JP7815946B2 - Display device and wavelength conversion substrate - Google Patents

Description

The present invention relates to a display device. It also describes a wavelength conversion substrate that can be suitably used in this display device.

In recent years, there has been active development of self-luminous display devices such as micro LED (Light Emitting Diode) displays and organic electroluminescence (hereinafter also referred to as "organic EL") displays. Micro LED displays are display devices that have a structure in which LED elements approximately 2 μm to 50 μm in size are arranged in a matrix, and display is achieved by individually driving each of the multiple LED elements. Such self-luminous display devices can display without using liquid crystal as a display functional layer that switches between light transmission and non-transmission, and therefore have superior visibility, especially in dark places, compared to liquid crystal display devices, which have the issue of light leakage when displaying black.

Micro LED displays can be broadly divided into those that use three types of LED elements (red, green, and blue light), and those that use only single-color LED elements that emit light in the blue to near-ultraviolet wavelength range. In micro LED displays, each LED element serves as the display function layer. Systems that use three types of LED elements (red, green, and blue light) offer superior brightness and lifespan. However, issues include increased costs due to the additional LED element mounting process and difficulty in control due to the different driving voltages for each LED element, and many efforts are being made to resolve these issues.

One solution is to use monochromatic LED elements. This method simplifies the manufacturing process by using only one type of LED element, and achieves color display by stacking a wavelength conversion layer that converts the wavelength of light emitted from the LED element into red, green, and blue. The wavelength conversion layer can be, for example, a layer in which quantum dots or inorganic phosphors are dispersed.
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 this light source into red, green, and blue.

Patent Document 2 discloses a technique for laminating a plurality of phosphor layers in order to effectively utilize light emitted from light-emitting elements such as LEDs and organic EL devices.
In Patent Document 2, two or more phosphor layers are patterned and stacked by photolithography to maximize the conversion efficiency of light emitted from a light-emitting element. Light emitted from the light-emitting element is first absorbed by the lower phosphor layer, and the light emitted from the lower phosphor layer is absorbed by the upper phosphor layer and re-emitted. This down-conversion of the wavelength of the emitted light improves the conversion efficiency.

Patent Document 3 discloses a technique for mixing phosphors in order to effectively utilize light emitted from a light emitting element such as an LED.
Patent Document 3 describes that a wavelength conversion layer in which a Mn ²⁺ -activated phosphor and a Eu ²⁺ phosphor are mixed in an appropriate weight ratio achieves both a wide color gamut and high luminous efficiency.

International Publication No. 2019/159702 International Publication No. 2013/133139 Japanese Patent Application Laid-Open No. 2019-29584

Although the details will be described later, the technology of Patent Document 2 has room for improvement in terms of insufficient down-conversion efficiency and productivity.
With respect to the technology of Patent Document 3, the inventors have discovered and solved new problems not described in Patent Document 3, and have completed the present invention.

In light of the above circumstances, the present invention aims to provide a display device that can achieve high luminous efficiency and high productivity.

A first aspect of the present invention is a display device comprising: an LED section in which a plurality of either near-ultraviolet LEDs or blue LEDs are arranged on a substrate; a partition wall having a lattice shape with a plurality of openings in a planar view and arranged so that the near-ultraviolet LEDs or the blue LEDs are located within the openings; a color filter section having red filters, green filters, and blue filters arranged so that the red filters, green filters, and blue filters overlap with the openings in a planar view; and a fluorescent light-emitting layer provided between the LED section and the color filter section, located within the openings in a planar view, and having a Eu ²⁺ -activated phosphor dispersed in a base resin.
The fluorescent-emitting layer has only a Eu ²⁺ -activated phosphor as a phosphor, and at least a portion of the fluorescent-emitting layer is a red conversion layer. The Eu ²⁺ -activated phosphor includes a first phosphor that uses light emitted from the LED section as excitation light and a second phosphor that uses fluorescence emitted by the first phosphor as excitation light, and the mass ratio of the first phosphor to the second phosphor is within a range of 2:1 to 1:2 .

A second aspect of the present invention is a wavelength conversion substrate comprising: a transparent substrate; a color filter provided on the substrate and having a red filter, a green filter, and a blue filter; partition walls having a lattice shape with a plurality of openings in a planar view and arranged so that any one of the red filter, the green filter, and the blue filter is located within the opening; and a fluorescent-emitting layer located within the opening in a planar view and having a Eu ²⁺ -activated phosphor dispersed in a base resin.
The fluorescent-emitting layer has only a Eu ²⁺ -activated phosphor as a phosphor, and at least a portion of the fluorescent-emitting layer is a red conversion layer, and the Eu ²⁺ -activated phosphor includes a first phosphor and a second phosphor that uses the fluorescence emitted by the first phosphor as excitation light, and the mass ratio of the first phosphor to the second phosphor is within a range of 2:1 to 1:2 .

The present invention provides a display device that can achieve high luminous efficiency and high productivity.

1 is a schematic cross-sectional view of a display device according to a first embodiment of the present invention. FIG. 10 is a schematic cross-sectional view showing a modified example of the display device. FIG. 4 is a schematic cross-sectional view of a display device according to a second embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a wavelength conversion substrate of the display device. FIG. 10 is a schematic cross-sectional view showing a modified example of the display device. FIG. 10 is a schematic cross-sectional view showing a wavelength conversion substrate according to a modified example of a display device. 10A and 10B are diagrams showing an excitation spectrum and a fluorescence spectrum of a first phosphor according to an experimental example. 10A and 10B are diagrams showing the excitation spectrum and the fluorescence spectrum of a second phosphor according to an experimental example. 10A and 10B are diagrams showing the excitation spectrum and the fluorescence spectrum of a third phosphor according to an experimental example. FIG. 10 is a diagram showing the emission spectrum of a sample in an experimental example. FIG. 10 is a diagram showing the emission spectrum of a sample in an experimental example. FIG. 10 is a diagram showing the emission spectrum of a sample in an experimental example. FIG. 10 is a diagram showing the fluorescence lifetime spectra of samples in experimental examples.

A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG.
In the following description, the same or substantially the same functions and components are denoted by the same reference numerals, and their description will be omitted or simplified, or will be described only when necessary.

In this specification, the term "planar view" refers to a state in which an observer views the surface of a display device, a wavelength conversion substrate, or the like, which will be described later, in the normal direction.
Ordinal numbers such as "first" and "second" in each structure are used to avoid confusion of the components and do not specify the order or quantity.
The LEDs used in the present invention include 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 indium gallium phosphide (AlGaInP). Gallium nitride (GaN) is mainly used for blue LEDs and near-ultraviolet LEDs, which will be described later as monochromatic LEDs.

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

The LED section 110 has a basic structure in which a plurality of LED elements 112 are arranged in a matrix on a substrate 111. One type of LED element is arranged on the substrate 111. The LED elements 112 in this embodiment emit light in the ultraviolet wavelength band and are, for example, micro LEDs with dimensions of approximately 2 μm to 50 μm.
There are no particular limitations on the structure of the LED element 112, and either a horizontal LED in which the n-side electrode and the p-side electrode are on the same side, or a vertical LED in which the n-side electrode and the p-side electrode sandwich the light-emitting portion in the thickness direction, can be used. Figure 1 shows a vertical LED.

The LED element 112 is a monochromatic near-ultraviolet LED that emits near-ultraviolet light. In this specification, "monochromatic emission" means that the half-width of the emitted light is 70 nm or less and that the emitted light has one emission peak within its wavelength range. The smaller the half-width of the LED element 112, the better. Furthermore, near-ultraviolet light refers to light with a wavelength in the range of 300 nm or more and less than 410 nm. A near-ultraviolet LED is an LED that has an emission peak in the wavelength range of 300 nm or more and less than 410 nm.

The partition walls 6 are formed on the substrate 111. In a plan view of the LED section 110, the partition walls 6 are in a lattice shape, and surround each of the LED elements 112 to isolate them from each other.
The partition walls 6 contain carbon and have the property of absorbing light. Carbon having low wavelength selectivity for visible light is preferable. "Low wavelength selectivity for visible light" means that there is almost no coloring of absorbed or reflected light in the wavelength range of 400 nm to 700 nm, and the color appears black or gray to the naked eye.
When the partition walls 6 are formed by a carbon dispersion in a resin, a photolithography technique can be applied. When the partition walls 6 are formed by a photolithography technique, an alkali-soluble photosensitive resin can be used.

The partition walls 6 are not limited to being light-absorbing, but may be light-reflective. The light-reflective partition walls may be configured, for example, by covering the surface of a resin core with a metal thin film.
The core can be formed by patterning an alkali-soluble photosensitive resin by a well-known photolithography technique, or by patterning a thermosetting resin layer by a dry etching technique.
Examples of photosensitive resins include resins obtained by reacting a linear polymer having a reactive substituent such as a hydroxyl group, a carboxyl group, or an amino group with a (meth)acrylic compound or cinnamic acid having a reactive substituent such as an isocyanate group, an aldehyde group, or an epoxy group, to introduce a photocrosslinkable group such as a (meth)acryloyl group or a styryl group into the linear polymer.

In each section separated by the partition walls 6, a fluorescent-emitting layer 1 is provided so as to cover the LED elements 112. The fluorescent-emitting layer 1 has a basic structure in which granular fluorescent material is dispersed in a transparent base resin.
Examples of the base resin include silicone resin, epoxy resin, phenol resin, polycarbonate resin, acrylic resin, polynorbulmene resin, modified resins thereof, hybrid resins, etc. Among these, silicone resin is preferred because of its excellent heat resistance and light resistance.

In this embodiment, the fluorescent light-emitting layer 1 is made up 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 configuration in which a first phosphor 2 that absorbs ultraviolet light and emits blue fluorescence is dispersed in a base resin. That is, the blue conversion layer 1A includes one type of phosphor.
Green conversion layer 1B has a configuration in which first phosphor 2 and second phosphor 3 that absorbs blue light and emits green fluorescence are dispersed in a base resin. That is, green conversion layer 1B includes two types of phosphors.
The red conversion layer 1C has a configuration in which a second phosphor 3 and a third phosphor 4 that absorbs green light and emits red fluorescence are dispersed in a base resin. That is, the red conversion layer 1C includes two types of phosphors.
The first phosphor 2, the second phosphor 3, and the third phosphor 4 are all Eu ²⁺ -activated phosphors, as will be described in detail later.
The particle diameter of each phosphor is preferably 0.1 μm or more and 15 μm or less. In this specification, the particle diameter at 50% of the integrated value in the particle size distribution obtained by photon correlation spectroscopy is defined as the "particle diameter." In simple terms, this can be defined as the arithmetic mean value of the diameters of the phosphor particles observed by observing a predetermined area of the cross section of the fluorescent-emitting layer 1 with a scanning microscope.

The fluorescent-emitting layer 1 can be easily fabricated by applying a dispersion liquid in which a predetermined phosphor is dispersed in a photosensitive resin as a base resin, and then patterning the layer using a photolithography technique. The thickness of the fluorescent-emitting layer 1 can be 1 μm or more and 50 μm or less. It may be formed to a thickness greater than 50 μm, but if it is too thick, it is likely to increase the process load during formation, such as wasted work time during coating and drying. If the thickness of the fluorescent-emitting layer 1 is 1 μm or more and 50 μm or less, it is easy to align the height with that of the partition walls 6.
The thickness of the fluorescent-emitting layer 1 is preferably equal to or less than the height of the partition walls 6. If the thickness of the fluorescent-emitting layer 1 is greater than the height of the partition walls 6, the light from the fluorescent-emitting layer 1 may leak into adjacent pixels.
The base resin is preferably made of a material that is resistant to heat degradation and that is unlikely to change in transmittance of light emitted from the LED element 112 even after heat treatment for 500 hours at 150° C. For example, it is preferable that the rate of change in transmittance before and after heat treatment for 500 hours at 150° C. be 5% or less at the LED's emission peak wavelength of 385 nm.

The partition wall 6 and the fluorescent-emitting layer 1 are covered with a transparent resin layer 7. The upper surface of the LED section 110 is flattened by the transparent resin layer 7.

The basic configuration of the color filter section 120 is well known and includes a black matrix (hereinafter sometimes referred to as "BM") 121 and multiple color filters. The number and combination of color filters in the color filter section can be set appropriately depending on the application, etc. The color filter section 120 of this embodiment has three types of color filters: a red filter R, a green filter G, and a blue filter B.

The black matrix 121 is formed in contact with the transparent resin layer 7. The black matrix 121 forms a lattice pattern having a plurality of openings in a plan view, and this lattice pattern overlaps the lattice pattern of the partition walls 6 in a plan view of the display device 100.
The method for forming the black matrix 121 is not particularly limited, but if an alkali-soluble photosensitive resist in which light-shielding carbon is dispersed is used, a grid pattern can be easily formed by known photolithography.

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

Examples of red organic pigments that can be used in the red filter R include C.I. 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 may be mixed with yellow pigments or orange pigments. Applicable yellow organic pigments include C.I. 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, 113, 114, 115, 116, 117, 118, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 16 Examples include 17, 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, and 214.
The red filter R preferably has a transmittance of 5% or less for light with a wavelength of 380 nm or more and 580 nm or less.

Examples of green pigments that can be used for the green filter G include C.I. Pigment Green 7, 10, 36, and 37. These green pigments may be mixed with the above-mentioned yellow pigment. Additionally, halogenated zinc phthalocyanine green pigments and halogenated aluminum phthalocyanine green pigments can also be suitably used.
The green filter G preferably has a transmittance of 5% or less for light with a wavelength of 380 nm or more and 480 nm or less.

Examples of blue pigments that can be used in the blue filter B include C.I. Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 60, 64, and the like.
These blue pigments may be mixed with a violet pigment, such as C.I. Pigment Violet 1, 19, 23, 27, 29, 30, 32, 37, 40, 42, or 50.

The pigments described above are dispersed in a transparent resin together with an organic solvent and a dispersant. The transparent resin is preferably a transparent resin having a visible transmittance of 90% or more, and is preferably an alkali-soluble photosensitive resin containing a resin precursor. The pigment content of the resin can be in the range of 15% to 65% by mass.
Examples of photosensitive resins include polyimide resins, epoxy resins, acrylic resins, melamine resins, phenolic resins, oxetane resins, siloxane resins, benzoxazine resins, and the like, which are obtained by reacting a linear polymer having a reactive substituent such as a hydroxyl group, a carboxyl group, or an amino group with a (meth)acrylic compound or cinnamic acid having a reactive substituent such as an isocyanate group, an aldehyde group, an epoxy group, or a silanol group, to introduce a photocrosslinkable group such as a (meth)acryloyl group or a styryl group into the linear polymer. Precursor monomers and oligomers include various acrylic acid esters and methacrylic acid esters 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, tricyclodecanyl (meth)acrylate, melamine (meth)acrylate, and epoxy (meth)acrylate, as well as (meth)acrylic acid, styrene, vinyl acetate, (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and acrylonitrile. These may be used alone or in combination of two or more. When the photosensitive resin is cured by irradiation with ultraviolet light at a wavelength of 365 nm or the like, a photopolymerization initiator or the like may be added to the photosensitive resin.

Each of the color filters R, G, and B is arranged so that one of them overlaps an opening in the black matrix 121 in a planar view. In a planar view of the display device 100, each of the color filters R, G, and B overlaps with the red conversion layer 1C, green conversion layer 1B, and blue conversion layer 1A, respectively. The red filter R, green filter G, and blue filter B may be arranged in contact with each other or spaced apart.

The operation of the display device 100 configured as above when in use will be described.
In the display device 100, a set of adjacent red filters R, green filters G, and blue filters B constitutes one pixel. In each pixel, the LED elements 122 corresponding to the red filters R, green filters G, and blue filters B are driven in accordance with the input video signal, changing the color and brightness of the pixel.

The excitation light emitted from the LED element 122 is incident on the fluorescent light-emitting layer 1 before reaching the color filter section 120 .
The excitation light incident on the blue conversion layer 1A is wavelength-converted into blue fluorescence by the first phosphor 2 and then incident on the blue filter B.
Most of the excitation light incident on the green conversion layer 1B is wavelength-converted into blue fluorescence by the first phosphor 2. A part of this blue fluorescence is wavelength-converted into green fluorescence by the second phosphor 3 and then incident on the green filter G.
Most of the excitation light incident on the red conversion layer 1C is wavelength-converted into green fluorescence by the second phosphor 3. A part of this green fluorescence is wavelength-converted into red fluorescence by the third phosphor 4 and then incident on the red filter R.

Phosphors 2, 3, and 4 used in this embodiment are all Eu ²⁺ -activated phosphors. In the present invention, the term "Eu ²⁺ -activated phosphor" refers to a phosphor activated only by Eu ²⁺ , and does not include Eu ²⁺ and Mn ²⁺ -coactivated BaMgAlO phosphors that are activated by other ions in addition to Eu ²⁺ .
Eu ²⁺ -activated phosphors have Eu ²⁺ as the luminescent center, and when the phosphor is irradiated with excitation light, the luminescent ion (Eu ²⁺ ) absorbs the excitation light, and the electrons at the ground level are excited to the excited level. When these excited electrons return to the ground level, the difference in energy is emitted as fluorescence. The luminescent ion Eu ²⁺ has a high transition probability because the transitions of emission and absorption are allowed transitions. On the other hand, Mn ²⁺ -activated phosphors have Mn ²⁺ as the luminescent ion, and the transitions of emission and absorption are forbidden transitions. Therefore, although the transition probability is low, they have the characteristic of being able to obtain emission with a narrow spectrum and improve color reproducibility.

The inventors have found that display devices using a combination of an Eu ²⁺ -activated phosphor and an Mn ²⁺ -activated phosphor suffer from problems such as a phenomenon in which the displayed image appears colored and a so-called crosstalk phenomenon in which the left and right images appear mixed during 3D display. The inventors have investigated the cause of these problems and have found that the Mn ²⁺ -activated phosphor is involved.
Mn ²⁺ -activated phosphors such as KSF phosphors have a wider wavelength range of peak wavelengths and are superior in color reproducibility than Eu ²⁺ -activated phosphors such as CASN phosphors and SCASN phosphors. On the other hand, their decay time, which is the time it takes for the fluorescent light intensity to reach 1/e (e is the base of the natural logarithm) after the light from the LED element has gone out, is about 10 milliseconds, which is 100 to 1000 times longer than the 1 to 10 microseconds of Eu ²⁺ -activated phosphors.
Crosstalk caused by the afterglow of the Mn ²⁺ -activated phosphor is particularly noticeable in, for example, an image in which telop characters flow on the screen, and reduces the display quality.

Based on the above findings, the inventors eliminated the Mn ²⁺ -activated phosphor from the fluorescent-emitting layer and configured it using only the Eu ²⁺ -activated phosphor, and further compensated for the slight degradation in color reproducibility that would result from this by providing a color filter unit 120.
In the display device 100 according to this embodiment, the above-described configuration achieves both high display quality with suppressed afterglow and sufficient color reproducibility.
Furthermore, since the LED element arranged in the LED section is of a single type and emits light of a single color, the manufacturing process is simple and the productivity is excellent.

In the green conversion layer 1B and red conversion layer 1C, phosphors that emit fluorescent light of different colors are mixed, which causes an energy transfer phenomenon via the Förster mechanism. Energy transfer via photoluminescence occurs when fluorescence emitted from one phosphor is used as excitation energy for another phosphor. The Förster mechanism involves the direct transfer of excitation energy between two nearby phosphors through electron resonance, without going through the processes of light emission and absorption. Because energy transfer between phosphors via the Förster mechanism occurs without going through the processes of light emission and absorption, there is little energy loss under optimal conditions.

In order to improve brightness through energy transfer, the different color phosphors must be located close to each other, and the emission wavelength of one of the different color phosphors that absorbs the excitation light emitted from the LED element and emits light 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-emitting layer 1 according to this embodiment, by mixing and dispersing two types of phosphors, the distance between the phosphors is shorter than if layers containing each of the two types of phosphors were stacked. As a result, energy transfer efficiency can be improved.

A modified example of the display device according to this embodiment is shown in Fig. 2. The display device 200 shown in Fig. 2 has blue LED elements 112A that emit blue light instead of the LED elements 112.
In this specification, blue light refers to light having a wavelength in the range of 410 nm or more and less than 490 nm, and a blue LED is an LED having an emission peak in the wavelength range of 410 nm or more and less than 490 nm.

The LED section 110A of the display device 200 has a scattering layer 1D instead of the blue conversion layer 1A, and a green conversion layer 1b instead of the green conversion layer 1B.
The scattering layer 1D has a configuration in which transparent light scattering particles 5 are dispersed in the above-mentioned base resin.
The green color conversion layer 1 b contains only the second phosphor 3 as a phosphor, and does not contain the first phosphor 2 .
The color filter section 120A has a transparent layer CL instead of the blue filter B. The transparent layer CL may be made of the same material as the transparent resin layer 7.
In the display device 200, by using a blue LED element 112A, the light from the LED element 112A is used as blue light without wavelength conversion, but in the red conversion layer 1C, wavelength conversion is performed in a manner roughly similar to that of the display device 100, and therefore the same effect is achieved.

A second embodiment of the present invention will be described with reference to Figures 3 to 6. In the following description, components that are common to those already described will be assigned the same reference numerals and duplicate descriptions will be omitted.

Figure 3 is a schematic cross-sectional view showing a display device 300 according to this embodiment. The display device 300 includes an LED section 310 and a wavelength conversion substrate 320. The LED section 310 has a configuration similar to that of the LED section 110 of the first embodiment, except that the partition wall 6 and the fluorescent-emitting layer 1 are removed.

4 shows the wavelength conversion substrate 320. The wavelength conversion substrate 320 has a configuration in which a black matrix 121 and color filters R, G, and B are formed in this order on a transparent substrate 321, and partition walls 6 and a fluorescent-emitting layer 1 are further formed thereon.
The display device 300 can be produced by placing a transparent adhesive layer 11 so as to cover the LED elements 122 of the LED section 310, and bonding the partition wall 6 side of the wavelength conversion substrate 320 to the adhesive layer 11 to bond the LED section 310 and the wavelength conversion substrate 320 together.

Although the positional relationship of the black matrix 121 in the display device 300 is slightly different from that in the display device 100 of the first embodiment, the wavelength conversion of the light emitted from the LED element 112 by the fluorescent light-emitting layer 1 is performed in roughly the same way as in the display device 100, and therefore the same effect is achieved.
The wavelength conversion substrate 320 according to this embodiment can contribute to the efficient manufacture of a display device that achieves both high display quality with suppressed afterglow and sufficient color reproducibility.

Modifications of this embodiment are shown in Figures 5 and 6. A display device 400 of the modification shown in Figure 5 is formed by bonding an LED section 310A and a wavelength conversion substrate 320A via an adhesive layer 11.
The LED section 310A has the same structure as the LED section 310, except that it has 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 has 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 has a configuration in which the monochromatic light source emits blue light, and provides substantially the same effects as the display device 200 described above.

The inventors have found that there is a suitable mixing ratio for the multiple types of Eu ²⁺ -activated phosphors contained in the fluorescent-emitting layer, which will be described below using experimental examples.

(Experimental Example 1: Study using ultraviolet LED)
The LED element used was an ultraviolet LED with an emission peak wavelength of 385 nm.
The materials used in the fluorescent-emitting layer are as follows:
Base resin: Silicone resin (Shin-Etsu Chemical Co., Ltd.)
First phosphor: Eu ²⁺ activated apatite phosphor (particle diameter 3.7 μm)
Second phosphor: Eu ²⁺ activated (Ba, Sr)GaS phosphor (particle diameter 4.6 μm)
Third phosphor: Eu ²⁺ activated SCASN phosphor (particle diameter 5.4 μm)
The excitation spectra and fluorescence spectra of the first phosphor, second phosphor, and third phosphor are shown in Figures 7, 8, and 9, respectively. It can be seen from Figures 7 to 9 that the emission peak wavelength of the above-mentioned ultraviolet LED is within the range of the excitation spectrum of the first phosphor, that the peak band of the fluorescence spectrum of the first phosphor is close to the peak band of the excitation spectrum of the second phosphor, and that the peak band of the fluorescence spectrum of the second phosphor is close to the peak band of the excitation spectrum of the third phosphor.

(1-1: Red color conversion layer)
The red conversion layer was prepared using the above-mentioned base resin and the second and third phosphors, which had been pulverized to a uniform particle size. The amount of the third phosphor was fixed at 20 parts by mass per 100 parts by mass of the base resin, and the amount of the second phosphor was varied to prepare the following four compositions.
Composition 1: 5 parts Composition 2: 10 parts Composition 3: 20 parts Composition 4: 30 parts Each composition was applied and patterned on a red filter formed using a color resist manufactured by Toyo Visual Solutions Co., Ltd. This resulted in samples 1 to 4 having a structure similar to the wavelength conversion substrate 320. Samples 1 to 4 each had a red conversion layer formed using compositions 1 to 4, respectively.
Each sample was placed with the red color conversion layer facing the LED element, and the LED element was made to emit light, and the emission spectrum was measured from the red filter side using a front luminance meter.

The emission spectra of Samples 1 to 4 are shown in Figure 10. The emission intensity at the peak wavelength was increased for all samples compared to when only the red filter was used. Since the results for Samples 2 to 4 were particularly good, it was considered that a ratio of the third phosphor to the second phosphor of approximately 4:2 to 2:4 is preferable.

(1-2: Green color conversion layer)
A green color conversion layer was prepared using a base resin and the first and second phosphors, each of which had been pulverized to a uniform particle size. The amount of the second phosphor was fixed at 20 parts by mass per 100 parts by mass of the base resin, and the amount of the first phosphor was varied to prepare the following four compositions.
Composition 5: 5 parts Composition 6: 10 parts Composition 7: 20 parts Composition 8: 30 parts Each composition was applied and patterned on a green filter formed using a color resist manufactured by Toyo Visual Solutions Co., Ltd. This resulted in samples 5 to 8 having a structure similar to the wavelength conversion substrate 320. Samples 5 to 8 each had a green conversion layer formed using compositions 5 to 8, respectively.
Each sample was placed with the green color conversion layer facing the LED element, and the LED element was made to emit light, and the emission spectrum was measured from the green filter side using a front luminance meter.

The emission spectra of samples 5 to 8 are shown in Figure 11. The emission intensity at the peak wavelength was increased for all samples compared to when only the green filter was used.

(Experimental Example 2: Study using blue LED)
A blue LED with a peak emission wavelength of 450 nm was used as the LED element.
Samples 1 to 4 used in Experimental Example 1-1 were arranged with the red color conversion layer facing the LED element side, and the LED element was made to emit light, and the emission spectrum was measured from the red filter side using a front luminance meter.

Figure 12 shows the emission spectra of Samples 1 to 4 in Experimental Example 2. The emission intensity at the peak wavelength was increased for all samples compared to when only the red filter was used. As with Experimental Example 1-1, a ratio of the third phosphor to the second phosphor of approximately 4:2 to 2:4 was considered preferable.

(Experimental Example 3: Study of decay time by phosphor)
The influence of the phosphors used in the green conversion layer on the decay time was examined. The compositions of the green conversion layers 1 and 2 used in the experiment are shown below.
Green color conversion layer 1
Base resin: Silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts Phosphor: Eu ²⁺ activated (Ba, Sr)GaS phosphor (particle diameter 4.6 μm) 30 parts Green color conversion layer 2
Base resin: 100 parts of the same as green conversion layer 1 Phosphor: Eu ²⁺ ,Mn ²⁺ co-activated BaMgAlO phosphor (particle diameter 3.9 μm) 30 parts The compositions for each conversion layer were applied and patterned on a green filter formed using a color resist manufactured by Toyo Visual Solutions Co., Ltd. This resulted in samples 9 and 10 having a structure similar to wavelength conversion substrate 320. Samples 9 and 10 each comprise green conversion layer 1 and green conversion layer 2.
Each sample was placed with the green color conversion layer facing the light source and irradiated with pulsed light to cause excitation and emission. The fluorescence emission intensity was measured multiple times while changing the time t (referred to as delay time) from when the pulsed light was turned off until the actual measurement of the spectrum began in the range of 0.05 ms to 20 ms.

The fluorescence lifetime spectra of Samples 9 and 10 are shown in Figure 13. Figure 13 also shows the fluorescence emission intensity at the delay time t=0.
In Sample 9, no signal was observed at the shortest delay time, t = 0.05 ms, and no emission was detected over the entire range. Therefore, in Sample 9, it was estimated that the fluorescence emission disappeared within 0.05 ms, and the decay time based on the above definition was considered to be less than 0.05 ms.
On the other hand, in Sample 10, a signal was observed at t = 0.05 ms, and then a decay curve in which the emission intensity exponentially decreased was obtained. The decay time based on the above definition was 3.6 ms.
From the above, it was found that the decay time of the conversion layer using the Eu ²⁺ -activated phosphor was on the order of submilliseconds, while the decay time of the conversion layer using the Eu ²⁺ -Mn ²⁺ co-activated phosphor was on the order of milliseconds, demonstrating the superiority of the conversion layer using the Eu ²⁺ -activated phosphor.

Each embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configurations are not limited to these embodiments, and modifications and combinations of configurations that do not depart from the gist of the present invention are also included.

For example, the present invention allows the following modifications.
Each fluorescent light-emitting layer contains light-scattering particles 5. The red conversion layer 1C contains the first phosphor 2. The display device 200 and the wavelength conversion substrate 320A use the blue conversion layer 1A and the blue filter B.

The color filter section and wavelength conversion substrate according to the present invention may be provided with layers to impart desired properties, such as a transmittance adjustment layer or an anti-reflection layer.

The fluorescent-emitting layer may contain quantum dots, which are nanometer-sized semiconductor particles that exhibit quantum confinement effects and can assist wavelength conversion when added to the fluorescent-emitting layer.
The amount of quantum dots added can be about 0.5% to 10% of the mass of the phosphor. Because quantum dots have poorer heat resistance and light resistance than phosphors, adding too much quantum dots may reduce the reliability of the display device or wavelength conversion substrate.
The heat resistance of the fluorescent-emitting layer can be evaluated by placing it in an oven at 150°C for 500 hours and measuring the change in its luminescence characteristics. The light resistance can be measured by irradiating it with a xenon lamp for 200 hours under conditions of a temperature of 40°C and a humidity of 70%, and measuring the change in its luminescence characteristics. From the viewpoint of reliability when a display device is constructed, it is preferable that the rate of change in the luminescence characteristics of the fluorescent-emitting layer after the heat resistance test or the light resistance test be 10% or less.
The luminescence characteristics to be used as an index can be selected from one or more of "internal quantum yield,""luminescence intensity at the main peak wavelength,""half width at the main peak wavelength,""opticaldensity," and the like.

1 Fluorescent light-emitting layer 2 First phosphor 3 Second phosphor 4 Third phosphor 6 Partition wall 100, 200, 300, 400 Display device 110, 110A, 310, 310A LED section 111 Substrate 112, 112A LED element 120, 120A Color filter section 320, 320A Wavelength conversion substrate B Blue filter G Green filter R Red filter 321 Transparent substrate

Claims (6)

an LED section in which a plurality of near-ultraviolet LEDs or a plurality of blue LEDs are arranged on a substrate;
a partition wall having a lattice shape in plan view with a plurality of openings, the near-ultraviolet LEDs or the blue LEDs being positioned within the openings;
a color filter section including a red filter, a green filter, and a blue filter, the red filter, the green filter, and the blue filter being arranged so as to overlap with the opening in a plan view;
a fluorescent-emitting layer provided between the LED section and the color filter section, positioned within the opening in a plan view, and including a base resin and a Eu ²⁺ -activated phosphor dispersed therein;
Equipped with
the fluorescent-emitting layer contains only the Eu ²⁺ -activated phosphor as a phosphor,
At least a part of the fluorescent-emitting layer is a red conversion layer, and the Eu ²⁺ -activated phosphor includes a first phosphor that uses light emitted from the LED section as excitation light and a second phosphor that uses fluorescence emitted from the first phosphor as excitation light, and a mass ratio of the first phosphor to the second phosphor is within a range of 2:1 to 1:2.
Display device. The particle size of the Eu ²⁺ -activated phosphor is 0.1 μm or more and 15 μm or less.
The display device according to claim 1 . the fluorescent-emitting layer has a change rate of 10% or less in light-emitting characteristics after 200 hours of irradiation with a xenon lamp;
The display device according to claim 1 . the thickness of the fluorescent-emitting layer is 1 μm or more and 50 μm or less;
The display device according to claim 1 . the fluorescent-emitting layer contains quantum dots;
The display device according to claim 1 . A transparent substrate,
a color filter provided on the substrate and having a red filter, a green filter, and a blue filter;
a partition wall having a lattice shape in plan view with a plurality of openings, the partition wall being arranged so that any one of the red filter, the green filter, and the blue filter is located within the opening;
a fluorescent-emitting layer located within the opening in a plan view, the fluorescent layer including a base resin and a Eu ²⁺ -activated phosphor dispersed therein;
Equipped with
the fluorescent-emitting layer contains only the Eu ²⁺ -activated phosphor as a phosphor,
At least a part of the fluorescent-emitting layer is a red conversion layer, and the Eu ²⁺ -activated phosphor includes a first phosphor and a second phosphor that uses the fluorescence emitted by the first phosphor as excitation light, and the mass ratio of the first phosphor to the second phosphor is within a range of 2:1 to 1:2.
Wavelength conversion substrate.