Band-edge emission enhanced organic light-emitting diode-based devices emitting multiple light wavelengths

Abstract

A light-emitting photonic crystal, including an organic light-emitting diode, capable of simultaneously emitting light at multiple wavelengths, and a method for fabricating the same are disclosed. The disclosed light-emitting photonic crystal emits light at wavelengths at the two edges of the stop band. A method for tuning the stop band width of the disclosed device is also disclosed.

Description

[Technical Field]

[0001] Inventors: John N. Magno and Gene C. Koch Cross-reference to priority application This application claims the benefit under 35 U.S.C. § 119(e) of the earlier filing dates of U.S. Provisional Patent Application No. 63 / 083,450, filed September 25, 2020, which is incorporated by reference in its entirety, and U.S. Provisional Patent Application No. 63 / 083,496, filed September 25, 2020, which is incorporated by reference in its entirety. [Background technology]

[0002] U.S. Patent Application No. 15 / 738,214, filed December 20, 2017, scheduled to issue October 5, 2021, as U.S. Patent No. 11,139,456, discloses a light-emitting photonic crystal device (referred to as BE-OLED) in which an organic light-emitting diode (OLED) is embedded within a single one-dimensional photonic crystal as a single zone or layer with a quarter-wave optical thickness. Typically, one of the low-index zones of the photonic crystal's alternating low-index / high-index zone structure contains the OLED structure. The function of a BE-OLED device relies on the formation of a "stop band" (also called a band gap) within the photonic crystal. The stop band is a range of optical wavelengths for which there is no solution to the wave equation for light propagation. That is, for these wavelengths, light-emitting molecules embedded in the photonic crystal cannot emit light in the direction of the alternating refractive index within the photonic crystal structure. In a photonic crystal, the central wavelength of the stop band has a value that is four times the optical thickness of each of the high and low refractive index zones within the photonic crystal. [Brief explanation of the drawings]

[0003] The following detailed description refers to the following drawings: [Figure 1] Computer-modeled reflectance spectra of two photonic crystal structures such as those in FIG. 2 are shown. [Figure 2] 1A-1C illustrate photonic crystal structures approximating embodiments of band-edge emission according to the present disclosure and photonic crystal structures approximating embodiments of band-edge emission. [Figure 3] 1 shows computer-modeled reflectance spectra of three photonic crystal structures. [Figure 4] 1 shows computer-modeled reflectance spectra of three photonic crystal structures. [Figure 5] 1 shows two photonic crystal structures that approximate band-edge emission embodiments according to the present disclosure. [Figure 6] 1 shows computer-modeled reflectance spectra of two photonic crystal structures. [Figure 7] 1 shows a photonic crystal structure that approximates a band-edge emitting embodiment of the present invention. [Figure 8] 1 shows computer-modeled reflectance spectra of two photonic crystal structures. [Figure 9] 1 shows a photonic crystal structure that approximates a band-edge emission embodiment of the present invention. [Figure 10] 1 shows computer-modeled reflectance spectra of two photonic crystal structures. [Figure 11] 1 illustrates the refractive index profile of a portion of a layer stack for one embodiment according to the present disclosure. [Figure 12] 1 illustrates aspects of various embodiments according to the present disclosure. [Figure 13] 1 illustrates aspects of various embodiments according to the present disclosure. [Figure 14] 1 shows computer-modeled reflectance spectra of two photonic crystal structures. [Figure 15] 1 shows computer-modeled reflectance spectra of photonic crystal stacks approximating embodiments of band-edge emitting devices according to the present disclosure and using two different methods of tuning the stop-band spectral width. DETAILED DESCRIPTION OF THE INVENTION

[0004] The light-emitting function of BE-OLED devices relies on the fact that in these devices, the edge of the stop band (typically the short-wavelength edge) overlaps with the emission spectral band of the electroluminescent material in the OLED structure. It is a property of photonic crystals that the density of states at the band-edge wavelength of the stop band associated with a photonic crystal is significantly higher than the density of states at the same wavelength in air or vacuum. The result is that the emission of the electroluminescent material is significantly enhanced over emission in other media. In addition, a significant portion of the light emitted in the band-edge states or modes is retained within the photonic crystal structure, illuminating the photoluminescent molecules with high luminous flux within the band-edge wavelength. This intense retained light stimulates additional emission from other molecules of the electroluminescent material that are in an excited state due to electrical excitation. Because light emitted in the band-edge propagation modes is forced to emit within a narrow band-like angle around the normal to the surface of the BE-OLED, and because stimulated emission replicates the propagation mode of stimulated light emission, light is emitted by the BE-OLED within a narrow cone-like angle. Emission within a narrow cone of angles around the surface normal of the BEOLED results in nearly complete outcoupling of light from the BE-OLED, making it much more energy efficient than conventional OLEDs.

[0005] The high energy efficiency and collimated emission of BE-OLEDs are highly desirable for many applications. Additionally, the narrow spectral emission band of these devices can also be highly desirable when highly saturated colors are required for the emission. However, the narrow spectral emission band poses a problem when BE-OLEDs are intended for use in applications requiring white light. Several solutions to this problem have already been explored. One is to place multiple BE-OLEDs adjacent to each other on the same substrate, emitting different colors. The problem with this approach is its manufacturing complexity and the difficulty of creating lamp optics that mix the colors together to produce uniform light chromaticity across the entire range of emission angles. U.S. Patent Application Publication No. 2018 / 0190929 describes a BE-OLED-based device in which a luminescent material is coated on the emitting surface of the BE-OLED that emits shorter wavelength light (e.g., blue or violet). Light from the BE-OLED is absorbed by a photoluminescent material, which generates photoluminescent emission from the material. The photoluminescent material used is capable of emitting white light. In this case, the emission spans a wide cone of angles, which may be undesirable in some applications. Additionally, if some of the shorter wavelength light from the BE-OLED leaks through the white photoluminescent top layer, the uniformity of the emission over the emission angle may be compromised. If a sufficient thickness of white photoluminescent material is coated to eliminate leakage of the BE-OLED emission, light absorption within the photoluminescent material may impair the energy efficiency of the device.

[0006] There is a need for BE-OLED-based devices that emit light at multiple wavelengths (eg, white light) within a narrow cone of angles and have uniform chromaticity over the range of emission angles.

[0007] U.S. Patent Application Publication No. 2018 / 0183007 discloses that band-edge emission enhanced organic light-emitting diodes (BE-OLEDs) can be fabricated with organic layers (e.g., layer 710 in FIG. 7 thereof) preferably having the same optical thickness λ / 4 as other material layers in the device, where λ is the center wavelength of the stop band created by the periodic structure of the BE-OLED. Device 250 depicted in FIG. 2 is such a device.

[0008] It has been found that BE-OLED devices can have organic layers as well as layer thicknesses of 3λ / 4. The reason for potentially incorporating such thicker organic layers into the device is that the thicknesses of the organic sublayers in layer 710 are primarily determined by electronic considerations in optimizing OLED performance. This is particularly important for blue-emitting devices, as the optical constraints of having relatively thin organic layers can conflict with the sublayer thicknesses required for optimal OLED performance.

[0009] It can be seen that layers 214 and 216 have the same spatial relationship to one another (in terms of optical thickness), as do layers 220 and 218. These layers also have the same phase relationship to one another. For this reason, the optical stack of device 200 functions as a single photonic crystal, producing a stop band with two band edges, in a manner similar to the optical stack of device 250. For similar reasons, devices having optical stacks including layers with thicknesses of 5λ / 4 and 7λ / 4, as well as 3λ / 4, also function as a single photonic crystal.

[0010] Surprisingly, we have learned that incorporating layers with greater optical thickness has significant performance advantages over thinner layers in BE-OLED structures. Adding layers with thicknesses of 3λ / 4 or 5λ / 4 narrows the width of the stop band created in the BE-OLED. By using thicker layers, the stop band of the BE-OLED can be narrowed sufficiently so that it can be used to emit two wavelengths of light, one at each end of the stop band.

[0011] FIG. 1 shows a computer-simulated optical reflectance spectrum 100 approximating a BE-OLED 200 having the structure shown in FIG. 2. The organic layer 202, with an optical thickness of 382.5 nm (physical thickness = 213 nm) and a refractive index of 1.77, has an optical thickness of 3λ / 4 compared to the center or design wavelength of the BE-OLED photonic crystal stack at 510 nm. The reflectance spectrum of this device (solid line) is plotted against the reflectance spectrum (dashed line) of a comparable device 250 (prior art from U.S. Patent Application No. 2018 / 0183007) with an organic layer optical thickness of λ / 4. The stop band narrows from approximately 167 nm wide to 132 nm wide. Thus, in the illustrated embodiment, the sidebands of the stop band, which peak at approximately 438 nm and 610 nm, are more reflective than devices with thinner organic layers.

[0012] Thicker organic layers, having an optical thickness of 5λ / 4, can be used in the device, resulting in a further reduction in the width of the stop band, as shown in FIG. 3, which is a plot 300 of the computer-modeled reflectance spectrum of the resulting device, compared to the modeled spectra of devices with organic layer thicknesses of λ / 4 and 3λ / 4.

[0013] FIG. 4 shows a plot 400 of the simulated reflectance spectra of structures 510 and 520 shown in FIG. 5 and compares it with the spectrum of structure 250. Structure 510 is similar to structure 250, except that the two n=1.39 (low refractive index) layers closest to the organic layers are thickened to 276 nm (3λ / 4 optical thickness). Structure 520 is similar to structure 200, except that the two n=1.39 (low refractive index) layers closest to the organic layers (n=1.77) are thickened to 276 nm (3λ / 4 optical thickness). From FIG. 4, it can be seen that increasing the thickness of the layers other than the organic layers from λ / 4 to 3λ / 4 also helps reduce the width of the stop band of the BE-OLED device.

[0014] Figure 6 shows the simulated reflectance spectrum of structure 710 shown in Figure 7 and compares it with the spectrum of structure 510. Structure 710 is similar to that of 510, except that the two additional n = 1.39 layers closest to the organic layer (n = 1.77) are thickened to 276 nm (3λ / 4 optical thickness). Adding the two additional n = 1.77 layers further reduces the width of the photonic stop band.

[0015] Figure 8 shows the simulated reflectance spectrum of structure 910 shown in Figure 9 and compares it with the spectrum of structure 250. Structure 910 is similar to structure 250, except that two of the n = 1.39 layers in structure 250 have been thickened from 92 nm to 674 nm (7λ / 4 optical thickness). As expected, this modification narrows the width of the stop band.

[0016] Another approach to narrowing the stop band width of a light-emitting photonic crystal is to modify the profile of the periodically varying refractive index crystals in a photonic crystal multilayer stack. Figure 10 shows the effect on the reflectance spectrum of a light-emitting photonic crystal containing alternating layers of magnesium fluoride and titanium dioxide, built around an OLED structure, of varying the ratio of the thickness "a" of the low-index (magnesium fluoride, refractive index A) layer to the thickness "b" of the high-index (titanium dioxide, refractive index B) layer, without changing the profile period from λ / 2. Figure 11 shows the refractive index profile of the layer stack for a ≠ b. The reflectance spectra for a = b = 0.25λ, a = 0.35λ and b = 0.15λ, and a = 0.39λ and b = 0.11λ are shown in Figure 10. It is clear that by changing "a" from 0.25λ to 0.39λ, the width of the stop band decreased by more than 30 nm.

[0017] In the description of embodiments of the present invention so far, it has been assumed that the layers comprised by the structures built on either side of the OLED structure within the single light-emitting photonic crystal each contain only two materials, one with a high refractive index and one with a low refractive index. It may be advantageous to interpose one or more intermediate refractive index layers between the higher and lower refractive index layers in the design of the single light-emitting photonic crystal.

[0018] If it is desired to produce a light-emitting device that generates light from only one (front) surface, a reflector, e.g., a metallic reflector, can be fabricated either between the single light-emitting photonic crystal and the substrate on which it is constructed, or on the opposite surface. If a metallic reflector is used, care should be taken that the metallic reflector introduces a quarter wave shift in the phase of the light, and therefore the layer directly adjacent to the metal surface should have an optical thickness increased by a thickness addition equal to λ / 4.

[0019] The organic layers within a single light-emitting photonic crystal according to the present disclosure need not be centered in the stack of layers that make up the single light-emitting photonic crystal, and may in fact be adjacent to the metallic reflector, if used, which may then function as an electrode or component of an electrode in the device.

[0020] 12 shows another embodiment 1200 according to the present disclosure. The BE-OLED 1202 includes a conventional OLED. The conventional OLED includes an anode 1218a, which may be composed of a transparent conductive oxide (such as indium tin oxide or indium zinc oxide); and a cathode, which may comprise, in order, a transparent conductive oxide layer 1218b and a very thin, low work function metal layer 1216. Other transparent anode and cathode structures can be used as long as the BE-OLED optical structure is not compromised. A conventional OLED structure may further comprise a hole injection layer 1206, a hole transport layer 1208, a layer comprising an electroluminescent material 1210, an electron transport layer 1212, and an electron injection layer 1216. A conventional OLED structure may further comprise a hole blocking layer, an electron blocking layer, or an exciton blocking layer (not shown).

[0021] In embodiment 1200, BE-OLED 1202 is constructed on substrate 1234 by first depositing a specularly reflective metal layer 1226 thereon. (The presence of this reflector 1226 is optional, depending on whether dual-sided emission from the device is desired.) Next, a pair of transparent material layers 1224 is constructed on reflective layer 1226. First, layer 1228 of transparent material having a relatively high refractive index is constructed on layer 1226, and then a relatively low refractive index layer 1242 is constructed on layer 1228. Unlike layer 1242 and the other optically functional refractive index zones constructed by BE-OLED 1202, layer 1228 may have an optical thickness of half the center wavelength of the stop band created by the photonic crystal structure within BE-OLED 1202. This half-wave thickness is intended to compensate for the phase shift that occurs in the light waves reflected from metal layer 1226. Meanwhile, another low-index layer 1242, made of the material of pair 1224, has an optical thickness of one-quarter the center wavelength of the stop band created by the photonic crystal structure in BE-OLED 1202. The layer pairs in the structure of device 1200 are described by reading Figure 12 from right to left. Therefore, we refer to layer pair 1224 as a high / low index layer pair.

[0022] Four more high / low refractive index layer pairs 1220 are constructed on pair 1224. These layer pairs each include a relatively high refractive index layer 1232 and a relatively low refractive index layer 1230. Layers 1230 and 1232 all have optical thicknesses equal to one-quarter of the central wavelength of the stop band created by the photonic crystal structure in BE-OLED 1202. Next, the layers of a conventional OLED structure are constructed in the following order: 1218a, 1206, 1208, 1210, 1212, 1214, 1216, and 1218b. Electrode layers 1218a and 1218b each have an optical thickness equal to one-quarter of the central wavelength of the stop band created by the photonic crystal structure in BE-OLED 1202. The other OLED layers 1206, 1208, 1210, 1212, 1214, and 1216 combine to create a single low-index zone 104 with an optical thickness equal to one-quarter of the center wavelength of the stop band created by the photonic crystal structure in the BE-OLED 1202. Five additional low / high-index layer pairs 1222 are constructed on top of the cathode layer 1218b. Like layer pair 1220, layer pair 1222 includes a relatively low-index layer 1230 and a relatively high-index layer 1232. All layers in layer pair 1222 have an optical thickness equal to one-quarter of the center wavelength of the stop band created by the photonic crystal structure in the BE-OLED 1202. The OLED structure 1204 and its associated electrodes need not be centered within the photonic crystal 1202 and may, in fact, be located adjacent to the reflector 1226, as long as the function of the BE-OLED 1202 is not adversely affected.

[0023] The layers of zone 1204, when added together, create a single, relatively low-index zone with an optical thickness equal to one-quarter of the center wavelength of the stopband created by the photonic crystal structure in BE-OLED 1202, so that the BE-OLED actually functions as a single photonic crystal. In exemplary embodiment 100, there are five high / index pairs on one side of a conventional OLED structure and five low / high index pairs on the other side. Configurations with fewer or more alternating index layers are possible and may be advantageous.

[0024] Device 1200 further includes a second 1-D photonic crystal structure 1250 built on top of BE-OLED 1202. To create photonic crystal 1250, five more low / high index layer pairs 1238 are first built on top of the last low / high index layer pair 1222 of BE-OLED 1202. These layer pairs include a relatively low index layer 1244 and a relatively high index layer 1246. Next, a relatively low index layer 1236 containing a photoluminescent material is built on top of the stack of layer pairs 1238. Finally, five more high / low index layer pairs 1240 are built on top of layer 1238. These index layer pairs 1240 also include a relatively low index layer 1244 and a relatively high index layer 1246. All layers of photonic crystal structure 1234 (1244, 1246, and 1236) have the same optical thickness, which is one-quarter of the desired center wavelength of the stop band of photonic crystal structure 1234.

[0025] When the device 1200 is energized, electrons flow from the cathode layer 1218b toward the center of the OLED structure 1204, and holes flow from the anode layer 1218a toward the same location. The electrons and holes meet in the emissive layer 1210, forming excitons on the molecules of the electroluminescent material. The layer thicknesses in the BE-OLED structure are selected so that one of the band edges of the photonic crystal stop band overlaps the emission band wavelength of the electroluminescent material. In most cases, the band edge at the short wavelength end of the stop band is selected to overlap the electroluminescent band. This not only allows the layers in the BE-OLED to be thicker and easier to fabricate, but also allows the OLED structure to include organic layers with functional thicknesses. The electroluminescent material is forced to emit light into band edge modes due to the optical environment within the photonic crystal. The light emitted into the band edge modes accumulates within the photonic crystal structure so that there is sufficient emission intensity in the emissive layer to stimulate emission from excitons on the emissive molecules as quickly as the excitons form. Since light emitted into band-edge modes propagates perpendicular to the plane of the layers in the device, light from stimulated emission does the same.

[0026] By varying the number of layer pairs in the BE-OLED structure and varying the refractive index difference between adjacent layers, the amount of light that escapes from the BE-OLED photonic crystal structure can be controlled. Light that escapes toward reflector 1226 is reflected back into the BE-OLED structure. Light that escapes in the opposite direction enters photonic crystal structure 1250. In addition, varying the number of layer pairs in the BE-OLED changes the width of the stop band and, therefore, the wavelengths at which the two band edges occur. Increasing the number of layer pairs decreases the width of the stop band.

[0027] The layer thicknesses in structure 1250 create a photonic crystal structure with a stop band at longer wavelengths than the light emitted by BE-OLED 1202, so that light emitted from BE-OLED 1202 passes relatively unimpeded through the first five layer pairs in structure 1250. For example, the light emitted by BE-OLED 1203 may be violet or blue light, while the short wavelength band edge of photonic crystal structure 1250 may be in the yellow portion of the visible spectrum.

[0028] The photoluminescent material in layer 1236 is selected so that its excitation spectrum overlaps with the emission band of BE-OLED 1202. Light entering layer 1236 from BE-OLED 1202 is absorbed, to some extent, by the photoluminescent material in layer 1236, thus forming excitons on the luminescent molecules. The thicknesses of the layers in structure 1250 are selected so that the band edge at the short wavelength end of the stop band of photonic crystal 1250 overlaps with the emission spectrum of the photoluminescent material in layer 1236. This material is therefore forced to emit its photoluminescent emission in the band edge modes associated with photonic crystal 1250. As with BE-OLED 1202, a portion of the light emitted by layer 1236 accumulates within structure 1250, stimulating further emission from the photoluminescent molecules in layer 1236. Light emitted backward from structure 1250 toward structure 1202 is reflected back by that structure or by reflector 1226. Light that is not retained within structure 1234 exits surface 1248 as a narrow, cone-shaped beam of light. The chromaticity or color temperature of light exit surface 1248 can be controlled by varying the concentration of photoluminescent material within layer 1236. The photoluminescent material can be present throughout the entire thickness of layer 1236 or in thinner sublayers within layer 1236. The photoluminescent material can also be present in two or more layers, with the photoluminescent material being in the center of structure 1250.

[0029] The light emitted by BE-OLED 1202 can be blue or violet light, and the light emitted by structure 1250 can be yellow light, in which case the light emitted from device 1200 is perceived as white light.

[0030] It is readily apparent that structure 1234 could alternatively be placed between BE-OLED 1202 and reflector 1226, with appropriate layer thickness tolerances for optical phase shift in reflector 1226, and if the photonic crystal comprised of BE-OLED does not reflect back the light emitted by layer 1236. Also, the configuration of OLED 1204 could be inverted with a cathode-facing reflector 1226 and an anode-facing structure 1250. It is also readily apparent that a second photonic crystal similar to structure 1250 could be constructed on surface 1248, but this third structure would emit light at a different wavelength than structures 1202 and 1234. For example, BE-OLED 1202 could emit blue light, structure 1250 could emit green light, and both the blue and green light could pump or excite photoluminescent molecules in the third structure into an additional third set of band-edge modes of the third photonic crystal, resulting in the emission of red light. The combined blue, green, and red emissions are perceived as white light, i.e., light whose chromaticity coordinates in the CIE 1931 2° XYZ color space lie in the rectangle defined by x=0.25 to 0.5 and y=0.2 to 0.45 on the chromaticity diagram of the CIE 1931 2° XYZ color space.

[0031] 13 shows another embodiment of the present invention 1300. The device includes a BE-OLED structure 1302 similar to structure 1202 described above, except for the addition of a layer 1324 of photoluminescent material. Like BE-OLED 1202, BE-OLED 1302 includes a conventional OLED. A conventional OLED includes an anode 1318a, which may be composed of a transparent conductive oxide (such as indium tin oxide or indium zinc oxide); and a cathode, which may comprise, in order, a transparent conductive oxide layer 1318b and a very thin, low work-function metal layer 1316. Other transparent anode and cathode structures can be used as long as the BE-OLED optical structure is not compromised. A conventional OLED structure may further comprise a hole injection layer 1306, a hole transport layer 1308, a layer comprising an electroluminescent material 1310, an electron transport layer 1312, and an electron injection layer 1316. A conventional OLED structure may also further comprise a hole blocking layer, an electron blocking layer, or an exciton blocking layer (not shown).

[0032] The BE-OLED 1302 is constructed on a substrate 1328 by first depositing a specularly reflective metal layer 1326 on the substrate 1328. (The reflector 1326 is optional, depending on whether double-sided emission from the device is desired.) A layer 1332 of transparent material is constructed on the reflective layer 1326. Unlike the other optically functional refractive index zones constructed by the BE-OLED 1302, layer 1332 may have an optical thickness of half the central wavelength of the stop band created by the photonic crystal structure within the BE-OLED 1302. This half-wave thickness is intended to compensate for the phase shift that occurs in the light waves reflected from the metal layer 1326.

[0033] Four refractive index layer pairs 1320 are constructed on layer 1332. Each of these layer pairs includes a relatively low refractive index layer 1336 and a relatively high refractive index layer 1338. Layers 1336 and 1338 all have an optical thickness equal to one-quarter of the center wavelength of the stop band created by the photonic crystal structure in BEOLED 1302. The refractive index layer pairs in the structure of device 1300 are described by reading FIG. 13 from right to left. Therefore, we refer to layer pair 1320 as a low / high refractive index layer pair.

[0034] Next, layer 1324, which includes a photoluminescent material, is constructed on top of the final refractive index layer pair 1320. This layer 1324 has a relatively low refractive index compared to the layers on either side of it. High / low refractive index layer pair 1322, including layers 1338 and 1336, is then constructed on top of layer 1324.

[0035] Next, the layers of a conventional OLED structure are constructed in the following order: 1318a, 1306, 1308, 1310, 1312, 1314, 1316, and 1318b. Electrode layers 1318a and 1318b each have an optical thickness equal to one-quarter of the center wavelength of the stop band created by the photonic crystal structure in BE-OLED 1302. The other OLED layers 1306, 1308, 1310, 1312, 1314, and 1316 combine to create a single low-index zone 1304 with an optical thickness equal to one-quarter of the center wavelength of the stop band created by the photonic crystal structure in BE-OLED 1302. Five additional low / high-index layer pairs 1320 are constructed on top of cathode layer 1318b. All layers of layer pair 1320 and 1322 have an optical thickness equal to one-quarter of the center wavelength of the stop band produced by the photonic crystal structure in BE-OLED 1302. OLED structure 1304 and its associated electrodes need not be centered within photonic crystal 1302, and in fact may be located adjacent to reflector 1326, so long as the function of BE-OLED 1302 is not adversely affected.

[0036] When the layers of zone 1304 are added together, a single relatively low refractive index zone is produced with an optical thickness equal to one-quarter of the central wavelength of the stop band produced by the photonic crystal structure within BE-OLED 1302, so that BE-OLED 1302 actually functions as a single photonic crystal.

[0037] When the device 1300 is energized, electrons flow from the cathode layer 1318b toward the center of the OLED structure 1304, and holes flow from the anode layer 1318a toward the same location. The electrons and holes meet in the emissive layer 1310, forming excitons on the molecules of the electroluminescent material. The layer thicknesses in the BE-OLED structure are selected so that the band edge at the short-wavelength end of the photonic crystal's stop band overlaps the emission band wavelength of the electroluminescent material. The electroluminescent material is forced to emit light into band-edge modes due to the optical environment within the photonic crystal. The light emitted into the band-edge modes accumulates within the photonic crystal structure such that there is sufficient emission intensity in the emissive layer to stimulate emission from excitons on the emissive molecules in layer 1310 as quickly as the excitons form. Because the light emitted into the band-edge modes propagates perpendicular to the layer plane in the device, light from stimulated emission does the same.

[0038] Light from emissive layer 1310, held within the photonic crystal structure of device 1300, is absorbed, to some extent, by the photoluminescent material in layer 1324, creating excitons that attenuate light generation. The photoluminescent material in layer 1324 is selected so that its emission spectrum overlaps the long-wavelength band edge of the stop band of the photonic crystal comprised by device 1300. The photoluminescent material in layer 1324 is thereby forced to emit light only into the band edge modes of the photonic crystal. As with the light generated in layer 1310, the light emitted into the band edge modes accumulates within the photonic crystal structure such that there is sufficient emission intensity in that layer to stimulate emission from excitons on the emissive molecules in layer 1324 as quickly as the excitons form. Because light emitted into the band edge modes at the long-wavelength band edge propagates perpendicular to the plane of the layers in the device, light from stimulated emission in layer 1324 does the same.

[0039] Because the emission of device 1300 occurs at both band edges of the stop band, device 1300 emits at two distinct wavelengths. For example, a device can be fabricated that emits violet or blue light in the short-wavelength band edge mode and red light in the long-wavelength band edge mode. By varying the concentration of photoluminescent material in layer 1324, the ratio of the amount of short-wavelength light to the amount of long-wavelength light generated can be varied.

[0040] By varying the number of layer pairs in the BE-OLED structure 1300 and varying the refractive index difference between adjacent layers, the amount of light retention in the BE-OLED photonic crystal structure can be controlled. (We learned that varying the number of layer pairs can alter the width of the stop band created by the photonic crystal. Surprisingly, we found that adding more layer pairs narrows the spectral width of the stop band. Thus, by adjusting the layer thickness and number of layer pairs, we can tune the width of the stop band in a predictable and controllable manner not previously appreciated. If the layer thickness was varied in multiples of λ / 2, increasing the layer thickness would be expected to have no effect.) In the device 1300 of FIG. 13 , the photoluminescent layer 1324 is located between the OLED structure 1304 and the reflector 1326. It is readily apparent that layer 1324 could alternatively be placed between the OLED structure 1304 and the light-emitting surface 1330. Also, the configuration of the OLED 1304 could be inverted, with the reflector 1326 facing the cathode and the light-emitting surface 1330 facing the anode.

[0041] In a variation of BE-OLED structure 1300, the second emissive material in the device, equivalent to that in layer 1324 of FIG. 13, emits light, at least to some extent, through electroluminescence rather than photoluminescence. To achieve this, the second material must be located in close proximity to the electroluminescent material in layer 1310 and therefore is not located in a separate layer, such as layer 1324, which optically functions as a separate quarter-wave thick layer of the device. In most cases, there will be a separate, very thin layer comprising the second electroluminescent material and one or more host materials located directly adjacent to emitter layer 1310. Alternatively, the second electroluminescent material may actually be constituted by layer 1310 or may be in a layer separated from layer 1310 by another, very thin layer. In either case, layer 1310, the layer containing the second light-emitting material, and other associated layers of organic materials that function similarly to layers 1306, 1308, 1312, 1314, and 1316 must still combine to form a single low refractive index zone having a thickness equal to one-quarter of the center wavelength of the stop band created by the photonic crystal structure in BE-OLED 1302.

[0042] In this alternative version of device 1300, the molecules of the second electroluminescent material are energized to emit light when excited-state energy is transferred from the first electroluminescent material in layer 1310 to the molecules by Förster-type (dipole-dipole bond-mediated) or Dexter-type (electron transfer-mediated) exciton transfer, although some energy transfer through emission by the electroluminescent material in layer 1310 and absorption by the second electroluminescent material may also be possible. As with the emissive material in layer 1324, the second electroluminescent material is selected so that its emission spectrum overlaps the long-wavelength band edge of the stop band of the photonic crystal comprised by device 1300. The second electroluminescent material is thereby forced to emit light only into the band edge modes of the photonic crystal. As with the light generated in layer 1324, the light emitted into the band edge modes accumulates within the photonic crystal structure such that there is sufficient emission intensity in that layer to induce emission from excitons on the emissive molecules in the layer comprising the second emissive material as rapidly as exciton formation. As with device 1300, light is emitted in both long and short wavelength emission bands on either side of the stop band of the device.

[0043] 14 shows yet another embodiment of the present invention, device 1400. Device 1400 combines the functionality of device 1200 with the functionality of device 1300, resulting in a device that can emit light at three wavelengths, for example, red, green, and blue.

[0044] The structure of BE-OLED 1402 is essentially the same as that of device 1300. Layers, layer pairs 1420 and 1422, and electrodes 1418a and 1418b in structure 1404 all serve the same functions as the equivalent structures found in device 1300: layers, layer pairs 1320 and 1322, and electrodes 1318a and 1318b in structure 1304. Photonic crystal structure 1440 functions in essentially the same manner as structure 1250 in device 1200. Layer pairs 1444 and 1446, and layer 1442 serve essentially the same purpose as layer pairs 1238 and 1240, and layer 1236 in device 1200.

[0045] When the device 1400 is energized, electrons flow from the cathode layer 1418b toward the center of the OLED structure 1404, and holes flow from the anode layer 1418a toward the same location. The electrons and holes meet in the emissive layer 1410, forming excitons on the molecules of the electroluminescent material. The layer thicknesses in the BE-OLED structure are selected so that the band edge at the short-wavelength end of the photonic crystal's stop band overlaps the emission band wavelength of the electroluminescent material. The electroluminescent material is forced to emit light into band-edge modes due to the optical environment within the photonic crystal. The light emitted into the band-edge modes accumulates within the photonic crystal structure such that there is sufficient emission intensity in the emissive layer to stimulate emission from excitons on the emissive molecules in layer 1410 as quickly as the excitons form. Because the light emitted into the band-edge modes propagates perpendicular to the plane of the layers in the device, light from stimulated emission does the same.

[0046] Light from emissive layer 1410, held within the photonic crystal structure of BE-OLED 1402, is absorbed, to some extent, by the photoluminescent material in layer 1424, creating excitons that attenuate light generation. The photoluminescent material in layer 1424 is selected so that its emission spectrum overlaps the long-wavelength band edge of the stop band of the photonic crystal formed by structure 1402. The photoluminescent material in layer 1424 is thereby forced to emit light only into the band edge modes of the photonic crystal. As with the light generated in layer 1410, the light emitted into the band edge modes accumulates within the photonic crystal structure such that there is sufficient emission intensity in that layer to stimulate emission from excitons on the emissive molecules in layer 1424 as quickly as the excitons form. Because light emitted into band edge modes at the long-wavelength band edge propagates perpendicular to the plane of the layers in the device, light from stimulated emission in layer 1424 does the same. The photoluminescent material may be present throughout the entire thickness of layer 1424, or may be present in thinner sublayers within layer 1424. By varying the number of layer pairs in BE-OLED structure 1402 and varying the refractive index difference between adjacent layers, the amount of light that escapes from the BE-OLED photonic crystal structure can be controlled. Light that escapes toward reflector 1426 is reflected back into BE-OLED structure 1402. Light that escapes in the opposite direction enters photonic crystal structure 1440.

[0047] The layer thicknesses in structure 1440 are selected to create a photonic crystal structure that has a stop band at wavelengths longer than the two wavelengths of light emitted by BE-OLED 1402. Thus, light exiting BE-OLED 1402 passes relatively unimpeded through the first five layer pairs in structure 1440.

[0048] The photoluminescent material in layer 1442 is selected so that its excitation spectrum overlaps with one or both of the emission bands of BE-OLED 1402. Light entering layer 1442 from BE-OLED 1402 is absorbed, to some extent, by the photoluminescent material in layer 1436, thus forming excitons on the luminescent molecules. The thicknesses of the layers in structure 1440 are selected so that the band edge at the short wavelength end of the stop band of photonic crystal 1440 overlaps with the emission spectrum of the photoluminescent material in layer 1442. This material is therefore forced to emit its photoluminescent emission in the band edge modes associated with photonic crystal 1440. As with BE-OLED 1402, a portion of the light emitted by layer 1442 accumulates within structure 1440, stimulating further emission from the photoluminescent molecules in layer 1442. Light emitted backward from structure 1440 toward structure 1402 is reflected back by reflector 1426. Light that is not retained within structure 1440 exits surface 1430 as a narrow, cone-shaped beam of light. The chromaticity or color temperature of light exit surface 1430 can be controlled by varying the concentration of photoluminescent material in layers 1424 and 1442. The photoluminescent material can be present throughout the entire thickness of layer 1442 or in thinner sublayers within layer 1442. The photoluminescent material can also be present in two or more layers in the center of structure 1440.

[0049] As with device 1300, an alternative variation of device 1400 may omit layer 1424, replacing it with a second electroluminescent material proximate layer 1410. This material also emits light in band-edge modes at the long wavelength edge of the stop band of the photonic crystal structure of layer assembly 1402.

[0050] In device 1400, the primary source of excitons in structure 1402 is the emissive material with the shortest emission wavelength of the three emissive materials used in the device. Because short-wavelength (e.g., blue or violet) emitters are sometimes the least efficient, and the human eye's greatest sensitivity is at green to yellow wavelengths, it may be desirable for the primary source of excitons in an RGB light-emitting device to be an emissive material that emits in the green to yellow wavelength range. An RGB light-emitting device that meets this requirement could consist of a conventional blue-emitting BE-OLED overlaid with a green- and red-emitting BE-OLED having the structure of embodiment 1300.

[0051] In describing embodiments 1200, 1300, and 1400, when referring to emissive or electroluminescent materials, the term material is not meant to be limited to substances containing a single molecular species. There has been considerable recent progress in the development of electroluminescent exciplexes containing multiple molecular species, and the term material is meant to describe these electroluminescent materials, as well as other electroluminescent materials containing multiple molecular species, as a single emissive molecular species.

[0052] It is clear that the spectral distribution output wavelengths of Embodiments 1300 and 1400 strongly depend on the width of the stop band generated by the photonic crystal structure. The square wave profile of the structure in Embodiments 1200, 1300, and 1400 results in a spectrally fairly wide stop band exceeding 200 nm. A strategy for narrowing the spectral width of the stop band is to change the refractive index alternating profile. As discussed above, the graph shown in FIG. 11 shows a method for narrowing the width of the stop band in the photonic crystal of the present invention. This figure shows a plot of refractive index versus thickness of an alternative refractive index profile 1102 of the photonic crystal. The period of the refractive index variation remains λ / 2, where λ is the central wavelength of the photonic crystal stop band. However, the optical thickness a of the low refractive index layer of Material A is λ / 4 < a < λ / 2, and the thickness b of the high refractive index layer of the material is 0 < b < λ / 4. FIG. 5 shows the reflection from the computer-simulated photonic crystal structure versus wavelength for the varying ratio of layer thickness a to layer thickness b (a + b = 0.50). It is clear that as the ratio of a to b increases, the width of the stop band generated by the photonic crystal structure of the BE-OLED decreases. These simulations were generated using a refractive index of 1.39 for the low refractive index material (e.g., MgF2) and 2.36 for the high refractive index material (e.g., TiO2) because the limits of the modeling program for the refractive indices of the cathode transparent metal oxide layer and the anode transparent metal oxide layer were also set to 2.36 and the organic layer was modeled as having a uniform refractive index of 1.80.

[0053] Another approach to narrowing the spectral width of the stop band produced by the photonic crystal structure of a BE-OLED is to increase the thickness of one or more of the layers of the photonic crystal structure, which have an optical thickness of λ / 4, by λ / 2, as discussed above and demonstrated, for example, in FIG. 1 , resulting in layers with optical thicknesses of 3λ / 4, 5λ / 4, or 7λ / 4. This may also prove useful when producing blue-emitting BE-OLED structure 1402 in device 1400, because increasing the thickness of organic layer 1404 provides more freedom in selecting sublayer thicknesses to optimize the device's electronic function. The approach of varying the ratio of a to b may also be combined with the approach of increasing layer thicknesses by λ / 2. For example, results for a device with an organic layer optical thickness of 3λ / 4, or 375 nm, and a = 0.39 and b = 0.11 are plotted in FIG. 15 . For comparison, the reflectance band of this device is plotted against a device with a = b = 0.25 and an organic layer optical thickness of λ / 4.

[0054] Figure 16 shows the combined reflectance spectrum of a light-emitting device similar to device 1400 of Figure 14. Light is emitted in three photonic crystal band-edge emission bands A, B, and C.

[0055] In various embodiments, the organic light emitting diode device includes a single light emitting photonic crystal further comprising an organic electroluminescent emitter material disposed within the single light emitting photonic crystal, the electroluminescent emitter material being localized in a zone having an optical thickness less than 10% of the total optical thickness of the photonic crystal. In these embodiments, the organic electroluminescent emitter material has a free-space emission spectrum that at least partially overlaps with a stop band of the photonic crystal, and the photonic crystal emits light at a wavelength corresponding to the edge of the stop band that the organic electroluminescent emitter material overlaps. Also in these embodiments, the single light emitting photonic crystal is composed of a stack of layers of varying refractive index, with the lower refractive index layers comprising the organic electroluminescent emitter material.

[0056] In various embodiments of light-emitting devices according to the present disclosure, the lower refractive index layers in the first single light-emitting photonic crystal that include an organic electroluminescent emitter material may also include additional organic materials that each have a lower refractive index relative to an adjacent layer, and the organic materials are at least one of a charge carrier transport material, a charge carrier injection material, or a charge carrier injection material.

[0057] In various embodiments of light-emitting devices according to the present disclosure, the organic light-emitting diode device includes a single light-emitting photonic crystal that includes a stack of layers with a periodic modulation of refractive index with a period of λ / 2, where λ is equal to the center wavelength of the photonic crystal stop band. This modulation is uniformly periodic in terms of the layers' optical thickness, not in terms of their physical thickness. The layers configured with one modulation period can be two in number and of the same thickness, but the layers can be two in number and of different optical thickness, resulting in a narrower stop band. There may also be more than two layers configured with one optical thickness modulation period.

[0058] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may include one or more material layers having an optical thickness equal to (2n+1)λ / 2, where n can have a value between 1 and 3, and λ is equal to the center wavelength of the photonic crystal stop band. The presence of these layers does not prevent the stack of layers from functioning as a single photonic crystal, but serves to narrow the width of the photonic crystal stop band. One to seven of these (2n+1)λ / 2-thick layers may be introduced, depending on the required reduction in stop band width and the total number of these layers in the photonic crystal. One of the (2n+1)λ / 2-thick layers may include an organic electroluminescent emitter material.

[0059] In various embodiments of light emitting devices according to the present disclosure, a single light emitting photonic crystal included in an organic light emitting diode device may include a distributed Bragg reflector.

[0060] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index in the form of a square wave modulation, which, if present, is uniformly periodic in terms of the optical thickness of the layers, rather than in terms of their physical thickness.

[0061] In various embodiments of light-emitting devices according to the present disclosure, the organic light-emitting diode device may include a single light-emitting photonic crystal with an emission transmission axis perpendicular to the layer constituted by the single light-emitting photonic crystal.

[0062] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device can be spatially oriented such that the molecules of the organic electroluminescent emitter material maximize stimulated light emission parallel to the transmission axis of the light emission.

[0063] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may include an organic light-emitting diode such that the electrodes and organic layers of the organic light-emitting diode form part of a structure having a periodically varying refractive index.

[0064] In various embodiments of light-emitting devices according to the present disclosure, the single light-emitting photonic crystal included in the organic light-emitting diode device has a band edge of a stop band at which the measured free-space radiance of the luminescent light emitted by the electroluminescent emitter can occur at a wavelength that is greater than one-quarter of the measured peak free-space radiance of the emission spectrum of the emitter material.

[0065] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device has a band edge of a stop band that may occur at a wavelength where the optical absorption for a single pass of light through the emitter layer is less than 1%.

[0066] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device has a band edge of a stop band that may occur at a wavelength where the optical absorption for a single pass of light through the emitter layer is less than ½%.

[0067] In various embodiments of light-emitting devices according to the present disclosure, the single light-emitting photonic crystal included in the organic light-emitting diode device may include a layer of organic material centrally located in the stack of layers constituted by the single light-emitting photonic crystal, which layer of organic material may include an organic electroluminescent emitter material.

[0068] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may include a layer of organic material that is off-center of the stack of layers comprised by the single light-emitting photonic crystal, and the layer of organic material may include an organic electroluminescent emitter material.

[0069] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device can include a layer of organic material adjacent to a layer of reflective metal, which can include an organic electroluminescent emitter material.

[0070] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band with short-wavelength and long-wavelength band edges that are less than 160 nanometers apart.

[0071] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band with short-wavelength and long-wavelength band edges that are less than 110 nanometers apart.

[0072] In various embodiments of light-emitting devices according to the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band with short-wavelength and long-wavelength band edges that are less than 70 nanometers apart.

[0073] Various embodiments of light-emitting devices according to the present disclosure include a first single-emissive photonic crystal having an organic electroluminescent emitter material disposed within the single photonic crystal, the organic electroluminescent emitter material being contained in a zone having less than 10% of the total optical thickness of the photonic crystal. In these embodiments, the organic electroluminescent emitter material in the first single-emissive photonic crystal has a free-space emission spectrum that at least partially overlaps with a stop band of the photonic crystal, and the photonic crystal emits light at a wavelength corresponding to the edge of the stop band where the organic electroluminescent emitter material overlaps. In these embodiments, the first single-emissive photonic crystal is comprised of a stack of layers of varying refractive index, with the lower refractive index layer comprising the organic electroluminescent emitter material. In these embodiments, the light-emitting device further includes one or more other single-emissive photonic crystals, each having a photoluminescent material disposed within the single photonic crystal, the photoluminescent material in each of the other single-emissive photonic crystals having a free-space emission spectrum that at least partially overlaps with the stop band of the photonic crystal. In these embodiments, each of the other single emitting photonic crystals emits light at a wavelength corresponding to the edge of the stop band, and each of the other single emitting photonic crystals has a periodically varying refractive index, and light emission from one or more of the other single emitting photonic crystals is generated when light from a first single emitting photonic crystal is absorbed by the photoluminescent material in the other single emitting photonic crystal, causing the other single emitting photonic crystal to emit photoluminescent light.

[0074] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, each of the plurality of single light-emitting photonic crystals may further include a series of layers of varying refractive index.

[0075] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the lower refractive index layers in the first single light-emitting photonic crystal that include an organic electroluminescent emitter material may also include additional organic materials that each have a lower refractive index relative to adjacent layers, and the organic materials are at least one of a charge carrier transport material, a charge carrier injection material, or a charge carrier injection material.

[0076] In various embodiments of the light emitting device according to paragraph 87 of the present disclosure, the light emitting device may be constructed on a substrate, which may be transparent, allowing light from the light emitting device to be emitted from the bottom of the substrate.

[0077] In various embodiments of the light emitting device according to paragraph 87 of the present disclosure, the light emitting device may be constructed on a substrate with a metallic reflector interposed between the light emitting device and the substrate.

[0078] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the light-emitting device may be constructed on a substrate comprising one or more other single light-emitting photonic crystals located on the opposite side of the first single light-emitting photonic crystal from the substrate.

[0079] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the light-emitting device may be constructed on a substrate comprising one or more of one or more other single light-emitting photonic crystals located between the first single light-emitting photonic crystal and the substrate.

[0080] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the light-emitting device may comprise an anode interposed between a zone in which an electroluminescent emitter constituted by a first single light-emitting photonic crystal is localized and a substrate.

[0081] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the light-emitting device may comprise an anode, with a zone in which an electroluminescent emitter constituted by a first single light-emitting photonic crystal is localized, interposed between the anode and a substrate.

[0082] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, in at least one of the one or more other single-light-emitting photonic crystals, the photoluminescent material may be comprised in a single layer comprised by the single-light-emitting photonic crystal, and the photoluminescent material may be present in only a portion of the thickness of the single layer.

[0083] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, at least one or more of the one or more other single light-emitting photonic crystals may include two or more layers that include a photoluminescent material.

[0084] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, a first single light-emitting photonic crystal having an organic electroluminescent emitter material disposed within the first single light-emitting photonic crystal and another single light-emitting photonic crystal having a photoluminescent material disposed within the other single light-emitting photonic crystal may be comprised of a light-emitting device that may emit a mixture of blue or violet and yellow light, and this mixture of emitted light may be perceived as white light.

[0085] In various embodiments of a light-emitting device according to paragraph 87 of the present disclosure, a first single light-emitting photonic crystal having an organic electroluminescent emitter material disposed within the first single light-emitting photonic crystal and two other single light-emitting photonic crystals having different photoluminescent materials disposed within each of the other two single light-emitting photonic crystals may be comprised of a light-emitting device. The light-emitting device may emit a mixture of blue or violet, green, and red light, and the emitted mixture of light may be perceived as white light. The emitted mixture of light may have chromaticity coordinates in the CIE 1931 2° XYZ color space that lie in a rectangle defined by x=0.25 to 0.5 and y=0.2 to 0.45 on the CIE 1931 2° XYZ color space chromaticity diagram.

[0086] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the photoluminescent material comprised by at least one of the other single light-emitting photonic crystals is an organic photoluminescent material.

[0087] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the photoluminescent material configured with at least one of the other single luminescent photonic crystals is an organometallic photoluminescent material. The organometallic photoluminescent material may be an organic iridium photoluminescent material.

[0088] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the layer comprising the electroluminescent material may be located adjacent to a metallic reflector.

[0089] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the first single light-emitting photonic crystal included in the organic light-emitting device may include one or more material layers having an optical thickness equal to (2n+1)λ / 2, where n may have a value between 1 and 3, and λ is equal to the central wavelength of the photonic crystal stop band. The presence of these layers does not prevent the stack of layers from functioning as a single photonic crystal, but serves to narrow the width of the photonic crystal stop band. One to seven of these (2n+1)λ / 2-thick layers may be introduced, depending on the required reduction in the stop band width and the total number of these layers in the photonic crystal. One of the (2n+1)λ / 2-thick layers may include an organic electroluminescent emitter material.

[0090] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, the organic light-emitting diode device includes a first single light-emitting photonic crystal that includes a stack of layers with a periodic modulation of refractive index with a period of λ / 2, where λ is equal to the central wavelength of the photonic crystal stop band. This modulation is uniformly periodic in terms of their optical thickness, not in terms of the physical thickness of the layers. The layers configured with one modulation period may be two in number and of the same thickness, but the layers may be two in number and of different optical thickness, resulting in a narrower stop band. There may also be three or more layers configured with one optical thickness modulation period.

[0091] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, a first single light-emitting photonic crystal included in the organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 160 nanometers apart.

[0092] In various embodiments of a light-emitting device according to paragraph 87 of the present disclosure, a first single light-emitting photonic crystal included in the organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 110 nanometers apart.

[0093] In various embodiments of the light-emitting device according to paragraph 87 of the present disclosure, a first single light-emitting photonic crystal included in the organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 70 nanometers apart.

[0094] In various embodiments of light-emitting devices according to the present disclosure, the single light-emitting photonic crystal comprises an organic electroluminescent emitter material disposed within the single light-emitting photonic crystal, the electroluminescent emitter material being localized in a zone having an optical thickness less than 10% of the total optical thickness of the photonic crystal. In these embodiments, the organic electroluminescent emitter material has a free-space emission spectrum that at least partially overlaps with a stop band of the photonic crystal, and the electroluminescent emitter material emits light at a wavelength corresponding to the short-wavelength edge of the stop band with which the organic electroluminescent emitter material overlaps. In these embodiments, the single light-emitting photonic crystal is composed of a stack of layers of varying refractive index, with the lower refractive index layer comprising the organic electroluminescent emitter material. Also in these embodiments, the single light-emitting photonic crystal may further comprise a second light-emitting material.

[0095] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the light emitting material may be an electroluminescent material.

[0096] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the luminescent material may be a photoluminescent material.

[0097] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the lower refractive index layers within the single light-emitting photonic crystal that include an organic electroluminescent emitter material may also include additional organic materials that each have a lower refractive index relative to an adjacent layer, and the organic materials are at least one of a charge carrier transport material, a charge carrier injection material, or a charge carrier injection material.

[0098] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the luminescent material may have a free-space emission spectrum that at least partially overlaps with the long-wavelength edge of the stop band of the photonic crystal. The photoluminescent material may emit light at a wavelength corresponding to the long-wavelength edge of the stop band.

[0099] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting material may be an organic material.

[0100] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting material may be an organometallic material.

[0101] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the light emitting material may be constituted by a single layer of photonic crystal.

[0102] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting material may be located in two or more layers.

[0103] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the band edges of the stop bands may be less than 140 nm apart in wavelength.

[0104] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the light emitting device may emit light in two distinct emission bands. The emitted light may be perceived as white light.

[0105] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting material may be an electroluminescent material, which may be located in the same layer as the organic electroluminescent emitter.

[0106] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the light emitting device may be constructed on a substrate.

[0107] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the light emitting device may be constructed on a transparent substrate, which may allow light to be emitted from the bottom of the substrate.

[0108] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, a metallic reflector may be interposed between the substrate and the light emitting device.

[0109] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting material may be constituted by a single layer, and a layer containing an organic electroluminescent material may be interposed between the layer containing the light-emitting material and the metallic reflector.

[0110] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting material may be constituted by a single layer, and the layer containing the light-emitting material may be interposed between the layer containing the organic electroluminescent material and the metallic reflector.

[0111] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting device may comprise an anode and a substrate, and the anode may be interposed between the zone in which the organic electroluminescent material is localized and the substrate.

[0112] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the light-emitting device may comprise an anode and a substrate, and the zone in which the organic electroluminescent material is localized may be interposed between the anode and the substrate.

[0113] In various embodiments of the light emitting device according to paragraph 108 of the present disclosure, the light emitting device may include a metallic reflector, and the layer including the organic electroluminescent material may be located adjacent to the metallic reflector.

[0114] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the single light-emitting photonic crystal included in the organic light-emitting device may include one or more material layers having an optical thickness equal to (2n+1)λ / 2, where n may have a value between 1 and 3, and λ is equal to the central wavelength of the photonic crystal stop band. The presence of these layers does not prevent the stack of layers from functioning as a single photonic crystal, but serves to narrow the width of the photonic crystal stop band. One to seven of these (2n+1)λ / 2-thick layers may be introduced, depending on the required reduction in stop band width and the total number of layers in the photonic crystal. One of the (2n+1)λ / 2-thick layers may include an organic electroluminescent emitter material.

[0115] In various embodiments of the light-emitting device according to paragraph 108 of the present disclosure, the organic light-emitting diode device includes a single light-emitting photonic crystal that includes a stack of layers with a periodic modulation of refractive index with a period of λ / 2, where λ is equal to the central wavelength of the photonic crystal stop band. This modulation is uniformly periodic in terms of the optical thickness of the layers, not in terms of the physical thickness of the layers. The layers configured with one modulation period may be two in number and of the same thickness, but the layers may be two in number and of different optical thicknesses, resulting in a narrower stop band. There may also be more than two layers configured with one optical thickness modulation period.

[0116] In various embodiments of a light-emitting device according to paragraph 108 of the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 160 nanometers apart.

[0117] In various embodiments of a light-emitting device according to paragraph 108 of the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 110 nanometers apart.

[0118] In various embodiments of a light-emitting device according to paragraph 108 of the present disclosure, a single light-emitting photonic crystal included in an organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 70 nanometers apart.

[0119] In various embodiments of light-emitting devices according to the present disclosure, the light-emitting photonic crystal includes an organic electroluminescent emitter material disposed within the single light-emitting photonic crystal, the electroluminescent emitter material being localized in a zone having an optical thickness less than 10% of the total optical thickness of the photonic crystal. In these embodiments, the organic electroluminescent emitter material has a free-space emission spectrum that at least partially overlaps with a stop band of the photonic crystal, and the electroluminescent emitter material emits light at a wavelength corresponding to the short-wavelength edge of the stop band that the organic electroluminescent emitter material overlaps. In these embodiments, the single light-emitting photonic crystal is comprised of a stack of layers of varying refractive index, with the lower refractive index layer comprising the organic electroluminescent emitter material. In these embodiments, the single light-emitting photonic crystal may further include a second light-emitting material. In these embodiments, the light-emitting device further includes one or more other single light-emitting photonic crystals, each having a photoluminescent material disposed within the single photonic crystal, the photoluminescent material having a free-space emission spectrum that at least partially overlaps with the stop band of the photonic crystal. In these embodiments, each of the other single emitting photonic crystals emits light at a wavelength corresponding to the edge of the stop band, and each of the other single emitting photonic crystals has a periodically varying refractive index, and light emission from one or more of the other single emitting photonic crystals is generated when light from a first single emitting photonic crystal is absorbed by the photoluminescent material in the other single emitting photonic crystal, causing the other single emitting photonic crystal to emit photoluminescent light.

[0120] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting material may be an electroluminescent material.

[0121] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the luminescent material may be a photoluminescent material.

[0122] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the lower refractive index layers in the first single light-emitting photonic crystal that include an organic electroluminescent emitter material may also include additional organic materials that each have a lower refractive index relative to adjacent layers, and the organic materials are at least one of a charge carrier transport material, a charge carrier injection material, or a charge carrier injection material.

[0123] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the luminescent material may have a free-space emission spectrum that at least partially overlaps with the long-wavelength edge of the stop band of the first single-emitting photonic crystal. The photoluminescent material may emit light at a wavelength corresponding to the long-wavelength edge of the stop band.

[0124] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be an organic material.

[0125] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be an organometallic material.

[0126] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be constituted by a single layer of a first single light-emitting photonic crystal.

[0127] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be located in two or more layers.

[0128] In various embodiments of a light emitting device according to paragraph 133 of the present disclosure, the band edges of the stop bands may be less than 140 nm apart in wavelength.

[0129] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting device may emit light in three distinct emission bands. The emitted light may be perceived as white light.

[0130] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting device may emit light in four distinct emission bands. The emitted light may be perceived as white light.

[0131] In various embodiments of a light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be an electroluminescent material, which may be located in the same layer as the organic electroluminescent emitter.

[0132] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting device may be constructed on a substrate.

[0133] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting device may be constructed on a transparent substrate, which may allow light to be emitted from the bottom of the substrate.

[0134] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, a metallic reflector may be interposed between the substrate and the light emitting device.

[0135] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be constituted by a single layer, and a layer containing an organic electroluminescent material may be interposed between the layer containing the light-emitting material and the metallic reflector.

[0136] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting material may be constituted by a single layer, and the layer containing the light-emitting material may be interposed between the layer containing the organic electroluminescent material and the metallic reflector.

[0137] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may comprise an anode and a substrate, and the anode may be interposed between the zone in which the organic electroluminescent material is localized and the substrate.

[0138] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may comprise an anode and a substrate, and the zone in which the organic electroluminescent material is localized may be interposed between the anode and the substrate.

[0139] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the lower refractive index layers within the single light-emitting photonic crystal that include an organic electroluminescent emitter material may also include additional organic materials, each having a lower refractive index relative to adjacent layers, where the organic materials are at least one of a charge carrier transport material, a charge carrier injection material, or a charge carrier injection material, and additionally a light-emitting material.

[0140] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may include a metallic reflector, and the layer including the organic electroluminescent material may be located adjacent to the metallic reflector.

[0141] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the first single light-emitting photonic crystal included in the organic light-emitting device may include one or more material layers having an optical thickness equal to (2n+1)λ / 2, where n may have a value between 1 and 3, and λ is equal to the central wavelength of the photonic crystal stop band. The presence of these layers does not prevent the layer stack from functioning as a single photonic crystal, but serves to narrow the width of the stop band of the first single light-emitting photonic crystal. One to seven of these (2n+1)λ / 2-thick layers may be introduced, depending on the required reduction in stop band width and the total number of layers in the first single light-emitting photonic crystal. One of the (2n+1)λ / 2-thick layers may include an organic electroluminescent emitter material.

[0142] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the organic light-emitting diode device includes a first single light-emitting photonic crystal that includes a stack of layers with a periodic modulation of refractive index with a period of λ / 2, where λ is equal to the central wavelength of the photonic crystal stop band. This modulation is uniformly periodic in terms of their optical thickness, not in terms of the physical thickness of the layers. The layers configured with one modulation period may be two in number and of the same thickness, but the layers may be two in number and of different optical thickness, resulting in a narrower stop band. There may also be three or more layers configured with one optical thickness modulation period.

[0143] In various embodiments of a light-emitting device according to paragraph 133 of the present disclosure, the first single light-emitting photonic crystal included in the organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the first single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 160 nanometers apart.

[0144] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the first single light-emitting photonic crystal included in the organic light-emitting diode device may have a periodic modulation of the refractive index of light, and the first single light-emitting photonic crystal may include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 110 nanometers apart.

[0145] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, The first single light-emitting photonic crystal included in the organic light-emitting diode device comprises: may have a periodic modulation of the refractive index of light; The first single light-emitting photonic crystal can include a period of the periodic modulation sufficient to produce a stop band having short-wavelength and long-wavelength band edges that are less than 70 nanometers apart.

[0146] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, each of the other single light-emitting photonic crystals may further include a series of layers of varying refractive index.

[0147] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the lower refractive index layers in the first single light-emitting photonic crystal that include an organic electroluminescent emitter material may also include additional organic materials that each have a lower refractive index relative to adjacent layers, and the organic materials are at least one of a charge carrier transport material, a charge carrier injection material, or a charge carrier injection material.

[0148] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting device may be constructed on a substrate, which may be transparent, allowing light from the light emitting device to be emitted from the bottom of the substrate.

[0149] In various embodiments of the light emitting device according to paragraph 133 of the present disclosure, the light emitting device may be constructed on a substrate with a metallic reflector interposed between the light emitting device and the substrate.

[0150] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may be constructed on a substrate comprising one or more other single light-emitting photonic crystals located on the opposite side of the first single light-emitting photonic crystal from the substrate.

[0151] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may be constructed on a substrate comprising one or more of one or more other single-emitting photonic crystals located between the first single-emitting photonic crystal and the substrate.

[0152] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may comprise an anode interposed between a zone in which an electroluminescent emitter constituted by a first single light-emitting photonic crystal is localized and a substrate.

[0153] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the light-emitting device may comprise an anode, with a zone in which an electroluminescent emitter constituted by a first single light-emitting photonic crystal is localized, interposed between the anode and a substrate.

[0154] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, in at least one of the one or more other single-light-emitting photonic crystals, the photoluminescent material may be comprised of a single layer comprised of that single-light-emitting photonic crystal, and the photoluminescent material may be present in only a portion of the thickness of that single layer.

[0155] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, at least one or more of the one or more other single light-emitting photonic crystals may include two or more layers that include a photoluminescent material.

[0156] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, a first single light-emitting photonic crystal having an organic electroluminescent emitter material disposed within the first single light-emitting photonic crystal and another single light-emitting photonic crystal having a photoluminescent material disposed within the other single light-emitting photonic crystal may be comprised of a light-emitting device that may emit a mixture of blue or violet light and yellow light, and this mixture of emitted light may be perceived as white light.

[0157] In various embodiments of a light-emitting device according to paragraph 133 of the present disclosure, a first single light-emitting photonic crystal having an organic electroluminescent emitter material disposed within the first single light-emitting photonic crystal and two other single light-emitting photonic crystals having different photoluminescent materials disposed within each of the other two single light-emitting photonic crystals may be comprised of a light-emitting device. The light-emitting device may emit a mixture of blue or violet, green, and red light, and the emitted mixture of light may be perceived as white light. The emitted mixture of light may have chromaticity coordinates in the CIE 1931 2° XYZ color space that lie in a rectangle defined by x=0.25 to 0.5 and y=0.2 to 0.45 on the CIE 1931 2° XYZ color space chromaticity diagram.

[0158] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the photoluminescent material comprised by at least one of the other single-emitting photonic crystals is an organic photoluminescent material.

[0159] In various embodiments of the light-emitting device according to paragraph 133 of the present disclosure, the photoluminescent material configured with at least one of the other single-emitting photonic crystals is an organometallic photoluminescent material. The organometallic photoluminescent material may be an organic iridium photoluminescent material.

[0160] In the various embodiments described above, references to organic materials may be considered to include organometallic materials.

[0161] In the various embodiments described above, references to organic materials may be considered to include combinations of organic materials that are capable of producing exciplex emission when energized.

Claims

1. a single light-emitting photonic crystal, the single light-emitting photonic crystal comprising a photonic crystal stop band and an organic electroluminescent emitter material disposed within the single light-emitting photonic crystal having a center wavelength of the stop band; the organic electroluminescent emitter material comprises an organic light-emitting material localized in a zone having less than 10% of the optical thickness of the single light-emitting photonic crystal; the organic electroluminescent emitter material has a free-space emission spectrum that at least partially overlaps with a stop band of the single light-emitting photonic crystal; the single light-emitting photonic crystal emits light at a wavelength corresponding to an edge of the stop band where the organic electroluminescent emitter material overlaps; the single light-emitting photonic crystal further comprises a stack of layers with different refractive indices; the layer of lower refractive index material comprises said organic electroluminescent emitter material; the layer stack has a periodic modulation of refractive index, measured in optical thickness, with a modulation period of λ / 2, where λ is equal to the center wavelength of the single light-emitting photonic crystal stop band; the stack of layers of different refractive indexes that make up the single light-emitting photonic crystal includes at least one pair of layers of materials having different refractive indices, each pair including a first material layer having a higher refractive index and a second material layer having a lower refractive index; A single light-emitting photonic crystal, wherein the first material layer and the second material layer do not have the same optical thickness.

2. 10. The single light-emitting photonic crystal of claim 1, wherein the modulation period of the refractive index through the layer stack is interrupted 1 to 7 times by the insertion of constant refractive index layers having an optical thickness equal to (2n+1)λ / 4, where n is an integer between 1 and 3, and λ is the center wavelength of the stop band of the photonic crystal.

3. 3. The single light-emitting photonic crystal of claim 2, wherein the modulation period of the refractive index modulation through the layer stack is interrupted once by a layer having a thickness of 3λ / 4, and the layer interrupting the refractive index modulation of the layer stack comprises the organic electroluminescent emitter material.

4. 10. The single light-emitting photonic crystal of claim 1, wherein the edge of the stop band occurs at a wavelength where the measured radiance of free-space luminescent emission by the organic electroluminescent emitter material is greater than one-quarter of the peak radiance of the free-space emission spectrum of the organic electroluminescent emitter material.

5. The method of claim 1, further comprising: one or more additional luminescent photonic crystals, each having a photoluminescent material disposed within the single luminescent photonic crystal; in each of the other single light-emitting photonic crystals, the photoluminescent material has a free-space emission spectrum that at least partially overlaps with the stop band of the photonic crystal; each of the additional single light-emitting photonic crystals emits light at a wavelength corresponding to an edge of a stop band; each of the additional single light-emitting photonic crystals has a periodically varying refractive index; 2. The single luminescent photonic crystal of claim 1, wherein light emission from the one or more other single luminescent photonic crystals is generated when light from a first single luminescent photonic crystal is absorbed by the photoluminescent material in the other single luminescent photonic crystal, causing the other single luminescent photonic crystal to emit photoluminescent light.

6. The single light-emitting photonic crystal stop band defines a short wavelength edge and a long wavelength edge; further comprising: the single light-emitting photonic crystal emitting light at a wavelength corresponding to the short wavelength edge of the stop band; a second organic electroluminescent emitter material disposed within the single light-emitting photonic crystal; the second organic electroluminescent emitter material has a free-space emission spectrum that at least partially overlaps with a stop band of the photonic crystal; 10. The single light-emitting photonic crystal of claim 1, wherein said photonic crystal also emits light at a wavelength corresponding to the long wavelength edge of said stop band overlapped by said second organic electroluminescent emitter material.

7. 10. The single light-emitting photonic crystal of claim 1, wherein the layers comprising the organic electroluminescent emitter material and additional organic material, each having a low refractive index corresponding to an adjacent layer, are located adjacent to a metallic reflector.

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