Cathode ray tube device with improved color filtering system

Halos occurring around bright light spots generated by cathode ray tube devices in which the light emitted by the tubes is filtered by filtering solutions are significantly reduced by the addition of cinnamic alcohol and/or cinnamaldehyde to the solution.

BACKGROUND OF THE INVENTION 
This invention relates to a new and novel CRT device for generating a 
bright color light spot of the type that is particularly useful for 
projection color television and information display. 
Green light radiation for use in projection color television in general is 
produced by the electron bombardment of a green luminescent 
terbium-activated phosphor such as a terbium-activated yttrium oxide or 
oxysulfide phosphor. The terbium-activated phosphor, when excited by 
electronic bombardment, produces a large amount of the desired fundamental 
radiation at 544 nm, but also produces significant amounts of troublesome 
radiations at 490 nm, 586 nm and 620 nm. It has been proposed to eliminate 
the undesired radiations by positioning in the path of the green radiation 
a light beam filtering means comprising a light filtering solution held in 
place by a container, the portions of which in the path of the green 
radiation are formed of glass transparent to the green radiation. 
Methods of achieving these results which have been proved successful at 
least in part are described in British Patent Application U.K. 2098393A, 
Kikuchi et al I.E.E.E. Transactions on Consumer Electronics, Vol. CE-27, 
No. 3, August 1981, pp. 478-484, copending U.S. application Ser. No. 
453,379, filed Dec. 27, 1982, now U.S. Pat. No. 4,547,699 and copending 
U.S. application Ser. No. 548,065 filed Nov. 2, 1983, now U.S. Pat. No. 
4,538,089 both filed by an inventor common to the instant application and 
both commonly assigned. 
It has been found however that because of the mismatch between the indices 
of refraction of the filtering solution and the glass plates forming the 
walls of the container through which the filtered radiation passes (which 
glass plate is hereinafter called the "face plate") a "halo" effect is 
produced around the projected spot due to reflections at the 
solution/glass interfaces. 
It is found that such an undesired halo effect not only is encountered when 
filtering solutions are employed for eliminating undesired radiation from 
cathode ray tube devices employed for generating bright green light spots 
but also when filtering solutions are employed with cathode ray tubes used 
for generating bright blue or bright red light spots as described for 
example in copending U.S. application Ser. No. 600,049, filed Apr. 13, 
1984, now U.S. Pat. No. 4,572,984 and copending U.S. application Ser. No. 
659,103 filed Oct. 9, 1984 both filed by one of the instant inventors and 
both commonly assigned. In all these cases the cause of the "halo" effect 
is the same, the mismatch of the indices of refraction at the 
solution/glass interface. 
BRIEF SUMMARY OF THE INVENTION 
A principle object of this invention is to provide a cathode ray tube (CRT) 
device for generating a bright color light spot in which the radiation 
from the tube is filtered by means of a filtering solution while 
suppressing of the "halo" effect around the projected bright spot is 
significantly reduced. 
Other objects of this invention will be apparent from the description that 
follows. 
According to the invention the applicants have found that the "halo" effect 
may be reduced to a significant extent by raising the index of refraction 
of the filtering solution closer to that of the glass by the addition of 
cinnamaldehyde, cinnamic alcohol or mixtures of these compounds to the 
filtering solution. 
It has been found that the addition of these compounds in amounts of from 
62% of saturation to saturation results in a significant decrease in the 
"halo" around the generated bright light spot. Thus these compounds may be 
added to the filtering solutions employed in the aforementioned patent 
applications and publications and in all cases produce a significant 
reduction in the "halo" effect.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
While the addition of any amount of the cinnamaldehyde or cinnamyl alcohol 
causes an increase in the index of refraction of the solution and thus 
tends to suppress the "halo" effect it is found that the most improved 
results are obtained when the cinnamic alcohol or cinnamaldehyde is 
employed within the range of 62% of saturation to saturation. As the 
solvent for the filtering solutions a combination of water and an 
aliphatic alcohol may be employed. Examples of such alcohols are ethylene 
glycol, 1,2-propanediol, 1,3-propanediol, glycerol, ethanol, propanol, 
isopropanol and methanol. Preferably from 20% to 80% of the weight of the 
solvent consists of the alcohol. In that case the solution not only acts 
as a filtering medium but is an excellent coolant for the tube during 
operation while rendering the tube resistant to freezing during storage. 
Optimum results are achieved when the solvent contains about 50% by weight 
of the alcohol. 
Among the bright light generating cathode ray tube devices in which this 
invention may be employed are the green light generating cathode tube 
device described in the above-mentioned U.S. application Ser. No. 453,379 
wherein a terbium-activated phosphor is employed and the resultant green 
radiation is filtered by means of a concentrated solution of praseodymium 
salt; the green light cathode ray tube device described in the 
above-mentioned U.S. application Ser. No. 548,065 wherein the phosphor 
employed is a terbium activated phosphor and in the radiation filtering 
device, a solution of a soluble praseodymium salt, sodium fluorescein and 
Fast Green FCF is employed; the blue light cathode ray tube generating 
device described in the above-mentioned U.S. application Ser. No. 600,049 
wherein a silver activated zinc sulfide phosphor is employed along with a 
filtering solution comprising a concentrated solution of a soluble erbium 
salt and methyl violet as well as the red light generating cathode ray 
tube device described in the U.S. application Ser. No. 659,103 employing a 
europium-activated phosphor and a concentrated solution of a soluble 
holmium salt and a soluble neodymium salt as a filtering solution. 
Examples of the praseodymium salts that may be employed are praseodymium 
acetate, praseodymium chloride, praseodymium bromide, praseodymium iodide 
and praseodymium nitrate, preferably in concentrations of about 6%-13% by 
weight. 
Preferably sodium fluorescein is used in concentrations of 0.008-0.012% and 
the Fast Green FCF is preferably used in concentrations of from 0.00005% 
to 0.0012%. 
Examples of the erbium salts that may be employed are erbium chloride, 
erbium bromide, erbium iodide and erbium nitrate preferably in a 
concentration from 20-40% by weight while the preferred concentration of 
the Methyl Violet 2B is 0.0004-0.0008% by weight. 
Examples of the holmium salts that may be employed are the holmium 
chloride, iodide and nitrate. Examples of the neodymium salts that may be 
employed are the neodymium bromide, chloride, iodide and nitrate. 
Preferably about 40-75 grams of the holmium salt, 40-75 ms of the 
neodymium salt per 100 ml of solvent are used with the total concentration 
of the holmium and the neodymium salt preferably not exceeding 120 grams 
per 100 ml of solvent. 
If the filtering solution is to function not only to suppress the undesired 
radiations but also as the coolant for the tube the solution is preferably 
carried on the external surface of the tube face plate and is held in 
place by a glass plate sealed to the outer surface of the face plate. 
However if no coolant effect is required the solution need not be carried 
directly on the face plate of the tube but may be carried in a container 
located outside the external surface of the face plate of the tube as long 
as the container is in the path of the radiation emitting from the tube 
and is transparent to the radiation of the tube. 
Preferably, the index of refraction of the filtering solution container, 
particularly of those portions in the path of the radiation emitting from 
the CRT, should match that of the face plate of the tube. 
For a more complete understanding of the invention, the invention will now 
be described in greater detail with reference to FIG. 1 of the drawing 
which is a cross-sectional view of a preferred embodiment of the CRT 
device of the invention. 
A solution of 4 milligrams of Na-fluorescein, 1.4 g of Pr(NO.sub.3).sub.3 
and 0.02 mg of Fast Green FCF in 25 ml of a 50% water-50% ethylene glycol 
solvent is prepared. To 1 ml of this solution there is added 1.7 ml of 
cinnamic alcohol and an additional 0.8 ml of ethylene glycol to insure 
complete miscibility. A 5 mm thick layer 1 of the resulting light 
filtering solution is applied to the external surface 3 of the glass face 
plate 5 of a cathode ray tube supplied with envelope 9 and containing an 
electron gun 11 positioned to emit a beam of electrons and cause this beam 
of electrons to impinge on the surface of a green luminescent screen 13 
formed of terbium-activated yttrium oxysulfide (P45) phosphor deposited on 
the internal surface of the face plate 5. The solution layer 1 is held in 
place on the external surface of the face plate 5 by transparent glass end 
plate 17 and seals 19. The face plate 5 and the transparent end plate 17 
are made of glass having an index of refraction of n.sub.D =1.51. The 
index of refraction of the layer 1 of the light filtering solution is 
1.4933. Practically no "halo" is noted around the projected green light 
spot produced by this device. 
The substitution of a filtering solution identical with that employed in 
the device of the invention except for the elimination of the cinnamic 
alcohol results in the production of a green light spot in which a highly 
visible "halo" is noted around the projected green light spot. In this 
case the index of refraction of the solution layer is found to be 1.4230. 
Although the present invention has been described with reference to 
particular embodiments thereof, it will be understood that numerous 
modifications can be made by those skilled in the art without actually 
departing from the scope of the invention.