Two-component phosphor in a cool white lamp

Fluorescent lamps containing a two-component phosphor system consisting essentially of europium activated barium magnesium aluminate as a blue emitter and manganese and antimony activated calcium chlorofluorapatite as a yellow emitter use less energy to achieve at least comparable brightness as a standard cool white lamp with a suitable color rendering index.

BACKGROUND OF THE INVENTION 
This invention relates to cool white fluorescent lamps and to two-component 
phosphors incorporated therein. More particularly it relates to cool white 
lamps that contain two-component phosphors and as a result yield higher 
lumens per watt with a suitable color rendition then do prior cool white 
lamps. 
The color characteristics of light emitted from a fluorescent lamp depend 
on the choice of phosphors used to coat the internal walls of the lamp 
envelope. Emission spectra of luminescence centers in most phosphors 
consist of a single band peak at one particular wavelength. Therefore, in 
order to have white light it is necessary to either apply a mixture of 
phosphors or use a single phosphor containing more than one kind of 
luminescent center (such as the alkaline earth halophosphates). It is not 
enough to obtain the desired chromaticity coordinates and there are an 
infinite number of possible combinations of bands that would result in the 
same set of coordinates. It is also necessary that the lamp produce an 
acceptable luminous flux (brightness) and satisfactory optimum color 
rendition for all regions of the visible spectrum. 
There are four standard lamps used today, daylight, cool white, white, and 
warm white and the desired chromaticity coordinates for these lamps are 
given hereinafter. 
While it is possible to determine by theoretical computations the spectral 
energy distribution for a theoretical blue component and a theoretical 
yellow component that upon being blended together will yield a lamp having 
either brightness or color rendition maximized, such theory has to be 
tailored to the restraints as they exist in nature. In theory, a 
combination of a line emitting blue component and a line emitting yellow 
component would yield a lamp having the maximum brightness. Such a lamp 
however, cannot be produced for a number of reasons. First, phosphors 
having a line emission do not exist. Secondly, even if they existed the 
color rendition would be extremely poor because only two colors would be 
emitted and would result in color distortion in the area lighted by the 
lamp. Until recently the primary emphasis was placed upon color rendition 
with a suitable brightness. The single component halophosphates having two 
luminescent centers have been used to produce the aforementioned four 
white colors. The energy shortage, however, has shifted the emphasis to 
maximize lumens per watt of energy with an acceptable color rendition 
enabling a lower energy input to achieve the same level of brightness. 
While in theory, a two-component blend can produce warm white, there is no 
known binary combination of lumiphors that will yield that color, however, 
it has been discovered that binary blends can be made which will produce 
the other three colors. 
U.S. Pat. No. 4,075,532 discloses that europium-activated barium magnesium 
aluminate can be used with a calcium fluoraapatite to achieve a cool white 
lamp. However, the teachings are primarily directed to the 
europium-activated strontium chloroapatite. In FIG. 3 of the foregoing 
patent the europium-activated strontium chloroapatite is represented by 
number 41 on the portion of the CIE diagram contained in that figure. The 
x and y coordinates for that phosphor are x=0.152 and y=0.027. No data are 
given for the europium-activated barium magnesium aluminate. The 
europium-activated barium magnesium aluminate has a higher y value than 
the europium-activated strontium chloropatite therefore when combined with 
a calcium fluorapatite the resulting combination will not yield a material 
having an emission within the cool white ellipse. Since the europium 
activated barium magnesium aluminate is a more efficient phosphor than 
europium activated strontium chloroapatite, it is desirable to utilize the 
aluminate material. 
It is believed therefore that a two-component phosphor system which 
utilizes europium-activated barium magnesium aluminate and a halo 
phosphate phosphor to achieve a cool white lamp having a higher efficiency 
then the standard cool white lamp would be an advancement in the art. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this invention to provide a lamp employing a 
two-component blend including europium-activated barium magnesium 
aluminate that emits light similar to cool white, however, such a lamp has 
a higher lumen watt output then the present cool white lamps. 
In accordance with this invention lamps use less energy to achieve a 
comparable or a higher brightness than standard cool white lamps, and have 
suitable color rendering indexes are achieved by utilizing a specific 
two-component phosphor system that consists of essentially of 
europium-activated barium magnesium aluminate in specified amounts and a 
second component having a peak emission in the yellow region consisting 
essentially of manganese and antimony activated calcium 
chloro-fluorapatite having specific amounts of chlorine added to the 
molecule.

For a better understanding of the present invention, together with other 
and further objects, advantages and capabilities thereof, reference is 
made to the following disclosure and appended claims in connection with 
the above-described drawings. 
DETAILS OF THE PREFERRED EMBODIMENTS 
The chromaticity coordinates for the standard lamps are as follows: 
______________________________________ 
Lamp X Y 
______________________________________ 
Daylight 0.313 0.337 
Cool White 0.372 0.375 
White 0.409 0.394 
Warm White 0.440 0.403 
______________________________________ 
In theory, the binary blends which would yield the maximum brightness are 
represented in the following table and as previously reported by Walter, 
one of the inventors of this invention, in Applied Optics, Vol. 10, page 
1108, (1971). 
______________________________________ 
% Blue 
Component Line Emission 
Line Emission 
Lamp In The Blend 
Blue Yellow 
______________________________________ 
Daylight 29.1% 444 567.6 
Cool White 
19.0% 444 573.5 
White 13.5% 444 576.7 
Warm White 
9.7% 444 579.6 
______________________________________ 
As previously mentioned phosphors having line emission do not exist in 
nature and lamps employing such phosphors (even if they did exist) would 
not yield a color rendition acceptable for most purposes. It is necessary 
that phosphor having a band emission be used and into the color rendering 
index, as defined in the aforementioned article, should be at least about 
45. 
Also it is possible to calculate the theoretical two-component system that 
would yield a lamp having a suitable color rendition and brightness. These 
theoretical systems are given in the table below. 
______________________________________ 
Cool Warm 
Daylight 
White White White 
______________________________________ 
BLUE 
Peak (Nanometers) 
486 507 522 537 
50% Bandwidth 
(Nanometers) 111 121 128 135 
YELLOW 
Peak (Nanometers) 
601.0 606.8 611.7 614.4 
50% Bandwidth 
(Nanometers) 85 44 44 44 
% of Yellow Component 
60.9% 63.5% 60.5% 58.5% 
______________________________________ 
These data were also reported in Applied Optics, supra. In that article an 
arithmetic mean of the brightness index and the color rendering index was 
assumed. It has been found, however, that a CRI of from 45 to 50 is 
satisfactory for some major purposes where color is not the prime 
consideration. Such purposes include lighting in warehouses, garages, 
tunnels, corridors, etc.. 
Cool White is defined as a color having x and y coordinates of 0.372 and 
0.375 respectively. The lighting industry has accepted a somewhat broader 
definition as being any light source that falls within a relatively small 
oval having the forementioned coordinates at a center as shown by 20 in 
FIG. 2. The x value is for cool white phosphor therefore can vary about 
0.363 to 0.381 and the y values can vary from about 0.364 to about 0.386 
as long as the combined x and y colors fall within the cool white ellipse 
that is shown in the FIG. 2. 
Any phosphor blends must have color coordinates such that when the 
compensation through the mercury emission is made that a line connecting 
each of them will pass through the standard cool white oval. 
With particular reference to FIG. 2, the chromaticity of various phosphor 
compositions represented by the formula, 
EQU Ca.sub.5-w-x-y Cd.sub.w Mn.sub.x Sb.sub.y (PO.sub.4).sub.3 F.sub.1-y-a 
Cl.sub.a O.sub.y 
wherein 
w is from 0 to about 0.05 
x is from about 0.13 to about 0.17 
y is from about 0.02 to about 0.04 
a is from 0 to about 0.1 have been found to have emissions that fall along 
line A in FIG. 2. The composition represented by the formula 
EQU Ca.sub.4.775 Cd.sub.0.037 Mn.sub.0.157 Sb.sub.0.031 (PO.sub.4).sub.3 
F.sub.0.969 O.sub.0.031 
has an emission represented by point 22 in FIG. 2. As the chlorine content 
increases from 0 to 0.1 the x value increases and the y value decreases 
along A. Point 24 represents a composition wherein 10% of the fluorine is 
replaced by chlorine. When the emission of these phosphors is combined 
with the emission characteristics of the mercury in a standard fluorescent 
lamp, the combined emission falls along line B in FIG. 2. 
The blue-emitting phosphors which are useful in the practice of this 
invention are europium activated barium magnesium aluminates of the 
formula 
EQU Ba.sub.w Mg.sub.x Eu.sub.y Al.sub.11 O.sub.16.5+w+x+y 
wherein 
w is from about 0.05 to about 1.2 
x is from about 0.05 to about 1.2 
y is from about 0.025 to about 0.125 
stated in another manner, the phosphor composition consists essentially of 
a host consisting essentially of from about 0.4 to about 9.8 mole percent 
of barium oxide from about 0.4 to about 9.8 mole percent of magnesium 
oxide and from about 80.4 to about 99.2 mole percent of aluminum oxide, on 
an Al O.sub.1.5 basis, and as an activator, from about 0.025 moles to 
about 0.125 moles of divalent europium per mole of host. These materials 
in a standard lamp have chromaticity coordinates of x=0.152 and y=0.086 
and are represented by point 26 in FIG. 2. 
As can be appreciated manganese and antimony-activated calcium 
fluoroapatite and the europium-activated barium manganese aluminate can 
not be combined to yield a color falling within the cool white ellipse. It 
has been found that from about 0.5% to about 2% of the fluorine in the 
calcium fluoroapatite must be replaced with chlorine in order to achieve a 
lamp that has a color that fall within the cool white ellipse. A line, D, 
connecting point 22 and 24 in FIG. 2 passes to the left of the cool white 
ellipse. Increasing the chlorine value of about 2% replacement causes a 
line to pass to right to the cool white ellipse. It is therefore believed 
apparent that it is crucial that the chlorine content be kept within the 
0.5% to the 2.0% limits in order for a cool white lamp to be achieved. As 
is shown in FIG. 2 lines C and D from point 26 (the color coordinates for 
the europium activated barium magnesium aluminates) which are tangent to 
the cool white ellipse 20 intersect line B at points which correspond to 
the forgoing 0.5% and 2.0% replacement. Thus in the formula for the 
calcium chlorofluorapatite, a is from about 0.005 to about 0.02. 
With particular reference to FIG. 1, the sealed glass envelope 1 has the 
lead-in wires 2, 3, sealed through one of its ends and corresponding 
lead-in wires sealed through the other end. The usual coiled-coil 4 of 
tungsten wire is supported between, and electrically connected to, the 
pair of lead-in wires 2, 3, and a similar coil is supported by and 
connected to the lead-in wires at the other end of the envelope 1. An 
insulating base piece 5 having contact pins 6 and 7, each pin being 
connected to one of the lead-in wires, held in the metal cap 8, which is 
fixed by the cement 9 to one end of the envelope 1, and a similar base 
piece 16, having contact pins 10 and 11, is cemented to the other end by 
cup 12. 
The tungsten coils carry the usual electron-emitting coating of alkaline 
earth oxides, generally including also a small percentage of zirconium 
dioxide. 
A filling of inert gas such as argon, neon, krypton, and mixtures thereof, 
at about 2 millimeters of mercury pressure, and the usual small quantity 
of mercury is inside the glass envelope 1. The lamp has the usual stem 
press 14 and sealed exhaust tube 15. 
On the inside surface of the envelope, is a layer 13 of the phosphor 
materials previously described. To aid in the present manufacturing of 
fluorescent lamps the individual phosphors are preblended to give a 
uniform mixture prior to depositing the phosphors, however, this invention 
is not limited to providing a uniform blend if other techniques are used 
to manufacture lamps. All that is required is that each phosphor be 
relatively uniformly deposited over the internal surfaces of the glass 
envelope. 
The amount of the relative components that are used will depend upon 
whether a blend in the sense of the uniform admixture is utilized or 
whether a uniform distribution of two distinct layers are used. In the 
event two distinct layers are used, the amount of the inner layer will be 
decreased from the amount that is used in a blend. As is appreciated in 
the art if two phosphors having the same efficiency were utilized the 
amount of each phosphor that would be used when a blend is employed would 
be in the inverse relationship to the respective distances between the 
cool white target and the x and y coordinates of each of the individual 
phoshors when plotted on the CIE diagram. Thus in the practice of the 
present invention when a blend is employed from about 2 to about 15% by 
weight of the blue emitting phosphor is required with the efficiencies of 
the particular phosphors. If a two-layer approach is used the amounts of 
the inner layer would be decreased from that required in a blend, For 
example that if the blue-emitting material is used as the inner layer, the 
amount required is reduced by as much as 90 percent of that required in a 
blend and a similar reduction is achieved if the yellow-emitting phosphor 
is used as the inner layer. Thus in practice of the present invention from 
about 0.2% to about 70% by weight of the total phosphor utilized can be 
the blue emitting compound, that is the europium activated barium 
manganesium aluminate and the balance is the yellow emitting phosphor. 
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 made 
therein without departing from the scope of the invention as defined by 
the appended claims.