Plasma picture screen with terbium(III)-activated phosphor

Details Plasma picture screen with terbium(III)-activated phosphor Plasma picture screen with terbium(III)-activated phosphor

2001-05-18

2002-10-08

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With gas or vapor

Three or more electrode discharge device

C313S582000, C313S486000

Reexamination Certificate

active

06462473

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a plasma picture screen provided with a front plate, which comprises a glass plate on which a dielectric layer and a protective layer are provided, with a carrier plate provided with a phosphor layer comprising a red and a blue phosphor as well as a green, Tb
3+
-activated phosphor, with a ribbed structure which subdivides the space between the front plate and the carrier plate into plasma cells which are filled with a gas comprising xenon, and with one or several electrode arrays on the front plate and the carrier plate for generating corona discharges in the plasma cells.
BACKGROUND AND SUMMARY
Plasma picture screens render possible color pictures with high resolution and large screen diagonal and have a compact construction. A plasma picture screen comprises a hermetically closed glass cell which is filled with a gas, with electrodes in a grid arrangement. The application of a voltage causes a gas discharge which generates light in the ultraviolet range (145 to 185 nm). This light can be converted into visible light by means of phosphors and be emitted through the front plate of the glass cell to the viewer.
Phosphors which are particularly efficient under vacuum UV excitation are used for plasma picture screens. Frequently used green-emitting phosphors are, for example, Zn
2
SiO
4
:Mn (ZSM) and BaAl
12
O
19
:Mn (BAL). Both materials show a saturated green emission color with a high y-value of y>0.7. A disadvantage of both materials is their comparatively long decay time t
{fraction (1/10)}
, for example, 30 ms for Zn
2
SiO
4
with 2.5% Mn. The cause of this is that the transition
4
T
1
→
6
A
1
relevant for the emission of the light is spin-forbidden. In addition, the decay time t
{fraction (1/10)}
and the color point of a Mn
2+
-activated phosphor are strongly dependent on the Mn
2+
concentration. A further disadvantage is the sensitivity of Mn
2+
to an oxidation to Mn
3+
or Mn
4+
, which reduces the stability of the phosphors.
By contrast, Tb
3+
-activated phosphors are temperature stable and photostable, because Tb
3+
does not readily oxidize to Tb
4+
. A further advantage of these phosphors over Mn
2+
-activated phosphors is their shorter decay time t
{fraction (1/10)}
, which lies between 2 and 10 ms, depending on the host lattice.
U.S. Pat. No. 6,004,481 accordingly describes a green-emitting Tb
3+
-activated phosphor for use in plasma picture screens which has the composition (Y
1-x-y-z
Gd
x
Tb
y
Ce
z
)BO
3
, with 0.0<x<0.2, 0.01<y<0.1, and 0.0<z<0.1.
A major disadvantage of Tb
3+
-activated phosphors is their yellowy-green color point, which has a low y-value of y<0.62.
The invention has for its object to provide a plasma picture screen with a Tb
3+
-activated phosphor whose green pixels provide light with an improved color point.
This object is achieved by means of a plasma picture screen provided with a front plate, which comprises a glass plate on which a dielectric layer and a protective layer are provided, with a carrier plate provided with a phosphor layer comprising a red and a blue phosphor as well as a green, Tb
3+
-activated phosphor, with a ribbed structure which subdivides the space between the front plate and the carrier plate into plasma cells which are filled with a gas comprising xenon, and with one or several electrode arrays on the front plate and the carrier plate for generating corona discharges in the plasma cells, wherein the gas comprises xenon in a proportion of between 5 and 30% by volume.
It is particularly highly preferred that the proportion of xenon in the gas is 10% by volume.
An increased proportional quantity of xenon in the gas surprisingly increases the y-value of the color point of Tb
3+
-activated phosphors. The result is that the green pixels of a plasma picture screen with a Tb
3+
-activated phosphor show a sufficiently saturated green.
It is furthermore preferred that the green Tb
3+
-activated phosphor is chosen from the group (In
x
Gd
1-x
)BO
3
:Tb (0≦x≦1), Y
2
SiO
5
:Tb, CeMgAl
11
O
19
:Tb, (Y
1-x-y
Gd
x
Pr
y
)BO
3
:Tb (0≦x≦1, 0≦y≦0.05), GdMgB
5
O
10
:Ce,Tb and LaPO
4
:Ce,Tb.
These Tb
3+
-activated phosphors are particularly efficient green-emitting phosphors when excited by VUV light.
It may be particularly highly preferable for the green Tb
3+
-activated phosphor to comprise (Y
1-x-y
Gd
x
Pr
y
)BO
3
:Tb (0≦x≦1, 0≦y≦0.05).
This phosphor has a short decay time t
{fraction (1/10)}
=8 ms and a high y-value>0.61 of its color point.


REFERENCES:
patent: 5903381 (1999-05-01), Watanabe et al.
patent: 6004481 (1999-12-01), Rao
patent: 6008582 (1999-12-01), Asano et al.
patent: 6344715 (2002-02-01), Tokunaga et al.

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