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White Light Emitting Diodes (white + light_emitting_diode)

Distribution by Scientific Domains
Physics and Astronomy71%

Selected Abstracts

A Novel Narrow Band Red-Emitting Phosphor for White Light Emitting Diodes

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2009
Sivakumar Vaidyanathan
Research on down conversion phosphor materials is the key for the development of solid-state lighting (SSL). Especially finding alternative red phosphor for white light emitting diodes (LEDs) based on blue or near ultraviolet (NUV) LEDs is important research task. In this view, we have synthesized a series of Eu3+ -substituted La2W2,xMoxO9 (x=0,2, in step of 0.3) red phosphor and characterized by X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from triclinic to cubic structure for x>0.2. All the compositions show broad charge transfer (CT) band due to CT from oxygen to tungsten/molybdenum and red emission due to Eu3+ ions. Select compositions show high red emission intensity compared with the commercial red phosphor under NUV/blue ray excitation. Hence, this candidate can be a possible red phosphor for white LEDs. [source]

Preparation and luminescent properties of Eu2+ -activated glass ceramic phosphor precipitated with ,-Ca2SiO4 and Ca3Si2O7

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009
Takayuki Nakanishi
Abstract Eu2+: calcium silicate glass ceramics (GC) containing ,-Ca2SiO4 and Ca3Si2O7 crystal phosphors were fabricated by cerammization process from a GC that were prepared by a novel GC preparation; frozen sorbet method. The GC obtained (as-made GC) consisted of glass and spherical ,-Ca2SiO4 crystal phases with size of about 20,40 ,m. After post-ceramization, Ca3Si2O7 crystals were also precipitated. Judging from the cathodoluminescence (CL) mapping images, two emission bands peaked at 515 nm and 600 nm were observed from different parts in the GC. The observed photoluminescence (PL) have two broad emission bands at 515 nm from Eu2+: ,-Ca2SiO4 and at 600 nm from Eu2+:Ca3Si2O7. With increasing heat-treatment temperature, the color coordinates shifted from green range to center region, which corresponds to pure white in the CIE chromaticity diagram. Eu2+ doped calcium silicate GC containing ,-Ca2SiO4 and Ca3Si2O7 are suitable phosphor as the use of phosphor converting white light emitting diode (pc-wLED) with high color rendering. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A Novel Narrow Band Red-Emitting Phosphor for White Light Emitting Diodes

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2009
Sivakumar Vaidyanathan
Research on down conversion phosphor materials is the key for the development of solid-state lighting (SSL). Especially finding alternative red phosphor for white light emitting diodes (LEDs) based on blue or near ultraviolet (NUV) LEDs is important research task. In this view, we have synthesized a series of Eu3+ -substituted La2W2,xMoxO9 (x=0,2, in step of 0.3) red phosphor and characterized by X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from triclinic to cubic structure for x>0.2. All the compositions show broad charge transfer (CT) band due to CT from oxygen to tungsten/molybdenum and red emission due to Eu3+ ions. Select compositions show high red emission intensity compared with the commercial red phosphor under NUV/blue ray excitation. Hence, this candidate can be a possible red phosphor for white LEDs. [source]

Successful fabrication of white light emitting diodes by using extremely high external quantum efficiency blue chips

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008
Yukio 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 LEDs

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007
Yukio 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]

Photon-assisted tunneling in GaN nanowire white light emitting diodes

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
P.-C. Yeh
Abstract We reported intensive greenish white light electroluminescence, accompanied with 364 nm bandedge emission from GaN nanowires/p-GaN light emitting diode operated in the high-field forward bias regime. Strong bandedge emission, dominant over visible luminescence from bandgap state transitions, was also observed in the reverse bias regime. These observations were ascribed to a formation of n+ -p tunnel junction in the high-field regime and emission mechanism due to photon-assisted tunneling process. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]