JP2009152073A - Phosphor for electroluminescent, and electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phosphor for an inorganic EL element that suppress luminance degradation and that excel in luminescent quality, and to provide an inorganic EL element. <P>SOLUTION: Sulfur is further introduced into the luminescent layer of this inorganic EL element, by forming a sulfur-added layer on the surfaces of ZnS-based phosphor particles or adding a sulfur additive in a dispersant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inorganic electroluminescence (EL) element, in particular, a distributed AC EL element, and a phosphor used therefor.

  For example, an EL element is known as a thin light source used for a backlight of a mobile phone or the like. Examples of the EL element include an inorganic EL element, a light emitting diode, and an organic EL element. Among them, a dispersion type AC EL element that is one of the inorganic EL elements is widely used.

  Conventionally, zinc sulfide (ZnS) -based phosphors have been used as phosphors for distributed AC EL devices (see, for example, Patent Document 1). As this ZnS-based phosphor, for example, a material obtained by adding an activator made of Cu to a host material made of ZnS, or a coactivator (in addition to a ZnS matrix material and a Cu activator). Co-activator) to which Cl is added can be used. In the distributed AC EL device using this ZnS; Cu, Cl phosphor, when voltage is applied, Cu enters the ZnS crystal lattice and becomes an acceptor, and constitutes a light emission center together with donor impurities such as Cl. Cu that does not fit in the crystal lattice precipitates in a needle shape along the lattice defects of the crystal and can exist as copper sulfide. When a voltage is applied to the element, the electric field concentrates on the tip of needle-shaped copper sulfide. From acicular copper sulfide, electrons are emitted from the tip close to the positive electrode side and holes are emitted from the tip close to the negative electrode side. In the ZnS crystal, electrons are trapped by donor impurities and holes are trapped by acceptors. When the direction of the electric field is reversed, the trapped electrons jump out and move to the counter electrode side to recombine with the holes trapped in the acceptor, thereby generating EL light emission.

However, since electrons to be trapped by the impurity donor may enter sulfur defects generated in the light emitting layer during driving, even if the direction of the electric field is reversed, the necessary electrons do not jump out, As a result, there has been a problem that the light emission luminance is lowered.
JP 2005-132947 A

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a phosphor for an inorganic EL element and an inorganic EL element, in which luminance deterioration is suppressed and light emission quality is excellent.

  The phosphor for inorganic electroluminescence of the present invention includes phosphor particles containing zinc sulfide as a base material, and a layer containing a sulfur additive provided on at least a part of the surface of the phosphor particles. And

  The inorganic electroluminescent device of the present invention includes a pair of electrodes, and phosphor particles containing zinc sulfide as a base material interposed between the electrodes, a light emitting layer containing a sulfur additive, and a dispersant. It is characterized by that.

  When the present invention is used, the luminance degradation is suppressed, and an inorganic EL element having excellent light emission quality can be obtained.

  The phosphor for an inorganic EL element of the present invention includes ZnS-based phosphor particles containing ZnS as a base material, and a sulfur additive layer is formed on at least a part of the phosphor particle surface.

  The inorganic EL device of the present invention has a pair of electrodes and a light emitting layer provided between the electrodes. The light emitting layer includes ZnS-based phosphor particles, a sulfur additive, and a dispersant for dispersing them. Containing.

  One aspect of the inorganic EL element according to the present invention is an inorganic EL element using the phosphor for an inorganic EL element of the present invention, and the light emitting layer has a sulfur additive layer formed on at least a part of the surface thereof. And the dispersing agent for dispersing the phosphor.

  On the other hand, in another aspect of the inorganic EL device according to the present invention, the light emitting layer contains ZnS-based phosphor particles, a sulfur additive, and a dispersant in which these are individually dispersed.

  In one aspect of the inorganic EL device according to the present invention, the sulfur additive is present in the sulfur additive layer formed on at least a part of the surface of the phosphor particles, and in another aspect, the phosphor particles are dispersed. Further added to the dispersant.

  The sulfur additive used here is used as a sulfur source contained in the light emitting layer used in the present invention, and is distinguished from a ZnS-based compound used as phosphor particles. Alternatively, a material containing sulfur may be used.

  In still another aspect of the inorganic EL device of the present invention, it is possible to provide a layer containing sulfur on at least a part of the surface of the phosphor particles, and to further contain sulfur in the dispersant.

  According to the present invention, a ZnS phosphor is provided by providing a sulfur additive layer on the surface of ZnS phosphor particles and / or applying a dispersant added with a sulfur additive on the surface of ZnS phosphor particles. Sulfur is further introduced around the particles, and sulfur defects generated in the phosphor during the operation of the inorganic EL element can be compensated with sulfur existing around the phosphor particles, thereby suppressing a decrease in emission luminance. I can do it.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing a cross-sectional structure of an example of the inorganic EL element of the present invention.

As shown in the figure, this inorganic EL element is a so-called dispersion type AC EL element, and is formed on a transparent substrate 1 made of, for example, glass, a transparent electrode 2 formed thereon by ITO or the like, and a transparent electrode 2. Further, for example, a light emitting layer 3 containing a dispersing agent such as ZnS; Cu, Cl phosphor, S, and cyanoethyl cellulose, a dielectric layer 4 made of, for example, BaTiO ₃ formed on the light emitting layer 3, and a dielectric On the transparent substrate 1 so as to seal the back electrode 5 made of, for example, Al formed by vapor deposition on the layer 4 and the transparent electrode 2, the light emitting layer 3, the dielectric layer 4, and the back electrode 5. And a moisture-proof film 6. Here, the phosphor particles 31 modelly show a part of the phosphor particles dispersed in the dispersant 32.

  When a voltage is applied from a power source 7 provided between the transparent electrode 2 and the back electrode 5 of the distributed AC EL element, EL is obtained from the light emitting layer 3 close to the transparent electrode 2 in the direction of the transparent electrode 2.

  Zn in the light emitting layer 3 is contained in, for example, a coating layer provided on the phosphor particles 31 and / or a dispersant 32 that disperses the phosphor particles 31.

  As a method for forming a coating layer on the surface of the phosphor particles, for example, a method in which phosphor particles are placed in a mesh cage and resistance heating vapor deposition is performed using S as a target, an electron beam vapor deposition method, a sputtering method, an ion plating method, a CVD method. For example, the existing vapor deposition method.

  In the present invention, for example, at least one activator selected from copper, fluorine, chlorine, bromine, iodine, and manganese can be added to the ZnS base material.

  The mixing molar ratio of the base material and the activator varies depending on the combination.

  For example, in the case of ZnS; Cu, Cl, 0.1 to 0.5 mol% of Cu and 1 to 15 mol% of Cl can be added to ZnS. Within this range, the light emission luminance and light emission efficiency of the phosphor are good.

  The ZnS-based phosphor used in the present invention preferably has a volume average particle size of 5 μm to 30 μm.

  As the dispersant, for example, cyanoethyl cellulose having a relatively high dielectric constant as an organic binder, polyester resin, or the like can be used.

  The weight ratio between the dispersant and the phosphor can be set to 55 to 70:45 to 30, for example.

  The light emitting layer can have a thickness of 30 to 100 μm after drying. When a light-emitting layer having a thickness in this range is used, necessary luminance can be obtained and the inorganic EL element can be driven at a low voltage.

  As the transparent electrode, for example, indium tin oxide (ITO), lead oxide (ZnO), or the like can be used.

  The transparent electrode layer preferably has a film thickness of 300 nm to 1 μm from the viewpoint of high visible light transmittance and low resistance to prevent power loss in the electrode layer.

  As a method for forming the transparent electrode layer, in addition to sputtering, a vapor-phase thin film forming method such as vapor deposition, a screen printing method, and a coating method such as a roll coater can be used.

As the dielectric layer, for example, a material in which a powder of BaTiO ₃ , SrTiO ₃ , TiO ₂ or the like is dispersed in an organic binder similar to the phosphor can be used.

  The film thickness of the dielectric layer can be 20 μm to 60 μm. Within this range, the dielectric constant of the layer can be increased while ensuring the withstand voltage.

  The thickness of the back electrode layer can be formed in the range of 300 nm to 1 μm. In addition to Al, a conductive material such as Ag, Cu, or C can be used as the electrode material.

  As the moisture-proof film, for example, a film such as PCTFE, PTFE, or PFA can be used. The thickness of the moisture-proof film can be 20 μm to 200 μm.

  EXAMPLES Hereinafter, an Example is shown and this invention is demonstrated more concretely.

Example 1
ZnS powder with an average particle diameter of 1 μm, 0.3 mol% Cu ₂ S powder with respect to ZnS, and 10 mol% NaCl powder are mixed and calcined at 1000 ° C. for 2 hours in 1 atmosphere of H ₂ S gas. Done. ZnS: Cu, Cl phosphor particles having a volume average particle diameter of 20 μm were obtained.

  ZnS: Cu, Cl phosphor particles are put in a mesh cage, sulfur is formed on the surface of the ZnS: Cu, Cl phosphor by resistance heating vapor deposition using sulfur as a target, and the present invention is applied. A ZnS-based phosphor with a sulfur additive layer was obtained.

  The sulfur-coated phosphor and a DuPont product name EL ink 8155 as a binder resin were mixed at a weight ratio of 55:45 to prepare a phosphor ink for screen printing.

  For example, a 300-nm-thick transparent electrode layer was formed on a 3 mm-thick glass substrate by sputtering indium oxide (ITO) to form a pattern. On the glass substrate in which the transparent electrode layer was formed, the said phosphor ink was apply | coated and dried by screen printing, and the light emitting layer which has a thickness of 30 micrometers was obtained.

A dielectric layer containing a dielectric powder such as BaTiO ₃ was formed on the light emitting layer by screen printing and drying.

  As screen printing ink, a dielectric layer paste for electroluminescence panel, product name Dotite FEL-615 manufactured by Fujikura Kasei Co., Ltd. was used. The film thickness of the dielectric layer after drying was 30 μm.

  On the dielectric layer, Al was deposited to form a back electrode layer having a thickness of 300 nm.

  Furthermore, the PCTFE film was laminated on the substrate on which the transparent electrode layer, the light emitting layer, the dielectric layer, and the back electrode layer were formed, and sealed to obtain a distributed AC EL device according to the present invention.

  The obtained dispersion type AC EL element was driven at 200 V AC, 8 kHz for 24 hours, and the initial luminance and the luminance after 24 hours were measured using a Topcon luminance meter BM-8, and the initial luminance was set to 100%. In this case, the relative luminance after 24 hours was obtained, and it was a good result of 75%.

As a modification of Example 1, when preparing phosphor particles, the average particle size of ZnS powder was changed to 1 to 20 μm, and the amount of Cu ₂ S powder added to ZnS was 0.2 to 1 mol%. The amount of NaCl powder added to ZnS was changed to 1 to 15 mol%, and the mixture was baked at 1000 ° C. for 2 to 4 hours in 1 atmosphere of H ₂ S gas. Various ZnS: Cu, Cl phosphors having an average particle diameter of 5 to 30 μm were obtained.

  These ZnS: Cu, Cl phosphor particles were put in a mesh basket, and a sulfur layer was formed on the phosphor surface in the range of an average film thickness of 100 nm to 1 μm using resistance heating vapor deposition.

  A phosphor coated with sulfur and a binder resin (trade name EL ink 8155 manufactured by DuPont Co., Ltd.) are mixed at a mixing weight ratio of 55 to 70:45 to 30 to mix various fluorescent materials for screen printing. Body ink was made.

  On the glass substrate, ITO or ZnO was used to form a transparent electrode layer by sputtering while changing the film thickness from 300 nm to 1 μm.

  On the glass substrate in which the transparent electrode layer was formed, the above-mentioned various phosphor inks were applied and dried by screen printing so that the film thickness after drying was 30 to 100 μm to obtain a light emitting layer.

A dielectric layer containing a dielectric powder such as BaTiO ₃ was formed on the light emitting layer by screen printing and drying. As the screen printing ink, a pressure-resistant dielectric layer paste for an electroluminescence panel (Fujikura Kasei Co., Ltd .: Dotite FEL-615) was used, and screen printing was performed so that the film thickness after drying was 20 to 60 μm.

  Further, a back electrode layer was formed on the dielectric layer by changing the film thickness in the range of 300 nm to 1 μm by Al deposition.

  For the purpose of enhancing the moisture-proof effect, the transparent electrode layer, the light-emitting layer, the light-emitting layer, the light-emitting layer, the dielectric layer, and the back electrode layer are formed on the substrate on which the thickness is changed in a range of 20 μm to 100 μm. Lamination with a PCTFE film was performed so as to enclose the dielectric layer and the back electrode layer, thereby obtaining a distributed AC EL device.

  When the relative luminance after driving for 24 hours with respect to the initial luminance was measured in the same manner for the obtained dispersion type AC EL device, good results were obtained.

Example 2
The same ZnS: Cu, Cl phosphor particles as in Example 1, sulfur, and the same binder resin as in Example 1 are mixed at a weight ratio of 55:10:35 to produce phosphor ink for screen printing. did.

  On the glass substrate which has the transparent electrode layer with a film thickness of 300 nm formed in the same manner as in Example 1, the phosphor ink was applied by screen printing and dried to obtain a light emitting layer having a film thickness of 30 μm. .

A dielectric layer containing a dielectric powder such as BaTiO ₃ is screen-printed on the light emitting layer and dried. As the screen printing ink, a pressure-resistant dielectric layer paste for electroluminescence panel (Fujikura Kasei Co., Ltd .: Dotite FEL-615) was used. The film thickness of the dielectric layer after drying was 30 μm.

  On the dielectric layer, Al was vapor-deposited to form a 300 nm-thick back electrode layer to obtain an inorganic EL element.

  The transparent electrode layer, the light emitting layer, the dielectric layer, and the back electrode layer are sealed for the purpose of enhancing the moisture-proof effect on the substrate on which the transparent electrode layer, the light emitting layer, the dielectric layer, and the back electrode layer are formed. A PCTFE film having a thickness of 40 μm was laminated.

  For the obtained dispersion type AC EL element, the relative luminance after driving for 24 hours with respect to the initial luminance was measured, and a good result of 58% was obtained.

Comparative Example 1
A dispersion type AC EL device was obtained in the same manner as in Example 1 except that the sulfur additive layer was not formed on the surface of the phosphor particles.

  For the obtained dispersion type AC EL element, the relative luminance after driving for 24 hours with respect to the initial luminance was measured in the same manner, and a slightly inferior result of 51% was obtained.

The schematic diagram showing the cross-section of an example of the inorganic EL element concerning this invention

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Transparent electrode, 3 ... Light emitting layer, 4 ... Dielectric layer, 5 ... Back electrode, 6 ... Moisture-proof film, 10 ... Dispersion type | mold alternating current EL element, 31 ... Phosphor particle, 32 ... Dispersant

Claims (7)

  An inorganic electroluminescent phosphor comprising phosphor particles containing zinc sulfide as a base material and a layer containing a sulfur additive provided on at least a part of the surface of the phosphor particles.   The inorganic material according to claim 1, wherein the phosphor particles further contain at least one element selected from the group consisting of copper, fluorine, chlorine, bromine, iodine, and manganese as an activator. Phosphor for electroluminescence.   The inorganic electroluminescent phosphor according to claim 1 or 2, wherein the sulfur additive is added in an amount of 0.2 mol% to 1 mol% with respect to the phosphor particles.   An inorganic electroluminescent device comprising: a pair of electrodes; and a phosphor layer containing zinc sulfide as a base material interposed between the electrodes, a light emitting layer containing a sulfur additive, and a dispersant. .   The inorganic electroluminescent device according to claim 4, wherein the phosphor particles further include a layer containing a sulfur additive on at least a part of a surface thereof.   The inorganic electroluminescent element according to claim 4 or 5, wherein the phosphor particles and the sulfur additive are separately dispersed in the dispersant.   The inorganic electroluminescence device according to any one of claims 4 to 6, wherein the sulfur additive is added in an amount of 10 mol% to 60 mol% with respect to the phosphor particles.

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