Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2000-04-12
2003-01-07
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C252S30140H
Reexamination Certificate
active
06504297
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a green-emitting phosphor composition and a cathode ray tube (CRT) manufactured using the same, and more particularly, to a green-emitting phosphor composition having improved luminance characteristics, degradation characteristics and afterglow characteristics, and a CRT adopting the same.
2. Description of the Related Art
Recently, with the advent of HDTV (high definition television) broadcasting, demands for projection type CRTs which can attain 40-inch or larger screens have been increasing for both home and business purposes. In the case of a projection type CRT, the fluorescent screen of a projection type CRT requires a brightness of several to several tens of times that of a direct viewing type CRT because an image is projected onto 40-inch, 52-inch or lager screens. Thus, the fluorescent screen of a projection type CRT should be excited under the condition in which a high-density current of several to several tens of times that of a direct viewing type CRT is applied. However, this results in deterioration of luminance, which is particularly serious in green-emitting phosphors which contribute to about 70% of the luminance.
As components of the conventional green-emitting phosphor, Y
3
Al
5
O
12
:Tb, Y
3
(Al, Ga)
5
O
12
:Tb, LaOCl:Tb, Zn
2
SiO
4
:Mn, InBO
3
:Tb or Y
2
SiO
5
:Tb, which have improved characteristics compared to Y
2
O
2
S:Tb, Gd
2
O
2
S:Tb or ZnS:Cu, Al, are used alone. However, these single-substance green-emitting phosphors do not fulfil all characteristics required for a projection type CRT. Thus, mixed green-emitting phosphors obtained by mixing Zn
2
SiO
4
:Mn or InBO
3
:Tb with Y
3
(Al, Ga)
5
O
12
:Tb, Y
2
SiO
5
:Tb or pigment-attached Y
3
(Al, Ga)
5
O
12
:Tb in an appropriate mixture ratio are put into practical use.
For example, Japanese Patent Laid-Open Publication No. hei 4-161483 describes a mixed green-emitting phosphor obtained by mixing Zn
2
SiO
4
:Mn with Y
3
(Al, Ga)
5
O
12
:Tb in order to improve color purity. Also, U.S. Pat. No. 4,559,469 describes a mixed green-emitting phosphor obtained by mixing Zn
2
SiO
4
:Mn with Y
2
SiO
5
:Tb in order to improve color purity.
However, the Zn
2
SiO
4
:Mn phosphor used for improving color purity in the mixed green-emitting phosphor for a projection type CRT, has poor degradation characteristic under the condition in which a high-density current is applied, while exhibiting excellent color purity. Thus, a decrease in the luminance is large with the passing of time. Also, due to a long afterglow time, the amount of the Zn
2
SiO
4
:Mn phosphor mixed with another phosphors is restricted. To avoid such a problem, there has been an attempt to improve luminance and afterglow characteristics by mixing a fluoride compound instead of the Zn
2
SiO
4
:Mn phosphor, as disclosed in U.S. Pat. No. 4,336,313.
Conclusively, the Zn
2
SiO
4
:Mn phosphor mixed for improving color purity in the mixed green-emitting phosphor for a projection type CRT has a very long afterglow time, that is, about 30 ms, and has poor luminance and degradation characteristics. Thus, as the amount of the mixed Zn
2
SiO
4
:Mn phosphor increases, luminance and degradation characteristics of the mixed green-emitting phosphor become poorer.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a new green-emitting phosphor composition which can replace a conventional green-emitting phosphor composition containing a Zn
2
SiO
4
:Mn phosphor.
It is another object of the present invention to provide a cathode ray tube (CRT) manufacturing using the new green-emitting phosphor composition.
Accordingly, to achieve the first object, there is provided a green-emitting phosphor composition comprising:75 to 95 wt % of a phosphor of the formula Y
2
SiO
5
-Tb, and 5 to 25 wt % of a phosphor of the formula SrGa
2
S
4
:Eu.
Preferably, the phosphor of the formula Y
2
SiO
5
:Tb contained in the composition is 85 to 95 wt %, and the phosphor of the formula SrGa
2
S
4
:Eu contained in the composition is 10 to 15 wt %.
To achieve the second object, there is provided a cathode ray tube manufacturing using the green-emitting phosphor composition.
REFERENCES:
patent: 4336313 (1982-06-01), Peters et al.
patent: 4559469 (1985-12-01), Welker et al.
patent: 6168892 (2001-01-01), Ohara et al.
patent: 2001/0008363 (2001-07-01), Sanghera et al.
patent: 2001/0013591 (2001-08-01), Park et al.
patent: 405089800 (1993-04-01), None
patent: 1982-0001593 (1982-09-01), None
Heo Gyeong-jae
Jeong Joa-young
Yoon Won-ho
Clove Thelma Sheree
Lowe Hauptman & Gilman & Berner LLP
Patel Nimeshkumar D.
Samsung SDI & Co., Ltd.
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