US2310863A

US2310863A - Luminescent screen

Info

Publication number: US2310863A
Application number: US375906A
Authority: US
Inventors: Humboldt W Leverenz
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1941-01-25
Filing date: 1941-01-25
Publication date: 1943-02-09
Anticipated expiration: 1960-02-09
Also published as: GB560092A

Description

Feb. 9, 1943. H W LEVERENZ 2,310,863

LUMINESCENT SCREEN Filed Jan. 25, 1941 2 Sheets-Sheet l I@ 1w. Iggy). i@ I.

INVENTOR Kgmw ATTORNEY Feb. 9, 1943. H, W LEVERENZ 2,310,863

LUMINESCENT SCREEN Filed Jan. 25, 1941 2 Sheets-Sheet 2 fig, 4.

51777.51/ 77 q /UML 1 /x MAMA IN'VENTOR wmold W ATTORNEY Patented Feb. 9, 1943y arent erica L'KIITMYNESOEN'E SCREEN poration of Delaware Application January 25, will, Serial No. 375.9% d Claims. (Ci. d- 80) This invention relates to luminescent screens and more particularly to the method ci fabrican ing luminescent screens suitable fornse in colo'r television systems using cathode ray tubes.

it has been proposed in connection with color television systems to utilize, at the receiving point, a cathode ray tube having a luminescent screen adapted to be bombarded by a *beam of electrons to reproduce the colored image of the object transmitted. The screen is composed of a layer in which alternate lines corresponding to the cathode ray transversals luminesce blue and yellow-orange for a two-color system, instead oi the ordinary screen comprising a layer of a luminescent material emitting substantially white light under bombardment. For a trl-color system the screen would be composed of different strips of luminescent material arranged in a predetermined pattern adjacent to each other, each strip luminescing with blue, green or red light. The signals received from the transmitting station would comprise three groups, the first group being generated by light from the object whose image is to be transmitted, passing through a, blue lter, the second group being generated by light from the object passing through a green illter, and the third group of signals'being generated by light from the object passing through a red illter.

At the receiver the cathode ray beam within the cathode ray tube would be modulated by the three groups of signals successively, the beam being advanced in a vertical direction at the conclusion of each group of signals. By making the strips of different luminescent materials narrow, the observer would preceive a color corresponding to the integrated values of blue, green and red luminescent light to give the effect of the color of the elemental area underconsideration of the object transmitted, due to the perslstency of vision. It will be appreciated that the strips of luminescent material must be very narrow in order to rst of all provide a system having adequate resolution and definition, and secondly, to provide a reasonable size screen. My invention thus makes possible the production of such luminescent screens in a. very simple, emcient manner. with reasonable ease and facility.

In accordance with my invention, a number of thin plates, such as glass, metal, mica, or plastic for example, are stacked together. The separate luminescent materials are then settled. dusted, or sprayed upon the edges of separate stacks. 'I'he plates are then separated and restacked in the desired combination. The restacked group of plates having luminescent material on one edge is then used to. "prin the luminescent screen upon a support to provide the iinal screen.

.it will thus be appreciated that my ,new method of preparing luminescent screens is exceedingly simple, and provides a screen having high resolution and deilnition for color work as `well as making possible accurate color reproduction. Ac-

cordingly, it is one of the objects of my invention to provide a new and improved composite luminescent screen for excitation by radiant energy.

Another object of my invention is to provide a method for easily producing composite luminescent screens suitable for color television reproductions.

Another object of my invention is to provide a method for forming a composite two-color luminescent screen for cathode ray receiving tubes for television systems.

Still another object of my invention is to provide a tri-color or multi-color composite luminescent screen for use in a cathode ray tube for reproducing colored television images.

Other objects of my invention will become apparent to those skilled in the art upon reading the following detailed description taken together with the drawings.

In the drawings, Figures la, 1b and lc show, as a step in my new method, the individual stacks of plates carrying luminescent material on their edges; Fig. 2 shows an intermediate step in my method of forming luminescent screens in which the plates have been restacked according to a predetermined order; Fig. 3 shows a further step in my method of forming luminescent screens in which the alternate strips of luminescent material are printed on the final support surface: Fig. 4 shows schematically a screen made in accordance with my invention, while Fig. 5 shows schematically a luminescent screen made in accordance with my invention and enclosed in a cathode ray tube.

Turning now to the drawings, and assuming that a tri-color screen is to be fabricated, as an example, a plurality of thin plates 3 are stacked together to form a group I, upon which is sprayed or settled, according to methods well known'in the art, blue emitting luminescent material I. Another stack 1 of similar plates 9 has green emitting luminescent material il sprayed or settled upon their edges, while the third stack I3 has red emitting luminescent material il alllxed to the edges of the plates I5. It will be appreciated that the plates may be of any suitable material such as glass, mica, or plastic, for example.

It the plates are glass, the glass may be of the type from which microscope slides are fabricated.

As is well known, the thickness of these slides canbemade as thin as 0.1 mm.

The stacks I, 'I and I3 arethen separated into their

individual plates

3, 9 and I5. 'I'he individual plates are then restacked sequentially in the order 3-9-I5, with edges bearing the luminescent material 5, Il, I1 lying in a common plane, as shown in Fig. 2 to form a stack oi which the thickness is equal to the desired height of the finished screen, and in which the individual plates alternate in sequence.

It will be appreciated, therefore, that the edges o! the restacked plates will form a surface of strips of luminescent materials running in the repeated sequental order of blue, green and red.

Since the luminescent materials adhere well or firmly to the edges of the plates, the particles of luminescent material can be transferred to a suitably prepared support surface by providing a surface whose adhesive property is greater than that' of the

plates

3, 9 and I5. l

In carrying out this step, referring to Fig. 3, the final support surface I9. such as' glass, for example, has deposited thereon a binder coating of dilute alkali silicates or borates or organic binders such as nitrocellulose and alcohol or amyl acetate. With certain luminescent materials it is, of course, only necessary to moisten the glass support surface I 0, with amyl acetate or water to provide sufficient adhesion. The stack or interleaved

plates

3, 9 and I5 is then inverted and pressed against the binder layer 2l, so that the edges bearing the luminescent material 5, II

and Il are in contact therewith. The lumines.

cent material 5, II and I1 is thereupon transferred to the support surface I9 to form the finished screen shown in Fig. 4 in which the strips of diilerent luminescent materials 1, II and Il are ailixed to the support I9 .by way of the binder medium 2|.

Suitable groups of materials for providing the multi-colored luminescent strips are silver-activated zinc sulfide, zinc silicate and zirconium silicate for blue; for green luminescing material, alpha-willemite activated with manganese and zinc cadmium sulfide activated with silver may -be used. Red luminescing material may be chromium-activated aluminum berylliate or zinc cadmium sulfide activated by silver. It will be noted that zinc cadmium suliide activatedvby silver may have its color vary from blue through yellow and green to red by merely increasing the quantity of cadmium during the processing of the l material, but the use of it to produce blue light is not as desirable as other materials have greater eiiiciency at this end of the spectrum.

It will be understood that I have described `the processing of the screen in connection with atricolor system. Where it is desired to use a twocolor system, then the alternate strips of a material may be suitably chosen from blue and yellow luminescing materials, and for the yellow luminescing material, zinc cadmium sulfide activated by silver manganese-activated beta-willemite or zinc beryllium silicate activated by manganese may be used.

It will be appreciated, of course, where a twocolor system is to be provided, only two stacks of plates are necessary, but the steps in the process of settling the luminescent materials out on the edges of the stack, restacking the plates, and finally printing them on an adhesive surface upon those described above in connection with the tri-color screen.

The finished screen 'may then be molmted withinacathode ray tube 3l showninFigJlnd the screen adapted to be bombarded by a beam of electrons 35 emitted from an electron gun 33. The beam 35 may be deflected by suitably poeltioned electromagnetic coils 39 and II positioned at right angles to each other to deflect the beam in mutually perpendicular direction. It will, o! course, be understood that while electromagnetic deilecting coils have been shown, electrostatic deilecting systems positioned within the tube may be used, as is well known in the art. Purthermore, it will be appreciated that if the support member I3 is made of thin glass, then the screen may be indirectly viewed, although the screen, if formed of an opaque support member I9 may be directly viewed.

It will be further appreciated that instead o! using plates, rods may be used UD'On which the luminescent material is settled out, and thereafter the rods restacked to provide a cross-hatch color screen of the type shown in the Zworykin Patent 1,691,324, by following the steps in the process above outlined in connection with the three-color screen.

While thescreen has been described as en example in connection with excitation of cathode ray beams, it will be further appreciated that the screen may also be used for excitation by other forms of radiant energy such as ultra violet light, X-ray, and thelike.

It will be readily understood that high quality denition is easily provided by my method of forming luminescent screens for television sygtems. For example, in a three-color television system having 400 line deilnition, the total number of strips of luminescent material will be three times 400 or 1200 strips. Since glass plates may be hadasthin as 0.1 mm. theheightoi'sucha screen will be 120 mm. or approximately 4% inches high, which is not unreasonable for a projection type tube. On the other hand, i! the plates are made as thick as 0.2 mm. then the two will be approximately 91/2 inches, corresponding terial, each of said sets being coated with e. di!- a suitable support member, are identical with ferent luminescent material, separating the Individual plates of all of said stacks, restacking said plates in accordance with a predetermined order, and transferring the luminescent material on the edges of the restacked plates to a final support surface.

2. 'I'he method of preparing a luminescent screen which comprises the steps of stacking e plurality of thin plates together, depositing a layer of luminescent material upon the edges of said stacked plates, forming a second stack oi' platee. depositing a second luminescent material upon the edges of said second stack of plates, forming a third stack of plates, depositing a third luminescent material upon the edges of said third stack of plates. interleaving-the plates of said first, second and third stacks, and transferring the luminescent material from said interleaved plates to a support surface.

3. The steps in the method of preparing a luminescent screen which comprises coating a support surface with a binder, stacking together a plurality of plates having luminescent material deposited on at least one edge of each plate, and impressing said luminescent material upon the binder coated on the support member.

4. 'I'he method of preparing a luminescent screen which comprises the steps of stacking a plurality of thin plates together, depositing a layer of luminescent material upon the edges of said stacked plates, forming a secondstack of plates, depositing a second luminescent material upon the edges of said second stack of plates, forming a third stack of plates. depositing a third luminescent material upon the edges of said third stack of plates, interleaving according to a predetermined order the plates of said rst, second and third stacks, and transferring the luminescent material from said interleaved plates to a support surface.

support surface.

5. The steps in the method of preparing a luminescent screen which comprise coating a support surface with a binder, stacking together a plurality of plates having luminescent material deposited on the edges thereof, and transferring said luminescent material upon the binder coated on the support surface by impressing said edges upon the said binder.

6. The method of preparing a luminescent screen which comprises the steps of stacking a plurality of thin plates together, settling from suspension a layer of luminescent material upon the edges of said stacked plates, forming a second stack of plates, settling from suspension a second luminescent material upon the edges of said second stack of plates, forming a third stack of plates, settling from suspension a third luminescent material upon the edges of said third stack of plates, interleaving according to a predetermined order the plates of said first, second, and third stacks, and transferring the luminescent material from said interleaved plates to a HUMIBOLDT W. LEVERENZ.