(12) United States Patent
`Baretz et al.
`
`I 1111111111111111 11111111111111111111 1111111111 1111111111 1111111111 11111111
`US006600175B1
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,600,175 Bl
`*Jul. 29, 2003
`
`(54) SOLID STATE WHlTE LIGHT EMITTER
`AND DIS PLAY US[NG SAME
`
`(75)
`
`Inventors: Bruce Barctz, Wesl Milford, NJ (US);
`Micbael A. Tischler, Danbury, CT (US)
`
`(73)
`
`As.signcc: Advanced Technology Materials, Tnc.,
`Danbury, CT (US)
`
`( • ) Notice:
`
`This patent issued on a cooiiauecl pros(cid:173)
`ecution application filed under 37 CFR
`l.53(cl), and is subject 10 tbe twenty year
`palcol
`term provisions of 35 U.S.C.
`154(a)(2).
`
`Subject 10 any clisclairner, tbe term of tbis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 1212 clays.
`
`(21) Appl. No.: 08/621,937
`
`(22)
`
`Filed:
`
`Mar_ 26, 1996
`
`(51)
`(52)
`
`(58)
`
`(56)
`
`lnt. C J.7 ................................................ H0lL 33/00
`U.S. C l .
`........................... 257/100; 257/88; 257/98;
`257/99
`Field of Search .............................. 257/88, 98, 99,
`257/100
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`• 7/1971 Geusic ..................... ... 257/98
`3,593,055 A
`• IO/J973 Mitsuhala .................... 257/98
`3,763,405 A
`1/1976 Mita ........................... 257/98
`3,932,881 A
`•
`4,992,704 A
`2/1991 S tinson ...................... 315/312
`5,126.214 A • 6/ 1992 Tokailin ...................... 257/99
`• 5/ 1993 O'Conner ................... 257/98
`5,208.462 A
`4/1995 Linman et al. ............. 428/690
`5,405,709 A
`5,583,349 A
`• 12/1996 Norman ....................... 257/88
`5,660,461 A
`• 8./1997 Ignatius ....................... 257/8S
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`
`60170194
`04289691
`
`9/1985
`10/1992
`
`J P
`
`5-152609
`
`• 6/ 1993
`
`257/98
`
`OTHER PUllLICATIONS
`
`Sato, Y. ct al, ·'Full-Color Fluorescent Display Devices
`Using a Near-UV Light Emilting Diode", Jpn. J. Appl.
`Phys. vol. 35 (1996) pp. L 838-L839.
`J.I. Pankove and E.R. Levin, ·'Scanoing Electron Micros(cid:173)
`copy Studies o[ GaN" J. Appl. Phys. vol. 46, (1975), pp.
`1647- 1652.
`I. Akasaki, et al., ''Pbotolumiaesceoce of Mg-<loped p-type
`GaN and Electroluroioesccace of GaN p-o Ju nction LED" J.
`Lumion., vol. 48-49, (1991) pp. 666-670.
`H. Amano et al., UV and Blue Electrolurninesceace from
`AI.GaN:Mg/GaN LED treated eith Low-Energy Electron
`Beam Irradiation (LEEBI), Inst. Phys. Con[ Ser. vol. 106,
`(1990), pp. 725-730.
`Munch et al, "Silicon Carbide Ligb1-Emi11ing Diodes with
`Epitaxial Juactioas" Solid Stale Elec/ronics, vol. 19, (1976)
`p. 871.
`Zhang Jin Chao ct al., White Light Emi11ing Glasses, Journal
`of Solid State Chemistry, 93, 17-29 (1991), pp. 17-29.
`
`(List continued on next page.)
`
`Primary Examiner-Jerome Jackson
`(74) Allorney, Agent, or Firm-Stevea J.
`Margaret Chappuis
`
`lluJtquist;
`
`(57)
`
`ABSTRACT
`
`A ligbt emitting assembly comprising a solid state device
`coupleable with a power supply constructed and arranged 10
`power the solid state device to emit from the solid state
`device a first, relatively shorter wavelength radiation, and a
`dowo-converting luminophoric medium arranged in rcceiv(cid:173)
`iag relationship to said first, relatively shorter wavelength
`radiation, and which in exposure to said first, rclat,vely
`shorter wavelength radiation, is excited to responsively emit
`second, relatively longer wavelength radiation. In a specific
`cmbodimenl, monochromatic blue or UV light output from
`a ligbt-emiuing diode is down-cooverted 10 wbite light by
`packaging the diode ,vith fluorescent organic aad/or inor(cid:173)
`ganic Iluorescers aad phosphors in a polymeric matrix.
`
`26 Claims, 3 Drawing Sheets
`
`11
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`/10
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`14
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`17
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`16
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`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:15)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:20)
`
`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:20)
`
`

`

`US 6,600,175 Bl
`Page 2
`
`0'11-IER PUBLICKllONS
`
`S hosaku Tanaka, et al., Bright White-Light Elec1rolumines(cid:173)
`cence Based on NonradiaLive Energy Transfer in Ce- and
`Eu---<loped SrS Thin Films, Appl. Phys. Leu. 51 (21), Nov.
`23, 1987, pp. 1661-1663.
`M. Berggren et al., White Light From aa Electroluminescent
`Diode Made From poly[3(4-octylphenyl)-2,2'-bithiophene)
`and an Oxadiazole Derivatives, J. Appl. Phys. 76 (11), Dec.
`l, 1994, pp. 7530--7534.
`
`J . Kido et al., Wbite Lighl-Emilling Organic Electro lumi(cid:173)
`nescent Devices Using 1he poly(N-vinylcarbazole) Emitter
`Layer Doped witb Three Fluoresce(cid:143) L Dyes, Appl. Phys.
`Lett., 64 (7) Feb. 14, J 994, pp. 815-817.
`N. El Joubar et al., White Ligh t Genera tion Using Fluores(cid:173)
`• Io ns, J. De
`cent Glasses Activated by Ce3
`• , 'lb 3+ and Mn2
`P hysique rv, Collogue C2, supplement au j . de Physique Ill,
`vol. 2, Oct. 1992, pp. 257-260.
`
`• cited by examiner
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:15)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:21)
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`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:21)
`
`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 1 of' 3
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`US 6,600,175 Bl
`
`FIGUREl
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`FIGURE2
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`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:22)
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`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 2 of 3
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`US 6,600,175 Bl
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`FIGURE3
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`18
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`FIGURE4
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`G- -
`G- -G- -G- -G- -G- -
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`30
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`controller
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`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:23)
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`U.S. Patent
`
`Jul. 29, 2003
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`Sheet 3 of 3
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`US 6,600,175 Bl
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`FIGURES
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`41
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`43
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`40
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`I
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`63
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`46
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`48
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`47
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`FIGURE6
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`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:15)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:24)
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`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:24)
`
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`

`US 6,600,175 Bl
`
`1
`SOLID STATE WHITE LIGHT EMITTER
`AND DlSPLAY USLNC SAME
`
`FIELD OF THE INVENTION
`
`This invention relates to solid stale l.ight cmiuing devices
`sucb as ligbt emilling diodes aacl more particularly to sucb
`devices which produce white light.
`
`2
`whose breakage makes tbe lamp useless, and by extension,
`the message on tbe sign board illegible. Due 10 severe
`environmental conditions on roadways, glass breakage of
`incaadcsccnl and fluorescent lamps is an all too frequent
`mishap. Tbe solid state LED lamp bas no filaments to break
`and is housed witbin a durable plastic casing, as the primary
`device envelope or package ( typically being of considerable
`thickness), thereby exhibiting a high level of imperviousness
`10 ex1rcme ou tdoor envi ronmental stresses. With respect to
`10 outdoor signage appl.icalions, displays can contain up to 1
`million or more pixels or lamps. Thus 1be maintenance costs
`related to replacement of non-operational incandescent
`lamps o r miniature fluorescent (or neon) lamps arc high and
`unfortunately, continual.
`Hence, an emerging trend in the manufacturing and
`marketing or informat ional displays or signage, especially
`for outdoor usage, is to u tilize solid state LED lamps as
`replacemeot for more conventional incandescent bulbs. The
`major end user benefits arc the lower power consumption
`20 costs and the longer operatio nal lifetime (hence, reducing
`maintenance costs). A fu rther benefit is the rapid relaxation
`times of a sol.id state device affording an opportunity to
`display rapidly changing information messages incorporat-
`ing video or lifelike animation.
`Given the desirability of white light displays (e.g., com-
`mercial bank '·time and temperature" message boards, sta(cid:173)
`dium scoreboards), considerable effort bas been expended to
`produce white light LEDs. Although the recent availability
`ofthe blue LED makes a full colo r, and by extension a white
`30 light display realiwble, conventionally it has been consid(cid:173)
`ered tba t such a display would require multiple LEDs. The
`multiple LEDs would be then incorporated into complicated
`and expensive L ED modules to obtain the required broad
`band illumination necessary 10 provide white light. Even if
`35 a discrete LED lamp were constructed that provides white
`illumination (as opposed 10 the utilization of a multitude of
`single die, single color discrete LED lamps in a module or
`sub-assembly), the current state of the an requires the
`utilization of multiple LED dies and typically at least four
`40 electrical leads 10 power these dies. U.S. Pat. No. 4,992,704
`issued 10 Stinson teaches a variable color 1.ight emiuiog
`diode having a unitary housing of c lear molded solid epoxy
`supporting three LED dies characterized as producing color
`hues of red, green and blue, respectively. There have been
`45 some recent introductions of commercial "full-color" LED
`lamps, that arc essentially discrete lamps which afford a
`means of producing white ligbt. All currently avai lable
`examples of such lamps cootain a minimum of three LED
`dies (or cbips)----One red, one green and one blue, encapsu-
`so lated in a s ingle epoxy package. "The chips arc powered via
`at least 4 electrical leads. These compUcated multiple die,
`variable color devices provide an expensive aod complicated
`me thod of o[eriog white l.ight illumination. furthermore,
`these multiple die white lamps are rather inefficient in the
`55 present state of the an, offering luminosity far below that
`realized by exis ting monochromatic light emitting diode
`lamps, even when a very la rge quantity of dies are fuoc(cid:173)
`tionally incorporated into the discrete lamp assembly.
`The utility of solid state lamps that offer white light
`60 illumination is dear. However, at present there is a very
`limited number of such solid state lamps available. In
`s ignagc applications where a small pixel of light is fre(cid:173)
`quently required to offer the highest possible resolu tion of
`tbe message or video image, the most practical solid state
`65 lamps for display applications are tbe LED lamps. The LED
`lamp can bave very narrow angles of irradiance and are very
`small in size when compared with other means of providing
`
`15
`
`BACKGROUND OF THE INVENTION
`Sol.id state Ugbt emitting devices, including sol.id state
`lamps including LEDs arc extremely useful because they
`potentially oJier lower fabrication costs and long term
`durabil.ity benefits over conventional iocanclescent and Quo-
`res~-ent lamps. Due 10 their long operation (bum) time and
`low power consumption, sol.id state light emitting devices
`frequently provide a functional cost benefit, even when their
`initial cost is greater than that of conventional lamps.
`However, because large scale semiconduc to r manufacturing
`techniques can be used, many solid state lamps can be
`produced at extremely low cost. One such device is the sol.id
`state light emitting diode (LED) which has low fabrication
`costs, long operational lifetimes and low ma.intcoance costs.
`Light cmining diodes (LEDs), aod similarly constructed 25
`super luminescent d.iodes and semiconductor d.iode lasers,
`are commercially available and a wide variety of designs
`and manufacturing techniques have been developed. In
`addition to applications sucb as indicator l.ights on home and
`consumer app liances, audio v isual equipment, telecommu-
`11ica1ion devices and automotive ins1rume(cid:143) 1 markings, sucb
`LEDs have found considerable application in indoor and
`outdoor informational displays. But until recently, LEDs
`have produced light only in the red, green or amber ranges
`and have no t been generally s uitable for replacing, for
`exa mple, incandescent bulbs, with normally a wbite
`luminescence, io a wide variety of display applications. The
`recent introduction of a bright blue LED, however, allows
`white light LED systems to be realized and lbus has the
`potential to open the display market 10 LEDs by providing
`a practical means to achieve both full color and white light
`illumination.
`Toe practical advantages of LED displays over those
`using incandescent bulbs are many. The operational lifetime
`(in this ca5e, defined as continual illumination) of a LED is
`on tbe order of tea years or over 50,000 hours, whereas
`incandescent bulbs often burn out in the order of2000 hours,
`thus leaving an empty pixel in the display message. Such
`recurrent failu res make a display unreadable aad , therefore,
`not useful. These conditions (i.e., broken or missing pixels)
`require constant repair leading lo a s ig nificant maintenance
`problem for providers of display signs based o o incandes(cid:173)
`cent illumination devices. With the loog operational lifetime
`of a LED-based sign bo-ard, the pixels rarely bum out and the
`illuminated message remains legible over lo ng operatio na l
`periods.
`Similarly, LED lamps are considerably more robust.
`Whe n exposed 10 s tress, rnecbanical s hocks, o r temperature
`varia tions often encounte red in an outdoor environment they
`are less likely to fail than incandesce nt lamps. This allribute
`is especially importanL when the signage is utilized io an
`environment such as vehicula r traffic, e.g., roadway signage
`10 mark highway construction sites, bridges, tunnels, or
`traffic control markings, in which perishable fiJameots used
`in the incandescent lamps frequently break due to constant
`vibrational motion. Further, incandescent and fluorescent
`lamps are constructed with fragile g lass exterior casings
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:15)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:25)
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`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:25)
`
`

`

`US 6,600,175 Bl
`
`3
`a radiant surface. However, the methods of fabricating while
`LED lamps are limited. A conventional approach is 10
`fabricate a large c lus ter of red, green and blue LED d iscrete
`lamps, housed in mulliple lamp (up 10 30) su basscmblies or
`modules. By providing multiple power sources 10 control all
`of the discrete lamps, 1bese large modules can appear, from
`a distance, lo provide white light by 1he spatial mixing of
`blue, green and red sub-pixels of light g iven off by the
`ind ividual discrete LED lamps 1ha1 comprise 1he modu le.
`While the lamps that make up the modules may be indi- 10
`vidually addressable, and hence, offer the o pponunity 10,
`selectively and individually, provide red, green and blue
`light (or co mbinations thereof), such modular systems are
`complex and costly means o( provid ing white ligh t for a
`solid state display. Furl he r, as these modules are rather large, 15
`the ultimate resolution of the display will always be lower
`than that of a conve111ional single lamp pixel display.
`Whereas multiple discrete LED dies housed within a
`s ingle polymeric matrix (as taught by Stinson) may provide
`a discrete LED lamp such that the illumination could appear 20
`while to an observer, 1he individual LED dies would s1·il)
`need 10 be individually powered and the lamp would require
`mu ltiple leads in order to effect the simultaneous emission of
`mulliple wavelength lig ht. Thus, this mulliple die LED lamp
`would be rather expensive 10 fabricate, and would require 25
`expens ive and complicated circuitry to power and control ia
`an outdoor display. Despite these problems, both methods
`point 10 the utility of generating white illuminance.
`h would thus be highly desirable 10 develop a s imp le solid
`state LED lamp, with a minimum of power leads, (i.e., 2) 30
`exactly as practiced in single colo r LED lamps, s ucb !hat
`three domains of red, g reen aod blue light are generated and
`yet the white light ernis.5ion is apparent 10 an observer, all
`wh ile offering significantly reduced die costs (one versus
`three) and low fabrication coslS in the design of correspond- 35
`ing displays and s ignagc, high medium resolution (small
`pixel or lamp size), rapid switching 10 the on and off states
`(10 enhance live video imaging), and with a high luminous
`efficiency.
`It is well known that so-called lluorescenl lamps provide 40
`w hile light illumination. In a Ouorescenl lamp, 1hc Hg vapor
`in the vacuum tube is excited by an e lectrical discharge. The
`excited Hg atoms emit light, primarily in the ultraviolet
`region (e.g., 254 nm, 3 13 nm, 354 nm), which is absorbed
`by the inorganic phosphors coaling the inside walls of the 45
`tube. The phosphors then emil ligh1. These inorganic phos(cid:173)
`phors arc designed as s uc h to offer while light emission by
`"down-converting" (i.e., transforming a higher frequency,
`shorter wavelength form of energy 10 a lower frequency,
`longer wavelength form of energy) the ultraviole t emissions 50
`of the excited states of atomic Hg into a broad spectrum of
`emitted light which appears as white 10 the observer.
`However, these light emilling devices are aol solid-s tale, and
`miniaturization of these Ouorescent bulbs 10 provide suitable
`pixel resolution for display applications bas never beea 55
`practically accomplished. Io fact, Lhe primary application of
`miniature lluorcscent lamps (wi th long operational lifetimes,
`but unfonuoa tely high power consumption when compared
`with solid s tate LED lamps) in displays is 10 provide back
`lighting lo liquid crystals 1bat are individually addressed al 60
`11:Je pixel level. Furthe rmore, these miniature lluoresceal
`lamps remain fragile light emitting devices by virtue of their
`glass housings and arc unsuitable for use in display appli(cid:173)
`cations in which the lamps are exposed 10 extreme enviroo(cid:173)
`me111al s tresses. Such slresses can nol only break the glass 65
`housing, bul effect delamioation of the powder coatings
`from the interior wall of the glass housing. It would be
`
`4
`desirable to generate white light by radiative energy transfer,
`where the luminescent ceaters are an integral pan of the
`assemb ly such that a Ll1ick, dillicuJt-to-fraclure housiag
`structure (plate or bulb) could provide white illumioalioo
`from the inte rior 1hickoes.s of sucb housing s tructure, and not
`from a semi-permanent powder coaling placed on one side
`of a housing surface.
`In a forther example of gene rating white light, in the
`absence of phosphor coatings, it was disclosed in Chao, et
`al., "White Light Emitting Glasses," Journal of Solid State
`Chemistry 93, 17-29 (1991) (sec also El Jouhari, N., ct
`a l.," White light generation using fluorescent glasses acti(cid:173)
`vated by Ce3
`·, To3
`• and Mnz.. ions," Journal de Physique lV,
`Colloque C2, supplement au Journal de Physique 111, Vol(cid:173)
`ume 2, October 1992, C2-257 10 C2-260), 1ha1 vitreous
`materials are capable or ge(cid:143) eraling white light by simulla(cid:173)
`neous emission of blue, green and red emitting fluorescent
`centers in 8 20 3 -based glass that simultaneously contain
`• , and Ma2 + as activators. These glasses provide
`Ce:;., l b 3
`while illumination by offering the blue emission of Ce3
`+ as
`well as by lhe transfer of excited stale energy from the Ce3
`+
`10 Te3+ and Mnz.., whose luminescence occurs respectively
`in 1he green and red parts of 1he visible light spectrum.
`Mixed rare earlh borates caa be used 10 provide while
`ligbl illumination, via clown conversion, with excitation of
`the borate powders with a primary (ultraviolet) radiation
`between 250 nm and 300 nm. Similarly, for cathode ray
`applications, white light-emitting mixed fluorescent materi(cid:173)
`als caa be made by care ful formulation of greea lluorescenl
`ma terials (48 10 53% w/w), red fluorescent materials (37 10
`40% w/w) and blue fluorescent materials (10 10 13% w/w).
`While the devices in the above examples vary in coacept
`and construcLion, they demonstrate the utilization of red,
`green and blue Uuorescent materials, a ll inorganic in
`composi1ioo, which when excited by photons or elcctroo
`beams, can release multiple wavelengths of secoadary light
`emission (luminescence of either lluoresceat or phosphores(cid:173)
`cent character) to exhibit white light 10 the observer. T his is
`generally true, even if microscopic domains of discrete
`colored light emission can be observed on the Lambertiao
`surface of the light emilliog device.
`Tanaka, S., el al., "Brighi white-light electroluminesceoce
`based oa nonradiative energy transfer in Ce- and Eu-doped
`SrS films," App. Phys. Lell. 51 (21), Nov. 23, 1987,
`1662-1663, describes the generation of a while-light emit(cid:173)
`ting thin-film elec1rolumiaescen1 (EL) device using Ce- and
`Eu-eloped s trontium sulfide (SrS) inorganic phosphors. In
`the EL exci1atio n of the SrS:Ce,Eu device, nonradialive
`energy transfer from the Ce:;. luminescent center 10 the Eu2
`+
`luminescent center plays an important role in generating
`broad EL emission extending from the b lue 10 the red,
`thereby geaerating white light.
`Similarly, some recent discussions of AlGaN electrolu(cid:173)
`minescent systems with Zn and S i dopanlS have indicated
`lbaL some white light caa be generated. While ii is useful for
`a single device 10 be construc ted in which dopaots olfor a
`multitude of luminescent wavelengths, dopants invariably
`alter the e lectrical aud la1tice structures of semiconductors
`and as such, the performance of these devices are consid(cid:173)
`erably poorer tban for corresponding semiconductors free of
`dopant 1ha1 emil monochromatic irradiation, as a result of
`being dopant-free.
`Un til receatly, most ligbl emitting diodes have been
`semiconductor-based and most e lectroluminescent devices
`have been inorganic based. While o rganic materials have
`been utilized 10 prepare certain thin-film e lectroluminescent
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:15)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:26)
`
`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:26)
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`

`US 6,600,175 Bl
`
`s
`devices, ao organic based LEDs are commercially available.
`Further, organic-based LEDs are at present plagued by
`extremely short operational lifetimes due to degradation of
`the organic charge-transfer materials. In al l o f these systems,
`the organic materials, used io thin films oo conducting
`inorganic substrates such as ITO, are actively participating
`in the electron-hole recombinatio11 necessary to generate an
`excited state, and, by subsequent radiative decay, ligh t.
`Recently, the literature has discussed approaches directed
`to fabricating organic LED or electroluminescent devices
`and ia certain cases, white light emission bas been observed
`from these experimental designs. As an example, white light
`from aa electroluminescent diode made from poly[3(4-
`oclylpheayl)-2,2'-bithiopheae] aad aa oxadiazole derivative
`have been reported. Spectroscopic analysis indicates that the 15
`apparent white light is composed of blue (410 run), green
`(530 am),aacl red-orange (520 am) lumioesceot centers.
`Electroluminescent devices incorporating the red fluo resc(cid:173)
`ing material Rbodarni(cid:143) e onto an inorganic substrate have
`been effective in yielding some white light as well.
`White light emissioC1 from thin film organic e lectrolumi(cid:173)
`nescent cells based on poly(vinylcarbazole PVK) tbia films
`on !TO-coated g lass has also been recently reported. lne cell
`has the construction of Mg:Ag:Alq:TAZ:doped PVK:ITO(cid:173)
`:Glass where the conducting ITO layer injects holes into the
`o rganic based PVK tbi(cid:143)
`film layer which has high bole drift
`mobilities. Simultaneously, electrons are injected by the
`tris(8-quinolato) aluminum (111) complex layer Alq, into the
`bole blocking electron transporting layer composed o[ the
`organic molecule 3-(4'tert-butylphenyl)-4-phenyl-5 -(4'(cid:173)
`bipheayl)-l,2,4-tria.zole, TAZ. At the interface o[ the organic
`poly(vinlycarbazole) layer with the TAZ layer, recombina(cid:173)
`tion of ho les and electrons take place which excites the
`organic, aromatic, carbazole pendant moie ty that comprises
`the polymer. II is well known that the excited carbazole 35
`moiety within the polymer aggregates in the excited state
`leads to blue excimer emis.sioa, in the absence of quenchers
`or clopants. In th e example o f
`th e o rganic
`Mg:/\g:Alq:TAZ:clopecl PVK:JTO:Glass electroluminescent
`device, the quenchers of cxcimeric em ission, arc the dopants
`b lue emitting L,l,4,4 -tetraphe nylbuta-1,3-dicne (TPB),
`g reen emitting 7-clietbylamiao-3-(2'be(cid:143) wtbiazoyl)coumari(cid:143)
`(Coumarin-6), and red emitting clicyanomethylene-2-
`metbyl-6-p-dimethylami(cid:143) ostyryl-4H-pyra(cid:143) (DCM-1).
`U.S. Pat. No. 5,045,709 issued Apr. 11, 1995 to .I. E.
`Lillman et al.discloses a white ligh t emiuing internal junc(cid:173)
`tion organic electrolumjnescent device comprising an anode,
`an organic eleclrolurninesce(cid:143)
`t medium aacl a cathode. l11e
`organic e lectroluminescent medium [unhercomprises a hole
`injecting and transport ing zone contiguous with the anode,
`and an electron injecting and transporting zone contiguous
`with the cathode. Tbe e lectron injecting and transporting
`zone further comprises an electron injocting layer in contact
`with the cathocle. The portion of the organic e lectrolumi(cid:173)
`nescent medium between the the electron injecting layer and
`the hole injecting and transporting zone emits white light in
`response 10 the hole-electron recombination, and comprises
`a fluorescent material and a mixed ligand aluminum chelate.
`Japanese Patent Publication 04289691 of Mitsubishi
`Cable Industries, Ltd., published Oct. 14, 1992, discloses an 60
`e lectroluminescent device comprising a fluorescent dye(cid:173)
`fixed s ilica layer coated with a transparent e lectrode layer, a
`luminescing (light-ernilling) layer containing a pbosphor, a
`backside e lectrode layer, a water-sorbing layer, aa encapsu(cid:173)
`lating film, aad aa insulating layer.
`la the Mitsubishi pa1e(cid:143) 1 publication, the silica layer may
`be formed by a sol gel process using metal alkoxicles in a
`
`10
`
`6
`solvent such as ethanol, isopropaaol, or dimethyl ether. A
`Rhod amine 6G-doped silica layer is described to exhibit
`white luminescence. The lumincscing layer may be for
`example on the o rder of 15 microns in thickness, aad is
`formed by a sol gel technique yielding ZaS or ZnCdS doped
`with a dopant such as copper, aluminum, manganese,
`chlorine, boron, yttrium, o r rare earth dopant. The luminesc(cid:173)
`ing layer may also contain scattered phosphor material. The
`average grain size of grains in the luminescing layer is
`generally greater than 10 microns, and preferably is in the
`range of from 1.5 to 40 microns. TI1e luminescing layer may
`for example contain from 30 to 80% phosphor. A disclosed
`advantage of the foregoing structure is that one ca(cid:143) change
`the phosphor in the luminesciag layer, and thereby change
`the color o f the wbole material.
`Japanese Patent Publica tion 601701 94 of Sony
`Corporation, published Sep. 3, 1985, discloses a white
`light-emiuing electroluminescent device with a luminescent
`layer containing a mixture of a blue-greea-emilli(cid:143) g phos(cid:173)
`phor aad Rhodami(cid:143) e S. Since Rhodarnine S strongly lluo-
`20 resces orange by excitation with a bluish-green ligh t, a white
`light of bigb luminosity may be obtained even at low
`voltage. This reference discloses a phosphor emitting blue(cid:173)
`green light, ia which ZaS .is eloped with Cu and Cl, as well
`as a phosphor emitting yellow light, in which ZnS is eloped
`25 with Cu and Mn. ZnS may also be eloped with Cu and Br to
`produce g reen light.
`The Sooy patent publication d iscloses a multilayer e lec(cid:173)
`troluminescent article, including sealing layers of protective
`film o[ a material such as Aclar polymer, a polyester layer,
`30 a transparent electrode formed of indium tin oxide (ITO), a
`light-emiu i(cid:143) g layer, and a backside e lectrode. The light(cid:173)
`emitting layer may comprise 50-95% by weight of ZnS
`eloped with the aforementioned dopant species (e.g., 0.045%
`wt. Cu, aacl 0 .020% wt. Cl) aacl 5-50% wt. Rboclamine S.
`No t withstanding the progress made in using organic
`Ouorescers as luminesceot sites within either electron(cid:173)
`transport or hole-transport layers and affording thin-film
`interfacial bole-electro(cid:143) recombination, the current state of
`the art finds it clillicull to generate organic based L ED dies
`40 with reasonable operational lifetimes. By their very nature,
`these donor-acceptor complexes arc prone to reaction with
`the surrounding medium. As a result, many of these organic
`molecules degrade UJlcler constant excitatiOCI to the excited
`state aad consequently the organic-based LEDs fail. Those
`45 fluorcsccrs w ith extremely high quantum y ie lds of
`fluorescence, which by definition necessitate s hort excited
`state lifetimes and are unlikely to be quenched o r clegraclecl
`by oxygen or o ther reactants, clo not have suffic ient electro(cid:143)
`or hole transport properties to allow for device-wide local-
`so izecl hole-electro(cid:143)
`recomb inatio n in the ground state.
`However, their proximity to the holes, as clopants in a hole
`transporting layer, as an example, may make the excited
`states o[ tbe luminopbors more easily oxidized tban would
`normally be the case. This would be especially true for
`55 e xc ited state species, even if the ground state of the lumi(cid:173)
`nophors are stable to the holes in the bole-transporting layer.
`Similarly argumen ts regarding excited state reduction would
`be applicable for dopants seq uestered within aa electron-
`transport layer.
`It would be most desirable, then, if a white light emitting
`LED device could be fabricated that took advantage of the
`s imultaneous emission of red, green and blue luminescent
`centers, using both inorganic and organic nuorescers or
`phosphors without requiring theses species 10 be ia proxi-
`65 ma te contact with the transporting layers.
`It is the purpose of the preseat invention to provide wliile
`light solid state luminescent devices using a single die,
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:15)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:27)
`
`(cid:57)(cid:44)(cid:61)(cid:44)(cid:50)(cid:3)(cid:40)(cid:91)(cid:17)(cid:3)(cid:20)(cid:19)(cid:19)(cid:24)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:19)(cid:19)(cid:19)(cid:27)
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`US 6,600,175 Bl
`
`7
`which initially provi.de monochromatic radiation and
`wherein the monochromatic radiation is convened lo poly(cid:173)
`chromatic wh ite light, thus providing a solid state illumina(cid:173)
`tion device with white illuminancc, without the need for
`mu ltiple power leads or for more than one discrete LED
`lamp.
`
`8
`FIG. 2 is a schematic elevational cross-sec1ional view of
`a another white light generating assembly according to
`another cmbodimeot of the invention.
`FIG. 3 is a schematic elcvational cross-sectional view, in
`enlarged scale, of a portion of the device of FIG. 1.
`FIG. 4 is a schematic representation of a display which
`may usefully employ the device of FIGS. 1 and/or 2.
`FIG. 5 is a schematic eleva1ional view of an electrolumi(cid:173)
`nescent cell device according 10 another embodimeat of the
`invention.
`FIG. 6 is a schematic representation o( the generalized
`light emitting assembly of the present invention.
`
`IO
`
`SUMMARY OF THE INVENTION
`The present invention relates broadly to a light emitting
`assembly comprising a solid state device which is s