Properties of transparent Ce:YAG ceramic phosphors for white LED
TL;DR: In this article, a transparent Ce:YAG ceramic phosphors were synthesized from the oxide powder which was produced by co-preparation method of the hydroxides.
About: This article is published in Optical Materials.The article was published on 2011-03-01. It has received 458 citations till now. The article focuses on the topics: Chromaticity & Ceramic.
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TL;DR: In this article, an innovative luminescent material, transparent Ce:YAG phosphor-in-glass (PiG) inorganic color converter, is developed to replace the conventional resin/silicone-based phosphor converter for the construction of high-power WLED.
Abstract: Currently, the major commercial white light-emitting diode (WLED) is the phosphor-converted LED made of the InGaN blue-emitting chip and the Ce3+:Y3Al5O12 (Ce:YAG) yellow phosphor dispersed in organic epoxy resin or silicone. However, the organic binder in high-power WLED may age easily and turn yellow due to the accumulated heat emitted from the chip, which adversely affects the WLED properties such as luminous efficacy and color coordination, and therefore reduces its long-term reliability as well as lifetime. Herein, an innovative luminescent material: transparent Ce:YAG phosphor-in-glass (PiG) inorganic color converter, is developed to replace the conventional resin/silicone-based phosphor converter for the construction of high-power WLED. The PiG-based WLED exhibits not only excellent heat-resistance and humidity-resistance characteristics, but also superior optical performances with a luminous efficacy of 124 lm/W, a correlated color temperature of 6674 K and a color rendering index of 70. This easy fabrication, low-cost and long-lifetime WLED is expected to be a new-generation indoor/outdoor high-power lighting source.
480 citations
TL;DR: Transparent polycrystalline ceramics have found various applications, such as laser hosts, infrared windows/domes, lamp envelopes and transparent armors, due mainly to their processing flexibility in fabricating items with large sizes and complex shapes and more importantly costeffectiveness as mentioned in this paper.
453 citations
TL;DR: In this article, two classes of down conversion materials: phosphors and semiconductor quantum dots (QDs) are discussed and the challenges in the development of down converters that satisfy all these criteria.
Abstract: The wavelength down conversion approach to solid-state lighting (SSL) uses down conversion materials to produce visible light when excited by near-UV or blue emission from InGaN LEDs. This review discusses two classes of down conversion materials: phosphors and semiconductor quantum dots (QDs). Strong absorption of the excitation wavelength; high luminous efficacy of radiation, which enables white light with a high color rendering index and a low correlated color temperature; high quantum efficiency; and thermal and chemical stability are some of the criteria for down converters used in SSL. This review addresses the challenges in the development of down converters that satisfy all these criteria. We will discuss the advantages and disadvantages of several phosphor compositions for blue and near-UV LEDs. The use of core/shell architectures to improve the photoluminescence and moisture resistance of phosphors is presented. QDs are another class of down conversion materials for near-UV and blue LEDs. Strategies to improve the photostability and reduce the thermal quenching of QDs include strain-graded core/shell interfaces and alloying. We discuss Cd-containing II–VI QDs, and Cd-free III–V and I–III–VI QDs and their potential for SSL applications. Finally, a description of different methods to integrate the phosphors and QDs with the LED is given.
344 citations
TL;DR: In this paper, the authors investigated the possibility of thermal ionization as a cause of the quenching process by measuring thermoluminescence (TL) excitation spectra at various temperatures.
Abstract: Y3Al5O12(YAG):Ce3+ is the most widely applied phosphor in white LEDs (w-LEDs) because of strong blue absorption and efficient yellow luminescence combined with a high stability and thermal quenching temperature, required for the extreme operating conditions in high-power w-LEDs. The high luminescence quenching temperature (∼600 K) has been well established, but surprisingly, the mechanism for temperature quenching has not been elucidated yet. In this report we investigate the possibility of thermal ionization as a cause of this quenching process by measuring thermoluminescence (TL) excitation spectra at various temperatures. In the TL excitation (TLE) spectrum at room temperature there is no Ce3+:5d1 band (the lowest excited 5d level). However, in the TLE spectrum at 573 K, which corresponds to the onset temperature of luminescence quenching, a TLE band due to the Ce3+:5d1 excitation was observed at around 450 nm. On the basis of our observations we conclude that the luminescence quenching of YAG:Ce3+ at ...
270 citations
References
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Book•
21 Mar 1997
TL;DR: The physics of gallium nitrides and related compounds GaN growth p-Type GaN obtained by electron beam irradiation n-Type GAN p-type GaN InGaN Zn and Si co-doped GaN double-heterostructure blue and blue green LEDs inGaN single-quantum-well structure LEDs room-temperature pulsed operation of laser diodes emission mechanisms of LEDs and LDs room temperature CW operation of InGAN MQW LDs latest results as discussed by the authors.
Abstract: Physics of gallium nitrides and related compounds GaN growth p-Type GaN obtained by electron beam irradiation n-Type GaN p-Type GaN InGaN Zn and Si co-doped InGaN/AlGaN double-heterostructure blue and blue-green LEDs inGaN single-quantum-well structure LEDs room-temperature pulsed operation of laser diodes emission mechanisms of LEDs and LDs room temperature CW operation of InGaN MQW LDs latest results - lasers with self-organized InGaN quantum dots
3,805 citations
TL;DR: Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders (>99.99 wt% purity) as mentioned in this paper.
Abstract: Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders (>99.99 wt% purity). The average grain size and relative density of the 1.1 at.% ND:YAG ceramics obtained were about 50 {micro}m and 99.98%, respectively. An oscillation experiment was performed on a cw laser by the diode laser excitation system using the fabricated ceramics. The experimental results indicated an oscillation threshold and a slope efficiency of 309 mW and 28%, respectively. These values were equivalent or superior to those of the 0.9 at.% ND:YAG single crystal fabricated by the Czochralski method.
1,098 citations
TL;DR: In this paper, a mixture of aluminum and yttrium nitrates was co-precipitated using ammonium hydrogen carbonate as precipitants, and the resulting YAG powders showed good dispersity and excellent sinterability.
Abstract: YAG precursors were co-precipitated from a mixed solution of aluminum and yttrium nitrates using ammonia water and ammonium hydrogen carbonate as precipitants, respectively. Phase evolution of the precursors during calcination and sinterability of the resultant YAG powders were compared between the two methods. The use of ammonia water produced a hydroxide precursor with an approximate composition of Al(OH)3·0.3[Y2(OH)5(NO3)·3H2O] which transformed to pure YAG at about 1000°C via YAlO3 phase. Severe agglomeration caused poor sinterability of the resultant YAG powders. The use of ammonium hydrogen carbonate produced a carbonate precursor with an approximate composition of NH4AlY0.6(CO3)1.9(OH)2·0.8H2O. The precursor directly converted to pure YAG at about 900°C. The precursor was loosely agglomerated and the resultant YAG powders showed good dispersity and excellent sinterability. For the same calcination temperature of 1100°C, YAG powders from the hydroxide precursor and the carbonate precursor densified to ∼81.2 and ∼99.8% of the theoretical, respectively, by vacuum sintering at 1500°C for 2 h.
318 citations
Book•
25 Apr 2002
TL;DR: The Nature of Color, Light Sources and Illuminants, and Trichromatic Theory: Foundations of Color Specification System and General References Index.
Abstract: Chapter 1 The Nature of Color Chapter 2 Light Sources and Illuminants Chapter 3 Trichromatic Theory Chapter 4 CIE Color Specification System Chapter 5 Uniform Color Systems Chapter 6 Color Mixtures and Colorants Chapter 7 Color Measurements Chapter 8 The Human Eye General References Index
288 citations
TL;DR: In this article, a new technology was achieved by combining blue InGaN LED and YAG phosphor, which achieved the efficacy of 10 lm/W and color temperature of 3000K-10000K.
Abstract: High bright and white light emitting diodes(LEDs) were fabricated. White LEDs are the fourth color made for commercial use following blue, green and red. White LEDs typically have the efficacy of 10 lm/W and the color temperature of 3000K-10000K. This new technology was achieved by combining blue InGaN LED and YAG phosphor. Compared with incandescent lamps, advantages such as wide color variation, life beyond 10000hr, no burn-out, reduced sensitivity to variation and little heat generation are expected.
257 citations