Patent Publication Number: US-2012043532-A1

Title: Light emitting device

Description:
TECHNICAL FIELD 
     The present invention relates to an electric-field light emitting device (electroluminescence device), which emits light by application of an electric field, and particularly to an electroluminescence device that can emit light with high efficiency. 
     BACKGROUND ART 
     Electroluminescence devices (EL devices), such as an organic EL device, an LED (light emitting diode), and a semiconductor laser, are structured in such a manner that electrode layers, a light emitting layer and the like are deposited (stacked, superposed or the like) one on another on a substrate. Generally, light generated in the light emitting layer is extracted through a transparent electrode. However, when light enters the interface of the light-extracting-side layer at an angle greater than or equal to a critical angle by influence of the refractive index of each layer, total reflection occurs. Therefore, the light is trapped in the electroluminescence device, and it is impossible to extract the light therefrom. Hence, highly efficient extraction of emitted light is difficult. For example, when the refractive index of the transparent electrode is the refractive index of ITO (indium-tin oxide) or the like, which is often used as the material of the transparent electrode, the light extraction efficiency is said to be approximately 20%. 
     For example, in an organic EL device, it is known that when an organic material is present in an excited state for a long period of time, the chemical bond of the organic material breaks inherently, and that the light emitting performance of the organic EL device deteriorates as time passes. It is essential to solve this problem when the organic material is used as the material of the electroluminescence device (light emitting device). Further, as long as fluorescence is used, generation efficiency at an upper level (an upper energy level or state) is theoretically limited to 25%, and it is impossible to increase the light emitting efficiency more than this level. In principle, when phosphorescence is used and intersystem crossing is promoted, it is possible to induce the upper level including only triplets. Therefore, the theoretical limit may be increased to the range of 75% to 100%. However, the lifetime of the triplet in the upper level is longer than that of fluorescence, which is emitted in allowed transition, and the probability of collision between excitons is high. Therefore, the light emitting efficiency is lower. Further, the device deteriorates faster, and the durability of the device is low. 
     As described above, the light emitting efficiency and the extraction efficiency of the EL device are low. Therefore, the utilization efficiency of the emitted light is extremely low. Hence, the utilization efficiency needs to be improved. 
     As an approach to improving the light emitting efficiency (or enhancing light emission), W. Li et al., “Emissive Efficiency Enhancement of Alq 3  and Prospects for Plasmon-enhanced Organic Electroluminescence”, Proc. of SPIE, Vol. 7032, pp. 703224-1-703224-7, 2008 (Non-Patent Document 1) proposes a method of utilizing a plasmon enhancement effect. In the method of utilizing the plasmon enhancement effect, metal (island form pattern is desirable) is arranged in the vicinity (for example, a few dozens of nanometers) of the light emitting layer to enhance the light emission. Plasmons (or localized plasmons) are induced on the surface of the metal by radiation of dipoles from the light emitting layer. After energy is absorbed, light is radiated again, and the newly emitted light enhances the light emission. Therefore, the new transition to light emission by plasmons is added to the light emitting process of the light emitting device. Hence, the lifetime (excitation lifetime) in the upper level can be reduced. When the plasmon enhancement is utilized, improvement in the light emitting efficiency and improvement in durability by reduction of the excitation lifetime may be expected. 
     As an approach to improving the light extraction efficiency, Japanese Unexamined Patent Publication 2007-165284 (Patent Document 1) discloses an EL device including a light scattering layer. The light scattering layer is provided to solve the problem that the light extraction efficiency is low because light emitted from a light emitting layer is totally reflected at the interface between the light emitting layer and a layer next to the light emitting layer, and confined or trapped in the device. The light scattering layer includes a dielectric layer and metal microparticles contained in the dielectric layer. In the EL device, when total reflection occurs, the metal microparticles resonate by near field light scattered from the interface of the light emitting layer, and plasmons are induced. Light is radiated by the induced plasmons, and the radiation light is extracted from the device. Patent Document 1 describes that the light confined in the light emitting layer can be scattered to the outside of the light emitting layer. 
     However, in Non-Patent Document 1, enhancement of light emission by the plasmon enhancement effect is confirmed only in a light-excitation-type light emitting device (photoluminescence device: PL device), and no successful case has been reported. Non-Patent Document 1 describes that insertion of a metal layer into the EL device causes charge trap, thereby inhibiting the flow of electrons and positive holes from the electrodes to the light emitting layer. Further, Non-Patent Document 1 describes that the carrier balance is broken, and the light emission is suppressed rather than being enhanced. 
     Meanwhile, in the EL device disclosed in Patent Document 1, the metal microparticle is arranged in a dielectric layer. Therefore, the effect of charge trap can be prevented. However, the movement (transport) layer of charges (electrons and holes) is divided by the dielectric layer. Therefore, the flow of electrons and holes is also inhibited, and a risk of affecting light emission exists. 
     DISCLOSURE OF INVENTION  
     In view of the foregoing circumstances, it is an object of the present invention to provide an EL device that can achieve high light emitting efficiency without lowering the durability of the device. 
     An electroluminescence device of the present invention is an electroluminescence device comprising: 
     electrodes; 
     a plurality of layers that are deposited one on another between the electrodes; and 
     a light emitting region between the plurality of layers, the light emitting region emitting light by application of an electric field between the electrodes, wherein at least one microparticle that induces plasmon resonance on the surface thereof by the light emitted from the light emitting region is arranged in the vicinity of the light emitting region or in the light emitting region, and wherein the microparticle is a core-shell-type microparticle including at least one metal microparticle core and an insulation shell that covers the at least one metal microparticle core. 
     Here, the term “electroluminescence device” is used as a general term for a device that emits light by application of an electric field, and which includes an organic EL device, an inorganic EL device, a light emitting diode (LED), and a semiconductor laser (LD: laser diode). 
     In the electroluminescence device of the present invention, it is desirable that at least a part of the at least one core-shell-type microparticle is arranged in the light emitting region and/or on the surface of the light emitting region. 
     Further, in the electroluminescence device of the present invention, it is desirable that a multiplicity of core-shell-type microparticles are dispersed in the light emitting region. 
     To achieve a more effective plasmon effect, it is desirable that the at least one core-shell-type microparticle is arranged in such a manner that a distance between the surface of at least one metal microparticle core in the at least one core-shell-type microparticle and the light emitting region is less than or equal to 30 nm. Further, it is desirable that the particle diameter of the metal microparticle core is greater than or equal to 10 nm and less than or equal to 1 um (micro meter). Here, the term “particle diameter” refers to the longest diameter (length) of the metal microparticle core. 
     When the core-shell-type microparticle or the metal microparticle core is an elongated microparticle, in which the aspect ratio of the major axis of the elongated microparticle to the minor axis of the elongated microparticle, the minor axis being perpendicular to the major axis, is greater than 1, it is desirable that a multiplicity of elongated microparticles are arranged in such a manner that the minor axes of the elongated microparticles are oriented in a direction substantially perpendicular to the surfaces of the electrodes. 
     When the electroluminescence device is an organic EL device, it is desirable that the plurality of layers include at least an electron transport layer, a light emitting layer, and a positive hole transport layer, and each of which is an organic layer. When the electroluminescence device is structured in such a manner, it is desirable that the core-shell-type microparticles are dispersed on the surface of the electron transport layer or the positive hole transport layer, or in the electron transport layer or the positive hole transport layer. 
     The electroluminescence device of the present invention includes a microparticle in the vicinity of a light emitting region or in the light emitting region. The microparticle induces plasmon resonance on the surface thereof by light emitted from the light emitting region. The microparticle is structured as a core-shell-type microparticle including at least one metal microparticle core and an insulation shell that covers the at least one metal microparticle core. When the microparticle is structured in such a manner, the metal microparticle (metal microparticle core) is coated with an insulator. Therefore, the flow of electrons and positive holes are not prevented by charge trap. Further, transition to light emission by plasmons can enhance light emission and reduce the lifetime (excitation lifetime) in the upper level. Consequently, it is possible to greatly improve the light emission efficiency and the durability of the device by reduction of the excitation lifetime. 
     Further, in the electroluminescence device of the present invention, the entire surface of the metal microparticle (metal microparticle core) is covered with an insulator. Therefore, the core-shell-type microparticle may be placed on the surface of the light emitting layer or in the light emitting layer. When the metal microparticle core is provided on the surface of the light emitting layer or in the light emitting layer, transition to light emission by plasmons is more effectively induced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ] 
         FIG. 1  is a schematic diagram illustrating the structure of layers of an EL device (organic EL device) according to an embodiment of the present invention; 
       [ FIG. 2 ] 
         FIG. 2  is a schematic cross-sectional diagram illustrating the structure of a core-shell-type microparticle including a plurality of metal microparticle cores; 
       [ FIG. 3 ] 
         FIG. 3  is a schematic diagram illustrating the structure of layers of an EL device including elongated core-shell-type microparticles; 
       [ FIG. 4 ] 
         FIG. 4  is a schematic diagram illustrating the structure of layers of an EL device including metal microparticle cores in a light emitting layer; and 
       [ FIG. 5 ] 
         FIG. 5  is a schematic diagram illustrating the structure of layers of an inorganic LED according to an embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     &lt;Electroluminescence (EL) Device&gt; 
     With reference to drawings, an electroluminescence device (EL device) according to embodiments of the present invention will be described.  FIG. 1  is a schematic cross-sectional diagram illustrating the structure of an EL device according to the present embodiment. In  FIG. 1 , elements are appropriately illustrated at different scales from the actual sizes thereof so that the elements are easily recognizable. 
     As illustrated in  FIG. 1 , an electroluminescence device (EL device)  1  includes an anode  11 , a positive hole transport layer  13 , a light emitting layer (light emitting region)  14 , an electron transport layer  15 , and a cathode  16  on a light-transmitting substrate (transparent substrate)  10 , which transmits light. In the EL device (organic EL device)  1 , a multiplicity of core-shell-type microparticles  20 , as microparticles that induce plasmon resonance by light emitted from the light emitting layer  14 , are dispersed in the positive hole transport layer  13 . The core-shell-type microparticle  20  includes a metal microparticle core  22  and an insulation shell  21 , which covers (coats) the metal microparticle core  22 . The insulation shell  21  is made of a light transmitting material, which transmits the light emitted from the light emitting layer  14 . Here, the term “light-transmitting” means that the transmittance with respected to the emitted light is higher than or equal to 70%. 
     The light-transmitting substrate  10  is not particularly limited, and a glass substrate, a quartz substrate, a flexible substrate made of polymer or the like may be used. 
     The light emitting layer  14  is not particularly limited as long as it is adoptable as a light emitting layer of an organic EL device. For example, the light emitting layer  14  may be made of a phenanthroline derivative (BCP) or the like. The organic EL device  1  emits light when electrons and positive holes injected from the anode  11  and the cathode  16 , respectively, recombine with each other in the region of the light emitting layer  14 . 
     The core-shell-type microparticle  20  is arranged in the vicinity of the light emitting region (light emitting layer)  14  so that plasmon resonance is induced by the light emitted from the light emitting region  14 . 
     The position at which the core-shell-type microparticle  20  is arranged is not particularly limited as long as the metal microparticle (metal microparticle core)  22  of the core-shell-type microparticle  20  is located in a region in which plasmon resonance by the light emitted from the light emitting layer  14  is inducible. When the distance between the light emitting layer  14  and the metal microparticle (metal microparticle core)  22  is too long, it becomes difficult to induce plasmon resonance by the emitted light, and it is impossible to achieve an effective light emission enhancement effect. Therefore, it is desirable that distance d between the surface of the metal microparticle (metal microparticle core)  22  and the light emitting layer  14  is less than or equal to 30 nm. In the organic EL device of the present embodiment, the metal microparticle (metal microparticle core)  22  is covered by the insulation shell  21 . Therefore, the core-shell-type microparticle  20  including the metal microparticle core  22  may be arranged in the light emitting layer  14 , and the electrodes layers (anode and cathode)  11 ,  16 . 
     As the material of the metal microparticle (metal microparticle core)  22 , a material that induces plasmon resonance by emitted light should be used. For example, Ag (silver), Au (gold), Cu (copper), Al (aluminum), Pt (platinum) or an alloy containing one of these metals as a main component (greater than or equal to 80%) may be used. When the emitted light has a wavelength in the visible light range, silver is desirable, because silver can induce surface plasmon resonance in the visible light range because of the plasma frequency. When the wavelength of the emitted light is not in the visible light range, for example, if the wavelength of the emitted light is in an infrared ray range, it is desirable that the material is gold. 
     Meanwhile, as the material of the insulation shell  21 , an insulator such as SiO 2 , Al 2 O 3 , MgO, ZrO 2 , PbO, B 2 O 3 , CaO and BaO, which transmits the emitted light, may be used. 
     Each of the layers  13  through  15  is designed to have a refractive index and a thickness so that the light emitting layer is located at the loop of the standing wave formed in the organic EL device. 
     As described in the section, “Background Art” of this specification, when a metal member, such as a metal microparticle, in an exposed state is inserted into the layers of the EL device, charges are trapped in the metal during application of an electric field, because the work function of the metal is higher than the work function of each layer. Therefore, the flow of charges is prevented, and the carrier balance is broken. Consequently, the efficiency of recombination of charges becomes lower, and the light emission is suppressed rather than being enhanced. When the metal microparticle is arranged in a dielectric layer, the influence of the charge trap may be prevented. However, a movement (transport) layer of charges (electrons and positive holes) is blocked by the dielectric layer. Therefore, the flow of electrons and positive holes is also prevented, and a risk of affecting light emission exists. 
     In the present embodiment, the core-shell-type microparticle  20 , as a metal member that induces plasmon resonance on the surface thereof by emitted light, is used to prevent such an adverse effect on light emission. The core-shell-type microparticle  20  is formed, for example, by using a silver microparticle as the metal microparticle core  22  and a dielectric, such as SiO 2 , as the insulation shell  21 . The silver microparticle  22 , which contributes to plasmon resonance, is covered by the insulation shell  21 . Therefore, even when an electric field is applied between the electrodes, charges (electrons or positive holes) are not trapped in Ag, and the charges flow through the movement layer that has a higher conductivity than that of the dielectric layer. Hence, the flow of charges is not prevented, and the light emitting layer can achieve the plasmon enhancement effect. 
     Next, an example of a method for producing the EL device  1  of the present embodiment will be described briefly. 
     The anode  11  made of ITO (indium-tin oxide) is formed on the glass substrate  10  by vapor deposition. As the core-shell-type microparticle  20 , a microparticle  22  of Ag having a particle diameter of 50 nm is coated with SiO 2    21  with the thickness of 10 nm. Next, the core-shell-type microparticles  20  are dispersed in dichloromethane, in which a triphenyl diamine derivative (TPD), as a positive hole transport material, is dissolved. Further, the solution is applied to the anode  11  by spin coating, and the solvent is dried. Accordingly, the positive transport layer  13 , in which the core-shell-type microparticles  20  are dispersed, is formed. 
     Next, a phenanthroline derivative (BCP), as a light emitting material, and Alq3(tris-(8-hydroxyquinoline)aluminum), as an electron transport material, are sequentially deposited by vapor deposition to form the light emitting layer  14  and the electron transport layer  15 , respectively. Finally, the cathode  16  made of Al is formed to obtain the organic EL device  1 . 
     In the aforementioned example, the core-shell-type microparticles are dispersed in the positive hole transport layer  13 . Alternatively, as described above, the core-shell-type microparticles  20  may be arranged or dispersed in any layer between the electrodes as long as plasmon resonance by the emitted light is inducible in the region in which the core-shell-type microparticles  20  are arranged. When the core-shell-type microparticles  20  are present in the light emitting region  14 , it is possible to more effectively induce plasmon resonance, and that is desirable. 
     In  FIG. 1 , the multiplicity of core-shell-type microparticles  20  are present. However, even if only one core-shell-type microparticle  20  is present, it is possible to enhance the light emission effect by the plasmon resonance. 
     In  FIG. 1 , a single metal microparticle core  22  is provided in an insulation shell  21 . Alternatively, a core-shell-type microparticle  20 ′ including a plurality of metal microparticle cores  22 ′ in an insulation shell  21 ′, as illustrated in  FIG. 2 , may be adopted. 
     The particle diameter of the metal microparticle core  22  of the core-shell-type microparticle  20  is not particularly limited as long as localized plasmons are induced. It is desirable that the particle diameter of the metal microparticle core  22  is less than or equal to the wavelength of the emitted light. Optionally, the particle diameter may be greater than or equal to 10 nm and less than or equal to 1 um (micro meter). 
     It is desirable that the thickness of the insulation shell  21  does not prevent induction of localized plasmons at the metal microparticle cores  22  by the emitted light. It is desirable that a distance between the light emitting layer  14  and the surface of the metal microparticle core  22  is less than or equal to 30 nm to effectively induce plasmons by the light emitted from the light emitting layer  14 . Therefore, it is desirable that the position at which the core-shell-type microparticle  20  is arranged, the structure or arrangement of the layer, and the thickness of the insulation shell  21  are designed so that effective plasmon resonance is induced. Here, the thickness of the insulation shell  21  is an average distance between the surface of the insulation shell  21  and the surface of the metal microparticle core when only one metal microparticle  22  is included in the insulation shell  21 . When the plurality of metal microparticle cores  20 ′ are included in the insulation shell  21 ′, as illustrated in  FIG. 2 , the thickness of the insulation shell  21 ′ is an average value of a shortest distance between the surface of the insulation shell  21 ′ and each of the metal microparticle cores  22 ′. 
     As illustrated in  FIG. 3 , in an organic EL device  2  according to another embodiment of the present invention, a multiplicity of elongated microparticles are used as core-shell-type microparticles  20 ″ or the metal microparticles cores  22 ″ (the aspect ratio of the major axis of the elongated microparticle to the minor axis of the elongated microparticle, which is perpendicular to the major axis, is greater than 1). In the organic EL device  2 , the multiplicity of elongated core-shell-type microparticles  20 ″ maybe arranged in such a manner that the minor axes of the microparticles are oriented in a direction substantially perpendicular to the surfaces of the electrodes. 
     When the organic EL device  2  is structured in such a manner, it is possible to obtain scattered light the intensity of which is higher on the light extraction side because of the anisotropy of the form of the elongated core-shell-type microparticle  20 ″. Hence, it is possible to achieve higher light emission efficiency. 
     Further, as illustrated in  FIG. 4 , according to another embodiment of the present invention, the core-shell-type microparticle  20  may be arranged in such a manner that the metal microparticle (metal microparticle core)  22  is located in the light emitting layer  14 . As already described, when the metal microparticle  22  is present in the light emitting region (light emitting layer)  14 , transition to light emission by plasmon resonance is more effectively induced. 
     In an organic EL device  3 , illustrated in  FIG. 4 , the core-shell-type microparticle  20  is present in both of a layer (the positive hole transport layer  13 ) next to the anode  11  and the light emitting layer  14 . When the organic EL device  3  is structured in such a manner, it is possible to easily produce the organic EL device  3  by providing the core-shell-type microparticles  20  by spin coating, as described above. 
     The organic EL devices  1  through  3  include microparticles  20  ( 20 ′,  20 ″) , which induce plasmon resonance on the surface thereof by light emitted from the light emitting region (light emitting layer)  14 , in the vicinity of the light emitting region  14  or in the light emitting region  14 . Further, the microparticle  20  ( 20 ′,  20 ″) includes at least one metal microparticle core  22  ( 22 ′,  22 ″) and an insulation shell  21  ( 21 ′,  21 ″) , which covers the at least one metal microparticle core  22  ( 22 ′,  22 ″) . When the microparticle  20  ( 20 ′,  20 ″) is structured in such a manner, the metal microparticle (metal microparticle core)  22  ( 22 ′,  22 ″) is coated with the insulation shell  21  ( 21 ′,  21 ″). Therefore, the flow of electrons and positive holes is not prevented by charge trap, and it is possible to induce transition to light emission by plasmons, thereby achieving a light emission enhancement effect and an effect of reducing the lifetime (excitation lifetime) in the upper level. Accordingly, it is possible to greatly improve the light emission efficiency and the durability of the device by the reduction of the excitation lifetime. 
     In the organic EL devices  1  through  3 , the entire surface of the metal microparticle  22  ( 22 ′,  22 ″) is covered by the insulation shell  21  ( 21 ′,  21 ″) . Therefore, the metal microparticle  22  ( 22 ′,  22 ″) may be arranged on the surface of the light emitting region (light emitting layer)  14  or in the light emitting region (light emitting layer)  14 . When the metal microparticle  22  ( 22 ′,  22 ″) is provided on the surface of the metal layer  14  or in the metal layer  14 , transition to light emission by plasmons is more effectively induced. 
     For example, in the EL devices as described above, layers are sequentially deposited on the substrate from the anode side, and light is extracted from the anode side. Each of layers other the metal thin-film may be formed by using the material and deposition methods of conventional organic EL devices. 
     In the above embodiments, each of the cathode, the electron transport layer, the light emitting layer, the positive hole transport layer, the anode, and the like may be made of materials selected from various well-known materials, each having an appropriate function. Further, a positive hole block layer, an electron block layer, a protective layer or the like may be provided. 
     Further, in each of the embodiments, an organic EL device in which the plurality of layers including the light emitting layer are organic compound layers has been described. Alternatively, the EL device of the present invention may be an inorganic EL device, in which the plurality of layers including the light emitting layer are inorganic compound layers. Further, the EL device of the present invention may be appropriately applied to a light emitting diode (LED) including a plurality of semiconductor layers and a semiconductor laser. 
     Next, an example in which the present invention is applied to an inorganic LED will be described.  FIG. 5  is a diagram illustrating an example in which the core-shell-type microparticles  20  are dispersed in an InGaN/GaN multilayer quantum well structure of a blue LED. 
     The inorganic LED  4  illustrated in  FIG. 5  may be produced, for example, in the following manner. First, a sapphire substrate  30  is prepared, and a low-temperature buffer layer (GaN)  37  and an n-type clad layer  35  (n-GaN) are sequentially deposited on the (001) surface of the sapphire substrate  30  by using organic metal vapor phase growth method (Metal Organic Chemical Vapor Deposition: MOCVD). After then, the sapphire substrate  30  on which the low-temperature buffer layer (GaN)  37  and the n-type clad layer  35  (n-GaN) are deposited is removed from the chamber. Further, the core-shell-type microparticles  20  are dispersed on the n-type clad layer  35  by spin coating. 
     In this example, the core-shell-type microparticles  20  were applied and dispersed by spin coating by using a coating liquid (application solution). In the coating liquid, the core-shell-type microparticles were dispersed in dichloromethane. The core-shell-type microparticle  20  included a Ag microparticle with a particle diameter of 50 nm, and the Ag microparticle was coated with a coating of SiO 2  with a thickness of 10 nm. After the spin coating, the solvent was dried. 
     Further, the multilayer quantum well structure (light emitting layer)  34  and a p-type clad layer (p-GaN)  33  were sequentially deposited. The multilayer quantum well structure  34  may be produced, for example, by alternately depositing quantum well of In 0.2 Ga 0.8 N and a barrier layer of GaN by using the MOCVD method. The p-type clad layer  33  may also be deposited by using the MOCVD method. 
     Next, electrode portions of the inorganic LED are formed. First, photolithography and etching are performed to partially expose the n-type clad layer  35 . Next, an ITO (indium-tin oxide), as a transparent electric current diffusion layer  38 , is deposited on the p-type clad layer  33 . Finally, Cr/Au is vapor-deposited, as electrodes  31  and  36 , on the electric current diffusion layer  38  and an n-type semiconductor layer  35  by using an EB method. Accordingly, the LED structure is completed. 
     The inorganic LED  4  and the aforementioned organic EL devices have different device structures from each other. However, the inorganic LED  4  has a similar structure to the organic EL device  1  through  3  in that the inorganic LED  4  includes microparticles  20 , which induce plasmon resonance on the surface thereof by light emitted from the light emitting region (light emitting layer)  34 , in the vicinity of the light emitting region  34  or in the light emitting region  34 . Further, the inorganic LED  4  has a similar structure in that the core-shell-type microparticle of the inorganic LED  4  includes at least one metal microparticle core  22  and an insulation shell  21  that covers the at least one metal microparticle core  22 . Therefore, the inorganic LED  4  achieves beneficial effects similar to the effects of the organic EL devices  1  through  3 . Therefore, the inorganic LED  4  can achieve high light emission efficiency and high durability by reduction of the excitation lifetime. 
     In the organic LED  4 , the core-shell-type microparticle  20  may be arranged in the quantum well structure  34 , which is a light emitting layer. When the core-shell-type microparticle  20  is arranged in such a manner, plasmons are highly efficiently induced on the metal microparticle core  22  of the core-shell-type microparticle  20  in the light emitting layer by the light emitted in the light emitting layer. Therefore, it is possible to very effectively achieve the light emission enhancement effect and the effect of reducing the lifetime (excitation lifetime) in the upper level by transition to light emission by plasmons. 
     Further, the EL device of the present invention may be appropriately applied to a display device or element, a display, a back light, an electronic photograph, a light source for lighting, a light source for recording, a light source for exposure, a light source for readout, a sign or mark, a signboard, an interior decoration or object, optical communication, and the like.