance, transpiration rate and Fv/Fm compared to R. Supplementation of green (G) and far‐red (FR) did not enhance perilla growth. Reduction or absence of B decreased leaf thickness, adaxial and abaxial epidermis, and palisade and spongy mesophyll. Total phenolic content, antioxidant capacity, rosmarinic acid content and caffeic acid content of green perilla were higher under R, R8B2 and RGB + FR, while greater values were obtained in red perilla under R. Accumulation of perillaldehyde, luteolin and apigenin presented different trends from those of rosmarinic and caffeic acids in both cultivars. CONCLUSIONS: Growth and accumulation of bioactive compounds in green perilla were greater than in red perilla under similar light quality, and R LEDs or a higher R ratio in combination treatments were suitable for cultivating high‐quality green and red perilla plants in closed‐type plant factories. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

A hybrid surface structure, incorporating an Ag-grid-based aluminum-doped zinc oxide (AZO) transparent conductive layer (TCL), a microhole array, 45°-sawtooth sidewalls, and an SiO2 nanoparticle (NP)/microsphere (MS) passivation layer, is proposed for the characteristic improvement of GaN-based light-emitting diodes (LEDs). In order to optimize the contact behavior between the AZO and p-GaN layers, a 2-D Ag grid is applied on the contact interface. Because series resistance Rs is reduced by the conductive Ag-grid pattern, a lower forward voltage and a better current spreading ability are obtained. Compared with a conventional GaN LED with an injection current of 200 mA, the proposed device exhibits a forward voltage of 4.01 V, reduced from 4.34 V, and presents 33%, 34.4%, 45.4%, 33.1%, and 45.3% enhancements in the light output power (LOP), luminous flux, luminous efficacy, external quantum efficiency (EQE), and wall-plug efficiency (WPE), respectively. Moreover, a more effective current spreading in the light emission mapping image and a higher intensity in the far-field pattern are achieved. Improvements of both electrical and optical properties verify that the proposed device is promising for practical applications in solid-state lighting. [ABSTRACT FROM AUTHOR]

This article concerns the problem of light-emitting diode (LED) compact thermal modeling. The methods currently used to generate such models either require some proprietary information from a device manufacturer or the resulting model element values that do not have any physical interpretation. The methodology proposed in this article allows the generation of compact thermal models based only on measurements of device dynamic temperature responses. The experimental procedure to generate the models is illustrated here with an example of color LEDs. The experiments demonstrated that it is possible to obtain in this way compact models that for various colors of emitted light and in different cooling conditions produce accurate simulation results. Furthermore, the compact model element values can be related to specific regions in the real structures. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) have broad application prospects in displays such as full-color light-emitting diodes (LEDs) and micro-LEDs. However, an ultrahigh concentration of QDs is required to eliminate the pumping light for achieving high color purity, leading to significant reduction in the photoluminescence (PL) intensity of the QDs and the generation of much more heat. In this article, the PL intensity, thermal performance, and color purity of QD-LEDs were comprehensively improved by introducing a pumping-light absorber (PLA). Results indicate that the PLA packaging structure achieves a color purity that is similar to that of a conventional structure with ultrahigh QD concentration; the radiant power of blue light was reduced by 81.6% and this leads to a large shift in the color coordinates from (0.18, 0.26) to (0.20, 0.57). Moreover, the PLA packaging structure results in higher electroluminescence (EL) intensity and lower operating temperatures than the conventional structure. This is because of the higher color-conversion efficiency and partial transfer of thermal energy to the PLA layer. In particular, the EL intensity of the QD-LEDs increased by 25.1% and the steady-state temperature was reduced to 58.9 °C, which is 19.75% lower than that of a conventional structure (73.4 °C). In addition, the PLA packaging structure works equally well with ultraviolet (UV) pumping sources to achieve a higher color purity (enhancing the color gamut by 50.1% when using a 405-nm source). [ABSTRACT FROM AUTHOR]

In this article, an electrical doping method to realize the high n-type doping for a germanium (Ge) layer in a low-doped n-type Ge metal-oxide-semiconductor (MOS) structure in the accumulation condition is proposed, which maintains the initial crystal quality of Ge. The direct-bandgap electroluminescence (EL) from Ge light-emitting diode (LED) has been demonstrated with 1.5– 1.6μm infrared emission using the metal/graphene/high-k/ interfacial layer (IL)/n-Ge MOS structure fabricated on bulk-Ge substrate. An onset current density of 5 A cm−2 is observed, which is, up to now, the lowest onset current density compared with the Ge LEDs fabricated on unstrained Ge substrates. These results indicate the superiority of the electrical doping method and the interface passivation technique on yielding the high-performance Ge-based LEDs and lasers. [ABSTRACT FROM AUTHOR]

Nanoplasmonics represents one of the most extensive research fields in optics on the nanoscale and has emerging applications in sensors, light-emitting devices, and photovoltaic devices. It offers a number of effects and can be combined with existing technologies by a number of approaches, the colloidal techniques representing the easiest implementation in the existing and emerging photonic components and devices. In this article, plasmonic effects are discussed in terms of three major physical phenomena (incident field enhancement, photon density of states enhancement, and nonradiative decay enhancement) in the context of various photonic processes and devices related to Raman scattering, photo- and electroluminescence, photovoltaics, photochemistry, and photodetectors. A number of instructive examples are given for metal nanospheres and nanorods showing how size, shape, core-shell design, and ambient environment can be used to get maximal use of the favorable factors while keeping unfavorable ones at reasonably safe level. A number of aspects of plasmonically enhanced secondary radiation are emphasized which have not gained close consideration to date. Among them, the following properties are discussed: the decisive role of scattering component of metal–dielectric extinction spectrum overlapping with incident and emitted/scattered light wavelength, valuable contribution to enhancement factors from spacers used to prevent emission quenching but simultaneously affecting the extinction spectrum, a pronounced dependence of enhancement factors on dielectric permittivity of the substrate, dielectric shell, and ambient medium. [ABSTRACT FROM AUTHOR]

The recently proposed diffusion-driven charge transport (DDCT) method can allow a paradigm shift in the design of optoelectronic devices, by changing both the current injection principle and the device structure. The DDCT injection technique is based on the bipolar electron and hole diffusion currents that are used to electrically inject charge carriers into an active region (AR) located outside the p-n junction. In this article, we study an interdigitated back-contacted DDCT–light-emitting diode (LED) based on a GaInP/GaAs double heterojunction (DHJ) structure consisting of lateral heterojunctions (LHJs) located above a uniform AR. The structure uses single-sided electrical injection and is suitable for large-area applications and thin-film devices with near-surface ARs. Our analysis, based on charge transport simulations, suggests that the structure permits more efficient current spreading and lower surface recombination than conventional structures, leading to a very high internal quantum efficiency (IQE) and injection efficiency exceeding 99%. Particularly, we investigate the implications of using the new structure for improving the efficiency of LEDs, bringing them closer to the threshold of electroluminescent cooling (ELC). The results predict an above-unity internal power conversion efficiency for the DDCT–LEDs, substantially exceeding the efficiency of conventional reference devices, highlighting the new possibilities that DDCT devices offer especially for high-power ELC at room temperature. [ABSTRACT FROM AUTHOR]

Current imbalance in multistring light-emitting diodes (LEDs) is a critical issue. It may cause overcurrent in one or more LED strings, leading to rapid degradation. In this paper, a mixed high-order compensation networks-based wireless power transfer system is proposed to generate multiple constant current outputs. It is composed of an LCC resonant network in the transmitting side, a series resonant network, and multiple CLC resonant rectifiers in the receiving side. The CLC resonant rectifiers are connected in parallel to form multiple independent output channels, and each channel is then connected to an LED string. Based on the analysis of the T resonant circuit and the modeling of coupling coils, multiple constant output currents can be derived. As a result, current balance can be achieved, which is very suitable for driving multistring LEDs. The proposed system also offers a modular, scalable, and maintenance-free design, which can significantly reduce the construction cost and the control complexity. In addition, the inverter in the transmitting side can achieve zero phase angle. A laboratory prototype with dual independent output currents is built to verify the proposed method. The experimental results agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Nowadays, due to the advancement of design and manufacturing technology, there are many consumer products with high reliability. Similarly, the competition in the business sector influences the product development time to become shorter and that makes it difficult for manufacturers to evaluate the reliability of current products before new products are released to the market. This phenomenon is manifested in the lighting industry, especially for the high power white light-emitting diodes (LEDs) as these products have a long lifetime and high reliability. Currently, the standard to predict the lifetime of LEDs is based on a deterministic nonlinear least squares method which has low prediction accuracy. To overcome this, degradation models are being used to study the reliability of such products, considering the uncertainties and the quality characteristics whose degradation over a period of time can be related to the product lifetime. A stochastic approach based on gamma distributed degradation (GDD) is proposed in this study to estimate the long-term lumen degradation lifetime of phosphor-converted white LEDs. An accelerated thermal degradation test was designed to gather luminous flux degradation data which was analyzed based on maximum likelihood estimation (MLE) and the method of moments (MM) to estimate the parameters for the GDD model. The MLE method has shown superiority over MM in terms of the estimation of the model parameters due to its iterative algorithm being likely to find the optimal estimation. The lifetime prediction results show that the accuracy of the proposed method is much better than the TM-21 nonlinear least squares (NLS) approach which makes it promising for future industrial applications. [ABSTRACT FROM AUTHOR]

Light-emitting mymargin diode (LED) chips in quantum dot (QD)-converted LEDs serve simultaneously as a heat source and a heat sink, but it remains unclear which of these is the major factor that affects the operating temperature of QDs. Here, we investigated the thermal and optical performances of QD-converted LEDs using QD-on-chip and QD-remote-chip packaging structures, to better understand the thermal effect of LED chips on QDs. Our results indicated that the QD-on-chip structure achieved the same optical performance as the QD-remote-chip structure, while the former can save QD usage up to 75.9% owing to the higher absorption probability of QDs closer to the blue source. Most importantly, the QD-on-chip structure largely reduced the maximal surface temperature from 82.7 °C to 60.2 °C at 250 mA, and had a longer operating lifetime compared with the QD-remote-chip structure. Simulations revealed that the QD-remote-chip structure could suppress the heat transfer from chips to QDs; however, the hot spot remained in QDs, owing to the heavy conversion loss and low thermal conductivity of the silicone matrix; consequently, the QD-on-chip structure had better heat dissipation (lower temperature) for QDs closer to the chip that served as heat sinks. Therefore, it is suggested to place QDs near the heat sink with high thermal conductivity, such as the LED chip, for heat dissipation; this is better than removing QDs for blocking the heat generated by the LED chip. [ABSTRACT FROM AUTHOR]

This article presents an investigation of the modulation bandwidths of quantum-dot (QD) light-emitting diodes (QLEDs). The QLEDs used in our study are red-emissive CdSe/ZnS QLEDs, which have a structure of indium tin oxide (ITO)/poly(3.4-ethylene-dioxythiophene) polystyrene sulfonate (PEDOT:PSS)/TFB/QD/ZnO/Al and an emitting area of 2 or 4 mm2. We find that at a small injection current (below ~10 mA), the effects of the resistance–capacitance (RC) time constant and the carrier lifetime on the bandwidths of the QLEDs are comparable, while at a large injection current, the bandwidths are mainly determined by the carrier lifetime. The response time of the QDs is not a limiting factor. The bandwidths of the QLEDs increase with the injection current and are eventually limited by the damage threshold current of the devices. At the same injection current, the QLED that has a smaller emitting area provides a larger current density, and thus exhibits a larger bandwidth. At an injection current of 28 mA, the 2-mm2 QLED provides a bandwidth of 11.4 MHz and a luminance value of 156 000 cd/m2, and the 4-mm2 QLED provides a bandwidth of 8.2 MHz and a luminance value of 97 000 cd/m2. Our investigation provides a guideline for QLED-bandwidth optimization and useful information for the further development of QLEDs for lighting, display, and communication applications. [ABSTRACT FROM AUTHOR]

Green spectral range, which has the highest human eye sensitivity, is one of the most fundamental colors in lighting and display. Quantum dots (QDs) offer exceptional optical properties including high quantum yield (QY), strong absorption, and narrow emission linewidths for efficient green-emitting diodes. In this article, we demonstrated QD-based light-emitting diodes (QD-LEDs) that operate at a luminous efficiency (LE) level of 95 lumens per electrical watt, the luminous efficacy of optical radiation of 409 lumens per optical watt, and external quantum efficiency (EQE) of 23.3% in the green spectral region. For that, we synthesized 1-octanethiol-capped CdSe/ZnS QDs with an absolute QY of 91% and integrated them in a liquid matrix that allows conservation of the QD efficiency in device architecture. Our simulations were in agreement with the performance of the fabricated QD-LEDs, and they showed that the QD-LEDs can be further improved to reach LE levels over 250 lm/W. [ABSTRACT FROM AUTHOR]

Solar simulators replicate the spectrum of sunlight and are essential for the research, development, and quality control of photovoltaic devices. The purpose of this paper is to explore the optimization of solar simulators based on light-emitting diodes (LEDs) and hybrid LED-halogen lamp combinations in a series of simulations, by taking into account newly defined criteria of the IEC 60904-9:2020 standard: new spectral ranges, requirements for the so-called A+ class spectrum, spectral coverage, spectral deviation, and spectral mismatch factors. We reveal new ways to configure LED-based solar simulators with just four light source types to achieve A+ class spectrum. Even with A+ class spectrum significant spectral mismatch effects can remain, but may be reduced by adding or adjusting light sources. We demonstrate optimum combinations of light sources necessary for the reduction of spectral mismatch effects in the cases of crystalline silicon (c-Si) cells or both amorphous silicon (a-Si) and c-Si cells. Simulations of the current–voltage characteristics of an encapsulated aluminum back-surface field (Al-BSF) Si solar cell were performed using Synopsys TCAD (Technology Computer-Aided Design) software to reveal the expected differences of the open-circuit voltages and the short-circuit currents in a real-life operation scenario. The advantages of higher spectral coverage and more precise photogenerated current values are envisaged for hybrid solar simulators with comparable numbers of different light source types. The manufacturability of several proposed simulator designs is demonstrated by a series of proof-of-concept experiments. [Display omitted] • A+ class spectrum can be achieved with only four distinct types of light sources. • 365 nm and 1050 nm LEDs nearly eliminate spectral mismatch effects in c-Si cells. • Hybrid A+ class solar simulator of five source types with 97% spectral coverage. • Simultaneous optimization of photocurrent, spectral coverage, and spectral mismatch. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the degradation mechanisms of UV-B AlGaN-based light-emitting diodes (LEDs) submitted to constant current stress beyond the typical application conditions. We demonstrate the existence of two main degradation mechanisms that significantly impact the relative amplitude of the main quantum well (QW) peak at 310 nm and of a parasitic peak at ~340 nm related to the electron overflow toward the last quantum barrier before the p-side. These mechanisms are thoroughly investigated by means of electrical and optical measurements, and by photocurrent (PC) spectroscopy. We demonstrate that in the first 50 h of stress, degradation is caused by an increased defect density in the last quantum barrier and/or carrier escape from the QWs, which results in a decrease in the QW emission and in an increase in the parasitic peak at 340 nm. For longer stress times, degradation is dominated by a diffusion process, causing an increase in defect density and nonradiative recombination in the LED. This has a direct impact on both the QW peak and the parasitic peak, which show a significant decrease for long stress times. PC spectroscopy demonstrates that the defects responsible for degradation are most likely located next to mid-gap, thus acting as efficient nonradiative recombination centers. [ABSTRACT FROM AUTHOR]

Lumen, chromaticity, and correlated color temperature CCT are the three main performance indicators of failure of high-power white light-emitting diodes (LEDs) (HPWLEDs). The existing data-driven (DD) method to predict the life of LEDs often considers that three performance indicators are independent, or only one or two performance indicators are used for prediction, which may not be accurate enough. To solve this problem, a method based on Archimedean Copula function is proposed to describe the correlation of multiple performance indicators. The test data reported from LUXEON is used as an example to establish a 3-D life prediction model by combining the thresholds of three performances to predict the life of LEDs, and the application of Copula function is explained. The results show that there is a little influence on life prediction of LEDs among the different Copula function structures, while the difference between considering single performance and multi-performance is obvious. The mean time to failure (MTTF) of which is proven to be more conservative than the L70 life predicted by the conventional method. [ABSTRACT FROM AUTHOR]

To enhance the heat dissipation of high-power light-emitting diodes (LEDs), corona wind based on corona discharge was promoted. In this paper, we aimed at reinforcing the intensity of corona wind by modifying the needle electrode with graphene solution. To explore the differences in the graphene-coated electrode and the original bare electrode on the electrical characteristics, the intensity of corona wind, and LED heat dissipation, a corona wind cooling system and a thermal test system were built for the experimental study. The results showed that the graphene-coated electrode system could produce corona wind at a lower voltage. In addition, the discharge current of the graphene-coated electrode system is higher than that of the bare electrode system under the same discharge voltage. The graphene-coated electrode system can induce a faster corona wind and the highest speed is about 3.4 m/s, showing that it is more efficient than the bare electrode system in corona wind production. Moreover, the temperature drop of LEDs for the graphene-coated system is greater, which means that the corona wind cooling system can reduce the junction temperature of the LED chips effectively. Ultimately, as the discharge power increases, the average convective heat transfer coefficient increases. Indeed, the result of this paper can be used for the wide variety of the graphene-coated corona wind generator application as a promising technology for the LED heat management. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are emerging lighting sources. However, it is still difficult to obtain good optical consistency of LEDs from the same batch due to phosphor sedimentation. In this paper, we introduce the centrifugation method to enhance the optical consistency of LEDs. The phosphor gradient concentration model is proposed to simulate the changes of phosphor concentration in different centrifugation time and acceleration. Moreover, the effect of these parameters on the optical performance of LEDs is discussed. The simulation results reveal that increasing centrifugal acceleration and time can enhance the optical consistency of LEDs by changing the phosphor distributions. It is suggested that the centrifugation parameters with 20 times gravitational acceleration and 6 min centrifugation time can ensure high optical consistency for LEDs, which can be taken as a reference to balance optical performance and consistency. Experimental results validate that the proposed method is beneficial to improve the optical consistency, including luminous flux and color coordinates, compared to LEDs without centrifugation. [ABSTRACT FROM AUTHOR]

Recent advances in the photoluminescent cooling of doped glasses provoke the question of whether similar progress is possible in electroluminescent cooling (ELC), and if so, what are the conditions for observing it at high powers. Here, we establish a simulation framework for III–V intracavity double-diode structures (DDSs) intended for studying ELC and introduce and analyze the most relevant figures of merit for the recently measured devices exhibiting the highest reported quantum efficiency of 70%. In essence, the DDSs optically couple a GaInP/GaAs double heterojunction light-emitting diode (LED) and a GaAs p-n homojunction photodetector (PD), integrated as a single device. The modeling framework couples the drift-diffusion charge transport model with a photon transport model and uses our recent experimental measurements for validation and the extraction of important material parameters. Results show that the model can accurately describe the experimental behavior over many orders of magnitude and suggest that the internal efficiency of the LED already exceeds the cooling threshold. Directly observing cooling in the presently studied devices, however, is still hindered by bottlenecks arising from the surface recombination at the LED walls and recombination losses in the PD. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are considered as a next-generation lighting due to their high luminous efficiency, low power consumption, and long lifetime. However, the low heat dissipation of LEDs is an inevitable roadblock. Here, a high heat-conducting Cu nanoparticle (NP) paste was prepared and demonstrated for high-power LEDs. The effects of sintering temperature on the electrical and thermal properties of the Cu NP paste were investigated. The junction temperature change and thermal resistance of LEDs were measured and compared with the traditional die-attach materials. Consequently, the Cu NP paste sintered at 250 °C possesses low electrical resistivity of $5.1~{ \mu \Omega \cdot }$ cm and high thermal conductivity of 142.37 W/(m.K). The packaged LEDs display the low thermal resistance of 6.58 K/W and the low junction temperature change of 3.22 °C, which are significantly lower than those of LEDs packaged by the traditional die-attach materials. These results demonstrate that the promising Cu NP paste provides a feasible and effective strategy for enhancing the heat dissipation of high-power LEDs. [ABSTRACT FROM AUTHOR]

While highly thermally conductive underfill material has been proposed as a solution for reducing the thermal resistance of flip-chip light-emitting diode (FCLED) packages, studies up until this point have not taken into account the layout of the underlying metallic interconnects and its impact on thermal resistance. This paper provides a deeper investigation into how interconnect spacing affects thermal resistance in conjunction over a range of underfill thermal conductivities. Test vehicles utilizing FCLEDs and copper–tin interconnects were fabricated, tested for thermal resistance, and simulated with ANSYS finite-element analysis software. A follow-up parametric study was performed, in which the effectiveness of increasing underfill thermal conductivity was demonstrated to be highly dependent on the distance between conductive metal interconnects. It was found that when the gap between interconnects is sufficiently small, the thermal conductivity of the underfill plays a negligible role in the overall thermal resistance of the FCLED package. For instance, when the gap is $200~\mu \text{m}$ , an underfill with a relatively high thermal conductivity of 1.0 $\text{W}\cdot \text{m}^{-1}\cdot \text{K}^{-1}$ underfill only reduces thermal resistance ($\Theta _{\mathrm {JC}}$) versus a no-underfill scenario by 2.6% more than does an underfill with a thermal resistance of 0.25 $\text{W}\cdot \text{m}^{-1}\cdot \text{K}^{-1}$. This effect can be leveraged during package design to allow for unfilled underfill materials to be used, reducing cost and process time. [ABSTRACT FROM AUTHOR]

Light-emitting diode (LED)-based visible light communication (VLC) has recently been promoted by the lighting industry for providing services and information for consumers in shopping malls. Communication system designs require well-defined signal-to-noise ratio (SNR). Being semiconductor devices, both LEDs and photodetectors are highly temperature-sensitive. This paper explores the electrical and thermal sensitivities of LED and photodetector together for VLC applications, and highlights the discoveries that the SNR of LED-based VLC could vary substantially over the full operating power range of the LED lighting systems. A new analysis of the SNR based on the photoelectrothermal theory has been developed. It can be used as the theoretical and design tool to predict such SNR variations. The validity of the new analysis has been confirmed with practical measurements that are consistent with theoretical predictions. The analytic approach can in principle be used as a design tool for LED-based VLC. [ABSTRACT FROM AUTHOR]