Electroluminescent lamps and phosphors

Electroluminescent phosphors, electroluminescent panels and lamps made with such phosphors, and a process and apparatus for treating phosphors are disclosed in which the phosphor particles are coated with a very thin coating of SiO.sub.2, to protect the phosphor particles from aging due to moisture intrusion. The phosphor particles are coated in a cold wall reactor by the pyrolytic decomposition of silane in the presence of heat and oxygen to a coating thickness of approximately between 0.1 and 3.0 microns. The apparatus and method of coating includes the placement of a quantity of phosphor in a cup-shaped heated reactor bowl and subjecting the particles to a temperature of about 490.degree. C. and an atmosphere of silane and oxygen, while continuously mechanically agitating the particles with a blade arrangement in which the particles are continuously rotated and turned so as to expose the surfaces of the heated particles to the reaction atmosphere. Panels and lamps made from such phosphors may be die cut and trimmed, have an increased life as compared to panels and lamps made with untreated phosphors, and exhibit a minimum of color shift during the lifetime of the panel.

This invention relates to improved electroluminescent lamps and phosphors, 
and to a method of making such improved phosphors. 
Conventional electroluminescent lamps have panels which are made with 
electroluminescent phosphors, such as copper activated zinc sulfide, 
embedded in a resin layer between a pair of electrodes. Such conventional 
lamps suffer from aging and degradation due to moisture, such as by the 
migration of water molecules into the matrix of the phosphor crystals. The 
aging process is accompanied by a loss in brightness, for a given level of 
excitation, and a shift in color of the lamp, both in the lamp's lighted 
and unlighted status. As a result, it has become necessary to go to 
extraordinary lengths to protect such lamp and panels against moisture. 
The lighted panels of conventional lamps also do not lend themselves to 
manufacturing processes which include die cutting, punching, perforating, 
or trimming through the active phosphor layer, as such operations will 
either immediately short out the lamp, or will result in a premature loss 
of brightness in the vicinity of the cut, and often accompanied by 
eventual failure of the entire lamp. Such behavior of conventional lamps 
severely restrict the use of electroluminesent lamps in many commercial 
applications which require punching, die cutting or the like, in a 
low-cost and mass-produced panel and/or in which moisture is present. 
Electroluminescent lamps which lack extraordinary external protection 
against the infusion of moisture are not only prone to suffer from loss of 
output, i.e., aging, but as noted above are observed to have a shift 
toward the color pink where the lamp output was originally white. Further, 
where the natural color of such a lamp in its unlighted condition is an 
overall light tan, such lamps have been observed, with aging, to take on 
an overall gray or black color. In many cases, such a change in color is 
undesirable or unacceptable. 
The desirability of encapsulating electroluminescent phosphors to retard 
aging has been recognized. Both organic and inorganic coatings have been 
suggested, with varying degrees of success. One approach, as disclosed in 
the patents of Allinikov, U.S. Pat. No. 4,097,776 issued June 27, 1978 and 
Olson et al, U.S. Pat. No. 4,508,760 issued Apr. 2, 1985, includes the use 
of organic or polymer resin materials for encapsulation. In Allinikov, the 
phosphor particles are immersed in a solution of liquid crystal material 
and stirred, and thereafter dried to form a resin coating. In Olson et al, 
specific polymers are vacuum deposited on the surface of the crystals. 
Resin coated phosphors have not found general use in the manufacture of 
electroluminescent lamps since they suffer from many of the same problems 
as do conventional resin embedded particles, that is, that the resins do 
not fully exclude moisture and may interact with the phosphor. When such 
resin encapsulated particles are used as a substitute for conventional 
uncoated particles, they may be mixed with a resin adhesive and applied, 
as by screen printing or by a blade, to a substrate in the manufacture of 
the lamp. The intermediate resin coating surrounding the particles is 
usually no better in preventing aging than is the adhesive or casting 
resin itself. 
The prior art also contains a number of attempts to provide an inorganic 
barrier or coating on the phosphor particles, including Piper, U.S. Pat. 
No. 2,944,177 issued July 5, 1960. In Piper, phosphor crystals or 
particles are mixed with a glass frit, and then heated to approximately 
530.degree. F. until the glass fuses, producing a phosphor and glass 
aggolomerate This is then cooled and crushed until the resulting particles 
are sufficiently small so as to be applied as a glass coated particle in 
lieu of conventional electroluminescent phosphor grains. However, the 
glass fusing and crushing process of Piper has not come into general usage 
because of two principal disadvantages. First, in crushing or grinding, 
many of the phosphor particles themselves are ruptured or broken and 
exposed, and are therefore subject to the normal effects of aging Further, 
the process produces too much glass in relation to the phosphor content, 
without close control of the thickness of the glass deposition with 
respect to the phosphor particles. 
Brooks, U.S. Pat. No. 3,264,133 of Aug. 2, 1966 discloses the coating of 
the phosphor particles with an inorganic coatings, such as barium titanate 
and titanium dioxide, to provide a high dielectric coating. While Brooks 
achieves an enhancement in brightness due to an increase in dielectric 
constant, it is not apparent that these coatings are useful to extend the 
life of the phospor or exclude moisture. 
In a number of related patents, Fischer has described the aging process in 
zinc sulfide phosphors and provides recipes for rendering the phosphors 
less immune to aging and for coating the phosphors with inorganic 
phosphates. These patents include U.S. Pat. Nos. 4,143,297 issued Mar. 6, 
1979; 4,181,753 issued Jan. 1, 1980; and 4,263,339 issued Apr. 21, 1981. 
The aging process is described in '297 as being aggravated by sulfur 
vacancies in the crystal lattice structure, which vacancies exhibit a 
negative charge and the presence of which Fischer believes promotes the 
diffusion of the positively charged copper ions within the grains of the 
phosphor. Fischer further believes that the copper out-diffuses to the 
surface and the electroluminescent mechanism becomes inoperative due to 
this form of aging. It is also clear that the aging is accelerated by the 
presence of moisture and electrolysis of the zinc and copper. As an 
intermediate step, Fischer treats his phosphor prior to coating by 
immersion in molten sulfur under heat and pressure in an autoclave. In 
'753, the disclosure is enhanced by the suggestion that metals may be 
added to the sulfur bath. 
After the sulfur process, Fischer boils the treated powder in a 
concentrated phosphoric acid to form an insoluble zinc phosphate skin 
around each particle. The light transmissive qualities of this coating are 
not disclosed. Patent '753 discloses a further intermediate step, prior to 
the phosphoric acid bath, of heating the sulfur treated particles in 
hydrogen peroxide to convert the zinc sulfide surface to a zinc oxide 
surface and thereafter treating in phosphoric acid to convert the zinc 
oxide to the zinc phosphate coating. 
Fischer also suggests that the particles can be glass coated, and states 
that the coating "can also consist of chemically vapor-deposited glass . . 
. produced by pyrolytic decomposition of metal-organic vapors." No example 
is given in Fischer of the metal-organic vapors, of any process for 
accomplishing the process, or of any lamp using such phosphors. 
Attempts have been made to coat phosphor particles with glass, i. e., 
silicon dioxide, and include the U.S. Pat. No. 3,408,223 of Shortes, 
issued Oct. 29, 1968. Shortes was not concerned with the coating of 
phosphor particles for use in electroluminescent lamps and therefore was 
not concerned about extending the life of such a lamp or the phosphors 
therein, or the exclusion of water vapors from interaction with the 
phosphor particles. Rather, Shortes was concerned with the manufacture of 
a cathode ray tube phosphor which had selectively higher electron energy 
ionization thresholds, and disclosed the coating of phosphor particles by 
subjecting the phosphors to a tetraethoxysilane atmosphere under high 
temperature conditions, and subjecting the phosphor particles repeatedly 
to such atmosphere by recirculating the atmosphere and/or the phosphor 
particles therethrough so as to provide a silicon dioxide coating. Shortes 
contains no disclosure of the thickness or character of the coating, or of 
the efficacy of the use of such a treated phosphor particle in an 
electroluminescent environment. 
U.S. Defense Department Technical Report AFFDL-TR-68-103 "Improving the 
Performance of Electroluminescent Lamps at Elevated Temperatures," July 
1968 by Thompson et al, published by United States Air Force Flight 
Dynamics Laboratory, ASFC, Wright-Patterson Air Force Base, Ohio, 
discloses the coating of electroluminescent particles with various 
refractory materials including silicon dioxide, titanium dioxide, and 
beryillium oxide, among others. All of the coatings were applied by the 
pyrolysis of chemical vapors at atmospheric pressure in a heated fluidized 
bed reactor. The silicon dioxide coatings were applied by the 
decomposition of tetraethyl orthosilicate Si(OC.sub.2 H.sub.5).sub.4 or 
silicon tetrachloride SiCl.sub.4, with reactor temperature of 400.degree. 
C. There is no mention in this respect of silicon coated phosphors used in 
an electroluminescent lamp. Rather, the authors concentrated primarily on 
the use of titanium and beryllium coated phosphors in making, and then 
testing electroluminescent lamps at very high operating temperatures. The 
titanium coated particles tended to fuse together or cluster into groups 
of coated particles, and it was difficult to maintain the desired phosphor 
population in a lamp, apparently due to the shape of the particles and the 
quantity of coating included. Accordingly, the overall lamp brightness was 
reduced due to the reduced phosphor particle populations as compared to a 
conventional lamp using uncoated phosphors. The authors, however, 
indicated that the silicon dioxide coated zinc sulfide phosphor was given 
an accelerated water vapor resistance test, not otherwise described, and 
indicated that the material "looked like it showed promise." 
SUMMARY OF THE INVENTION 
This invention relates particularly to an electroluminescent lamp 
incorporating phosphor particles which are coated with a thin coating of 
silicon dioxide, and to such phosphors and the method of making the same. 
Applicants have discovered that an electroluminescent lamp made with a 
phosphor in which the individual phosphor particles are coated with a very 
thin coating of silicon dioxide, provides surprising and unexpected 
results. Such a lamp has been found to have aging characteristics which 
closely parallel those of fully incased lamps. In addition, such lamps 
according to this invention do not initially suffer any substantial loss 
in brightness by reason of the presence of the coating on the phosphor 
particles, and do not exhibit the characteristic color shifts with aging 
which have been observed in conventional lamps. Also, the lamps, and the 
panels from which such lamps are made according to this invention, may be 
cut, punched, or otherwise severed through the active phosphor coating 
with minimal darkening, discoloration or loss of brightness at the exposed 
edges. 
The invention also includes the method and apparatus by which 
electroluminescent phosphors are treated, by the application of a thin 
homogeneous coating of silicon dioxide to the particles, in the nature of 
one micron or less in thickness. A cold wall reactor is disclosed, which 
provides for the heating of phoshor particles to a temperature sufficient 
to decompose silane in the presence of oxygen, while providing for the 
stirring and agitation of the particles so that all sides are uniformly 
coated. 
More particularly, the coating method employed by the coating apparatus of 
this invention includes the steps of heating the phosphor particles to be 
coated and while so heated, subjecting the particles to an atmosphere of 
silane and oxygen such as to cause silicon dioxide to be directly 
vapor-deposited uniformly over the surfaces of the phosphor particles. 
Examination confirms the formation of a thin clear glass coating fully 
surrounding the individual particles. To enhance the coating process, an 
electrostatic charge may be applied to the gas ions or between the gas 
ions and the particles to enchance migration of the gas ions and their 
combination on the surfaces of the phosphor particles. More particularly, 
the phosphor to be treated is subject to a controlled environment of 
SiH.sub.4 and O.sub.2, at an elevated temperature above that required to 
decompose the SiH.sub.4, such as about 480.degree. C., while causing the 
particles to be moved, tumbled, or stirred, and preferably while directing 
the gases to the particles' surfaces so as to form complete glass coatings 
on the particles. 
The improved phosphor, according to this invention, exhibits a clear 
coating of silicon dioxide as far as discernible, in a single thin layer 
between 0.1 and 3.0 microns in thickness, and preferably between 0.4 and 
1.0 microns. The thickness of the layer does not vary materially between 
phosphor particles of different sizes. Since the silicon dioxide layer is 
formed in a continuous process, the layer on the particles is homogeneous 
and free of demarcation lines or changes in crystalline structure in 
relation to its thickness. This single, homogeneous layer of silicon 
dioxide is attributed to the cold wall reactor and process of this 
application, and by the use of silane as the silicon donating compound, 
and oxygen, in the process. 
It is accordingly an important object of this invention to provide an 
electroluminescent phosphor and a lamp employing such phosphors, highly 
resistant to aging due to moisture or water molecule intrusion. 
Another object of this invention is the provision of a lamp, as outlined 
above, characterized by uniform light output throughout the service life, 
with a minimum of color shift either in the energized or unenergized 
condition. 
A still further object of the invention is the provision of a flexible 
electroluminescent lamp including a panel section which may be die-cut, 
trimmed and punched, without any substantial loss of light output or 
darkening around the cut edges, and without premature failure of the lamp. 
A further object of the invention is the provision of a method of applying 
a uniformly thin and uniformly distributed silicon dioxide coating to 
electroluminescent particles for use in lamps. 
Another object of the invention is the provision of a cold wall reactor 
apparatus useful in the controlled application of silicon dioxide coating 
to phosphors. 
A further object of the invention is the method of coating 
electroluminescent phosphors and phosphors so coated by the pyrolitic 
decomposition of silane in the presence of an oxygen carrier. 
These and other objects and advantges of the invention will be apparent 
from the following description, the accompanying drawings and the appended 
claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Phosphor processed in accordance with this invention is coated with silicon 
dioxide by chemical vapor deposition in a cold wall reactor illustrated in 
FIGS. 1-4. The reactor 10 has a generally cylindrical container wall 12 
closed by a lid 13 and a bottom 14. The wall 12 of the reactor is chilled 
by a cooling coil 15, which coil has an inlet 16 at the top and an outlet 
at the bottom. The cooling coil may be embedded in the wall or may be 
formed closely to the wall interior as shown or wrapped about the exterior 
of the wall. The coil 15 cools the wall to maintain a temperature 
substantially below that in which the silica is deposited on the 
electroluminescent phosphor crystals. 
The cold wall reactor 10 has a base 20 mounted on the floor 14 by a tripode 
consisting of three adjusting screws 22, shown for the purpose of 
illustration as being in one line, but which actually occupy 120.degree. 
relative positions, by means of which the base may be adjusted with 
respect to the floor 14. The base 20 supports an annular bowl retainer 25. 
The cup retainer 25 is heated by an electrical resistance heater 26 with 
leads 27 and 28 extending therefrom. 
The central portion of the retainer 25 defines a cylindrical opening which 
receives a high temperature reactor bowl 30 (FIG. 2). The base of the bowl 
30 is generally flat with vertical sides. The bowl 30 has embedded therein 
a thermocouple 32 with a pair of wires 33 thereto. The reactor bowl 30 
receives a quantity of phosphor to be treated to an elevated temperature. 
A combined stirring, scraping and smoothing blade arrangement illustrated 
generally at 35 is received within the bowl for scraping, lifting, 
spreading and smoothing the heated electroluminescent phosphor 50 within 
the bowl 30, as rotated by an adjustable stirring rod 36. The lower end of 
the rod 36 is received within a conical central depression 38 (FIG. 2), 
formed in the bowl, forming a centering bearing for the rod 36. The blade 
arrangement 35 is mounted on the lower end of the stirring rod 36. As 
shown in FIG. 1, the upper end of the rod is adjustably driven by a 
coupler 37 to a 0.5 rpm DC drive motor 40, mounted on legs 42 on the cover 
13. 
With further reference to FIGS. 2 and 3, the blade arrangement 35 includes 
sheet metal lifting and scraping blade 44 and a smoothing blade 45. The 
blades 44 and 45 extend generally radially outwardly from the rod 36, and 
are welded, such as by spot welding to opposite sides of the rod, as shown 
in FIGS. 2 and 3. The lifting and scraper blade 44 defines an angulated 
mixing paddle, with a lower flat edge 44 which rides along the flat bottom 
of the reactor bowl 30. The block 44 has a radial length extending to the 
vertical walls of the bowl, and firm about a 30.degree. angle to the 
floor. The blade 44 runs submerged in the phosphor and its inclined 
surface gently engages the phosphor 50 in the bowl and causes the phosphor 
to be lifted along the surface, turned, and deposited behind it in its 
direction of travel, as illustrated in FIG. 2. 
The opposed smoother blade 45 is also paddle-shaped and has a lower 
straight edge 45' in spaced relation to the floor of the bowl 30. The 
blade 45 follows the blade 44 by approximately one-half turn or 
180.degree., and smooths the upper surface 52 of the phosphor 50 after it 
has been turned by the lifting and scraping blade 44. 
A third blade indicated generally at 60 is mounted on an arm 61 for 
rotation with the rod 36 and has an outer paddle-like or leaf-like end 62, 
as best shown in FIG. 3. The blade end 62 engages phosphor in the corners 
of the bowl and along the bowl wall, and moves it in a pile away from the 
wall for engagement and leveling by the following blade 45. 
The cold wall reactor 10 includes a pair of gas diffuser nozzles, shown in 
FIG. 1. A first nozzle 63 is mounted on the end of a depending tube 64, 
and a second nozzle 65 is mounted on the end of a depending tube 66. One 
or more additional inlet tubes (not shown) may be mounted in the cover 
such as for applying other gasses used as dopants. 
The tubes 64 and 66 depend through the cover 13 and extend partially into 
the interior of the reactor 10. The nozzles 63 and 65 are pointed 
downwardly toward the bowl 30, and one of these nozzles, such as the 
nozzle 63, emits a nitrogen-silane mixture while the other nozzle 65 emits 
oxygen. The tube 64 is connected to means (not shown) by which silane gas 
(SiH.sub.4) is blended with nitrogen, in an approximate ratio of 1 to 2% 
silane to 99 to 98% nitrogen. An amount of oxygen through the nozzle 65 is 
sufficient to provide a Molar concentration of 3 to 1 or greater oxygen to 
silane. If desired, a small impeller 70, driven by a motor 72, may be 
employed to assure circulation of the products within the reactor. 
In use, a crystalline phosphor, of the general kind described below, is 
deposited in the bowl 30 approximately to the level of the blade 45. For a 
five-inch diameter bowl, approximately 15 grams of phosphor crystals are 
placed in the bowl. Pure nitrogen is then introduced through the nozzle 63 
to flood the interior and to expel any other gases, through an outlet tube 
79 in the cover 13. At the same time, the heating element 26 is turned on 
and a temperature controller permits the reactor bowl to heat up to 
100.degree. C., to allow the temperature to stabilize. The motor 40 may 
now be turned on. By viewing the process through a top-viewing window 72, 
one can observe that the phosphor crystals are being smoothed by the blade 
45 and turned by the blade 44. If the level of phosphor appears uneven, 
the level of the bowl may be adjusted by the screws 22. 
Following this, the temperature may be increased to approximately 
200.degree. C., allowed to stabiize, and then increased to 400.degree. C. 
and stabilized. After such stabilization, silane gas is blended with the 
nitrogen in the ratios defined above and brought in through inlet tube 64 
and nozzle 63, and oxygen is admitted through the nozzle 65, and the 
reactor temperature is raised to 450.degree. C., allowed to stabilize, and 
then increased to 490.degree. C. As an example, satisfactory results have 
been obtained with flow rates of 1.29 liters per minute of a silane 
nitrogen mixture and 1.85 liters per minute of oxygen, in which the ratio 
of silane to nitrogen was 1% silane, 99% nitrogen. 
Cooling water is forced through the cooling coils 15 from the inlet 16 to 
the outlet 17, to maintain the wall of the reactor 12 substantially cooler 
than the quantity of phosphor 50 and the bowl 30. This prevents unwanted 
reactions on these surfaces and encourages the reaction to take place on 
the phosphor itself. 
The circulating impeller 70 and motor 72 assures that the gases are 
circulated to prevent stratification of temperature. It has been found 
that if the temperature at any one location becomes too high, a silica 
dust tends to form which acts as a contaminate to the phosphor. On the 
other hand, if the gases become too cold, they will unduly chill the 
exposed layer of phosphor on the surface of the bowl 30 and substantially 
increase the reaction time. The silane at the reaction temperature 
490.degree. C. undergoes a pyrolytic decomposition to form pure silica and 
hydrogen. The amount of hydrogen produced by the reaction is very small, 
and due to the large quantity of nitrogen present, it is not as hazard. 
The slow rotation of the stirring rod 36 causes the blade 44 to scrape the 
heated phosphor 50 from the bottom of the bowl 30 and gently lift the same 
over the top of the blade, where it freefalls behind the blade, thus 
gently turning the phosphor particles to expose new heated particles to 
the reaction gases at the surface where the major portion of the coating 
process occurs. The particles are heated by contact with the bowl surfaces 
then turned and brought to the surface for reaction by the action of the 
blades. The blade 44 thus runs substantially submerged in the pool of 
phosphor particles 50, as shown by the broken outline view in FIG. 3, 
while the smoothing blade 45 has its bottom edge 45' spaced above the 
bottom of the bowl, and smooths the phosphor at the surface, also tending 
to rotate or turn the top phosphor particles as it passes. The blade 45 
also levels the row of phosphor made by the paddle end 62 of the arm 60. 
The combined actions of the blade arrangement 35 assures that each 
particle is smoothly and completely encapsulated and covered as shown in 
FIG. 4, and further resists the tendency of the phosphor particles to 
group together or form in clumps. 
The reactor 10 is allowed to run for approximately 1.5 to 2.5 hours at the 
final temperature, and then is shut down. The phosphor crystals, as 
magnified approximately 1200 times are shown in FIG. 4 as having a uniform 
coating 80 of silicon dioxide, which coating is fully continuous about 
each particle with very little evidence of clumping of particles. Further, 
the coating 80 is approximately the same thickness for each of the 
individual particles 50a, b, c, and d, regardless of the shape or size of 
the particles. 
Good results have been obtained by the use of a blended white phosphor, 
primarily copper or magnesiumactivated zinc sulfide, in accordance with 
Sylvania Specification No. 830. This phosphor is found to have a size 
distribution as follows: 5% exceeds 39.5 microns; 50% exceeds 27 microns; 
95% exceeds 14.6 microns. In general, the phosphor particles have a size 
distribution in which about 90% of the particles are between 14 and 62 
microns in size, as measured by a Coulter counter. 
The chemical vapor deposition provides a uniformly thin continuous layer, 
relatively constant thickness with a minimum thickness in the order of 0.1 
micron and a maximum thickness in the order of 3 microns. Preferably, the 
coating thickness is between 0.4 and 1.0 micron. Such an extremely thin 
coating, in relation to the size of the phosphor particle, permits the 
highest possible electrical field across the particles and the presence of 
the coating does not adversely affect or substantially reduce the amount 
of active phosphor which may be applied to any given electroluminescent 
panel. 
The method and apparatus also permit relatively low temperature deposition 
which is not harmful to the electroluminescent crystals. The apparatus is 
of simple construction and relatively easy to operate. Further, the 
crystals of the phosphor are not in constant motion, and are covered or 
coated in essentially a single process. 
Test panels were made employing phosphor which has been conditioned in 
accordance with this invention and compared with identical test panels 
using uncoated phosphor. The test panels were compared to panels which 
were completely sealed in polychlorotrifluoroethylene, such as "Aclar", 
available from Allied Chemical Company, after the panel was completed, for 
total exclusion of moisture. 
In each of the test panels, a base resin was prepared for the phosphor 
layer, for the dielectric layer, for the electrode layer, and for a 
protective overlayer of the same resin material, namely a polyester base 
consisting of approximately 50% cyclohexanone, 16.7% diethylene glycol 
monobutyl ether acetate and 33.3% polyester adhesive 49001 of Dayton 
Chemicals Division. This base resin was then mixed approximately 72% 
processed phosphor to 27% resin for the phosphor layer, 55% barium 
titanate for the dielectric layer, and 71% flaked silver for the 
conductive layer. 100% resin was used for the protective layer. Each of 
the layers was activated by approximately 0.4% to approximately 1.6% 
Adcoat Catalyst F of Morton-Thiokol, Inc. to reduce curing time. All 
percentages are by weight. 
Lamps constructed for the purpose of the evaluation of the conditioned 
phosphor in accordance with this invention are illustrated in FIG. 5. Each 
of the test lamps was constructed on a clear flexible base 100 of PET 
(biaxially oriented polyethylene terephthalate) material, to which had 
been applied a transparent electrode which is diagrammatically illustrated 
at 102. The transparent electrode is a metalized, vapor deposited 
indium-tin-oxide conductive coating having a resistance in the order of 
175.+-.25 ohms per square, and is shown in exaggerated thickness. 
The base 100 with electrode 102 thereon was heat treated at 121.degree. C. 
for 30 minutes, to stabilize the film to prevent warping during the 
ink-drying process. 
The phosphor resin layer 105 was applied to the base 100 on the electrode 
102 by screen printing after the phosphor had been blended with the resin, 
as identified above, by thoroughly mixing with a spatula to wet out all of 
the phosphor particles. The resulting phosphor ink had a viscous 
cream-like consistency. The phosphor ink was applied through a 157-mesh 
screen and dried at 110.degree. C. for thirty minutes. 
The barium titanate layer 110 was prepared in accordance with the above 
formula, in which the resin was added to the powder followed by mixing 
with a spatula to wet all particles, followed by mixing in a blender at 
high speed for 10 minutes, and then rolled overnight. Prior to mixing with 
the resin, the barium titanate powder was sieved and dried at 250.degree. 
C., to eliminate all moisture prior to blending with the resin. The barium 
titanate layer 110 was applied as two layers, one directly on top of the 
other, through a 95-mesh screen. Each layer was dried at 110.degree. C. 
for 50 minutes. 
The silver electrode layer 112 was prepared in accordance with the 
above-defined formula by mixing with the resin with a spatula to wet all 
particles, then mixed in a high speed blender for 10 minutes and rolled 
overnight, in the same manner as that of the layer 110. The silver 
electrode layer was applied through a 330-mesh screen as a single layer 
and dried for 40 minutes at 110.degree. C. 
Finally, a clear protective layer 115 of resin was applied to the silver 
layer through a 195 mesh screen, and dried for one hour at 110.degree. C. 
All test lamps were die-cut to 2 inches by 4 inches in size. 
The lead attachments to the test panels were made as shown in FIG. 6. Wire 
mesh power leads such as the lead 120 was attached to the silver electrode 
112 of a test panel 125 by means of a conductive transfer adhesive 124, 
and laminated in place. Electrode attachment may also be made by use of 
conductive epoxy or adhesive. The connection is protected by a layer 128 
of Tedlar tape, and applied to the wire mesh leads 120, and to the panel 
edge, for mechanical support. A similar lead attachment was used for the 
transparent electrode 102. 
Performance tests were made on the test lamps constructed, as defined 
above, with coated and uncoated phosphors, and compared against the 
performance of a totally "Aclar" encapsulated electroluminescent lamp. The 
lamps were tested under three different environmental test conditions: (A) 
Humidity, with Lamps Operating; (B) Humidity with Lamps Not Operating; and 
(C) Standard Laboratory Conditions (SLC) with Lamps Operating. Two each of 
the test lamps were used in each test and the results averaged between 
them. All electroluminescent lamps, at the beginning of each test, were 
energized to 12 foot Lamberts. The voltage and frequency operating 
condition for each type of lamp was as follows: 
______________________________________ 
Lamp Type Voltage (VAC) 
Frequency (Hz) 
______________________________________ 
Unprocessed phosphor 
140 700 
Processed phosphor 
200 900 
"Aclar" Encased 
100 400 
______________________________________ 
A diagram (FIG. 7) of the Humidity with Lamps Operating (A) is shown below. 
The lamps were operated for nineteen hours and off for five hours. The 
temperature was 43.degree. C. and the humidity was 95% RH except for one 
hour where the temperature (22.degree. C.) and humidity (30% RH) were 
lowered to allow access into the chamber for light readings. 
The Humidity with Lamps Not Operating test (B) was performed under the same 
temperature and humidity conditions as (A) above. The lamps were lit 
during the one hour test at 22.degree. C. temperature and 30% RH to obtain 
light readings. 
The SLC test (C) was conducted with lamps operating continuously. The 
temperature and humidity under SLC were approximately 
22.degree.-24.degree. C. and 40%-60% RH, respectively. 
The cumulative results for the three lamp types versus the three test 
conditions is shown in Table 1. The performance graphs for these are shown 
in FIGS. 8 and 9. 
Test C 
Humidity--Non-operating 
In this test, all lamps performed equally well, and did not experience a 
color change, edge darkening or brightness loss. 
Test A (FIG. 8) 
Humidity--Operating 
The "Aclar" lamp was about equal to the lamp with processed phosphor and 
superior to the lamp with unprocessed phosphor. 
The processed phosphor lamp and the "Aclar" lamp remained white in color, 
while the unprocessed phosphor lamp turned pink. 
Edge and panel darkening was very pronounced with the unprocessed phosphor 
panel. The "Aclar" lamp did not show this phenomenon and the processed 
phosphor lamp exhibited only slight darkening. 
All lamps lost brightness during the humidity test cycle. After 480 hours, 
the unprocessed phosphor, processed phosphor and "Aclar" lamps had 
retained 20, 30 and 35%, respectively, of their initial brightness. 
Test B (FIG. 9) 
SLC--Operating 
All lamps retained their white operating color. Only the unprocessed 
phosphor lamp showed the edge and panel darkening phenomenon. The 
brightness retention of the processed phosphor lamp and the "Aclar" lamp 
were essentially equivalent at 51% and 54%, respectively. The unprocessed 
phosphor lamp retained 43% of its original brightness value. 
TABLE 1 
__________________________________________________________________________ 
Humidity Humidity SLC 
Non-Operating 
Operating Operating 
LAMP A B C A B C A B C 
__________________________________________________________________________ 
Unprocessed 
Phosphor 
White 
No 100 Pink 
Yes 20 White 
Yes 
43 
Processed 
Blue v. 
Phosphor 
White 
No 100 White 
slight 
30 White 
No 51 
"Aclar" White 
No 100 White 
No 35 White 
No 54 
__________________________________________________________________________ 
A = panel color after 480 hours 
B = edge darkening 
C = percentage brightness retained after 480 hours 
Significantly, the lamps which contained phosphor coated in accordance with 
this invention performed approximately equal to the "Aclar" encased lamp. 
The lamps retained their original desirable white color, edge darkening 
was negligible, and the lamps further retained their original overall 
light tan color in the unlighted condition, while lamps using the 
unprocessed or uncoated phosphor showed a shift to gray color in the 
unlighted condition. Table No. 2, below, shows the results of color change 
in the X and Y coordinates based on the standard CIE chromoticity chart 
and system of coordinates when lamps incorporating coated or processed 
phosphor were operated under standard laboratory conditions and under 
conditions of high humidity, as previously defined in FIGS. 9 and 8, 
respectively, and as compared with test lamps made with untreated phosphor 
under the same conditions. It will be seen by reference to Table 2 that 
the lamps which contained phosphor coated in accordance with this 
invention exhibited less color shift than did lamps employing untreated 
phosphor. 
TABLE 2 
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SCL Humidity 
Ohrs 336 hrs Ohrs 1000 hrs 
______________________________________ 
Processed Phosphor 
X 0.313 0.333 0.376 0.459 
Y 0.361 0.375 0.346 0.426 
Unprocessed Phosphor 
X 0.345 0.379 0.345 0.471 
Y 0.352 0.368 0.359 0.527 
______________________________________ 
An important advantage of lamps made employing the phosphor processed 
according to this invention resides in the fact that the lamps may be 
trimmed, die-cut or punched, after manufacture, through the operative 
layers, with only minimal edge darkening, even under the severe humidity 
and temperature conditions of test A, FIG. 8. 
While the method and product herein described, and the form of apparatus 
for carrying this method into effect, constitute preferred embodiments of 
this invention, it is to be understood that the invention is not limited 
to this precise method, product and form of apparatus, and that changes 
may be made therein without departing from the scope of the invention, 
which is defined in the appended claims.