GB2057751A - Two color write-through direct- viewing storage tube - Google Patents

Abstract

Two color write-through information displayed by a direct-viewing bistable storage tube is achieved by admixing particles 64 of a first, storage, phosphor with surface-killed particles 66 of a second phosphor to form a dielectric layer on a conductive layer 60 having an array of collector electrode members 18. The collector electrode members 18 are formed from particles of a third, surface-killed, conductive phosphor. The storage phosphor and surface-killed phosphors operate at different voltage levels to simultaneously display storage and write-through information in three different colors. <IMAGE>

Description

SPECIFICATION Two color write-through direct-viewing storage tube Background of the Invention Color write-through is known whereby phosphor particles of two different luminescent spectra are admixed together in an appropriate ratio to form a phosphor target that will luminesce at least at two different colors. One of the phosphor particles is a low voltage luminescent storage phosphor and the other of the phosphor particles is nonluminescent at low voltages but is an efficient emitter of a different color at higher voltages so that nonstored or write-through information can be displayed in a color different from the stored information. This type of storage target can best be made in accordance with the teaching of U.S. Patent Application Serial No.

802,615, filed June 2, 1977, (corresponding to published W. German Specification No.

2,824,102).

The phosphor target can also have admixed therewith other phosphor particles having a third color in order to provide a two color write-through direct-viewing storage tube. The essential drawback for such a target would be the paucity of low voltage luminescent phosphor particles throughout the target and that the stored information would be quite dim and difficult to discern.

Summary of the Invention The present invention relates to cathode ray storage tubes and more particularly to a direct-viewing bistable storage tube that displays two color write-through information which is different from the color of the stored information.

The present invention is realized according to the present invention by a direct-viewing storage CRT target having a storage dielectric layer of admixed phosphor material. The admixed material includes two phosphors having different color emission characteristics; one a low voltage luminescent phosphor and the other a phosphor that emits light of a color different at a higher voltage, preferably distinctly different, from that of the low voltage luminescent phosphor. An array of collector electrodes extend through the storage dielectric layer for collecting secondary electrons that are emitted from the charge image stored by the storage phosphor and these collector electrodes are formed from a conductive nonstoring phosphor having a color different from the phosphors in the admixed dielectric layer.

One of the admixed phosphors has a dead layer which eliminates low voltage luminance and this dead layer enables the operating level of the target to be raised thereby enabling the luminance of the stored information to be increased. The collector phosphors also have a dead layer and are conductive thereby collecting secondary electrons but they do not luminesce unless excited by higher voltage electrons at which time they luminesce a different color than the admixed phosphors.

A primary object of the present invention is to provide a direct-viewing bistable storage tube in which write-through information is in two colors.

Another object of the present invention is the provision of a bistable storage target for use with a direct-viewing bistable tube which will display write-through information in two colors and stored information in a color different from the write-through information.

A further object of the present invention is to provide a bistable storage target that will display stored information at a higher luminance while simultaneously displaying nonstored information in two different colors which are different from the color of the stored information.

An additional object of the present invention is the provision of a bistable storage target that contains an array of collector electrode members which are formed from conductive phosphor particles having a dead layer surrounding each phosphor particle.

Still a further object of the present invention is to provide a bistable storage target that has an admix of two different phosphor particles that emit different colors forming the storage phosphor layer; one of the phosphor particles being storage dielectric particles to emit light of its color, the other phosphor particles having a dead layer surrounding each of the particles to inhibit low voltage luminance and to raise the operating level of the target thereby enabling the stored information to be displayed with a higher luminance.

Still an additional object of the present invention is the provision of a bistable storage target that can be operated to display refresh multicolor information simultaneously with stored information.

Further objects, features and advantages of the present invention will become evident as the following detailed description is read in conjunction with the accompanying drawing.

Brief Description of the Drawing Figure 1 is a diagrammatic view of a directviewing storage cathode ray tube in accordance with the present invention, together with associated circuitry; and Figure 2 is a fragmentary cross-sectional view taken along line 2-2 of Fig. 1, showing on an enlarged scale a preferred embodiment of a storage target in accordance with the present invention.

Detailed Description of Preferred Embodiment Referring first to Fig. 1, a direct-viewing bistable storage tube 10 includes an evacuated envelope 1 2 having a transparent face plate 1 4 at one end. Supported by faceplate 1 4 is a storage target 1 6 that includes a conductive target electrode 1 8 and a storage dielectric layer 20. Mounted in the opposite end of the tube is a writing gun 22 comprising a cathode 24, a control grid 26, and a focusing and accelerating anode structure 28 for forming a beam 30 of high velocity electrons directed toward target 16. Beam 30 is deflected by signals applied to horizontal deflection plates 32 and vertical deflection plates 34 by conventional deflection circuits 36.Storage tube 10 is additionally provided with one or more flood guns 38 for bombarding the storage dielectric uniformly with low velocity electrons. The cathodes of the flood guns are conected to a low voltage, suitably ground potential (0 volts).

A plurality of electrodes is disposed on the inner surface of envelope 1 2 intermediate flood guns 38 and target 1 6. These electrodes preferably are provided as spaced coatings, or bands, of a conductive material such as silver, graphite, or the like. A first wall band electrode 40 functions primarily as a focusing electrode for the flood electrons emitted by guns 38. It is connected to a suitable positive voltage, about + 250 volts, for example. A second wall band electrode 42 spaced from electrode 40 and connected to a less positive voltage, e.g., about + 1 50 volts, functions as a focusing and collimating electrode.A third wall band electrode 44 spaced from electrode 42 is connected to a still less positive voltage, e.g., about + 1 25 volts, and also functions as a focusing and collimating electrode. A fourth wall band electrode 46 is located intermediate and spaced from electrode 44 and storage target 1 6. Electrode 46 is connected to a still less positive voltage (about + 75 volts) and functions as a focusing and collimating electrode, but may also act as an auxilliary collector for secondary electrons emitted by the storage target at its periphery. As a result of the collimating action of the wall band electrodes, flood gun electrons are substantially uniformly distributed over the surface of target 1 6.

It should be noted that a conventionai resistive coating 48, such as Aquadag, is provided on the interior of the funnel portion of envelope 1 2 and is electrically connected to an isolation shield (not shown) in writing gun 22.

Coating 48 thus serves as an extension of the writing gun's second anode (not shown). The voltages applied to wall band electrodes 40, 42, 44, and 46 are suitably adjusted to provide optimum focusing and collimation of the flood gun electrons, and the specific values given herein and shown on the drawing are by way of example only.

Target electrode 1 8 is suitably connected to the midpoint of a voltage divider consisting of resistors 50 and 52. Resistor 50 is adjusted so that a potential of about + 200 to + 300 volts is applied to the target electrode.

The cathode of writing gun 22 is connected to a high negative D.C. potential, suitably about - 6000 volts via the movable contact of switch 23. The control grid 26 is connected to the movable contact of a double pole, double throw switch 53. In the STORE position of switch 53 and switch 23 in connection with - 6KV, grid 26 is connected to a negative D.C. potential - VG1 to provide a suitable grid-to-cathode reverse bias to cause writing beam 30 to bombard target 1 6 with high velocity electrons. When struck by the writing beam, dielectric layer 20 emits secondary electrons, which are then collected by electrode 1 8. The written area of the layer is driven positive by the secondary emission, and retained at a relatively positive potential after beam 30 has passed by low energy electrons emitted by flood guns 38.In this well known manner a stored charge image is formed on the dielectric layer. In the W. T. or write-through mode of operation of switch 53, the control grid is connected to the output of a rectangular pulse generator 54, which applies positive-going voltage pulses 56 to the grid. Pulses 56 have a maximum voltage level equal to -VG1, and a minimum (more negative) voltage level sufficient to turn off the writing gun. Switching the writing beam off for a portion of the time it is bombarding a particular area of the target ailows the charge image formed in the storage dielectric to be discharged by the flood electrons. The writethrough image is thus prevented from being stored. A more complete description of pulsed write-through operation may be had by reference to U.S. Patent No. 3,430,093 to Winningstad.

Referring now to Fig. 2, there is illustrated in cross section the storage target incorporated in storage tube 1 0. Target 1 6 includes a transparent substrate body in the form of faceplate 14, which is provided with a thin, conductive tin oxide film 60. A multiplicity of raised "dots" 62 of a surface-killed conductive phosphor material is distributed in a regu- lar pattern over the exposed surface of film 60. The conductive phosphor material is preferably P-22 blue (ZnS:Ag) coated with a cobalt sulfide precipitate that is diffused into the phosphor particles by heat treatment according to the teaching in U.S. Patent Nos.

3,664,862; 3,767,459 and 3,826,679. The dots, which suitably have a generally cylindrical or conical configuration, are electrically connected to the tin oxide film. Thus, conductive film 60 and phosphor dots 62 together form collector or target electrode 18. Disposed on conductive film 60 and surrounding dots 62 is an at least semi-continuous storage dielectric layer 20. Dots 62 extend through layer 20 and have their outer ends exposed and they collect secondary electrons that are emitted from adjacent positively-charged charge images. Due to the dead layer surrounding each of the phosphor particles of dots 62, they will not luminesce except at - 8KV or above depending on the thickness of the dead layer.

According to the present invention, layer 20 comprises an admixture of phosphor particles, including particles 64 of a phosphor capable of bistable storage of charge images, and particles of another phosphor 66. Phosphor 66 is a surface-killed phosphor and it is chosen to have a color emission different, and preferably substantially different, from that of phosphor 64 when bombarded by high energy electrons, and to have a substantially lower light output efficiency when bombarded by low energy flood gun electrons. Due to the surface-killed phosphor particles 66 being present in layer 20 will raise the operating level of the storage target which will increase the luminance of the stored information. Suitable phosphors meeting these criteria include the red-emitting P-22R phosphors, such as Y202S:Eu, Y203:Eu, Gd202S:Eu, Gd203:Eu and YVO4:Eu.The red phosphor particles 66 have their surfaces killed to provide a dead layer of a desired thickness. One way in which the dead layer can be obtained surrounding each of the red phosphor particles of the oxysulfides (Gd2O2S:Eu and Y202S:Eu) is to air bake the target at a temperature between 450"C and 550"C. See J. W. Haynes and J.

J. Brown, "Preparation and Luminance of selected Eu+3-activated rare earth-oxygen-sulfur-compounds", Journal Electrochem Society, Vol. 11 5 p 1060 (1969). This produces an oxysulfate dead layer having a thickness depending on the time of bake at the prescribed temperature. Another way to obtain the dead layer at the surface of each of the red phosphor particles for each of the above rare earth oxides or oxysulfides is to slurry the red phosphor particles in a phosphoric acid solution at a controlled temperature between room temperature and 80"C and also controlled phosphor-to-solution concentration so that the pH of the solution should be less than 4.5. This forces a surface reaction to produce a rare earth phosphate dead layer having a thickness depending upon the foregoing variables. See U.S.Patent No. 3,607,371 and 3,927,240 for phosphate coating of phosphors. Phosphor 64 suitably is a green-emitting storage phosphor such as P-1 (Zn25i04: Mn).

The two types of phosphor particles are uniformly admixed, either dry or in slurry form, and deposited on conductive film 60 of target electrode 1 8 in a known manner, for example using the procedure outlined in U.S.

Patent No. 3,956,662 to McTeague, et al.

The ratio of the two types of phosphor in the admixture may range from about 10% to about 80% by weight of phosphor 64, with the balance being phosphor 66. A preferred composition comprises about 24% by weight P-1, about 56% dead layer red phosphor (or a mixture of P-22R phosphors) of the rare earth type mentioned above and about 20% of P-22 blue as the collector electrodes 62. A storage target provided with a dielectric layer of the preferred composition will exhibit a green display of stored charge images and an orange and a blue display of write-through charge images. The admixed layer contains about 33% by weight of P-1 phosphor and about 67% by weight of P-22R phosphor.

In one mode of write-through operation, switch 23 is connected with - 6KV while switch 53 remains at its W.T. position. This will result in the stored information being displayed in green color, if information has been stored, and the write-through information being displayed in an orange color which is a combination of the red and green phosphors.

In another mode of write-through operation, switch 23 is connected to - 8KV while switch 53 is at its W.T. position. If stored information is displayed in its green color, write-through information will be displayed in a blue color due to emission from phosphors 66, 64 plus dots 62 which will be different from the write-through information when switch 23 is in the - 6KV position and also different from the stored information.

In a further mode of write-through operation, switch 23 is switched between - 6KV and - 8KV while switch 53 is at its W.T.

position. If stored information is displayed in its green color, write-through information will be displayed in the orange and blue colors that are different from the stored information.

The writing gun voltages can be less than 6KV or greater than - 8KV depending upon instrument design.

Of course, the tube can operate in a stored mode only or in one or both color writethrough modes as desired. Thus, the CRT can be operated as a refresh multicolor monitor with bistable storage capability.

It will be understood that color coding of write-through information is not restricted in application to the storage tube target structure exemplified herein. Other suitable target structures include those described in U.S. Patent Nos. 3,293,474 to Gibson, Jr.; 3,401,293 to Morris; 3,531,675 to Frankland; and 3,614,820 to Morris.

About 20% of each of the collector electrode members 62 can be metallic powder instead of 100% conductive phosphor to insure proper operating range of the CRT because resistance of the phosphor dot collectors may be too high thereby decreasing the collection efficiency of the secondary electrons and lowering the operating range of the CRT.

If desired, about 20% of collector electrode members 62 can be formed from metallic powder whereas the remainder can be con ductive phosphor. Alternatively, the array of dots can be made of the admixture of phosphors 64 and 66 surrounded by a layer of conductive phosphor.

Brighter write-through information is displayed by the present target because collectors 62 also emit light at write-through voltages above - 8KV. Also, by killing the surface of the red phosphor particles with a phosphate layer, this raises the operating level of the storage target thereby increasing the luminance of the green phosphor particles which also compensates for the loss in storage luminance of green phosphor particles due to the admix of the red phosphor particles to form the phosphor layer. The killed surfaces of the conductive phosphor collector electrode members will collect secondary electrons during storage operation and they will not luminesce except above a threshold voltage level.

A dual electron gun structure can also be used in place of the switched voltage sources to a single cathode if desired.

From the above it should be obvious to one of ordinary skill in the art that various changes may be made in the above-described preferred embodiment without departing from the scope of the invention as defined by the following

Claims (11)

claims. CLAIMS

1. A direct-viewing cathode ray storage tube, comprising: an evacuated envelope having a light transparent faceplate; a storage target including a storage dielectric of phosphor material mounted within said envelope; means for bombarding said storage dielectric with a beam of high velocity electrons to form a charge image thereon; and means for bombarding said storage dielectric with low velocity electrons to cause bistable storage of charge images having a potential at least equal to a critical minimum voltage necessary for such storage; means to present charge images having a potential below said critical minimum voltage;; said phosphor material comprising a substantially uniform admixture that includes a first phosphor capable of bistable storage of charge images and a second surface-killed phosphor having a color emission different from that of said first phosphor and having a light output efficiency in response to bombardment by said low velocity electrons that is lower than that of said first phosphor, such that bombardment of the admixed meterial by said high velocity electrons causes the emission of a light image of a certain perceived color, and bombardment of said material by said low velocity electrons causes the emission of a light image corresponding to a stored charge image, the latter light image being of a perceptibly different color, the surface-killed phosphor causing said tube to operate at a higher operation level.

2. The storage tube of claim 1, wherein said phosphor target comprises an admixture of P-1 phosphor and surface-killed P-22R phosphor.

3. The storage tube of claim 2 wherein said P-22R phosphor is selected from the group consisting of Y202S:Eu, Y203:Eu, YVO4:Eu, Gd202S:Eu, Gd203:Eu and mixtures thereof.

4. The storage tube of claim 2, wherein said admixture of said storage target contains about 3% by weight of P-l phosphor, the balance of about 67% being surface-killed P-22R phosphor.

5. A direct viewing storage target for a cathode ray tube, comprising: a light transparent substrate of electrically insulative material, means supported by said substrate defining a collector electrode, and a dielectric layer of phosphor material on one side of said substrate, said phosphor material comprising a substantially uniform admixture of phosphor particles, including particles of a first phosphor capable of bistable storage of charge images and particles of a second surface-killed phosphor that emits light of a different color than said first phosphor in response to bombardment by high velocity electrons from a cathode ray storage tube writing gun, and that has a light output efficiency lower than said first phosphor in response to bombardment by low velocity electrons from a cathode ray storage tube flood gun, the surface-killed phosphor causing said target to operate at a higher operating level.

6. The target of claim 5, wherein said first phosphor is P-l phosphor and said second phosphor is surface-killed P-22R phosphor.

7. The target of claim 6, wherein said admixture of said storage target contains about 33% by weight of said P-1 phosphor, the balance of about 67% being surface-killed P-22 phosphor.

8. The target of claim 7, wherein said surface-killed P-22R phosphor is selected from the group consisting of Y202S:Eu, Y203:Eu, YVO4:Eu, Gd202S:Eut Gd203:Eu, and mixtures thereof.

9. A direct-viewing cathode ray storage tube, comprising: an evacuated envelope having a light trans parent faceplate; a storage target mounted within said envel ope including conductive means having an array of collector electrode means electrically connected to said conductive means and a storage dielectric layer of phosphor material covering said conduCtive means with said col lector electrode means extending through said storage dielectric layer and having outer ends of said collector electrode means exposed; means for bombarding said storage target with a beam of high velocity electrons to form a charge image thereon; means for bombarding said storage dielectric layer with low velocity electrons to cause bistable storage of charge images having a potential at least equal to a critical minimum voltage necessary for such storage;; means to present charge images having a potential below said critical minimum voltage; said storage dielectric layer comprising a substantially uniform admixture that includes a first phosphor capable of bistable storage of charge images and a second surface-killed phosphor having a color emission different from that of said first phosphor and having a light output efficiency in response to bombardment by said low velocity electrons that is lower than that of said first phosphor, such that bombardment of the admixed material by said high velocity electrons causes the emission of a light image of a certain perceived color, and bombardment of said material by said low velocity electrons causes the emission of a light image corresponding to a storaged charge image which has a perceptibly different color from said certain perceived color, the surface-killed phosphor causing said tube to operate at a higher operating level.

1 0. The storage tube of claim 9 wherein said collector electrode means comprises conductive phosphor material having a color emission different from that of said first and second phosphor when bombarded by said beam of high velocity electrons.

11. The storage tube of claim 10 wherein said conductive phosphor material comprises surface-killed phosphor particles.

1 2. The storage tube of claim 11 wherein said storage dielectric layer comprises an admixture of P-1 phosphor and surface-killed P-22R phosphor and said conductive phosphor material comprises surface-killed P-22B phosphor.

1 3. The storage tube of claim 1 2 wherein said surface-killed P-22R phosphor is selected from the group consisting of Y202S:Eu, Y203:Eu, YVO4:Eu, Gd203:Eu, Gd2O2S:Eu or mixtures thereof.

1 4. The storage tube of claim 1 2 wherein said surface-killed conductive phosphor material comprises ZnS:Ag coated with CoS.

1 5. The storage tube of claim 12 wherein said storage target contains about 24% by weight of P-1 phosphor, about 56% by weight of surface-killed P-22R phosphor and the balance being surface-killed P-22B phosphor.

1 6. A direct-viewing storage target for use with a cathode ray tube, comprising: a light transparent member of electricallyinsulative material; a conductive layer on one surface of said member; and phosphor means covering said conductive layer, said phosphor means defining a first phosphor engaging said conductive layer and a second phosphor electrically connected to said conductive layer, said first phosphor including an admixture of two phosphor particles, one of the phosphor particles of said admixture being low voltage storage phosphor and the other of the phosphor particles of said admixture being luminescent at a higher voltage and at a color different from the color of said storage phosphor, said second phosphor defining collector electrode means for collecting secondary electrons emitted from charge images of said first phosphor and being luminescent at a voltage higher than the other phosphor particles and at a color different from the colors of said storage phosphor and other phosphor particles.

1 7. A direct-viewing storage cathode ray tube substantially as herein described with reference to the accompanying drawings.