Mixed green-emitting phosphor and cathode ray tube using the...

Electric lamp and discharge devices – Cathode ray tube – Screen

Reexamination Certificate

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C252S30140R, C252S30140H, C252S30140F

Reexamination Certificate

active

06304027

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a mixed green-emitting phosphor and a cathode-ray tube using the same, and in more detail, to a mixed green-emitting phosphor for use in a projection cathode-ray tube which has an excellent luminance saturation characteristic under high current density and a cathode-ray tube using the same.
In a green-emitting phosphor for use in a general cathode-ray tube, ZnS-based phosphors, such as ZnS:Cu,Au,Al phosphor, ZnS:Cu,Al phosphor, etc., are generally used.
However, cathode-ray tubes which are operated under high current density and high voltage drive have recently attracted much attention as cathode-ray tubes become large and high-definition. Therefore, a phosphor of high luminance especially under high current density, is needed. However, since the conventional ZnS-based phosphors are unable to provide sufficient luminance effects under high current density, the rare earth phosphors have been used recently.
As examples of rare earth green-emitting phosphors which are activated under high current density, such as in the projection cathode-ray tube, Y
3
(Al,Ga)
5
O
12
:Tb phosphor, InBO
3
:Tb phosphor, Y
2
SIO
5
:Tb phosphor, LaOCl:Tb phosphor, Zn
2
SiO
4
:Mn phosphor, or mixtures thereof can be enumerated.
The Y
3
(Al,Ga)
5
O
12
:Tb phosphor has good current-luminance saturation characteristics and high emitting luminance.
The Y
2
SiO
5
:Tb phosphor is known as having high color purity, short afterglow time and, especially, good luminance saturation characteristics.
For the LaOCl:Tb phosphor, it has good current-luminance saturation characteristics and high color purity.
Zn
2
SiO
4
:Mn phosphor is known as not having good luminance saturation and afterglow characteristics, but having excellent color purity.
The InBO
3
:Tb phosphor has a high resistance under high current density, is suitable for use in the projection cathode-ray tube, and has good color purity. Meanwhile, the afterglow time is long so as to mix with the phosphor whose afterglow time is short when applied to a cathode-ray tube.
There are many mixed green-emitting phosphors prepared by mixing the above-mentioned rare earth-based phosphors. As one example, U.S. Pat. No. 4,924,139 discloses a mixed phosphor of InBO
3
:Tb with Y
3
(Al,Ga)
5
O
12
:Tb whose color purity is excellent and whose afterglow time is short.
However, the above mentioned phosphors and the mixed phosphors thereof have undesirable luminance saturation and deterioration characteristics. Accordingly, there are many problems that should be improved in the known phosphors.
SUMMARY OF THE INVENTION
It is an object of the present invention, for improving the problems occurring when the phosphors are activated under high current density, to provide a mixed green-emitting phosphor which has excellent luminance saturation characteristics and deterioration characteristics, by mixing phosphors having excellent characteristics but without using InBO
3
:Tb phosphor.
It is another object of the present invention to provide a cathode ray tube whose luminance and luminance saturation characteristics are very good, and which is manufactured using the mixed green-emitting phosphor of the present invention.
To accomplish the above-mentioned first object, there is provided in the present invention, a mixed green-emitting phosphor manufactured by mixing and containing Y
3
(Al,Ga)
5
O
12
:Tb, LaOCl:Tb, Y
2
SiO
5
:Tb and Zn
2
SiO
4
:Mn phosphors in the following concentrations: about 20 to 60 weight percent of Y
3
(Al,Ga)
5
O
12
:Tb phosphor, no more than about 30 weight percent of LaOCl:Tb phosphor, no more than about 50 weight percent of Y
2
SiO
5
:Tb phosphor, and no more than about 20 weight percent of Zn
2
SiO
4
:Mn phosphor.
Desirably, the mixed green-emitting phosphor is manufactured by mixing and contains Y
3
(Al,Ga)
5
O
12
:Tb, LaOCl:Tb, Y
2
SiO
5
:Tb and Zn
2
SiO
4
:Mn phosphors in amounts of: about 20 to 50 weight percent of Y
3
(Al,Ga)
5
O
12
:Tb phosphor, no more than about 20 weight percent of LaOCl:Tb phosphor, no more than about 40 weight percent of Y
2
SiO
5
:Tb phosphor, and no more than about 10 weight percent of Zn
2
SiO
4
:Mn phosphor.
The first object of the present invention can be also accomplished by a mixed green-emitting phosphor manufactured by mixing and containing Y
3
(Al,Ga)
5
O
12
:Tb, Y
2
SiO
5
:Tb and Zn
2
SiO
4
:Mn phosphors in the following concentrations: about 20 to 60 weight percent of Y
3
(Al,Ga)
5
O
12
:Tb phosphor, no more than about 60 weight percent of Y
2
SiO
5
:Tb phosphor, and no more than about 20 weight percent of Zn
2
SiO
4
:Mn phosphor without using LaOCl:Tb phosphor.
When three phosphors as mentioned above are mixed so as to manufacture the mixed phosphor of the present invention, an excellent effect also could be obtained, though using up to about 60 weight percent of Y
2
SiO
5
:Tb phosphor.
Desirably, the mixed green-emitting phosphor is manufactured by mixing and contains Y
3
(Al,Ga)
5
O
12
:Tb, Y
2
SiO
5
:Tb and Zn
2
SiO
4
:Mn phosphors in amounts of: about 30 to 60 weight percent of Y
3
(Al,Ga)
5
O
12
:Tb phosphor, no more than about 50 weight percent of Y
2
SiO
5
:Tb phosphor, and no more than about 10 weight percent of Zn
2
SiO
4
:Mn phosphor.
The other object of the present invention is accomplished by a cathode-ray tube having fixed to a surface thereof a mixed green-emitting phosphor manufactured by mixing and containing Y
3
(Al,Ga)
5
O
12
:Tb, LaOCl:Tb, Y
2
SiO
5
:Tb and Zn
2
SiO
4
:Mn phosphors in amounts of: about 20 to 60 weight percent of Y
3
(Al,Ga)
5
O
12
:Tb phosphor, no more than about 30 weight percent of LaOCl:Tb phosphor, no more than about 50 weight percent of Y
2
SiO
5
:Tb phosphor, and no more than about 20 weight percent of Zn
2
SiO
4
:Mn phosphor.
The other object of the present invention can be also accomplished by a cathode-ray tube comprising a mixed green-emitting phosphor manufactured by mixing and containing Y
3
(Al,Ga)
5
O
12
:Tb, Y
2
SiO
5
:Tb and Zn
2
SiO
4
:Mn phosphors in the following concentrations: about 20 to 60 weight percent of Y
3
(Al,Ga)
5
O
12
:Tb phosphor, no more than about 60 weight percent of Y
2
SiO
5
:Tb phosphor, and no more than about 20 weight percent of Zn
2
SiO
4
:Mn phosphor.


REFERENCES:
patent: 4924139 (1990-05-01), Morita et al.
patent: 5196763 (1993-03-01), Yang et al.
patent: 5363013 (1994-11-01), Matsukiyo et al.
patent: 5790851 (1982-06-01), None
patent: 01215884 (1989-08-01), None
patent: 0211694 (1990-01-01), None
patent: 91-16901 (1991-11-01), None

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