Note: Descriptions are shown in the official language in which they were submitted.
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BACXGROUND OF THE INVENTION
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This invention relates to zinc sulfide phosphors, and
more particularly relates to zinc suIfide cathodoluminescent
phosphors coactivated by gold, copper and aluminum.
A standard green phosphor used widely in the production
of cathode ray tubes for color television is a zinc cadmium
sulfide coactivated with copper and aluminum. The presence
of cadmium in these phosphors is known to have certain
beneficial effects. For example, the amount o cadmium may
be adjusted to vary x and y coordinate values within a
permissible range. Nevertheless its cost and handling pre-
cautions could lead eventually to the use of cadmium-free
cathode ray tube phosphors. Furthermore, phosphors contain-
ing cadmium tend to exhibit yellow body coLor and undesirable
shifts in body color during processing, so called "bake
shifts".
While zinc sulfide phosphors coactivated with copper and
aluminum having green cathodoluminescent emissions have been
known for some time, (see for example, U.S. Patent 2,623,858,
issued to Kroger on December 30, 1952), such phosphors are
characterized by low brightness levels and by the presence
of significant blue emissions, relulting in low purity of
green emissions. Such characteristics~render these phosphors
unsuitable for use in conventional tri-dot color cathode ray
tubes for color television.
In United StatesPatent 4,038,205, issued to ~enry B.
Minnier and H. David Layman on JuIy 26, 1977, and assigned
to the present assignee, a critical firing process is claimed
whereby the green emitting zinc sulfide: copper, aluminum
phosphor is improved in both color purity (by the substantial
suppression of blue emissions) and brightness, rending such
phosphors candidates for replacement of the present zinc~
cadmium sulfide: copper, aluminum phosphors in color cathode
ray tubes. ~
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It h~5 been discoye~ed th~t the ~ddition o~ yold as
as ~n acti~ator to ~ zinc sul~ide phosphox coactivated with
copper and aluminum results in cathodoluminescent emissions
having color cooxdina.tes shi~ted to higher ~ values, enabling
consideration o such phosphors as cand.idates fox xeplace-
ment o the zinc~cadmium sulfide- copper, aluminum
green phosphor in colox cathode ray tu~es ~or colox television.
As used herein the terms "x" and "y" coordinate
values refer to values on a standard chromaticity diagram as
de~ined by CIE ~Commission InternationaIe de L'Elairaje~
as determined by impinyement of a cathode ray heam upon a
packed sample of thQ phosphor po~der.
According to the present invention, there is provided
a 2inc sulfide cathodoluminescent phosphor coactivated by
gold, copper and aluminum, said gold, copper and aluminum
being present in the ranges of about 350 to 550 parts per
million/ 50 to 150 and 300 to 600 parts per million respect-
ivel~, and wherein the phosphor upon cathodoluminescent
emission exhibits x and y coordinate values within the
range o .3~0 to ~345 and .570 to .580 respectively.
Some embodiments of the invention will now be
described with reference to the examples belo~:
It is essential for the achievement of the advantages
described herein that the zinc sulfide phosphor contain all
three coactivators and may vary over a broad range, the a~lount
of gold typicall~ ranging from 20 to 900 parts per million,
copper from 50 to 250 parts per million and aluminum from
200 to 1,000 parts per million. However,it ls in general
preferred for the green component of a tri-dot color
cathode ray tube for color television to maintain the activa-
3q tor le~els within the ranges o 35~ to 550 parts per million
gold, 50 to 150 parts per million copper and 300 to 600 parts
per million alurl~inum, resultiny in x and ~ coordinate values
'J, within the range of .3~0 to 34$ and .570 to .580 respectivel~.
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Specific combinations of Au, Cu and Al which will result
in desired x and y coordinate values may be determined by
reference to the following regression analysis equations for
x and y as a function of Xl, X2 and X3, where:
Xl =(ppm Au -600)
X =(ppm Al/27)
2(ppm Au + ppm Cu)
X =(ppm Cu -150)
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The equations are as follows:
(1) x = 0.2662 -0.0013Xl +0.0162X2 +0 .00459X3 -0.0005X12
-O . 00043X22 -O . 00187X32 ~0.00297~1X2 -0.00274XlX3
-O.00187X2X3
(2) y = 0.606 -0.00057Xl -0.00235X2 +0.00496X3 -0.00027XlX2
-0.00017XlX3 -0.000495X2X3 ~0.000137Xl -0.000139X2
-O.00332X32
While the preparation of the phosphors of the invention
can be by any conventional method known in the art, in order
to aid the practitioner, an exemplary preparatory technique
will now be described.
Zinc sulfide, made by bubbling H2S gas through a solu-
tion of zinc sulfate, is dry blended with sources of gold,
copper and aluminum in the desired levels. Such sources of
activators include by way of example nitrates, carbonates,
sulfates, sulfides, chlorides and bromides. A flux of an
alkali metal hallde or alkaline earth metal halide, usually
the chloride or bromlde, and optionally sulfur, is added to
the blend and the mixture is then fired under a CS2 astmos-
phere at a temperature
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within the range of about 950 to 1050C for a time of from
about 1 to 2 hours, and then allowed to cool. The flux is
removed by washing and the powder is dried. Color and
brightness of the powder are then read on a packed bed of
the powder subjected to 14 kilovolt cathode rays.
The following are specific examples of the above process.
In all cases, the activators were introduced as a "mix"
prepared as follows:
Gold sulfide was prepared by dissolving chloroauric acid
trihydrate in water, adding zinc sulfide powder, and
bubbling H2S gas through the solution so as to yield a mixed
sulfide containing about 1500 parts per million of gold by
weiqht (gold mix).
Zinc sulfide powder was added to copper sulfate solution
and processed the same as the gold mix so as to yield a mix
containing about 5,000 parts per million of copper by weight
(copper mix).
Zinc sulfide and aluminum chloride were slurried in
water and the slurry was evaporated to dryness. The result-
ing zinc sulfide contained about lC,000 parts per million
of aluminum by weLght (aluminum mix).
-EXAMPLE I
To 47.2 grams of zinc sulfide, 0.9 grams of gold mix,
1.28 grams of aluminum mix and 0.64 grams of copper mix
were added, corresponding to levels of these activators in
parts per million of 27 gold, 64 copper, and 256 aluminum.
Two grams of a flux mix in the ratio of 90 parts by weight
sulfur and 30 parts by weight potassium bromLde were added
to the mixture andthe mixture was blended. It was then placed in a
quartz tray and flred for about 2~ hours at about 1850F under a flowing
CS2 atmosphere. The powder was then cooled and washed to remove soluble
flux, followed ~y drying. The resulting sal-~le was formed into a packed
bed and subjected to 14~V cathode rays and the color coordinates and
brightness were measured vs. a standard zinc-
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cadmium sulfide coactivated with copper and aluminum in the
amoun~s of about 50 parts per million copper and 100 parts
per million aluminum. The m~lar ratio of zinc to cadmium
in the standard was 14.45:1. The standard had x and y
coordinate values of 0.340 and 0.595 respectively and was
assigned a brightness level of 100 percent. The sample pro-
duced x and y coordinate values of 0.271 and 0.557 respect-
ively and a brightness of 91 percent.
EXAMPLE II
The procedure of Example I was repeated except that 41.38
grams of zinc sulfide were mixed with 6.7 grams of gold mix,
1.28 grams of aluminum mix and 0.64 grams of copper mix,
corresponding to levels of activators in parts per million
of 200 gold, 64 copper and 256 aluminum. This sample yielded
x and y coordinate values of 0.291 and 0.573 respectively
- ` and a relative brightness of 85 percent of standard.
EXAMPLE III
The procedure of Example I was repeated except that 29.88
grams of zinc sulfide were mixed with 18.2 grams of gold
mix, 1.28 grams of alumlnum mix and 0.64 grams of copper mix,
corresponding to levels of these actlvators in parts per
million of 546 gold, 64 copper and 256 aluminum. This
sample yielded x and y coordinate values of 0.307 and 0.573
respectively and a brightness of 77 percent of~standard.
EXAMPLE IV
The procedure of Example I was repeated except that
21.75 grams of zinc sulflde were mixed with 25 grams of gold
mix 1.75 grams of aluminum mix and 1.5 grams of copper mix,
corresponding to levels of these activators in parts per
million of 750 gold, 150 copper and 350 aluminum. The
sample yielded x and y coordinate values of 0.299 and 0.5~6
respectively, and a relative brightness of 72 percent of
standard.
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EXAMPLE V
The procedure of Example I was repeated except that25.5
gramsof zinc sulfide were mixed with 20 grams of gold mix,
3 grams of aluminum mix and 1.5 grams of copper mix, corres-
ponding to levels of these act-vators in parts per million
of 600 gold, 150 copper and 600 aluminum. This sample
yielded x and y coordinate values of 0.325 and 0.582 respec-
tively, and a relative brightness of 70 percent of standard.
EXAMPLE VI
The procedure of Example I was repeated except that
27.75 grams of zinc sulfide were mixed with 20 grams of gold
mix, 1.75 grams of aluminum mix and 0.5 grams of copper mix,
- corresponding to levels of these activators in parts per
million of 600 gold, 50 copper and 350 aluminum. This
sample yielded a phosphor with x and y coordinate values of
0.309--and 0.568 respectively in a relative brightness of
76 percent of standard.
The results of these six samples are tabulated below in
Table I.
TABLE I
x y Brightness
Std. ZnCdS:Al, Cu 340 .595 100
SAMPLE Cu Al Au
(in parts per million)
1 64 256 27 .271 .557 91%
2 64 256 200 .291 .573 85
3 64 256 546 .307 .573 77~
4 150 350 750 .299 .586 ~72%
150 600 600 .325 .582 ~70
6 50 350 600 .309 .568 76
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While there has been shown and described what are at
present considered the preferred embodiments of the
invention, it will be obvious to those skilled in the art
that various changes and modifications may be therein
without departing from the scope of the invention as defined
by the appended claims.
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