A process for producing aluminate-based phosphor

Abstract: The present invention provides a method for producing an aluminate-based phosphor or a luminescent aluminate-based phosphor, which comprises calcining an aluminum compound having a BET specific surface area of 100 m 2 /g or more.

Description: The present relates to a method for producing an aluminate-based phosphor. More particularly, the present invention relates to a method for producing an aluminate-based phosphor having extremely uniform cation composition, used for various displays of emitting type such as a plasma display panel (PDP). Further, the present invention relates to a method for producing a luminescent aluminate-based phosphor. More particularly, the present invention relates to a method for producing a luminescent aluminate-based phosphor used for a luminous material which is excited by ultraviolet and visible lights to show afterglow property for a long period of time. Recently, there are investigations of an aluminate-based phosphor which is excited by a vacuum ultraviolet ray radiated by rare gas discharge, to emit lights. For example, there are known BaMgAl 10 O 17 :Eu and BaMgAl 14 O 23 :Eu as a blue light emitting phosphor, and BaAl 12 O 19 :Mn and BaMgAl 14 O 23 :Mn as a green light emitting phosphor. For example, a blue phosphor (BaMgAl 10 O 17 :Eu or BaMgAl 14 O 23 :Eu) can be produced by preparing a mixture of 1) a barium compound, 2) an europium compound, 3) a magnesium compound and 4) an aluminum compound as raw materials and calcining, in a weak reductive atmosphere, the mixture as a precursor. In this method, however, solid compounds of respective constituent ions are used as raw materials and mixing thereof is conducted by physical mixing such as ball milling. The precursor obtained by physical mixing such as ball milling reveals poor dispersion of constituent ions, e.g. barium, europium, magnesium and aluminum ions and a blue phosphor after calcination does not easily obtain uniform composition. When dispersion of the constituent ions is poor, particularly when dispersion of europium ions acting as light emitting center is poor, portions of higher concentration of europium emerge locally, causing reduction in emitting brilliance which is called concentration quench. Consequently, for obtaining a phosphor having excellent emitting efficiency, it has been desired to obtain a phosphor precursor in which dispersion of constituent ions is more excellent and to produce a phosphor having a uniform composition from said precursor. On the other hand, there are conventionally used, as a luminescent phosphor, self emitting nocturnally luminous paints obtained by adding a radioative substance to a phosphor, for a night display or a nocturnal clock. Recently, there are wide investigations on application of a luminescent phosphor containing no radioative substance which shows afterglow property for a long period of time. As the luminescent phosphor, for example, europium-activated strontium aluminate (SrAl 2 O 4 :Eu) is mainly investigated. It is well known that the property of a phosphor is influenced by dispersibility of constituent ions of the phosphor, and the light emitting efficiency becomes higher when dispersibility of constituent ions of the phosphor is more excellent, particularly, when dispersibility of an activating agent and co-activating agent is more excellent. It is said that also in a luminescent phosphor, afterglow brilliance becomes higher when dispersibility of constituent ions is more excellent. Further, it is well known that the light emitting property of a phosphor is significantly influenced by trace impurities. Therefore, for obtaining aluminate which is substrate of a luminescent aluminate-based phosphor, there are used as the main raw material, a high purity aluminum compound powder such as highly purified α-alumina or high purity γ-alumina and high purity aluminum hydroxide. As the aluminum compound, there is often used alumina such as α-alumina or γ-alumina and it is known that, if alumina is used, high temperature calcination at 1600°C or more is required for obtaining a luminescent aluminate-based phosphor in single-phase in which dispersion of constituent ions is excellent. In this case, members of apparatuses such as a calcination furnace required are limited to expensive materials. Therefore, for obtaining a luminescent aluminate-based phosphor having excellent light emitting efficiency and afterglow brilliance, it has been desired to produce a luminescent aluminate-based phosphor in which dispersion of constituent ions is more excellent. US 4,818,433 A discloses a manufacturing process of a luminescent phosphor composition having a predominantly blue peak emission which essentially consists of lanthanum cerium aluminate phosphor represented by the formula La 1-x Ce x Al y O (3/2)(y+1) (wherein 0.10 < x < 1.0 and 11.0 ≤ y ≤ 12.5). JP 11 140438 A discloses a luminous fluorescent body useful as indoor or outdoor night display comprising an alkali earth metal aluminate as a mother crystal and a rare earth metal element as an activator, wherein an organophosphorous compound is coated on the surface of the particles of said luminous fluorescent body. An object of the present invention is to provide a method which can easily produce an aluminate-based phosphor which has excellent light emitting efficiency and in which dispersion of constituent ions is excellent. Another object of the present invention is to provide a method which can easily produce a luminescent aluminate-based phosphor which has excellent light emitting efficiency and higher afterglow brilliance and in which dispersion of constituent ions is excellent. These objects could be achieved on the basis of the finding that an aluminate-based phosphor and a luminescent aluminate-based phosphor in which dispersion of constituent ions is extremely excellent can be produced easily when a specific aluminum compound is used as a raw material. Namely, the present invention provides a method for producing an aluminate-based phosphor comprising calcining an aluminum compound having a BET specific surface area of 100 m 2 /g or more. The present invention also provides a method for producing a luminescent aluminate-based phosphor comprising calcining an aluminum compound having a BET specific surface area of 100 m 2 /g or more. As the calcination raw material used for obtaining an aluminate-based phosphor, there is used an aluminum compound having a BET specific surface area of 100 m 2 /g or more, and aluminum hydroxide or aluminum oxide having a BET specific surface area of 100 m 2 /g or more is preferable, aluminum hydroxide having a BET specific surface area of 100 m 2 /g or more is more preferable, aluminum hydroxide having a BET specific surface area of 180 m 2 /g or more is further preferable and aluminum hydroxide having a BET specific surface area of 200 to 300 m 2 /g is particularly preferable. When the BET specific surface area of the aluminum compound is less than 100 m 2 /g, mixing with other compound is difficult, and an aluminate-based phosphor in which dispersion of constituent ions is excellent is not easily obtained. Further, any aluminum compound may be used provided the BET specific surface area of the aluminum compound is not less than 100 m 2 /g, and it is preferable to use aluminum hydroxide, and for example, aluminum hydroxide obtained by hydrolysis of an aluminum alkoxide is more preferable since a BET specific surface area of 100 m 2 /g or more is easily attainable and flocculation of primary particles is weak. As the aluminum hydroxide, aluminum hydroxide which is heat-treated to provide α-alumina having an alumina purity of 99.9 wt% or more is preferable since it enhances fluorescent properties such as brilliance, and aluminum hydroxide which is heated to provide α-alumina having an alumina purity of 99.9 wt% or more, obtained by hydrolysis of an aluminum alkoxide is used more preferably. As the powdery compound of Ba, Mg, Eu, Mn, Sr, Ca, Ce and Tb constituting an aluminate, there can be used an oxide, or a compound which is decomposed at higher temperature to become an oxide, such as a hydroxide, carbonate, nitrate, halide or oxalate. When the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to composite oxide substrate represented by the general formula x1M10·y1Mgo·z1Al 2 O 3 (M1 is at least one metal element selected from Ba, Sr and Ca), it is preferable that mixing is effected so that x1 is 0.5 to 4.5, y1 is 0 to 4, and z1 is 0.5 to 20. For example, when the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to a composite oxide substrate represented by the general formula x11(Ba, Sr)O · y11MgO · z11Al 2 O 3 , it is preferable that x11 is in the range of 0.9 to 1.7, y11 is in the range of 1.5 to 2.1, and z11 is 8. For example, when the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to a composite oxide substrate represented by the general formula x12(Ba, Sr)O · z12Al 2 O 3 , it is preferable that x12 is in the range of 1.0 to 1.5, and z12 is 6. For example, when the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to a composite oxide substrate represented by the general formula x13SrO · z13Al 2 O 3 , it is preferable that x13 is in the range of 3.9 to 4.1, and z13 is 7. When the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from Tb and Mn to composite oxide substrate represented by the general formula x2CeO 1.5 ·y2M2O·z2Al 2 O 3 (M2 is at least one metal element selected from Mg and Mn), it is preferable that x2 is in the range of 0.9 to 1.1, y2 is in the range of 0.9 to 1.1, and z2 is 5.5. As the raw material of Eu and Mn which becomes an activating agent for causing light emission, there can be used an oxide, or a compound which is decomposed at higher temperature to become an oxide, such as a hydroxide, carbonate, nitrate, halide and oxalate. Regarding the addition amount, for example, when the aluminate-based phosphor is an aluminate-based phosphor prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to a composite oxide substrate represented by the general formula x11(Ba, Sr)O · y11MgO · z11Al 2 O 3 , it is preferable that the addition amount of Eu is in the range of 0.01all to 0.2x11, and the addition amount of Mn is 0.15yll or less. For example, when the aluminate-based phosphor is an aluminate-based phosphor prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to a composite oxide substrate represented by the general formula x12(Ba, Sr)O · z12Al 2 O 3 , it is preferable that the addition amount of Eu is in the range of 0.01x12 to 0.15x12, and the addition amount of Mn is 0.20x12 or less. For example, when the aluminate-based phosphor is an aluminate-based phosphor prepared by adding an activating agent which is at least one metal element selected from Eu and Mn to a composite oxide substrate represented by the general formula x13SrO · z13A1 2 O 3 , it is preferable that the addition amount of Eu is in the range of 0.02x13 to 0.06x13. For example, when the aluminate-based phosphor is an aluminate-based phosphor prepared by adding an activating agent which is at least one metal element selected from Tb and Mn to a composite oxide substrate represented by the general formula x2CeO 1.5 · y2M2O · z2Al 2 O 3 , it is preferable that the addition amount of Tb is in the range of 0.3x2 to 0.5x2, and the addition amount of Mn is 0.15y2 or less. As the mixing method of these raw materials, any method can be used, and there are exemplified mixings using a ball mill, V shaped mixer or stirring apparatus to yield a precursor. Then, the method for calcining a precursor of an aluminate-based phosphor may be any method, and for example, the precursor can be filled in an alumina boat and calcinated at given temperature in given gas atmosphere to obtain phosphors of various colors. Further, if necessary, a phosphor powder having further excellent crystallinity and higher brilliance can be expected to be produced by mixing a reaction promoter (flux) such as boron oxide or aluminum fluoride to the above-mentioned raw materials. For example, when a precursor of a blue phosphor (BaMgAl 10 O 17 :Eu or BaMgAl 14 O 23 :Eu) is calcinated, it is preferable to calcinate the precursor in a reductive atmosphere, at a temperature in the range of 1000 to 1700°C for 0.5 to 40 hours, once or more. For providing the reductive atmosphere, a method in which a graphite block is placed in a boat filled with a precursor and a method in which calcination is conducted an a nitrogen-hydrogen atmosphere or a rare gas hydrogen atmosphere are listed. These atmospheres may contain water vapor. Further, when a precursor of a green phosphor (BaAl 12 O 19 :Mn or BaMgAl 14 O 23 :Mn) is calcinated, the precursor is calcinated in a surrounding atmosphere or an oxygen atmosphere, at a temperature in the range of 1000 to 1700°C for 0.5 to 40 hours, once or more. Additionally, the aluminate-based phosphor obtained after calcination may also be subjected to treatment such as dispersion, water-washing, drying and sieving. The aluminate-based phosphor obtained in the present invention contains particles having a primary particle size of 5 µm or less in an amount of 80 wt% or more, preferably contains particles having a primary particle size of 0.05 µ m or more and 5 µm or less in an amount of 80 wt% or more, the primary particle size being smaller than that of an aluminate-based phosphor obtained by a usual method. As described above, by making the primary particle size of a phosphor smaller and making the particle distribution sharper, it becomes possible, for example, to coat the phosphor efficiently in minute discharge space such as display cells of PDP, and to produce various displays of light emission type such as PDP, manifesting higher emission brilliance. The aluminate-based phosphor obtained by the present invention has excellent light emitting property under vacuum ultraviolet ray excitation and is extremely useful as an aluminate-based phosphor used in various displays such as a plasma display panel (PDP) since dispersion of constituent ions in the phosphor is extremely excellent. Further, it has become apparent that the aluminate-based phosphor obtained by the present invention shows excellent light emitting property not only under vacuum ultraviolet ray excitation but also under ultraviolet ray, cathode ray or X-ray excitation. Namely, the present invention provides a method for producing an aluminate-based phosphor which can be excited by energies in wide ranges such as vacuum ultraviolet ray, ultraviolet ray, cathode ray or X-ray and manifests excellent light emitting property. More particularly, if the aluminum hydroxide of the present invention is used, it can be expected that dispersed condition of constituent ions other than aluminum becomes more excellent, the crystallinity of the aluminate-based phosphor obtained by the present invention becomes excellent, and chromaticity is enhanced, as compared with the case using other aluminum compound. Further, when the aluminum hydroxide of the present invention is used, flocculated condition of the aluminate-based phosphor primary particles obtained by the present invention becomes weaker as compared with the case using other aluminum compound, and the following processes such as crushing can be simplified. According to the present invention, an aluminate-based phosphor in which dispersion of constituent ions is extremely excellent can be produced easily, and an aluminate-based phosphor manifesting excellent light emitting efficiency can be provided at low cost. This aluminate-based phosphor is extremely useful in the industrial field as a phosphor used in various displays such as a plasma display panel (PDP). Then, the method for producing a luminescent aluminate-based phosphor will be illustrated. As the calcinations raw materials of a luminescent aluminate-based phosphor, the same compounds as described above are listed. As the powdery compound of Eu, Dy, Nd, Sr, Ca, Pb, Zn and Bi constituting an aluminate, there can be used an oxide, or a compound which is decomposed at higher temperature to become an oxide, such as a hydroxide, carbonate, nitrate, halide and oxalate. When the luminescent aluminate-based phosphor is a compound prepared by adding Eu as an activating agent and further adding at least one metal element selected from Dy and Nd as a co-activating agent to a composite oxide substrate represented by the general formula x1MO·z1Al 2 O 3 (M is Sr or Ca), it is preferyble that x is in the range of 0.5 to 1.1, and z is 1. For example, when the luminescent aluminate-based phosphor is a compound prepared by adding Eu as an activating agent and further adding Nd as a co-activating agent to a composite oxide substrate represented by the general formula x2caO. z2Al 2 O 3 , it is preferable that x2 is in the range of 0.9 to 1.1, and z is 2. As the raw material of Eu as an activating agent and Dy and Nd as a co-activating agent for causing light emission, there can be used an oxide, or a compound which is decomposed at higher temperature to become an oxide, such as a hydroxide, carbonate, nitrate, halide and oxalate. Regarding the addition amount, for example, when the luminescent aluminate-based phosphor is a luminescent, aluminate-based phosphor prepared by adding Eu as an activating agent and Dy as a co-activating agent to a composite oxide substrate represented by the general formula x1SrO·z1Al 2 O 3 , it is preferable that the addition amount of Eu is in the range of 0.01x1 to 0.1x1, and the addition amount of Dy is in the range of 0.02x1 to 0.2x1. For example, when the luminescent aluminate-based phosphor is a compound prepared by adding Eu as an activating agent and further adding Nd as a co-activating agent to a composite oxide substrate represented by the general formula x2CaO · z2Al 2 O 3 , it is preferable that the addition amount of Eu is in the range of 0.01x2 to 0.1x2, and the addition amount of Nd is in the range of 0.02x2 to 0.2x2. At least one of the metal elements La, Ce, Pr, Sm, Gd, Tb, Ho, Er, Tm, Yb, Lu, Mn, Sn and Bi can be added as a co-activating agent to a composite oxide substrate represented by the general formula xMO · zAl 2 O 3 , in an amount of 0.001x to 0.1x. As the mixing method of these raw materials, any method can be used, and there are exemplified mixings using a ball mill, V shaped mixer or stirring apparatus to yield a precursor. As the method for calcining a precursor of a luminescent aluminate-based phosphor, the same methods as described above are listed. The luminescent aluminate-based phosphor obtained in the present invention contains particles having a primary particle size of 5 µm or less in an amount of 80 wt% or more, the primary particle size being smaller than that of a luminescent aluminate-based phosphor obtained by a usual method. As described above, by making the primary particle size of a phosphor smaller and making the particle distribution sharper, it becomes possible to disperse a phosphor efficiently in making paste, and to produce a resin composition having high emission brilliance. More specifically, when the aluminum hydroxide of the present invention is used, it can be expected that dispersed condition of constituent ions other than aluminum becomes more excellent, the crystallinity of the aluminate-based phosphor becomes excellent, and afterglow property is enhanced, as compared with the case using other aluminum compound. Further, when the aluminum hydroxide of the present invention is used, flocculated condition of the luminous material primary particles becomes weaker as compared with the case using other aluminum compound, and the following processes such as crushing can be simplified. The luminescent, aluminate-based phosphor obtained in the present invention has excellent afterglow property and is extremely useful as a luminous material since dispersion of constituent ions in the phosphor is extremely excellent. According to the present invention, a luminescent aluminate-based phosphor in which dispersion of constituent ions is extremely excellent can be produced easily, and a luminescent aluminate-based phosphor manifesting excellent light emitting efficiency and longer life can be provided at low cost. This luminescent aluminate-based phosphor is extremely useful in the industrial field. Example The following examples will illustrate the present invention further in detail below, but do not limit the scope of the present invention. Example 1 4.91 g of aluminum hydroxide (BET specific surface area: 250 m 2 /g), 1.26 g barium carbonate, 0.12 g of europium oxide and 0.69 g of basic magnesium carbonate were mixed sufficiently in a ball mill, and the resulted precursor was calcinated for 2 hours at 1450°C in a weak reductive atmosphere to obtain a blue phosphor. Evaluation by a scanning electric microscope revealed that the primary particle size of the resulted blue phosphor was 1 µm or less. Further, XRD evaluation (phase identification evaluation by minute X-ray diffraction apparatus: Ru-200 manufactured by Rigaku) revealed BaMgAl 10 O 17 :Eu single phase. Example 2 A blue phosphor was obtained in the same manner as in Example 1 except that 8.47 g of aluminum hydroxide was replaced by 6.2 g of alumina. Evaluation by a scanning electric microscope revealed that the primary particle sizes of the resulted blue phosphors were all 0.05 µm or more and 1 µm or less. This blue phosphor was irradiated with an ultraviolet ray using an Excimer 146 nm lamp (manufactured by Ushio Inc.) in a vacuum chamber of 6.7 Pa (5×10 -2 Torr) or less to show blue strong emission which was measured by a brilliance meter (BM-7, manufactured by TOPCON) to find a light emission brilliance of 28.09 cd/m 2 , being stronger than that of a conventional article. Also when this phosphor was excited by an ultraviolet ray, cathode ray or X-ray of 254 nm or 365 nm, blue light emission of high brilliance was shown. Further, the X ray diffraction was measured in the same manner as in Example 1, and it was found that the resulted phosphor had BaMgAl 10 O 17 :Eu single phase. Example 3 6.71 g of aluminum hydroxide (BET specific surface area: 250 m 2 /g) obtained by a hydrolysis reaction of aluminum isopropoxide, 13.73 g of strontium carbonate, 0.35 g of europium oxide and 0.90 g of dysprosium oxide were mixed sufficiently in a ball mill, and the mixture was calcinated for 3 hours at 1300°C in a weak reductive atmosphere to obtain (Sr 0.93, Eu 0.02, Dy 0.05)O · Al 2 O 3 . The resulted (Sr 0.93, Eu 0.02, Dy 0.05)O · Al 2 O 3 revealed high afterglow brilliance of yellow green color.

Claims: A method for producing an aluminate-based phosphor comprising calcining an aluminum compound having a BET specific surface area of 100 m 2 /g or more. A method for producing a luminescent aluminate-based phosphor comprising calcining an aluminum compound having a BET specific surface area of 100 m 2 /g or more. The method according to Claim 1 or 2, wherein the aluminum compound is aluminum hydroxide or aluminum oxide. The method according to any one of Claims 1 to 3, wherein the aluminum compound is aluminum hydroxide. The method according to any one of Claims 1 to 4, wherein the aluminum compound is aluminum hydroxide obtained by hydrolysis of an aluminum alkoxide. A. The method according to any one of Claims 1 to 5, wherein the aluminum compound is aluminum hydroxide which is heated to provide α-alumina having a purity of 99.9 wt% or more. The method according to Claim 1, wherein the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from the group consisting of Eu and Mn to a composite oxide substrate represented by the general formula x1M1O · y1MgO · zlAl 2 O 3 , M1 is at least one metal element selected from Ba, Sr and Ca, x1 is 0.5 to 4.5, y1 is 0 to 4, and z1 is 0.5 to 20. The method according to Claim 1, wherein the aluminate-based phosphor is a compound prepared by adding an activating agent which is at least one metal element selected from Tb and Mn to a composite oxide substrate represented by the general formula x2CeO 1.5 · y2M2O · z2Al 2 O 3 , M2 is at least one metal element selected from Mg and Mn, x2 is 0.9 to 1.1, y2 is 0.9 to 1.1, and z2 is 5.5. The method according to Claim 2, wherein the luminescent aluminate-based phosphor is a compound prepared by adding Eu as an activating agent and further adding at least one metal element selected from Dy and Nd as a co-activating agent to a composite oxide substrate represented by the general formula xMO · zAl 2 O 3 , M is Sr or Ca, x is 0.5 to 1.1, and z is 1. The method according to Claim 9, wherein the luminescent aluminate-based phosphor is a compound prepared by further adding at least one metal element selected from Pb, Zn and Bi to a composite oxide substrate represented by the general formula xMO · zAl 2 O 3 .

Inventors: MIYAZAKI SUSUMU, ONO KEIJI, MIYAZAKI, SUSUMU, ONO, KEIJI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 2000
Main classification: C09K11
IPC codes: C09K11