JP2011076726A - Electroluminescent element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroluminescent element achieving high luminescent light emission from each quantum dot and high color purity in a narrow-band spectrum. <P>SOLUTION: The electroluminescent element is constructed by layering a transparent electrode 12 serving as a first electrode, a first electron capturing-emitting layer 13, a first insulating layer 14, a first buffer layer 15, a light emitting active layer 20, a second buffer layer 16, a second insulating layer 17, a second electron capturing-emitting layer 18, and a metal electrode 19 serving as a second electrode sequentially on a transparent glass substrate 11. Surface levels are formed in the boundaries between the first and second electron capturing-emitting layers 13 and 18 and the first and second insulating layers 14 and 17 contacting the electron capturing-emitting layers. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electroluminescent device, and more particularly to an electroluminescent device having a light emitting active layer containing so-called quantum dots and a method for manufacturing the same.

  In recent years, attention has been focused on the application of phosphors having a quantum dot structure to light-emitting elements as a technique for developing self-luminous flat displays. Usually, a quantum dot refers to a state that achieves carrier confinement in all three dimensions in real space, but a quantum dot here refers to the confinement of carriers in all three dimensions in real space. It is defined as the structure that creates the state to be realized. As an example of this quantum dot, the inorganic semiconductor particle (core part) having a spherical shape with a diameter of several nanometers and a relatively small band gap energy, and a relatively band gap covering the surface of the inorganic semiconductor particle -There is a composite material composed of a high energy coating (shell layer). Such a quantum dot has a feature that it can artificially define a gap energy and emit a desired color by precisely controlling its size (diameter).

  The present inventors have developed an all-inorganic electroluminescent device using the quantum dots produced by a wet chemical synthesis technique (see, for example, Patent Document 1 and Patent Document 2). This electroluminescent element has a double insulation structure in which a light emitting active layer containing quantum dots is sandwiched between carrier barrier layers, and excites and emits light by injecting carriers into the quantum dots by applying an alternating electric field. It is a quantum dot light emitting inorganic electroluminescence (EL) element.

  The electroluminescent element has a structure in which a first electrode, a first insulating layer, a light emitting active layer including quantum dots, a second insulating layer, and a second electrode are sequentially stacked on a substrate. Here, the light emitting active layer is formed by forming a large number of quantum dots on a substrate by using a so-called electrospray ion beam deposition method (hereinafter referred to as an ES-IBD method) disclosed in Patent Document 1. The first insulating layer is formed by sequentially irradiating and depositing the surface of the first insulating layer in the form of an ion beam. The raw material used in this ES-IBD method is a solution in which an organic ligand functioning as a surfactant is bonded and attached to the surface of the quantum dot shell layer in a colloidal form in a solvent. In this method, the bond of the organic ligand is dissociated while changing the quantum dot into an ion beam. Therefore, in this ES-IBD method, most of the quantum dots deposited on the deposition substrate side are deposited in a state where the organic ligands are excluded, so that there is an advantage that unnecessary impurities are reduced in the light emitting active layer. is there. Therefore, according to this method, a high-quality light-emitting active layer hardly affected by impurities can be formed.

  Moreover, as an electroluminescent element disclosed by the said patent document 1, the light emitting active layer consists of the buffer layer and quantum dot which consist of inorganic-semiconductor materials, and there exists a thing of the state by which the quantum dot was included in the buffer layer.

International Publication No. 2007/142203 International Publication No. 2008/013069

  When the above-mentioned electroluminescent device is applied to a self-luminous flat display, an emission peak other than the emission spectrum derived from the confinement level in the quantum dot is used in order to further increase the emission intensity and improve the color purity of the emission. Improvements such as suppression of the occurrence of this are desired. Such an improvement is intended to prevent a decrease in the quantum confinement effect in the quantum dots, a decrease in emission intensity due to an interaction with a close well or formation of a subband, and a broadening of the emission spectrum.

  In addition, in the electroluminescence device that applies an alternating electric field as described above, the interface state between the light emitting active layer and the insulating layer is considered to contribute to supplying electrons to the light emitting active layer. It is desired to increase the number of emitted electrons to be supplied.

  The present invention was created by paying attention to such problems, and the purpose of the present invention is to provide electroluminescence that emits light from a light-emitting active layer with high intensity and that light emitted from a quantum dot has a narrow band spectrum and high color purity. It is to provide an element.

  A feature of the present invention is that a light-emitting active layer including quantum dots is sandwiched between a pair of buffer layers made of an inorganic semiconductor material, the quantum dots are included in the buffer layers, and an insulation is provided outside each of the pair of buffer layers. Electrodes are arranged so as to sandwich layers, and an electroluminescent element that emits light from the light-emitting active layer by applying an AC voltage to these electrodes, between the buffer layer and the electrode, at the interface with the layer to be joined The gist is that an electron capture / emission layer forming a surface state is disposed.

  In the present invention, since a surface state or an interface state is formed at the interface between the electron capture and emission layer and the layer to be joined, there is an action of capturing electrons, and electrons are easily emitted when an AC voltage is applied. can do. Therefore, the generation of electrons at the surface level can be promoted, the amount of electrons supplied to the light emitting active layer can be increased, and the light emission intensity can be improved.

  Here, as an electron capture / emission layer for generating electrons, a single metal atom having a work function of 3.0 eV or less (preferably 2.5 eV or less) or a compound containing the metal atom, a trap level and a vacuum A material having a level energy difference of 3.0 eV or less (preferably 2.5 eV or less), a metal oxide having a composition with a non-stoichiometric ratio (particularly a metal oxide having a composition with oxygen deficiency), or the like. It is preferable.

  In a simple substance of a metal atom having a work function of 3.0 eV or less (preferably 2.5 eV or less) or a compound containing the metal atom, electrons are easily generated with metal ionization. In addition, a material having an energy difference between a trap level and a vacuum level of 3.0 eV or less (preferably 2.5 eV or less), or a metal oxide having a composition with a non-stoichiometric ratio (particularly, a composition having oxygen vacancies). (Metal oxide) has an electrically unstable bond and electron distribution, and thus has an action of capturing and releasing electrons and holes. At the trap level, excited electrons are trapped in positive charges, and thus electrons are emitted by applying an alternating voltage between the electrodes. The electrons thus emitted are accelerated by the electric field, and obtain sufficient energy for excitation for light emission of the quantum dots.

  The arrangement position of the electron capture / emission layer is preferably interposed between the buffer layer and the insulating layer or between the insulating layer and the electrode.

  In addition, the electron capture / emission layer may be a stack of a plurality of layers, or the layers may be made of different materials.

  By making the electron capture and emission layer a multi-layered structure, it can be expected to promote the generation of carriers from the surface level between layers, and the number of injected carriers per unit time contributing to light emission in the quantum dot is increased. And can be applied to applications that require higher luminance.

  According to the present invention, it is possible to realize an electroluminescent device that emits light from the light emitting active layer with high brightness, and emits light from the quantum dots with a narrow band spectrum and high color purity.

1 is a perspective view showing an electroluminescent element according to a first embodiment of the present invention. It is process sectional drawing which shows the state in which the transparent electrode in the electroluminescent element which concerns on the 1st Embodiment of this invention was formed. It is process sectional drawing which shows the state in which the 1st electron capture emission layer was formed in the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the state in which the 1st insulating layer and 1st buffer layer in the electroluminescent element which concern on the 1st Embodiment of this invention were formed. It is process sectional drawing which shows the state which formed the light emission active layer in the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the state which formed the 2nd buffer layer in the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the state in which the 2nd insulating layer, the 2nd electron capture discharge | release layer, and the metal electrode in the electroluminescent element which concern on the 1st Embodiment of this invention were formed. It is sectional drawing which shows the electroluminescent element which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the electroluminescent element which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the electroluminescent element which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the electroluminescent element which concerns on the 5th Embodiment of this invention.

  Hereinafter, an electroluminescent element according to an embodiment of the present invention will be described with reference to the drawings. However, it should be noted that the drawings are schematic, and the thicknesses and ratios of the layers are different from actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description.

[First embodiment]
(Schematic configuration of electroluminescent element)
FIG. 1 is a sectional view showing an electroluminescent element according to the first embodiment of the present invention. As shown in the figure, an electroluminescent element 10A is formed on a transparent substrate 11 made of glass, plastic, or the like, in order, a transparent electrode 12 as a first electrode, a first electron capture / emission layer 13, and a first insulating layer 14. The first buffer layer 15, the light emitting active layer 20, the second buffer layer 16, the second insulating layer 17, the second electron capture and emission layer 18, and the electrode 19 as the second electrode are laminated. As shown in FIG. 1, in the electroluminescent element 10A, an alternating current drive source 30 is connected to the transparent electrode 12 and the electrode 19 and an alternating electric field is applied, thereby emitting light from the light emitting active layer 20 from the transparent substrate 11 side. It is made to emit.

(About the light emitting active layer)
The light emitting active layer 20 is formed by depositing a number of substantially spherical quantum dots. The light emitting active layer 20 is formed to have a thickness of 20 to 100 nm by using the ES-IBD method. Each quantum dot has a nanocrystal structure in which the surface of the core portion is covered with a shell layer. Such a quantum dot can artificially define the gap energy and emit a desired color by precisely controlling the material and crystal size of the core portion.

  In the present embodiment, the diameter of the core portion is 1.9 nm, 2.4 nm, and 5.2 nm sequentially, and the thickness of the shell layer is sequentially 0.4 nm, 1.0 nm, and 1.4 nm. did. In this embodiment, quantum dots are used in which the core portion is formed of cadmium selenide (CdSe) and the shell layer is formed of zinc sulfide (ZnS) or zinc selenide (ZnSe). In addition to the CdSe, the core portion of the quantum dot in the present embodiment is appropriately made of a material composed of CdS, PbSe, HgTe, CdTe, InP, GaP, InGaP, GaAs, InGaN, GaN, or a mixed crystal thereof. Selectable.

(About electrodes)
The transparent electrode 12 is made of tin-doped indium oxide (ITO) with a thickness of about 100 nm. The electrode 19 is made of gold (Au) and has a thickness of about 50 nm. The transparent electrode 12 can be made of any transparent conductor such as zinc-doped indium oxide (IZO), indium gallium zinc oxide (IGZO), conductive zinc oxide (ZnO), amorphous oxide conductor, etc. in addition to ITO. It doesn't matter. The film thickness of the electrode 19 is appropriately increased or decreased depending on the material so that the required electrical conductivity can be obtained. The electrode 19 may be the same material as the transparent electrode described above, or may be a metal electrode.

(About the electron capture and emission layer)
In the present embodiment, the first and second electron capture / emission layers 13 and 18 are formed of barium tantalum oxide (BaTaO _x ) having oxygen vacancies. The film thicknesses of the first and second electron capture / emission layers 13 and 17 are 0.1 to 50 nm. BaTaOx with oxygen vacancies is a metal oxide with a non-stoichiometric composition and has an electrically unstable bond and electron distribution, so it captures and emits electrons and holes. have. The work functions of BaOx and BaTaOx having oxygen vacancies are reported to be 0.99 to 1.6 eV and 1.1 to 2.0 eV, respectively, and electrons are easily generated with metal ionization.

  At the trap levels of the first and second electron capture / emission layers 13 and 18, the excited electrons are trapped by positive charges, and thus electrons are emitted by applying an AC voltage between the electrodes. The electrons thus emitted are accelerated by the electric field and obtain sufficient energy for light emission from the quantum dots.

  In particular, in the present embodiment, both the first and second electron capture / emission layers 13 and 18 are formed by sputtering, and the second electron capture / emission layer 18 is formed directly on the second buffer layer 16. If this is attempted, there is a problem that the second buffer layer 16 is damaged or heat is generated by sputtering and collision of relatively heavy Ba atoms. Therefore, when the second electron capture / emission layer 18 is formed of barium tantalum oxide, it is necessary to form a film on the second insulating layer 17. In addition, by bonding the second electron capture / emission layer 18 on the second insulating layer 17, surface states are formed at the bonding interface, and electrons can be captured. At this time, the second insulating layer 17 is preferably as thin as about 100 nm or less.

(Insulation layer)
The first insulating layer 14 and the second insulating layer 17 are formed of tantalum oxide (TaO _x ) to a thickness of about 50 to 500 nm. The first insulating layer 14 and the second insulating layer 17 are not limited to tantalum oxide, but are optical such as silicon nitride, silicon oxide, yttrium oxide, alumina, hafnium oxide, barium tantalum oxide, and the like. The material can be selected from materials having general transparency and electrical insulation.

(About the buffer layer)
The first buffer layer 15 and the second buffer layer 16 are made of the same material as ZnS or ZnSe, which is the material of the shell layer in the quantum dots. These film thicknesses are about 1-20 nm.

  In addition, the 1st buffer layer 15 and the 2nd buffer layer 16 are the states which included the quantum dot and couple | bonded with the quantum dot. In other words, this combined state refers to a state in which the quantum dots are passivated in the first buffer layer 15 and the second buffer layer 16 instead of being simply dispersed in the matrix. For example, the quantum dots themselves are brought into a thermal non-equilibrium state, while retaining the three-dimensional quantum well structure that is the essence of the quantum dots, the surface decoration molecules of the quantum dots are detached, and the shell layer surfaces of individual quantum dots are Or the state which the shell layer surface and the buffer layer are chemically bonding is said.

The electroluminescent element 10A according to the present embodiment has been described above, but the work function of the first and second electron capture / emission layers 13 and 18 for generating electrons is 3.0 eV or less (preferably 2. 5 eV or less) or a compound containing the metal atom, a material having an energy difference between the trap level and the vacuum level of 3.0 eV or less (preferably 2.5 eV or less), or a composition with a non-stoichiometric ratio. It is preferable to use a metal oxide having a characteristic (particularly a metal oxide having a composition with oxygen deficiency).

(Operation / Effect of Electroluminescent Device According to First Embodiment)
In the present embodiment, a surface level is formed at the interface between the first and second electron capture / emission layers 13 and 18 and the first and second insulating layers 14 and 17 bonded to the first and second electron capture / emission layers 13 and 18. The amount of electrons supplied to the light-emitting active layer can be increased by enhancing the capture and generation of electrons, thereby improving the light emission intensity. Therefore, light emission from the light emitting active layer 20 in the electroluminescent element 10A has high luminance. Further, in the present embodiment, in order to enhance the so-called quantum confinement effect in the quantum dots, there is an advantage that light emission from the quantum dots has a narrow band spectrum and high color purity.

(Method for manufacturing electroluminescent element)
Next, a method for manufacturing the electroluminescent element according to this embodiment will be described with reference to FIGS.

  First, as shown in FIG. 2, a transparent substrate 11 such as glass or plastic having a transparent electrode 12 made of ITO (Indium Tin Oxide) formed in advance is prepared. In the present embodiment, the transparent substrate 11 is a glass substrate, and the transparent electrode 12 has a film thickness of, for example, 100 nm and a surface roughness Ra of, for example, about 50 nm. The transparent substrate 11 is subjected to ultrasonic cleaning with an organic solvent and then blown and dried with an inert gas.

Thereafter, as shown in FIG. 3, on the transparent electrode 12, a sputtering method by barium tantalum oxide (BaTaO _x) barium tantalum oxide using a sintered body with a target (BaTaO _x) in becomes the first electron capture emitting Layer 13 is formed. In this case, barium tantalum oxide (work function 2.1 eV) with adjusted oxygen deficiency was formed by adjusting the amount of oxygen introduced into the sputtering apparatus. The film thickness of the first electron capture / emission layer 13 is in the range of 0.1 to 20.0 nm.

Next, as shown in FIG. 4, a first insulating layer 14 is formed on the first electron capture / emission layer 13 with an insulator such as tantalum oxide (TaO _x ). The TaOx film was formed by reactive sputtering in an Ar + O ₂ mixed gas atmosphere of a metal Ta target using a normal high frequency (13.56 MHz) magnetron sputtering apparatus. The temperature of the substrate during deposition was from room temperature to 200 ° C. The film thickness of the first insulating layer 14 is in the range of 50 to 500 nm.

  Subsequently, as shown in FIG. 4, the first buffer layer 15 is formed on the first insulating layer 14 by using, for example, a molecular beam epitaxy (MBE) method. The film thickness of the first buffer layer 15 is 1 to 20 nm.

  Next, as shown in FIG. 5, the light emitting active layer 20 is formed on the first buffer layer 15. In the present embodiment, the light emitting active layer 20 is formed by depositing quantum dots using an ES-IBD apparatus.

  Next, as shown in FIG. 6, the second buffer layer 16 is formed on the light emitting active layer 20 under the same conditions as the first buffer layer 15. The film thickness of the second buffer layer 16 is also 1 to 20 nm, which is the same as that of the first buffer layer 15.

  Thereafter, as shown in FIG. 7, the second insulating layer 17, the second electron capture / emission layer 18, and the electrode 19 are sequentially stacked on the second buffer layer 16. The second insulating layer 14 is formed with the same material and thickness as the first insulating layer 14. The second electron capture / emission layer 18 is formed with the same material and thickness as the first electron capture / emission layer 13. The electrode 19 is formed by depositing Au to a thickness of, for example, 50 nm. The material of the electrode 19 may be a metal or a transparent conductive material.

  As described above, the method for manufacturing the electroluminescent element according to the first embodiment has been described. However, the second electron capture / emission layer 18 is stacked not on the second buffer layer 16 but on the second insulating layer 17. Therefore, it is possible to prevent the second buffer layer 16 and the underlying light emitting active layer 20 from being damaged by the sputtering method. As a result, the quantum dots are not damaged and the size does not change, and the spectrum of light emitted from the quantum dots can be prevented from changing. In such an electroluminescent element 10A, the light emission spectrum from the quantum dots 21 can suppress light emission having a wavelength other than the wavelength derived from the quantum dots, and has an effect of preventing the light emission spectrum from becoming a broadband.

[Second Embodiment]
FIG. 8 is a cross-sectional view of an electroluminescent element 10B according to the second embodiment of the present invention. The electroluminescent element 10B according to the present embodiment is different only in the position of the first electron capture / emission layer 13 in the electroluminescent element 10A according to the first embodiment. That is, in the present embodiment, the first electron capture / emission layer 13 is disposed on the first insulating layer 14 without being disposed between the first insulating layer 14 and the transparent electrode 12. The operations and effects of the electroluminescent element 10B according to the present embodiment are the same as those of the first embodiment.

[Third embodiment]
FIG. 9 is a cross-sectional view of an electroluminescent element 10C according to the third embodiment of the present invention. The electroluminescent element 10C is configured such that the first electron capture / emission layer 13 and the second electron capture / emission layer 18 in the electroluminescent element 10A according to the first embodiment are each composed of two layers. The electron capture and emission layers 13A and 13B and the second electron capture and emission layers 18A and 18B are configured. Other configurations in the present embodiment are the same as those in the first embodiment.

  In the present embodiment, the first electron capture / emission layers 13A and 13B and the second electron capture / emission layers 18A and 18B each having a two-layer structure are formed of the same material. By adopting such a structure, in this embodiment, the amount of electrons supplied to the light emitting active layer is increased by promoting the capture and generation of electrons at the surface level at the interface between the electron capture and emission layers. Thus, the emission intensity can be improved.

[Fourth embodiment]
FIG. 10 is a cross-sectional view of an electroluminescent element 10D according to the fourth embodiment of the present invention. The electroluminescent device 10D has a first electron capture / emission layer 13 and a second electron capture / emission layer 18 in the electroluminescent device 10A of the first embodiment, and each of the two layers. One of the first electron capture / emission layer 13C and the second electron capture / emission layer 18C, which is one layer, is formed of metal. Even if a non-transparent metal material is used for either one, light emission can be extracted from the transparent surface side as long as the materials forming the opposite layer with the light emitting active layer interposed therebetween are all transparent. At this time, it is possible to use an opaque material for all sides using the metal material. Other configurations, operations, and effects in the present embodiment are the same as those in the third embodiment.

[Fifth embodiment]
FIG. 11 is a cross-sectional view of an electroluminescent element 10E according to the fifth embodiment of the present invention. The electroluminescent element 10E uses a silicon substrate 21 instead of glass. The electroluminescent device 10E includes an electrode 19, a first electron capture / emission layer 13, a first insulating layer 14, a first buffer layer 15, a light emitting active layer 20, a second buffer layer 16 on a silicon substrate 21 in order. A second insulating layer 17, a second electron capture / emission layer 18, and a transparent electrode 12 are formed. In the electroluminescent element 10E of the present embodiment, light emission is emitted to the transparent electrode 12 side.

  Since the operation, operation, and effect of the electroluminescent element 10E according to the present embodiment are substantially the same as those of the first embodiment, description thereof is omitted.

<Experimental example>
In the configuration of the electroluminescent element 10A according to the first embodiment, the first buffer layer 15 and the second buffer layer 16 are formed of ZnS, and the first and second electron capture / emission layers 13 and 18 are not provided ( A comparative example) and a case (example) were prepared. The electric fields of Examples 1 to 3 in which the thicknesses of the first and second electron capture / emission layers 13 and 18 are different from 5 nm (Example 1), 20 nm (Example 2), and 200 nm (Example 3). A light emitting element was manufactured and the behavior was observed.

As a result, in the comparative example without the first and second electron capture / emission layers 13 and 18 and Examples 1 to 3, the behavior changes (different), and the electroluminescence element of 5 nm to 20 nm has an emission start voltage. The effect of decreasing the emission spectrum from 80 V to 40 V, increasing the emission intensity, and narrowing the emission spectrum was confirmed.
[Other embodiments]

  As mentioned above, although each embodiment of this invention was described, this invention is not limited to these, The following changes are also the application scope of this invention.

  For example, the material of the first and second electron capture / emission layers 13 and 18 used in the above embodiments has a conduction band edge level larger than that of the material of the core part of the quantum dot, and the valence electrons. The material can be appropriately selected from inorganic materials having a band edge level smaller than the valence band edge level of the material of the core portion. The electron capture / emission layer may be an atomic layer made of a single element or a compound containing these. Specifically, elements such as Ca, Ba, Sr, Cs, Ce, Gd, La, Ag, Pb, Zn, Al, and Bi having a work function of 3.0 eV or less can be given.

  In the fifth embodiment, the silicon substrate 21 having an opaque substrate is used. However, other inorganic materials may be used as long as the electrode 19 can be formed even if it is an opaque material. It is also possible to apply a plastic substrate having flexibility.

10A, 10B, 10C, 10D, 10E ... Electroluminescent device 11 ... Transparent substrate 12 ... Transparent electrode 13, 13A, 13B, 13C ... First electron capture / emission layer 14 ... First insulating layer 15 ... First buffer layer 16 ... First 2 buffer layer 17 second insulating layer 18 second electron capture and emission layer 19 electrode 20 light emitting active layer 21 silicon substrate 30 AC drive source

Claims (9)

A light-emitting active layer containing quantum dots is sandwiched between a pair of buffer layers made of an inorganic semiconductor material, and quantum dots are included in the buffer layer, and electrodes are arranged so that an insulating layer is sandwiched between each of the buffer layers. Is an electroluminescent element that emits light from the light-emitting active layer by applying an alternating voltage to these electrodes,
An electroluminescent device comprising: an electron capture / emission layer that forms a surface state at an interface with a layer to be bonded between the buffer layer and the electrode.   2. The electroluminescent device according to claim 1, wherein the electron capture and emission layer is made of a material having an energy difference between a trap level and a vacuum level of 3.0 eV or less.   2. The electroluminescent device according to claim 1, wherein the electron capture / emission layer is made of a single metal atom having a work function of 3.0 eV or less or a compound containing the metal atom.   3. The electroluminescent device according to claim 1, wherein the electron capture / emission layer is a metal oxide having a composition with a non-stoichiometric ratio.   The electroluminescent device according to claim 4, wherein the metal oxide has a composition having oxygen vacancies.   The electroluminescent device according to claim 1, wherein the electron capture / emission layer is interposed between the buffer layer and the insulating layer.   The electroluminescent device according to claim 1, wherein the electron capture / emission layer is interposed between the insulating layer and the electrode.   The electroluminescent device according to any one of claims 1 to 7, wherein the electron capture / emission layer is formed by laminating a plurality of layers.   The electroluminescent device according to claim 8, wherein the plurality of layers are made of different materials.

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