Patent Publication Number: US-5529853-A

Title: Organic electroluminescent element

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic electroluminescent element, and particularly, to an organic electroluminescent element improved in durability. 
     2. Description of the Related Arts 
     The rapid diversification of data processing apparatuses in recent years has invited an increasing demand for a flat-type display element that can save electricity and space compared with a CRT(cathode-ray-tube). A crystalline liquid display element and a plasma display element are typical flat-type display elements; however, another flat-type display element, a self-luminous electroluminescent element(EL element), that enables a sharp, clear display has been attracting considerable attention recently. The EL element can be made of either organic or non-organic material, and the non-organic EL element has been already put into practical use. 
     The non-organic EL element emits light, or luminesces, when electrons fully accelerated in an imposed electric field collide with a luminous material and excite the luminous material. However, to accelerate the electrons to a sufficient speed, a high voltage must be applied, which undesirably increases the costs of peripheral apparatuses. On the other hand, the organic EL element luminesces when charges, or namely holes and electrons injected from their respective electrodes, re-combine in the luminous material. Unlike the acceleration, the injection of the holes and electrons requires a low voltage. In addition, with organic compounds, a desired luminous color can be created by changing a molecular structure thereof. These are the major reasons why the organic EL elements have been attracting considerable attention as being a potential display element. 
     For further understanding, the organic EL element will be described more in detail. The typical organic EL element has an SH-A structure, an SH-B structure, or a DH structure. In the SH-A structure, a hole-transport layer and a luminous layer are formed, one on top of the other, between a hole-injecting electrode and an electron-injecting electrode; in the SH-B structure, the luminous layer and an electron-transport layer are formed, one on top of the other, between the hole- and electron-injecting electrodes; in the DH structure, three layers--the hole-transport, luminous, and electron-transport layers--are alternatively layered between the hole- and electron-injecting electrodes. The hole-injecting electrode is made of a material having a large work function such as gold or ITO(an oxide of In and Sn), while the electron-injecting electrode is made of a material having a small work function such as Mg. All of the hole-transport, luminous, and electron-transport layers are made of organic materials; the hole-transport layer is made of the organic material of p-type, while the electron-transport layer of n-type; the luminous layer is made of the organic material of n-type in the SH-A structure, p-type in the SH-B structure, and neutral in the DH structure. In any case, the organic EL element luminesces when the holes and electrons injected from their respective electrodes re-combine in the luminous layer and at the surface contacting with the hole- and/or electron-transport layers. 
     The demand for practical applications of the organic EL element has been increasing. Yet, this potential display element is now facing several problems to be solved urgently to be commercially useful : one of them is improvement in durability. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has an object to provide an organic EL element improved in durability. 
     The above object is fulfilled by an EL element comprising a hole-injecting electrode, an electron-injecting electrode, and an organic film layer including at least an organic luminous material formed between the hole- and electron-injecting electrodes, characterized in that the luminous material is a metal complex polymer. 
     The organic film layer may be made of a mixture of the organic luminous material and an organic hole-transport material. 
     The metal complex polymer used as the organic luminous material may be a compound expressed by Chemical Formula 101 and Chemical Formula 102. ##STR1## 
     The organic hole-transport material may be a compound expressed by Chemical Formula 103. ##STR2## 
     The organic film layer may consist of an organic luminous layer and an organic hole-transport layer, and the organic luminous layer may be made of the metal complex polymer used as the luminous material. 
     The organic film layer may consist of an organic luminous layer and an organic electron-transport layer, and the organic luminous layer may be made of the metal complex polymer used as the luminous material. 
     The organic film layer may consist of an organic luminous layer, an organic electron-transport layer, and a hole-transport layer, and the organic luminous layer may be made of the metal complex polymer used as the luminous material. 
     The above object is also fulfilled by an EL element comprising a hole-injecting electrode, an electron-injecting electrode, and an organic film layer including at least an organic luminous material formed between the hole- and electron-injecting electrodes, characterized in that the organic film layer is made of an inner complex salt having 2 or more ligands. 
     The organic film layer may consist of an organic luminous layer and an organic hole-transport layer, and the organic luminous layer may be made of the inner complex salt having 2 or more ligands. 
     The inner complex salt composing the organic luminous layer may be expressed by Chemical Formula 104. ##STR3## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 105. ##STR4## 
     The organic film layer may consist of an organic luminous layer and an organic electron-transport layer, and the organic luminous layer may be made of the inner complex metal having 2 or more ligands. 
     The organic electron-transport layer may be made of any inner complex salt. 
     The organic film layer may consist of an organic luminous layer, an organic electron-transport layer, and an organic hole-transport layer, and the organic luminous layer may be made of the inner complex salt having 2 or more ligands. 
     The inner complex salt composing the organic luminous layer may be expressed by Chemical Formula 106. ##STR5## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 107. ##STR6## 
     The organic electron-transport layer may be made of a compound expressed by Chemical Formula 108. ##STR7## 
     The organic electron-transport layer may be made of the inner complex salt. 
     The inner complex salt having 2 or more ligands composing the organic luminous layer may be a compound expressed by Chemical Formula 109. ##STR8## 
     The inner complex metal composing the organic electron-transport layer may be a compound expressed by Chemical Formula 110. ##STR9## 
     The above object is also fulfilled by an EL element comprising a hole-injecting electrode, an electron-injecting electrode, and an organic film layer including at least an organic luminous material formed between the hole and electron-injecting electrodes, characterized in that the organic film layer is made of 10-hydroxybenzo [h] quinoline--metal complex expressed by Chemical Formula 111 and Chemical Formula 112. ##STR10## 
     The organic film layer may consist of an organic luminous layer and an organic hole-transport layer, and the organic luminous layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The 10-hydroxybenzo [h] quinoline--metal complex composing the organic luminous layer may be a compound expressed by Chemical Formula 113. ##STR11## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 114. ##STR12## 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the dopant. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the base material. 
     The 10-hydroxybenzo [h] quinoline--metal complex serving as the base material may be a compound expressed by Chemical Formula 115. ##STR13## 
     The phtaloperinone expressed by Chemical Formula 116 may serve as the dopant. ##STR14## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 117. ##STR15## 
     The organic film layer may consist of an organic luminous layer and an organic electron-transport layer. 
     The organic film layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the dopant. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the base material. 
     The organic electron-transport layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic film layer may consist of an organic luminous layer, an organic hole-transport layer, and an organic electron-transport layer. 
     The organic luminous layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the dopant. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the base material. 
     The organic electron-transport layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The 10-hydroxybenzo [h] quinoline--metal complex in the organic electron-transport layer may be a compound expressed by Chemical Formula 118. ##STR16## 
     The organic hole-transport layer may be a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 119. ##STR17## 
     The organic luminous layer may be made of phtaloperinone expressed by Chemical Formula 120. ##STR18## 
     A central metal of the 10-hydroxybenzo [h] quinoline--metal complex may be selected from a group consisting of metals belonging to the second and the third groups of the periodic table. 
     The above object is also fulfilled by an EL element comprising an organic film layer including at least an organic luminous material between a hole-injecting electrode and an electron-injecting electrode, characterized in that the organic film layer is made of one of a metal complex polymer, an inner complex salt having 2 or more ligands, and 10-hydroxybenzo [h] quinoline--metal complex expressed by Chemical Formula 121 and Chemical Formula 122. ##STR19## 
     The organic film layer may be made of a mixture of an organic luminous material and an organic hole-transport material. 
     The organic luminous material may be the metal complex polymer. 
     The metal complex polymer may be a compound expressed by Chemical Formula 123 and Chemical Formula 124. ##STR20## 
     The organic hole-transport material may be a compound expressed by Chemical Formula 125. ##STR21## 
     The organic film layer may consist of an organic luminous layer and an organic hole-transport layer. 
     The organic luminous layer may be made of one of the metal complex polymer, the inner complex salt having 2 or more ligands, and the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may be made of the metal complex polymer. 
     The organic luminous layer may be made of the inner complex salt having 2 or more ligands. 
     The inner complex salt composing the organic luminous layer may be a compound expressed by Chemical Formula 126. ##STR22## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 127. ##STR23## 
     The organic luminous layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The 10-hydroxybenzo [h] quinoline--metal complex composing the luminous layer may be a compound expressed by Chemical Formula 128. ##STR24## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 129. ##STR25## 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the dopant. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the base material. 
     The 10-hydroxybenzo [h] quinoline--metal complex serving as the base material may be a compound expressed by Chemical Formula 130. ##STR26## 
     Phtaloperinone expressed by Chemical Formula 131 may serve as the dopant. ##STR27## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 132. ##STR28## 
     The organic film layer may consist of an organic luminous layer and an organic electron-transport layer. 
     The organic luminous layer may be made of one of the metal complex polymer, the inner complex metal having 2 or more ligands, and the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may be made of the metal complex polymer. 
     The organic luminous layer may be made of the inner complex salt having 2 or more ligands. 
     The organic electron-transport layer may be made of any inner complex salt. 
     The organic luminous layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the dopant. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the base material. 
     The organic electron-transport layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic film layer may consist of an organic luminous layer, an organic electron-transport layer, and an organic hole-transport layer. 
     The organic luminous layer may be made of one of the metal complex polymer, the inner complex salt having 2 or more ligands, and the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may be made of the metal complex polymer. 
     The organic luminous layer may be made of the inner complex salt having 2 or more ligands. 
     The inner complex salt composing the organic luminous layer may be a compound expressed by Chemical Formula 133. ##STR29## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 134. ##STR30## 
     The organic electron-transport layer may be made of a compound expressed by Chemical Formula 135. ##STR31## 
     The organic electron-transport may be made of the inner complex salt. 
     The inner complex salt may be a compound expressed by Chemical Formula 136. ##STR32## 
     The inner complex salt may be a compound expressed by Chemical Formula 137. ##STR33## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 138. ##STR34## 
     The organic luminous layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the dopant. 
     The organic luminous layer may consist of a dopant and a base material, and the 10-hydroxybenzo [h] quinoline--metal complex may serve as the base material. 
     The organic electron-transport layer may be made of the 10-hydroxybenzo [h] quinoline--metal complex. 
     The 10-hydroxybenzo [h] quinoline--metal complex composing the organic luminous layer may be a compound expressed by Chemical Formula 139. ##STR35## 
     The organic hole-transport layer may be made of a diamine derivative. 
     The diamine derivative may be a compound expressed by Chemical Formula 140. ##STR36## 
     The organic luminous layer may be made of phtaloperinone expressed by chemical Formula 141. ##STR37## 
     The a central metal of the 10-hydroxybenzo [h] quinoline --metal complex may be selected from a group consisting of metals belonging to the second and the third groups of the periodic table. 
     The metal complex polymer retains a large molecular weight and does not easily crystalize. Therefore, the film made of the metal complex polymer as the luminous material does not easily deposit crystalline. As a result, improved film forming properties, particularly in stability, are obtained and hence the durability of the organic EL element is enhanced. 
     Likewise, the inner complex salt having two or more ligands does not easily crystalize; moreover, it luminesces at the solid state. Therefore, the film made of the inner complex salt used as the luminous material does not easily deposit crystalline, and thus enhancing the durability of the organic EL elements as well. 
     In addition, when the electron-transport layer is also made of any inner complex salt, the electron-transport layer and luminous layer have similar molecular structures. Therefore, the surfaces of these two layers fit smoothly, which contributes to enhancing luminous characteristics. 
     Also, given that 10-hydroxybenzo [h] quinoline-metal complex luminesces at the solid state and retains an excellent fluorescence yield, the 10-hydroxybenzo [h] quinoline-metal makes an ideal luminous layer that luminesces efficiently. Further, given that 10-hydroxybenzo [h] quinoline-metal complex retains excellent electron-transport properties, it can be used for the electron-transport layer and the basic material for the luminous layer. The resulting organic El element exhibits high luminance as well. 
     As has been stated, when the luminous layer luminesces efficiently, retaining a high luminance at a lower voltage and a lower current density, physical load is decreased, which enhances the durability of the resulting organic EL element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjugation with the accompanying drawings which illustrate specific embodiments of the invention. In the drawings: 
     FIG. 1 is a sectional view of an organic EL element in accordance with the first embodiment of the present invention; 
     FIGS. 2A through 2G are views showing a variety of structures of a metal complex polymer; 
     FIG. 3 is a sectional view of an organic EL element in accordance with EXAMPLE 1 of the second embodiment of the present invention; and 
     FIG. 4 is a sectional view of an organic EL element in accordance EXAMPLES 1, 2 with the third embodiment of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIRST EMBODIMENT 
     A metal complex polymer, which retains a large molecular weight and hence does not easily crystalize, is used as a luminous material in the first embodiment. 
     EXAMPLE 1 
     FIG. 1 is a sectional view of an organic EL element in accordance with the first embodiment. On a glass substrate 1, a hole-injecting electrode 2 (1000 Å in thickness) is placed, on top of which an organic luminous layer 3 (1000 Å) and further an electron-injecting electrode 4 (2000 Å) are placed. 
     The hole-injecting electrode 2 is made of ITO(an oxide of In and Sn). The organic luminous layer 3 is made of a mixture of a luminous material and a material transporting holes; the mixture contains thirty per cent hole-transport material by weight. The luminous material is a metal complex polymer, PSPy-sal-leu-Zn, expressed by Chemical Formula 1 below, while the hole-transport material is a diamine derivative(TPD) expressed by Chemical Formula 2 below. The electron-injecting electrode 4 is made of an Mg-In alloy in the ratio of 10 : 1. ##STR38## 
     Firstly, the explanation of a process for producing the luminous material, PPSy-sal-leu-Zn emitting strong blue light, will be given. 
     To begin with, 2 g of PSPy was dissolved in 100 ml of methanol. Then, 1 mmol of DL leucine(α-amino acid) was added to this reaction system and dissolved with slight heat. Further, 1 mmol of salicylaldehyde was added, and the reaction system was vigorously stirred. Subsequently, 30 ml of methanol solution containing 1 mmol of zinc acetate was added, and the reaction system was stirred for 2 hours at room temperature. As a result, the metal complex polymer, PPSy-sal-leu-Zn, appeared. 
     Secondly, the explanation of a process for producing the organic EL element of the first embodiment will be given. 
     A film of ITO, which serves as the hole-injecting electrode 2, was formed on the glass substrate 1, thence washed with a neutral detergent and rinsed with water, and further dipped in acetone and ethanol, each for 20 minutes, for ultrasonic rinse. Then, the substrate 1 with the hole-injecting electrode 2 was dipped in boiling ethanol for 1 minute and immediately dried with air blow. Methanol solution containing both PSPy-sal-leu-Zn of the luminous material and TPD(30 wt %) of the hole-transport material was dropped onto the hole-injecting electrode 2 to form an even film thereon by the spin-coating technique; the film thus formed serves as the organic luminous layer 3. When the film was dried completely, the electron-injecting electrode 4 of Mg-In alloy was formed by vacuum evaporation coating on top of the organic luminous layer 3. The conditions for the vacuum evaporation coating were: the degree of vacuum at 1×10 6  Torr, the temperature of the glass substrate 1 at 20° C., and the evaporation coating speed at 3 Å/sec. 
     The organic EL element produced in this way is referred to as (a 1 ) element hereinafter. 
     EXAMPLE 2 
     An organic EL element was produced in the same way as EXAMPLE 1 except that PSPy-sal-phgly-Zn expressed by Chemical Formula 3 was used instead of PSPy-sal-leu-Zn as the luminous material. ##STR39## 
     PSPy-sal-phgly-Zn was produced in the same way as PSPy-sal-leu-Zn except that phenylglycine was used as the α-amino acid instead of DL leucine. 
     The organic EL element produced in this way is referred to as (a 2 ) element. 
     To evaluate the characteristics of (a 1 ) and (a 2 ) elements, following two experiments were carried out. 
     EXPERIMENT 1 
     The luminous characteristics of (a 1 ) and (a 2 ) elements were evaluated, and the result is set forth in Table 1 below with the required voltage and current density. 
     
                                           TABLE 1                                 
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                             PEAK                                         
              CURRENT        WAVE                                         
       VOLTAGE                                                            
              DENSITY                                                     
                     LUMINANCE                                            
                             LENGTH                                       
                                   LUMINOUS                               
ELEMENT                                                                   
       (V)    (V/cm.sup.2)                                                
                     (cd/m.sup.2)                                         
                             (nm)  COLOR                                  
__________________________________________________________________________
a.sub.1                                                                   
       20     100    100     455   BLUE                                   
a.sub.2                                                                   
       20     120    80      150   BLUE                                   
__________________________________________________________________________
 
    
     EXPERIMENT 2 
     Further, the film stability of (a 1 ) and (a 2 ) elements was evaluated. The stability was evaluated by examining the luminance of both the elements which have been allowed to stand in dry air for a certain period. It has been confirmed that both (a 1 ) and (a 2 ) elements still emit satisfactory blue light up to 2 weeks. In comparison, a conventional organic EL element, for example, the one made of 1,1,4,4-tetraphenyl-1,3-butadiene, emits satisfactory blue light only for one day. This means that the metal complex polymer used as the luminous material retains excellent film forming properties, and thus improving durability of the organic EL element. 
     OTHER COMMENTS 
     FIG. 2A shows the metal complex polymer of a pendant structure used in the first embodiment; however, the metal complex polymer can be of any structure shown in FIGS. 2B through 2G; the resulting organic EL element obtains the same effects. [For further information, see &#34;Metal Complex Polymer&#34;, Takeo Saegusa et al, Kagaku-Dojin-Sha] 
     The organic hole-transport layer is not formed in this embodiment, but the organic luminous layer 3 includes the hole-transport material instead. The organic electron-transport layer and/or hole-transport layer, however, may be additionally formed between the electrodes, forming the organic EL element of the SH-A, SH-B, or DH structure. 
     SECOND EMBODIMENT 
     An inner complex salt having two or more ligands, which does not easily crystalize and luminesces at the solid state, is used as the luminous material in the second embodiment. 
     EXAMPLE 1 
     FIG. 3 is a sectional view of an organic EL element of the SH-A structure in accordance with EXAMPLE 1. On a glass substrate 1, a hole-injecting electrode 2 (1000 Å) is placed, on top of which an organic hole-transport layer 3 (500 Å), an organic luminous layer 4 (500 Å), and further an electron-injecting electrode 4 (2000 Å) are placed. 
     The hole-injecting electrode 2 is made of ITO, and the organic hole-transporting layer 3 is made of TPD expressed by Chemical Formula 4 below. The organic luminous layer 4 is made of an inner complex salt, azomethine-picoline-zinc, expressed as Chemical Formula 5, and the electron-injecting electrode 5 is made of an Mg-In alloy in the ratio of 10 : 1. ##STR40## 
     Firstly, the explanation of a process for producing the luminous material, azomethine-picoline-zinc, will be given. 
     To begin with, 15.25 mmol of DL leucine was dissolved in 20 ml of methanol with slight heat, and 15.25 mol of salicylaldehyde and 3 ml of picoline were added to this reaction system. Then the solution becomes turbid in yellow. Further, 30 ml of methanol solution containing 15.25 mmol of zinc acetate was added, and the reaction system was refluxed for 2 hours. As a result, the inner complex salt, azomethine-picoline-zinc emitting strong blue light, appeared. Since this inner complex salt was solvable to methanol, water was added to precipitate the inner complex salt, which was purified by sublimation. 
     Zinc, a central metal in the inner complex salt, has a cation with a valence of 2 and a coordination number of 4. Whereas one of the ligands, azomethine, has an anion with a valence of 2 and a donor number of 3; the other ligand, picoline, is neutral and has a donor number of 1. This structure renders the coordination number and charges of the metal complex neutral, composing the inner complex salt. Given that the inner complex salt has a low polarity and emits light in the solid state as well as being applicable to sublimation, it can be an material for the organic EL element. 
     Secondly, the explanation of a process for producing the organic EL element of EXAMPLE 1 of the second embodiment will be given. 
     A film of ITO, which serves as the hole-injecting electrode 2, was formed on the glass substrate 1, thence washed with a neutral detergent and rinsed with water, and further dipped in acetone and ethanol, each for 20 minutes for ultrasonic rinse. Then, the substrate 1 with the hole-injecting electrode 2 was dipped in boiling ethanol for 1 minute and immediately dried with air blow. Then, a film of TPD, which serves as the organic hole-transport layer 3, was formed on the hole-injecting electrode 2 by vacuum evaporation coating. Further, a film of azomethine-picoline-zinc was formed on the organic hole-transport layer 3 by the vacuum evaporation coating; the film thus formed serves as the organic luminous layer 4. Further, the electron-injecting electrode 5 made of the Mg-In alloy was formed on the organic luminous layer 4. The conditions for each vacuum evaporation coating were: the degree of vacuum at 1×10 6  Torr, the temperature of the glass substrate 1 at 20° C., and the evaporation coating speed at 2 Å/sec. 
     The organic EL element produced in this way is referred to as (b 1 ) hereinafter. 
     EXAMPLE 2 
     An organic EL element was produced in the same way as EXAMPLE 1 of the second embodiment except for the following: 
     1) the organic hole-transport layer, and organic luminous layer were of 500 Å and 100 Å in thickness, respectively, and the organic electron-transport layer of 400 Å was additionally formed by the vacuum evaporation coating. 
     2) Eu(TTA) 3  (phen) expressed by Chemical Formula 6 below, (TTA represents 2-thenoyltrifluoroacetone, and phen represents 1, 10-phenanthroline), was used as the luminous material. 
     3) OXD-7 expressed by Chemical Formula 7 below was used as the electron-transport material. ##STR41## 
     Eu(TTA) 3  (phen) used as the luminous material is produced in the following way: 
     To begin with, 9 mmol of TTA and 3 mmol of phen were dissolved in 20 ml of ethanol at room temperature. Further, 3 ml of 1-N NaOH solution was added and this reaction system was heated at 60° C. At the same time, 3 mmol of EuCl 3 .6H 2  O was dissolved in 10 ml of water, and the solution was dropped into the reaction system by an open system. Subsequently, the reaction system was stirred for 1 hour at 60° C. As a result, precipitates appeared. The precipitates produced in this way were filtered off by suction and purified by sublimation to produce the inner complex salt. 
     Europium, the central metal in this metal complex, has a cation with a valence of 3 and a coordination number of 8. Whereas one of the ligands, TTA, has an anion with a valance of 1 and a donor number of 2, and the other ligand, phen, is neutral with a donor number of 2. This structure renders the coordination number and charges of the metal complex neutral, composing the inner complex salt. 
     The organic EL element produced in this way is referred to as (b 2 ) hereinafter. 
     EXAMPLE 3 
     An organic EL element of the DH structure was produced in the same way as EXAMPLE 2 of the second embodiment except that the organic luminous layer is made of the inner complex salt, azomethine-picoline-zinc expressed by Chemical Formula 5, and the organic electron-transport layer is made of tBU-PBD expressed by Chemical Formula 8. ##STR42## 
     The organic EL element produced in this way is referred to as (b 3 ) hereinafter. 
     EXAMPLE 4 
     An organic EL element of the DH structure was produced in the same way as EXAMPLE 3 of the second embodiment except that the organic electron-transport layer is made of an inner complex salt, azomethine-pyridine-zinc, expressed by Chemical Formula 9. ##STR43## 
     The organic EL element produced in this way is referred to as (b 4 ) element. 
     To evaluate the characteristics of (b 1 ) through (b 4 ) elements, the following two experiments were carried out. 
     EXPERIMENT 1 
     The luminous characteristic of (b 1 ) through (b 4 ) elements were evaluated, and the result is set forth in Table 2 with the required voltage and current density. 
     
                                           TABLE 2                                 
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                             PEAK                                         
              CURRENT        WAVE                                         
       VOLTAGE                                                            
              DENSITY                                                     
                     LUMINANCE                                            
                             LENGTH                                       
                                   LUMINOUS                               
ELEMENT                                                                   
       (V)    (V/cm.sup.2)                                                
                     (cd/m.sup.2)                                         
                             (nm)  COLOR                                  
__________________________________________________________________________
b.sub.1                                                                   
       18     150    800     450   BLUE                                   
b.sub.2                                                                   
       20     200    20      640   RED                                    
b.sub.3                                                                   
       20     180    600     453   BLUE                                   
b.sub.4                                                                   
       20     130    900     450   BLUE                                   
__________________________________________________________________________
 
    
     Of all the elements, the luminance comparison between (b 3 ) and (b 4 ) is noteworthy: although both use the same inner complex salt in the organic luminous layer, (b 4 ) elements exhibits a higher luminance at a lower current density than (b 3 ) element. This is because that the organic luminous layer and organic electron-transport layer are made of similar inner salt complexes in (b 4 ) element, retaining substantially the same molecular structure in both the layers. Thus, the surface of the two layers fit more smoothly than they do in (b 3 ) element, which contributes to obtaining higher luminance characteristics. 
     EXPERIMENT 2 
     The film stability of (b 1 ) through (b 4 ) elements was evaluated. The stability was evaluated by examining the luminous of each element which have been allowed to stand in dry air for a certain period. It has been confirmed that (b 1 ) element emit satisfactory light up to 5 days; (b 2 ) element 3 days; (b 3 ) element 2 days. Whereas (b 4 ) element emit satisfactory blue light up to 2 weeks. This is because that (b 4 ) element uses inner complex salt both in the organic luminous and electron-transport layers, which prevents crystalline precipitation more effectively than the other elements using the inner complex salt only in the organic luminous layer. Accordingly, (b 4 ) element emits satisfactory light for a longer period than the other elements. 
     The experiment shows that the inner complex salt used as the luminous material exhibits excellent film forming properties, and thus improving the durability of the organic EL element. 
     OTHER COMMENTS 
     It should be noted that the kinds of ligands and the number of the ligands of inner complex salt are not limited to a range specified in this embodiment. Also, the organic EL element of this embodiment can be formed in the SH-B structure besides the SH-A structure and DH structure. 
     THIRD EMBODIMENT 
     10-hydroxybenzo [h] quinoline-metal complex, which luminesces at the solid state and retains an excellent fluorescence yield, is used as the luminous material in the third embodiment. 
     EXAMPLE 1 
     FIG. 4 is a sectional view of an organic EL element of the SH-A structure in accordance with EXAMPLES 1, 2 of the third embodiment. On a glass substrate 1, a hole-injecting electrode 2 (1000 Å) is placed, on top of which an organic hole-transport layer 3 (500 Å), an organic luminous layer 4 (500 Å), and further an electron-injecting electrode 5 (2000 Å) are placed. 
     The hole-injecting electrode 2 is made of ITO, and the organic hole-transport layer 3 is made of TPD expressed by Chemical Formula 10 below. The organic luminous layer 4 is made of 10-hydroxybenzo [h] quinoline-beryllium complex(Bebq 2 ) expressed by Chemical Formula 11 below, and the electron-injecting electrode 5 is made of an Mg-In alloy in the ratio of 10 : 1. ##STR44## 
     Firstly, the explanation of a process for producing the luminous material of EXAMPLE 1 of the third embodiment will be given. 
     To begin with, 1.53 g(7.84 mmol) of 10-hydroxybenzo [h] quinoline was dissolved in 40 ml of mixed solution of methanol and ethanol in a flask with heat to produce alcoholic quinoline solution; the ratio of methanol to ethanol was 1 : 1. Then, 0.69 g(3.92 mmol) of BeSo 4 .4H 2  O was dissolved in 100 ml of pure water in another flask to produce beryllium solution. Beryllium solution was gradually added to alcoholic quinoline solution while being stirred, then a substance emitting strong blue-green light appeared. To fully precipitate the substance, the pH of the solution was adjusted to mild alkaline from neutral by adding 1N NaOH solution. The precipitates were filtered off by suction and dried for 2 hours at 80° C. with heat, and sublimated by the train sublimation technique using a sublimation-purification unit. [For further information, see the paper of H. J. Wagner, R. O. Loutfy, C. K. Hsiao, J. Mater, Sci., 17, 2781(1982)] It is confirmed that the crystallites of the luminous material thus produced emit strong blue-green light having a peak wave length of 510 nm. 
     The organic EL element was produced in the same way as EXAMPLE 1 of the second embodiment except that Bebq 2  was used instead of azomethine-picoline-zinc. 
     The organic EL element produced in this way is referred to as (c 1 ) element hereinafter. 
     To make the improvement of the present invention obvious, a comparative example is produced. 
     COMPARATIVE EXAMPLE 1 
     An organic EL element of the SH-A structure was produced in the same way as the EXAMPLE 1 of the third embodiment except that 8-hydroxyquinoline-alminium complex(Alq 3 ) expressed by Chemical Formula 12 below was used instead of Bebq 2 . ##STR45## 
     The organic EL element produced in this way is referred to as (x 1 ) element hereinafter. 
     To evaluate the characteristics of (c 1 ) and (x 1 ) element, the following experiment was carried out. 
     EXPERIMENT 1 
     The luminous characteristics of (c 1 ) and (x 1 ) elements were evaluated, and the result is set forth in Table 3 with the required voltage and current density. 
     
                                           TABLE 3                                 
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                             PEAK                                         
              CURRENT        WAVE                                         
       VOLTAGE                                                            
              DENSITY                                                     
                     LUMINANCE                                            
                             LENGTH                                       
                                   LUMINOUS                               
ELEMENT                                                                   
       (V)    (V/cm.sup.2)                                                
                     (cd/m.sup.2)                                         
                             (nm)  COLOR                                  
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c.sub.1                                                                   
       19     595    18620   516   GREEN                                  
x.sub.1                                                                   
       20     600    14000   525   GREEN                                  
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     Table 3 shows that (c 1 ) element exhibits an excellent luminance at a lower voltage, proving itself to be highly efficient compared with (x 1 ) element. 
     The maximum luminance of (x 1 ) element, 14000 cd/cm 2 , is also excellent compared with a typical organic EL element; however, (c 1 ) exhibits a far more better value, 18620 cd/cm 2 . 
     EXAMPLE 2 
     An organic EL element was produced in the same way as EXAMPLE 1 of the third embodiment except that the organic luminous layer 4 additionally contains phtaloperinone which is an orange fluorescent pigment expressed as Chemical Formula 13. The ratio of Bebq 2  to phtaloperinone was 100 : 2. ##STR46## 
     The organic EL element produced in this way is referred to as (c 2 ) element. 
     Also, to make the improvement of the present invention obvious, a comparative example was produced. 
     COMPARATIVE EXAMPLE 2 
     An organic EL element was produced in the same way as EXAMPLE 2 of the third embodiment except that Alq 3  was used instead of Bebq 2 . 
     The organic EL element produced in this way is referred to as (x 2 ) hereinafter. 
     To evaluate the characteristics of (c 2 ) and (x 2 ) elements, the following experiment was carried out. 
     EXPERIMENT 2 
     The luminous characteristics of (c 2 ) and (x 2 ) elements were evaluated, and the result is set forth in Table 4 with the required voltage and current density. 
     
                                           TABLE 4                                 
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                             PEAK                                         
              CURRENT        WAVE                                         
       VOLTAGE                                                            
              DENSITY                                                     
                     LUMINANCE                                            
                             LENGTH                                       
                                   LUMINOUS                               
ELEMENT                                                                   
       (V)    (V/cm.sup.2)                                                
                     (cd/m.sup.2)                                         
                             (nm)  COLOR                                  
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c.sub.2                                                                   
       20     200    2500    590   ORANGE                                 
x.sub.2                                                                   
       21     220    1700    590   ORANGE                                 
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     Table 4 shows that (c 2 ) element does not emit green light which is inherent to Bebq 2 , but orange light inherent to phtaloperinone instead. This means that Bebq 2  serves as a base material while phtaloperinone serves as a dopant in the organic luminous layer 4. 
     Table 4 also shows that (c 2 ) element exhibits a higher luminance at a lower voltage and a lower current density than (x 2 ) element. Thus, using Bebq 2  as the base material in the organic luminous layer enables an organic EL element with high luminance and efficiency. 
     EXAMPLE 3 
     An organic EL element of DH-structure was produced. On a glass substrate, an organic hole-transport layer (500 Å) is placed, on top of which an organic luminous layer (100 Å), an organic electron-transport layer (400 Å), and an electron-injecting electrode are placed one on another. 
     An organic EL element was produced in the same way as EXAMPLE 1 of the third embodiment except that a film of Bebq 2  was additionally formed on the organic luminous layer by the vacuum evaporation coating; the film thus formed serves as the organic electron-transport. 
     The organic EL element produced in this way is referred to as (c 3 ) element. 
     To make the improvement of the present invention obvious, a comparative example was produced. 
     COMPARATIVE EXAMPLE 3 
     An organic EL element was produced in the same way as EXAMPLE 3 of the third embodiment except that the organic electron-transport layer was made of 8-hydroxyquinoline-magnesium complex (Mgq 2 ) expressed by Chemical Formula 14. ##STR47## 
     The organic EL element produced in this way is referred to as (x 3 ) hereinafter. 
     To evaluate the characteristics of (c 3 ) and (x 3 ) elements, the following experiment was carried out. 
     EXPERIMENT 3 
     The luminous characteristics of (c 3 ) and (x 3 ) elements were evaluated, and the result is set forth in Table 5 with the required voltage and current density. 
     
                                           TABLE 5                                 
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                             PEAK                                         
              CURRENT        WAVE                                         
       VOLTAGE                                                            
              DENSITY                                                     
                     LUMINANCE                                            
                             LENGTH                                       
                                   LUMINOUS                               
ELEMENT                                                                   
       (V)    (V/cm.sup.2)                                                
                     (cd/m.sup.2)                                         
                             (nm)  COLOR                                  
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c.sub.3                                                                   
       19     190    1000    590   ORANGE                                 
x.sub.3                                                                   
       22     210    700     590   ORANGE                                 
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     Table 5 shows that (c 3 ) element emits light more efficiently than (x 3 ) element. 
     As has been explained, by making the organic luminous layer with 10-hydroxybenzo [h] quinoline-metal complex, the organic EL element efficiently emits light, and when it does so, the physical load can be decreased, increasing the durability. 
     OTHER COMMENTS 
     It should be noted that 10-hydroxybenzo [h] quinoline--metal complex can be used as the dopant in the organic luminous layer as well. 
     In addition, beryllium is used as a central metal for 10-hydroxybenzo [h] quinoline-metal complex in this embodiment. However, beryllium can be replaced with any metal belonging to the second and third groups of the periodic table. 
     In this embodiment, the ratio of ligand to metal was 2 : 1 in 10-hydroxybenzo [h] quinoline-metal complex. However, the ratio may be 3 : 1 instead. 
     The detailed explanation is omitted; however, the organic luminous layer can be made of 10-hydroxybenzo [h] quinoline-metal complex in the SH-B structure and DH structure besides the SH-A structure. Likewise, the organic electron-transport layer can be made of 10-hydroxybenzo [h] quinoline-metal complex in the SH-B structure besides the DH structure. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted that various changes and modification will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.