Display device and wavelength conversion substrate

Abstract

A display device 100 includes: an LED section 110 having only one of a plurality of near-ultraviolet LEDs and blue LEDs disposed on a substrate 111; a partition 6 configured as a grid with a plurality of openings in plan view, with the LEDs located within the openings; a color filter section 120 having a red filter R, a green filter G, and a blue filter B, each filter being configured to overlap with the openings in plan view; and a fluorescent light-emitting layer 1 disposed between the LED section and the color filter section, located within the openings in plan view, wherein an Eu2+ activated phosphor is dispersed in a matrix resin. The fluorescent light-emitting layer has only the Eu2+ activated phosphor as the phosphor, and at least a portion of the fluorescent light-emitting layer includes a first phosphor that uses light emitted from the LED section as excitation light and a second phosphor that uses the fluorescence emitted from the first phosphor as excitation light, both serving as Eu2+ activated phosphors.

Description

Technical Field

[0001] The present invention relates to a display device and a wavelength conversion substrate applicable to the display device. This case claims priority based on Special Application No. 2022-062932 filed in Japan on April 5, 2022, and the contents of the application are cited here. Prior Art

[0002] In recent years, the development of self-luminous display devices, such as Micro LED (Light Emitting Diode) displays and organic electroluminescent (hereinafter referred to as "organic EL") displays, has flourished. Micro LED displays utilize a matrix structure that arranges LED elements ranging in size from approximately 2μm to 50μm. These displays are driven independently to generate a display. Because these self-luminous displays utilize liquid crystals that switch between transparent and opaque display layers, they offer superior visibility in dark environments, compared to liquid crystal displays, which suffer from light leakage when displaying black.

[0003] Micro LED displays can be broadly categorized into two types: those using three types of LED elements—red, green, and blue—and those using single-color LED elements that emit light in the blue to near-ultraviolet wavelength range. In a Micro LED display, each LED element serves as a display layer. The approach using three types of LED elements—red, green, and blue—offers excellent brightness and lifespan. However, challenges include increased costs due to the increased number of LED element installations and the difficulty of controlling the driving voltage, which varies from element to element. Numerous efforts have been made to address these issues.

[0004] One countermeasure is to use single-color LEDs. This approach simplifies the manufacturing process by using only one type of LED. A color display is achieved by stacking wavelength conversion layers that convert the wavelength of light emitted by the LED to red, green, and blue. For example, a layer containing dispersed quantum dots or inorganic phosphors is used as the wavelength conversion layer. Patent Document 1 discloses the use of a monochromatic light source that emits ultraviolet light and a color conversion layer or phosphor layer that converts the light emitted from the light source into red, green, and blue.

[0005] In order to effectively utilize light emitted from light-emitting elements such as LEDs and organic ELs, Patent Document 2 discloses a technique for stacking a plurality of phosphor layers. Patent Document 2 aims to maximize the conversion efficiency of light emitted from a light-emitting element by patterning two or more phosphor layers using photolithography and then laminating them simultaneously. Light emitted from the light-emitting element is first absorbed by the lower phosphor layer, and then the upper phosphor layer absorbs the light emitted by the lower phosphor layer and re-emitted. This wavelength-down conversion of the emitted light improves conversion efficiency.

[0006] In order to effectively utilize light emitted from a light-emitting element such as an LED, Patent Document 3 discloses a technology for mixing phosphors. Patent Document 3 describes a wavelength conversion layer formed by mixing Mn 2+ activated phosphor and Eu 2+ phosphor in an appropriate weight ratio to achieve both a wide color gamut and high luminous efficiency. [Prior Art Literature] [Patent Document]

[0007] Patent Document 1 International Publication No. 2019 / 159702 Patent Document 2 International Publication No. 2013 / 133139 Patent Document 3 Japanese Patent Application Laid-Open No. 2019-29584 Summary of the Invention

[0008] [Problems to be solved by the invention]

[0009] The details will be described later, but the technology of Patent Document 2 still has room for improvement in terms of insufficient down-conversion efficiency and productivity. Regarding the technology of Patent Document 3, the inventor discovered and solved new problems not described in Patent Document 3, thereby completing the present invention.

[0010] In view of the above, an object of the present invention is to provide a display device that can achieve high luminous efficiency and high productivity. [Methods used to solve the problem]

[0011] A first aspect of the present invention is a display device comprising: an LED portion having only a plurality of near-ultraviolet LEDs and a plurality of blue LEDs arranged on a substrate; a partition configured in a lattice shape having a plurality of openings when viewed from above, with the near-ultraviolet LEDs or the blue LEDs located within the openings; a color filter portion having a red filter, a green filter, and a blue filter, the red filter, the green filter, and the blue filter being configured to overlap with the openings when viewed from above; and a fluorescent light-emitting layer disposed between the LED portion and the color filter portion and located within the openings when viewed from above, with Eu2+-activated phosphors dispersed in a matrix resin. The fluorescent light-emitting layer has only Eu 2+ activated phosphor as a phosphor, and at least a portion of the fluorescent light-emitting layer includes a first phosphor that uses the light emitted from the LED part as excitation light and a second phosphor that uses the fluorescence emitted by the first phosphor as excitation light as Eu 2+ activated phosphor.

[0012] A second aspect of the present invention is a wavelength conversion substrate comprising: a transparent substrate; a color filter disposed on the substrate and comprising a red filter, a green filter, and a blue filter; a partition configured in a grid pattern having a plurality of openings when viewed from above, with any one of the red filter, the green filter, and the blue filter located within the opening; and a fluorescent light-emitting layer located within the opening when viewed from above, with Eu2+-activated phosphors dispersed in a matrix resin. The fluorescent light-emitting layer only has Eu 2+ activated phosphor as the phosphor, and at least a part of the fluorescent light-emitting layer includes a first phosphor and a second phosphor that uses the fluorescence emitted by the first phosphor as excitation light as the Eu 2+ activated phosphor. [Effects of the Invention]

[0013] According to the present invention, a display device capable of achieving high luminous efficiency and high productivity can be provided. Simple diagram description

[0014] FIG1 is a schematic cross-sectional view of a display device according to a first embodiment of the present invention. FIG2 is a schematic cross-sectional view showing a modified example of the display device. FIG3 is a schematic cross-sectional view of a display device according to a second embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a wavelength conversion substrate in the display device. FIG5 is a schematic cross-sectional view showing a modified example of the display device. FIG6 is a schematic cross-sectional view showing a wavelength conversion substrate in a display device according to a modification. FIG. 7 is a diagram showing the excitation spectrum and the fluorescence spectrum of the first phosphor in the experimental example. FIG. 8 is a graph showing the excitation spectrum and fluorescence spectrum of the second phosphor in the experimental example. FIG. 9 is a diagram showing the excitation spectrum and fluorescence spectrum of the third phosphor in the experimental example. FIG. 10 is a graph showing the emission spectra of samples of the experimental example. FIG. 11 is a graph showing the emission spectra of samples of the experimental example. FIG12 is a graph showing the emission spectra of samples of the experimental example. FIG. 13 is a graph showing the fluorescence lifetime spectra of samples of the experimental example. Implementation Method

[0015] [Modes for carrying out the invention]

[0016] Hereinafter, a first embodiment of the present invention will be described with reference to FIG1 and FIG2. In the following description, the same or substantially the same functions and components are denoted by the same symbols, and their descriptions (repeated descriptions) are omitted or simplified, or are described only when necessary.

[0017] In this specification, "top view" refers to a state where an observer views a surface of a display device and a wavelength conversion substrate, etc., which will be described later, from a normal direction. The ordinal numbers "first" and "second" in each component are added to avoid confusion between the components and do not specify the order or quantity. The LEDs used in this invention utilize compounds such as aluminum gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP), indium gallium nitride (InGaN), gallium nitride (GaN), aluminum gallium nitride (AlGaN), gallium phosphide (GaP), zinc selenide (ZnSe), and aluminum gallium indium phosphide (AlGaInP). The blue LEDs and near-ultraviolet LEDs described later, which emit monochromatic light, primarily utilize gallium nitride (GaN).

[0018] 1 is a partial cross-sectional view of a display device 100 according to this embodiment. As shown in FIG1 , the display device 100 includes an LED unit 110 and a color filter unit 120 .

[0019] The LED unit 110 has a basic structure consisting of a plurality of LED elements 112 arranged in a matrix on a substrate 111. The LED elements arranged on the substrate 111 are of a single type. In other words, the LED unit 110 only has a plurality of LED elements 112 (e.g., near-ultraviolet LED elements 112 described later) arranged on the substrate 111. The LED elements 112 in this embodiment emit light in the ultraviolet wavelength band, for example, micro-LEDs with a size of approximately 2μm to 50μm. The structure of LED element 112 is not particularly limited. It can be a horizontal LED, where the n-side and p-side electrodes are on the same side, or a vertical LED, where the n-side and p-side electrodes sandwich the light-emitting portion in the thickness direction. Figure 1 shows the structure of a vertical LED as LED element 112.

[0020] LED element 112 is a near-ultraviolet LED that emits monochromatic near-ultraviolet light. In this specification, "monochromatic emission" means that the half-width at half-maximum of the emitted light is less than 70 nm, and that there is a single emission peak within the wavelength range of the emitted light. The smaller the half-width at half-maximum of LED element 112, the better. Furthermore, near-ultraviolet light refers to light with a wavelength between 300 nm and less than 410 nm. A near-ultraviolet LED has an emission peak within the wavelength range between 300 nm and less than 410 nm.

[0021] A partition 6 is formed on the substrate 111. When viewed from above, the partition 6 has a lattice-like pattern, surrounding each LED element 112 and isolating it from other LED elements. Specifically, the partition 6 is configured to have a lattice-like pattern with multiple openings when viewed from above, and the LED elements 112, which are near-ultraviolet LEDs, are located within these openings. Separator 6 contains carbon, which has the property of absorbing light. Carbon with low wavelength selectivity for visible light is preferred. "Low wavelength selectivity for visible light" means that the material exhibits little absorption or reflection of light within the wavelength range of 400 nm to 700 nm, resulting in a visually black or gray color. When the spacers 6 are formed by carbon dispersion in a resin, a photolithography method can be applied. When the spacers 6 are formed by photolithography, an alkali-soluble photosensitive resin can be used.

[0022] The spacer 6 is not limited to a light-absorbing one, but may also be a light-reflecting one. A light-reflecting spacer may be formed by, for example, covering the surface of a resin core with a metal film. The core can be formed by patterning an alkali-soluble photosensitive resin using known photolithography methods, or by patterning a layer of thermosetting resin using dry etching methods. Examples of photosensitive resins include resins obtained by reacting a (meth)acrylic acid compound or cinnamic acid having a reactive substituent such as an isocyanate group, an aldehyde group, or an epoxy group with a linear polymer having a reactive substituent such as a hydroxyl group, a carboxyl group, or an amino group to introduce photocrosslinkable groups such as a (meth)acryl group or a styryl group into the linear polymer. Here, "(meth)acrylic compound" means both or either "acrylic compound" or "methacrylic compound." Furthermore, "(meth)acryl" means both or either "acryl" or "methacryl." The same applies to the description of "(meth)acrylate" and the like described below.

[0023] Fluorescent layer 1 is arranged in each section divided by partitions 6, covering LED elements 112. Specifically, fluorescent layer 1 is positioned between LED section 110 and color filter section 120 and, when viewed from above, is located within the openings of the grid pattern of partitions 6. Fluorescent layer 1 has a basic structure consisting of granular phosphors dispersed in a transparent matrix resin. Examples of the matrix resin include silicone resins, epoxy resins, phenol resins, polycarbonate resins, acrylic resins, polynorbornene resins, modified resins thereof, and mixed resins. Among these, silicone resins are preferred due to their excellent heat resistance and light resistance.

[0024] In this embodiment, the fluorescent light emitting layer 1 is composed of three conversion layers: a blue conversion layer 1A, a green conversion layer 1B, and a red conversion layer 1C. The blue conversion layer 1A has a structure in which a first phosphor 2, which absorbs ultraviolet light and emits blue fluorescence, is dispersed in a matrix resin. In other words, the blue conversion layer 1A contains a single type of phosphor. The green conversion layer 1B has a structure in which a first phosphor 2 and a second phosphor 3, which absorbs blue light and emits green fluorescence, are dispersed in a matrix resin. In other words, the green conversion layer 1B contains two types of phosphors. The red conversion layer 1C has a second phosphor 3 and a third phosphor 4 that absorbs green light and emits red light, dispersed in a matrix resin. In other words, the red conversion layer 1C contains two types of phosphors. The first phosphor 2, the second phosphor 3, and the third phosphor 4 are all Eu 2+ activated phosphors. Details will be described later. The particle size of each phosphor is preferably between 0.1 μm and 15 μm. In this specification, the particle size at the 50th percentile of the cumulative value in the particle size distribution determined by photon correlation spectroscopy is defined as "particle size." Simply put, the arithmetic mean of the diameters of the phosphor particles observed in a specified cross-section of the phosphor layer 1 can be defined as "particle size" by observing the arithmetic mean of the diameters of the phosphor particles observed using a scanning electron microscope.

[0025] The fluorescent layer 1 can be easily formed by applying a dispersion containing a photosensitive resin as a matrix resin and dispersing a specific phosphor therein, then patterning the dispersion using photolithography. The thickness of the fluorescent layer 1 can be between 1 μm and 50 μm. While thicknesses exceeding 50 μm are possible, excessive thickness can lead to significant engineering overhead, such as wasted time in coating and drying operations. As long as the thickness of the fluorescent layer 1 is between 1 μm and 50 μm, it can be easily adjusted to the same height as the spacers 6. The thickness of the fluorescent layer 1 is preferably less than the height of the partition 6. If the thickness of the fluorescent layer 1 is greater than the height of the partition 6, light from the fluorescent layer 1 may leak to adjacent pixels. The matrix resin is preferably a material that is not easily degraded by heat. For example, after heat treatment at 150°C for 500 hours, the transmittance of light emitted from the LED element 112 is not easily changed. For example, the change in transmittance before and after heat treatment at 150°C for 500 hours is preferably 5% or less at the LED's peak emission wavelength of 385 nm.

[0026] The spacers 6 and the fluorescent light emitting layer 1 are covered with a transparent resin layer 7. The upper surface of the LED portion 110 is flattened by the transparent resin layer 7.

[0027] The basic structure of the color filter unit 120 is conventional, comprising a black matrix (hereinafter sometimes referred to as "BM") 121 and a plurality of color filters. The number and combination of color filters in the color filter unit can be appropriately determined depending on the application, etc. In this embodiment, the color filter unit 120 includes three color filters: red filters R, green filters G, and blue filters B.

[0028] The black matrix 121 is formed in contact with the transparent resin layer 7. The black matrix 121 is formed in a grid pattern having a plurality of openings when viewed from above. This grid pattern overlaps with the grid pattern of the spacers 6 when viewed from above the display device 100. In other words, when viewed from above the display device 100, the openings in the grid pattern of the spacers 6 overlap with the openings in the grid pattern of the black matrix 121. There is no particular limitation on the method for forming the black matrix 121. If an alkali-soluble photosensitive photoresist in which light-shielding carbon is dispersed is used, a grid pattern can be easily formed using known photolithography.

[0029] Each color filter R, G, B can be formed using a dispersion in which an organic pigment of the corresponding color is dispersed in a resin. Examples of the resin include acrylic acid.

[0030] Examples of red organic pigments that can be used for the red filter R include CI Pigment Red 7, 14, 41, 48:2, 48:3, 48:4, 81:1, 81:2, 81:3, 81:4, 146, 168, 177, 178, 179, 184, 185, 187, 200, 202, 208, 210, 246, 254, 255, 264, 270, 272, and 279. These red pigments can also be mixed with yellow pigments and orange pigments. Examples of applicable yellow organic pigments include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 10, 12, 13, 14, 15, 16, 17, 18, 24, 31, 32, 34, 35, 35:1, 36, 36:1, 37, 37:1, 40, 42, 43, 53, 55, 60, 61, 62, 63, 65, 73, 74, 77, 81, 83, 93, 94, 95, 97, 98, 100, 101, 104, 106, 108, 109, 110, and 113. , 114, 115, 116, 117, 118, 119, 120, 123, 126, 127, 128, 129, 147, 151, 152, 153, 154, 155, 156, 161, 162, 164, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 187, 188, 193, 194, 199, 198, 213, 214, etc. The red filter R is preferably one whose transmittance for light with a wavelength of 380 nm to 580 nm is 5% or less.

[0031] Examples of green pigments that can be used in the green filter G include CI Pigment Green 7, 10, 36, and 37. These green pigments can also be mixed with the aforementioned yellow pigments. Furthermore, zinc phthalocyanine halide green pigments and aluminum phthalocyanine halide green pigments can also be used as appropriate. The green filter G is preferably one whose transmittance of light with a wavelength of 380 nm to 480 nm is 5% or less.

[0032] Examples of blue pigments that can be used for the blue filter B include CI Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 60, and 64. Violet pigments can also be mixed with these blue pigments. Examples of the violet pigment include CI Pigment Violet 1, 19, 23, 27, 29, 30, 32, 37, 40, 42, and 50.

[0033] The aforementioned pigments are dispersed in a transparent resin along with an organic solvent and a dispersant. The transparent resin preferably has a transmittance of 90% or greater in the visible light region and is preferably an alkali-soluble photosensitive resin containing a resin precursor. The pigment can be contained in an amount ranging from 15% to 65% by mass relative to the resin. Examples of the photosensitive resin include polyimide resins, epoxy resins, acrylic resins, melamine resins, phenol resins, cyclohexane resins, silicone resins, and benzophenone resins, which are obtained by reacting a (meth)acrylic acid compound or cinnamic acid having a reactive substituent such as an isocyanate group, an aldehyde group, an epoxy group, or a silanol group with a linear polymer having a reactive substituent such as a hydroxyl group, a carboxyl group, or an amino group to introduce a photocrosslinkable group such as a (meth)acryloyl group or a styryl group into the linear polymer. Examples of monomers and oligomers serving as precursors include various acrylates and methacrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, cyclohexyl (meth)acrylate, polyethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tricyclodecyl (meth)acrylate, melamine (meth)acrylate, and epoxy (meth)acrylate; (meth)acrylic acid; styrene, vinyl acetate, (meth)acrylamide, N-methylol (meth)acrylamide; and acrylonitrile. These can be used alone or in combination. When curing the photosensitive resin by irradiation with ultraviolet light having a wavelength of 365 nm or more, a photopolymerization initiator or the like may be added to the photosensitive resin.

[0034] The color filters R, G, and B are arranged so that, in a plan view, any one of them overlaps with an opening in the black matrix 121. As described above, the openings in the grid pattern of the spacer 6 overlap with the openings in the grid pattern of the black matrix 121. Therefore, the color filters R, G, and B are arranged so that, in a plan view, any one of them overlaps with an opening in the grid pattern of the spacer 6. The color filters R, G, and B may be arranged so as to overlap with the openings of the grid pattern of the partition 6 in a plan view. In a top view of the display device 100, the color filters R, G, and B overlap with the red conversion layer 1C, the green conversion layer 1B, and the blue conversion layer 1A, respectively. The red filter R, the green filter G, and the blue filter B can be arranged to contact each other or spaced apart.

[0035] Next, the operation when using the display device 100 configured as described above will be described. In the display device 100, a combination of adjacent red filters R, green filters G, and blue filters B constitutes a single pixel. In each pixel, the LED element 112 corresponding to the red filter R, green filter G, and blue filter B is driven in response to an input image signal, changing the pixel's color and brightness.

[0036] The excitation light emitted from the LED element 112 enters the fluorescent layer 1 before reaching the color filter portion 120 . The excitation light incident on the blue conversion layer 1A is wavelength-converted by the first phosphor 2 into blue phosphor light, which then enters the blue filter B. In other words, the first phosphor 2 uses the light emitted from the LED unit 110 (LED element 112) as the excitation light. Most of the excitation light incident on the green conversion layer 1B undergoes wavelength conversion in the first phosphor 2, turning it into blue phosphor light. A portion of this blue phosphor light undergoes wavelength conversion in the second phosphor 3, turning it into green phosphor light, which then enters the green filter G. In other words, the second phosphor 3 uses the phosphor light emitted by the first phosphor 2 as excitation light. Most of the excitation light incident on the red conversion layer 1C undergoes wavelength conversion in the second phosphor 3, turning it into green phosphor light. A portion of this green phosphor light undergoes wavelength conversion in the third phosphor 4, turning it into red phosphor light, which then enters the red filter R. In other words, the third phosphor 4 uses the phosphor light emitted by the second phosphor 3 as excitation light.

[0037] Phosphors 2, 3, and 4 used in this embodiment are all Eu2+-activated phosphors. In this disclosure, "Eu2+-activated phosphors" refer to phosphors activated solely by Eu2+ and do not include Eu2+- and Mn2+-coactivated BaMgAlO phosphors, which can be activated by other ions besides Eu2+. Eu2+-activated fluorescent systems have Eu2+ as the luminescent center. When excitation light strikes the phosphor, the luminescent ion (Eu2+) absorbs the excitation light, exciting an electron in the ground state to an excited state. When this excited electron returns to the ground state, the energy difference is released as fluorescence. Because the Eu2+ ion undergoes both luminescence and absorption transitions, the transition probability is high. On the other hand, the Mn2+-activated fluorescent system has Mn2+ as the luminescent ion, and its luminescence and absorption transitions are forbidden. Despite this low transition probability, it produces a narrow spectral emission and improves color reproducibility.

[0038] The inventors of this application have discovered that display devices that use both Eu2+-activated and Mn2+-activated phosphors can exhibit undesirable effects, such as tinting of displayed images and the mixing of left and right images during 3D displays, known as crosstalk. The inventors have investigated the causes and identified the Mn2+-activated phosphor as the cause. Compared to Eu2+-activated phosphors like CASN and SCASN, Mn2+-activated phosphors like KSF have a narrower half-width at half-maximum (FWHM) and superior color reproducibility. However, after the LED light is turned off, the afterglow time (the time it takes for the fluorescence intensity to reach 1 / e (e is the base of the natural logarithm)) is approximately 10 milliseconds, 100 to 1000 times longer than the 1 to 10 microseconds of Eu2+-activated phosphors. Crosstalk caused by afterglow of Mn2+-activated phosphors can be noticeable in images such as those with moving scrolling text on the screen, resulting in reduced display quality.

[0039] Based on this discovery, the inventors of this application eliminated the Mn2+-activated phosphor from the fluorescent light-emitting layer, using only Eu2+-activated phosphor. Furthermore, the resulting slight decrease in color reproducibility was compensated by providing the color filter section 120. The display device 100 of this embodiment has the above-described structure, thereby achieving both high display quality by suppressing afterglow and sufficient color reproducibility. In addition, since the LED element configured in the LED part has only one type of single-color light emission structure, the manufacturing process is simple and the productivity is excellent.

[0040] In the green conversion layer 1B and the red conversion layer 1C, the mixing of phosphors emitting different colors results in energy transfer via the Förster mechanism. This energy transfer, caused by photoluminescence, occurs by utilizing the light emitted by one phosphor as excitation energy for another. The Förster mechanism bypasses the process of emission and absorption of light, instead transferring excitation energy directly between two adjacent phosphors through electron resonance. Because energy transfer between phosphors via the Förster mechanism occurs without the need for emission and absorption, under optimal conditions, energy loss is minimal.

[0041] To increase brightness through energy transfer, phosphors of different colors must be placed close to each other, or the wavelength of light emitted by the phosphor that absorbs the excitation light emitted by the LED element must be close to the maximum absorption wavelength of the other phosphor. In the green conversion layer 1B and red conversion layer 1C of the fluorescent light-emitting layer 1 of this embodiment, by mixing and dispersing two types of phosphors, the distance between the phosphors is shortened compared to stacking layers containing the two phosphors separately. This improves energy transfer efficiency.

[0042] FIG2 shows a modified example of the display device according to this embodiment. Display device 200 shown in FIG2 includes a blue LED element 112A that emits blue light, instead of LED element 112. Specifically, in LED section 110A of display device 200, only a plurality of blue LED elements 112A are arranged on substrate 111. In this specification, blue light refers to light with a wavelength of 410 nm or more and less than 490 nm, and a blue LED refers to an LED with a light emission peak in the wavelength range of 410 nm or more and less than 490 nm.

[0043] The LED section 110A of the display device 200 has a scattering layer 1D instead of the blue conversion layer 1A, and has a green conversion layer 1b instead of the green conversion layer 1B. The scattering layer 1D has a structure in which transparent light scattering particles 5 are dispersed in the matrix resin. The green conversion layer 1 b contains only the second phosphor 3 as a phosphor, and does not contain the first phosphor 2 . The color filter portion 120A includes a transparent layer CL instead of the blue filter B. The material of the transparent layer CL can be the same as that of the transparent resin layer 7 . The display device 200 uses the blue LED element 112A and uses the light from the LED element 112A as blue without wavelength conversion. However, the red conversion layer 1C performs wavelength conversion substantially similar to that of the display device 100, and thus exhibits the same effect.

[0044] The second embodiment of the present invention will be described below with reference to Figures 3 to 6. In the following description, the same reference numerals are used for the components common to those already described, and repeated descriptions are omitted.

[0045] 3 is a schematic cross-sectional view of a display device 300 according to this embodiment. The display device 300 includes an LED unit 310 and a wavelength conversion substrate 320. The LED unit 310 has a configuration in which the spacer 6 and the fluorescent layer 1 are removed from the LED unit 110 of the first embodiment.

[0046] 4 shows a wavelength conversion substrate 320. The wavelength conversion substrate 320 has a structure in which a black matrix 121 and color filters R, G, and B are sequentially formed on a transparent substrate 321, and a partition 6 and a fluorescent light-emitting layer 1 are further provided thereon. The display device 300 can be manufactured by disposing a transparent adhesive layer 11 in a manner covering the LED element 112 of the LED unit 310 and bonding the partition 6 side of the wavelength conversion substrate 320 to the adhesive layer 11 to adhere the LED unit 310 and the wavelength conversion substrate 320.

[0047] The positional relationship of the black matrix 121 of the display device 300 is slightly different from that of the display device 100 of the first embodiment, but the wavelength conversion of the light emitted from the LED element 112 by the fluorescent light-emitting layer 1 is roughly the same as that of the display device 100, so the same effect is achieved. The wavelength conversion substrate 320 in this embodiment can be helpful for efficiently manufacturing a display device that achieves both high display quality by suppressing afterglow and sufficient color reproducibility.

[0048] 5 and 6 , a modified example of this embodiment is shown. The display device 400 of the modified example shown in FIG5 is formed by bonding an LED unit 310A and a wavelength conversion substrate 320A via an adhesive layer 11 . The LED unit 310A has the same structure as the LED unit 310, except that it includes a blue LED element 112A instead of the LED element 112. The wavelength conversion substrate 320A has the same structure as the wavelength conversion substrate 320, except that it includes a scattering layer 1D, a green conversion layer 1b, and a transparent layer CL instead of the blue conversion layer 1A, the green conversion layer 1B, and the blue filter B. That is, the display device 400 is configured with a monochromatic light source that emits blue light, and has substantially the same effects as the above-mentioned display device 200.

[0049] The inventors have discovered that the multiple types of Eu 2+ activated phosphors contained in the fluorescent light emitting layer have an optimal mixing ratio. This is demonstrated below using experimental examples.

[0050] (Experimental Example 1: Discussion on Using UV LED) An ultraviolet LED with a peak emission wavelength of 385 nm is used as the LED element. The materials used for the fluorescent light-emitting layer are as follows. Base resin: Silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd.) First phosphor: Eu 2+ activated apatite phosphor (particle size 3.7μm) Second phosphor: Eu2+ activated (Ba, Sr)GaS phosphor (particle size 4.6μm) Third phosphor: Eu 2+ activated SCASN phosphor (particle size 5.4 μm) The excitation and fluorescence spectra of the first, second, and third phosphors are shown in Figures 7, 8, and 9, respectively. Figures 7 to 9 show that the peak emission wavelength of the UV LED is within the excitation spectrum of the first phosphor. The peak region of the fluorescence spectrum of the first phosphor is close to the peak region of the excitation spectrum of the second phosphor, and the peak region of the fluorescence spectrum of the second phosphor is close to the peak region of the excitation spectrum of the third phosphor.

[0051] (1-1: Red conversion layer) The red conversion layer was fabricated using the aforementioned matrix resin and the second and third phosphors, which had been ground to uniform particle size. The amount of the third phosphor was fixed at 20 parts by mass per 100 parts by mass of the matrix resin, while the amount of the second phosphor was varied to produce the following four compositions. Composition 1: 5 parts (the amount of the second phosphor is 5 parts by mass) Composition 2: 10 parts (the amount of the second phosphor is 10 parts by mass) Composition 3: 20 parts (the amount of the second phosphor is 20 parts by mass) Composition 4: 30 parts (the amount of the second phosphor is 30 parts by mass) Each composition was applied to a red filter formed using a color resist manufactured by TOYO VISUAL SOLUTIONS and patterned. This yielded samples 1-4 having structures similar to wavelength conversion substrate 320. Samples 1-4 each had a red conversion layer formed using compositions 1-4. For each sample, the red conversion layer was placed toward the LED element side, the LED element was made to emit light, and the emission spectrum was measured from the red filter side using a front luminance meter.

[0052] Figure 10 shows the emission spectra of samples 1-4. For all samples, the peak wavelength emission intensity increases compared to the case with only the red filter. Because samples 2-4 showed particularly good results, the optimal ratio (mass ratio) of the third phosphor to the second phosphor is believed to be approximately 4:2 to 2:4 (within the range of 2:1 to 1:2).

[0053] (1-2: Green conversion layer) A green conversion layer was fabricated using a matrix resin and first and second phosphors that had been ground to uniform particle size. The amount of second phosphor was fixed at 20 parts by mass per 100 parts by mass of matrix resin, while the amount of first phosphor was varied to produce the following four compositions. Composition 5: 5 parts (the amount of the first phosphor is 5 parts by mass) Composition 6: 10 parts (the amount of the first phosphor is 10 parts by mass) Composition 7: 20 parts (the amount of the first phosphor is 20 parts by mass) Composition 8: 30 parts (the amount of the first phosphor is 30 parts by mass) Each composition was applied to a green filter formed using a color resist manufactured by TOYO VISUAL SOLUTIONS and patterned. This yielded samples 5-8 having a structure similar to wavelength conversion substrate 320. Samples 5-8 each had a green conversion layer formed using compositions 5-8. For each sample, the green conversion layer was placed toward the LED element side, the LED element was made to emit light, and the emission spectrum was measured from the green filter side using a front luminance meter.

[0054] The luminescence spectra of samples 5 to 8 are shown in Figure 11. For all samples, the luminescence intensity at the peak wavelength increases compared to the case with only the green filter.

[0055] (Experimental Example 2: Discussion on Using Blue LED) A blue LED having a peak emission wavelength of 450 nm was used as the LED element. For samples 1 to 4 used in Experimental Example 1-1, the red conversion layer was placed toward the LED element side, the LED element was made to emit light, and the emission spectrum was measured from the red filter side using a front luminance meter.

[0056] Figure 12 shows the luminescence spectra of samples 1-4 from Experimental Example 2. For all samples, the luminescence intensity at the peak wavelength increases compared to the case with only the red filter. Similar to Experimental Example 1-1, the ratio (mass ratio) of the third phosphor to the second phosphor is considered to be optimally between 4:2 and 2:4 (within the range of 2:1 to 1:2).

[0057] (Experimental Example 3: Study on the afterglow time caused by phosphors) The following discusses the effect of the phosphors used in the green conversion layer on the afterglow time. The compositions of the green conversion layers 1 and 2 used in the experiment are shown below. Green conversion layer 1 Matrix resin: Silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts (100 parts by mass) Phosphor: Eu2+ activated (Ba, Sr)GaS phosphor (particle size 4.6 μm) 30 parts (30 parts by mass) Green conversion layer 2 Matrix resin: 100 parts (100 parts by mass) of the same as green conversion layer 1 Phosphor: 30 parts by mass of Eu2+, Mn2+ co-activated BaMgAlO phosphor (particle size 3.9 μm) The compositions of each conversion layer were applied to a green filter formed using a color resist manufactured by TOYO VISUAL SOLUTIONS and patterned. This yielded samples 9 and 10 with structures similar to wavelength conversion substrate 320. Samples 9 and 10 included green conversion layer 1 and green conversion layer 2, respectively. For each sample, the green conversion layer was positioned toward the light source and irradiated with pulsed light, causing it to emit light. The time t from when the pulsed light was turned off to when the spectrum measurement actually began (called the delay time) was varied from 0.05ms to 20ms, and the intensity of the fluorescence was measured multiple times simultaneously.

[0058] The fluorescence lifetime spectra of samples 9 and 10 are shown in Figure 13. Figure 13 also shows the fluorescence intensity at the delay time t=0. For Sample 9, no signal was observed at the shortest delay time, t = 0.05ms, and no luminescence was detected across the entire range. Therefore, for Sample 9, it is presumed that the fluorescence disappeared within 0.05ms, and the afterglow time obtained according to the above definition is determined to be less than 0.05ms. On the other hand, for sample 10, a signal was observed at t = 0.05 ms, and a decay curve was obtained showing an exponential decrease in luminous intensity thereafter. According to the above definition, the afterglow time is 3.6 ms. From the above, we can see that the afterglow time of the conversion layer using Eu2+ activated phosphor is in the sub-millisecond level, and the afterglow time of the conversion layer using Eu2+ and Mn2+ co-activated phosphor is in the millisecond level, showing the superiority of the conversion layer using Eu2+ activated phosphor.

[0059] The above describes in detail various embodiments of the present invention with reference to the drawings, but the specific configuration is not limited to these embodiments and also includes changes and combinations of the configurations that do not depart from the scope of the present invention.

[0060] For example, the present invention can be modified as follows. ･Each layer of the fluorescent light-emitting layer contains light scattering particles 5 ･The red conversion layer 1C contains the first phosphor 2 The blue conversion layer 1A and the blue filter B are used in the display device 200 and the wavelength conversion substrate 320A.

[0061] The color filter unit and wavelength conversion substrate of the present invention may be provided with a layer such as a transmittance adjustment layer and an antireflection layer to impart desired characteristics.

[0062] The fluorescent light-emitting layer may also contain quantum dots. Quantum dots are nanometer-sized semiconductor particles with quantum confinement effects. By adding them to the fluorescent light-emitting layer, they can assist in wavelength conversion. The amount of quantum dots added can be approximately 0.5% to 10% of the phosphor's mass. Since quantum dots are less heat-resistant and light-resistant than phosphors, excessive additions can reduce the reliability of display devices and wavelength conversion substrates. The heat resistance of the fluorescent layer can be evaluated by placing it in a 150°C oven for 500 hours and measuring the change in its luminescence characteristics. Light resistance can be measured by irradiating it with a xenon lamp for 200 hours at 40°C and 70% humidity. From the perspective of reliability when constructing a display device, the change in the luminescence characteristics of the fluorescent layer after heat resistance and light resistance tests is preferably 10% or less. One or more of the luminescence characteristics to be considered as indicators may be selected from "internal quantum yield," "luminescence intensity at the main peak wavelength," "full width at half maximum at the main peak wavelength," and "optical concentration." [Possibility of Industrial Application]

[0063] The present invention can be used in a display device that can achieve high luminous efficiency and high productivity.

[0064] 1: Fluorescent layer 2: First phosphor 3: Second phosphor 4: Third phosphor 6: Partition 100, 200, 300, 400: Display device 110,110A,310,310A:LED 111:Substrate 112,112A:LED components 120,120A: Color filter unit 320,320A: Wavelength conversion substrate 321:Transparent substrate B: Blue filter G: Green filter R: Red filter

Claims

1. A display device comprising: an LED section having only one of a plurality of near-ultraviolet LEDs and a blue LED disposed on a substrate; a partition configured to be a grid with a plurality of openings in plan view, wherein the near-ultraviolet LEDs or the blue LEDs are located within the openings; a color filter section having a red filter, a green filter, and a blue filter, wherein the red filter, the green filter, and the blue filter are configured to overlap with the openings in plan view; and a fluorescent light-emitting layer disposed between the LED section and the color filter section, wherein an Eu2+ activated phosphor is located within the openings in plan view, wherein an Eu2+ activated phosphor is dispersed in a matrix resin; the fluorescent light-emitting layer having only the Eu2+ activated phosphor as a phosphor. At least a portion of the fluorescent light-emitting layer is a red conversion layer, comprising a first phosphor that uses the light emitted from the LED as excitation light and a second phosphor that uses the fluorescence emitted from the first phosphor as excitation light as the Eu2+ activating phosphor, wherein the mass ratio of the first phosphor to the second phosphor is in the range of 2:1 to 1:

2.

2. The display device of claim 1, wherein the particle size of the Eu2+ activated phosphor is between 0.1 μm and 15 μm.

3. The display device of claim 1, wherein the rate of change of the luminescent properties of the fluorescent light-emitting layer after 200 hours of irradiation by a xenon lamp is less than 10%.

4. The display device of claim 1, wherein the thickness of the fluorescent light-emitting layer is more than 1 μm and less than 50 μm.

5. The display device of claim 1, wherein the fluorescent light-emitting layer contains quantum dots.

6. A wavelength conversion substrate comprising: a transparent substrate; a color filter disposed on the substrate, having a red filter, a green filter, and a blue filter; a partition configured as a grid having a plurality of openings in plan view, wherein any one of the red filter, the green filter, and the blue filter is located within the openings; and a fluorescent light-emitting layer located within the openings in plan view, wherein an Eu2+ activated phosphor is dispersed in a matrix resin; the fluorescent light-emitting layer having only the Eu2+ activated phosphor as a phosphor, at least a portion of the fluorescent light-emitting layer being a red conversion layer comprising a first phosphor and a second phosphor that uses the fluorescence emitted by the first phosphor as excitation light as the Eu2+ activated phosphor, wherein the mass ratio of the first phosphor to the second phosphor is in the range of 2:1 to 1:2.

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