JP2008147084A - Oxide electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide electroluminescent element containing, as an electroluminescent material, an oxide having a perovskite type crystalline structure expressed by general formula: RMO<SB>3</SB>, where R is a rare-earth element, and M is Al, Mn or Cr, and emitting ultraviolet light. <P>SOLUTION: This oxide electroluminescent element has an electroluminescent layer between electrodes facing each other. The oxide electroluminescent element is characterized in that (1) the electroluminescent layer contains the oxide having the perovskite type crystalline structure expressed by general formula: RMO<SB>3</SB>, where R is a rare-earth element, and M is Al, Mn or Cr; (2) the oxide further contains at least one kind selected from a group comprising transition metals and alkaline earth metals; and (3) light having a wavelength of 200-400 nm is emitted by applying a pulse voltage having a frequency of 0.1 to 10 kHz at electric field intensity above 10<SP>4</SP>V/cm between the electrodes to set a local maximum value of the density of a current flowing between the electrodes not smaller than 10 μA/cm<SP>2</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oxide electroluminescence device and a driving method thereof.

  Current electroluminescent materials can be broadly classified into inorganic materials and organic materials. Inorganic electroluminescent materials are superior in long-term stability to organic electroluminescent materials, and have the advantage of emitting light even under severe conditions such as high temperatures.

  For example, ZnS doped with Mn is known as an inorganic electroluminescent material (see Non-Patent Documents 1 and 2). This electroluminescent material has been put into practical use as a light emitting element material, but can emit only yellow to orange light.

In light of the fact that the emission color of the conventional electroluminescent material is limited to yellow to orange, the present inventor has made an electroluminescence that emits green light made of an oxide having a perovskite crystal structure as a result of earnest research. The material is completed. Specifically, the rare earth element is R, M represents Al, Mn, or Cr, and is an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ (Patent Document 1).

  In addition to the above-described technology for emitting green light, if a technology for obtaining red light having a wavelength longer than that of yellow can be established, the three primary colors of light (RGB: RGB) are combined by combining other electroluminescent materials that emit blue light. Red, green, and blue) can be expressed, and by combining these three primary colors, light in a wide range of visible wavelengths can be obtained. And this technique is useful at the point which can be applied to uses, such as a display, illumination, and various light sources. Furthermore, if red light emission is obtained from the electroluminescent material capable of emitting green light, it is highly useful in that the need to prepare different electroluminescent materials for each luminescent color can be reduced.

  At present, as a result of intensive studies in view of the above problems, the present inventor obtained red light emission when applying a pulse voltage having a frequency of 1 kHz or higher in the electroluminescent material capable of emitting green light. The knowledge that it can be found. That is, the present inventor has found that electroluminescence of green and red can be obtained by selecting the frequency of the applied pulse voltage in the electroluminescent material having a perovskite crystal structure.

  In addition to the above green and red color development, if electroluminescence with a shorter wavelength than green is obtained, electroluminescence in a wide wavelength range is possible, and by mixing these color developments, the freedom to obtain visible light of various colors The degree increases. If ultraviolet light (light of 200 to 400 nm) is obtained in the electroluminescent material, since the ultraviolet light can be used as an excitation light source of the fluorescent material, the degree of freedom of color development finally obtained is further expanded.

However, a technique for extracting ultraviolet light has not yet been found in the electroluminescent materials and oxide electroluminescent materials having a perovskite crystal structure.
International Publication No. WO2005 / 042669 Pamphlet YA Ono, Electroluminescent Displays, World Scientific, 1995, Singapore Trigger Vol.18, No.3, pp.21-23 (1999)

The present invention is an electroluminescent device comprising a rare earth element as R, M representing Al, Mn or Cr, and an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ as an electroluminescent material. Therefore, it is a main object to provide an element that emits ultraviolet light.

  As a result of intensive studies, the present inventor has determined that the current density flowing between the electrodes is within a specific range with respect to the electroluminescent layer in which the electroluminescent material is sandwiched between a pair of electrodes. In the case of applying a specific pulse voltage, it has been found that ultraviolet light can be obtained, and the present invention has been completed.

That is, the present invention relates to the following oxide electroluminescent element and its driving method.
1. An oxide electroluminescent device having an electroluminescent layer between opposing electrodes,
(1) The electroluminescent layer includes R as a rare earth element, M represents Al, Mn, or Cr, and includes an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ .
(2) The oxide further contains at least one selected from the group consisting of transition metals and alkaline earth metals,
(3) A pulse voltage having a frequency of 0.1 Hz to 10 kHz is applied between the electrodes at an electric field strength of 10 ⁴ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more. By emitting light having a wavelength of 200 to 400 nm,
An electroluminescent element characterized by the above.
2. By applying a pulse voltage with a frequency of 0.1 Hz to 1 kHz at an electric field strength of 10 ⁵ V / cm or more between the electrodes so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more, Item 2. The electroluminescent device according to Item 1, wherein the device emits light having a wavelength of 200 to 400 nm and light having a wavelength of more than 400 nm and not more than 2500 nm.
3. 2. The electroluminescent element according to item 1, wherein the rare earth element R is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.
4). 2. The electroluminescent device according to item 1, wherein the transition metal is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.
5. 2. The electroluminescent element according to item 1, wherein the alkaline earth metal is at least one selected from the group consisting of Ca, Sr and Ba.
6). The electroluminescence device according to Item 1, wherein the content of the transition metal with respect to the oxide is 0.05 to 2% in terms of mol% of the transition metal with respect to M.
7). The electroluminescent device according to Item 1, wherein the content of the alkaline earth metal with respect to the oxide is 0.05 to 2% in terms of mol% of the alkaline earth metal with respect to M.
8). 2. The electroluminescent element according to item 1, wherein at least one of the opposing electrodes contains at least one selected from the group consisting of gold and aluminum.
9. 2. The electroluminescent device according to item 1, wherein at least one of the opposing electrodes is transparent.
10. Item 2. The electroluminescent device according to Item 1, further comprising a light reflecting layer.
11. 2. The electroluminescent device according to item 1, wherein the oxide is YAlO ₃ containing Ti and / or Ca.
12 2. The electroluminescent device according to item 1, wherein the oxide is LaAlO ₃ containing Ti and / or Ca.
13. 2. The electroluminescent element according to item 1, wherein the electroluminescent element is connected to a power source, and a resistor is further connected in series with the electroluminescent element between the electrode and the power source.
14 A method for driving an oxide electroluminescent device having an electroluminescent layer between opposing electrodes, wherein (1) the electroluminescent layer is R for a rare earth element, M is Al, Mn or Cr, An oxide having a perovskite crystal structure represented by the formula: RMO ₃ ;
(2) The oxide further contains at least one selected from the group consisting of transition metals and alkaline earth metals,
(3) A pulse voltage having a frequency of 0.1 Hz to 10 kHz is applied between the electrodes at an electric field strength of 10 ⁴ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more. To emit light having a wavelength of 200 to 400 nm,
A driving method characterized by that.
15. By applying a pulse voltage with a frequency of 0.1 Hz to 1 kHz at an electric field strength of 10 ⁵ V / cm or more between the electrodes so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more, Item 15. The driving method according to Item 14, wherein light having a wavelength of 200 to 400 nm and light having a wavelength exceeding 400 nm and not more than 2500 nm are emitted simultaneously.
16. Item 15. The driving method according to Item 14, wherein the oxide is YAlO ₃ containing Ti and / or Ca.
17. Item 15. The driving method according to Item 14, wherein the oxide is LaAlO ₃ containing Ti and / or Ca.

Hereinafter, the oxide electroluminescence device of the present invention and the driving method thereof will be described.

The oxide electroluminescent element of the present invention has an electroluminescent layer between opposed electrodes,
(1) The electroluminescent layer includes R as a rare earth element, M represents Al, Mn, or Cr, and includes an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ .
(2) The oxide further contains at least one selected from the group consisting of transition metals and alkaline earth metals,
(3) A pulse voltage having a frequency of 0.1 Hz to 10 kHz is applied between the electrodes at an electric field strength of 10 ⁴ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more. Thus, light having a wavelength of 200 to 400 nm (ultraviolet light) is emitted.

The electroluminescent layer includes R as a rare earth element, M represents Al, Mn, or Cr, and contains an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ . Note that the electroluminescent layer may be substantially formed of the above oxide.

  The rare earth element R is not limited, and examples thereof include Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among these, Y, La, Nd, and Sm are particularly preferable.

  M may be Al, Mn or Cr, and among these, Al is preferable.

  The oxide further contains at least one of a transition metal and an alkaline earth metal. As these containing modes, a mode of substitution (doping) with a part of the rare earth element R is preferable. By containing at least one of a transition metal and an alkaline earth metal, oxygen defects serving as a light emission center (color center) in the oxide are preferably stabilized.

  Although it is not limited as a transition metal, For example, at least 1 sort (s) selected from the group which consists of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn is preferable. Among these, Ti, Mn, Fe and Cu are preferable, and Ti is more preferable.

  Although it is not limited as an alkaline-earth metal, For example, at least 1 sort (s) selected from the group which consists of Ca, Sr, and Ba is preferable. Among these, Ca and Sr are more preferable, and Ca is most preferable.

  The content of the transition metal and / or alkaline earth metal with respect to the oxide is not limited, but the total amount of the transition metal and alkaline earth metal with respect to M is expressed in terms of mol%, and is about 0.05 to 2%. Preferably, about 0.1 to 1.5% is more preferable.

  When the content of the transition metal and / or alkaline earth metal is too large, light absorption in the ultraviolet to visible region in the electroluminescent layer increases, so that the generated ultraviolet light is absorbed by the electroluminescent layer and light emission is weakened. There is a fear. When the content is set within the above range, it is preferable because ultraviolet light is easily generated due to stabilization of the emission center and absorption into the electroluminescent layer is small.

Specifically, YAlO ₃ (yttrium aluminate), LaAlO ₃ (lanthanum aluminate), etc. containing Ti as a transition metal are preferable as the oxide. Further, YAlO ₃ and LaAlO ₃ containing Ca as an alkaline earth metal are also preferable. These oxides are obtained by substituting (doping) a part of trivalent Y or La constituting the crystal lattice in YAlO ₃ or LaAlO ₃ with tetravalent Ti or divalent Ca.

  The oxide may be single crystal, polycrystalline, or amorphous. The single crystal oxide can be synthesized by, for example, a floating zone method. Polycrystalline and amorphous oxides can be synthesized by, for example, a sintering method, a sputtering method, a laser ablation method, a metal salt pyrolysis method, a metal complex pyrolysis method, a sol-gel method using alkoxide as a raw material, and the like.

  A method for synthesizing a single crystal oxide by the floating zone method will be exemplified below. The floating zone method is carried out by storing a sintered body of various powders, which are raw materials for oxides, in a furnace and then heating and melting the sintered body with a heating means such as a halogen lamp or a xenon lamp.

For example, in the case of a YAlO ₃ single crystal, a sintered body of a mixture of Y ₂ O ₃ powder and Al ₂ O ₃ powder is heated and melted in an infrared condenser having a heating means such as a xenon lamp or a halogen lamp. It can be suitably synthesized by the floating zone method.

The sintered body used as a raw material for the floating zone method may be a sintered body having a composition of YAlO _{3 or} a sintered body in a state where Y ₂ O ₃ and Al ₂ O ₃ are mixed. Sintering conditions for producing the sintered body that is a raw material of the floating zone method are not particularly limited, but the sintering temperature is preferably about 600 to 1100 ° C. Although the sintering time at the time of manufacturing the said sintered compact can be adjusted according to temperature, about 0.5 to 24 hours are preferable and about 1 to 12 hours are more preferable. The sintering atmosphere is not limited, and may be an oxidizing atmosphere (such as air) or a reducing atmosphere containing hydrogen.

In addition, when manufacturing a sintered compact, a transition metal and / or a compound containing a transition metal and / or a compound containing an alkaline earth metal are added to a mixture of Y ₂ O ₃ powder and Al ₂ O ₃ powder. Alternatively, an alkaline earth metal can be doped. For example, when doping with Ti, TiO ₂ may be added. Moreover, what is necessary is just to add CaO, when doping Ca.

Next, the obtained YAlO ₃ single crystal can be cut and polished into a thin plate to form an electroluminescent layer. The electroluminescent layer made of this single crystal oxide has the characteristics that the electroluminescence efficiency is high and the loss in which the emission intensity is reduced by scattering is the smallest. Note that the crystal plane of the oxide having a perovskite crystal structure and the plane of the electroluminescent layer are not limited from the viewpoint of directionality.

The electroluminescent layer can also be produced by a method in which a YAlO ₃ single crystal obtained by the floating zone method is pulverized to an average particle diameter of about 1 to 5 μm, and then a paste containing compression molding or pulverized material is formed and dried. In this method, even an electroluminescent layer having a shape difficult to produce by cutting and polishing can be easily formed. As a liquid component contained in the paste, for example, toluene, alcohol, water or the like can be used.

  Hereinafter, a method for synthesizing a polycrystalline oxide by a sintering method will be exemplified. This method is carried out by performing pulverization, compression, and sintering using various powders as raw materials for oxides as raw materials.

For example, in the case of LaAlO ₃ polycrystal, a mixture of La ₂ O ₃ powder and Al ₂ O ₃ powder is pulverized by a ball mill to form a slurry, dried, re-pulverized and then compressed and sintered in a furnace. By doing so, it can be suitably synthesized.

In addition, when manufacturing a sintered compact, a transition metal and / or a compound containing a transition metal and / or a compound containing an alkaline earth metal are added to a mixture of Y ₂ O ₃ powder and Al ₂ O ₃ powder. Alternatively, an alkaline earth metal can be doped. For example, when doping with Ti, TiO ₂ may be added. Moreover, what is necessary is just to add CaO, when doping Ca.

  Although sintering conditions are not specifically limited, As for sintering temperature, about 1400-1800 degreeC is preferable. Although sintering time can be adjusted according to temperature conditions (temperature rising rate etc.), about 0.5 to 24 hours are preferable and about 1 to 12 hours are more preferable. The sintering atmosphere is not limited, and may be an oxidizing atmosphere (such as air) or a reducing atmosphere containing hydrogen.

Next, the obtained LaAlO ₃ polycrystal can be formed into an electroluminescent layer by, for example, compressing or forming a paste containing a pulverized product after pulverization to an average particle size of about 1 to 5 μm. This sintering method is preferable because an electroluminescent layer with a small amount of impurities can be obtained by a relatively simple method.

  Although the thickness of an electroluminescent layer is not specifically limited, About 0.005-0.5 mm is preferable and about 0.01-0.1 mm is more preferable.

The electric conductivity of the electroluminescent layer is preferably about 10 ^{−6 to 1} S / cm, and more preferably about 10 ^{−5 to} 0.1 S / cm. The electrical conductivity of the electroluminescent layer is adjusted, for example, by controlling the concentration of transition metal and / or alkaline earth metal contained in the oxide. It is desirable to adjust these concentrations as long as the ultraviolet light extraction efficiency is not lowered.

  The electroluminescent layer is sandwiched between the opposing electrodes. An electrode is not specifically limited, The electrode (anode and cathode) used for a well-known electroluminescent element can be used.

  As the anode, a material having a high work function is preferable. Specific examples include metals such as gold and platinum; and transparent metal oxides such as indium-tin oxide (ITO). Among these, gold is preferable.

  The gold is substantially free from changes such as oxidation and is easily formed as a uniform thin film on the surface of the electroluminescent layer as an anode. Further, since the gold thin film electrode reflects light well, the reflection efficiency is high when light generated from the electroluminescent layer is reflected by the gold thin film electrode and taken out to the outside. The gold thin film electrode is formed by, for example, DC sputtering. This method allows electrodes to be formed under relatively mild conditions and in a short time, so that the electroluminescent layer is not exposed to severe redox conditions. There is almost no risk of obstruction.

  On the other hand, since the ITO is transparent, there is an advantage that light emission can be extracted through the ITO electrode. However, ITO may be difficult to form a thin film as compared with gold, and there is a risk of short circuit and non-uniform work function. The forming method is not DC sputtering but RF sputtering, vacuum deposition, or the like. Moreover, since ITO is an oxide in that case, it is necessary to manage oxidation-reduction conditions appropriately. Furthermore, since it is often exposed to strict conditions as compared with the gold thin film production conditions, depending on the conditions, there is a possibility that the physical property change of the electroluminescent layer occurs during the formation of the ITO electrode thin film, making it difficult to emit light.

As the cathode, a material having a small work function is preferable. Specifically, metals such as calcium, sodium, magnesium, and aluminum are preferable. Magnesium is preferably used as an alloy (for example, obtained by co-evaporation) or a mixture with silver or indium from the viewpoint of oxidation resistance and adhesion to the electroluminescent layer. Aluminum is most practical in consideration of stability over time because it is less oxidized in the atmosphere than calcium, sodium and magnesium. Aluminum is also preferable because it reflects light well and can easily form a uniform thin film under mild conditions such as vacuum deposition.

  As a combination of the anode and the cathode, for example, a combination of gold and aluminum is preferable.

  Although the thickness of an electrode is not limited, Usually, about 20-1000 nm is preferable and about 50-500 nm is more preferable.

  As the structure of the electroluminescent element, a laminate of a lower electrode / electroluminescent layer / resistance / upper electrode is the simplest structure. Either the lower electrode or the upper electrode is used as an anode or a cathode. The electrode on the side from which light emission is extracted (at least one) is preferably transparent. Transparency includes translucency as long as light emission can be extracted. In addition, light emission may be extracted by using a comb-shaped opaque electrode.

The electroluminescent element may include an auxiliary layer (such as an insulating layer), a substrate, and the like as necessary. Next, a specific structure of the electroluminescent element is given.
1) Structure consisting of lower electrode / insulating layer / electroluminescent layer / resistance / transparent upper electrode,
2) Structure consisting of glass substrate / transparent lower electrode / electroluminescent layer / resistance / transparent upper electrode,
3) Structure consisting of (substrate of plastic, ceramics, etc.) / Lower electrode / electroluminescent layer / resistance / transparent upper electrode.

  The above 1) has an insulating layer for preventing dielectric breakdown. The emitted light can be extracted through the transparent upper electrode.

  In 2) above, the glass substrate and both electrodes are transparent, and light emission can be extracted from both sides of the electroluminescent layer.

  The structure 3) has an opaque substrate. The emitted light can be extracted through the transparent upper electrode.

  Note that the structure of the electroluminescent element is not limited to the above, and includes a structure in which a plurality of sets of electroluminescent layers and upper electrodes are stacked on the lower electrode formed on the substrate.

  The insulating layer prevents dielectric breakdown due to an excessive current, and can be placed between one or both of the electroluminescent layer and the upper electrode and between the electroluminescent layer and the lower electrode.

The material of the insulating layer is not particularly limited as long as an insulating effect can be obtained. For _{example, SiO 2, SiON, Al 2} O 3, Si 3 N 4, SiAlON, Y 2 O 3, BaTiO 3, Sm 2 O 3, Ta 2 O 5, BaTa 2 O 6, PbNb 2 O 6, Sr (Zr , Ti) O ₃ , SrTiO ₃ , PbTiO ₃ , HfO _{3 and the} like. Insulating ceramics combining these can also be used.

  The thickness of the insulating layer is desirably thin as long as insulation can be obtained. Usually, about 50-800 nm is preferable and about 100-400 nm is more preferable.

  The electroluminescent element preferably further includes a light reflecting layer. The light reflecting layer is usually provided on the side opposite to the side from which emitted light is extracted. By providing the light reflecting layer, directivity is generated in light emission, and the intensity (luminance) of light is increased. As the light reflecting layer, for example, a transparent material having a high refractive index can be used in addition to a glittering material such as aluminum, silver, and gold. The thickness of the light reflecting layer is not limited, but is preferably 100 nm or more, particularly 200 nm or more from the viewpoint of reflection efficiency.

It said electroluminescent device (1) as the maximum value of the current density flowing between the electrodes is 10 .mu.A / cm ² or more, between the electrodes, the frequency 0.1Hz~10kHz pulse voltage electric field strength 10 ⁴ V / cm By applying as described above, ultraviolet light of 200 to 400 nm is emitted. Further, the electroluminescent device (2) as the maximum value of the current density flowing between the electrodes is 10 .mu.A / cm ² or more, between the electrodes, the electric field strength 10 ⁵ V pulse voltage having a frequency 0.1Hz~1kHz By applying at / cm or more, 200 to 400 nm ultraviolet light and light exceeding 400 nm and 2500 nm or less (visible to near infrared light) are simultaneously emitted.

In any of the cases (1) and (2), the maximum value of the current density flowing between the electrodes may be set to 10 μA / cm ² (0.01 mA / cm ² ) or more. ² or more is preferable, and 1 mA / cm ² or more is more preferable. The maximum value of the current density refers to the maximum value of the current density that instantaneously flows between the electrodes when a pulse voltage is applied.

In the case of (1) above, a pulse voltage having a frequency of 0.1 Hz to 10 kHz is applied at an electric field strength of 10 ⁴ V / cm or more. The frequency is preferably 0.1 Hz to 1 kHz, and more preferably 1 Hz to 1 kHz. The electric field strength may be 10 ⁴ V / cm or more, preferably 10 ⁵ V / cm or more, and more preferably 10 ⁶ V / cm or more. By applying a pulse voltage under such conditions, ultraviolet light having a wavelength of 200 to 400 nm can be obtained.

In the case of (2) above, a pulse voltage having a frequency of 0.1 Hz to 1 kHz is applied at an electric field strength of 10 ⁵ V / cm or more. The frequency is preferably 0.1 Hz to 100 Hz, and more preferably 1 Hz to 100 Hz. Field strength may be at 10 ⁵ V / cm or more, but preferably as long as 5 × 10 ⁵ V / cm or more, more preferably equal to 10 ⁶ V / cm or more. By applying a pulse voltage under such conditions, ultraviolet light having a wavelength of 200 to 400 nm and light of more than 400 nm and not more than 2500 nm (for example, 410 to 2500 nm) (visible to near infrared light) can be obtained simultaneously.

  The power source for generating the pulse voltage is not limited, and for example, a bipolar power source that can apply the pulse voltage at the above frequency can be used.

  Although the waveform of the pulse voltage is not limited, a waveform (bipolar symmetric drive waveform) obtained by adding a relaxation time without voltage application to a rectangular rectangular wave is preferable. That is, it is preferable to change the applied voltage periodically over time from zero → positive (constant value, constant time) → zero (relaxation time) → negative (constant value, constant time) → zero (relaxation time). The positive / negative voltage application time and the relaxation time vary depending on the frequency of the pulse voltage. When this waveform is used, since the pulse voltage rises (or drops) steeply from zero to a positive and negative maximum value, carrier injection from the electrode to the electroluminescent layer is likely to occur. In addition, the electroluminescent layer is allowed to cool during the relaxation time, and an excessive temperature rise is easily suppressed. Thereby, it is considered that strong ultraviolet light emission and ultraviolet / near infrared light emission can be easily obtained at the same time. On the other hand, when a rectangular wave with no relaxation time or a sine wave or triangular wave without a steep voltage change is used, the light emission characteristics tend to be weaker than when a bipolar symmetric drive waveform is used. In addition, when a pulse voltage is applied using a bipolar power supply, both of the counter electrodes may function as both an anode and a cathode.

Note that a resistor is preferably connected in series with the electroluminescent element between the electrode and the power source.
In order to extract ultraviolet light from the electroluminescent layer, it is necessary that a current flow through the electroluminescent layer. At this time, when a relatively low voltage is applied, there is little risk of damage to the electroluminescent layer without connecting resistors in series. On the other hand, when a relatively high voltage is applied, an excessive current flows through the electroluminescent layer, and the electroluminescent layer may be damaged due to a large Joule heat. Therefore, in particular, when a high voltage is applied, it is necessary to connect a resistor in series.

  Further, connecting the resistors in series is advantageous in addition to protecting the electroluminescent layer. That is, it is considered that ultraviolet light is easily generated by connecting a resistor. In other words, by connecting resistors in series, the electroluminescent layer and the resistor work together like a capacitor when a pulse voltage is applied between the electrodes, and accumulate more charge than when no resistor is connected. -It is believed that it emits and a large electric field is applied to the electroluminescent layer, thus making it easier to generate ultraviolet light.

The preferred magnitude of the resistance varies depending on the material, thickness, etc. of the electroluminescent layer. For example, the electroluminescent layer is YAlO ₃ , LaAlO _3, etc., and has a diameter of 2-3 mm and a thickness of 0.1-0. In the case of a 3 mm disk, the resistance value is desirably set as follows. That is, in the case of the above (1), it is desirable to connect a resistance of 1Ω to 1MΩ (preferably 10Ω to 100 kΩ, more preferably 10Ω to 10 kΩ) in series. In the case of (2) above, it is desirable to connect a resistance of 1Ω to 100 kΩ (preferably 1Ω to 10 kΩ, more preferably 1Ω to 1 kΩ) in series. Even when the connected resistance is smaller than 1Ω or when no resistance is connected, light emission is observed although it is weak.

  The mechanism by which ultraviolet light (and visible to near-infrared light) is generated from the electroluminescent layer depending on the driving conditions is not clear, but is considered as follows.

  That is, it is considered that no current flows through the electroluminescent layer when a pulse voltage is applied under the driving conditions for obtaining only visible light as has been clarified by the inventors. That is, when only visible light is obtained, carriers (electrons and holes) accelerated by a high voltage collide with the emission center in the electroluminescent layer, the emission center is excited, and then returns to the ground state. It is considered that light emission has occurred.

  On the other hand, when ultraviolet light is generated, carriers (electrons and holes) are injected from the electrode into the electroluminescent layer to form electron-hole pairs in the electroluminescent layer, and then electrons. It is conceivable that light emission is generated by exciting the light emission center in the electroluminescent layer when recombination with holes. When the applied voltage is increased based on the driving conditions for generating ultraviolet light, the generated ultraviolet light intensity increases, and in addition, visible to near-infrared light is generated simultaneously. As a cause of this phenomenon, for example, the generated ultraviolet light may excite the electroluminescent layer that is a phosphor, and as a result, the electroluminescent layer may generate fluorescence in the visible to near-infrared wavelength region. .

  In addition, ultraviolet light generated by applying a pulse voltage, or ultraviolet light and visible to near-infrared light cannot be generally described, but the pulse voltage is relatively low frequency and high voltage, and the connected resistance is low resistance. Tend to be strong, and weak when high frequency, low voltage, high resistance. When the frequency of the pulse voltage is low, the relatively long time during which the pulse voltage is applied at the maximum value is relatively appropriate for the time required for carrier injection into the electroluminescent layer and subsequent light emission. It is thought that it was. In addition, when the frequency of the pulse voltage is low, the time during which the voltage is not applied becomes long, so that the temperature of the electroluminescent layer that has risen due to Joule heat at the time of voltage application is sufficiently increased until immediately before the pulse voltage of the next period is applied. It is thought that it is advantageous for lowering, and such a relatively long cooling process may have acted to generate strong electroluminescence.

  In the electroluminescent element of the present invention, simultaneous emission of ultraviolet light (wavelength 200 to 400 nm) and visible to near infrared light (wavelength 400 to 2500 nm) can be obtained by changing the applied frequency applied to the electroluminescent element. That is, by selecting the driving conditions, in the electroluminescent device made of the same oxide, in addition to red and green, ultraviolet light, further ultraviolet light and visible to near infrared light can be generated.

  The ultraviolet light can also be used as an excitation light source for various phosphors. For example, a large number of electroluminescent elements of the present invention are arranged, a display panel combined with an appropriate phosphor is manufactured, and driving conditions are controlled for each electroluminescent element, so that light in various wavelength ranges can be obtained. Can be removed from the display panel.

  The present invention will be described below with reference to examples. However, the present invention is not limited to the examples.

Example 1
1% (mol% of Ti with respect to Al) titanium-doped YAlO ₃ single crystal (yellowish brown translucent) was obtained by the floating zone method.

  The single crystal was cut and polished to obtain a circular thin plate having a diameter of about 2.9 mm and a thickness of 0.137 mm.

  An aluminum electrode layer (cathode) having a thickness of 150 nm was formed on one side of the circular thin plate by a vacuum deposition method. A semicircular gold electrode layer (anode) having a thickness of 75 nm was formed on the half of the surface opposite to the cathode formation surface by DC sputtering. This produced the electroluminescent element.

  A platinum wire was connected to the cathode and anode of the electroluminescent element, and the end was connected to a bipolar power source. A 100Ω resistor was connected in series between the bipolar power source and the cathode (which may be the anode).

When a pulse voltage having a frequency of ± 4.4 × 10 ⁶ V / m and 1 kHz is applied to the electroluminescent element from a bipolar power source, several intense light emission appears in the wavelength range of 290 to 430 nm, and the peak wavelength Was 336 nm. Moreover, several weak light emission was seen in wavelength 220-250nm and 760-780nm. When a pulse voltage was applied, the maximum value of the current density flowing between the electrodes was 1 mA / cm ² or more.

  Here, as the pulse voltage waveform, a waveform obtained by adding a relaxation time without voltage application to a bipolar rectangular wave (bipolar symmetric drive waveform) was used. That is, the applied voltage was periodically changed from zero to positive (constant value, constant time) → zero (relaxation time) → negative (constant value, constant time) → zero (relaxation time) over time. The positive / negative voltage application time and the relaxation time vary depending on the frequency of the pulse voltage. In addition, when a rectangular wave, sine wave or triangular wave having no relaxation time was used as the pulse voltage waveform, weak ultraviolet light emission was observed.

  The relationship between the emission wavelength (nm) and the emission intensity (arbitrary unit) is shown in FIG.

Example 2
As in Example 1, a circular thin plate having a diameter of about 2.9 mm and a thickness of 0.137 mm made of a YAlO ₃ single crystal doped with 1% (mol% of Ti with respect to Al) was prepared, and an aluminum electrode having a thickness of 150 nm was prepared. A layer (cathode) and a semicircular gold electrode layer (anode) having a thickness of 75 nm were formed to produce an electroluminescent device.

  A platinum wire was connected to the cathode and anode of the electroluminescent element, and the end was connected to a bipolar power source. A 1 kΩ resistor was connected in series between the bipolar power source and the cathode or anode.

When a pulse voltage having an electric field intensity of ± 3.7 × 10 ⁶ V / m and a frequency of 50 Hz is applied to the electroluminescent element from a bipolar power source, several intense light emission appears in the wavelength range of 290 to 430 nm, and the peak wavelength Was 338 nm. Moreover, several moderately strong light emission was observed at wavelengths 515-555 nm and 760-780 nm, and weak light emission was observed at wavelengths 220-250 nm. Furthermore, a wide range of light emission was observed at a wavelength of 430 to 800 nm. When a pulse voltage was applied, the maximum value of the current density flowing between the electrodes was 1 mA / cm ² or more.

  Here, as the waveform of the pulse voltage, a bipolar symmetric drive waveform was used as in the first embodiment. In addition, when a rectangular wave, sine wave or triangular wave having no relaxation time was used as the pulse voltage waveform, weak ultraviolet light emission was observed.

  FIG. 2 shows the relationship between the emission wavelength (nm) and the emission intensity (arbitrary unit).

Example 3
As in Example 1, a circular thin plate having a diameter of about 2.9 mm and a thickness of 0.137 mm made of a YAlO ₃ single crystal doped with 1% (mol% of Ti with respect to Al) was prepared, and an aluminum electrode having a thickness of 150 nm was prepared. A layer (cathode) and a semicircular gold electrode layer (anode) having a thickness of 75 nm were formed to produce an electroluminescent device.

  A platinum wire was connected to the cathode and anode of the electroluminescent element, and the end was connected to a bipolar power source. A 1 kΩ resistor was connected in series between the bipolar power source and the cathode or anode.

When a pulse voltage having an electric field intensity of ± 1.1 × 10 ⁶ V / m and a frequency of 1 Hz is applied to the electroluminescent element from a bipolar power source, several intense light emission appears in the wavelength range of 260 to 400 nm, and the peak wavelength Was 328 nm. Moreover, several light emission (slightly weak-slightly strong) was seen by wavelength 515-555 nm, 580-600 nm, 760-780 nm. Furthermore, a wide range of strong light emission was observed at a wavelength of 400 to 800 nm, and the intensity of this wide light emission was maximum at around 700 to 800 nm. When a pulse voltage was applied, the maximum value of the current density flowing between the electrodes was 1 mA / cm ² or more.

  Here, as the waveform of the pulse voltage, a bipolar symmetric drive waveform was used as in the first embodiment. In addition, when a rectangular wave, sine wave or triangular wave having no relaxation time was used as the pulse voltage waveform, weak ultraviolet light emission was observed.

  FIG. 3 shows the relationship between the emission wavelength (nm) and the emission intensity (arbitrary unit).

Example 4
A YAlO ₃ single crystal (light brown translucent) doped with 0.1% (mol% of Ti with respect to Al) titanium was also obtained by the floating zone method.

  The single crystal was cut and polished to obtain a circular thin plate having a diameter of about 2.1 mm and a thickness of 0.137 mm.

  An aluminum electrode layer (cathode) having a thickness of 150 nm was formed on one side of the circular thin plate by a vacuum deposition method. A semicircular gold electrode layer (anode) having a thickness of 75 nm was formed on the half of the surface opposite to the cathode formation surface by DC sputtering. This produced the electroluminescent element.

  A platinum wire was connected to the cathode and anode of the electroluminescent element, and the end was connected to a bipolar power source. A 1 MΩ resistor was connected in series between the bipolar power source and the cathode (which may be the anode).

When a pulse voltage having a frequency of ± 6.6 × 10 ⁶ V / m and 10 Hz is applied to the electroluminescent element from a bipolar power source, several intense light emission appears in the wavelength range of 290 to 410 nm, and the peak wavelength Was 337 nm. Furthermore, a wide range of light emission was observed at a wavelength of 550 to 800 nm. When a pulse voltage was applied, the maximum value of the current density flowing between the electrodes was 1 mA / cm ² or more.

  Here, as the waveform of the pulse voltage, a bipolar symmetric drive waveform was used as in the first embodiment. In addition, when a rectangular wave, sine wave or triangular wave having no relaxation time was used as the pulse voltage waveform, weak ultraviolet light emission was observed.

  FIG. 4 shows the relationship between the emission wavelength (nm) and the emission intensity (arbitrary unit).

Example 5
YAlO ₃ single crystal (white translucent) doped with 0.1% (mol% of Ca to Al) calcium was obtained by the floating zone method.

  The single crystal was cut and polished to obtain a circular thin plate having a diameter of about 2.0 mm and a thickness of 0.245 mm.

  An aluminum electrode layer (cathode) having a thickness of 150 nm was formed on one side of the circular thin plate by a vacuum deposition method. A semicircular gold electrode layer (anode) having a thickness of 75 nm was formed on the half of the surface opposite to the cathode formation surface by DC sputtering. This produced the electroluminescent element.

  A platinum wire was connected to the cathode and anode of the electroluminescent element, and the end was connected to a bipolar power source. A 1 MΩ resistor was connected in series between the bipolar power source and the cathode (which may be the anode).

When a pulse voltage having a frequency of ± 3.3 × 10 ⁶ V / m and 10 Hz is applied to the electroluminescent element from a bipolar power source, several strong light emission appears in the wavelength range of 230 to 430 nm, and the peak wavelength Were 395 nm (maximum peak in the ultraviolet region), 338 nm (second largest peak in the ultraviolet region), and 329 nm (third largest peak in the ultraviolet region). Moreover, several light emission (slightly weak-slightly strong) was seen by wavelength 515-555 nm and 610-800 nm. Furthermore, although it was weak at wavelength 430-800 nm, wide light emission was seen. When a pulse voltage was applied, the maximum value of the current density flowing between the electrodes was 1 mA / cm ² or more.

  Here, as the waveform of the pulse voltage, a bipolar symmetric drive waveform was used as in the first embodiment. In addition, when a rectangular wave, sine wave or triangular wave having no relaxation time was used as the pulse voltage waveform, weak ultraviolet light emission was observed.

  FIG. 5 shows the relationship between the emission wavelength (nm) and the emission intensity (arbitrary unit).

When a pulse voltage was applied in the same manner as described above using 0.5% (mol% of Ca relative to Al) calcium-doped LaAlO ₃ single crystal (light yellow translucent), emission in the ultraviolet wavelength region was obtained.

On the other hand, when the maximum value of the current density is out of the range of claim 1, for example, 0.1 μA / cm ² or less, the pulse voltage applied between the electrodes is within the range of claim 1. That is, even when the frequency was 0.1 Hz to 10 kHz and the electric field intensity was 10 ⁴ V / cm or more, generation of ultraviolet light could not be observed.

It is a figure which shows the relationship between the light emission wavelength of the electroluminescent element of Example 1, and light emission intensity. It is a figure which shows the relationship between the light emission wavelength of the electroluminescent element of Example 2, and light emission intensity. It is a figure which shows the relationship between the light emission wavelength of the electroluminescent element of Example 3, and light emission intensity. It is a figure which shows the relationship between the light emission wavelength of the electroluminescent element of Example 4, and light emission intensity. It is a figure which shows the relationship between the light emission wavelength of the electroluminescent element of Example 5, and light emission intensity.

Claims (17)

An oxide electroluminescent device having an electroluminescent layer between opposing electrodes,
(1) The electroluminescent layer includes R as a rare earth element, M represents Al, Mn, or Cr, and includes an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ .
(2) The oxide further contains at least one selected from the group consisting of transition metals and alkaline earth metals,
(3) A pulse voltage having a frequency of 0.1 Hz to 10 kHz is applied between the electrodes at an electric field strength of 10 ⁴ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more. By emitting light having a wavelength of 200 to 400 nm,
An electroluminescent element characterized by the above. By applying a pulse voltage with a frequency of 0.1 Hz to 1 kHz between the electrodes at an electric field strength of 10 ⁵ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more, The electroluminescent element according to claim 1, which emits simultaneously light having a wavelength of 200 to 400 nm and light having a wavelength of more than 400 nm and not more than 2500 nm.   The electroluminescent device according to claim 1, wherein the rare earth element R is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.   The electroluminescent device according to claim 1, wherein the transition metal is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn.   The electroluminescent element according to claim 1, wherein the alkaline earth metal is at least one selected from the group consisting of Ca, Sr, and Ba.   2. The electroluminescent device according to claim 1, wherein the content of the transition metal with respect to the oxide is 0.05 to 2% in terms of mol% of the transition metal with respect to M. 3.   2. The electroluminescent device according to claim 1, wherein the content of the alkaline earth metal with respect to the oxide is 0.05 to 2% in terms of mol% of the alkaline earth metal with respect to M. 3.   The electroluminescent element according to claim 1, wherein at least one of the opposing electrodes contains at least one selected from the group consisting of gold and aluminum.   The electroluminescent element according to claim 1, wherein at least one of the opposing electrodes is transparent.   The electroluminescent element according to claim 1, further comprising a light reflecting layer. The electroluminescent device according to claim 1, wherein the oxide is YAlO ₃ containing Ti and / or Ca. The electroluminescent device according to claim 1, wherein the oxide is LaAlO ₃ containing Ti and / or Ca.   The electroluminescent element according to claim 1, wherein the electroluminescent element is connected to a power source, and a resistor is further connected in series with the electroluminescent element between the electrode and the power source. A method of driving an oxide electroluminescent device having an electroluminescent layer between opposing electrodes,
(1) The electroluminescent layer includes R as a rare earth element, M represents Al, Mn, or Cr, and includes an oxide having a perovskite crystal structure represented by a general formula: RMO ₃ .
(2) The oxide further contains at least one selected from the group consisting of transition metals and alkaline earth metals,
(3) A pulse voltage having a frequency of 0.1 Hz to 10 kHz is applied between the electrodes at an electric field strength of 10 ⁴ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more. To emit light having a wavelength of 200 to 400 nm,
A driving method characterized by that. By applying a pulse voltage with a frequency of 0.1 Hz to 1 kHz between the electrodes at an electric field strength of 10 ⁵ V / cm or more so that the maximum value of the current density flowing between the electrodes is 10 μA / cm ² or more, The driving method according to claim 14, wherein light having a wavelength of 200 to 400 nm and light having a wavelength exceeding 400 nm and not more than 2500 nm are simultaneously emitted. The driving method according to claim 14, wherein the oxide is YAlO ₃ containing Ti and / or Ca. The driving method according to claim 14, wherein the oxide is LaAlO ₃ containing Ti and / or Ca.

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