JP2013243005A - Inorganic electroluminescent element, method of manufacturing the same, and light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inorganic EL element which achieves high-luminance light emission suitable for low-voltage driving at 100 V or lower, and to provide a light-emitting device which can be miniaturized.SOLUTION: The inorganic EL element comprises a first electrode layer, a phosphor laminated structure, and a second electrode layer. In the phosphor laminated structure, a phosphor layer of perovskite type oxide or the like and a transparent conductor layer are alternately laminated so as to sandwich the transparent conductor layer between the phosphor layers. The inorganic EL element of the present invention emits light with high luminance by applying a voltage to a first electrode and a second electrode on the upper and lower sides of the phosphor laminated structure.

Description

  The present invention relates to an inorganic electroluminescent element (hereinafter referred to as an inorganic EL element) having a low voltage and high luminance emission characteristic, a method for producing the same, and a light emitting device using the inorganic EL element.

  In recent years, research and development on inorganic EL elements and organic EL elements have been promoted as light-emitting devices used for display devices such as displays and lighting devices.

  A sulfide phosphor such as ZnS is used in inorganic EL devices that are currently in practical use. Sulfides degrade by reacting with moisture and air in the air. For this reason, there is a drawback that a device that does not come into contact with the outside air is required at the time of manufacturing the material and the element and after the element is completed.

Oxide phosphors are chemically stable, and research and development of oxide perovskite structures are underway. The present inventors have disclosed an oxide perovskite phosphor ((Ca _1−x Sr _x ) _1−y Pr _y ) TiO ₃ : 0 ≦ x ≦ 1, 0.001 ≦ y ≦ 0.2, typically , (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ ) to produce an inorganic EL element that emits red light (see Patent Document 1). This oxide phosphor is not deteriorated by moisture or oxygen in the air. For this reason, it can be produced in the air by an inexpensive and simple film forming process such as a solution coating method or a spray method. Further, sealing of the element is not necessary.

  At present, since the drive voltage of inorganic EL is 200 V or more, there is a problem that the drive power supply circuit is enlarged.

  Examples of conventionally known inorganic EL elements include the following inorganic thin film EL elements (see Patent Documents 2 and 3). Patent Document 2 shows an inorganic thin film EL element in which a first electrode layer, a first insulating layer, a light emitting layer, a second insulating layer, and a second electrode layer are stacked in this order on a ceramic substrate. It has been shown that uniform light emission is emitted when an alternating voltage is applied between the first electrode layer and the second electrode layer. Patent Document 3 discloses an inorganic thin film EL in which an electrode layer made of a transparent conductive layer is provided on a glass substrate, and a first insulating layer, an inorganic light emitting layer, a second insulating layer, and a back electrode layer are stacked in this order. Elements are shown.

International Publication No. 2009/104595 JP 2007-157501 A JP 2006-134691 A

A conventional inorganic EL element has a high driving voltage, particularly a light emission starting voltage of 300 V or more, and requires a high voltage. For example, light emission was started at a voltage of 300 V or higher, and the luminance was about 100 cdm ⁻² at 350 V. For this reason, there is a problem that the drive power source is increased in size and the entire system cannot be reduced in size. In order to obtain high luminance, it is necessary to have a high driving voltage (typical driving voltage is 300 V or more), so it is difficult to emit light with high luminance by low voltage driving.

  The present invention is intended to solve these problems, and an object of the present invention is to provide a high-intensity inorganic thin film EL element with a simple structure. It is another object of the present invention to provide an EL element that is driven at a low voltage and has high luminance by using an inorganic thin film. It is another object of the present invention to provide a light emitting device using the inorganic EL element of the present invention. Moreover, it aims at providing the manufacturing method suitable for the inorganic EL element of this invention.

  In the present invention, the luminance of the inorganic phosphor film of the light emitting layer in the structure of the conventional inorganic thin film EL element is greatly improved by making the transparent conductor layer sandwiched between the inorganic phosphor films. It is. In order to achieve the above object, the present invention has the following features.

  The present invention is an inorganic electroluminescent device comprising a first electrode, a phosphor laminate structure, and a second electrode, wherein the phosphor laminate structure comprises at least one inorganic phosphor layer. It is characterized by being laminated via an intermediate layer made of a transparent conductor. The inorganic phosphor layer is preferably a perovskite oxide. Moreover, it is preferable that the said transparent conductor is a transparent conductive oxide. The inorganic electroluminescent element of the present invention can also include a conductive layer between the phosphor laminate structure and the first electrode. The light-emitting device of the present invention is characterized by having a plurality of the inorganic electroluminescent elements of the present invention.

  This invention is a manufacturing method of the inorganic electroluminescent element of this invention, Comprising: The said fluorescent substance laminated structure forms each layer into a film by the solution coating method, It is characterized by the above-mentioned.

According to the present invention, the luminance is dramatically improved by adopting a phosphor laminated structure in which a plurality of inorganic phosphor layers are laminated via an intermediate layer made of at least one transparent conductor. Whereas it was about the maximum 2Cdm ^-2 conventionally, according to the present invention, a high luminance of about up 20Cdm ^-2 can be obtained with high luminance than 2cdm ^-2. Light is emitted from a driving voltage of about 20 to 30 V, and a luminance of about 1 to 16 cdm ⁻² is obtained at a driving voltage of 30 to 100 V. The maximum luminance obtained was 16 cdm ⁻² at 5 kHz AC and 45V.

As in the present invention, the luminance is further improved by providing a conductive layer between the first electrode and the phosphor laminate structure. The drive voltage is emitted from around 20-30V, and the brightness of about 5-51 cdm ^-2 is obtained at the drive voltage of 30-100V. If a conductive layer is provided between the first electrode and the phosphor laminate structure, the luminance can be increased by 3 to 4 times compared to the case where the conductive layer is not provided. The maximum luminance obtained was 51 cdm ^-2 at 5 kHz AC and 43 V.

  According to the present invention, when a perovskite oxide is used as a phosphor having a phosphor layered structure, a phosphor having excellent chemical stability can be obtained. Further, when an oxide is used as the transparent conductor having a phosphor laminate structure, a phosphor laminate structure having excellent chemical stability can be obtained.

  Since the light-emitting device of the present invention emits light with high luminance when driven at a low voltage of 100 V or less, the light-emitting device can be miniaturized. According to the light emitting device of the present invention, it is possible to contribute to downsizing of the entire system such as a lighting device, a light source, a display device such as a display.

  The inorganic EL element of the present invention has an advantage that the film forming method is not limited. For example, since it can be produced in the atmosphere by a solution coating method, it is possible to form a film with a simple apparatus, and it is industrially useful because a large area can be realized. Moreover, composition control of each layer to be laminated can be easily performed by using a solution coating method.

The figure which shows the basic structure of this invention. FIG. 3 is a diagram showing a transmission spectrum of each layer of Example 1. A (thick solid line) is a quartz glass plate, B (dotted line) is a sample obtained by depositing (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ on the quartz glass plate, and C (dashed line) is Sn _0.95 Sb on the quartz glass plate. A sample in which _0.05 O ₂ is formed and D (thin line) indicates a sample in which Pt is formed on a quartz glass plate. The figure which shows the structure of a comparative example. The figure which shows the X-ray-diffraction pattern of Example 1 and a comparative example. 2 is an enlarged view of an X-ray diffraction pattern of Example 1. FIG. 4 is a TEM image of a cross section of the EL element of Example 1. FIG. FIG. 3 is an excitation / emission spectrum of the EL device of Example 1. FIG. The EL spectrum of Example 1. The figure which shows the voltage dependence of an electric current and a brightness | luminance when an alternating voltage is applied to the EL element of Example 1. FIG. The figure which shows the voltage dependence of an electric current and a brightness | luminance when an alternating voltage is applied to the element of a comparative example. FIG. 4 is a diagram showing frequency dependence of current and luminance when an alternating voltage is applied to the EL element of Example 1. FIG. 6 is a diagram showing voltage dependency of current and luminance when a DC voltage is applied to the EL element of Example 1. FIG. 6 shows a structure of an EL element of Example 2. The figure which shows the voltage dependence of an electric current and a brightness | luminance when an alternating voltage is applied to the EL element of Example 2. FIG.

  Embodiments of the present invention will be described below. The basic structure of the present invention will be described with reference to FIG. In the inorganic EL element of the present invention, the phosphor laminated structure serving as the light emitting layer has a structure in which a transparent conductor layer is sandwiched between inorganic phosphor layers. As shown in FIG. 1, a transparent conductor layer (21, 22) is provided as an intermediate layer between the inorganic phosphor layers (11, 12, 13), and is laminated. In the example shown in FIG. 1, the phosphor layer 11, the transparent conductor layer 21, the phosphor layer 12, the transparent conductor layer 22, and the phosphor layer 13 are laminated through two transparent conductor layers. This is an example in which three phosphor layers are laminated. Thus, the phosphor laminated structure of the present invention is a structure in which the transparent conductor layers are sandwiched between the inorganic phosphor layers and alternately laminated. A structure in which two phosphor layers are laminated via one transparent conductor layer may be used. The transparent conductor layer only needs to be laminated as an intermediate layer between the plurality of phosphor layers, and a large number of three or more transparent conductor layers can be provided as the intermediate layer. A maximum of about 100 layers is considered preferable. The number of layers is caused by the fact that the light emission cannot be transmitted when the transparency is lowered due to the transparency of the phosphor layer and the transparent conductor layer.

  The inorganic EL element of the present invention emits light with high luminance by providing a first electrode and a second electrode above and below the phosphor layered structure and applying a voltage through these electrodes. The substrate 5 in FIG. 1 is an example of the first electrode, and the upper electrode 3 is an example of the second electrode. For the inorganic EL element having the phosphor layered structure of the present invention, a conventionally known electrode structure of an EL element can be employed.

An oxide phosphor layer can be used for the phosphor layer of the present invention. For example, a perovskite oxide phosphor can be used, including Sn perovskite oxide, ASnO ₃ perovskite oxide substituted with Ca, Sr, Ba, Sr _{n + 1} Ti _n O _{3n + 1} perovskite oxide, Pr Substituted (CaSrBa) TiO ₃ and Pr-substituted CaTiO ₃ are known. For example, an oxide perovskite phosphor ((Ca _1−x Sr _x ) _1−y Pr _y ) TiO ₃ : 0 ≦ x ≦ 1, 0.001 ≦ y ≦ 0.2 may be used. For example, (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ .

For the transparent conductor layer of the present invention, materials used for known transparent electrodes can be used, and tin oxide-based, zinc oxide-based, and indium oxide-based transparent conductive oxides are used. For example, ITO (indium tin oxide), ATO (Sn—Sb oxide), and the like are preferable. For example, Sn _1-z Sb _z O ₂ : 0.01 ≦ z ≦ 0.2 was used as the antimony oxide.

  The thickness of the phosphor layer is preferably 200 nm to 300 nm. In the case of spin coating, the phosphor layer is coated a plurality of times, and a transparent conductor layer is provided thereon. The thickness of the transparent conductor layer is preferably 30 nm to 50 nm. The total thickness of the phosphor laminate structure is preferably 500 nm to 1500 nm. The thickness of the phosphor layer and the thickness of the transparent conductor layer are preferably about 3: 1 to 5: 1.

A conductive substrate can be used for the first electrode. The first electrode may have a structure in which a conductive layer is provided over a nonconductive substrate. As the conductive substrate, for example, an Nb 0.1-1% substituted SrTiO ₃ (001) single crystal polished substrate having electrical conductivity can be used. Further, a metal substrate or an ITO substrate may be used.

  The second electrode is preferably a transparent conductive layer. As the second electrode, a metal such as Pt, Au, Ti, Ni, or Al is used. Even a metal layer is 20 nm to 60 nm thick and thin, and therefore has sufficient transparency. A transparent electrode such as ITO can also be used.

  It is preferable to use a material having transparency as the material constituting the phosphor laminate structure and the electrode.

  A conductor layer may be further provided between the phosphor laminate structure and the electrode. The conductor layer is preferably a transparent metal layer, and can be provided as a thin metal layer. Pt is preferred.

  The inorganic EL element of the present invention is manufactured by adopting a conventionally known method for manufacturing an inorganic phosphor film and a method for manufacturing a transparent conductor film that has been conventionally performed for manufacturing a transparent electrode or the like. Can do. The inorganic phosphor film is formed by spin coating, aerosol deposition, PLD (pulse laser deposition), vapor deposition, sputtering, CVD, or the like. The transparent conductor film is formed by spin coating, aerosol deposition, PLD (pulse laser deposition), vapor deposition, sputtering, CVD, or the like. A solution coating method such as a spin coating method has advantages such as that a film can be formed with a simple apparatus and that the area can be easily increased, and the composition control is easy. preferable.

Example 1
This embodiment will be described with reference to FIG. As shown in FIG. 1, the inorganic EL element of this example includes a substrate 5, a phosphor layer 11, a transparent conductor layer 21, a phosphor layer 12, a transparent conductor layer 22, a phosphor layer 13, and an electrode 3. .

(1. Preparation of phosphor precursor solution)
The molar ratio of metal ions is (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ , the weight molar concentration of Ti is 0.20 mmol / g, acetylacetone is equimolar with Ti, and the solvent is an acetic acid-water mixed solution (solution A solution of 10 to 15 wt.% Of water with respect to the total amount and a total amount of about 20 to 30 g was prepared by the following procedure.

First, about 15 g of acetic acid, 4.5 g of ion-exchanged water, and 6 mmol of acetylacetone were added to a 100 ml beaker, and after stirring well, about 6 mmol of titanium tetraisopropoxide Ti (OC ₃ H ₇ ) ₄ was added. The solution was stirred at about 105 ° C. for 20 minutes. Necessary amounts of CaCO ₃ , SrCO ₃ , and Pr (CH ₃ COO) ₃ .xH ₂ O calculated from the Ti concentration were placed in this solution and dissolved by stirring at about 90 ° C. for 30 minutes. Finally, acetic acid was added so that the weight molar concentration of Ti was 0.20 mmol / g. The resulting solution was a yellow, slightly suspended colloidal solution.

(2. Preparation of transparent conductor precursor solution)
A solution in which the molar ratio of Sn and Sb was 95: 5, the molar concentration of Sn was 0.15 mmol / g, and the solvent was acetic acid was prepared by the following procedure.

SnCl ₂ .2H ₂ O was dissolved in ion-exchanged water, and an aqueous solution of NH ₄ HCO ₃ was added to the aqueous solution to obtain a precipitate. The precipitate was removed by suction filtration and dried at room temperature. Next, this precipitate was dissolved by stirring in acetic acid at about 105 ° C. to obtain a Sn acetic acid solution. Next, Sb ₂ O ₃ was dissolved in acetic acid to prepare an Sb acetic acid solution. Finally, an Sn acetic acid solution and an Sb acetic acid solution were mixed so that the molar ratio of Sn and Sb was 95: 5 to prepare an Sn _0.95 Sb _0.05 O ₂ transparent conductor precursor solution.

(3. Film formation)
On a 10 mol × 10 mm 1 mol% Nb-doped SrTiO ₃ single crystal substrate 5 (Furuuchi Chemical, surface (100) plane, resistivity 0.02 Ωcm), phosphor layer 11, transparent conductor layer 21, phosphor layer 12, transparent The conductor layer 22 and the phosphor layer 13 were formed in the following order. Film formation was performed by a spin coating method (rotation speed 2500 rpm, rotation time 15 s). The phosphor layer is coated four times, the transparent conductor layer thereon is coated once, the phosphor layer is further coated four times, the transparent conductor layer is coated once thereon, and the phosphor thereon The layer was coated 4 times. In FIG. 1, the layer coated four times is schematically shown by a dotted line layer.

Prior to film formation, the substrate (Nb-doped SrTiO ₃ single crystal) was baked in an electric furnace at 700 ° C. for 10 minutes to remove organic substances on the surface. The substrate was taken out from 700 ° C. to room temperature and cooled for 2 minutes. A precursor solution of a phosphor or a transparent conductor was dropped on the substrate, and a film was formed by spin coating (rotation speed 2500 rpm, rotation time 15 s). This was put into an electric furnace at 700 ° C. and baked for 10 minutes. This cooling / spin coating / firing was repeated a specified number of times (14 times in the present example) in the above film formation, then placed in an electric furnace at 900 ° C., annealed for 10 minutes, and taken out to room temperature.

(4. Production of electrodes)
The top surface of the prepared phosphor laminate structure was lightly polished with a cerium oxide abrasive. After polishing, the abrasive was washed away with water and a neutral detergent. Since the conductivity of the surface of Nb-doped SrTiO ₃ was lost by firing, the corners of the device were scraped with a file. A Pt electrode having a thickness of about 2 mm × 5 mm and a thickness of several nanometers was formed on the uppermost surface of the phosphor multilayer structure by sputtering at two locations at room temperature for 30 seconds to form the upper electrode 3. A copper wire was connected to the Pt upper electrode and the Nb-doped SrTiO ₃ lower electrode (the corner cut with a file) with a silver paste to obtain an EL element.

(5. Characteristics of each layer)
The transmittance and resistivity of each layer constituting the EL element of this example were examined. In order to investigate the transmittance, a sample in which a (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ thin film was formed (coated twice) on a quartz glass plate was prepared. In order to investigate the transmittance and electrical resistivity, a sample in which a Sn _0.95 Sb _0.05 O ₂ thin film was formed (coated twice) on a quartz glass plate was prepared. In order to measure the transmittance and electrical resistivity of the Pt thin film, a sample was prepared by sputtering a Pt thin film on a quartz glass plate at room temperature for 30 seconds.

A sample in which (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ is formed on a quartz glass plate, a sample in which Sn _0.95 Sb _0.05 O ₂ is formed, and a sample in which Pt is formed are all samples. The character placed underneath was seen through and was transparent.

FIG. 2 shows the transmission spectra of the quartz glass plates used for these samples and the substrate (the vertical axis represents transmittance% and the horizontal axis represents wavelengths of 200 to 800 nm). A (thick solid line) is a quartz glass plate, B (dotted line) is a sample obtained by depositing (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ on the quartz glass plate, and C (dashed line) is Sn _0.95 Sb on the quartz glass plate. A sample in which _0.05 O ₂ is formed, D (thin line) is a sample in which Pt is formed on a quartz glass plate. The transmission spectrum of the thin film formed on the quartz glass plate was measured with a spectrophotometer. Both (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ film and Sn _0.95 Sb _0.05 O ₂ film showed a transmittance of 80 to 90% in the visible light region. The Pt thin film showed a transmittance of about 70% in the entire wavelength region measured.

Regarding the electrical resistivity, the sheet resistance of the Sn _0.95 Sb _0.05 O ₂ thin film formed on the quartz glass plate was 706 Ω / □. The sheet resistance of the thin film was measured by the 4-terminal method. From the film thickness (about 40 nm), the electrical resistivity is about 6 × 10 ⁻³ Ωcm. The sheet resistance of the Pt thin film formed on the quartz glass plate was 243Ω / □.

(Comparative example)
Except for the transparent conductor layer having the structure of Example 1, other than that, a comparative example was produced by the same composition and production method as in Example 1. FIG. 3 shows the structure of the EL element of the comparative example. The phosphor layer 10 was formed on a 10 mol × 10 mm 1 mol% Nb-doped SrTiO ₃ single crystal substrate 5 (Furuuchi Chemical, surface (100) plane, resistivity 0.02 Ωcm). The film formation was performed by the same spin coat method as in Example 1. The phosphor layer was prepared by coating 12 times. In the figure, the layer coated 12 times is schematically shown by a dotted line layer. Similar to Example 1, a Pt electrode was prepared as the upper electrode 3.

(6. X-ray diffraction of EL elements of Example 1 and Comparative Example)
In FIG. 4, the X-ray-diffraction pattern of the laminated structure of Example 1 and a comparative example is shown. A solid line shows the element of Example 1, and a dotted line shows the element of a comparative example. In any case, a 200 diffraction peak of Nb-doped SrTiO ₃ is observed in the vicinity of 46 to 47 °, and (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ of 200 (pseudocubic indexed) diffraction is observed on the high angle side. A peak was observed. In addition, a 110 diffraction peak of (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ was observed around 32.8 °. In the powder sample, the intensity of the 110 diffraction peak is larger than the intensity of the 200 diffraction peak, but in the case of Example 1 and the comparative example, the 200 diffraction peak is overwhelmingly larger. From this, in the case of Example 1 and the comparative example, the ratio of both (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ crystal grains growing in the same direction as the Nb-doped SrTiO ₃ single crystal is large. I understand. The intensity ratio of the 110 diffraction peak and the 200 diffraction peak is not much different between Example 1 and the comparative example. The crystal structure was examined with a powder X-ray diffractometer (CuKα ray). Photoluminescence (PL) characteristics were examined with a spectrofluorometer.

In FIG. 5, the enlarged view of the X-ray-diffraction pattern of Example 1 is shown. In addition to the 110 diffraction peak of (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ , a broad shoulder was observed near 34 °. This coincides with the position of the 101 diffraction peak of the Sn _0.95 Sb _0.05 O ₂ crystal. Assuming these two diffraction peaks, the results of the least square fitting were as follows: solid line, dotted line (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ 110 diffraction peak), broken line (Sn _0.95 Sb _0.05 O ₂ crystal) 101 diffraction peak). The circles are actually measured values. The experimental results were well reproduced by fitting. From the line width obtained by the fitting and the Scherrer equation, the grain size of the (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ crystal was estimated to be 48 nm, and the grain size of the Sn _0.95 Sb _0.05 O ₂ crystal was estimated to be 6 nm.

(7. TEM image of Example 1)
FIG. 6 shows a TEM image of a cross section of the element of Example 1. The surface of this sample was examined in a state where it was not polished with CeO ₂ and a Pt electrode was not formed. The interface between (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ layer and Sn _0.95 Sb _0.05 O ₂ layer was clearly observed. The three (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ layers are each formed by coating four times, but the uppermost (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ layer has a clear interface between the coats. Was not observed. On the other hand, three interfaces were observed in each of the two (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ layers close to the substrate, and cavities (white spots) were observed at various portions of the interface. The (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ layer is formed from particles having a diameter of about 50 nm, and the Sn _0.95 Sb _0.05 O ₂ layer is formed from particles having a diameter of about several nm. This result corresponds well to the result of X-ray diffraction.

The thickness of the Sn _0.95 Sb _0.05 O ₂ layer prepared in Example 1 is about 40 nm, and the thickness of the (Ca _0.6 Sr _0.4 ) _0.998 Pr _0.002 TiO ₃ layer is 230 to 250 nm (about 60 nm per coating). there were.

(8. Photoluminescence characteristics of Example 1)
When the EL device of Example 1 was irradiated with UV light having a wavelength of 340 nm in a dark place, red light emission was confirmed on the entire surface. Moreover, although it was weaker than the surroundings, red light emission was also confirmed on two Pt electrodes. This indicates that both ultraviolet light and red light are transmitted through the Pt electrode, and it can be seen that there is no contradiction with the transmittance measurement results.

FIG. 7 shows the excitation / emission spectrum of the EL device of Example 1. The emission spectrum was excited at 340 nm and the excitation spectrum was monitored at 613 nm. In the figure, the solid line shows the excitation spectrum (λem = 613 nm), and the dotted line shows the emission spectrum (λex = 340 nm). The emission spectrum showed emission peaks around 613 nm and 700 nm. All of the peaks are observed in the powder sample, and light emission is caused by the ff transition of Pr3 +. The excitation spectrum showed peaks around 340 nm and 300 nm. A peak at 340 nm is also observed in the powder sample, and is based on the interband transition of the host crystal ((Ca _0.6 Sr _0.4 ) TiO ₃ ).

(9. Electroluminescence characteristics of Example 1 and Comparative Example)
The state of light emission when an alternating voltage of 5 kHz and 40 V was applied to one Pt electrode of Example 1 was examined. It was confirmed that the entire Pt electrode to which voltage was applied emitted red light. FIG. 8 shows this emission spectrum. The EL spectrum of FIG. 8 showed a peak near the wavelength of 612 nm, and an emission spectrum having substantially the same shape as the photoluminescence spectrum of FIG. 7 was observed.

FIG. 9 shows voltage dependency of current and luminance when an alternating voltage of 1 kHz and 5 kHz is applied to Example 1. The horizontal axis represents voltage (V), the left vertical axis represents current (mA), and the right vertical axis represents luminance (0 to 20 cdm ⁻² ). A circle mark indicates a case of 1 kHz, a square mark indicates a case of 5 kHz, black indicates a current, and white indicates a luminance. In both cases of 1 kHz and 5 kHz, light emission began to be confirmed visually from around 20-30 V. Brightness at 40V, when the 1kHz 4.0cdm ^-2, was 9.7Cdm ^-2 at 5 kHz. The maximum luminance was 16.5 cdm ⁻² at 5 kHz and 50V. The IV curve has a downwardly convex shape, and the slope increases as the voltage increases near the voltage at which light emission starts. With a driving voltage of 30 to 100 V, a luminance of about 1 to 17 cdm ⁻² can be obtained. Note that the EL characteristics are obtained by amplifying the function generator sine wave AC voltage with a bipolar amplifier to a circuit in which the manufactured EL element and a 1 kΩ resistor are connected in series, and the AC voltage between the EL element terminals (effective value). The alternating current (effective value) flowing through the element was measured simultaneously with a digital multimeter and the luminance was measured with a luminance meter.

FIG. 10 shows voltage dependency of current and luminance when an alternating voltage of 1 kHz and 5 kHz is applied to the element of the comparative example. The vertical and horizontal axes are the same as those in FIG. A circle mark indicates a case of 1 kHz, a square mark indicates a case of 5 kHz, black indicates a current, and white indicates a luminance. In both cases of 1 kHz and 5 kHz, no luminescence was observed visually even at 55 to 60 V, and the luminance was less than sensitivity (0.01 cdm ⁻² ). The IV curve has an upwardly convex shape, and the slope decreases as the voltage increases.

FIG. 11 shows the frequency dependence of luminance and current when an AC voltage of 40 V is applied to Example 1. The horizontal axis represents frequency (kHz), the left vertical axis represents current (mA), and the right vertical axis represents luminance (cdm ^-2 ). Black indicates current and white indicates luminance. As the frequency increases, both current and brightness increase. The frequency was 1 to 8 kHz and the luminance was about 1 to 9.5 cdm ⁻² . The maximum luminance was 9.5 cdm ⁻² at 8 kHz.

FIG. 12 shows the voltage dependence of current and luminance when a DC voltage is applied to Example 1. Here, the Pt electrode is the ground. The horizontal axis represents voltage (V), the left vertical axis represents current (mA), and the right vertical axis represents luminance (cdm ⁻² ). Black indicates current and white indicates luminance. As the voltage was increased to the negative side, current began to flow rapidly from around -20 V, and light emission began to be observed at the same time. However, the luminance was about 0.09 to 0.14 cdm ^−2, which was 1-2 orders of magnitude smaller than when the AC voltage was applied. On the other hand, when the voltage was increased to the plus side, the current started to increase gradually from around 30 V, but the value was much smaller than the minus side, and no light emission was observed.

From the comparison between the above Example 1 and the comparative example, as shown in the present invention, the phosphor layer is formed by alternately laminating a plurality of layers through the intermediate layer of the transparent conductor layer, so that the intermediate layer composed of the transparent conductor layer is formed. It can be seen that light emission with a high luminance of about 1 to 17 cdm ⁻² can be obtained at a low voltage (AC voltage) of about 30 to 100 V, compared with the case where no layer is provided. The dramatic improvement in luminance was achieved by inserting the conductor layer between the phosphor layers because the transparent conductor layer formed a double Schottky junction and was large enough to emit EL light. This is thought to be because the electric field can be formed at the junction interface, and it acts as a capacitor for storing electrons.

  Although only the results up to about 50V are shown in the figure, it is conceivable that light emission with high luminance is similarly performed at 50V to 100V.

(Example 2)
This embodiment will be described with reference to FIG. The inorganic EL element of this example is an example in which a conductive film is further provided between the substrate and the phosphor layer in the structure of Example 1. As shown in FIG. 13, it includes a substrate 5, a metal conductive film 4, a phosphor layer 11, a transparent conductor layer 21, a phosphor layer 12, a transparent conductor layer 22, a phosphor layer 13, and an electrode 3. This example was produced by the same composition and manufacturing method as in Example 1 except for the metal conductive film 4. Platinum (metal conductive film 4) was sputtered on a 10 mm × 10 mm 1 mol% Nb-doped SrTiO ₃ single crystal substrate 5 at 600 ° C. for 10 minutes (film thickness 100 to 200 nm). The phosphor layer 11, the transparent conductor layer 21, the phosphor layer 12, the transparent conductor layer 22, and the phosphor layer 13 were formed in this order to produce an inorganic EL element. Film formation was performed by spin coating as in Example 1. In the formation of each layer, cooling, spin coating, and firing were performed in the same manner as in Example 1. An electrode was formed on the surface of the laminated structure in the same manner as in Example 1 to produce an inorganic EL element.

FIG. 14 shows voltage dependency of current and luminance when an alternating voltage of 1 kHz and 5 kHz is applied to the EL element of Example 2. The horizontal axis represents voltage (V), the left vertical axis represents current (mA), and the right vertical axis represents luminance (0 to 100 cdm ⁻² ). A circle mark indicates a case of 1 kHz, a square mark indicates a case of 5 kHz, black indicates a current, and white indicates a luminance. As in Example 1, light emission began to be confirmed visually from around 20 to 30 V in both cases of 1 kHz and 5 kHz. Brightness at 40V, when the 1kHz 12cdm ^-2, a 35Cdm ^-2 at 5 kHz, was 3 to 4 times of the device of Example 1. The maximum luminance was 51 cdm ^-2 at 5 kHz and 43V. Further, the current slightly decreased as compared with the device of Example 1.

  As in this example, the luminance is further improved by providing a conductive layer such as a metal conductive film between the conductive substrate serving as the lower electrode and the lowermost fluorescent layer of the fluorescent laminate structure. And the current can be reduced. The conductive layer in Example 2 is not limited to Pt metal but may be other conductive metal. This is considered to be due to the reflection of light toward the substrate by Pt metal or the like, or the formation of a Schottky junction between the conductive layer and the phosphor layer.

(Example 3)
In the structure of Example 1, ITO (indium tin oxide) was used as the transparent conductor layers 21 and 22, and other materials and manufacturing methods were produced in the same manner as in Example 1. ITO was formed by spin coating. The same characteristics as in Example 1 were obtained.

Example 4
In the structure of Example 2, ITO (indium tin oxide) was used as the transparent conductor layers 21 and 22, and other materials and manufacturing methods were produced in the same manner as in Example 2. ITO was formed by spin coating. The same characteristics as in Example 2 were obtained.

In each of the embodiments described above, the example of the composition of (Ca, Sr, Pr) TiO ₃ was used as the phosphor layer, but the same effect can be obtained by using other phosphor layers. In particular, an oxide phosphor layer is chemically stable, and a perovskite oxide phosphor is more preferable. Further, although the example was red, other colors have the same effect.

As the transparent conductor layer used as the intermediate layer of the phosphor laminate structure of the present invention, Sn _1-z Sb _z O ₂ was used in the examples. However, as long as it is transparent and can form a conductor layer. Have the same effect.

  In the embodiment, the number of layers of the phosphor laminated structure of the present invention is an example of three phosphor layers. However, the number of phosphor layers is not limited to three but may be plural. As the number of layers increases, a high applied voltage is required and the drive power supply becomes large. Furthermore, it is conceivable that light emission becomes weak due to a decrease in crystallinity of the upper layer due to an increase in the number of layers. It can be stacked up to about 100 layers. The phosphor layer is preferably 2 to 5 layers.

  The examples shown in the above embodiment are described for easy understanding of the invention, and are not limited to this embodiment.

  The inorganic EL element of the present invention has high luminance EL characteristics driven at a low voltage of 100 V or less, is excellent in chemical stability, and can be miniaturized, so it is used for lighting devices, various light sources, displays, etc. it can.

3 Electrode 4 Metal conductive film 5 Substrate (lower electrode)
10, 11, 12, 13 Phosphor layer 21, 22 Transparent conductor layer

Claims (6)

An inorganic electroluminescence device comprising a first electrode, a phosphor laminate structure, and a second electrode,
The phosphor laminate structure is an inorganic electroluminescent element in which a plurality of inorganic phosphor layers are laminated via an intermediate layer made of at least one transparent conductor.   2. The inorganic electroluminescent device according to claim 1, wherein the inorganic phosphor layer is a perovskite oxide.   2. The inorganic electroluminescent device according to claim 1, wherein the transparent conductor is a transparent conductive oxide.   The inorganic electroluminescent element according to claim 1, further comprising a conductive layer between the phosphor laminated structure and the first electrode.   A light emitting device comprising a plurality of the inorganic electroluminescence elements according to claim 1.   2. The method of manufacturing an inorganic electroluminescent element according to claim 1, wherein each layer of the phosphor laminated structure is formed by a solution coating method.