Note: Descriptions are shown in the official language in which they were submitted.
3ArKGROUND OF THE Ii1VE~JTIO~I
This invention relates to luminescent materials of
the type genexally classified as phosphors; i.e~, materials
which, upon being impinged by a given frequency of radiation,
will emit radiation of a different frequency. In particular,
the inventio`n relates tG a novel orange-red emitting, UV
excitable phosphor of the general composition lead-manganese
activated calcium metasilicate having incorporated therein a
given amount of CaF20 Lead-manganese activated calcium meta-
silicate is a known orange-red emitting, W excitable phosphor.
A particular type of this phosphor is known as Sylvania No. 290,
and is available from GTE Sylvania Incorporated, Towanda,
Pennsylvania. The phosphor is excitable by 254 nm radiation
(ultra violet) and is used in fluorescent lamps. The phosphor
has a relatively high synthesis temperature; i.e., in the
neighborhood of 1975F to 2050F, it being known that synthesis
temperatures lower than the above, e.g., 1860F, will produce
an under-reacted and nonluminescent material. Since the higher
the firing or synthesizing temperature the greater will be the
cost of the phosphor, it would be an advance in the art if a
lower ~iring temperature could be achieved while maintaining
the emission and excitation characteristics of the known material.
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OBJECTS AND SVMMARY OF_THE_INVENTION
It is, therefore, an object of this invention to
obviate the disadvantages of the prior art. ~ ;
It is another object of the invention to provide a ``~
new phosphor material that is less costly to produce than similar
materials.
Yet another object of the invention is the provision
of a method for making such a phosphor.
These objects are accomplished in one aspect of the ~
invention by a luminescent composition of matter which consists ~ ~-
essentially of lead-manganese activated calcium metasilicate
containing a small amount of calcium difluoride. Emission and `~
excitation spectra of the new material are equal to that of the
older phosphor without the CaF2, and it can be synthesized at `~
a much lower temperature, thereby reducing the cost of prepara-
tion.
DESCRIPTION OF THE PREFERRED EMBODIMENTS `~
For a better understanding of the present invention,
together with other and further objects, advantages and cap- ;
abilities thereof, reference is made to the following disclosure `~
and appended claims~
~:~
In one aspect of the invention there is provided a
luminescent composition of matter consisting essentially of a
host matrix of calcium fluoride silicate containing an activator
consisting essentially of lead and manganese and wherein the ~ `-
said composition has the approximate general formula lCaF2 5Ca- ~ ;
MnSiO3:Pb and the composition range is 0.05-0.5 mole CaF2 per ;
mole of Ca-MnSiO3:Pb. ~
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In the preparation of lead-manganese activated calciurn ;-
metasilicate of type No. 290, the synthesis Piring is carried
out in the temperature range of 1975-2050F. With firing of
the above composition at lower temperatures, say 1860F, the
reaction products are under-reacted and nonluminescent.
It has been discovered that the inclusion of calcium
difluoride in the above composition lowers the synthesis firing
to about 1860F, at which temperature a phosphor material is now ~-~
produced which, as compared to the No. 290, has equivalent color ;~
emission and brightness. The calcium difluoride modified pro- ;
duct has the crystal structure of mixed wollastonite and
fluorite minerals.
In the ternary system CaO+activator-CaF2-SiO2 with`lead ;
plus manganese the activator at a composition formulated to
provide a ratio of 1 mole or slightly more of silica per l mole
of calcium plus manganese, any CaF2 over the very small amount ~ ;
required to form Ca-MnSiO3:PbF2 remains as uncombined CaF2:Mn
(fluorite) in the fired product. The fired product in this case,
with x equaling an indefinite quantity, can be expressed as:
Ga-MnSiO3 : x PbF2 x Ca-MnF2.
~ Manganese activated fluorite, such as appears in the
above-described product, emits ~reen with some lag under spark
discharge tube excitation but is inert under ultraviolet
excitation. It, therefore, contributes nothing`to emission ~ `
brightness or color under UV excitation and, since it has ~;
very little absorption of the emission of its companion
Ca-MnSiO3:Pb, its presence does not appreciably depreciate the
total emission intensity.
In Table I, the data show the effect of varying CaF2 `;
doped into a constant amount of lead-manganese activated calcium
metasilicate mix prior to firing on emission color and bright-
ness when fired at 1860F. Note that sample A fired without
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calcium fluoride catalyst was under-reacted and nonluminescent.
The X-ray diffraction patterns of samples B to F inclusive
shows mixture ofL3 CaSiO3 and CaF2 with increasing CaF2 in-
tensity from sample s to sample F.
TABLE I ;~
Moles MolesRelative Emission
Sample Ca-Mn SiO3: Pb CaF2 Intensity -~
, _ ~
No. 290 (Ca-MnSiO3:Pb Phosphor)100.0
A 1.00 None Inert
B 1.00 0.10 100.0
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C 1.00 0.20 101.0
D 1.00 0.30 100.5
E 1.00 0.40 100.0
F 1.00 0.50 99.0
Calcium carbonate, manganous carbonate, silicic acid,
lead fluoride, and calcium fluoride are weighed out in amounts `~
corresponding to a mole ratio of 1.0 calcium carbonate plus ~`
manganous carbonate to about 1.125 silicic acid and about 0.005
to 0.007 lead fluoride and about 0.10 to 0.50 calcium fluoride.
Any mixture of starting materials that when fired form
luminescent lead-manganese activated wollastonite-fluorite
mixed crystal structure material, may be used without departing
from the scope of this disclosure. For example, Sylvania Type
No. 290 lead-manganese activated calcium metasilicate may be
easily converted to ~ CaSiO3-CaF2 crystal structure by simply -~;
doping with calcium fluoride and firing at abaut 1~60F.
The prefired mixture is rendered homogeneous by wet
milling or other suitable means. Water is removed from wet `~
milled mixtures usually by filtering and drying prior to the ;
firing step. The mix is then placed in boats or crucibles and
fired in an atmosphere of air or nitrogen. The optimum firing
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temperature depends on -the amount of ca]cium fluoride used as a
catalyst and the firing time on the firing container~charge
size.
Particular examples of the preparation of these
phosphors are described below:
EXAMPLE 1
Weigh the following materials in finely-powdered form
into a 4 gallon pebble mill containing a standard 28 pound
charge of flint pebbles:
Mole Batch ~
Ratio Grams ~ `
CaCO3 0.940 1600 g
MnCO3 (44% Mn) 0.060 128. ~ -~
SiO2 x H2O (90% Sio2~ 1.125 1277.
PbF2 0.006 26. ;~
CaF2 0.200 265.
Add 6 liters deionized water to the mill and then roll it for
~ 12 hours at 47 rpm. Then filter as much water as possible from
- the slurry before drying it to near bone dry in an oven at
about 120C, then break up the oven dried cake by passing it
through a Mikropulverizer or by any other suitable means.
Then fire a portion of the pulverized material in a nitrogen ;
atmosphere for 1 hour at 1860F in a silica boat 6 inches long
by 3 inches wide by 2-l/2 inches deep filled level full and then
cool it in nitrogen to room temperature. Break up the material
with mortar and pestle or okher suitable means and then refire
it in a nitrogen atmosphere in a 6 inch by 3 inch by 2-l/2
inch deep silica boat for 2 hours at 1860F and then cool it
in nitrogen to room temperature. When broken up by mortaring
or other means the material will be a soft white body colored
product having equivalent emission color and brightness under
about 254 nm radiation to Sylvania Type No. 290 lead-manganese
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activated calcium metasilicate phosphox. -~
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EXAMPLE 2 -~
. . .
Fire a portion of wet milled, dried, pulverized raw
mix as described in Example 1 in air for 4 hours at 1860E in
a crucible of 2 liter volume about 8 inches tall filled full
and then cool it in air to room temperature. Break up the
fired, cooled cake and then re~ire it in air in a 2 liter
crucible for 4 hours at 1860F and then cool it in air to room
temperature. When broken up by hammermilling or other suitable
means the material will be soft white body colored having
equivalent emission color and brightness under about 254 nm
radiation to Sylvania Type No. 290 phosphor. ~- -
EXAMPLE 3
Weigh out and combine materials at the mole ratio
composition described in Example l. Render the mix homogeneous -~
by dry blending in a twin shell blender and then by passing dry ;
through a Mikropulverizer. Fire and refire in 2 liter volume
crucibles the same procedure described in Example 2. -~
While there have been shown and described what are
at present considered the preferred embodiments of the in~
` vention, it will be obvious to those skilled in the art that -~
various changes and modifications may be made therein without
departing from the scope of the invention as defined by the ;`
appended claims. ~
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