Method of producing aluminate phosphor

Details Method of producing aluminate phosphor Method of producing aluminate phosphor

2001-12-17

2004-02-10

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

Compositions containing halogen; e.g., halides and oxyhalides

C313S643000, C313S582000, C313S584000

Reexamination Certificate

active

06689292

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for producing an aluminate phosphor.
BACKGROUND OF THE INVENTION
An aluminate phosphor is used in a vacuum ultra-violet radiation excited light emitting element such as a plasma display panel (hereinafter referred to as PDP) and a rare gas lamp. For instance, in a PDP, a phosphor is applied on inner walls of a multiplicity of discharge microspaces (hereinafter referred to as “display cells”) provided in matrix. It should be noted that discharge electrodes provided in each display cell, and a rare gas such as He-Xe, Ne-Xe, or Ar is capsulated in the space of the cell, so that discharge is caused in the rare gas when a voltage is applied to the discharge electrodes, thereby radiating vacuum ultra-violet rays. The phosphor is excited by the vacuum ultra-violet rays, thereby emitting visible rays. Here, by specifying positions of the display cells to emit light, images are displayed. Furthermore, by using phosphors emitting light of blue, green, and red colors that are three primary colors of light, full-color display can be carried out. It is difficult to increase the screen size in the case of cathode ray tubes or color liquid crystal displays, but PDPs make it possible, and further, they can be made flat panel displays. Therefore, expectations are placed on PDPs as displays in public spaces and for use in TV sets with large screens.
Apart from the PDPs, rare gas lamps for illumination are known as vacuum ultra-violet radiation excited light emitting elements. The rare gas lamp has the same configuration as the PDP having only one cell, and a phosphor is applied on inner walls of a light emitting section thereof. In the case of the rare gas lamp also, as in the case of the PDP, vacuum ultra-violet rays are generated by discharge in the rare gas, and the vacuum ultra-violet rays are converted into visible light by the phosphor, whereby light is emitted. The rare gas lamps are used for illumination, and attract attentions from the viewpoint of environment preservation since they do not use mercury, unlike the fluorescent lamps.
Known as the aluminate phosphor is, for instance, a compound containing a complex oxide expressed by a composition formula
x
1
M
1
O—
y
1
MgO—
z
1
Al
2
O
3
as a substrate, and an activator. As to typical examples thereof, BaMgAl
10
O
17
:Eu, BaMgAl
14
O
23
:Eu, etc., which contain Eu as the activator and in which M
1
is Ba, are known as blue light emitting phosphors, and BaAl
12
O
19
:Mn, BaMgAl
14
O
23
:Mn, etc., which contain Mn as the activator and in which M
1
is Ba, are known as green light emitting phosphors.
It is also known that each of these aluminate phosphors is produced by mixing compounds in powder form that contain metal elements composing the aluminate phosphor at a predetermined ratio such that a target aluminate phosphor is generated, and calcining the obtained powder mixture in a reducing atmosphere. For instance, it is known that an aluminate phosphor expressed by a composition formula of Ba
0.9
Eu
0.1
MgAl
10
O
17
is obtained by mixing a barium compound, a europium compound, a magnesium compound, and an aluminum compound at a ratio of Ba:Eu:Mg:Al=0.9:0.1:1:10, and calcining the obtained powder mixture in an atmosphere containing hydrogen, that is, a reducing atmosphere.
Such an aluminum phosphate is used in display cells of a PDP or the like. Since a PDP is required to have a high emission luminance, a phosphor for use in display cells of a PDP is also required to have a high emission luminance. Furthermore, a rare gas lamp for illumination is also required to have a high emission luminance, and hence, a phosphor for use in a rare gas lamp is also required to have a high emission luminance.
However, the method in which compounds containing metal elements composing an aluminate phosphor are simply mixed in powder form and a powder mixture obtained is calcined, that is, the method in which a powdery mixture is used as a precursor, has had a drawback in that a phosphor obtained does not have a sufficient emission luminance.
An object of the present invention is to provide an aluminate phosphor having a high emission luminance, a method for producing the same, and a vacuum ultra-violet radiation excited light emitting element in which the aluminate phosphor is used.
SUMMARY OF THE INVENTION
In such a situation, the inventors of the present invention, as a result of earnest studies, found that in the case where a precipitate mixture produced by using an &agr;-alumina powder, an aqueous solution containing a cation of a metal composing the aluminate phosphor, and a precipitant that precipitates the cation is used as a specific precursor to obtain an aluminum phosphor, the obtained aluminate phosphor has a significantly high emission luminance, and consequently they completed the present invention.
More specifically, the present invention is to provide an aluminate phosphor excellent in practical application that is obtained by mixing an &agr;-alumina powder, an aqueous solution containing a cation of a metal composing the aluminate phosphor, and a precipitant that precipitates the cation, and drying and calcining an obtained mixture of precipitates, to provide a method for producing the same, and to provide a light emitting element in which the same is utilized.
The present invention is to provide the foregoing method further arranged so that the aluminate phosphor contains a complex oxide expressed by a composition formula of
x
1
M
1
O—
y
1
MgO—
z
1
Al
2
O
3
(M
1
represents at least one metal element selected from the group consisting of Ba, Sr, and Ca, x
1
satisfies 0.5≦x
1
≦4.5, y
1
satisfies 0≦y
1
≦4, and z
1
satisfies 0.5≦z
1
≦20) as a substrate, and at least one of Eu and Mn as an activator. The present invention is to provide the aforementioned method further arranged so that the aluminate phosphor contains a complex oxide expressed by a composition formula of
x
2
CeO
1.5
—y
2
M
2
O—
z
2
Al
2
O
3
(M
2
represents Mg and/or Mn, x
2
satisfies 0.9≦x
2
≦1.1, y
2
satisfies 0.9≦y
2
≦1.1, and z
2
satisfies z
2
=5.5) as a substrate, and at least one of Tb and Mn as an activator.
Furthermore, the present invention is to provide an aluminate phosphor obtained by the foregoing producing method in which the aluminate phosphor comprises not less than 80 weight % a primary particle diameter of not less than 0.05 &mgr;m and not more than 30 &mgr;m. Furthermore, the present invention is to provide a vacuum ultra-violet radiation excited light emitting element in which the foregoing aluminate phosphor is used.
It should be noted the mean primary particle diameter is a number-average value of particle diameters determined using photographs taken by the scanning electronic microscope.
DETAILED DESCRIPTION OF THE INVENTION
The following description will depict the present invention in more detail.
An aluminate phosphor of the present invention is characterized in that an &agr;-alumina powder, an aqueous solution containing a cation of a metal, and a precipitant that precipitates the cation are mixed, and an obtained mixture of precipitates is used as a precursor of the aluminate phosphor.
Here, examples of the cation in the aqueous solution containing the cation of a metal composing the aluminate phosphor include cations of Ba, Mg, Eu, Mn, Sr, Ca, Tb, Ce, and Zn. Examples of aqueous solutions containing such cations include an aqueous solution of a water-soluble salt formed with such a cation, for instance, a halogenide, or a nitrate. Therefore, when a blue light emitting phosphor (BaMgAl
10
O
17
:Eu, BaMgAl
14
O
23
:Eu, etc.) is produced, an aqueous solution of a water-soluble salt containing ions of Ba, Mg, and Eu may be used. Likewise, when a green light emitting phosphor (BaAl
12
O
19
:Mn, BaMgAl
14
O
23
:Mn, etc.) is produced, an aqueous solution of a water-soluble salt containing ions of Ba, Mg, and Mn may be used.
The water used for preparing the aqueous solution containing the cation in the producing method of the present in

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