The degradation mechanism of high power InGaN/GaN blue light emitting diodes （LEDs） is investigated in this paper. The LED samples were stressed at room temperature under 350-mA injection current for about 400 h. Th...The degradation mechanism of high power InGaN/GaN blue light emitting diodes （LEDs） is investigated in this paper. The LED samples were stressed at room temperature under 350-mA injection current for about 400 h. The light output power of the LEDs decreased by 35% during the first 100 h and then remained almost unchanged, and the reverse current at-5 V increased from 10^-9 A to 10^-7 A during the aging process. The power law, whose meaning was re-illustrated by the improved rate equation, was used to analyze the light output power-injection current （L-I） curves. The analysis results indicate that nonradiative recombination, Auger recombination, and the third-order term of carriers overflow increase during the aging process, all of which may be important reasons for the degradation of LEDs. Besides, simulating L-I curves with the improved rate equation reveal that higher-than-third-order terms of carriers overflow may not be the main degradation mechanism, because they change slightly when the LED is stressed.展开更多
The well crystalline YAG：Ce^3＋ phosphor was synthesized by sold-state method, and the temperature dependence of excitation and emission spectra of YAG：Ce^3＋ phosphor were investigated in the temperature range from...The well crystalline YAG：Ce^3＋ phosphor was synthesized by sold-state method, and the temperature dependence of excitation and emission spectra of YAG：Ce^3＋ phosphor were investigated in the temperature range from room temperature to 573 K. With temperature increasing, it was noted that the emission intensity of as-repared phosphors decreased considerably more rapidly when pumped by 460 nm than by 340 nm. The temperature-intensity curves under different excitation wavelengths were obtained using an Arrhenius function, and the corresponding activation energies were also obtained respectively. Thus, the experimental phenomenon was discussed in terms of nonradiative decay rate. The effects of as-prepared phosphors on the performance of the white LED with changing temperature were also studied.展开更多
This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours＇ current stress, the reverse leakage current of this l...This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours＇ current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode.展开更多
The origin of anomalous luminescence efficiency enhancement of short-term aged GaN-based blue light-emitting diodes was studied. We found that the intensity of the electroluminescence and photoluminescence spectra wer...The origin of anomalous luminescence efficiency enhancement of short-term aged GaN-based blue light-emitting diodes was studied. We found that the intensity of the electroluminescence and photoluminescence spectra were both increased in the very beginning period of aging. With the help of a rate-equation model, we concluded that this kind of luminescence efficiency enhancement is a joint effect of the defect reduction in active layers and the changes out of active layers, for example the Mg acceptor annealing.展开更多
为了动态控制用于植物生长的人工光源，该文提出一种以光子数作为评价标准，使红蓝光比例连续可调的LED植物生长光源的配光方法。综合考虑红、蓝2种波段光源及其他光谱的作用，该文采用白光LED与红光LED 组合配比，以正向电流下 LED 的...为了动态控制用于植物生长的人工光源，该文提出一种以光子数作为评价标准，使红蓝光比例连续可调的LED植物生长光源的配光方法。综合考虑红、蓝2种波段光源及其他光谱的作用，该文采用白光LED与红光LED 组合配比，以正向电流下 LED 的光谱密度数据作为计算基础，提出配光设计算法，实现红蓝成分有效光子数维持一定的要求下，红光与蓝光光子数比在指定区间（4：1～9：1之间）连续可调，从而满足植物不同生长状态对光质成分的需要。展开更多
Studies on the use of gas phase applications of light emitting diodes(LEDs) in photocatalysis are scarce although their photocatalytic decomposition kinetics of environmental pollutants are likely different from those...Studies on the use of gas phase applications of light emitting diodes(LEDs) in photocatalysis are scarce although their photocatalytic decomposition kinetics of environmental pollutants are likely different from those in aqueous solutions.The present study evaluated the use of chips of visible light LEDs to irradiate nitrogen doped titania(N-TiO2) prepared by hydrolysis to decompose gaseous benzene,toluene,ethyl benzene,m-xylene,p-xylene,and o-xylene.Photocatalysts calcined at different temperatures were characterized by various analytical instruments.The degradation efficiency of benzene was close to zero for all conditions.For the other compounds,a conventional 8 W daylight lamp/N-TiO2 unit gave a higher photocatalytic degradation efficiency as compared with that of visible-LED/N-TiO2 units.However,the ratios of degradation efficiency to electric power consumption were higher for the photocatalytic units that used two types of visible-LED lamps(blue and white LEDs).The highest degradation efficiency was observed with the use of a calcination temperature of 350 oC.The average degradation efficiencies for toluene,ethyl benzene,m-xylene,p-xylene,and o-xylene were 35%,68%,94%,and 93%,respectively.The use of blue-and white-LEDs,high light intensity,and low initial concentrations gave high photocatalytic activities for the photocatalytic units using visible-LEDs.The morphological and optical properties of the photocatalysts were correlated to explain the dependence of photocatalytic activity on calcination temperature.The results suggest that visible-LEDs are energy efficient light source for photocatalytic gas phase applications,but the activity depends on the operational conditions.展开更多
Light emitting diodes(LEDs) are gaining recognition as a convenient and energy-efficient light source for photocatalytic application. This review focuses on recent progress in the research and development of the degra...Light emitting diodes(LEDs) are gaining recognition as a convenient and energy-efficient light source for photocatalytic application. This review focuses on recent progress in the research and development of the degradation of dyes in water under LED light irradiation and provides a brief overview of photocatalysis, details of the LEDs commonly employed, a discussion of the advantages of LEDs over traditional ultraviolet sources and their application to photocatalytic dye degradation. We also discuss the experimental conditions used, the reported mechanisms of dye degradation and the various photocatalytic reactor designs and pay attention to the different types of LEDs used, and their power consumption. Based on a literature survey, the feasibility, benefits, limitations, and future prospects of LEDs for use in photocatalytic dye degradation are discussed in detail.展开更多
基金Project supported by the National Basic Research Program of China(Grant Nos.2011CB301905 and 2013CB328705)the National High Technology Research and Development Program of China(Grant No.2009AA03A198)the National Natural Science Foundation of China(Grant Nos.61076012 and 61376012)
文摘The degradation mechanism of high power InGaN/GaN blue light emitting diodes （LEDs） is investigated in this paper. The LED samples were stressed at room temperature under 350-mA injection current for about 400 h. The light output power of the LEDs decreased by 35% during the first 100 h and then remained almost unchanged, and the reverse current at-5 V increased from 10^-9 A to 10^-7 A during the aging process. The power law, whose meaning was re-illustrated by the improved rate equation, was used to analyze the light output power-injection current （L-I） curves. The analysis results indicate that nonradiative recombination, Auger recombination, and the third-order term of carriers overflow increase during the aging process, all of which may be important reasons for the degradation of LEDs. Besides, simulating L-I curves with the improved rate equation reveal that higher-than-third-order terms of carriers overflow may not be the main degradation mechanism, because they change slightly when the LED is stressed.
基金the Key Technologies R&D Program of Shandong Province (2006gg2201014)Tianjin Natural Science Foundation (07JCYBJC06400)Tianjin Education Committee Science and Technology Development Foundation
文摘The well crystalline YAG：Ce^3＋ phosphor was synthesized by sold-state method, and the temperature dependence of excitation and emission spectra of YAG：Ce^3＋ phosphor were investigated in the temperature range from room temperature to 573 K. With temperature increasing, it was noted that the emission intensity of as-repared phosphors decreased considerably more rapidly when pumped by 460 nm than by 340 nm. The temperature-intensity curves under different excitation wavelengths were obtained using an Arrhenius function, and the corresponding activation energies were also obtained respectively. Thus, the experimental phenomenon was discussed in terms of nonradiative decay rate. The effects of as-prepared phosphors on the performance of the white LED with changing temperature were also studied.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60990314, 60976009, 60577146, U0834001)the National Key Basic Research and Development Project (973) of China (Grant No. 2007CB307004)
文摘This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours＇ current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode.
文摘The origin of anomalous luminescence efficiency enhancement of short-term aged GaN-based blue light-emitting diodes was studied. We found that the intensity of the electroluminescence and photoluminescence spectra were both increased in the very beginning period of aging. With the help of a rate-equation model, we concluded that this kind of luminescence efficiency enhancement is a joint effect of the defect reduction in active layers and the changes out of active layers, for example the Mg acceptor annealing.
文摘为了动态控制用于植物生长的人工光源，该文提出一种以光子数作为评价标准，使红蓝光比例连续可调的LED植物生长光源的配光方法。综合考虑红、蓝2种波段光源及其他光谱的作用，该文采用白光LED与红光LED 组合配比，以正向电流下 LED 的光谱密度数据作为计算基础，提出配光设计算法，实现红蓝成分有效光子数维持一定的要求下，红光与蓝光光子数比在指定区间（4：1～9：1之间）连续可调，从而满足植物不同生长状态对光质成分的需要。
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2011-0027916)
文摘Studies on the use of gas phase applications of light emitting diodes(LEDs) in photocatalysis are scarce although their photocatalytic decomposition kinetics of environmental pollutants are likely different from those in aqueous solutions.The present study evaluated the use of chips of visible light LEDs to irradiate nitrogen doped titania(N-TiO2) prepared by hydrolysis to decompose gaseous benzene,toluene,ethyl benzene,m-xylene,p-xylene,and o-xylene.Photocatalysts calcined at different temperatures were characterized by various analytical instruments.The degradation efficiency of benzene was close to zero for all conditions.For the other compounds,a conventional 8 W daylight lamp/N-TiO2 unit gave a higher photocatalytic degradation efficiency as compared with that of visible-LED/N-TiO2 units.However,the ratios of degradation efficiency to electric power consumption were higher for the photocatalytic units that used two types of visible-LED lamps(blue and white LEDs).The highest degradation efficiency was observed with the use of a calcination temperature of 350 oC.The average degradation efficiencies for toluene,ethyl benzene,m-xylene,p-xylene,and o-xylene were 35%,68%,94%,and 93%,respectively.The use of blue-and white-LEDs,high light intensity,and low initial concentrations gave high photocatalytic activities for the photocatalytic units using visible-LEDs.The morphological and optical properties of the photocatalysts were correlated to explain the dependence of photocatalytic activity on calcination temperature.The results suggest that visible-LEDs are energy efficient light source for photocatalytic gas phase applications,but the activity depends on the operational conditions.
基金support of the MSIP (Ministry of Science, ICT & Future Planning, Project No. 132S-5-3-0610)the National Research Foundation of Korea (NRF) funded by the Korean Government (MEST, No. 2011-0027916)
文摘Light emitting diodes(LEDs) are gaining recognition as a convenient and energy-efficient light source for photocatalytic application. This review focuses on recent progress in the research and development of the degradation of dyes in water under LED light irradiation and provides a brief overview of photocatalysis, details of the LEDs commonly employed, a discussion of the advantages of LEDs over traditional ultraviolet sources and their application to photocatalytic dye degradation. We also discuss the experimental conditions used, the reported mechanisms of dye degradation and the various photocatalytic reactor designs and pay attention to the different types of LEDs used, and their power consumption. Based on a literature survey, the feasibility, benefits, limitations, and future prospects of LEDs for use in photocatalytic dye degradation are discussed in detail.
