GB1584500A - Cathode ray display tube with barrier layer penetration screen - Google Patents

Description

(54) CATHODE RAY DISPLAY TUBE WITH BARRIER LAYER PENETRATION SCREEN (71) We, WESTINGHOUSE ELEC TRIC CORPORATION of Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania, United States of America, a corporation organised and existing under the laws of the State of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to cathode ray display tubes, and more particularly to voltage penetration display tubes wherein plural layers of phosphor of different emissive colors comprise the display screen.A dual display can be effected by having phosphors of different persistence, with the rear phosphor layer nearest the electron gun actuated by relatively lower energy electron beams. The front phosphor layer, typically disposed on the interior surface of the faceplate is actuated by a higher energy electron beam which also actuates the rear phosphor layer in passing through the rear layer. The front phosphor is typically the longer persistence phosphor.

Such voltage penetration display tubes can be used for dual display radar screens or any other dual information display. where the one shorter persistence phosphor layer provides relatively static information such as target data. The long persistence phosphor layer is used to generate the more dynamic display information. such as radar tracking information which moves across the screen.

The different emissive colors of the separate phosphor layers contribute to operator ease in interpreting the display information. In order to achieve a high quality dual display with good color contrast between the different colored data and without smearing or blurring of data which is moved across the screen. a reasonably sharp penetration voltage separation must be achieved for actuation of the separate phosphor layers.

The prior art shows a variety of barrier layer materials provided between the phosphor layers or otherwise to provide an actuation voltage cut-off between the separate phosphor layers. A barrier layer of nonconducting material such as silica, alumina, silicates, magnesia, or refractory oxides is taught by U.S. 3,911,310. A barrier layer of thin light transmissive metal such as aluminum or magnesium, as well as insulating layers of alumina or silica, or conductive oxides, is taught by U.S. 3,603,792. The individual phosphor particles of one phosphor layer are coated with a metal penetration barrier in U.S. 3,721,849.

It has been discovered that light transmissive, non-luminescent magnesium fluoride provides a very effective voltage penetration barrier layer between two phosphor layers of different color and persistence in a display tube.

In order that the invention can be more clearly understood, a convenient embodiment thereof will now be described, by way of example, with reference to the accompanying drawing which is a representation of a display tube with an enlarged sectional view of the screen structure.

Referring to the drawings. a cathode ray tube 10 includes a neck portion 12, a funnel portion 14. and a faceplate portion 16. An electron gun 18 is shown in phantom sealed in the neck of the tube 10 and is externally connected to electronic drive systems. A phosphor display screen 20 is disposed on the interior surface 22 of the faceplate portion 16 of the tube. The faceplate 16 and remaining tube portions are conventional glass which are typically frit sealed together to form the tube.

The phosphor display screen 20 comprises a front phosphor layer 24 which is deposited as a thin uniform layer upon the interior surface 22 of the faceplate. The front phosphor layer 24 is typically a manganese activated magnesium fluoride phosphor, designed as P-33 by the Joint Electron Devices Engineering Council (JEDEC). This P33 phosphor has an orange cathodoluminescent emission when excited by a cathode ray beam, and long duration orange phosphorescence. By way of example, a phosphor of about 6-7 micron average diameter particle size is deposited in layer 24 to a weight of about 5 milligrams per cubic centimeter. The phosphor layer 24 is gravity settled from a water based slurry as are the next two succeeding layers.

A barrier layer 26 of finely divided magnesium fluoride is deposited on the front phosphor layer 24. This barrier layer 26 of magneisum fluoride is unactivated and noncathodoluminescent, while being highly transmissive to visible light. The magnesium fluoride by way of example has an average diameter particle size of about 4-5 microns, and is deposited as barrier layer 26 to a layer weight of about 3.5 milligrams per cubic centimeter, which provides the requisite layer thickness to substantially absorb electron energy from the CRT electron beam accelerated to 8 kilovolts or less.

A rear phosphor layer 28 is deposited on the barrier layer 26. A typical rear phosphor is terbium activated, gadolium oxy-sulfide, P-43 (JEDEC). By way of example, the P-43 phosphor used here has an average diameter particle size of about 2 microns, and is deposited as a very thin layer 28 to a weight of about 1.2 milligrams per cubic centimeter.

ThisP-43 phosphor is an efficient green emitter when actuated by a cathode ray beam and has a much shorter luminescent persistence than the front phosphor P-33.

A thin anode electrode film layer 30 of aluminum is vacuum deposited on the rear phosphor layer 28 to complete the phosphor screen 20. It is conventional practice to deposit a thin planar organic lacquer upon the rear phosphor layer, which is dried to form a smooth base for the vacuum deposited aluminum layer 30. The lacquer is removed during brakeout and exhaust of the tube prior to sealing.

During tube operation the anode layer 30 has a high electric potential applied thereto to accelerate electrons emitted from gun 18, to impinge the phosphor screen 20. When an 8 KV electric potential is applied the electrons pass through the anode layer 30 and actuate the rear phosphor layer 28 to produce green emission which passes through the light transmissive barrier layer 26 and also through the light transmissive front phosphor layer 24 and faceplate for viewing the display. The information displayed from the short persistence rear phosphor layer is retained on the screen only while actively scanned by electrons.When a 16 KV potential is applied to anode layer 30, the electron beam not only causes rear phosphor layer 28 to luminesce, but the beam also passes through the magneisum fluoride barrier layer 26 to actuate the front phosphor layer 24 producing long persistence orange emission, which mixes with the green emission from the rear phosphor layer to form a yellow-green display of other information to the viewer, such as radar information, with the more persistent orange information remaining visible to the viewer.

The thickness of the various layers can be varied, with variation of the magnesium fluoride barrier layer affecting the voltage penetration cut-off valve, with the thicker the layer, the higher the penetration voltage required.

Other phosphors can be used for the front and rear phosphor layers, with fluoride phosphors such as P-25, or P-38 as well as the P-33, phosphor described for the front phosphor layer, while short persistent P-l phosphor is also a good selection for the rear phosphor layer. The phosphors may be selected with comparable persistence characteristic, and rely solely on the difference in the emission colors for providing the dual display information.

WHAT WE CLAIM IS: 1. A cathode ray voltage penetration display tube having a display screen disposed on the interior surface of the display faceplate portion of the tube, which display screen comprises a front cathodoluminescent phosphor layer of a predetermined emission color disposed on the interior surface of the faceplate, an inert, light transmissive, electron energy barrier layer of magnesium fluoride disposed on the front phosphor layer, a rear phosphor layer of a second predetermined emission color which is actuated by the cathode ray electron beam of the operating tube, which magnesium fluoride barrier layer substantially absorbs electrons which are below a first energy level, while electrons at higher energy levels are transmitted through the barrier layer to actuate the front phosphor layer.

2. A display tube according to claim 1, wherein the rear phosphor layer is formed of a phosphor material which has a longer cathodoluminescent persistence than the front phosphor layer.

3. A display tube according to claim 1 or 2, wherein the magneisum fluoride barrier layer thickness is determined to substantially absorb 8 KV accelerated electrons and pass 16 KV accelerated electrons.

4. A display tube set forth in claim 1, 2 or 3, wherein the front phosphor is cathodoluminescent magnesium fluoride while the barrier layer is unactivated non-luminescent magnesium fluoride.

5. Cathode ray voltage penetration dis

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. layer 24 is typically a manganese activated magnesium fluoride phosphor, designed as P-33 by the Joint Electron Devices Engineering Council (JEDEC). This P33 phosphor has an orange cathodoluminescent emission when excited by a cathode ray beam, and long duration orange phosphorescence. By way of example, a phosphor of about 6-7 micron average diameter particle size is deposited in layer 24 to a weight of about 5 milligrams per cubic centimeter. The phosphor layer 24 is gravity settled from a water based slurry as are the next two succeeding layers. A barrier layer 26 of finely divided magnesium fluoride is deposited on the front phosphor layer 24. This barrier layer 26 of magneisum fluoride is unactivated and noncathodoluminescent, while being highly transmissive to visible light. The magnesium fluoride by way of example has an average diameter particle size of about 4-5 microns, and is deposited as barrier layer 26 to a layer weight of about 3.5 milligrams per cubic centimeter, which provides the requisite layer thickness to substantially absorb electron energy from the CRT electron beam accelerated to 8 kilovolts or less. A rear phosphor layer 28 is deposited on the barrier layer 26. A typical rear phosphor is terbium activated, gadolium oxy-sulfide, P-43 (JEDEC). By way of example, the P-43 phosphor used here has an average diameter particle size of about 2 microns, and is deposited as a very thin layer 28 to a weight of about 1.2 milligrams per cubic centimeter. ThisP-43 phosphor is an efficient green emitter when actuated by a cathode ray beam and has a much shorter luminescent persistence than the front phosphor P-33. A thin anode electrode film layer 30 of aluminum is vacuum deposited on the rear phosphor layer 28 to complete the phosphor screen 20. It is conventional practice to deposit a thin planar organic lacquer upon the rear phosphor layer, which is dried to form a smooth base for the vacuum deposited aluminum layer 30. The lacquer is removed during brakeout and exhaust of the tube prior to sealing. During tube operation the anode layer 30 has a high electric potential applied thereto to accelerate electrons emitted from gun 18, to impinge the phosphor screen 20. When an 8 KV electric potential is applied the electrons pass through the anode layer 30 and actuate the rear phosphor layer 28 to produce green emission which passes through the light transmissive barrier layer 26 and also through the light transmissive front phosphor layer 24 and faceplate for viewing the display. The information displayed from the short persistence rear phosphor layer is retained on the screen only while actively scanned by electrons.When a 16 KV potential is applied to anode layer 30, the electron beam not only causes rear phosphor layer 28 to luminesce, but the beam also passes through the magneisum fluoride barrier layer 26 to actuate the front phosphor layer 24 producing long persistence orange emission, which mixes with the green emission from the rear phosphor layer to form a yellow-green display of other information to the viewer, such as radar information, with the more persistent orange information remaining visible to the viewer. The thickness of the various layers can be varied, with variation of the magnesium fluoride barrier layer affecting the voltage penetration cut-off valve, with the thicker the layer, the higher the penetration voltage required. Other phosphors can be used for the front and rear phosphor layers, with fluoride phosphors such as P-25, or P-38 as well as the P-33, phosphor described for the front phosphor layer, while short persistent P-l phosphor is also a good selection for the rear phosphor layer. The phosphors may be selected with comparable persistence characteristic, and rely solely on the difference in the emission colors for providing the dual display information. WHAT WE CLAIM IS:

1. A cathode ray voltage penetration display tube having a display screen disposed on the interior surface of the display faceplate portion of the tube, which display screen comprises a front cathodoluminescent phosphor layer of a predetermined emission color disposed on the interior surface of the faceplate, an inert, light transmissive, electron energy barrier layer of magnesium fluoride disposed on the front phosphor layer, a rear phosphor layer of a second predetermined emission color which is actuated by the cathode ray electron beam of the operating tube, which magnesium fluoride barrier layer substantially absorbs electrons which are below a first energy level, while electrons at higher energy levels are transmitted through the barrier layer to actuate the front phosphor layer.

2. A display tube according to claim 1, wherein the rear phosphor layer is formed of a phosphor material which has a longer cathodoluminescent persistence than the front phosphor layer.

3. A display tube according to claim 1 or 2, wherein the magneisum fluoride barrier layer thickness is determined to substantially absorb 8 KV accelerated electrons and pass 16 KV accelerated electrons.

4. A display tube set forth in claim 1, 2 or 3, wherein the front phosphor is cathodoluminescent magnesium fluoride while the barrier layer is unactivated non-luminescent magnesium fluoride.

5. Cathode ray voltage penetration dis

play tubes substantially as described herein with particular reference to the accompanying drawing.