High-power White LEDs Research Articles

The effect of Lu3+ doping upon YAG:Ce phosphor ceramics for high-power white LEDs

Intense green emission is extremely significant to the color rendering index (CRI) of white LEDs. Various green-emitting YLuAG:Ce phosphor ceramics were successfully prepared by vacuum sintering. The effects of Lu3+ doping on structure and luminescence property were investigated in detail. In comparison with YAG:Ce, YLuAG:Ce ceramics own smaller grain size, better luminescence performance and higher thermal stability. The photoluminescence (PL) intensity of YLuAG:Ce ceramics increases by 23.6 % due to the “light scattering enhanced effect”. Furthermore, the Ce3+ emission is obviously blue-shifting from 533 nm to 519 nm, and the intensity of YLuAG:Ce ceramics reduces only about 8.9 % at 250 °C, showing better thermal stability (vs 11.1 % of YAG:Ce). The LE of LED packaged by YLuAG:Ce ceramic is up to 148.88 lm/W when the doping Lu3+y is 2.1. The above results show that tailored YLuAG:Ce phosphor ceramic is a potential green-emitting color converter for high-power LEDs (hp-LEDs).

Low cost high intensity LED illumination device for high uniformity solar testing

Indoor testing of solar thermal absorbers requires an artificial light source with controlled emitted power and uniform illumination over the targeted sample. There are several devices described in literature which adopt different types of light sources and geometrical configurations, but they do not attain high uniformity, high power density, illumination of a large area and compactness simultaneously. The proposed solar simulator is composed of four identical high-power white LED arrays of 30 mm diameter each, placed on a supporting and cooling structure having a minimum volume of 26 cm × 26 cm × 8 cm. A numerical model has been developed, based on a ray tracing software, in order to define the optimal architecture. It has then been experimentally validated with measurements of the power density map, carried out with a 1% uncertainty pyranometer. Data shows that the built system is very stable over time and provides an illumination uniformity higher than 98% on a surface of 11 cm × 11 cm, which reduces to 95% on a surface of 15 cm × 15 cm. The power density can be adjusted within the 390–1360 W m−2 range without affecting uniformity, and the system is easily scalable to illuminate larger surfaces. It represents a suitable solution for various laboratory purposes requiring stable, uniform and high intensity illumination.

Transfer Data from PC to PC Based on Li-Fi Communication Using Arduino

Light Fidelity (Li-Fi) is a new technology that has been developed in the last few years and still needs more investigation and experiments to prove its perfection to be an alternative solution for wireless fidelity (Wi-Fi) technology. Li-Fi utilizes light as a medium of communication instead of traditional radio frequencies as in Wi-Fi. Li-Fi technology has the essential features compared to Wi-Fi, such as its ideal for high-density wireless data coverage in a confined area and reducing radio interferences issues. In this paper, a PC-to-PC wireless data transfer system is proposed based on Li-Fi technology. Data is transmitted from transmitter Pc via the light of an array of high-power white LEDs connected to Arduino UNO. The data is then received on the PC receiver using a photodiode, connected to another Arduino UNO device, to sense the light and decode it to its original format. This work aims to improve the transmission and reception mechanism by increasing the data bit rate. After experimenting, the evaluation results showed that the data bit rate was improved using the proposed transmission mechanism and reached up to 147 bps with an accuracy of 100%, over 20 cm as a distance between the transmitter and receiver.

Enhancing light sources color homogeneity in high-power phosphor-based white LED using ZnO particles

Color uniformity is one of the essentials for the on-going development of WLED. To achieve a high color uniformity index, increasing the scattering events within the phosphor layers was reported to be the most efficient method and in this article, ZnO is the chosen material to apply in this method. After analyzing the scattering properties through the scattering cross-section , scattering coefficient and scattering phase function , the which outcomes comfirm that ZnO can enhance the scattered light in the phosphor layers. Moreover, the findings from the study of ZnO concentration from 2% to 26% suggest that color uniformity also depends on the fluctuation of ZnO concentration, therefore, to control color uniformity the focus should be implied on both size and concentration of ZnO. The experimental results from this research show that the luminous flux of WLED is at the peak if the concentration of ZnO is at 6%, and when the concentration of ZnO is at 18% and has 100 nm particles size, the ΔCCT reaches the lowest level. The final choice should be based on the desired characteristic of WLEDs, however, if the WLED need to excel in both luminous flux and ΔCCT then 6% ZnO concentration with particles size from 100 nm-300 nm is the optimal choice.

The Effects of ZnO particles on the color homogeneity of phosphor-converted high-power white LED light sources

Color homogeneity is one of the goals to continuously improve WLED. Among the methods for enhancing the color uniformity of WLEDs, improving scattering in phosphor layer is considered to be the most effective. In this paper, ZnO is used for that purpose. The results show that ZnO particle size significantly affects scattering in the phosphor layer, which is a vital factor to analyze scattering, scattering sand surface, scattering coefficient and scattered phase function C_sca (D,λ), μ_sca (λ) and ρ(θ,λ). In addition, the concentration of ZnO was also analyzed with values from 2% to 22%. Color homogeneity depends not only on size but also on the concentration of added ZnO. Therefore, color homogeneity control is the control of ZnO size and concentration. The proposed result is 10% ZnO for the highest lumen of LED. With 14% and 500 nm of ZnO particles, ΔCCT reaches the lowest. Depending on the production needs, manufacturers can choose the most appropriate way. However, with both required lumen and ΔCCT, 14% ZnO is suitable for ZnO sizes.

Multi Frequency on RGB Lighting LED Driver Technique

In this paper, we conducted RGB incident light intensity of the high power white lighting LED. The current control 50% duty cycle pulse signal source with appropriate semiconductor carrier frequency response are supply to the RGB white lighting LED. Although, the carrier relaxation time of the red blue and green light in the white lighting LED are not the same value which depend on the carrier different of the energy level. The measurement show that the lowest duty cycle appropriate pulse signal for only blue or UV base white LED give more relative light intensity than normal (low frequency) signal within 11%.

Selection of Remote Phosphor Led Packages for Improving Luminous Flux

In this paper, the first issue presented and analyzed by several experiments is the influence of the distance between phosphor layers in the dual-layer and triple-layer remote package on luminous flux and color rendering property. During the simulation, it was realized that it was possible to create a suitable distance to create higher quality white light-emitting diodes (WLEDs) by adjusting the distance between the phosphor layers. According to the study results, 0.1 mm is the most reasonable distance between two phosphor layers so that the performance of the multi-chip white light LED (MCW LED) can get the best optimal effect. Through a series of experiments, it has been proved that the efficiency of the two-layer structure gives optical properties higher than the three-layer structure related to distance. The highest achievable lumen output is 0.6 mm for the triple-layer structure and 0.1 mm for dual-layer structure. Meanwhile, the color rendering index changes insignificantly when the distance increases. The triple-layer package is not practical for high-power white LEDs due to the high cost and low conversion efficiency. The dual-layer remote phosphor package with a 0.1 mm phosphorus gap is the optimal structure of WLED in improving luminous efficiency and color rendering index. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

Comparison of nonlinear equalizers for high-speed visible light communication utilizing silicon substrate phosphorescent white LED.

Compared with multicolor-chip integrated white LEDs, phosphor-based white LEDs are more attractive for daily illumination due to lower cost and complexity, and thus they are preferable for future commercial use of visible light communication (VLC) systems. However, the application of phosphorescent white LEDs has a lower data rate than multicolor-chip integrated LEDs because of severe nonlinear impairments and limited bandwidth caused by the slow-responding phosphor. In this paper, for the first time we propose to employ phosphorescent white LEDs based on silicon substrate with adaptive bit-loading discrete multitone (DMT) modulation and a memoryless polynomial based nonlinear equalizer to achieve a high-speed VLC system. We also present a comprehensive comparison among nonlinear equalizers based on the Volterra series model, memory polynomial model, memoryless polynomial model and deep neural network (DNN) with experimental results utilizing a silicon substrate phosphorescent white LED, and provide detailed suggestions on how to choose the most suitable nonlinear mitigation scheme considering different practical conditions and the tradeoff between complexity and performance. Beyond 3.00 Gb/s DMT VLC transmission over 1-m indoor free space is successfully demonstrated with bit error rate (BER) under the 7% forward error correction (FEC) limit of 3.8×10-3. As far as we know, this is the highest data rate ever reported for VLC systems based on a single high-power phosphorescent white LED.

Synthesis of Red-Emitting CdSe/CdS/ZnS Core/Shell/Shell Quantum Dots

CdSe/CdS/ZnS Core/Shell/Shell Quantum Dots is synthesized of using a different surfactant, which is a mixture of octa decyl phosphonic acid (ODPA) and Oleic Acid (OA). An interfused CdSe//ZnS core formation was generated, which showed a significant blue shift from CdSe QDs. The interfused core showed the maximum QY. The CdSZnS shell favourably resulted in a significant red-shift in PL is useful for the fabrication of high power white blight LEDs

Lifi Based Audio Communication for Coal Mine Parameter Monitoring and Automatic Control System

Li-Fi (Light Fidelity) is a quick and shoddy optical rendition of correspondence. The principle segments of this correspondence framework are a high power white LED which goes about as a correspondence source and a silicon Photo diode which demonstrates great reaction to noticeable wavelength locale filling in as the getting component. An essential factor while planning Li-Fi is Line of Sight (LoS). The LED can be turned on and off to create advanced series of 0s. Information is coded in the light which changes into new information by shifting the glinting rate of the LED. Since the speed of the light is exceptionally quick, the transmitted yield is gotten as voice signs to the specialists at the coal mineshaft. Coal mining and oring includes the disclosure of coal and its troublesome works of extraction, notwithstanding its evacuation and deal in the generation of concrete industry. Most wounds occurring in the underground mines incorporates the falling of rocks, slips and blasts. Harmful gas is produced amid the season of mining and oring forms. The mining laborers are influenced by lung illness by breathing in residue and lethal gas in Coal mining condition. This data is implied to the specialists at the coal mineshaft from the higher authorities through Li-Fi as a voice motions in this work

Color converter based on transparent Ce:YAG ceramic by different package structure for high-power white LED

Ce: GdYAG ceramics and CaAlSiN3: Eu2+ phosphor were fabricated by solid-state reaction. CaAlSiN3: Eu2+ phosphor films with different content were manufactured on Ce: YAG ceramic by the spin-coating method. The Ce: YAG ceramics doping with different Gd3+ content is labeled as Gd-doping structure. The red phosphor film placing Ce: YAG ceramic close to the chips is labeled as R–Y structure, similarly, the red phosphor film adjacent to the chips is named as Y-R structure. The main emission peak has redshift with Gd content increase. The PL spectra have a shift to the red region with the increasing of the red phosphor content in the R–Y structure and Y-R structure. As-prepared samples were further fixed on the substrate to manufacture the ceramic covered film (CCF)-based LEDs and ceramic-based LEDs. The color temperature can be regulated through the three structure. The luminous efficacy in the R–Y structure, Y-R structure, and Gd-doping structure is 89.16 lm/w, 86.8 lm/w, and 62.9 lm/w at about 3500K, respectively. The CRI in the R–Y structure, Y-R structure, and Gd-doping structure is 64.6,68.8, and 62.2 at about 3500K, respectively. The temperature in the R–Y structure, Y-R structure, and Gd-doping structure 83.3 °C, 81 °C, and 124.7 °C at about 3500K, respectively. The heat dissipation capability of R–Y structure and Y-R structure are superior to that of the Gd-doping structure. The result shows that the R–Y structure has the best luminous efficacy at a similar CCT which improved 41.7% comparing to the Gd-doping structure. The Y-R structure has the best CRI (improve 10.6% comparing to the Gd-doping structure) and heat dissipation capability (decreased 35.1% comparing to the Gd-doping structure) at a similar CCT. The way of Ce: YAG ceramic coated CaAlSiN3: Eu2+ phosphor will be a promising candidate to achieve warm white for high power LEDs.

Thermostability and reliability properties studies of transparent Ce:GdYAG ceramic by Gd substitution for white LEDs

Yttrium Aluminum Garnet transparent ceramics with different Gd3+ concentrations ((Ce0.001GdxY0.999-x)3Al5O12) ceramics were prepared by the conventional solid state reaction technology and vacuum sintering method, and the ceramic-based LEDs with blue LED were prepared by flip chips and Chip on board package. The extreme circumstance of −40 °C and 150 °C alternate environments, high humidity and high temperature as well as xenon lamp aging test for a long time are mentioned to explore the reliability of phosphor ceramics, respectively. And the thermostability and the effect of Gd3+ doping on the PL properties of ceramics were also investigated. What is more, the effects on the optical performance of the ceramic-based LEDs have been also investigated. As Gd3+ concentration added from 0 to 0.5, the PL spectra peaks of phosphor shifted from 542 nm to 575 nm under the excitation of 460 nm. It can be summarized that the increase of Gd3+ concentration could not improve the thermostability, but enhance the reliability when the x value is x is not greater than 0.4. What is more, the ceramics-based LED of x = 0.3 instead of x = 0.4 has the best reliability after the xenon lamp aging and thermal cycling test. And the ceramics-based LED of x = 0.45 has the best reliability after the high humidity and high temperature test. Compared with Ce:YAG and Ce:LuAG ceramics, although the increase of Gd3+ concentration decreases the thermostability and luminous efficiency, the Gd substitution can enhance the reliability and solve the lack of red light in the spectrum of Ce:YAG and Ce:LuAG ceramics, which has improved the performance of Ce:GdYAG ceramics for high-power warm white LEDs.

Tunable blue/yellow emission in high-power white LED devices packaged with Ce:(Y, Gd)AG transparent ceramics

Abstract White LEDs have been widely used in various lighting applications. However, applying them to high lumen density systems remains a challenging issue due to the aging of the organic packing materials. In this paper, Ce:(Y, Gd)AG transparent ceramics with different Gd3+ substitution concentrations were fabricated via solid-state reaction method under different sintering temperatures and used to construct high-power white LED devices to evaluate their optical, luminescence, and thermal properties. The energy band structure of Ce3+ was effectively tailored by the energy level compressing and orbital hybridisation effects, resulting in the tunability of the blue/yellow emission of the devices and the luminescence redshift of Ce:(Y, Gd)AG ceramics. The transmittance of Ce:(Y, Gd)AG transparent ceramics had almost no impact on the photoluminescence spectra yet exhibited strong dependence on the Gd3+ substitution concentration. The emitted light of LED devices packaged with the ceramics changed from blue-white to yellow-white while increasing Gd3+ concentrations from 0.0 to 30.0 at.%. The as-assembled white LED devices exhibited excellent heat dissipation performance, uniform intensity distribution, and strong intensity in the forward direction. The industrialisation of Ce:YAG transparent ceramics-based LED devices can be accelerated especially in high-power lighting.

A novel red phosphor Ba2La4Y4(SiO4)6O2:Eu3+ with high quantum yield and thermal stability for warm white LEDs

A novel silicate oxyapatite red phosphor Ba2La4Y4(SiO4)6O2:Eu3+ was synthesized by solid state reaction method. The results show that Eu3+ ions replace La3+ ions can lead to higher luminescence intensity than replacing Y3+ ions. Moreover, Ba2La4Y4(SiO4)6O2:Eu3+ shows a high quantum yield of 67.46% and high thermal stability (the luminescence intensity remains 94.1% of its initial PL intensity at 125 °C, and maintains 77.6% at 150 °C) by regulating the relative content of Y3+ ions and La3+ ions. Finally, a warm white LED with low CCT of 3306 K, high luminous efficiency of 33.55 lm/W and Ra of 91 was achieved by combining Ba2Y4La4(SiO4)6O2:Eu3+ red phosphor with BaMgAl10O17:Eu2+ blue phosphor and (Sr, Ba)2SiO4:Eu2+ green phosphor under 395 nm NUV chips. All the results manifest that the red phosphor Ba2Y4La4(SiO4)6O2:Eu3+ can be used as a potential NUV-excited red phosphor for high-performance high-power warm white LEDs.

Taguchi method-assisted optimization of multiple effects on the optical and luminescence performance of Ce:YAG transparent ceramics for high power white LEDs

Ce:YAG transparent ceramics have great potential in white LEDs, especially under high power packaging technology, due to their superior thermal performance.

Simple mass-preparation and enhanced thermal performance of Ce: YAG transparent ceramics for high power white LEDs

Ce: YAG transparent ceramics have great potential in the high power white light-emitting diodes based on chip packaging technology due to the superior optical property and thermal conductivity. However, it is still a challenging issue to explore a simple and efficient mass-preparation method and to solve the heat dissipation problem. In this study, the batched Ce: YAG ceramics with different Ce3+ concentrations were fabricated by Isobam gel casting plus vacuum sintering. Their optical properties were systematically investigated and the temperature change, thermal distribution and heat flux were effectively analyzed by ANSYS software. All ceramics were obtained in the optimized 76.0 wt% solid loading slurries composed of 0.3 wt% ammonium citrate tribasic and 0.5 wt% Isobam. The temperature difference between the simulation and the experiment of the Ф16 mm and Ф20 mm Ce: YAG ceramics was 0.57 °C and 3.48 °C at about 120 s in transient thermal state, which indicated that the simulation result was credible. Meanwhile, when the diameter of ceramic was increased by 4 mm, the average temperature was lowered by 20–30 °C with the decreasing rate of 5–7.5 °C/mm. Therefore, both simulation and experimental results proved that properly increasing the ceramic area was a simple and efficient method to solve the heat dissipation and high temperature problem, and Isobam gel casting had the potential advantages in the simple mass-fabrication of transparent ceramics.

Luminescence properties of Li2SrSiO4:Eu2+ silicate yellow phosphors with high thermal stability for high-power efficiency white LED application

Li2SrSiO4:Eu2+ yellow phosphors were synthesized by Polymerized Complex Method using TEOS and their thermal stability was investigated. The synthesized phosphors exhibited a broad yellow emission band around 560 nm. The optimum H2/N2 reduction temperature and Eu concentration are 900 °C and 0.5% respectively, which show the highest PL intensity and 6 times higher than samples synthesized by conventional solid-state reaction at the same condition. In order to investigate the thermal stability, PL properties in temperature range from 16.4 K to 583 K were examined. The PL intensity remains 80% above at high temperature (438 K) compared with room temperature. Activation energy and internal quantum efficiency of samples are estimated to be 0.43 eV and 62% respectively. Emission processes in Li2SrSiO4:Eu2+ phosphor were discussed with configuration coordinate model. The results reveal that Li2SrSiO4:Eu2+ yellow phosphors shows excellent thermal stability and have feasibility in replacement of YAG:Ce3+ yellow phosphors in white LEDs application.

Time evolution of packaged LED lamp degradation in outdoor applications

Degradation of Silicone used in high power white LEDs as molding material has significant impact on the LED's lifetime and efficacy. This work provides a detail study on the impact of moisture, temperature and thermal aging on the packaging materials by tracing its progression of degradation under high temperature and humidity conditions. Silicone degradation via discoloration and cracks formation is identified and its cracks depth is found to decrease as the time progressesdue to diffusion mechanism and this led to highly distorted surface. It is found that Silicone undergo hydrolysis, condensation, thermal oxidation and thermal aging over its lifespan, and discoloration is mainly due to hydrolysis while cracks formation is mainly due to thermal oxidation. The decrease in the crack depth is due to thermal aging where diffusion of silicon oligomer occurs.

Influence of Dual-layer and Triple-layer Remote Phosphor Package on Optical Properties of White LEDs

In this paper, the influence of the distance between phosphor layers in the dual-layer and triple- layer remote package on luminous flux and color rendering property is presented and analyzed. During the simulation, it is recognized that an appropriate distance can produce higher quality of the multi-chip white LED (MCW-LEDs) through adjusting the distance between two and three phosphor layers. According to the research results, 0.1mm is the outstanding distance between two phosphor layers so that the performance of MCW-LEDs can be accomplished the best optimal effect. In addition, the simulation results show that the dual-layer structure yielded higher optical properties than the triple-layer structure in relation to the distance. The highest lumen output of triple layer-structure can be achieved at the distance of 0.6 mm and dual-layer structure is 0.1 mm. Meanwhile, the color rendering index (CRI) changes insignificantly when the distance increases. Triple layer package is not practical for high power white LEDs due to high cost and low conversion efficiency. Dual-layer remote phosphor package with the distance between two phosphor layers of 0.1mm is an optimal structure of LEDs in improving the luminous efficiency and the color quality.

Low-frequency noise characteristics of high-power white LED during long-term aging experiment

Low-frequency electrical and optical noise characteristics of a high power white InGaN LED and the cross-correlation coefficient between these fluctuations are investigated during the long-term ageing experiment (28000 h). The analysis of cross-correlation shows that the correlated part of the low-frequency electrical noise, which indicates physical processes in the active area of the LED, varies during the ageing experiment. Two main stages are distinguished considering the rapid changes of the noise characteristics. The initial stage (after the first 1100 h) is followed by the decrease in the noise power at low forward currents and the increase in the light output. The final stage (after 28000 h) is characterized by a strong growth of the low-frequency noise, the decrease of the light output and the increase of the correlated part of electrical and optical fluctuations. These changes mean a failure in the active layer of the LED. The optical output decomposition into two spectral parts, the radiation generated by the LED chip and the radiation generated by the phosphor layer, enables evaluation of the phosphor layer influence on the degradation process of device optical characteristics. Despite the fact that this layer contributes to the variation of the LED chromatic properties, the cross-correlation analysis has shown that the phosphor layer does not act as a possible noise source during the ageing experiment.