JP2003217861A - Electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel electroluminescent element of a long life improved in performance, using an inexpensive process. <P>SOLUTION: This electroluminescent element of the present invention has at least a positive electrode 2 for injecting a positive hole, a luminous layer 3 having a luminescent area, and a negative electrode 4 for injecting an electron. The luminous layer 3 contains at least one kind of inorganic phosphor of which the average particle size is 100 nm or less, and at least one kind of medium for dispersing the inorganic phosphor, a band gap of the medium is wider than that of the inorganic phosphor, and an ionization potential of the inorganic phosphor is lower than that of the medium. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel electroluminescent device containing ultrafine fluorescent material.

[0002]

2. Description of the Related Art An electroluminescence device is a light emitting device which utilizes the electroluminescence of a solid and fluorescent substance. At present, an inorganic electroluminescence device using an inorganic material as a light emitter has been put into practical use and is used in a liquid crystal display. Some applications are being developed for backlights and flat displays.

However, since the voltage required for light emission of an inorganic electroluminescent element is as high as 100 V or more and it is difficult to emit blue light, it is difficult to achieve full color by the three primary colors of RGB.

On the other hand, research on electroluminescence devices using organic materials has been attracting attention for a long time and various studies have been made. However, since the luminous efficiency is very poor, full-scale practical research has not progressed. It was

However, in 1987, Kodak C.I.
W. Tang et al. Proposed an organic electroluminescence device having a function-separated laminated structure in which an organic material is divided into two layers, a hole transport layer and a light emitting layer, and 1000 cd / m ² or more despite a low voltage of 10 V or less. It was revealed that a high emission luminance of [C. W. Tan
g and S. A. Vanslyke: Appl. P
hys. Lett, 51 (1987) 913, etc.].

From then on, the organic electroluminescence element has begun to attract attention, and even now, much research is being conducted on an organic electroluminescence element having a similar function-separated laminated structure.

However, since the organic electroluminescent element using these low-molecular light emitting materials is generally produced by using a vacuum vapor deposition apparatus, an organic electroluminescent element which can be produced by an inexpensive method with high equipment cost is required. It was wanted.

In order to meet this demand, there is an organic electroluminescence device using a polymer light emitting material. This element is described in J. H. Burrough
es et al., Nature, vol. 347, p. 539,
It is described in 1990 etc.

Although these have been vigorously developed in recent years, there has been a limit in increasing the area by the spin coating method.
Although a method of manufacturing using an inkjet method has also been proposed, the lifetime and the uniformity of light emission during continuous light emission are problems.

Further, the biggest problem when these low-molecular or high-molecular organic compounds are used as a light-emitting material is that the life during driving is short. Although many studies have been made on this issue so far, it remains a big problem. Furthermore, in order to obtain white light emission, blue is conventionally used,
A general method is to obtain a white color by mixing a plurality of red, green, blue, and yellow light-emitting materials as dopants in the same layer as the host material, or mixing them in different layers to obtain white. Since the deterioration is different, there is a serious drawback that the chromaticity changes.

Further, conventionally, inorganic phosphors have been used for CRT, P
It is widely used for displays such as DP, lighting, and inorganic EL. In recent years, it has become clear that the quantum yield of fluorescence is improved by making a phosphor into a nanosize.

An example in which an inorganic fluorescent material is applied to a light emitting material is well known as the above-mentioned inorganic EL, but few examples are applied to a current injection type light emitting device in which holes and electrons are injected to emit light. Although a light emitting material using a metal complex is widely known (for example, Ed., Miyata S.
eizou and Hari Singh Nalw
a, Organic Electroluminesc
ence Materials and Device
s, Chapter 9), these have a ligand composed of an organic material, which is different from a pure inorganic light emitting material.

Further, although a method of synthesizing yttrium aluminum garnet (YAG) ultrafine particles by a wet method has been reported, no reference has been made to their fluorescence emission, and this is a current injection type light emitting material. It has not been suggested to apply to. Regarding the fine particles of gallium nitride (GaN) doped with zinc, there is a report on photoluminescence as a powder thereof [Kanie
2nd Intern. Symp. On Blu
e Laser and Light Emittin
g Diodes p. 552 (1998)]. However, this report does not mention any application other than the use as a phosphor for field emission displays, and the particle size is 0.2μ to 3μ.
It was a big one.

In recent years, Bhargara et al. Have reported that europium (II) compound (EuSi ₂ ) and Si are sputtered on a silicon substrate in an argon gas atmosphere, and then annealed at 1000 ° C. to perform EuSi.
It has been reported that a device emitting white light can be obtained by obtaining a thin film of O ₃ and EuSiO ₄ and sputtering an ITO thin film as a cathode thereon [Appl.
Phys. Lett. , Vol. 74, p. 3203
(1999)]. However, this device has the drawbacks that a vacuum device is required, it is difficult to increase the area, and a treatment at a high temperature of 1000 ° C. is required.

As an example of a light emitting device using an ultrafine particle fluorescent material, Nature, 370, p354, 1994 or J. Appl. Phy. Vol. 82, p. 583
7. In 1997, Alivisatos et al. Reported the fabrication and performance of devices for ultrafine CdSe particles. A similar example can be found in Bawendi et al., Appl. Phys. L
ett. 66, p. 1316, 1995. However, these have low luminous efficiency and have not been put to practical use. In addition, since it is laminated with a polymeric light emitting material, there is a major drawback that the polymeric light emitting material emits light when the driving voltage is increased and the emission color changes.

Further, as an EL device using ultrafine particles, Japanese Patent Publication No. 1-18117 discloses a light emitting material comprising ultrafine particles, and a generation layer of a substance different from that of the light emitting material or a generation layer having different properties is formed on the surface thereof. Then, an ultrafine particle phosphor characterized by introducing a light emitting mechanism at the interface between the light emitting material and the generation layer by forming a hetero bond or a P-N junction is disclosed. However, only an AC driven device is shown as an application example thereof, and there is no disclosure of current injection type light emission.

Further, US Pat. No. 5,537,000 describes that an electroluminescent device for injecting holes and electrons is driven by a direct current by using an ultrafine particle semiconductor of 20 nm or less as a light emitting material. However, the efficiency and life were not at a level that was practically satisfactory. In Japanese Patent Application No. 8-315934, ultrafine particles are semiconductors and a light emitting element using them is described, but there is no description of a specific current injection type light emitting device.

[0018]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel electroluminescent device which uses an inexpensive process and has a long life and which has improved performance.

[0019]

DISCLOSURE OF THE INVENTION As a result of intensive studies, the present inventors have found that the object of the present invention can be achieved by the following means.

That is, in order to solve the above-mentioned problems, the electroluminescent device of the present invention comprises an anode for injecting at least holes, and
An electroluminescent device comprising a light emitting layer having a light emitting region and a cathode for injecting electrons, wherein the light emitting layer has at least one inorganic phosphor having an average particle size of 100 nm or less, and an inorganic phosphor dispersed therein. And a band gap of the medium is wider than that of the inorganic phosphor, and the ionization potential of the inorganic phosphor is smaller than the ionization potential of the medium.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 is an electroluminescent device including at least an anode for injecting holes, a light emitting layer having a light emitting region, and a cathode for injecting electrons, The layer contains at least one inorganic phosphor having an average particle size of 100 nm or less, and at least one medium for dispersing the inorganic phosphor, and the band gap of the medium is the band gap of the inorganic phosphor. The electroluminescent element is characterized in that the ionization potential of the inorganic phosphor is wider than the ionization potential of the medium, and does not require a high voltage like inorganic EL, and has high efficiency and long life.

According to a second aspect of the present invention, in the electroluminescent device according to the first aspect, the medium is a polymer compound, which has high efficiency and long life.

According to a third aspect of the present invention, in the electroluminescent device according to the second aspect, the polymer compound is a conductive polymer, which has high efficiency and long life.

According to a fourth aspect of the present invention, there is provided an electroluminescent device comprising at least an anode for injecting holes, a light emitting layer having a light emitting region, and a cathode for injecting electrons, wherein the light emitting layer has an average thickness. The compound is a compound containing at least one kind of inorganic phosphor having a particle size of 100 nm or less and at least one medium for dispersing the inorganic phosphor, and the medium is a compound that predominantly transports holes, and electron An electroluminescent device characterized by mixing a compound having transportability,
High efficiency and long life.

(Embodiment) FIG. 1 is a sectional view of an essential part of an electroluminescent device according to an embodiment of the present invention. In FIG. 1, 1 is a substrate, 2 is an anode, and 3 is an inorganic phosphor. The light emitting layer 4 indicates a cathode.

In the electroluminescent device of the present invention, holes are injected from the anode 2 into the light emitting layer 3 by passing a direct current or a pulsed current between the two electrodes 2 and 4, while electrons are emitted from the cathode 4. It is injected into the light emitting layer 3. The conductive polymer material of the light emitting layer 3 transports holes and / or electrons, and injects holes or electrons into the inorganic fluorescent substance that is ultrafine particles.

As a result, it is considered that excitons are generated in the ultrafine-particle inorganic phosphor and emit light when they are recombined, but the light emission mechanism has not been clarified.

In addition to the structure shown in FIG. 1, the structure of the electroluminescent device may be such that the cathode 4 is provided on the substrate 1 and the anode 2 is provided on the light emitting layer 3. Furthermore, it is preferable to provide a hole injection layer on the substrate 1 in order to facilitate hole injection, improve the smoothness of the substrate, and improve the interface characteristics.
It is particularly preferable to use a material having a value close to the ionization potential of the light emitting layer for the hole injection layer in order to improve the injection efficiency.

An electron transport layer may be provided between the light emitting layer 3 and the cathode 4. As the electron transport layer, Alq ₃ , G
Typical materials are aq ₃ , Bphen, PBD, TAZ, silole compounds and their derivatives.
Further, it is also preferable to provide an electron injection layer in order to improve the efficiency of electron injection from the cathode 4.

Each component of the electroluminescent device of the present invention will be described below.

First, as the inorganic phosphor contained in the light emitting layer 3, generally used inorganic phosphor materials can be widely used. Inorganic phosphors generally have a matrix crystal in which specific ions or lattice defects that are emission centers are dispersed. These luminescent centers are present at several atomic% or less. Examples of inorganic fluorescent substances containing these include, for example, a phosphor known as yttrium aluminum garnet (YAG) in which cerium is added as a luminescent center, a physics society of applied science, organic molecule / bioelectronics research group, Vol. ． 10, No. 3 (19
99) and the cited phosphors for display can be used. In addition, Eu (II) xSiyOz, an ultrafine particle phosphor made of GaN microcrystals
(X, y, z, can each take any value), for _{example, EuSiO 3, Eu 2 SiO 3} , Eu 2 SiO 5, Eu 3
Eu ²⁺ such as SiO ₅ , EuAl ₂ O ₄ , Eu ₂ Al ₂ O ₆
The derivative thereof, europium metasilicate, europium-activated calcium metasilicate, strontium metasilicate and the like can be preferably used. However, it is not limited to these.

The inorganic phosphors used in the present invention are so-called ultrafine particles, and the average particle size of the inorganic phosphors used in the present invention is preferably 100 nm or less, and more preferably 50 nm or less. Most preferably, it is 30 nm or less. When the average particle size is small, a more uniform thin film can be obtained, a more uniform light emitting device can be obtained, and luminous efficiency is increased.
In addition, when the particle size becomes smaller, the emission wavelength becomes shorter due to the so-called quantum size effect.

The particle size distribution can be used from polydisperse particles to monodisperse particles, but the uniformity of light emission can be improved by using particles that are more monodisperse than polydisperse particles.
It has excellent life characteristics.

The average particle size and particle size distribution of these ultrafine particles can be measured by a commercially available particle size distribution measuring device. For example, it is possible to measure particles of 3 nm or more with a dynamic light scattering particle size distribution measuring device (LB-500 manufactured by Horiba Ltd.). Further, those having a small particle size can be evaluated by taking a transmission electron micrograph.

Various methods are known as methods for producing the ultrafine particles used in the present invention. For example, conventionally known sol-gel method, spray pyrolysis method, supercritical water reaction crystallization method and coprecipitation method (Hongzhi Wang et al., M
atrial science and engine
There is a report on the synthesis of YAG ultrafine particles by Eering, A288, p1 (2000)). Further, a method of forming crystals in a polymer medium to produce ultrafine particles having a core / shell structure is also known (F. Caruso, Ad.
v. Mater. , Vol. 13, p14 (200
1). The ultrafine particles used in the present invention may be produced by any method, but it is most preferable in terms of cost to produce them by a wet method without using a vacuum device.

As the medium contained in the light emitting layer 3, it is preferable to use a polymer compound for dispersing the ultrafine particles. The polymer compound that can be used in the present invention is an ionization potential (I) of ultrafine particles that controls light emission.
Any compound can be used as long as it has a larger ionization potential than p). In addition, it is preferable that the band gap of the polymer compound in which the ultrafine particle phosphor is dispersed is larger than the band gap of the ultrafine particle phosphor because the light emission efficiency is further improved.

Further, it is preferable to use a conductive polymer compound as a medium contained in the light emitting layer 3. The higher the hole mobility and electron mobility of these polymer compounds, the more efficiently holes and electrons are injected. Therefore, it is desirable in terms of reduction of driving voltage and durability. The hole and electron mobilities can be measured by the TOF method (time of flight method).

As typical examples of the polymer compound specifically used, a π-conjugated polymer compound and a σ-conjugated polymer are used. Specific examples of the π-conjugated system include polyacetylene and its derivatives, polyparaphenylene and its derivatives, polyphenylenevinylene, poly (2,5-dialkoxy-p-phenylenevinylene, poly (2-methoxy-5- (2′-ethylhexyl) p -Phenylene vinylene and its derivative, polythiophene, alkylthiophene and its derivative, polypyrrole and its derivative, polyvinylcarbazole and its derivative, polyethylene oxide and its derivative, polycarbonate and its derivative, etc. The σ-conjugated polymer is polysilane and its derivative. Specific examples thereof include derivatives thereof, but the present invention is not limited thereto.

The glass transition temperature of these polymer compounds is preferably 100 ° C. or higher in order to improve the stability of the device, and those having a glass transition temperature of 120 ° C. or higher are particularly preferable for practical use.

The device of the present invention can be manufactured by a conventionally used method. That is, the spin coating method,
An inkjet method, a printing method, an alternate lamination method, or the like is used. For example, Junji Kido, CMC, OLED
It is described in Materials and Displays (2001).

Next, as the substrate 1, a transparent or semitransparent substrate can be used. In the present invention, the definition of transparent or semi-transparent refers to a degree of transparency that does not hinder the visual recognition of light emitted by the electroluminescent element.

Further, when the light of the electroluminescent element is not taken out from the substrate 1 side, that is, in FIG.
If taken from the side, the substrate 1 may be opaque.

As the substrate material, transparent or translucent soda-lime glass, barium-strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, quartz glass or other inorganic oxide glass, inorganic fluorine glass, etc. Inorganic glass such as fluoride glass, transparent or translucent polyethylene terephthalate, polycarbonate, polymethylmethacrylate, polyether sulfone, polyvinyl fluoride, polypropylene, polyethylene, polyacrylate, amorphous polyolefin, fluororesin, etc. A molecular film or the like can be used, and transparent or translucent As ₂ S ₃ , As
₄₀ S ₁₀ , S ₄₀ Ge _10, etc. chalcogenide glass, Zn
O, Nb ₂ O ₅ , Ta ₂ O ₅ , SiO, Si ₃ N ₄ , Hf
Materials such as metal oxides such as O ₂ and TiO ₂ and nitrides can be appropriately selected and used, and a laminated substrate in which a plurality of substrate materials are laminated can also be used.

Further, opaque Si (silicon), Ge
(Germanium), GaAs (gallium arsenide), InA
An inorganic semiconductor substrate such as s (indium arsenide), GaSb (gallium antimony), InSb (indium antimony), or an opaque metal such as Fe (iron), Al (aluminum), Cu (copper), Ag (silver), or the like. An alloy, a metal compound substrate or the like, or a polymer substrate of opaque plastic, a thermosetting resin, a photocurable resin or the like is used. Furthermore, a laminated substrate in which a plurality of these substrate materials are laminated can also be used.

A circuit composed of a transistor, a diode, a resistor / capacitor / inductor for driving the electroluminescent element may be formed on the surface or inside of the substrate 1.

Next, the anode 2 will be described. Anode 2
Is an electrode for injecting holes, and it is necessary to efficiently inject holes into the light emitting layer 3. As the anode 2,
Transparent electrodes can be used. The transparent electrode is a translucent conductive film, and its materials include indium tin oxide (ITO), tin oxide (SnO ₂ ), and zinc oxide (Zn oxide).
O) or the like, a transparent conductive film made of a mixture of metal oxides such as SnO: Sb (antimony), ZnO: Al (aluminum), or Al (aluminum), Cu ( Copper), Ti
A metal thin film such as (titanium) or Ag (silver), a metal thin film such as a mixed thin film or a laminated thin film of these metals, or a conductive polymer such as polypyrrole can be used. It is also possible to form a transparent electrode by laminating a plurality of these transparent electrode materials, and the transparent electrode is formed by resistance heating vapor deposition, electron beam vapor deposition, sputtering method, electric field polymerization method, chemical polymerization method or the like. The transparent electrode preferably has a thickness of 1 nm or more in order to have sufficient conductivity or prevent uneven light emission due to unevenness on the substrate surface. Further, in order to have sufficient transparency, it is desirable that the thickness be 500 nm or less.

Further, as the anode 2, in addition to the transparent electrode, Cr (chrome), Ni (nickel), Cu (copper),
A metal having a large work function such as Sn (tin), W (tungsten), Au (gold), an alloy thereof, an oxide, or the like can be used, and a laminated structure including a plurality of materials using these anode materials can also be used. You can When the transparent electrode is not used as the anode 2, the cathode 4 may be a transparent electrode. In this case, the anode 2 is preferably made of a material that reflects light.

An amorphous carbon film may be provided on the anode 2. In this case, both have a function as a hole injecting electrode. That is, holes are injected from the anode into the light emitting layer or the hole transport layer through the amorphous carbon film. The amorphous carbon film is formed between the anode and the light emitting layer or the hole transport layer by the sputtering method. Carbon targets obtained by sputtering include isotropic graphite, anisotropic graphite, glassy carbon and the like, and is not particularly limited, but isotropic graphite having high purity is suitable. Concretely showing the advantages of the amorphous carbon film,
When the work function of the amorphous carbon film is measured using a surface analyzer AC-1 manufactured by Riken Keiki, the work function of the amorphous carbon film is Wc = 5.40 eV. Here, the work function of ITO that is often used as an anode is WITO.
= 5.05 eV, holes can be efficiently injected into the light emitting layer or the hole transport layer by using the amorphous carbon film.
Further, when the amorphous carbon film is formed by the sputtering method, reactive sputtering is performed in a mixed gas atmosphere of nitrogen or hydrogen and argon in order to control the electric resistance value of the amorphous carbon film. Further, in the thin film forming technique such as the sputtering method, if the film thickness is 5 nm or less, the film has an island structure and a uniform film cannot be obtained. Therefore, when the thickness of the amorphous carbon film is 5 nm or less, the electric resistance becomes too high, and as a result, no current flows and efficient light emission cannot be obtained. Further, when the film thickness of the amorphous carbon film is 100 nm or more, the color of the film becomes blackish, and the light emitted from the electroluminescence device cannot be sufficiently transmitted.

The cathode 4 is an electrode for injecting electrons, and it is necessary to efficiently inject the electrons into the light emitting layer 3 (or the electron transporting layer or the electron injecting layer).
Metals such as l (aluminum), In (indium), Mg (magnesium), Ti (titanium), Ag (silver), Ca (calcium), Sr (strontium), oxides or fluorides of these metals, and Its alloy,
A laminate or the like is generally used. In addition, by forming an ultrathin film having high light transmittance using a metal having a small work function at the interface in contact with the light emitting layer 3 (or the electron transporting layer or the electron injecting layer) and laminating the transparent electrode thereon It is also possible to form a transparent cathode. Especially low work function Mg, Mg
-Ag alloy, Al described in JP-A-5-121172
-Li alloy, Sr-Mg alloy or Al-Sr alloy,
Al-Ba alloy or the like or LiO ₂ / Al or LiF / A
A laminated structure such as l is suitable as a cathode material. Resistance heating vapor deposition, electron beam vapor deposition, and sputtering are used as the film forming method.

At least one of the anode 2 and the cathode 4 may be a transparent electrode. Further, both may be transparent electrodes, but in order to improve the light extraction efficiency, it is preferable that one is a transparent electrode and the other is formed of a material that reflects light.

Further, a protective film is formed on the cathode 4 as necessary to shield the electroluminescent element from the outside air and ensure stability for a long time, and the laminate of the anode 2 to the cathode 4 is formed on the substrate 1. You may protect it so that it may be wrapped up above. That is, it is necessary for long-term reliability to provide a protective film to suppress the oxidation of the material and the reaction with moisture.

The material of the protective film is SiON or S.
A thin film made of an inorganic oxide such as iO, SiN, SiO ₂ , Al ₂ O ₃ , or LiF, an inorganic nitride, an inorganic fluoride, or a glass film made of an inorganic oxide, an inorganic nitride, an inorganic fluoride, or the like, or A thermosetting or photocurable resin, a silane-based polymer material having a sealing effect, or the like is used, and it is formed by vapor deposition, sputtering, or a coating method.

Here, a method of measuring the ionization potential and the band gap will be described. The ionization potential can be estimated by irradiating the material with ultraviolet rays and measuring the threshold excitation energy at which photoelectrons are emitted. As a simple method, a commercially available device (photoelectron spectroscopic device AC-1 manufactured by Riken Keiki Co., Ltd.) can be used for measurement in the atmosphere. The band gap can be evaluated by measuring the spectral absorption characteristics of the sample with a spectrophotometer and determining the energy at the absorption edge to regard it as the band gap.

In the device of the present invention, it was not clear whether holes and electrons could be efficiently injected into the ultrafine particle phosphor and recombination could be sufficiently performed. As a result of earnest research for efficient recombination, the inventors have achieved a dramatic increase in luminous efficiency by adopting a structure in which the band gap of the ultrafine particle phosphor is smaller than the band gap of the conductive polymer that is the medium. It was found to improve. This is probably due to the improved recombination efficiency, but details are unknown.

The electroluminescence device of the present invention can be driven by any driving method such as direct current driving, alternating current driving, and pulse driving. When the electroluminescent element of the present invention is used for a graphic display element, both a so-called passive driving method and an active driving method in which dots are driven can be used depending on the application. When using the pulse driving method, it is preferable to apply a reverse bias for the stability of the device.

Further, since the electroluminescence device of the present invention is a current injection type, it is effective to carry out constant current driving in order to suppress the variation between pixels. However, constant voltage driving can also be preferably used depending on the application.

The electroluminescent device of the present invention includes a display such as a mono-color display and a full-color display, a backlight, an image sensor, a print head,
It can be used as a light source such as illumination.

The electroluminescent element of the present invention is, for example,
The display device can be used as a display device for displaying an image, and these display devices are displays of portable information terminals such as mobile phones, PHSs and PDAs, displays of televisions, personal computers, car navigations, AV equipments such as stereos and radios. It can be used for displays and the like. Furthermore, it can be used for a lighting device as a light source of a laser printer, a scanner, or the like. Alternatively, it can be used as a lighting device as a simple light source such as a lighting fixture such as an interior light or a light stand.

Among these, considering the advantages of the electroluminescent device of the present invention such as low power consumption, easy weight reduction and thinness, and fast response speed, display as an image display in various electronic devices. It is preferably used for a device or a lighting device as a light source such as a laser printer or a scanner.

[0060]

EXAMPLES Next, examples of the present invention will be described.

Example 1 <Synthesis of YAG Ultrafine Particle Phosphor> The synthesis was basically carried out according to the reference by Li et al. (Journal of the).
European Ceramic Chemistr
y, vol. 20, p. 2395 (2000)).

That is, ammonium hydrogen carbonate as a precipitating agent was gradually added to an aqueous solution of yttrium nitrate and aluminum nitrate (manufactured by Kanto Scientific Co., Ltd.). In addition, cerium nitrate is used as a material that becomes a luminescent center, and 0.5m of aluminum nitrate is used.
ol% was added. Stirring was performed with a magnetic stirrer. Then, methacrylic acid was added and stirring was continued.

Next, when the amount of ammonium hydrogen carbonate added was excessive, a precipitate was formed. The formed precipitate was filtered, thoroughly washed with distilled water and ethanol, and dried in nitrogen gas to obtain a powder.

<Preparation of Polymer Solution Dispersing Ultrafine Particles> The obtained YAG ultrafine particle powder was dispersed in a toluene solution of polyvinylcarbazole (PVK).

<Production of Device> PVK in which the above-mentioned YAG phosphor ultrafine particles are dispersed is spin-coated in a nitrogen atmosphere on a glass substrate (with a transmittance of 85% or more) of ITO, which has been thoroughly washed, to have a thickness of 50 nm. A thin film was obtained. The obtained thin film was dried in nitrogen at 100 ° C. for 1 hour. Next, this device was set in a vacuum vapor deposition apparatus, and lithium fluoride was vapor-deposited to a thickness of 2 nm as an electron injection layer. Subsequently, 100 nm of aluminum was vapor-deposited as a cathode. After that, the element was transferred to a nitrogen-substituted glove box, a UV curable resin for organic EL sealing (30Y296G made by ThreeBond) was applied to the periphery of the glass substrate, and the glass plate was adhered from the cathode side for sealing.

The ionization potential of PVK was 5.8 eV and the band gap estimated from the absorption edge was 3.5 eV.

<Evaluation of Device> ITO is applied to the completed light emitting device.
Was used as an anode and Al was used as a cathode, and DC driving was performed. The light emission starting voltage was 7V. The brightness was 500 cd / m ² when a voltage of 10 V was applied. The brightness was measured with a BM-8 luminescent meter manufactured by Topcon. The emission spectrum was measured with a multi-channel analyzer manufactured by Hamamatsu Photonics and the main emission peak was 57
It was confirmed to be in the vicinity of 0 nm. The emission color was yellow.

Next, this device was subjected to a continuous lighting test at an initial luminance of 100 cd. Brightness is 95c after 1000 hours
Therefore, it can be seen that the life of this device is extremely excellent.

(Comparative Example 1) An ultrafine particle phosphor was prepared in the same manner as in Example 1, and MEH-PPV was used instead of PVK.
What melt | dissolved (made by Sebel Hegner) in toluene was used as a medium. The ionization potential of MEH-PPV was 5.5 eV. The band gap estimated from the spectral absorption was 2.3 eV.

The basic process was the same as in Example 1.

Further, when evaluated in the same manner as in Example 1, the light emission starting voltage was 15 V and the luminance when a voltage of 20 V was applied was 20 cd / m ² .

From this, it can be seen that the bandgap of the medium is larger than the bandgap of the ultrafine particle light emitter to be used and the ionization potential is larger, the light emission starting voltage and the brightness are excellent.

Example 2 Europium (II) Sirique
Compound (Eu₂SiO_Four) Is EuO and SiO ₂The original
The method described in the literature (J. Phys. Chem. Sol.
ods. Vol. 32, pp 159 (1971))
Was synthesized. The composition was analyzed with an X-ray analyzer.
Ro, EuSiO₃, EuSiO_Four, Eu₃SiO_Five, Eu₂
SiO_FourWas a mixture of. UV crystal on this crystal
When irradiated and measured for luminescence, the peak of luminescence is 575.
It was observed in the vicinity of nm and the emission color was white. This crystal
Is pulverized to obtain ultrafine particles having an average particle size of 80 nm.
It was This ultrafine particle phosphor was used in the same manner as in Example 1
The solvent was dispersed in PVK.

When the ionization potential of the obtained powder was measured, it was 3.4 eV and the band gap was 2.
It was 1 eV. Next, in the same manner as in Example 1, the europium silicate fine particles were dissolved and dispersed in a toluene solution of PVK. This solution was spin-coated on a thoroughly cleaned ITO substrate on which amorphous carbon was sputtered with a thickness of 5 nm. After that, in an oxygen-free atmosphere, 200 ℃
It was dried at. Immediately, it was set in a vacuum vapor deposition apparatus, and then 2,5-bis (2 ', 2 "-bipyridin-6-yl) -1,1-dimethyl-3,4, -diphenylsilacyclopentadiene was vacuum deposited by 10 nm as an electron transport material. Lithium fluoride is evaporated to a thickness of 5 nm and aluminum is
It was vapor-deposited to 00 nm. When the manufactured element was driven at a constant voltage of 10 V with ITO as an anode and aluminum as a cathode, yellowish white light emission was obtained. When the luminance was measured with a luminance meter, it was 50 cd / m ² . Further, constant voltage driving was continued for 24 hours at 20 V, but the decrease in luminance was about 10%.

Comparative Example 2 When a similar experiment was conducted using polythiophene instead of PVK used in Example 2, slight light emission was observed even when the voltage was 40V.

[0076]

As described above, the electroluminescent device of the present invention has high luminous efficiency and excellent driving life.
It is possible to provide a novel electroluminescent device with improved performance, which uses an inexpensive process and has a long life.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part of an electroluminescent device according to an embodiment of the present invention.

[Explanation of symbols]

1 substrate 2 anode 3 light emitting layer 4 cathode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryuichi Hachinami             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 3K007 AB03 AB06 AB11 AB18 DA01                       DA04 EA03

Claims (4)

[Claims] 1. An electroluminescent device comprising at least an anode for injecting holes, a light emitting layer having a light emitting region, and a cathode for injecting electrons, wherein the light emitting layer has an average particle size of 100 nm or less. The inorganic phosphor contains at least one kind of inorganic phosphor and at least one medium for dispersing the inorganic phosphor, and the band gap of the medium is wider than the band gap of the inorganic phosphor. The ionization potential of
An electroluminescent device characterized by being smaller than the ionization potential of the medium. 2. The electroluminescent device according to claim 1, wherein the medium is a polymer compound. 3. The electroluminescent device according to claim 2, wherein the polymer compound is a conductive polymer. 4. An electroluminescent device comprising at least an anode for injecting holes, a light emitting layer having a light emitting region, and a cathode for injecting electrons, wherein the light emitting layer has an average particle size of 100 nm or less. A compound containing at least one kind of inorganic phosphor and at least one medium for dispersing the inorganic phosphor, wherein the medium is a compound that predominantly transports holes, and has an electron transporting ability to the medium. An electroluminescent device, characterized in that a compound having the same is mixed.