JP4032486B2 - EL element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EL (Electroluminescence) element used for, for example, a self-luminous segment display or matrix display of instruments, or a display of various information terminal devices, and more particularly to an EL element that emits blue light. .
[0002]
[Prior art]
Conventionally, as EL elements that emit blue light, for example, there are those described in the 1993 International Conference on Display Information Technology Digest p761-764. This is because an alkaline earth metal thiogallate (MGa) which is a group 2-13 group-16 compound semiconductor of the periodic table is formed on a substrate. ₂ S _Four , M = Ga, Sr, Ba), and an EL element formed by sandwiching a light emitting layer to which cerium (Ce) is added as a light emitting central element between a pair of upper and lower electrodes.
[0003]
[Problems to be solved by the invention]
However, with the conventional EL element, an EL element that emits blue light can be obtained, but there is a problem that sufficient blue light emission luminance cannot be obtained.
As shown in Japanese Patent Laid-Open No. 8-162273, Sr ₂ Ga ₂ S _Five : Although there is a description that high luminance can be achieved by using a light emitting layer in which a plurality of Ce thin films and ZnS thin films are laminated, according to the study by the present inventors, for the realization of good full color, etc. However, the light emission luminance is still insufficient, and higher luminance is desired.
[0004]
In view of the above problems, an object of the present invention is to increase the luminance of blue light emission in an EL element in which a light emitting layer is sandwiched between a pair of electrodes on a substrate.
[0005]
[Means for Solving the Problems]
The present inventors use an alkaline earth metal thiogallate that emits blue light as a base material in an EL element in which a light emitting layer is sandwiched between a pair of electrodes on a substrate, and a plurality of layers for high brightness. The luminescent layer formed by laminating was studied earnestly. As a result, this light emitting layer has a different element present, and when the voltage is applied, this different element moves, generating holes (holes) in the light emitting layer and promoting the movement of charges. I thought that the brightness would be improved. Book The invention has been made based on this finding.
[0006]
That is, Book In the present invention, the light emitting layer (14) is composed of a first layer (141, 143) that contributes to light emission using an alkaline earth metal thiogallate as a base material, and a base material different from the first layer (141, 143). A plurality of second layers (142, 144) are stacked, and an element serving as a light emission center is added to at least one of the first layers (141, 143). The layer (141, 143) includes at least one element constituting the second layer (142, 144).
[0007]
Accordingly, at least one element (addition element) constituting the second layer (142, 144) added to a part or the whole of the first layer (141, 143), that is, the first layer ( 141, 143) The additive element as a different element with respect to the constituent elements 141, 143) promotes the movement of electric charges, so that high luminance of blue light emission can be realized.
[0008]
In the first aspect of the invention, the thickness d1 of the first layer (141, 143) located on the substrate (11) side and the first layer (141, 141) located on the far side from the substrate (11). The thickness ratio d2 / d1 with respect to the thickness d2 of 143) is 3 or more and 12 or less. Claims 2, 4 In the described invention, as the alkaline earth metal thiogallate, the chemical formula MGaαSβ (where M is an element selected from Group 2 of the periodic table, 1.5 <α <2.0, 3.0 <β < 4.0). As a result, good blue light emission luminance can be realized. Here, examples of Group 2 elements of the periodic table include Be, Mg, Ca, Sr, Ba, and Ra. Note that MGaαSβ is preferably CaGaαSβ and SrGaαSβ or a complex thereof. Note that the additive elements are mixed by performing heat treatment after forming the first layer (141, 143) and the second layer (142, 144) by the MOCVD (Metal Organic Chemical Vapor Deposition) method or the like, When the first layer (141, 143) is diffused from the second layer (142, 144) or the first layer (141, 143) is formed, a material previously mixed in the raw material is used. It can be performed using a technique such as film formation.
[0009]
In addition, since the above method is used in mixing the additive element, due to manufacturing variations, etc. 3 As in the described invention, the additive element has a concentration distribution in the first layer (141, 143). Claims 4 In the described invention, the concentration of the additive element is higher in the vicinity of the interface with the adjacent second layer (142, 144) than in the center in the thickness direction of the first layer (141, 143). It is characterized by high distribution. This configuration can be realized by the diffusion method using the heat treatment.
[0010]
In other words, the present invention is arranged between the first layer (141, 143) and the second layer (142, 144), between the first layer (141, 143) and the second layer (142, 144). The third layer in which elements constituting the element are mixed is in a pseudo form. As a result, the amount of mobile charge in the EL element is remarkably increased, and high luminance can be obtained even with the same luminous efficiency.
[0015]
Claims 5 And claims 6 As described in the invention, a transition metal sulfide such as ZnS (zinc sulfide) can be used as the base material of the second layer (142, 144). Claims 7 As described in the invention, one or more elements selected from rare earth elements can be used as the element serving as the emission center.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below.
(First embodiment)
FIG. 1 is a schematic diagram showing a cross-sectional configuration of a thin film EL (electroluminescence) element (hereinafter referred to as an EL element) 100 according to the first embodiment. The EL element 100 is used for, for example, a self-luminous segment display or matrix display of instruments, or a display of various information terminal devices.
[0017]
The EL element 100 is configured by sequentially laminating the following thin films on a transparent glass substrate (substrate) 11 that is an insulating substrate.
A first transparent electrode (first electrode) 12 made of optically transparent tin-added indium oxide (ITO) is formed on the glass substrate 11, and an optically transparent silicon oxynitride (SiON) is formed on the upper surface thereof. ), A light emitting layer 14 made of calcium thiogallate with cerium added as the emission center, optically transparent silicon oxynitride (SiON) and tantalum pentoxide (Ta). ₂ O _Five ) And a second transparent electrode (second electrode) 16 made of optically transparent zinc oxide.
[0018]
Here, the EL element 100 can extract light from both the thin film forming surface of the glass substrate 11 and the opposite surface. One of the electrodes may be a metal electrode, and light may be extracted from the other transparent electrode side.
Note that the first and second transparent electrodes 12 and 16 are striped electrodes, and both form a matrix electrode orthogonal to each other. Therefore, the first and second transparent electrodes 12 and 16 are configured as a pair of electrodes on the glass substrate 11 with the light emitting layer 14 interposed between the both insulating layers 13 and 15.
[0019]
The light emitting layer 14 is an alkaline earth metal thiogallate MGaαSβ having a predetermined composition range (where M is an element selected from Group 2 of the periodic table, and 1.5 <α <2.0, 3.0 <β A plurality of first layers 141 and 143 that contribute to light emission having a base material of <4.0) and second layers 142 and 144 made of a base material different from the first layers 141 and 143 It is configured by stacking.
[0020]
Specifically, from the first insulating layer 13 toward the second insulating layer 15, a first layer (first light emitting layer) 141, a second layer 142, a first layer (second light emitting layer) 143, The second layer 144 is sequentially stacked.
Here, the predetermined composition range of the alkaline earth metal thiogallate MGaαSβ is obtained, for example, as shown in FIG. In FIG. 2, Ca is used as M, the Ca / Ga composition ratio (that is, α) is shown on the horizontal axis, and the blue light emission luminance (arbitrary unit) is shown on the vertical axis.
[0021]
Good blue light emission luminance is exhibited when the Ca / Ga composition ratio is greater than 1.5 and less than 2.0. The composition ratio β of S can be calculated from the stoichiometric ratio if α is determined, and 3.0 <β <4.0 is preferable. Similar results were obtained when M was another group 2 element (alkaline earth metal element) of the periodic table such as Sr.
In this example, calcium thiogallate CaGa1.8 S3.7 (that is, M = Ca, α = 1.8, β = 3.7) as the base material of the first layers 141 and 143, and the second layer ZnS (zinc sulfide), which is a sulfide of transition metal, is used as the base material of 142,144.
[0022]
In addition, an element which is a rare earth element and serves as a light emission center (Ce (cerium) in this example) is added to both the first layers 141 and 143. Here, it is preferable that an element serving as a light emission center is added to the first layer 143 located farther than the glass substrate 11.
In addition, Zn (zinc) which is an element constituting the second layers 142 and 144 is added to both the first layers 141 and 143. This added zinc is considered to move by itself when a voltage is applied in the first layers 141 and 143 to generate holes or the like, thereby promoting the movement of charges and contributing to the improvement of luminance.
[0023]
As shown in FIG. 3 to be described later, the concentration of the additive is higher in the vicinity of the interface with the adjacent second layers 142 and 144 than in the center in the thickness direction of the first layers 141 and 143. It is distributed to become. As a result, charge transfer in the vicinity of the interface is promoted, so that good emission efficiency and high emission luminance can be obtained, and since there is little Zn as a different element in the center, the first layer contributing to light emission Good crystallinity is maintained.
[0024]
Thus, in this example, the light-emitting layer 14 is composed of calcium thiogallate having calcium thiogallate CaGa1.8 S3.7 as a base material and cerium added as a light emission center: first layers 141 and 143 as cerium light-emitting layers; The second layers 142 and 144 are zinc sulfide thin films, and zinc is added to the first layers 141 and 143.
[0025]
Next, a method for manufacturing the EL element 100 will be described.
First, the first transparent electrode 12 is formed on the glass substrate 11 by sputtering. Specifically, the temperature of the glass substrate 11 was kept constant, and a film was formed using a mixed gas of argon and oxygen by applying high-frequency power (first electrode forming step).
Next, a first insulating layer 13 made of silicon oxynitride is formed on the first transparent electrode 12 by sputtering. Specifically, the temperature of the glass substrate 11 was kept constant, and film formation was performed at a high frequency power of 1 kW in a mixed gas of argon, enzyme, and nitrogen (first insulating layer forming step).
[0026]
Subsequently, the light emitting layer 14 is formed on the first insulating layer 13 in the above-described stacking order by metal organic chemical vapor deposition (MOCVD) (light emitting layer forming step). The formation method will be specifically described below.
First, a glass substrate 11 for film formation is set in a reaction furnace, and 1 × 10 6 using a turbo molecular pump or the like. ^-6 A vacuum was drawn so as to be equal to or lower than Torr. Next, the glass substrate 11 was maintained at a constant temperature of 550 ° C., and the inside of the reaction furnace was adjusted with an automatic pressure control device so as to have a reduced pressure atmosphere of 50 Torr.
[0027]
The calcium raw material has a sublimation or vaporization temperature lower than that of chloride or fluoride, and is easy to control the temperature, so that bisdipivaloyl methanated calcium (Ca (C ₁₁ H ₁₉ O ₂ ) ₂ ) Was used. And the raw material container filled with this raw material was hold | maintained at the fixed temperature with the precision within 230 +/- 1 degreeC.
Argon gas was used to transport the gasified calcium bisdipivaloyl methanate to the reactor. Just before the argon gas is introduced into the raw material container filled with the same raw material, the water is sufficiently removed by a dehydration filter, and the bisdipivaloyl methanated calcium is removed from the reactor with the argon gas from which water has been removed. Introduced.
[0028]
For gallium (Ga), a Group 13 element of the periodic table, triethylgallium (Ga (C ₂ H _Five ) _Three ) Was kept at 18 ° C., and the obtained raw material gas was introduced into the reactor using an argon carrier gas. As a supply gas for gallium which is a group 13 element material, trimethylgallium (Ga (CH _Three ) _Three ), Tributylgallium (Ga (C _Three H ₇ ) _Three ), Tridipivaloyl gallium methanide (Ga (C ₁₁ H ₁₉ O ₂ ) _Three It is possible to form in the same manner by adjusting the raw material temperature using an organic compound such as
[0029]
Sulfur (S), a group 16 element of the periodic table, is hydrogen sulfide diluted with argon gas (H ₂ S) was used as a raw material gas and introduced into the reactor. As a supply gas of sulfur which is a group 16 element raw material, in addition to hydrogen sulfide, dimethyl sulfur (S (CH _Three ) ₂ ), Diethyl sulfur (S (C ₂ H _Five ) ₂ ) And methyl mercaptan (S (CH _Three ) H), ethyl mercaptan (S (C ₂ H _Five ) H) may be used.
[0030]
Furthermore, in order to add a luminescent center element, tridipypyroyl methanide (Ce (C ₁₁ H ₁₉ O ₂ ) _Three ) Was used. First, tridipivaloyl methanated cerium was filled in a dedicated raw material container, and this raw material container was maintained at a constant temperature of 175 ° C., and the raw material was sublimated and gasified. The gasified tridodipivaloyl methanated cerium was transported with an argon carrier gas and supplied to the reactor.
[0031]
The above raw material gases are introduced into the reactor in the order of hydrogen sulfide, triethylgallium, calcium bisdipivaloylmethanated, and cerium, which is a luminescent center element, and are reacted and pyrolyzed. As a result, a first layer 141 as a calcium thiogallate: cerium light-emitting layer was formed to 90 nm (first light-emitting layer forming step).
[0032]
Next, a second layer 142 which is a zinc sulfide (ZnS) thin film was deposited on the first layer 141 to a thickness of 20 nm. Specifically, as a raw material for zinc (Zn) used for depositing zinc sulfide, diethyl zinc (Zn (C ₂ H _Five ) ₂ This was kept at 17 ° C., and the raw material gas was introduced into the reaction furnace with an argon carrier gas of 50 cc / min.
[0033]
In addition, sulfur (S) raw material is hydrogen sulfide diluted with hydrogen (H ₂ S) Gas was introduced into the reactor at a rate of 50 cc / min. Zinc sulfide was deposited by supplying the raw material gas to the glass substrate 11 heated to 450 ° C. under a 2 Torr reactor pressure (first zinc sulfide thin film forming step).
After the second layer 142 was deposited, a first layer 143 as a calcium thiogallate: cerium light emitting layer was again deposited at 390 nm (second light emitting layer forming step). Since a specific deposition method is the same as that of the first layer 141, a description thereof will be omitted.
[0034]
Further, a 50 nm thick second layer 144, which is a zinc sulfide thin film, was deposited on the first layer 143 (second zinc sulfide thin film forming step). As described above, the specific deposition method is the same as that of zinc sulfide 14-2, and thus will be omitted.
Then, the second insulating layer 15 made of silicon oxynitride is formed on the second layer 144, that is, the light emitting layer 14 (second insulating layer forming step). In this example, the second insulating layer 15 includes two insulating layers 151 and 152. The second insulating layer 15 can be formed by the same method as that for the first insulating layer 13 described above.
[0035]
First, after forming the second insulating layer 151 in the same manner as the first insulating layer 13 described above, the light emitting layer is crystallized, and Zn is diffused from the second layers 142 and 144 to the first layers 141 and 143. Heat treatment is performed (heat treatment step).
Specifically, the glass substrate 11 formed up to the second insulating layer 151 was placed in a heat treatment furnace sufficiently substituted with argon gas. 10 ^-Five A vacuum was drawn until the pressure became equal to or lower than Torr, and hydrogen sulfide gas diluted with argon at a rate of 0.2 cc / min was introduced therein, and the pressure in the heat treatment furnace was changed from 0.01 to 0.05 Torr with a pressure regulator. The range was adjusted.
[0036]
Next, the temperature was raised to 500 ° C. at a rate of 100 ° C./min, and the temperature was further raised to 650 ° C. at a rate of 60 ° C./min to perform heat treatment. Further, after reaching 650 ° C., the temperature was immediately lowered. Thus, zinc is diffused and added to both first layers 141 and 143.
A second insulating layer 152 made of tin-added tantalum oxide is formed on the glass substrate 11 after the heat treatment by a sputtering method. Specifically, the temperature of the glass substrate 11 was kept constant, a mixed gas of argon and oxygen was introduced into the sputtering apparatus, and film formation was performed with a high-frequency power of 1 kW.
[0037]
Finally, a second transparent electrode 16 made of a gallium-doped zinc oxide film is formed on the second insulating layer 15. Specifically, a material obtained by adding and mixing zinc oxide (ZnO) powder with gallium oxide (Ga2O3) as a vapor deposition material and forming into a pellet shape was used, and an ion plating apparatus was used as a film forming apparatus. Then, the inside of the ion plating apparatus was evacuated to a vacuum while keeping the temperature of the glass substrate 11 constant. Thereafter, argon gas was introduced, the pressure was kept constant, and the beam power and high frequency power were adjusted so that the film formation rate was in the range of 6 to 18 nm / min.
[0038]
The thickness of each layer is 200 nm for the first transparent electrode 12, 500 nm for the second transparent electrode, 150 nm for the first insulating layer 13, and 100 nm for silicon oxynitride and 200 nm for tantalum pentoxide among the second insulating layers. The film thickness of the entire light emitting layer is 550 nm. The film thickness of each of the above layers is described with reference to the central portion.
FIG. 3 shows the results obtained by measuring the amounts of calcium, gallium, zinc, and sulfur in the light emitting layer 14 with a secondary ion mass spectrometer (SIMS) for the EL element 100 according to this example. This shows the abundance of calcium, gallium, zinc and sulfur atoms (ions) in the depth direction from the device surface.
[0039]
As can be seen from FIG. 3, zinc is added to the first layers 141 and 143, which are cerium-added calcium thiogallate light-emitting layers, and the added state is adjacent to the center of the first layers 141 and 143. The zinc concentration increases toward the interface with the second layers 142 and 144. Incidentally, zinc was not added to the first layers 141 and 143 unless the heat treatment step for the Zn diffusion was performed.
[0040]
In addition, in the light-emitting layer 14, the composition ratio of calcium, gallium, and sulfur in the first layers 141 and 143 was measured by EPMA (Electron Probe Micro Analysis). The amount was 1.8. The amount of sulfur present with a calcium content of 1 was 3.7. Therefore, it is confirmed that the base material of the first layers 141 and 143 in this example is calcium thiogallate CaGa1.8 S3.7.
Here, an EL element 200 shown in FIG. 4 was produced as a comparative example. The EL element 200 includes a first electrode 2 made of an optically transparent ITO film, a tantalum pentoxide (Ta ₂ O _Five ) And the like, a light emitting layer 4, a second insulating layer 5, and a second electrode 6 made of an ITO film are sequentially laminated. The light emitting layer 4 is obtained by forming zinc sulfide films 41 and 43 on and under a calcium thiogallate (composition ratio is the same as in this example) thin film 42 to which cerium is added. The constituent elements 41 and 43 are not added.
[0041]
That is, in the EL element 200 of the comparative example, the zinc (Zn) of the zinc sulfide films 41 and 43 corresponding to the second layer is not added to the thin film 42 corresponding to the first layer. Unlike the EL element 100 of the embodiment, this corresponds to the prior art.
FIG. 5 shows a comparison between the emission luminance of the EL element 200 of this comparative example and the EL element 100 of this embodiment and the emission luminance (blue emission luminance) with respect to the applied voltage. The applied voltage-emission luminance characteristics shown in FIG. 5 are emission luminances obtained when an AC pulse voltage with a driving frequency of 60 Hz is applied between the pair of transparent electrodes 12 and 16 or between the electrodes 2 and 6. .
[0042]
When the light emission luminance at an applied voltage of a threshold value plus 40 V (about 235 V) is seen as practical light emission luminance, the EL element 100 of the present embodiment is about 1.5 times as large as the EL element 200 of the conventional structure. It was confirmed that light emission luminance was obtained.
Next, FIG. 6 shows a comparison between the emission color of the EL element 100 of this embodiment and the emission color of the EL element 200 of the comparative example. In FIG. 6, it shows as a CIE (International Lighting Commission: Commission Internationale de I'Eclairage) chromaticity coordinate diagram. The emission color of the EL element 100 of this embodiment is indicated by a white circle, and the EL element 200 of the comparative example is indicated by a black circle.
[0043]
The emission color of the EL element 200 of the comparative example is (X, Y) = (0.16, 0.19), whereas the emission color of the EL element 100 of this embodiment is (X, Y) = (0.15, 0.17), which maintains a good blue purity of the conventional level. As described above, it was confirmed that by using the EL element 100 of this embodiment, high emission luminance with high blue purity can be obtained.
[0044]
As described above, the light emitting layer 14 includes the first layers 141 and 143 in which Ce addition and Zn diffusion are performed on calcium thiogallate CaGa1.8 S3.7 as a base material, and the second layer 144 made of ZnS. As described above, if the base material of the first layers 141 and 143 is an alkaline earth metal thiogallate MGaαSβ in the predetermined composition range, both good blue purity and high luminance can be realized. .
[0045]
Further, as the base material of the second layer, other than ZnS, for example, CdS may be used as a transition metal sulfide, and Cd may be diffused in the first layer.
Next, in the EL element 100 of this embodiment, when the film thicknesses of the first layers 141 and 143 were changed, the influence on the light emission luminance was examined. The result is shown in FIG. Here, the total film thickness (thickness) of both the first layers 141 and 143 was the same. This is because if the total film thickness is too large, the threshold value of the applied voltage becomes excessive, which is not practically preferable.
[0046]
The horizontal axis of FIG. 7 indicates the film thickness ratio d2 / d1 between the film thickness d1 of the first layer 141 near the glass substrate 11 and the film thickness d2 of the first layer 143 far from the glass substrate 11. The vertical axis represents the light emission luminance, and the light emission luminance at a voltage exceeding the light emission threshold voltage by 40 V is plotted.
As shown in FIG. 7, the light emission luminance is higher when the film thickness ratio exceeds 1 than when the film thickness ratio is 1 (the film thickness of both the first layers 141 and 143 is the same). In addition, an element having a film thickness ratio of less than 1 has lower emission luminance than an element having a film thickness ratio of 1. Among these, the structure of the element having high emission luminance is preferably an element having a film thickness ratio of 3 to 12, more preferably 4 to 5.
[0047]
As described above, the luminance varies depending on the film thickness ratio of each of the first layers 141 and 143, and the light emission luminance is a structure in which the film thickness ratio of the first light emission and the second light emission layer is more than 1 and less than 15. High brightness can be obtained as compared with elements having the same film thickness ratio or less than 1 or 15 or more elements.
Here, the reason why the film thickness ratio has the optimum range is considered as follows. Due to the above restrictions, the total film thickness cannot be made too thick. Therefore, if the film thickness ratio is too large, the film thickness of the first layer 141 on the side of the glass substrate 11 becomes thin, and the light emission luminance cannot be secured. Conversely, if the first layer 143 far from the glass substrate 11 is too thin, the light emission luminance cannot be secured. Therefore, it is considered to have an optimal range.
[0048]
By the way, although the result of FIG. 7 was examined in the EL element 100 of FIG. 1, the case where the zinc of the second layers 142 and 144 is not added to the first layers 141 and 143 is also shown in FIG. The same tendency is obtained.
Thus, as a result of examining the relationship between the film thicknesses of the respective layers of the first layers 141 and 143 and the light emission luminance, the position of the first layer 141 located closer to the substrate 11 is more distant from the thickness of the first layer 141. It was found that the thickness of the first layer 143 to be increased is preferable for increasing the brightness.
[0049]
By the way, in the present embodiment, in addition to the above effects, the second layer 144 is a layer located farthest from the glass substrate 11 in the light emitting layer 14, and therefore the second layer 144 contributes to light emission. The first layer 143 to be peeled can be prevented, and the EL element 100 having excellent reliability can be provided.
In the above-mentioned publication shown in the problem column, the light emitting luminance is improved by interposing an intermediate insulating layer in the light emitting layer formed by laminating a plurality of layers. Since there is no need to interpose an insulating layer, for example, there is no problem of increasing the thickness of the light emitting layer, and the light emission luminance can be improved.
[0050]
(Other embodiments)
Note that when the first layers 141 and 143 are formed, film formation may be performed in such a manner that zinc which is an element constituting the second layers 142 and 144 is mixed in the raw material in advance.
In each of the above embodiments, the light emitting layer 14 has a structure in which two layers are stacked with the first layer and the second layer as a set of layers, but may have a stacked structure of three or more layers.
[0051]
Further, even in the EL element 100, if the intermediate insulating layer shown in the above-mentioned publication shown in the problem column is interposed, even higher luminance can be realized.
In addition, in this specification, the 2nd group, 13th group, and 16th group of the periodic table correspond to the 2A group, the 3A group, and the 6B group, respectively.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional configuration of a thin film EL element according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the composition ratio of alkaline earth metal thiogallate and blue light emission luminance.
FIG. 3 is a diagram showing a distribution state of each element in the light emitting layer of the embodiment.
FIG. 4 is a schematic diagram showing a cross-sectional configuration of a thin film EL element as a comparative example of the present invention.
FIG. 5 is a diagram showing a relationship between light emission characteristics of a thin film EL element and applied voltage.
FIG. 6 is a CIE chromaticity coordinate diagram showing emission colors of the embodiment and the comparative example.
FIG. 7 is a diagram showing the relationship between the film thickness ratio of the first layer and the light emission luminance in the light emitting layer of the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Glass substrate, 12 ... 1st transparent electrode, 14 ... Light emitting layer,
16 ... 2nd transparent electrode, 141, 143 ... 1st layer,
142, 144, second layer.

Claims (7)

In an EL element formed by sandwiching a light emitting layer (14) between a pair of electrodes (12, 16) on a substrate (11),
The light emitting layer (14) includes a first layer (141, 143) that contributes to light emission using alkaline earth metal thiogallate as a base material, and a base material different from the first layer (141, 143). The second layers (142, 144) are alternately and in direct contact with each other, and a plurality of layers are laminated.
An element serving as an emission center is added to at least one of the first layers (141, 143);
The first layer (141, 143) contains at least one element constituting the second layer (142, 144),
A thickness d1 of the first layer (141) located on the substrate (11) side and a thickness d2 of the first layer (143) located on the far side from the substrate (11) The ratio d2 / d1 is 3 or more and 12 or less, and the EL element.   The alkaline earth metal thiogallate has the chemical formula MGaαSβ (where M is an element selected from Group 2 of the periodic table, and 1.5 <α <2.0 and 3.0 <β <4.0). The EL element according to claim 1, wherein the EL element is represented by:   Elements constituting the second layer (142, 144) included in the first layer (141, 143) have a concentration distribution in the first layer (141, 143). The EL device according to claim 1 or 2. In an EL element formed by sandwiching a light emitting layer (14) between a pair of electrodes (12, 16) on a substrate (11),
The light emitting layer (14) has the chemical formula MGaαSβ (where M is an element selected from Group 2 of the periodic table, and 1.5 <α <2.0 and 3.0 <β <4.0). ), The first layer (141, 143) that contributes to light emission using alkaline earth metal thiogallate as a base material, and the first layer (141, 143) is a second layer made of a different base material. The layers (142, 144) are alternately and in direct contact with each other, and a plurality of layers are laminated.
An element serving as an emission center is added to at least one of the first layers (141, 143);
The first layer (141, 143) contains at least one element constituting the second layer (142, 144),
The elements constituting the second layers (142, 144) contained in the first layers (141, 143) are more in the thickness direction of the first layers (141, 143) than in the central portion. The EL device is characterized in that the concentration is higher in the vicinity of the interface with the adjacent second layers (142, 144) . The EL device according to any one of claims 1 to 4 , wherein the second layer (142, 144) is a sulfide of a transition metal. The EL device according to claim 5 , wherein the transition metal sulfide is ZnS. Element serving as the light emitting center, EL element according to any one of claims 1 to 6, characterized in that one or more elements selected from among rare earth elements.

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