DE2014511C - White luminescent fluorescent screen for a cathode ray tube - Google Patents

Description

The present invention relates to a phosphor screen for a cathode ray tube with a white luminescent phosphor mixture which essentially made of a blue luminescent, silver-activated zinc sulfide phosphor and a yellow luminescent Zinc cadmium sulfide phosphor.

Picture tubes for black and white television receivers usually contain a white luminescent fluorescent screen, that consists of a two-component mixture of a blue luminescent and a yellow luminescent Consists of fluorescent material. A phosphor screen of this type is called a P4 screen. One Mixture, which has been used commercially on a large scale for many years, consists of blue luminescent silver-activated zinc sulfide and yellow-emitting silver-activated zinc cadmium sulfide (RCA Review, 1947, pp. 554 to 563).

These and other white luminescent phosphor mixtures are also in the German patent application report R 2940 VIIlc / 2lg described, in which also activated zinc cadmium sulfide with copper as light relatively strongly absorbing phosphor is mentioned.

The disadvantage of the known fluorescent screens of this type is their sensitivity to poisoning by copper, which, even in such small quantities as is found in the atmosphere, reduces the luminescence efficiency. Fluorescent materials of this type must also be stable under the manufacturing conditions of the tube, they should be white Have body color, enable high luminance levels and cost little.

Accordingly, the present invention is intended to the object can be achieved, a luminescent screen with a white luminescent phosphor mixture indicate that is insensitive to foreign substances and has the desired properties mentioned above. According to the invention, this object is achieved in a fluorescent screen of the type mentioned at the outset solved that the yellow luminescent phosphor is a zinc cadmium activated with copper and aluminum

sulfide phosphor is at which the weight ratio from CdS to ZnS is between 12/88 and 17/83. The mixture preferably contains about 54 to 58 percent by weight of the blue luminescent phosphor and 46 to 42 percent by weight of the yellow luminescent Fluorescent.

A fluorescent screen made of this white lu;.; Incescent Compared to the known fluorescent screens, mixture is distinguished by its sensitivity to light against poisoning, stability in the manufacturing process.

ac white body color, high luminous intensity and low Material costs.

The invention is based on Ausführungsbe; play explained in more detail.

In one embodiment, the light

»5 layers of fabric made from a two-component mixture the approximately 56 percent by weight of a blue luminescent silver-activated zinc sulfide phosphor with et \ u-0.020 Weight percent silver as an activator, and about 44 weight percent eii. ° s yellow luminescent mii

Copper and aluminum activated zinc cadmium sulfide phosphor with about 0.007 weight percent cup fer as an activator and 0.007 percent by weight aluminum as a coactivator. The weight ratio of CdS / ZnS is about 15/85. The composition of the screen can be given by the following abbreviation be given:

56% ZnS: Ag (0.020) f 44 ° / ₀ 0.85 ZnS 0.15 CdS: Cu (0.007), Al (0.007).
Any known blue-emitting silver-activated zinc su fidleuchtstoff can be used as the blue luminescent phosphor. Blue luminescent phosphors which contain 0.010 to 0.030 percent by weight of silver as an activator are preferred. The gc'.b luminescent phosphor is selected from a composition range that can be defined as follows:

m ZnS η CdS: Cu (χ). Al (y) lie there

m between 0.83 and 0.8P parts by weight, η between 0.12 and 0.17 parts by weight, x between 0.005 and 0.009 percent by weight, γ between 0.005 and 0.009 percent by weight and m + η = 1.00.

The phosphors are particulate, with the individual particles in the size range between about 3 and 15 μm. The particles can make a thin one Coating of a translucent material, such as silicon dioxide or zinc silicate, has to be used in the manufacture of the luminescent screen to facilitate.

The present fluorescent screen can be used in a television picture tube or a display tube for another electronic device can be used. In both cases the screen contains a contiguous one Layer from the phosphor mixture. In other embodiments, the luminescent screen can be separate white luminescent areas alone or in combination

tion with separate areas that have different emission properties. The luminescent screen can can also be used for tubes that are not used to display or reproduce information.

The phosphor layer can be formed in the cathode ray tube by any screen forming method will. A cohesive fluorescent layer, as it is in telegraph tubes and the like is preferably made from a liquid by settling. In a preferred method the phosphor components are mixed with one another in an aqueous medium. The mixture is then poured into the open envelope of the cathode ray tube. If on the inside of the The front plate of the bulb has deposited a layer of the desired thickness from the phosphor mixture, win ' the excess liquid carefully removed without disturbing the detached screen. The screen will then dried, coated with an organic film and evaporated with an aluminum layer. After steaming, the screen will be at about 440 "C m air pickled to organic and other volatile Remove constituents. The tube is then completed in the usual manner.

The phosphor layer consists essentially of a mixture of 54 to 58 percent by weight of the building luminescent phosphor with 46 to 42 percent by weight of the yellow luminescent phosphor. The ratio can be selected according to the desired tint of the emitted white light will. Of course, a higher proportion of blue luminescent phosphor results in one bluish white, while higher proportions of yellow luminescent phosphor produce a more yellowish white ίο deliver. Outside the specified range, the light emitted too strong a blue or yellow tinge than that it could still be called white in the narrower sense.

The novelty of the present phosphor screen is that the two-component phosphor mixture as the one component contains a yellow luminescent phosphor which essentially consists of Zinc cadmium sulfide is made up of that with copper and aluminum is activated. The differences in the compositions of this activated with copper and aluminum, yellow luminescent phosphor and the one currently used extensively in P4 fluorescent screens silver-activated zinc cadmium sulfide phosphor can be found in the following list:

Yellow luminescent.
ZnCds phosphor "I. »ZnS 7th "CdS °, "Activator Firing temperature Cu-Al activated 83 to 88 17th until 12 0.005 to 0.009 1200 f 100 C Ag activated 45 to 55 55 to 45 0.010 to 0.030 900 l · 10OtC

Tubes with the present fluorescent screen have compared to tubes m ^{: t} the above-mentioned active silver

silver-activated yellow luminescent phosphor have the advantage that they are less sensitive to contamination, have greater stability during processing, have a whiter body color, enable greater light intensities and can be produced with lower material costs. 7 »should be noted in detail:

Insensitivity to poisoning

45

Attempts have already been made to develop yellow luminescent phosphors, which are also insensitive to are a contamination by copper, but this could only with some loss of luminescence efficiency can be achieved. The yellow luminescent phosphor activated with copper and aluminum according to the invention is so highly insensitive to contamination that it is practical can be described as safe from contamination. This advantage is achieved without any loss of efficiency achieved.

Processing stability

Sulphide based phosphors are known to decrease their luminescence efficiency during tube manufacturing suffers as a result of an interaction with the environment. Targeted experiments have shown that the present yellow luminescent phosphors activated with copper and aluminum are less sensitive in terms of a lowering efficiency in handling. This shows the following Table in which the efficiency of white luminescent P4 phosphor mixtures is listed, those with an ordinary blue luminescent phosphor and various yellow luminescent ones Zinc Cadmium Sulphide Phosphors were made:

Yellow more luminescent
P4 blend phosphor Initial efficiency
the yellow luminescent
Fluorescent Relative efficiency
of the P4 fluorescent screen Ag-activated with high activity
Degree
Ag-activated impurities
sensitive
Cu-Al activated 112%
100
114 114%
100
125

Body color ^{6s e} ' ^ne S ^e ' ^De ^ ' ^s orange body color, its tint im

is substantially proportional to the cadmium content.

Phosphors with a gas material made of solid lo- This body color produces luminescent pn in the white of zinc cadmium sulfide, the phosphor mixture usually has a color cast that is reflected in

aesthetically disturbing. The yellow body color also acts as an optical filter for blue Light and thereby reduces what can be achieved with the blue luminescent component of the mixture Luminance considerably. The tim 30% lower cadmium reverberation of the present yellow luminescent phosphor activated with copper and aluminum gives a considerably lighter body color than the known silver-attached yellow luminescent phosphor having. The lighter body color both contributes to an improvement in the appearance of the unexcited Luminescent screen as well as to an increase in the luminescence efficiency.

Light intensity

P4 phosphor mixtures, one with copper and aluminum activated, yellow emitting phosphor contain a significantly higher light intensity than comparable P4 fluorescent screens, which are silver activated, yellow luminescent Phosphors or such high efficiency phosphors are made. the ίο lighter body color and the greater stability in the Processing together result in P4 fluorescent screens with significantly greater brightness, as in the following comparison indicates:

Ag activated,
High efficiency Ag activated,
sensitive to contamination Cu-Al activated Attempt a 0.0784
0 0698 0.0688 0.0862
0.0767 luminance Attempt B 0.0671 - 0.0740 in sb Attempt C

material costs

The main part of the material costs for zinc cadas- mium sulfide phosphors is accounted for by the cadmium part. The current cost of raw cadmium oxide, as used in phosphor manufacture, is nearly three times the cost of zinc oxide. Since less cadmium is required with the present Cu-Al-activated yellow-emitting phosphors, the cost of the proportion of yellow-emitting phosphor can be reduced by about 2C%. Because of the higher effective efficiency d :, Cu-Al-activated yellow luminescent luminescent stop, the proportion of yellow-emitting luminescent material, which is required in combination with the blue luminescent luminescent material for the production of a white luminescent luminescent screen, can be reduced by about 5 " (from about 49 to about 44%) On the whole, the present phosphor mixture is etsv.i 14.4% cheaper than the known mixtures which contain a: · silver-activated yellow luminescent phosphor.

Claims (4)

Patent claims: 1. Fluorescent screen for a cathode ray tube with a white luminescent phosphor mixture, which essentially consist of a blue luminescent, silver-activated zinc sulfide phosphor and a yellow luminescent zinc cadmium sulfide phosphor, characterized in that that the yellow luminescent zinc cadmium sulfide phosphor with copper and aluminum is activated and contains CdS and ZnS in a weight ratio of 12/88 to 17/83. 2. fluorescent screen according to claim!, Characterized in that it consists essentially of 54 to 58 percent by weight blue luminescent phosphor and 46 to 42 percent by weight yellow luminescent Consists of fluorescent material. 3. fluorescent screen according to claim 1 or 2, characterized in that the blue luminescence generating phosphor with 0.01 to 0.03 percent by weight is silver-activated zinc sulfide and that the yellow luminescent phosphor with 0.005 to 0.009 weight percent copper and 0.005 to 0.009 weight percent aluminum is activated. 4. fluorescent screen according to claim 3, characterized in that the blue luminescent Phosphor made of zinc sulfide, which is activated with 0.020 percent by weight silver, and that the luminescent phosphor zinc cadmium sulfide which contains CdS and ZnS in a weight ratio of! 5/85 and 0.007 weight percent copper and 0.007 percent by weight aluminum as an activator.