US20020011780A1 - Organic electroluminescent apparatus - Google Patents
Organic electroluminescent apparatus Download PDFInfo
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- US20020011780A1 US20020011780A1 US09/151,346 US15134698A US2002011780A1 US 20020011780 A1 US20020011780 A1 US 20020011780A1 US 15134698 A US15134698 A US 15134698A US 2002011780 A1 US2002011780 A1 US 2002011780A1
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- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B33/00—Electroluminescent light sources
- H05B33/12—Light sources with substantially two-dimensional radiating surfaces
- H05B33/20—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the material in which the electroluminescent material is embedded
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
- H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
- H10K50/125—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers specially adapted for multicolour light emission, e.g. for emitting white light
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/80—Constructional details
- H10K50/85—Arrangements for extracting light from the devices
- H10K50/852—Arrangements for extracting light from the devices comprising a resonant cavity structure, e.g. Bragg reflector pair
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/80—Constructional details
- H10K59/875—Arrangements for extracting light from the devices
- H10K59/876—Arrangements for extracting light from the devices comprising a resonant cavity structure, e.g. Bragg reflector pair
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/30—Devices specially adapted for multicolour light emission
- H10K59/38—Devices specially adapted for multicolour light emission comprising colour filters or colour changing media [CCM]
Definitions
- the present invention pertains to organic electroluminescent apparatus and more specifically to apparatus for enhancing conversion of blue light to red light.
- LED arrays are becoming more popular as an image source in both direct view and virtual image displays.
- One reason for this is the fact that LEDs are capable of generating relatively high amounts of light (high luminance), which means that displays incorporating LED arrays can be used in a greater variety of ambient conditions.
- reflective LCDs can only be used in high ambient light conditions because they derive their light from the ambient light, i.e. the ambient light is reflected by the LCDs.
- Some transflective LCDs are designed to operate in a transmissive mode and incorporate a backlighting arrangement for use when ambient light is insufficient.
- transflective displays have a certain visual aspect and some users prefer a bright emissive display.
- these types of displays are generally too large for practical use in very small devices such as portable electronic devices.
- OED arrays are emerging as a potentially viable design choice for use in small products, especially small portable electronic devices such as pagers, cellular and portable telephones, two-way radios, data banks, etc.
- OED arrays are capable of generating sufficient light for use in displays under a variety of ambient light conditions (from little or no ambient light to bright ambient light). Further, OEDs can be fabricated relatively cheaply and in a variety of sizes from very small (less than a tenth millimeter in diameter) to relatively large (greater than an inch) so that OED arrays can be fabricated in a variety of sizes. Also, OEDs have the added advantage that their emissive operation provides a very wide viewing angle.
- a problem in the use of OEDs in displays is the generation of the colors necessary to achieve a full color display.
- Red, green and blue OEDs can be fabricated but they require different organic materials and, thus, each color must be fabricated separately.
- the colors achieved are not a pure primary color, but have a relatively broad spectrum.
- Emission of red light is very difficult to achieve in OEDs however, it is known to convert other colors, such as blue light, to red light.
- One such technique is disclosed in Japanese Publication, Kokai Patent No. Hei 8-286033 entitled “Red Emitting Device Using Red Fluorescent Converting Film”, published 1 November 1996. While converting blue light to red light, the efficiency of the conversion is unacceptably low, and the red light contains unacceptable levels of blue green components.
- organic electroluminescent apparatus including an organic electroluminescent device for emitting light having a broad spectrum.
- a color converting medium absorbs light coupled thereto and emits light in response to absorbed light.
- the color converting medium has first and second absorption peaks at first and second wavelengths and emits light at a third wavelength different than the first and second wavelengths.
- a microcavity structure is used to couple emitted light from the organic electroluminescent device to the color converting medium.
- the microcavity structure has a resonance such that the broad spectrum light received from the organic electroluminescent device is enhanced by the microcavity structure to enhanced light having first and second resonant peaks which substantially overlap the first and second absorption peaks, respectfully.
- FIG. 1 is an enlarged and simplified sectional view of organic electroluminescent apparatus in accordance with the present invention
- FIG. 2 is a graphical spectrum representation illustrating a broad spectrum light in relation to the absorption peaks of the color converting medium
- FIG. 3 is a graphical spectrum representation illustrating the enhancement of the broad spectrum light
- FIG. 4 is a graphical spectrum representation illustrating the enhanced broad spectrum light in relation to the absorption peaks of the color converting medium.
- FIG. 1 is an enlarged and simplified sectional view of organic electroluminescent apparatus 10 in accordance with the present invention.
- Organic electroluminescent apparatus 10 includes an organic electroluminescent device (OED), generally designated 11 and a microcavity 12 carried by a transparent substrate 13 , such as glass.
- OED organic electroluminescent device
- Microcavity 12 is positioned in alignment with the light output from OED 11 to enhance the light spectrum.
- OED 11 includes an upper metal electrical contact 15 , an electron transporting layer 16 , a hole transporting layer 17 and a lower electrical contact 18 .
- Upper electrical contact 15 essentially forms a reflective surface to reflect all light generated within OED 11 downwardly.
- Lower electrical contact 18 is formed of some electrically conductive material which is transparent to light generated in OED 11 , such as indium-tin-oxide (ITO) or the like and communicate the OED light output to the remainder of apparatus 10 .
- Electron transporting layer 16 and hole transporting layer 17 define an organic light emitting zone with either or both layers 16 and 17 emitting light in response to the recombination of holes and electrons therein. It will of course be understood that OED 11 could include from one organic layer to several, depending upon the material utilized.
- Microcavity structure 12 is illustrated in FIG. 1 as including OED 11 and a mirror stack 21 .
- Mirror stack 21 includes a plurality of layers of material having different indexes of refraction. The plurality of layers is divided into pairs of layers, one layer of each pair having a first index of refraction and another layer of each pair having a second index of refraction lower than the first index of refraction with each pair of layers cooperating to form a partial mirror and to reflect light.
- the plurality of layers can be formed from a variety of materials including various semi-transparent metals and various dielectrics.
- mirror stack 21 is preferably formed of, for example, alternate layers of TiO 2 and SiO 2 .
- each pair of layers of mirror stack 21 defines a partial mirror with an operating thickness of an integer multiple of one half wavelength of the emitted light so that all reflected light is in phase.
- the combined thickness of organic layers 16 and 17 and lower contact 18 is designed to position mirror stack 21 in spaced relationship from reflective upper contact 15 and define an optical length L 1 of microcavity structure 12 in cooperation with the OED 11 .
- Stack 21 further defines a light output for microcavity structure 12
- the optical length L 1 of microcavity structure 12 is generally designed such that light emitted from the light output has resonant peaks as will be described presently.
- a color converting medium (CCM) 23 is positioned on substrate 13 to receive enhanced light from microcavity structure 12 .
- CCM 23 is positioned on a surface of substrate 13 opposite microcavity structure 12 .
- CCM 23 can be positioned between microcavity structure 12 and substrate 13 .
- efficient RGB light emission can be achieved by combining an organic OED emitter with a CCM device, such as CCM 23 .
- CCM 23 is made up of organic fluorescent media which change the color of emitted light from blue-green to blue, green or red.
- a red fluorescent converting film is made by dispersing a first fluorescent pigment including, for example, rhodamine, and a second fluorescent pigment into a light transmitting medium.
- the first pigment has an absorption range from 450-610 nm and emits red light above 600 nm.
- the second pigment absorbs light in the blue region under 520 nm.
- an efficient CCM film (CCM 23 ) is provided which absorbs light as illustrated by absorption waveform 25 in FIG. 2.
- the light emitted from OED 11 is a broad spectrum light, for example in a blue-green spectrum as illustrated by waveform 27 in FIG. 2. It can be seen from FIG. 2, that the absorption of CCM 23 is not a uniform function of wavelengths, and there exists a valley 26 at approximately 490 nm. It should be noted that the blue-green spectrum emitted by OED 11 has a substantial portion overlying valley 26 . As a result, without the inclusion of microcavity structure 12 , CCM 23 would have to be very thick to absorb the light around 490 nm. Furthermore, if microcavity structure 12 were not employed, a small blue light spectrum component would remain around 490 nm even with a very thick CCM 23 reducing the quality of the emitted red light.
- microcavity structure 12 By employing microcavity structure 12 , the blue-green spectrum emitted by OED 11 is enhanced to resonant peaks as represented by waveforms 30 A and 30 B in FIG. 3, thus giving rise to saturated blue and green colors. This leads to much brighter blue and green colors ( 2 enhancement) when CCM 23 is used.
- the scale of FIG. 3 has been expanded to accommodate waveforms 30 A and 30 B, and waveform 27 . As can be seen by comparing waveform 27 with waveforms 30 A and 30 B, the intensity of the emitted light represented by waveform 27 has been greatly increased at approximately 450 nm and 540 nm, and the component at 490 nm has been greatly reduced. With reference to FIG.
- microcavity structure 12 by tuning microcavity structure 12 resonance to wavelengths near the absorption peaks (about 450 nm and about 540 nm) of CCM 23 , the absorption of blue-green colors can be maximized, which results in a maximum blue-green to red conversion efficiency.
- the broad spectrum light represented by waveform 25 is enhanced to resonant peaks represented by waveforms 30 A and 30 B which overlap absorption peaks 25 A and 25 B of waveform 25 at approximately 450 nm and 540 nm.
- all of the enhanced light from microcavity structure 12 is absorbed by CCM 23 and pure red light is emitted.
- the component of the broad spectrum light emitted by OED 11 corresponding to valley 26 has been shifted by enhancement to an absorbable wavelength (e.g.
Abstract
Description
- The present invention pertains to organic electroluminescent apparatus and more specifically to apparatus for enhancing conversion of blue light to red light.
- Light emitting diode (LED) arrays are becoming more popular as an image source in both direct view and virtual image displays. One reason for this is the fact that LEDs are capable of generating relatively high amounts of light (high luminance), which means that displays incorporating LED arrays can be used in a greater variety of ambient conditions. For example, reflective LCDs can only be used in high ambient light conditions because they derive their light from the ambient light, i.e. the ambient light is reflected by the LCDs. Some transflective LCDs are designed to operate in a transmissive mode and incorporate a backlighting arrangement for use when ambient light is insufficient. In addition, transflective displays have a certain visual aspect and some users prefer a bright emissive display. However, these types of displays are generally too large for practical use in very small devices such as portable electronic devices.
- Organic electroluminescent device (OED) arrays are emerging as a potentially viable design choice for use in small products, especially small portable electronic devices such as pagers, cellular and portable telephones, two-way radios, data banks, etc. OED arrays are capable of generating sufficient light for use in displays under a variety of ambient light conditions (from little or no ambient light to bright ambient light). Further, OEDs can be fabricated relatively cheaply and in a variety of sizes from very small (less than a tenth millimeter in diameter) to relatively large (greater than an inch) so that OED arrays can be fabricated in a variety of sizes. Also, OEDs have the added advantage that their emissive operation provides a very wide viewing angle.
- A problem in the use of OEDs in displays is the generation of the colors necessary to achieve a full color display. Red, green and blue OEDs can be fabricated but they require different organic materials and, thus, each color must be fabricated separately. Furthermore, the colors achieved are not a pure primary color, but have a relatively broad spectrum. Emission of red light is very difficult to achieve in OEDs however, it is known to convert other colors, such as blue light, to red light. One such technique is disclosed in Japanese Publication, Kokai Patent No. Hei 8-286033 entitled “Red Emitting Device Using Red Fluorescent Converting Film”, published 1 November 1996. While converting blue light to red light, the efficiency of the conversion is unacceptably low, and the red light contains unacceptable levels of blue green components.
- Accordingly, it is highly desirable to provide apparatus and a method of converting broad spectrum light to red light.
- It is a purpose of the present invention to provide a new and improved apparatus and a method of generating red light.
- It is a further purpose of the present invention to provide apparatus and a method of efficiently generating red light.
- The above problems and others are at least partially solved and the above purposes and others are realized in organic electroluminescent apparatus including an organic electroluminescent device for emitting light having a broad spectrum. A color converting medium absorbs light coupled thereto and emits light in response to absorbed light. The color converting medium has first and second absorption peaks at first and second wavelengths and emits light at a third wavelength different than the first and second wavelengths. A microcavity structure is used to couple emitted light from the organic electroluminescent device to the color converting medium. The microcavity structure has a resonance such that the broad spectrum light received from the organic electroluminescent device is enhanced by the microcavity structure to enhanced light having first and second resonant peaks which substantially overlap the first and second absorption peaks, respectfully.
- Referring to the drawings:
- FIG. 1 is an enlarged and simplified sectional view of organic electroluminescent apparatus in accordance with the present invention;
- FIG. 2 is a graphical spectrum representation illustrating a broad spectrum light in relation to the absorption peaks of the color converting medium;
- FIG. 3 is a graphical spectrum representation illustrating the enhancement of the broad spectrum light; and
- FIG. 4 is a graphical spectrum representation illustrating the enhanced broad spectrum light in relation to the absorption peaks of the color converting medium.
- DESCRIPTION OF THE PREFERRED EMBODIMENTS
- Turning now to the figures, FIG. 1 is an enlarged and simplified sectional view of organic
electroluminescent apparatus 10 in accordance with the present invention. Organicelectroluminescent apparatus 10 includes an organic electroluminescent device (OED), generally designated 11 and amicrocavity 12 carried by atransparent substrate 13, such as glass.Microcavity 12 is positioned in alignment with the light output from OED 11 to enhance the light spectrum. - In this embodiment, OED11 includes an upper metal
electrical contact 15, anelectron transporting layer 16, ahole transporting layer 17 and a lowerelectrical contact 18. Upperelectrical contact 15 essentially forms a reflective surface to reflect all light generated withinOED 11 downwardly. Lowerelectrical contact 18 is formed of some electrically conductive material which is transparent to light generated inOED 11, such as indium-tin-oxide (ITO) or the like and communicate the OED light output to the remainder ofapparatus 10.Electron transporting layer 16 andhole transporting layer 17 define an organic light emitting zone with either or bothlayers -
Microcavity structure 12 is illustrated in FIG. 1 as including OED 11 and amirror stack 21.Mirror stack 21 includes a plurality of layers of material having different indexes of refraction. The plurality of layers is divided into pairs of layers, one layer of each pair having a first index of refraction and another layer of each pair having a second index of refraction lower than the first index of refraction with each pair of layers cooperating to form a partial mirror and to reflect light. The plurality of layers can be formed from a variety of materials including various semi-transparent metals and various dielectrics. In a typical example,mirror stack 21 is preferably formed of, for example, alternate layers of TiO2 and SiO2. Generally, from 2 to 4 pairs of layers provides a reflectivity of approximately 0.74, which is believed to be optimal for the present purpose. As is understood by those skilled in the art, each pair of layers ofmirror stack 21 defines a partial mirror with an operating thickness of an integer multiple of one half wavelength of the emitted light so that all reflected light is in phase. - The combined thickness of
organic layers lower contact 18 is designed to positionmirror stack 21 in spaced relationship from reflectiveupper contact 15 and define an optical length L1 ofmicrocavity structure 12 in cooperation with the OED 11.Stack 21 further defines a light output formicrocavity structure 12, and the optical length L1 ofmicrocavity structure 12 is generally designed such that light emitted from the light output has resonant peaks as will be described presently. - A color converting medium (CCM)23 is positioned on
substrate 13 to receive enhanced light frommicrocavity structure 12. In this embodiment, CCM 23 is positioned on a surface ofsubstrate 13opposite microcavity structure 12. However, it will be understood thatCCM 23 can be positioned betweenmicrocavity structure 12 andsubstrate 13. Recently it has been demonstrated (see Japanese publication cited above) that efficient RGB light emission can be achieved by combining an organic OED emitter with a CCM device, such asCCM 23. CCM 23 is made up of organic fluorescent media which change the color of emitted light from blue-green to blue, green or red. To achieve an efficient CCM device, a red fluorescent converting film is made by dispersing a first fluorescent pigment including, for example, rhodamine, and a second fluorescent pigment into a light transmitting medium. The first pigment has an absorption range from 450-610 nm and emits red light above 600 nm. The second pigment absorbs light in the blue region under 520 nm. By combining the first and second pigments, an efficient CCM film (CCM23) is provided which absorbs light as illustrated byabsorption waveform 25 in FIG. 2. - The light emitted from OED11 is a broad spectrum light, for example in a blue-green spectrum as illustrated by
waveform 27 in FIG. 2. It can be seen from FIG. 2, that the absorption ofCCM 23 is not a uniform function of wavelengths, and there exists avalley 26 at approximately 490 nm. It should be noted that the blue-green spectrum emitted by OED 11 has a substantialportion overlying valley 26. As a result, without the inclusion ofmicrocavity structure 12,CCM 23 would have to be very thick to absorb the light around 490 nm. Furthermore, ifmicrocavity structure 12 were not employed, a small blue light spectrum component would remain around 490 nm even with a verythick CCM 23 reducing the quality of the emitted red light. - By employing
microcavity structure 12, the blue-green spectrum emitted byOED 11 is enhanced to resonant peaks as represented bywaveforms CCM 23 is used. The scale of FIG. 3 has been expanded to accommodatewaveforms waveform 27. As can be seen by comparingwaveform 27 withwaveforms waveform 27 has been greatly increased at approximately 450 nm and 540 nm, and the component at 490 nm has been greatly reduced. With reference to FIG. 4, by tuningmicrocavity structure 12 resonance to wavelengths near the absorption peaks (about 450 nm and about 540 nm) ofCCM 23, the absorption of blue-green colors can be maximized, which results in a maximum blue-green to red conversion efficiency. The broad spectrum light represented bywaveform 25 is enhanced to resonant peaks represented bywaveforms absorption peaks waveform 25 at approximately 450 nm and 540 nm. Thus all of the enhanced light frommicrocavity structure 12 is absorbed byCCM 23 and pure red light is emitted. The component of the broad spectrum light emitted byOED 11 corresponding tovalley 26 has been shifted by enhancement to an absorbable wavelength (e.g. 450 nm), increasing the light absorbed by the CCM and eliminating small spectrum components produced whenmicrocavity structure 12 is absent. Thus, efficiency is improved while improving the purity of the light emitted, and by thecombination microcavity 12 withCCM 23, it is possible to achieve a higher color-conversion efficiency for blue-green to red, and a brighter RGB display can be readily built based on this approach. - While we have shown and described specific embodiments of the present invention, further modifications and improvements will occur to those skilled in the art.
- We desire it to be understood, therefore, that this invention is not limited to the particular forms shown and we intend in the appended claims to cover all modifications that do not depart from the spirit and scope of this invention.
Claims (12)
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US09/151,346 US6362566B2 (en) | 1998-09-11 | 1998-09-11 | Organic electroluminescent apparatus |
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US09/151,346 US6362566B2 (en) | 1998-09-11 | 1998-09-11 | Organic electroluminescent apparatus |
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GB9910901D0 (en) * | 1999-05-12 | 1999-07-07 | Univ Durham | Light emitting diode with improved efficiency |
JP2002162934A (en) * | 2000-09-29 | 2002-06-07 | Eastman Kodak Co | Flat-panel display with luminance feedback |
KR20040101259A (en) * | 2002-03-06 | 2004-12-02 | 코닌클리케 필립스 일렉트로닉스 엔.브이. | Electronic display device |
US20060044493A1 (en) * | 2004-08-31 | 2006-03-02 | Motorola, Inc. | Highly readable display for widely varying lighting conditions |
US20090015142A1 (en) * | 2007-07-13 | 2009-01-15 | 3M Innovative Properties Company | Light extraction film for organic light emitting diode display devices |
US8179034B2 (en) * | 2007-07-13 | 2012-05-15 | 3M Innovative Properties Company | Light extraction film for organic light emitting diode display and lighting devices |
US8552639B2 (en) * | 2007-11-30 | 2013-10-08 | Samsung Display Co., Ltd. | White organic light emitting device |
US20100110551A1 (en) * | 2008-10-31 | 2010-05-06 | 3M Innovative Properties Company | Light extraction film with high index backfill layer and passivation layer |
US7957621B2 (en) * | 2008-12-17 | 2011-06-07 | 3M Innovative Properties Company | Light extraction film with nanoparticle coatings |
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US5315129A (en) * | 1990-08-20 | 1994-05-24 | University Of Southern California | Organic optoelectronic devices and methods |
US5405710A (en) * | 1993-11-22 | 1995-04-11 | At&T Corp. | Article comprising microcavity light sources |
US5409783A (en) * | 1994-02-24 | 1995-04-25 | Eastman Kodak Company | Red-emitting organic electroluminescent device |
US5478658A (en) * | 1994-05-20 | 1995-12-26 | At&T Corp. | Article comprising a microcavity light source |
US5814416A (en) * | 1996-04-10 | 1998-09-29 | Lucent Technologies, Inc. | Wavelength compensation for resonant cavity electroluminescent devices |
US5949187A (en) * | 1997-07-29 | 1999-09-07 | Motorola, Inc. | Organic electroluminescent device with plural microcavities |
US6140764A (en) * | 1998-07-20 | 2000-10-31 | Motorola, Inc. | Organic electroluminescent apparatus with mircrocavity |
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