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White LED (white + lead)
Selected AbstractsA Potential Red-Emitting Phosphor BaGd2(MoO4)4:Eu3+ for Near-UV White LEDJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Chongfeng Guo Red-emitting phosphor BaGd2,xEux(MoO4)4 has been successfully synthesized by a simple sol,gel method. The process of phosphor formation is characterized by thermogravimetric-differential thermal analysis and X-ray diffraction. Field-emission scanning electronic microscopy is used to characterize the size and the shape of the phosphor particles. Photo-luminescent property of the phosphor is also performed at the room temperature. The effects of firing temperature and Eu3+ activator concentration on the photoluminescence (PL) properties are elaborated in detail. PL characterization reveals that the sample with the firing temperature at 800°C and the concentration of Eu3+ at 0.7 shows the most intense emission, and its intensity is about three times stronger than that of phosphor prepared by solid-state method with the same composition and firing temperature. The new red-emitting phosphor shows an intense absorption at 396 nm, which matches well with commercial near-UV light-emitting diode (LED) chips, therefore, it is a good candidate of red phosphor used for near-UV white LEDs. [source] Recent Progress in GaN-Based Light-Emitting DiodesADVANCED MATERIALS, Issue 45 2009Haiqiang Jia Abstract In the last few years the GaN-based white light-emitting diode (LED) has been remarkable as a commercially available solid-state light source. To increase the luminescence power, we studied GaN LED epitaxial materials. First, a special maskless V-grooved c -plane sapphire was fabricated, a GaN lateral epitaxial overgrowth method on this substrate was developed, and consequently GaN films are obtained with low dislocation densities and an increased light-emitting efficiency (because of the enhanced reflection from the V-grooved plane). Furthermore, anomalous tunneling-assisted carrier transfer in an asymmetrically coupled InGaN/GaN quantum well structure was studied. A new quantum well structure using this effect is designed to enhance the luminescent efficiency of the LED to ,72%. Finally, a single-chip phosphor-free white LED is fabricated, a stable white light is emitted for currents from 20 to 60,mA, which makes the LED chip suitable for lighting applications. [source] A White LED Driver Using a Buck,Boost ConverterIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 5 2010Kei Eguchi Member Abstract For mobile backlighting applications, a white LED (WLED) driver using a buck,boost converter is proposed in this letter. Unlike conventional converters using boost converters, 2×/1.5× charge pumps, and so on, the proposed converter offers the negative stepped-down voltage to drive the LED's cathode only when the input voltage is insufficient to drive a 1× transfer mode. Furthermore, unlike the LED backlight using charge pumps, the proposed converter can adjust the output voltage by controlling the duty factor of the clock pulse. Thus, the proposed converter can realize high power efficiency. The validity of the proposed converter is confirmed by simulations and experiments. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Fluorescence spectra of Pr3+ ions in phosphate materials calculated by the DVME methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2009Y. Kowada Abstract Recently, fluorescence spectra of rare-earth ions in oxide materials are very attractive for the applications of the optical amplification in optical fiber communications, white LED, etc. However, it has been difficult to calculate the fluorescence spectra of rare-earth ions by the first principle method. In this study, we used the relativistic discrete-variational multielectron (DVME) method, which is a configuration-interaction (CI) calculation program using the molecular orbitals obtained by the relativistic DV-X, method. We applied this method for the calculation of the fluorescence spectrum of the Pr3+ ions in phosphate materials. The transition probability of the fluorescence was calculated in the same manner of the absorption. The obtained theoretical fluorescence spectrum was in good agreement with the experimental one, though the intensity of each peak was deeply dependent on the configuration of the surrounding structural units. The results suggested that the DVME method was useful for the calculation of not only absorption but also fluorescence spectra of rare-earth ions in oxide materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Visible light wireless transmission based on optical access network using white light-emitting diode and electroabsorption transceiverMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2010Yong-Hwan Son Abstract We propose the visible light communication (VLC) system based on optical access network using light-emitting diode (LED) and electroabsorption transceiver (EAT). The EAT based on electroabsorption modulator is used as an optical network unit in order to be connected with VLC link based on white LED and photodiode (PD). The proposed architecture is demonstrated experimentally, and its performance is verified through the experimental investigation of quality factor and eye pattern of 5 Mbps baseband data. The variation of performance is shown depending on both the existence of the ambient light and the distance between the LED array and PD. A total of 5 Mbps downlink and uplink transmission is verified through 23.2-km single-mode fiber and wireless channel experimentally. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:790,793, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25045 [source] Successful fabrication of white light emitting diodes by using extremely high external quantum efficiency blue chipsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008Yukio Narukawa Abstract We fabricated three types of high luminous efficiency white light emitting diodes (LEDs). The first is the white LED, which had a high luminous efficiency (,L) of 161 lm/W with the high luminous flux (,v) of 9.89 lm at a forwardbias current of 20 mA. The blue LED had a high power (,e) of 42.2 mW and high external quantum efficiency (,ex) of 75.5%. The second is the high luminous efficiency white LED with a low voltage (Vf) of 2.80 V, which was almost equal to the theoretical limit. ,L and wall-plug efficiency (WPE) is 169 lm/W and 50.8%, respectively, at 20 mA. They are approximately twice higher than those of a tri-phosphor fluorescent lamp (90 lm/W and 25%). The third is the high power white LED fabricated from the high power blue LED with high ,e of 651 mW at 350 mA. ,v, ,L and WPE of the high power white LED are 145 lm, 134 lm/W and 39.6% at 350 mA, respectively. Moreover, at 1 A, ,v and ,L were 361 lm and 97 lm/W, respectively. Thus ,v is equivalent to that of a 30 W-class incandescent lamp. And, ,L is slightly higher than that of a tri-phosphor fluorescent lamp. Moreover, we fabricated the high power near ultra-violet, bluish-green and green LEDs, whose ,e at 350 mA were 675 mA, 325 mW, and 236 mW, respectively. ,v of the green LED was 128 lm at 350 mA. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Recent progress of high efficiency white LEDsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007Yukio Narukawa Abstract We fabricated three types of white light emitting diodes (LEDs). The first is the white LED, which has a high general color rendering index (Ra) of 97 and CRI-No. 9 of 96. The CRI-No. 9 denotes the color reproduction in the red region. These values are higher than those of a tri-phosphor fluorescent lamp (Ra = 85 and CRI-No. 9 = 8). The second is the high efficiency white LED fabricated from the small-size high efficiency blue LED chip. The output power (Po), the external quantum efficiency (,ex) and wall-plug efficiency (WPE) of the small-size blue LED were 35.0 mW, 63.3% and 56.3%, respectively, at a forward-bias current of 20 mA. The luminous flux (,), luminous efficiency (,L) and WPE of the second white LED are 8.6 lm, 138 lm/W and 41.7%, respectively. The luminous efficiency is 1.5 times greater than that of a tri-phosphor fluorescent lamp (90 lm/W). The third is the high power white LED fabricated from the larger-size blue LED chip. Po, ,ex and W.P.E. are 458 mW, 47.2% and 39.7%, respectively, at 350 mA. ,, ,L and WPE of the third white LED are 106 lm, 91.7 lm/W and 27.7% at 350 mA, respectively. Moreover, , of 247 lm and 402 lm at 1 A and 2 A are obtained, respectively. , at 2 A is equivalent to the total flux of a 30 W incandescent lamp. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||