The Experts below are selected from a list of 1089 Experts worldwide ranked by ideXlab platform
Sheng Liu - One of the best experts on this subject based on the ideXlab platform.
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Controlling Phosphor Particle Distribution for High-Angular-Color-Uniformity and Low-Cost LEDs Based on Thermalcapillary Flow
IEEE Transactions on Electron Devices, 2021Co-Authors: Jie Liu, Sheng Liu, Weixiang Wang, Chen Zhang, Zheng Gong, Huai ZhengAbstract:Low cost and high performance are the pursuing goals of the light-emitting diode (LED) packaging. The Phosphor layer configuration of LEDs significantly influences optical performances. In this study, thermalcapillary flow was introduced in the Phosphor Coating by the blue laser local irradiation. It has been demonstrated to successfully manipulate the Phosphor particle distributions. In the Phosphor dispensing Coating, a centripetally concentrated particle distribution was realized and resulted in high angular color uniformity (ACU) and low-cost manufacture. Its angular correlated color temperature (CCT) deviation was reduced by more than 65%, compared to the traditional Phosphor dispensing Coating. Besides, the Phosphor amount is saved by about 12%. The mechanism of ACU enhancement is analyzed. The realized Phosphor particle distribution can inspire further development of the optimized Phosphor layer configuration.
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realization of high color uniformity for Phosphor converted white light emitting diodes through a stamp printed Phosphor Coating
IEEE Electron Device Letters, 2017Co-Authors: Zefeng Zhang, Huai Zheng, Sheng LiuAbstract:In this letter, we demonstrate a stamp-printed Phosphor Coating process to realize high angular color uniformity (ACU) for Phosphor-converted white light-emitting diodes. In the proposed Phosphor Coating method, the Phosphor gel is printed on desirable areas, where it forms variable geometries through the transfer of the stamp bump. The Phosphor Coating method shows high flexibility in its fabrication of various Phosphor layer geometries, including the frustum, inverted frustum, cube, and catenoid. ACU performances of different Phosphor layer geometries were measured. The obtained results show that the catenoid Phosphor layer with the side inward width of 0.07 mm shows an excellent uniform angular correlated color temperature (CCT) distribution. Its maximum CCT variation is only 150 K at the viewing angles ranging from -80° to 80° when the average CCT is approximately 6300 K. The analysis of the ACU performances of different Phosphor layer geometries is presented.
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enhancing acu of white leds by Phosphor Coating based on electrohydrodynamics
IEEE Photonics Technology Letters, 2017Co-Authors: Jiangping Sun, Huai Zheng, Yang Peng, Xing Guo, Zhiyin Gan, Sheng LiuAbstract:High angular color uniformity (ACU) is strongly required in many illumination applications. In this letter, we propose a low-cost and facile Phosphor Coating method based on electrohydrodynamics to realize high ACU for Phosphor-converted white light-emitting diodes (LEDs). By applying an electric field around a liquid Phosphor-silicone encapsulant, a normal force is induced on the air-liquid interface, resulting in a Phosphor layer with cone morphology. Consequently, the ACU of white LEDs with the cone Phosphor layer is greatly improved compared with that of white LEDs with the traditional spherical cap Phosphor layer. The angular correlated color temperature (CCT) deviations are as low as 393 and 40 K at the average CCTs of 6500 and 5000 K, respectively.
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heat and fluid flow in high power led packaging and applications
Progress in Energy and Combustion Science, 2016Co-Authors: Xiaobing Luo, Sheng Liu, Run Hu, Kai WangAbstract:Abstract Light-emitting diodes (LEDs) are widely used in our daily lives. Both light and heat are generated from LED chips and then transmitted or conducted through multiple packaging materials and interfaces. Part of the transmitted light converts into heat along the light propagation; in return, the accumulation of heat leads to the degradation of light output. The accumulated heat negatively influences the reliability and longevity of LEDs, and thus thermal management is critical for LED packaging and applications. On the other hand, in LED packaging processes, many fluid flow problems exist, such as Phosphor Coating, silicone injection, chip bonding, solder reflow, etc. Among them, Phosphor Coating is the most important process which is essential for LED performance. Phosphor gel is a kind of non-Newton fluid and its Coating process is a typical fluid-flow problem. Overall, since LED packaging and applications present many heat and fluid flow problems, obtaining a full understanding of these problems enables advancements in the development of LED processes and designs. In this review, the emphasis is placed on heat generation in chips, heat flow in packages and application products, fluid flow in Phosphor Coating process, etc. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art LED packaging and application technologies.
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Conformal Phosphor Coating for Phosphor-converted white LEDs on basis of dispensing process
2013 14th International Conference on Electronic Packaging Technology, 2013Co-Authors: Huai Zheng, Yiman Wang, Xiaobing Luo, Sheng LiuAbstract:We presented a kind of new conformal Coating Phosphor layer structure and method in this paper. In this method, we gained a compact Phosphor layer arrangement with inversed Phosphor distributions by substrate structure design and different curing method on basis of traditional dispensing process. Compared to traditional Phosphor dispensing packaging, this method can significantly enhance the angular color uniformity (ACU). The angular correlated color temperature (CCT) deviation is reduced as 149K at the average CCT of about 6000K.
Huai Zheng - One of the best experts on this subject based on the ideXlab platform.
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Controlling Phosphor Particle Distribution for High-Angular-Color-Uniformity and Low-Cost LEDs Based on Thermalcapillary Flow
IEEE Transactions on Electron Devices, 2021Co-Authors: Jie Liu, Sheng Liu, Weixiang Wang, Chen Zhang, Zheng Gong, Huai ZhengAbstract:Low cost and high performance are the pursuing goals of the light-emitting diode (LED) packaging. The Phosphor layer configuration of LEDs significantly influences optical performances. In this study, thermalcapillary flow was introduced in the Phosphor Coating by the blue laser local irradiation. It has been demonstrated to successfully manipulate the Phosphor particle distributions. In the Phosphor dispensing Coating, a centripetally concentrated particle distribution was realized and resulted in high angular color uniformity (ACU) and low-cost manufacture. Its angular correlated color temperature (CCT) deviation was reduced by more than 65%, compared to the traditional Phosphor dispensing Coating. Besides, the Phosphor amount is saved by about 12%. The mechanism of ACU enhancement is analyzed. The realized Phosphor particle distribution can inspire further development of the optimized Phosphor layer configuration.
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realization of high color uniformity for Phosphor converted white light emitting diodes through a stamp printed Phosphor Coating
IEEE Electron Device Letters, 2017Co-Authors: Zefeng Zhang, Huai Zheng, Sheng LiuAbstract:In this letter, we demonstrate a stamp-printed Phosphor Coating process to realize high angular color uniformity (ACU) for Phosphor-converted white light-emitting diodes. In the proposed Phosphor Coating method, the Phosphor gel is printed on desirable areas, where it forms variable geometries through the transfer of the stamp bump. The Phosphor Coating method shows high flexibility in its fabrication of various Phosphor layer geometries, including the frustum, inverted frustum, cube, and catenoid. ACU performances of different Phosphor layer geometries were measured. The obtained results show that the catenoid Phosphor layer with the side inward width of 0.07 mm shows an excellent uniform angular correlated color temperature (CCT) distribution. Its maximum CCT variation is only 150 K at the viewing angles ranging from -80° to 80° when the average CCT is approximately 6300 K. The analysis of the ACU performances of different Phosphor layer geometries is presented.
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enhancing acu of white leds by Phosphor Coating based on electrohydrodynamics
IEEE Photonics Technology Letters, 2017Co-Authors: Jiangping Sun, Huai Zheng, Yang Peng, Xing Guo, Zhiyin Gan, Sheng LiuAbstract:High angular color uniformity (ACU) is strongly required in many illumination applications. In this letter, we propose a low-cost and facile Phosphor Coating method based on electrohydrodynamics to realize high ACU for Phosphor-converted white light-emitting diodes (LEDs). By applying an electric field around a liquid Phosphor-silicone encapsulant, a normal force is induced on the air-liquid interface, resulting in a Phosphor layer with cone morphology. Consequently, the ACU of white LEDs with the cone Phosphor layer is greatly improved compared with that of white LEDs with the traditional spherical cap Phosphor layer. The angular correlated color temperature (CCT) deviations are as low as 393 and 40 K at the average CCTs of 6500 and 5000 K, respectively.
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dip transfer Phosphor Coating on designed substrate structure for high angular color uniformity of white light emitting diodes with conventional chips
Optics Express, 2013Co-Authors: Huai Zheng, Yiman Wang, Yong Zou, Xiaobing LuoAbstract:Angular color uniformity (ACU) is one of the most important optical parameters of white lighting emitting diodes (LEDs). In this paper, we proposed a kind of Phosphor Coating method to enhance ACU of Phosphor-converted white LEDs with conventional chips by the combination of substrate structure design and Phosphor dip-transfer Coating. Through this method, compact and optimal Phosphor layer arrangements for high ACU can be realized. Optical simulations and experiments were conducted to examine its ACU performance. Compared with conventional Phosphor dispensing Coating, the present method shows very high ACU performance. Extremely small angular correlated color temperature (CCT) deviations were obtained, which are less than 200K at average CCTs ranging from 4000K to 6000K.
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Conformal Phosphor Coating for Phosphor-converted white LEDs on basis of dispensing process
2013 14th International Conference on Electronic Packaging Technology, 2013Co-Authors: Huai Zheng, Yiman Wang, Xiaobing Luo, Sheng LiuAbstract:We presented a kind of new conformal Coating Phosphor layer structure and method in this paper. In this method, we gained a compact Phosphor layer arrangement with inversed Phosphor distributions by substrate structure design and different curing method on basis of traditional dispensing process. Compared to traditional Phosphor dispensing packaging, this method can significantly enhance the angular color uniformity (ACU). The angular correlated color temperature (CCT) deviation is reduced as 149K at the average CCT of about 6000K.
Xiaobing Luo - One of the best experts on this subject based on the ideXlab platform.
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heat and fluid flow in high power led packaging and applications
Progress in Energy and Combustion Science, 2016Co-Authors: Xiaobing Luo, Sheng Liu, Run Hu, Kai WangAbstract:Abstract Light-emitting diodes (LEDs) are widely used in our daily lives. Both light and heat are generated from LED chips and then transmitted or conducted through multiple packaging materials and interfaces. Part of the transmitted light converts into heat along the light propagation; in return, the accumulation of heat leads to the degradation of light output. The accumulated heat negatively influences the reliability and longevity of LEDs, and thus thermal management is critical for LED packaging and applications. On the other hand, in LED packaging processes, many fluid flow problems exist, such as Phosphor Coating, silicone injection, chip bonding, solder reflow, etc. Among them, Phosphor Coating is the most important process which is essential for LED performance. Phosphor gel is a kind of non-Newton fluid and its Coating process is a typical fluid-flow problem. Overall, since LED packaging and applications present many heat and fluid flow problems, obtaining a full understanding of these problems enables advancements in the development of LED processes and designs. In this review, the emphasis is placed on heat generation in chips, heat flow in packages and application products, fluid flow in Phosphor Coating process, etc. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art LED packaging and application technologies.
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adding an extra condition a general method to design double freeform surface lens for led uniform illumination
Journal of Solid State Lighting, 2014Co-Authors: Xiaobing LuoAbstract:Uniform illumination is an essential optical requirement for light-emitting diode (LED) applications. In this paper, a general method was proposed to design double freeform-surface lenses for uniform illumination of LED packages. Detailed algorithms of the design method were presented, in which the inner and outer surfaces of the lenses could be designed simultaneously. This problem can’t be solved unless providing an extra condition. Two kinds of extra conditions were introduced to design the lens and validate the method. Besides uniform illumination, the present method can also realize extra functions with providing different extra conditions, like conformal Phosphor Coating and minimum Fresnel loss. The present method can be extended to design various freeform-surface lenses for LED uniform illumination provided that different conditions are added based on different application requirements.
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dip transfer Phosphor Coating on designed substrate structure for high angular color uniformity of white light emitting diodes with conventional chips
Optics Express, 2013Co-Authors: Huai Zheng, Yiman Wang, Yong Zou, Xiaobing LuoAbstract:Angular color uniformity (ACU) is one of the most important optical parameters of white lighting emitting diodes (LEDs). In this paper, we proposed a kind of Phosphor Coating method to enhance ACU of Phosphor-converted white LEDs with conventional chips by the combination of substrate structure design and Phosphor dip-transfer Coating. Through this method, compact and optimal Phosphor layer arrangements for high ACU can be realized. Optical simulations and experiments were conducted to examine its ACU performance. Compared with conventional Phosphor dispensing Coating, the present method shows very high ACU performance. Extremely small angular correlated color temperature (CCT) deviations were obtained, which are less than 200K at average CCTs ranging from 4000K to 6000K.
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Conformal Phosphor Coating for Phosphor-converted white LEDs on basis of dispensing process
2013 14th International Conference on Electronic Packaging Technology, 2013Co-Authors: Huai Zheng, Yiman Wang, Xiaobing Luo, Sheng LiuAbstract:We presented a kind of new conformal Coating Phosphor layer structure and method in this paper. In this method, we gained a compact Phosphor layer arrangement with inversed Phosphor distributions by substrate structure design and different curing method on basis of traditional dispensing process. Compared to traditional Phosphor dispensing packaging, this method can significantly enhance the angular color uniformity (ACU). The angular correlated color temperature (CCT) deviation is reduced as 149K at the average CCT of about 6000K.
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angular color uniformity improvement for Phosphor converted white light emitting diodes by optimizing remote Coating Phosphor geometry
International Conference on Electronic Packaging Technology, 2012Co-Authors: Huai Zheng, Sheng Liu, Xiaobing LuoAbstract:Angular color uniformity (ACU) of a king of popular remote Phosphor Coating LED packaging with spherical Phosphor shape with uniform thickness was invested by the Monte Carlo ray tracing method. The simulation results indicate the yellowish ring can't be avoided under uniform Phosphor thickness in angular range of 0°-180°. The optimized Phosphor geometry was proposed whose thickness gradually reduces from the center to the edge. The optimized Phosphor geometry can improve ACU 45%, compared with the initial uniform thickness Phosphor layer.
A J Steckl - One of the best experts on this subject based on the ideXlab platform.
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elixir solid state luminaire with enhanced light extraction by internal reflection
IEEE\ OSA Journal of Display Technology, 2007Co-Authors: Steven C Allen, A J StecklAbstract:A Phosphor-converted light-emitting diode (pcLED) luminaire featuring enhanced light extraction by internal reflection (ELiXIR) with efficacy of 60 lm/W producing 18 lumens of yellowish green light at 100 mA is presented. The luminaire consists of a commercial blue high power LED, a polymer hemispherical shell lens with interior Phosphor Coating, and planar aluminized reflector. High extraction efficiency of the Phosphor-converted light is achieved by separating the Phosphor from the LED and using internal reflection to steer the light away from lossy reflectors and the LED package and out of the device. At 10 and 500mA, the luminaire produces 2.1 and 66 lumens with efficacies of 80 and 37 lm/W, respectively. Technological improvements over existing commercial LEDs, such as more efficient pcLED packages or, alternatively, higher efficiency green or yellow for color mixing, will be essential to achieving 150-200 lm/W solid-state lighting. Advances in both areas are demonstrated
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elixir solid state luminaire with enhanced light extraction by internal reflection
IEEE\ OSA Journal of Display Technology, 2007Co-Authors: Steven C Allen, A J StecklAbstract:A Phosphor-converted light-emitting diode (pcLED) luminaire featuring enhanced light extraction by internal reflection (ELiXIR) with efficacy of 60 lm/W producing 18 lumens of yellowish green light at 100 mA is presented. The luminaire consists of a commercial blue high power LED, a polymer hemispherical shell lens with interior Phosphor Coating, and planar aluminized reflector. High extraction efficiency of the Phosphor-converted light is achieved by separating the Phosphor from the LED and using internal reflection to steer the light away from lossy reflectors and the LED package and out of the device. At 10 and 500mA, the luminaire produces 2.1 and 66 lumens with efficacies of 80 and 37 lm/W, respectively. Technological improvements over existing commercial LEDs, such as more efficient pcLED packages or, alternatively, higher efficiency green or yellow for color mixing, will be essential to achieving 150-200 lm/W solid-state lighting. Advances in both areas are demonstrated
Haibo Rao - One of the best experts on this subject based on the ideXlab platform.
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self adaptive conformal remote Phosphor Coating of Phosphor converted white light emitting diodes
IEEE\ OSA Journal of Display Technology, 2016Co-Authors: Haibo Rao, Wei Zhang, Chunyu Zhou, Qi Zhang, Kun ZhangAbstract:Angular color uniformity (ACU) and luminous efficiency are the most important optical parameters of white light emitting diodes (WLEDs). In this paper, we proposed conformal–remote Phosphor Coating structure, including conformal silicone layer and Phosphor layer, to improve ACU and luminous efficiency of Phosphor-converted WLEDs (pc-WLEDs). Due to the effect of conformal silicone layer, the extraction efficiency of blue light increases and the thermal effect of Phosphor layer decreases, which improve the luminous efficiency. In addition, the structure composed by conformal silicone layer and self-adaptive Phosphor layer can better match spatial intensity distribution of the chip emitting light. The experimental results have verified that the conformal–remote Phosphor Coating structure shows very high ACU performance, compared with the conventional Phosphor Coating and self-adaptive remote Phosphor Coating structure. Besides, for the self-adaptive conformal–remote Phosphor Coating, the thickness of silicone layer absolutely had no effect on the luminous efficiency and ACU.
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an improved slurry method of self adaptive Phosphor Coating for white pc led packaging
IEEE\ OSA Journal of Display Technology, 2013Co-Authors: Haibo Rao, Wei Wang, Xianlong Wan, Linsong Zhou, Junyuan Liao, Da Zhou, Qiaolin Lei, Xuemei WangAbstract:For illumination-grade applications, the spatial homogeneity of the white light emitted is an important issue which is directly associated with the geometry and the composition of the color conversion layer in Phosphor-converted LEDs. In order to create a Phosphor Coating of high quality surrounding the LED chip surface, an improved slurry method with self-exposure technique was applied and investigated. The conformal Phosphor layer of self-adaptability to angular intensity distribution of LED emitting light was realized. Plasma treatment was introduced to improve the aging performance of white LEDs with this advanced slurry method. The effect of the self-adaptive Coating on the improvement of angular color uniformity of white LEDs was measured and discussed.
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self adaptive Phosphor Coating technology for white led packaging
Frontiers of Optoelectronics, 2012Co-Authors: Haibo Rao, Wei Wang, Xianlong Wan, Linsong Zhou, Kun Ding, Jirong Song, Likun Xie, Junyuan LiaoAbstract:Phosphor-converted light-emitting diodes (pc-LEDs), which employ blue LEDs with yellow Phosphors to generate white light illumination, is a widely used solidstate lighting source. In order to conduct a Phosphor layer Coating with high quality on LED chip, a self-adaptive Coating technology is introduced in this paper. A slurry Coating technique combined with self-exposure method is applied and developed to demonstrate the benefits of self-adaptive Coating layer. For self-exposure, the slurry Coating is exposed to the blue emission of LED itself other than to ultraviolet (UV) light outside to make photoresist crosslinking. Results of measurement indicate that white LEDs with self-adaptive Coating have shown self-adaptability to the angular distribution of intensity of blue light and performed higher spatial color uniformity than those with conventional Coating and other conformal Coating.
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Phosphor Coating technique with slurry method in application of white led
Proceedings of SPIE the International Society for Optical Engineering, 2007Co-Authors: Bin Hou, Haibo RaoAbstract:White light was realized through combining a cerium-doped yttrium aluminum garnet (YAG:Ce 3+ ) Phosphor with a gallium nitride (GaN)-based blue LED. In order to coat the high quality yellow Phosphor layer on a GaN chip, the slurry Coating technique was focused on because of the speed and Coating uniformity. The slurry method is based on a Phosphor suspension in a water-soluble photoresist, which is consisted of polyvinyl alcohol (PVA) and ammonium dichromate (ADC). And self-exposure of LED chip was employed as an optimized exposing way to make the photoresist crosslinking. The properties of the Phosphor layer in terms of profile, light intensity and uniformity and spectrum were investigated. To improve the qualities of Phosphor layer some additives were introduced such as polyvinyl acetate (PVAc) for improving adhesion strength, dispersants and defoamer for uniformity. The thickness of Phosphor layer was controlled by altering the time of exposure under UV or blue light. The Phosphor pattern with clear margins according to the mask and conformal shape were achieved in different substrates either glasses or LED chips. The white light output of high intensity and good uniformity due to the optimized thickness of Phosphor layer were achieved. A defect of photoresist is that the ADC would absorb parts of blue light emitted from LED chip and quench light output, especially in the high concentration, some approaches can be employed to diminish and avoid this defect, such as reduce the ADC's concentration, and find new photosensitizer to replace the ADC.