JP4609988B2 - Method for producing zinc oxide phosphor - Google Patents

Description

  The present invention relates to a method for producing a zinc oxide phosphor that emits fluorescence in the purple or green region by electron beam excitation, and more specifically, by using a Zn chelate complex as a starting material, spherical fine particles having almost uniform particle sizes. In addition, the present invention relates to a novel method for producing a zinc oxide phosphor that emits ultraviolet light or green light by electron beam excitation by controlling the firing temperature of the starting material.

  Zinc oxide phosphor has conductivity and emits green fluorescence efficiently even at a low acceleration voltage. Therefore, it is widely used as a low-voltage driven type green phosphor such as a fluorescent display tube. It's being used. This phosphor is known to be a so-called self-activated type in which Zn generated by oxygen deficiency of ZnO forms a light emission center, and is described as ZnO: Zn. The emission characteristics of ZnO are strongly related to the control of impurity levels existing in the crystal and the state of grain boundary interface levels existing in ceramics. For example, the green emission of ZnO: Zn is within the band gap. This is due to impurity levels such as oxygen vacancies existing in the substrate.

  On the other hand, when the crystallinity of zinc oxide is improved by eliminating lattice defects, the efficiency of band edge emission (exciton emission) having a band gap of 3.3 eV is increased, and as a result, ultraviolet emission having a peak at 385 nm is obtained. This zinc oxide having ultraviolet light emission is considered promising as one of the materials for realizing high efficiency of ultraviolet light emission, which has been actively performed in recent years.

ZnO: Zn that emits green fluorescence is generally obtained by adding a small amount of ZnS to ZnCO ₃ or ZnO, crushing and mixing, and then reducing and firing in a mixed atmosphere of nitrogen gas / hydrogen gas. In the pulverization / mixing step, the solid phases must be sufficiently mixed by a ball mill or the like so that the solid phases can be mixed uniformly. In addition, since the fired product is obtained in the form of a lump, in order to obtain a phosphor powder, the fired product must be pulverized and further washed with water, which makes the process very complicated.

  In addition, zinc oxide having ultraviolet emission can be obtained by increasing the crystallinity of zinc oxide as described above. For example, it is known that zinc oxide can be obtained by annealing in an oxygen atmosphere (Patent Document 1, etc.), and electrically active electrons based on defects in the zinc oxide crystal are treated with hydrogen plasma treatment. It is also known that the ultraviolet light emission intensity is increased by so-called passivating treatment that is inactivated by (Non-Patent Document 1).

  However, as described above, zinc oxide is considered to be promising as an ultraviolet light emitting element, and the high-crystallinity zinc oxide thin film obtained exclusively by PVD or CVD has been studied. At present, it has not been studied so much in the form of powder that tends to occur.

In addition, as the display becomes more accurate and denser in the future, it will be necessary to apply the phosphor to the phosphor screen more precisely and uniformly. To meet these demands, the phosphor itself must be in a powder state. It is necessary to increase the dispersibility and reduce the particle size. In order to satisfy such conditions, it is desired that the phosphor powder is a fine particle having a substantially spherical shape and a substantially uniform particle size. However, most of the powdered zinc oxide phosphors that are currently in practical use are distorted lump, and modification from such a viewpoint is required.
JP-A-8-127769 Jpn. J. Appl. Phys. Vol. 36 (1997) 289-291

  The present invention has been made under such circumstances, and its purpose is to form particles that are substantially spherical and have a uniform particle size so that the display can be easily adapted to high precision and high density as described above. The object is to provide a method capable of efficiently producing a form-controlled zinc oxide phosphor.

The method for producing a zinc oxide phosphor according to the present invention, which has achieved the above-mentioned problems,
(1) a step of producing a powder comprising an organometallic chelate complex of Zn;
(2) A step of firing the powder obtained in the step (1) to obtain a zinc oxide powder,
(3) It is characterized in that it includes a step of reducing the zinc oxide powder obtained in the step (2).

  The zinc oxide phosphor obtained by the present invention is in the form of a substantially spherical fine powder having a substantially uniform particle size, and a typical example of the phosphor is an ultraviolet ray having an emission peak near 390 nm by electron beam excitation. It is a light-emitting zinc oxide phosphor or a green light-emitting zinc oxide phosphor having an emission peak near 500 nm by electron beam excitation.

  In carrying out the above production method of the present invention, in the step (1), a Zn chelate complex aqueous solution obtained by reacting Zn and / or a Zn compound and an organic chelate forming agent is spray-dried to form a powder. , The Zn chelate complex powder, which is the precursor of the zinc oxide phosphor, can be efficiently obtained as a fine powder with a substantially spherical shape and uniform particle size by instantaneous drying. Thus, the zinc oxide phosphor obtained through the subsequent firing step and reduction step is also preferable because it can be obtained as a fine powder having a substantially spherical shape and a substantially uniform particle size. However, in the above description, “substantially spherical” means that each individual powder has a substantially spherical shape, and does not have to be a perfect spherical shape, but an oval shape, an oval shape, or a partially broken piece. It may be a piece, and the shape itself does not affect the light emission characteristics.

  As the organic chelate forming agent used in the present invention, an aminocarboxylic acid chelating agent and / or a salt thereof is optimal.

  According to the present invention, an ultraviolet light emitting type having an emission peak near 390 nm by electron beam excitation, or a green light emitting characteristic having an emission peak near 500 nm, and having a substantially spherical and fine powdery shape with substantially uniform particle diameters. A zinc oxide phosphor can be produced efficiently. The obtained zinc oxide phosphor is a green phosphor ZnO: Zn as a low voltage driving type green phosphor for a field emission display (FED) or a fluorescent display tube (VFD), and for an ultraviolet light emitting type, an ultraviolet ray. It can be used extremely effectively as a light emitting element, a laser light emitting element, an excitation source of a phosphor, and the like.

  The present invention is characterized in that Zn chelate complex powder is used as a raw material when producing a zinc oxide phosphor. The Zn chelate complex powder as a precursor here is prepared by reacting a zinc raw material (Zn and / or Zn compound) with an organic chelate forming agent to prepare a clear aqueous solution of an organic Zn chelate complex, and then spraying this aqueous solution, for example, by spray drying. Can be easily obtained.

  As the organic chelate forming agent, an aminocarboxylic acid chelating agent which is preferably not thermally decomposed at a temperature of about 200 ° C. is preferably used so as not to cause thermal decomposition in the drying step. In preparing the organic Zn chelate complex aqueous solution, it is preferable to use a chelating agent equivalent to or more than Zn to form a clear aqueous solution so that the Zn ions can completely form a complex salt.

  The organic Zn chelate complex powder obtained by using a clear aqueous solution of a Zn chelate complex as described above, preferably by adopting a method of instantly drying the clear aqueous solution by spray drying is amorphous and has molecular This is because the composition has a uniform composition at the level, and the appearance is obtained as a fine powder having a substantially spherical shape and uniform particle diameter. Moreover, as will be clarified in the examples described later, it can be manufactured with fewer steps compared to the conventional method of manufacturing a zinc oxide phosphor. Furthermore, by controlling the firing conditions of the organic Zn chelate complex powder, it is possible to easily produce a green light emitting zinc oxide phosphor and an ultraviolet light emitting zinc oxide phosphor by electron beam excitation.

  That is, the organic Zn chelate complex powder obtained by the spray drying method has a substantially spherical shape, which is the characteristic, and the particle size is almost uniform. It can be obtained as a zinc oxide phosphor powder. Moreover, if the powdering conditions at the time of spray drying are appropriately controlled, and the shape and particle size of the powder comprising the Zn chelate complex as the precursor are adjusted, the shape of the obtained zinc oxide phosphor powder and It is possible to arbitrarily adjust the particle size and further the particle size distribution.

  In addition, since the zinc oxide phosphor prepared from the organic Zn chelate complex powder is substantially spherical and does not have directionality as described above, it can be applied to various applications using an electron beam as an excitation source. Exhibits high suitability for excitation sources of phosphors, including ultraviolet light emitting devices and laser light emitting devices. However, in the present invention, as described above, individual powders are not limited to those having a substantially spherical shape, but are oval, oval, or crushed pieces in which a part thereof is broken. They may be included in the technical scope of the present invention.

  Next, the manufacturing method of a zinc oxide fluorescent substance is demonstrated in detail.

  (1) In producing the phosphor of the present invention, first, a powder composed of an organic Zn chelate complex is produced in the first step. The powder is produced, for example, as follows. First, Zn and / or Zn compound is reacted with an organic chelate forming agent to prepare a clear organic Zn chelate complex aqueous solution. This reaction is carried out in an aqueous medium, for example, at a temperature of 20 ° C to boiling point, preferably 50 to 70 ° C. A preferable aqueous solution concentration is 5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 20% by mass or less in terms of solid content, but it is of course not limited to these temperature range and concentration range.

  The amount of the organic chelate-forming agent used is preferably equal to or greater than that of Zn ions so that all Zn can be completely dissolved, and is preferably 1.0 to 1.5 times mol. If the Zn chelate complex is not completely dissolved, it is preferable to add ammonia, amine or the like and completely dissolve it.

  As the Zn raw material, metal zinc, carbonate, nitrate, hydroxide, oxide, and the like can be used, but particularly preferable in the present invention is metal zinc, carbonate from the viewpoint that no extra ions remain after the reaction. Hydroxides and oxides are preferable, and oxides and carbonates having good reactivity are most preferable.

  By the way, the most serious problem in producing a zinc oxide phosphor is the mixing of impurity elements, and sodium salts, potassium salts, etc. remain in the phosphor even after pyrolysis, especially among organometallic chelate complexes. Therefore, use should be avoided. Also, inorganic acids and inorganic acid salts (such as hydrochloric acid, sulfuric acid, phosphoric acid or their salts) and organic substances (such as thiol compounds) containing chlorine, sulfur, phosphorus, etc., are almost completely thermally decomposed during firing, but are uniform Since there is a possibility of adversely affecting the formation of a Zn chelate complex having a composition, it is desirable to suppress it as much as possible.

  Examples of the organic chelate forming agent used in the present invention include ethylenediaminetetraacetic acid, 1,2-cyclohexanediaminetetraacetic acid, dihydroxyethylglycine, diaminopropanoltetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminediacetic acid, ethylenediaminedipropionic acid, hydroxyethylenediaminetriacetic acid. , Glycol ether diamine tetraacetic acid, hexamethylenediamine tetraacetic acid, ethylenediamine di (o-hydroxyphenyl) acetic acid, hydroxyethyliminodiacetic acid, iminodiacetic acid, 1,3-diaminopropanetetraacetic acid, 1,2-diaminopropanetetraacetic acid Nitrilotriacetic acid, nitrilotripropionic acid, triethylenetetramine hexaacetic acid, ethylenediamine disuccinic acid, 1,3-diaminopropane disuccinic acid, glutamic acid-N, N-diacetic acid, Aspartic acid -N, N-diacetic acid, may be mentioned water-soluble aminocarboxylic acid chelating agents such as, can be used any of these monomers, oligomers or polymers.

  Use free acid type, ammonium salt or amine salt in consideration of chelate formation constant with Zn, stability of chelate complex, and solubility of chelate complex in water or alkaline aqueous solution. Is preferred.

  The organic Zn chelate complex aqueous solution prepared as described above is then pulverized by spray drying. The conditions for spray drying may be set as appropriate depending on the concentration of the aqueous solution, the solution processing speed, the amount of sprayed air, the amount of hot air, and the like. What is necessary is just to employ | adopt the temperature which can be dried. From this point of view, the drying temperature is preferably in the range of about 100 to 200 ° C, and more generally in the range of 140 to 180 ° C. In view of such a drying temperature, it is desirable to select an aminocarboxylic acid chelating agent used in the present invention that does not thermally decompose at a temperature of about 200 ° C. or lower.

  (2) The powder obtained in the step (1) is then fired to form a metal oxide powder. Preferred conditions at this time are as follows.

  When the powder containing the organic Zn chelate complex obtained in the step (1) is baked as it is, the organic component is thermally decomposed to become zinc oxide powder. When baked at 500 ° C. or higher, all organic components are decomposed and burned to become zinc oxide. However, if the baking temperature is less than 800 ° C., only a very weak light emission can be obtained even after subsequent reduction treatment. It is desirable to set it at 800 ° C. or higher. Note that the atmosphere during firing and heat treatment is not necessarily in air, and may be performed in an oxygen-enriched atmosphere, a neutral atmosphere, or a reducing atmosphere as necessary.

  (3) The zinc oxide powder obtained in the above step (2) is then subjected to a reduction treatment. For the reduction treatment at this time, the zinc oxide powder obtained in the step (2) may be heat-treated in a reducing atmosphere. A preferable heat treatment temperature is 500 to 1200 ° C, and more preferably 600 to 1000 ° C. The reducing atmosphere is not particularly limited as long as it is a weakly reducing atmosphere containing hydrogen, but an argon / hydrogen mixed atmosphere or a nitrogen / hydrogen mixed atmosphere is preferable. When the product fired at 900 ° C. in the above step (2) is reduced, green light emission with an emission peak of about 500 nm is obtained, and when the product fired at 1000 ° C. is reduced, ultraviolet light emission with an emission peak of about 390 nm is obtained. It is done.

  The steps (2) and (3) may be performed using different firing furnaces, or may be performed continuously by changing the firing atmosphere and temperature in one firing furnace. is there.

  As described above, according to the present invention, a process of producing an organic Zn chelate complex powder by decomposing an organic substance in the presence of oxygen to produce a zinc oxide powder, and treating the obtained zinc oxide powder in a hydrogen-containing reducing atmosphere. By carrying out the steps, a zinc oxide phosphor having ultraviolet emission whose emission peak is around 390 nm or a Zn phosphor having green emission whose emission peak is around 500 nm can be easily obtained.

  The organic Zn chelate complex powder used in practicing the present invention is prepared by reacting a Zn raw material with an organic chelate forming agent as described above to prepare a clear organic Zn chelate complex aqueous solution, and then drying the aqueous solution. However, it is desirable to employ a spray drying method for the drying at this time. That is, the spray-drying method is easy to obtain fine spherical particles having a uniform particle diameter as described above. As the organic chelate forming agent used here, an aminocarboxylic acid chelating agent is preferably used.

  The ultraviolet light emission type zinc oxide phosphor powder according to the present invention can be applied to various uses using an electron beam as an excitation source, for example, but it is extremely useful as an excitation source for phosphors such as an ultraviolet light emitting element and a laser light emitting element. Can be used effectively.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1
In a 1 liter beaker, 115 g of ethylenediaminetetraacetic acid (EDTA) and water were added to make the total amount 500 g, and then 54 g of aqueous ammonia was added and dissolved. While stirring this, 31 g of zinc oxide was added, and then the temperature was raised to 100 ° C. and stirring was continued for 0.5 hour to completely dissolve the mixture. Water was added to this solution to adjust the concentration to obtain a colorless and transparent aqueous Zn-EDTA complex solution.

  This solution was pulverized by a spray drying method at a drying temperature of 160 ° C. to obtain a Zn-EDTA complex powder. When the X-ray diffraction chart of this powder was confirmed, it showed a halo figure due to scattering of incident X-rays, and the crystal structure was amorphous.

  The complex powder was baked at 700 to 1000 ° C. for 3 hours in an air atmosphere using an open air electric furnace to thermally decompose and remove organic substances to obtain a zinc oxide powder. FIG. 1 is an SEM photograph of the powder when fired at 1000 ° C. in an air atmosphere, and it can be confirmed that the powder is a substantially spherical fine powder having a uniform particle diameter.

  FIG. 3 is an emission spectrum observed by irradiating a zinc oxide powder obtained by firing at 700 to 1000 ° C. for 3 hours in an air atmosphere with an electron beam of 30 kV at room temperature. Represents experiment No). When firing at 900 ° C. or higher in an air atmosphere, light emission having a peak near 500 nm appears, but it can be confirmed that the luminance is weak.

A zinc oxide phosphor powder was obtained by treating the zinc oxide powder obtained at each firing temperature in an air stream of Ar + H ₂ (3.8%) at 800 ° C. for 1 hour. FIG. 2 is an SEM photograph of zinc oxide powder obtained by firing in an air atmosphere at 1000 ° C. and then processing in a reducing atmosphere, and it can be confirmed that the shape before reduction is substantially maintained after the reducing atmosphere treatment. .

  An emission spectrum observed by irradiating the zinc oxide phosphor powder obtained at each firing temperature with an electron beam of 30 kV at room temperature is shown in FIG. 4 (the symbol in the figure represents Experiment No.). As is clear from this figure, only weak green light emission is confirmed when the firing temperature in the air atmosphere is 800 ° C. or lower, but green light emission with an emission peak wavelength of about 500 nm can be confirmed at 900 ° C. Further, it can be seen that at 1000 ° C., a very sharp ultraviolet light emission having an emission peak wavelength of 390 nm is exhibited.

It is a SEM photograph of the zinc oxide powder obtained by baking the Zn-EDTA complex powder described in the Example at 1000 ° C. for 3 hours in the air atmosphere. Is an SEM photograph of zinc oxide phosphor powder obtained by treating 800 ° C. × 1 hour in a stream of the zinc oxide powder Ar + H ₂ in FIG. 1 described (3.8%) in the examples. It is the emission spectrum observed by irradiating the electron beam of 30 kV at room temperature to the zinc oxide powder obtained by baking at 700-1000 degreeC for 3 hours by air atmosphere in the Example. It is the emission spectrum observed by irradiating a 30-kV electron beam at room temperature to the zinc oxide powder obtained by baking at 700-1000 degreeC for 3 hours by the atmospheric condition in the Example, and processing by a reducing atmosphere.

Claims (5)

A method for producing a zinc oxide phosphor, comprising:
(1) A step of producing a powder composed of an organometallic chelate complex of Zn by spray-drying an aqueous organometallic chelate complex solution of Zn obtained by reacting Zn and / or a Zn compound with an organic chelate forming agent ,
(2) A step of obtaining a zinc oxide powder by firing the powder obtained in the step (1) in air at 800 ° C. or higher ,
(3) An oxidation process comprising the step of reducing the zinc oxide powder obtained in the step (2) by heat treatment in an argon / hydrogen mixed atmosphere or nitrogen / hydrogen mixed atmosphere in a range of 500 to 1200 ° C. A method for producing a zinc phosphor.   The method for producing a zinc oxide phosphor according to claim 1, wherein the zinc oxide phosphor is an ultraviolet light emitting zinc oxide phosphor having an emission peak in the vicinity of 390 nm by electron beam excitation.   The method for producing a zinc oxide phosphor according to claim 1, wherein the zinc oxide phosphor is a green light emitting zinc oxide phosphor having an emission peak in the vicinity of 500 nm by electron beam excitation. The said zinc oxide fluorescent substance is a substantially spherical thing, The manufacturing method of the zinc oxide fluorescent substance in any one of Claims 1-3. The method for producing a zinc oxide phosphor according to any one of claims 1 to 4 , wherein an aminocarboxylic acid chelating agent and / or a salt thereof is used as the organic chelate forming agent.