Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
2000-05-04
2001-10-09
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C252S30160R
Reexamination Certificate
active
06299797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluorescent material for use in, for example, a field emission display (FED) and a manufacturing method therefor, and more particularly to an improvement in a yttrium oxide fluorescent material activated with europium.
2. Description of the Related Art
Particles of a yttrium oxide fluorescent material activated with europium (Eu)(Y
2
O
3
:Eu) are mainly prepared by two methods. That is, a method is employed with which powder of a yttrium oxide and powder of an europium oxide are mixed with each other by a ball mill. Then, powder of the mixed materials is baked. Another method has the step of dissolving powder of the yttrium oxide and powder of the europium oxide by using nitric acid. Then, the materials are co-precipitated as an oxalate which is then baked.
The latter method is an advantageous method which permits a fluorescent material excellent in light emitting efficiency to be obtained.
A variety of fluorescent materials are employed in displays of television receivers. Usually, the particle of the fluorescent material is several &mgr;m (3 &mgr;m to 10 &mgr;m).
In recent years, a variety of display units have been developed. From a viewpoint of reducing the thickness of the display, a plasma display (PDP), a field emission display (FED) and an electro-luminescence display (ELD) have attracted attention.
The structure of the FED cannot raise the accelerated voltage. Thus, there arises a problem in that the fluorescent material having a particle size of about several &mgr;m for use in the conventional CRT cannot sufficiently perform excitation. The reason for this lies in that the low acceleration voltage cannot enable electron beams to reach portions at which particles emit light.
Therefore, a nano-crystal fluorescent material having a nano particle size has been studied.
The nano-crystal fluorescent material is able to raise the probability of existence of light emitting portions adjacent to the surfaces of the particles. Thus, excitation is permitted even at the low acceleration voltage. That is, the nano-crystal fluorescent material is suitable for a fluorescent material for the FED unit.
For example, the FED unit can be excited at the low acceleration voltage as described above. Therefore, the distance for which electron beams are introduced is too short to sufficiently excite the FED by the fluorescent material particles each having the particle size of several &mgr;m.
Therefore, a fine nano-crystal fluorescent material suitable for the FED and precise CRT has been required.
Under the foregoing circumstances, the applicant of the present invention has disclosed a method of preparing nano-crystal fluorescent material of the yttrium oxide having europium by using liquid-phase reactions.
The yttrium oxide fluorescent material activated with europium (Y
2
O
3
:Eu) has a problem of unsatisfactorily low intensity of color (chromaticity). To raise the intensity of color (that is, to raise the chromaticity), the concentration of Eu must be raised. When the concentration of Eu is raised, the transaction of Eu results in the brightness being lowered (the foregoing phenomenon is called “concentration extinction”).
Therefore, the yttrium oxide fluorescent material activated with europium (Y
2
O
3
:Eu) is not permitted to raise the concentration of Eu to improve the intensity of color. Thus, improvement of the foregoing problem is an important factor. Also raising of the brightness is required.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a fluorescent material having excellent characteristics including the intensity of colors and brightness and suitable for a FED and a precise CRT and a manufacturing method thereof.
To achieve the foregoing object, according to one aspect of the present invention, there is provided a fluorescent material comprising: a yttrium oxide fluorescent material activated with europium, wherein the yttrium oxide fluorescent material is co-activated with zinc.
According to another aspect of the present invention, there is provided a method of manufacturing a fluorescent material comprising the steps of: using basic carbonate activated with europium and zinc as a precursor; and baking the precursor to prepare a yttrium oxide fluorescent material activated with europium and zinc.
The fluorescent material according to the present invention is prepared by bringing zinc into a solid solution state (a state in which zinc is uniformly introduced at the atom level) when a substance (the precursor) to be baked is prepared. The precursor is baked so that a fluorescent material is prepared. The obtained fluorescent material is in a state where zinc is uniformly dissolved in a yttrium oxide fluorescent material activated with europium (Y
2
O
3
:Eu) at the atom level. Thus, the color intensity and the brightness can considerably be improved.
The mainstream of the fluorescent material for use in a FED is a sulfide fluorescent material, such as ZnS:Cu, Al, ZnS:Ag or Al, Y
2
O
2
S:Eu. The foregoing sulfide fluorescent materials easily deteriorate and suffer from short lifetime.
Therefore, an oxide fluorescent material has attracted attention. As a red fluorescent material, the yttrium oxide fluorescent material activated with europium (Y
2
O
3
:Eu) is known. The developed color is distinct from red, that is, orange-like color is developed. To develop satisfactory red level (to raise the intensity), the concentration of Eu must be raised. In this case, the brightness is, however, lowered.
The present invention is structured to bring zinc into a solid solution state so that the intensity of color is raised without lowering of the brightness.
The manufacturing method is structured to use basic carbonate as the precursor. The basic carbonate is a low-cost material which can easily be handled. When the precursor is prepared by, for example, a liquid phase reaction, particles having a mean particle size of about tens of nm can be prepared. As an alternative to this, flux (a fusing agent) is employed to permit raising of the baking temperature. Thus, micron-size fluorescent material can be prepared.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.
REFERENCES:
patent: 6048469 (2000-04-01), Xiang et al.
Chemical Abstracts citation 1973-411264: abstract for JP 47019525 B4, Jun. 3, 1972.
Igarashi Takahiro
Ihara Masaru
Kusunoki Tsuneo
Ohno Katsutoshi
Kananen Ronald P.
Koslow C. Melissa
Rader Fishman & Grauer
Sony Corporation
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