Compositions – Inorganic luminescent compositions – Zinc or cadmium containing
Reexamination Certificate
2000-07-03
2002-05-28
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Zinc or cadmium containing
C252S30140R, C252S30140S, C252S30140P, C252S30140F, C252S30140H, C252S301500, C252S30160R, C252S30160P
Reexamination Certificate
active
06395196
ABSTRACT:
TECHNICAL FIELD
This application generally relates to a process for producing an electroluminescent phosphor and, more particularly, to a process that produces a phosphor having an extended half-life.
BACKGROUND ART
Electroluminescent phosphors are used for backlighting in LCD's, in copying machines, for backlighting membrane switches, for automotive dashboard and control switch illumination, for automotive exterior body lighting, for aircraft style information panels, for aircraft information lighting, and for emergency egress lighting. U.S. Pat. Nos. 3,014,873; 3,076,767; 4,859,361; 5,009,808 and 5,110,499 relate to methods for producing electroluminescent phosphors. The methods described in these patents result in electroluminescent phosphors that have achieved general commercial success; however, the lifetimes of these phosphors have left something to be desired. Since the cost of replacing devices utilizing these phosphors can be substantial, it would be an advance in the art to provide phosphors having a greater life expectancy.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to obviate the disadvantages of the prior art.
It is an object of the present invention to produce electroluminescent phosphors with a longer half-life than those heretofore produced. As used herein the half-life of a phosphor is that period of time for a given phosphor's light output to decrease to one half that of its original brightness.
This invention achieves these and other objects, in one aspect of the invention, by reacting an uncoated electroluminescent phosphor with antimony. The reaction takes place under the following conditions: A supply of antimony is placed in the bottom of an inert reaction vessel. A vapor permeable filter is placed on top of the antimony and a supply of an uncoated electroluminescent phosphor with given half-life is deposited on top of the vapor permeable filter. The reaction vessel is evacuated below one atmosphere and then heated to allow the antimony to react with the phosphor to produce a new phosphor with a half-life greater than the original phosphor.
BEST MODE FOR CARRYING OUT THE INVENTION
For a better under understanding of the present invention, together with other and further objectives, advantages and capabilities thereof, reference is made to the disclosure and claims in connection with the following description of some of the aspects of the invention.
The extended half-life of the electroluminescent phosphor gained by the practice of the process is shown by the examples in TABLE I:
TABLE I
Light Output
Temp
Time
Color
24
100
half-life
Sample
Element
° C.
hrs.
X
Y
Ft. Lamberts
Hours
% Improved
424-27-C
Control
.184
.435
31.6
26.9
652
424-27-2
Vac Treatment
500
72
.193
.471
31.1
23.9
390.5
424-76-1
Vac Treat with Sb
700
98
.201
.440
16.0
12.35
321.1
449-11-1
Vac Treat with Sb
500
72
.197
.447
20.7
20.1
2317.7
5.9×
449-78-1
Vac Treat with Sb
600
96
.194
.412
7.0
6.9
>990.8
449-90-1
Vac Treat with Sb
500
96
.191
.427
18.2
16.9
941.0
2.4×
484-5-2
Vac Treat with Sb
500
48
.191
.418
18.3
16.8
1105
2.4×
484-5-1
Vac Treat with Sb
500
288
.193
.434
14.3
13.1
863.8
2.2×
484-8-1
Vac Treat with Sb
500
24
.191
.422
17.5
17.9
1637.2
4.19×
484-32-2
Vac Treat with Sb
500
96
.195
.452
22.0
21.1
1235.6
3.16×
505-17-1
Vac Treat with Sb
450
24
.195
.443
34.2
29.9
767.5
1.9×
505-17-2
Vac Treat with Sb
450
7
.189
.424
29.1
25.1
687.9
1.76×
505-12-1
Vac Treat with Sb
475
24
.196
.445
28.8
25.4
960.2
2.46×
505-12-2
Vac Treat with Sb
475
14
.195
.445
29.2
25.7
990.2
2.54×
484-32-3
Vac Treat with Sb
475
96
.195
.437
23.4
22
1225.2
3.13×
In Table I, the color coordinates are from the standard C.I. E. Chromaticity Diagram; the Light Output is at the 24 hour and 100 hour periods and the ratings are in Ft. Lamberts; and the % Improved column figures are derived from the half-life of the indicated sample divided by the half-life of the vacuum fired control, Sample 424-27-2.
As can be seen from the table, when the electroluminescent phosphor prepared by the process claimed in this invention is compared to the non-treated, vacuum fired electroluminescent phosphor the phosphor treated with antimony has an extended half-life.
This invention provides a process for producing an electroluminescent phosphor that has an extended half-life. The invention is especially suited for zinc sulfide, copper activated phosphors or other zinc sulfide phosphors where copper is a co-activator. The method for producing the beginning phosphor comprised heating zinc sulfide in a furnace to an elevated temperature in the presence of a copper activator and halide fluxes to achieve an electroluminescent phosphor, cooling the phosphor to ambient temperature and washing the phosphor to remove the flux. The resulting ZnS:Cu phosphor was then dried. Phosphors created by this method are generally known. One such phosphor is a Type 723 electroluminescent phosphor (ZnS:Cu) available from Osram Sylvania, Inc., Towanda, Pa. Generally, the method is practiced by taking elemental antimony (Sb) and placing it in the bottom of an inert reaction vessel. In a preferred embodiment, a thick walled quartz glass tube is used but other inert reaction vessels may be used. The antimony is then covered with a vapor permeable filter, such as quartz wool, that allows vapor from the antimony to pass through A phosphor is placed on top of the wool plug. As noted above, in this specific embodiment a type 723 ZnS:Cu electroluminescent phosphor was used. The inert reaction vessel was then evacuated down below one atmosphere and sealed. The inert reaction vessel was then heated for a period of time allowing antimony vapor to pass through the vapor permeable filter and react with the phosphor thereby creating a new phosphor with a half-life greater than that of the original phosphor.
REFERENCES:
patent: 4263339 (1981-04-01), Fischer
patent: 53-141186 (1978-12-01), None
Gingerich Richard G. W.
Vanderpool Clarence D.
Koslow C. Melissa
McNeill William H.
Osram Sylvania Inc.
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