Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
2001-06-22
2004-01-20
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
Reexamination Certificate
active
06680004
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an aluminate fluorescent substance used in various types of light emission displays such as a plasma display panel (hereinafter, referred to as “PDP” and the like, and vacuum ultraviolet ray-excited, light-emitting diodes such as a rare gas lamp and the like, and a method of producing an aluminate fluorescent substance for use as a luminous material, which substance is excited by ultraviolet ray or visible light and exhibits afterglow for a long period of time.
BACKGROUND OF THE INVENTION
Recently, there are wide-spread developments of vacuum ultraviolet ray-excited, light-emitting diodes having a mechanism in which a fluorescent substance is excited by vacuum ultraviolet ray radiated by rare gas discharge to emit light, and development of PDPs is a typical example thereof. A PDP enables increase in size of an image plane which is difficult to achieve in cathode-ray tubes (CRT) and color liquid crystal displays, and are expected to be used for flat panel displays in public spaces or as a large screen television. A PDP is a display device obtained by placing a large number of fine discharging spaces (hereinafter, sometimes abbreviated as display cell) into a matrix arrangement. A discharge electrode is provided in each display cell and a fluorescent substance is applied on the inner wall of each display cell. Each display cell is filled with a rare gas such as He—Xe, Ne—Xe, Ar and the like, and by applying voltage on a discharge electrode, discharge occurs in the rare gas and vacuum ultraviolet ray are radiated. The fluorescent substance is excited by the vacuum ultraviolet ray and emits visible ray. Images are displayed by controlling the positions of display cells which emit light. By use of fluorescent substances emitting three primary colors, blue, green and red, full color display can be achieved.
A vacuum ultraviolet ray-excited light-emitting device other than a PDP is a rare gas lamp. A rare gas lamp emits light by a mechanism in which vacuum ultraviolet ray are generated by discharge in a rare gas, and the vacuum ultraviolet ray is converted into visible ray by a fluorescent substance. Rare gas lamps are advantageous from an environmental standpoint because they do not use mercury.
Aluminate fluorescent substances excited by vacuum ultraviolet ray radiated by discharge in a rare gas are known. As a blue light-emitting fluorescent substance, compounds using as a substrate a complex oxide of the composition formula x
1
M
1
O y
1
MgO.z
1
Al
2
O
3
, and containing Eu as an activator are known, and as typical examples thereof, compounds in which M
1
is Ba (BaMgAl
10
O
17
:Eu, BaMgAl
14
O
23
:Eu, and the like) are known.
As a green light-emitting fluorescent substance, compounds using as a substrate acomplex oxide of the composition formula x
1
M
1
O.y
1
MgO.z
1
Al
2
O
3
, and containing Mn as an activator are know, and as typical examples thereof, compounds in which M
1
is Ba (BaAl
12
O
19
:Mn, BaMgAl
14
O
23
:Mn, and the like) are known.
An aluminate fluorescent substance can be obtained, in general, by mixing compounds containing metal elements constituting the intended aluminate fluorescent substance in such a proportion as to form the intended aluminate fluorescent substance, and calcining the mixture in, for example, a reduction atmosphere. For example, an aluminate fluorescent substance of the composition formula: Ba
0.9
Eu
0.1
MgAl
10
O
17
can be produced by mixing a barium compound, europium compound, magnesium compound and aluminum compound so that Ba:Eu:Mg:Al=0.9:0.1:1:10, and calcining the produced mixture, for example, in an atmosphere containing hydrogen.
When a display cell such as a PDP and the like is produced using such an aluminate fluorescent substance, high light emitting brilliance is required. A fluorescent substance used in conventional display cells such as a PDP and the like has a primary particle size of about 2 to 5 &mgr;m, and is applied on the rear plate side of a display cell, namely, on a side surface and bottom surface of a display cell. Recently, it is required to apply a fluorescent substance particle not only on a side surface and bottom surface of a display cell in a PDP but also on the front plate side, namely, the top surface of a display cell, for further increasing light emitting brilliance of the PDP.
Further, a self-emitting luminous material having a mechanism in which a radiation substance is added to a fluorescent substance is conventional, and has been used for a nocturnal display or as a luminous clock. In these types of devices, light emission is caused by exciting the fluorescent substance by weak radiation generated from a trace amount of the radiation substance. Recently, fluorescent substances containing no radioactive substances have been studied for use as luminous material. These substances preserve day light and can emit light for a long period even at night, have excellent light emitting efficiency, and high after glow brilliance. Such a fluorescent substance includes, for example, strontium aluminate (SrAl
2
O
4
:Eu, etc.) and the like.
JP-A No. 2000-34480, for example, discloses “alkaline earth metal aluminate luminous fluorescent substance activated with a divalent europium, having a chemical composition RO.a(Al
1−x
Ga
x
)
2
O
3
.bM
m
O
n
.cB
2
O
3
.dEu
2+
(wherein, R represents one or more metals selected from the alkaline earth metals such as Ba, Sr, Ca, Mg and the like, and Zn, and M represents Y, Sc and/or Si), in which 0.3≦a≦8, 0≦b≦0.2, 0.001≦c≦0.3, 0.001≦d≦0.3, 0≦x≦1.0)” and describes that “afterglow brilliance and afterglow time can be simultaneously improved” . . . “by inclusion of at least one or more oxides selected from yttrium oxide, scandium oxide and silicon oxide”. However, there is a desire for further improvement in afterglow brilliance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing an aluminate fluorescent substance having a particle size suitable for various light emission type displays such as a PDP and the like, and vacuum ultraviolet ray-excited light emitting devices such as rare gas lamp and the like, and the displays and devices having high light emitting brilliance, an aluminate fluorescent substance obtained by this method, a fluorescent substance for a vacuum ultraviolet ray-excited light emitting device having this aluminate fluorescent substance, and a ultraviolet ray-excited light emitting device having this fluorescent substance.
Another object of the present invention is to provide an aluminate fluorescent substance for luminous material, the substance having high afterglow brilliance and being suitable for use in a luminous material.
These objects and another objectives are achieved by the present invention. Namely, the present invention provides a method of producing an aluminate fluorescent substance comprising the steps of mixing an &agr;-alumina powder having an average primary particle size of from about 0.05 &mgr;m to less than 0.3 &mgr;m with a metal salt, and calcining the resulting mixture. Further, the present invention provides a fluorescent substance for a vacuum ultraviolet ray-excited light emitting device, comprising 80 wt % or more of an aluminate fluorescent substance obtained by the above-mentioned production method and having a primary particle size of from about 0.05 &mgr;m to less than about 0.3 &mgr;m.
As used herein, the term “average primary particle size” is a number-average value of particle sizes read from a picture photographed by a scanning electron microscope.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be illustrated in detail below.
In the method of producing an aluminate fluorescent substance of the present invention, the average primary particle size of an &agr;-alumina powder used is from about 0.05 &mgr;m to less than 0.3 &mgr;m, and preferably from about 0.07 &mgr;m to about 0.28 &mgr;m or less, further preferably from about 0.1 &mgr;m to about 0.25 &mgr;m or less. Whe
Miyazaki Susumu
Ono Keiji
Koslow C. Melissa
Sumitomo Chemical Company Limited
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