(12) United States Patent
`US 7,071,616 B2
`(10) Patent N0.:
`Shimizu et al.
`
`(45) Date of Patent: Jul. 4, 2006
`
`USOO7071616B2
`
`(54) LIGHT EMITTING DEVICE WITH BLUE
`LIGHT LED AND PHOSPHOR
`COMPONENTS
`
`(56)
`
`References Cited
`U. S. PATENT DOCUMENTS
`
`(75)
`
`Inventors: Yoshinori Shimizu, Anan (JP); Kensho
`Sakano, Anan (JP); Yasunobu
`Noguchi, Anan (JP); Toshio
`Moriguchi, Anan (JP); Eiji Nakanishi,
`Anan (JP)
`
`(73) Assignee:
`
`Nichia Kagaku Kogyo Kabushiki
`Kaisha, Anan (JP)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 123 days.
`
`(21)
`
`(22)
`
`(65)
`
`Appl. No.:
`Filed:
`
`10/609,503
`
`Jul. 1, 2003
`Prior Publication Data
`
`US 2004/0004437 A1 Jan. 8, 2004
`
`Related US. Application Data
`
`(62) Division of application No. 09/458,024, filed on Dec. 10,
`1999, now Pat. No. 6,614,179, which is a division of
`application No. 09/300,315, filed on Apr. 28, 1999, now Pat.
`No. 6,069,440, which is a division of application No.
`08/902,725, filed on Jul. 29, 1997, now Pat. No. 5,998,925.
`
`(30)
`Jul. 29,
`Sep. 17,
`Sep. 18,
`Dec. 27,
`Mar. 31,
`
`(JP)
`(JP)
`(JP)
`(JP)
`(JP)
`
`Foreign Application Priority Data
`1996
`1996
`1996
`1996
`1997
`
`........................................ P 08-198585
`..... P08-244339
`..... P08-245381
`..... P08-359004
`........................................ P 09-081010
`
`
`
`(51)
`
`Int. Cl.
`H05B 33/00
`
`(2006.01)
`
`(52)
`(58)
`
`........................................ 313/506; 313/512
`US. Cl.
`Field of Classification Search ................. 313/504,
`313/506, 512, 486, 489, 498, 501, 502, 503;
`428/690
`
`3,510,732 A
`3,652,956 A
`3,691,482 A
`
`5/ 1970 Amans
`3/ 1972 Pinnow et a1.
`9/1972 Pinnow et a1.
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`DE
`DE
`EP
`
`3804293 A1
`9013615 U
`0 209 942 A1
`
`8/1989
`1/1991
`1/1987
`
`(Continued)
`OTHER PUBLICATIONS
`
`“White LED lamp: Efficient light£mitting; Manufacture
`cost half”, Nikkei Sangyo Shimbun, Sep. 13, 1996, Pub-
`lished by Nihon Keizai Shimbunsha.
`Shuji Nakamura,
`“InGaN/AlGaN blueilight£mitting
`diodes”, J. Vac. Sci. Technol. A 13 (3), May/Jun. 1995, pp.
`7057710.
`
`(Continued)
`
`Primary ExamineriJoseph Williams
`(74) Attorney, Agent, or FirmiBirch, Stewart, Kolasch &
`Birch, LLP
`
`(57)
`
`ABSTRACT
`
`A light source having a planar main surface capable of
`emitting a white light includes a blue LED, an optical guide
`plate having a planar main surface and an edge face receiv-
`ing injection of the light from the blue LED, and a coating
`material of transparent resin or glass containing fluorescent
`materials positioned between the blue LED and the optical
`guide plate. The fluorescent materials can be exited by
`absorption of a part of the blue light from the blue LED to
`emit fluorescent light and the fluorescent light can be mixed
`with a remaining part of the blue light to make white light
`in the optical guide plate.
`
`See application file for complete search history.
`
`15 Claims, 19 Drawing Sheets
`
`707
`706
`702
`
`
`
`WWW/I’ll
`
`
`
`,\‘\\\\\\
`‘‘“\€§E\\\§
`
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`
`l/I/I/I/II/I/I/II/W/III/IIIIII/I/
`
`
`703
`704
`
`705
`
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`US 7,071,616 B2
`
`Page 2
`
`US. PATENT DOCUMENTS
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`3,699,478 A
`3,819,974 A
`3,875,456 A
`4,298,820 A
`4,314,910 A
`4,550,256 A
`4,644,223 A
`4,716,337 A
`4,727,283 A
`5,006,908 A
`5,202,777 A
`5,257,049 A
`5,369,289 A
`5,471,113 A
`5,550,657 A
`5,578,839 A
`5,700,713 A
`5,798,537 A
`5,847,507 A
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`6,066,861 A
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`EP
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`EP
`GB
`GB
`JP
`JP
`JP
`JP
`JP
`
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`
`JP
`E
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`JP
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`JP
`JP
`JP
`JP
`JP
`JP
`JP
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`
`0 383 215 A
`0 500 937 Al
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`1589964
`4717684
`49106283
`5079379
`491221
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`
`49-122292
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`5245181
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`
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`529023107 6
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`62189770
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`62'20237 A
`6220237 A
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`291980
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`01-189695 A
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`3/1991
`5/1992
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`JP
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`JP
`JP
`JP
`JP
`JP
`JP
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`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
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`JP
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`W0
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`
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`563068
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`6208845
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`06260680
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`07099345 A
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`07_120754 A
`7-32638 U
`742152
`7_42152 U
`07176794 A
`07_235207 A
`07-288341
`7_321407
`08007614 A
`863119
`8170077
`09027642 A
`09-027642 A
`10036835 A
`11-500584
`2000-512806
`2001320094 A
`2002270020 A *
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`
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`
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`US 7,071,616 B2
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`* cited by examiner
`
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`U.S. Patent
`
`Jul. 4, 2006
`
`Sheet 1 0f 19
`
`US 7,071,616 B2
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`II
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` [III/‘
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` VIII/[Mill
`
`106
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`Fig.2
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`202
`
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`205
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 2 0f 19
`
`US 7,071,616 B2
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`Fig. 3A
`
`
`100
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 3 of 19
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`US 7,071,616 B2
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`Egomam
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`“ES£99935
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 4 0f 19
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`US 7,071,616 B2
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`Fig. 5A
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`JuL4,2006
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`Sheet 5 of 19
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`US 7,071,616 B2
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 6 0f 19
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`US 7,071,616 B2
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 7 0f 19
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`US 7,071,616 B2
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`Fig. 10 ,
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`Jul. 4, 2006
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`Sheet 8 0f 19
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`US 7,071,616 B2
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`Jul. 4, 2006
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`Sheet 9 0f 19
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`US 7,071,616 B2
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`Jul. 4, 2006
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`Sheet 10 0f 19
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`US 7,071,616 B2
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`Fig. 14A
`
`Brightness
`
`holding rate
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 11 0f 19
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`US 7,071,616 B2
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`Fig. 15A
`
`120
`
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`Jul. 4, 2006
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`Sheet 12 0f 19
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`US 7,071,616 B2
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`2.9.1
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`U.S. Patent
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 14 0f 19
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`US 7,071,616 B2
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`
`
`530
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`580
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`630
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`680
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 15 of 19
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`US 7,071,616 132
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`1
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 16 of 19
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`US 7,071,616 B2
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`Jul. 4, 2006
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`Sheet 17 0f 19
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`US 7,071,616 B2
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 18 of 19
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`US 7,071,616 B2
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`U.S. Patent
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`Jul. 4, 2006
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`Sheet 19 0f 19
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`US 7,071,616 B2
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`US 7,071,616 B2
`
`1
`LIGHT EMITTING DEVICE WITH BLUE
`LIGHT LED AND PHOSPHOR
`COMPONENTS
`
`This application is a divisional of application Ser. No.
`09/458,024, filed Dec. 10, 1999, now US. Pat. No. 6,614,
`179, which is a divisional of application Ser. No. 09/300,
`315, filed on Apr. 28, 1999, now US. Pat. No. 6,069,440,
`which is a divisional of application Ser. No. 08/902,725,
`filed on Jul. 29, 1997, now US. Pat. No. 5,998,925, the
`entire contents of which are hereby incorporated by refer-
`ence.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a light emitting diode
`used in LED display, back light source, traffic signal, trail-
`way signal,
`illuminating switch,
`indicator, etc. More
`particularly,
`it relates to a light emitting device (LED)
`comprising a phosphor, which converts the wavelength of
`light emitted by a light emitting component and emits light,
`and a display device using the light emitting device.
`2. Description of Related Art
`A light emitting diode is compact and emits light of clear
`color with high efliciency. It is also free from such a trouble
`as bum-out and has good initial drive characteristic, high
`vibration resistance and durability to endure repetitive
`ON/OFF operations, because it is a semiconductor element.
`Thus it has been used widely in such applications as various
`indicators and various light sources. Recently light emitting
`diodes for RGB (red, green and blue) colors having ultra-
`high luminance and high efliciency have been developed,
`and large screen LED displays using these light emitting
`diodes have been put into use. The LED display can be
`operated with less power and has such good characteristics
`as light weight and long life, and is therefore expected to be
`more widely used in the future.
`Recently, various attempts have been made to make white
`light sources by using light emitting diodes. Because the
`light emitting diode has a favorable emission spectrum to
`generate monochromatic light, making a light source for
`white light requires it to arrange three light emitting com-
`ponents of R, G and B closely to each other while diflusing
`and mixing the light emitted by them. When generating
`white light with such an arrangement, there has been such a
`problem that white light of the desired tone cannot be
`generated due to variations in the tone, luminance and other
`factors of the light emitting component. Also when the light
`emitting components are made of different materials, elec-
`tric power required for driving differs from one light emit-
`ting diode to another, making it necessary to apply different
`voltages different light emitting components, which leads to
`complex drive circuit. Moreover, because the light emitting
`components are semiconductor light emitting components,
`color tone is subject to variation due to the difference in
`temperature characteristics, chronological changes and oper-
`ating environment, or unevenness in color may be caused
`due to failure in uniformly m the light emitted by the light
`emitting components. Thus light emitting diodes are effec-
`tive as light emitting devices for generating individual
`colors, although a satisfactory light source capable of emit-
`ting white light by using light emitting components has not
`been obtained so far.
`
`In order to solve these problems, the present applicant
`previously developed light emitting diodes which convert
`the color of light, which is emitted by light emitting
`
`2
`
`components, by means of a fluorescent material disclosed in
`Japanese Patent Kokai Nos. 5-152609, 7-99345, 7-176794
`and 8-7614. The light emitting diodes disclosed in these
`publications are such that, by using light emitting compo-
`nents of one kind, are capable of generating light of white
`and other colors, and are constituted as follows.
`The light emitting diode disclosed in the above gazettes
`are made by mounting a light emitting component, having a
`large energy band gap of light emitting layer,
`in a cup
`provided at the tip of a lead frame, and having a fluorescent
`material that absorbs light emitted by the light emitting
`component and emits light of a wavelength different from
`that of the absorbed light (wavelength conversion), con-
`tained in a resin mold which covers the light emitting
`component.
`The light emitting diode disclosed as described above
`capable of emitting white light by mixing the light of a
`plurality of sources can be made by using a light emitting
`component capable of emitting blue light and molding the
`light emitting component with a resin including a fluorescent
`material that absorbs the light emitted by the blue light
`emitting diode and emits yellowish light.
`However, conventional light emitting diodes have such
`problems as deterioration of the fluorescent material leading
`to color tone deviation and darkening of the fluorescent
`material resulting in lowered efliciency of extracting light.
`Darkening here refers to, in the case of using an inorganic
`fluorescent material such as (Cd, Zn)S fluorescent material,
`for example, part of metal elements constituting the fluo-
`rescent material precipitate or change their properties lead-
`ing to coloration, or,
`in the case of using an organic
`fluorescent material, coloration due to breakage of double
`bond in the molecule. Especially when a light emitting
`component made of a semiconductor having a high energy
`band gap is used to improve the conversion efficiency of the
`fluorescent material (that is, energy of light emitted by the
`semiconductor is increased and number of photons having
`energies above a threshold which can be absorbed by the
`fluorescent material increases, resulting in more light being
`absorbed), or the quantity of fluorescent material consump-
`tion is decreased (that is, the fluorescent material is irradi-
`ated with relatively higher energy), light energy absorbed by
`the fluorescent material
`inevitably increases resulting in
`more significant degradation of the fluorescent material. Use
`of the light emitting component with higher intensity of light
`emission for an extended period of time causes further rare
`significant degradation of the fluorescent material.
`Also the fluorescent material provided in the vicinity of
`the light emitting component may be exposed to a high
`temperature such as rising temperature of the light emitting
`component and heat transmitted from the external environ-
`ment (for example, sunlight
`in case the device is used
`outdoors).
`Further, some fluorescent materials are subject to accel-
`erated deterioration due to combination of moisture entered
`
`from the outside or introduced during the production
`process, the light and heat transmitted from the light emit-
`ting component.
`When it comes to an organic dye of ionic property, direct
`current electric field in the vicinity of the chip may cause
`electrophoresis, resulting in a change in the color tone.
`SUMMARY OF THE INVENTION
`
`Thus, an object of the present invention is to solve the
`problems described above and provide a light emitting
`device which experiences only extremely low degrees of
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`US 7,071,616 B2
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`3
`deterioration in emission light intensity, light emission effi-
`ciency and color shift over a long time of use with high
`luminance.
`
`The present applicant completed the present invention
`through researches based on the assumption that a light
`emitting device having a light emitting component and a
`fluorescent material must meet the following requirements
`to achieve the above-mentioned object.
`The light emitting component must be capable of emitting
`light of high luminance with light emitting characteristic
`which is stable over a long time of use.
`The fluorescent material being provided in the vicinity of
`the high-luminance light emitting component, must show
`excellent resistance against light and heat so that the prop-
`erties thereof do not change even when used over an
`extended period of time while being exposed to light of high
`intensity emitted by the light emitting component
`(particularly the fluorescent material provided in the vicinity
`of the light emitting component is exposed to light of a
`radiation intensity as high as about 30 to 40 times that of
`sunlight according to our estimate, and is required to have
`more durability against light as light emitting component of
`higher luminance is used).
`With regard to the relationship with the light emitting
`component,
`the fluorescent material must be capable of
`absorbing with high efficiency the light of high monochro-
`maticity emitted by the light emitting component and emit-
`ting light of a wavelength different from that of the light
`emitted by the light emitting component.
`Thus the present
`invention provides a light emitting
`device, comprising a light emitting component and a phos-
`phor capable of absorbing a part of light emitted by the light
`emitting component and emitting light of wavelength dif-
`ferent from that of the absorbed light;
`wherein said light emitting component comprises a nitride
`compound semiconductor represented by the formula: Inf
`GajAlkN where Oéi, Oéj, Oék and i+j+k=1) and said
`phosphor contains a garnet fluorescent material comprising
`at least one element selected from the group consisting of Y,
`Lu, Sc, La, Gd and Sm, and at least one element selected
`from the group consisting of Al, Ga and In, and being
`activated with cerium.
`
`The nitride compound semiconductor (generally repre-
`sented by chemical formula IniGajAlkN where Oéi, 0%j,
`Oél and i+j +k=1) mentioned above contains various mate-
`rials including lnGaN and GaN doped with various impu-
`rities.
`
`The phosphor mentioned above contains various materi-
`als defined as described above, including Y3A15012:Ce and
`Gd3ln5012:Ce.
`Because the light emitting device of the present invention
`uses the light emitting component made of a nitride com-
`pound semiconductor capable of emitting light with high
`luminance, the light emitting device is capable of emitting
`light with high luminance. Also the phosphor used in the
`light emitting device has excellent resistance against light so
`that the fluorescent properties thereof experience less change
`even when used over an extended period of time while being
`exposed to light of high intensity. This makes it possible to
`reduce the degradation of characteristics during long period
`of use and reduce deterioration due to light of high intensity
`emitted by the light emitting component as well as extra-
`neous light (sunlight including ultraviolet light, etc.) during
`outdoor use, thereby to provide a light emitting device which
`experiences extremely less color shift and less luminance
`decrease. The light emitting device of the present invention
`
`10
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`45
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`50
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`60
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`65
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`4
`
`can also be used in such applications that require response
`speeds as high as 120 nsec., for example, because the
`phosphor used therein allows after glow only for a short
`period of time.
`The phosphor used in the light emitting diode of the
`present invention preferably contains an yttrium-aluminum-
`garnet fluorescent material that contains Y and Al, which
`enables it to increase the luminance of the light emitting
`device.
`
`In the light emitting device of the present invention, the
`phosphor may be a fluorescent material represented by a
`general
`formula (Re1_,Sm,)3(Al1_SGaS)5012:Ce, where
`Oérél and Oésél and Re is at least one selected from Y
`and Gd, in which case good characteristics can be obtained
`similarly to the case where the yttrium-aluminum-garnet
`fluorescent material is used.
`
`Also in the light emitting device of the present invention,
`it is preferable, for the purpose of reducing the temperature
`dependence of light emission characteristics (wavelength of
`emitted light,
`intensity of light emission, etc.),
`to use a
`fluorescent material represented by a general formula (Y1_
`p-q-erPCequr)3(A11_5Ga5)5012 as the phosphor, where
`Oépé 0.8, 0.003 E qé 0.2, 0.0003 éré 0.08 and 0% SE 1.
`Also in the light emitting device of the present invention,
`the phosphor may contain two or mare yttrium-aluminum-
`garnet fluorescent materials, activated with cerium, of dif-
`ferent compositions including Y and Al. With this
`configuration,
`light of desired color can be emitted by
`controlling the emission spectrum of the phosphor according
`to the property (wavelength of emitted light) of the light
`emitting component.
`Further in the light emitting device of the present
`invention, in order to have light of a specified wavelength
`emitted by the light emitting device, it is preferable that the
`phosphor contains two or more fluorescent materials of
`different compositions represented by general formula (Re 1_
`rSm,)3(All_SGaS)5012:Ce, where 0§r<1 and Oésél and Re
`is at least one selected from Y and Gd.
`
`Also in the light emitting device of the present invention,
`in order to control
`the wavelength of emitted light,
`the
`phosphor may contain a first fluorescent material repre-
`sented by general formula Y3(A11_SGaS)5012:Ce and a sec-
`ond fluorescent material represented by general formula
`Re3A15012:Ce, where 0% sé 1 and Re is at least one selected
`from Y, Gd and La.
`Al