United States Patent [19]
`Shimizu et al.
`
`US005998925A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,998,925
`Dec. 7, 1999
`
`[54] LIGHT EMITTING DEVICE HAVING A
`NITRIDE COMPOUND SEMICONDUCTOR
`AND A PHOSPHOR CONTAINING A
`GARNET FLUORESCENT MATERIAL
`
`[75] Inventors: Yoshinori Shimizu, Naka-gun; Kensho
`Sakano, Anan; Yasunobu Noguchi,
`Naka-gun; Toshio Moriguchi, Anan, all
`of Japan
`
`[73] Assignee: Nichia Kagaku Kogyo Kabushiki
`Kaisha, Tokushima, Japan
`
`[21] Appl. No.: 08/902,725
`[22]
`Filed:
`Jul. 29, 1997
`[30]
`Foreign Application Priority Data
`
`Jul. 29, 1996
`Sep. 17, 1996
`Sep. 18, 1996
`Dec. 27, 1996
`Mar. 31, 1997
`
`[JP]
`[JP]
`[JP]
`[JP]
`[JP]
`
`Japan .................................. .. 8-198585
`Japan
`.. 8-244339
`Japan
`.. 8-245381
`Japan
`8-359004
`Japan ................................. ... 9-081010
`
`Int. Cl.6 .............................. .. H01J 1/62; H01J 63/04
`[51]
`[52] US. Cl. ........................ .. 313/503; 313/498; 313/501;
`313/502; 257/103
`[58] Field of Search ................................... .. 313/498, 503,
`313/501, 502; 257/103
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,699,478 10/1972 Pinnow et al. ....................... .. 332/751
`4,298,820 11/1981 Bongers et al. .
`4,727,283
`2/1988 Van Kemenade et al. .
`5,798,537
`8/1998 Nitta ...................................... .. 257/103
`
`FOREIGN PATENT DOCUMENTS
`
`50-43913
`
`4/1975 Japan.
`
`55-4898
`62-20237
`1 —179471
`5 —15 2609
`7-099345
`7-176794
`8-007614
`9-027642
`
`1/1980
`1/1987
`7/1989
`6/1993
`4/1995
`7/1995
`1/1996
`1/1997
`
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`
`OTHER PUBLICATIONS
`
`“A NeW Phosphor for Frying—Spot Cathode—Ray Tubes for
`Color Television: YelloW—Emitting Y3a15O12—Ce3+”, G.
`Glasse et al., Applied Physics Letters, vol. 11, No. 2, pp.
`53—54 (1967).
`“Improved color rendition in high pressure mercury vapor
`lamps”, Mary V. Hoffman, Journal of IES, pp. 89—91 (1977).
`S. Nakamura, SPIE, 3002:26—35 (1997).
`Primary Examiner—Vip Patel
`Assistant Examiner—Michael J. Smith
`Attorney, Agent, or Firm—Birch, SteWart, Kolasch & Birch,
`LLP
`
`[57]
`
`ABSTRACT
`
`The White light emitting diode comprising a light emitting
`component using a semiconductor as a light emitting layer
`and a phosphor Which absorbs a part of light emitted by the
`light emitting component and emits light of Wavelength
`different from that of the absorbed light, Wherein the light
`emitting layer of the light emitting component is a nitride
`compound semiconductor and the phosphor contains garnet
`?uorescent material activated With cerium Which contains 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, and is
`subject to less deterioration of emission characteristic even
`When used With high luminance for a long period of time.
`
`23 Claims, 19 Drawing Sheets
`
`TCL 1037, Page 1
`
`

`

`US. Patent
`
`Dec. 7,1999
`
`Sheet 1 0f 19
`
`5,998,925
`
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`TCL 1037, Page 2
`TCL 1037, Page 2
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`

`

`U.S. Patent
`
`Dec. 7,1999
`
`Sheet 2 0f 19
`
`5,998,925
`
`Fig. 3A
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`
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`
`TCL 1037, Page 3
`
`

`

`US. Patent
`
`Dec. 7, 1999
`
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`5,998,925
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`TCL 1037, Page 4
`TCL 1037, Page 4
`
`

`

`U.S. Patent
`
`Dec. 7,1999
`
`Sheet 4 0f 19
`
`5,998,925
`
`Fig. 5A
`
`100
`
`Relative 50
`intensity
`(%)
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`200
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`400
`300
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`500
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`
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`
`100
`
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`600
`500
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`
`TCL 1037, Page 5
`
`

`

`U.S. Patent
`
`Dec. 7,1999
`
`Sheet 5 0f 19
`
`5,998,925
`
`Fig. 6
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`420
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`TCL 1037, Page 6
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`

`

`U.S. Patent
`
`Dec. 7,1999
`
`Sheet 6 0f 19
`
`5,998,925
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`TCL 1037, Page 7
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`

`

`U.S. Patent
`
`Dec. 7,1999
`
`Sheet 7 0f 19
`
`5,998,925
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`U.S. Patent
`US. Patent
`
`Dec. 7,1999
`Dec. 7,1999
`
`Sheet 8 0f 19
`Sheet 8 0f 19
`
`5,998,925
`5,998,925
`
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`TCL 1037, Page 9
`TCL 1037, Page 9
`
`

`

`U.S. Patent
`
`Dec. 7,1999
`
`Sheet 9 0f 19
`
`5,998,925
`
`1 3 A
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`TCL 1037, Page 10
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 10 0f 19
`
`5,998,925
`
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`TCL 1037, Page 11
`
`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 11 0f 19
`
`5,998,925
`
`Fig. 15A
`
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`TCL 1037, Page 12
`
`

`

`U.S. Patent
`US. Patent
`
`Dec. 7, 1999
`Dec. 7, 1999
`
`Sheet 12 0f 19
`Sheet 12 0f 19
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`5,998,925
`5,998,925
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`TCL 1037, Page 13
`TCL 1037, Page 13
`
`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 13 0f 19
`
`5,998,925
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`TCL 1037, Page 14
`
`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 14 0f 19
`
`5,998,925
`
`Fig. 18A
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`TCL 1037, Page 15
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 15 0f 19
`
`5,998,925
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`Fig. 19A
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`TCL 1037, Page 16
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 16 0f 19
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`5,998,925
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`430
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`530
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`580
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`TCL 1037, Page 17
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 17 0f 19
`
`5,998,925
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`Fig.
`21A
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`TCL 1037, Page 18
`
`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 18 0f 19
`
`5,998,925
`
`Fig.22A
`
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`TCL 1037, Page 19
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 19 0f 19
`
`5,998,925
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`TCL 1037, Page 20
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`

`

`5,998,925
`
`1
`LIGHT EMITTING DEVICE HAVING A
`NITRIDE COMPOUND SEMICONDUCTOR
`AND A PHOSPHOR CONTAINING A
`GARNET FLUORESCENT MATERIAL
`
`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)
`Alight emitting diode is compact and emits light of clear
`color with high efficiency. It is also free from such a trouble
`as burn-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 efficiency 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 diffusing
`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 mixing the light emitted by the
`light emitting components. Thus light emitting diodes are
`effective 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
`components, by means of a fluorescent material disclosed in
`Japanese Patent Kokai Nos. 5-152609, 7-99345, 7-176794
`and 8-8614. 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
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`in a cup
`large energy band gap of light emitting layer,
`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 efficiency 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 more
`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
`
`introduced during the production
`from the outside or
`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
`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.
`
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`3
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`(1) The light emitting component must be capable of
`emitting light of high luminance with light emitting char-
`acteristic which is stable over a long time of use.
`(2) 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).
`(3) 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 semi-
`conductor represented by the formula:
`IniGaJ-AlkN where
`0éi, 0éj, 0§k and i+j+k=1) and said phosphor contains a
`garnet fluorescent material comprising 1) at least one ele-
`ment selected from the group consisting of Y, Lu, Sc, La, Gd
`and Sm, and 2) 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 0éi, 0% j,
`0§k and i+j +k=1) mentioned above contains various mate-
`rials including InGaN and GaN doped with various impu-
`rities.
`
`The phosphor mentioned above contains various materi-
`als defined as described above, including Y3A15012:Ce and
`Gd3In5012: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
`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.
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`4
`In the light emitting device of the present invention, the
`phosphor may be a fluorescent material represented by a
`general formula (Re1_,Smr)3(All_5Ga5)sO12:Ce, where
`0§r<1 and 0§s§1 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_,deCequr)3(All_5Ga5)sO12 as the phosphor,
`where 0§p§0.8, 0.003éqé02, 0.0003éré0.08 and
`0 E sé 1.
`
`Also in the light emitting device of the present invention,
`the phosphor may contain two or more 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
`(Re1_,Smr)3(All_5Ga5)5012:Ce, where 0§r<1 and 0§s§1
`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(All_5Ga5)5012:Ce and a sec-
`ond fluorescent material represented by general formula
`Re3A15012:Ce, where 0§s§ 1 and Re is at least one selected
`from Y, Ga and La.
`Also in the light emitting device of the present invention,
`in order to control
`the wavelength of emitted light,
`the
`phosphor may be an yttrium-aluminum-garnet fluorescent
`material containing a first fluorescent material and a second
`fluorescent material, with different parts of each yttrium
`being substituted with gadolinium.
`Further in the light emitting device of the present
`invention, it is preferable that main emission peak of the
`light emitting component is set within the range from 400
`nm to 530 nm and main emission wavelength of the phos-
`phor is set to be longer than the main emission peak of the
`light emitting component. This makes it possible to effi-
`ciently emit white light.
`Further in the light emitting device of the present
`invention, it is preferable that the light emitting layer of the
`light emitting component contains gallium nitride semicon-
`ductor which contains In, and the phosphor is yttrium-
`aluminum-garnet fluorescent material wherein part of Al is
`substituted by Ga so that the proportion of Ga:Al is within
`the range from 1:1 to 4:6 and part of Y is substituted by Gd
`so that the proportion of Y:Gd is within the range from 4:1
`to 2:3. Absorption spectrum of the phosphor which is
`controlled as described above shows good agreement with
`that of light emitted by the light emitting component which
`contains gallium nitride semiconductor including In as the
`light emitting layer, and is capable of improving the con-
`version efficiency (light emission efficiency). Also the light,
`generated by mixing blue light emitted by the light emitting
`component and fluorescent light of the fluorescent material,
`is a white light of good color rendering and, in this regard,
`an excellent light emitting device can be provided.
`
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`5,998,925
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`5
`The light emitting device according to one embodiment of
`the present invention comprises a substantially rectangular
`optical guide plate provided with the light emitting compo-
`nent mounted on one side face thereof via the phosphor and
`surfaces of which except for one principal surface are
`substantially covered with a reflective material, wherein
`light emitted by the light emitting component is turned to
`planar light by the optical guide plate and the phosphor, and
`is output from the principal surface of the optical guide
`plate.
`The light emitting device according to another embodi-
`ment of the present invention has a substantially rectangular
`optical guide plate, which is provided with the light emitting
`component mounted on one side face thereof and the phos-
`phor installed on one principal surface with surfaces thereof
`except for the principal surface being substantially covered
`with a reflective material, wherein light emitted by the light
`emitting component is turned to planar light by the optical
`guide plate and the phosphor, and is output from the prin-
`cipal surface of the optical guide plate.
`The LED display device according to the present inven-
`tion has an LED display device comprising the light emitting
`devices of the present invention arranged in a matrix and a
`drive circuit which drives the LED display device according
`to display data which is input thereto. This configuration
`makes it possible to provide a relatively low-priced LED
`display device which is capable of high-definition display
`with less color unevenness due to the viewing angle.
`The light emitting diode according to one embodiment of
`the present invention comprises:
`a mount lead having a cup and a lead;
`an LED chip mounted in the cup of the mount lead with
`one of electrodes being electrically connected to the mount
`lead;
`a transparent coating material filling the cup to cover the
`LED chip; and
`a light emitting diode having a molding material which
`covers the LED chip covered with the coating material
`including the cup of the mount lead,
`the inner lead and
`another electrode of the LED chip, wherein
`the LED chip is a nitride compound semiconductor and
`the coating material contains at least one element selected
`from the group consisting of Y, Lu, Sc, La, Gd and Sm, at
`least one element selected from the group consisting of Al,
`Ga and In and a phosphor made of garnet fluorescent
`material activated with cerium.
`
`The phosphor used in the light emitting diode of the
`present
`invention preferably contains yttrium-aluminum-
`garnet fluorescent material that contains Y and Al.
`In the light emitting diode of the present invention, the
`phosphor may be a fluorescent material represented by a
`general formula (Re1_rSmr)3(All_5Ga5)sO12:Ce, where
`0§r<1 and 0§s§1 and Re is at least one selected from Y
`and Gd.
`
`Also in the light emitting diode of the present invention,
`a fluorescent material represented by a general formula
`(Y1_p_q_erpCequr)3(All_5Ga5)5012 may be used as the
`phosphor, where 0§p§0.8, 0.003éqé02, 0.0003éré0.08
`and 0§s§ 1.
`
`In the light emitting diode of the present invention, the
`phosphor preferably contain two or more yttrium-
`aluminum-garnet fluorescent materials, activated with
`cerium, of different compositions including Y and Al, in
`order to control the emitted light to a desired wavelength.
`In the light emitting diode of the present
`invention,
`similarly,
`two or more fluorescent materials of different
`
`6
`
`compositions represented by a general formula (Re1_,Smr)3
`(All_5 Ga5)5012:Ce, where 0§r<1 and 0§s§1 and Re is at
`least one selected from Y and Gd may be used as the
`phosphor in order to control the emitted light to a desired
`wavelength.
`invention,
`In the light emitting diode of the present
`similarly, a first fluorescent material represented by a general
`formula Y3(All_5Ga5)5012:Ce and a second fluorescent
`material represented by a general formula Re3A150122Ce,
`may be used as the phosphor where 0§s§ 1 and Re is at least
`one selected from Y, Ga and La, in order to control the
`emitted light to a desired wavelength.
`invention,
`In the light emitting diode of the present
`similarly, yttrium-aluminum-garnet fluorescent material a
`first fluorescent material and a second fluorescent material
`
`may be used wherein part of yttrium being substituted with
`gadolinium to different degrees of substitution as the
`phosphor, in order to control the emitted light to a desired
`wavelength.
`Generally, a fluorescent material which absorbs light of a
`short wavelength and emits light of a long wavelength has
`higher efficiency than a fluorescent material which absorbs
`light of a long wavelength and emits light of a short
`wavelength. It is preferable to use a light emitting compo-
`nent which emits visible light than a light emitting compo-
`nent which emits ultraviolet
`light
`that degrades resin
`(molding material, coating material, etc.). Thus for the light
`emitting diode of the present invention, for the purpose of
`improving the light emitting efficiency and ensure long life,
`it is preferable that main emission peak of the light emitting
`component be set within a relatively short wavelength range
`of 400 nm to 530 nm in the visible light region, and main
`emission wavelength of the phosphor be set to be longer than
`the main emission peak of the light emitting component.
`With this arrangement, because light converted by the
`fluorescent material has longer wavelength than that of light
`emitted by the light emitting component,
`it will not be
`absorbed by the light emitting component even when the
`light emitting component is irradiated with light which has
`been reflected and converted by the fluorescent material
`(since the energy of the converted light is less than the band
`gap energy). Thus the light which has been reflected by the
`fluorescent material or the like is reflected by the cup
`wherein the light emitting component is mounted, making
`higher efficiency of emission possible.
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a schematic sectional view of a lead type light
`emitting diode according to the embodiment of the present
`invention.
`
`FIG. 2 is a schematic sectional view of a tip type light
`emitting diode according to the embodiment of the present
`invention.
`
`FIG. 3A is a graph showing the excitation spectrum of the
`garnet fluorescent material activated by cerium used in the
`first embodiment of the present invention.
`FIG. 3B is a graph showing the emission spectrum of the
`garnet fluorescent material activated by cerium used in the
`first embodiment of the present invention.
`FIG. 4 is a graph showing the emission spectrum of the
`light emitting diode of the first embodiment of the present
`invention.
`
`FIG. 5A is a graph showing the excitation spectrum of the
`yttrium-aluminum-garnet fluorescent material activated by
`cerium used in the second embodiment of the present
`invention.
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`5,998,925
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`7
`FIG. 5B is a graph showing the emission spectrum of the
`yttrium-aluminum-garnet fluorescent material activated by
`cerium used in the second embodiment of the present
`invention.
`
`FIG. 6 shows the chromaticity diagram of light emitted by
`the light emitting diode of the second embodiment, while
`points A and B indicate the colors of light emitted by the
`light emitting component and points C and D indicate the
`colors of light emitted by two kinds of phosphors.
`FIG. 7 is a schematic sectional view of the planar light
`source according to another embodiment of the present
`invention.
`
`FIG. 8 is a schematic sectional view of another planar
`light source different from that of FIG. 7.
`FIG. 9 is a schematic sectional view of another planar
`light source different from those of FIG. 7 and FIG. 8.
`FIG. 10 is a block diagram 10 of a display device which
`is an application of the present invention.
`FIG. 11 is a plan view of the LED display device of the
`display device of FIG. 10.
`FIG. 12 is a plan view of the LED display device wherein
`one pixel is constituted from four light emitting diodes
`including the light emitting diode of the present invention
`and those emitting RGB colors.
`FIG. 13A shows the results of durable life test of the light
`emitting diodes of Example 1 and Comparative Example 1,
`showing the results at 25° C. and FIG. 13B shows the results
`of durable life test of the light emitting diodes of Example
`1 and Comparative Example 1, showing the results at 60° C.
`and 90% RH.
`
`FIG. 14A shows the results of weatherability test of
`Example 9 and Comparative Example 2 showing the change
`of luminance retaining ratio with time and FIG. 14B shows
`the results of weatherability test of Example 9 and Com-
`parative Example 2 showing the color tone before and after
`the test.
`
`FIG. 15A shows the results of reliability test of Example
`9 and Comparative Example 2 showing the relationship
`between the luminance retaining ratio and time, and FIG.
`15B is a graph showing the relationship between color tone
`and time.
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`FIG. 16 is a chromaticity diagram showing the range of
`color tone which can be obtained with a light emitting diode
`which combines the fluorescent materials shown in Table 1
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`and blue LED having peak wavelength at 465 nm.
`FIG. 17 is a chromaticity diagram showing