JPS5950195B2 - luminous screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a luminescent screen comprising a substrate having a luminescent layer having a single crystal structure and comprising at least one activator.

The invention also relates to a cathode ray tube equipped with such a luminescent screen.

Such a luminescent screen has a German patent no. It is disclosed in the specification of No. 810108.

Such luminescent screens are used, for example, in cathode ray tubes, such as television picture tubes, in electron microscopes, electron spectrometers, and for forming images in X-ray devices, such as X-ray image intensifiers. . German Patent No. 810,108 discloses that monocrystalline luminescent screens are obtained by growing an activated monocrystalline layer on an auxiliary plate, for example by vapor deposition or sublimation. In this case, it is preferable that the auxiliary plate itself is also made of a single crystal, and its lattice constant is the same or almost the same as that of the single crystal layer. Further, if desired, the auxiliary plate may be melted after another substrate, such as a glass plate, is applied to the auxiliary plate having the activated single crystal layer. However, in any case, such luminescent screens have a high excitation energy, the maximum permissible amount of heat that can be withstood is too small for many applications, and the light generated in the activated monocrystalline layer does not reach the substrate or auxiliary plate. It has the disadvantage that it is diffusely reflected at the interface with the active layer. Also used as a luminescent screen is one in which a powder phosphor is placed on a carrier.

However, this also has the disadvantage that the maximum allowable amount of heat is small because the heat is not dissipated very well from the phosphor particles. A further disadvantage here is that the resolution of the display screen is limited by the size of the particles. Furthermore, since the screen is composed of a very large number of particles, the specific surface area of the screen becomes large, which deteriorates the degree of vacuum of the cathode ray tube. Another structure, which produces the diffuse reflection described above, is disclosed in Dutch Patent No. 61,451.

The luminescent screen described here has a large number of rod-shaped luminescent crystals arranged on a carrier so that they are all approximately parallel to each other and their long axes are perpendicular or approximately perpendicular to the main surface of the carrier. However, this makes the direction of the excitation line substantially parallel to the long axis of the crystal. However, even with this construction, the drawback that the maximum permissible heat capacity of the luminescent screen is too small for many applications is not overcome.
Moreover, this case has the further disadvantage that the resolution is limited by the size of the individual crystals. An object of the present invention is to provide a luminescent screen that has a large maximum allowable amount of heat, has high resolution, and does not cause diffuse reflection.

According to the invention, a luminescent screen of the type described in the preamble is characterized in that the luminescent layer and the substrate are integrally formed in one self-supporting monocrystalline body.

In this way, since the substrate and the light-emitting layer are integrally constructed from one single crystal, there is naturally no crystallographic interface or grain structure, and therefore it is also possible that diffuse reflection occurs due to these. do not have. Furthermore, such an integral structure also improves heat dissipation from the light emitting layer to the base. Such single crystals can be made from a wide variety of materials, such as oxides, silicates, aluminates and gallates of rare earth metals. However, it is preferred that the single crystal body has a garnet crystal structure. The reason for this is that the garnet structure allows for extremely good heat dissipation from the light emitting layer. The thickness of the luminescent screen is preferably 0.3 to 2 mm. The reason for this is that if the thickness is made to this extent, it can be reliably self-supported without providing a separate substrate. The thickness of this endoluminescent layer is preferably 1 to 6 μm, particularly preferably 2 μm. This roughly corresponds to the depth that electrons can penetrate. In a first preferred embodiment of the luminescent screen according to the invention,
The single crystal body is made of yttrium-gallium garnet, and the part of the body that forms the light emitting layer contains 0.2 to 5% by weight of at least one type of activator selected from the group consisting of terbium and thulium. .

In this case, if terbium is used as the activator, efficient green light emission can be obtained, and if thulium is used as the activator, efficient blue light emission can be obtained. In a second preferred embodiment of the luminescent screen of the present invention, the single crystal body is made of gadolinium-gallium garnet, and the portion of the body that forms the luminescent layer contains 0.5 to 15% by weight of trivalent europium. .

In this way, efficient red light emission can be obtained. In a third preferred embodiment of the luminescent screen of the present invention, the single crystal body is made of yttrium-aluminum garnet, and the part of the body forming the luminescent layer is selected from the group consisting of cerium, terbium, and neodymium. 0.2 to 3% by weight of at least one type of active agent. In this case, efficient green luminescence can be obtained by using cerium and terbium, and substantially white luminescence can be obtained by using neodymium. To make such a luminescent screen according to the invention, a certain amount of activator can be diffused into the surface of the single crystal.

However, this takes a lot of time. As an alternative to the above method, it is possible to deposit a layer containing an activator, followed by a heat treatment. The activator layer is epitaxially grown from a liquid (flux) (LPE: LiquidP).
haseEpitaxy).

When the luminescent screen of the present invention is used in a cathode ray tube, a very bright bright spot (light spot) can be obtained.

This bright spot (light spot) can be used as a moving light source or a fixed light source, and can also be used to draw a very bright image. A very bright moving or stationary light source can illuminate the information carrier by means of a luminous flux, for example as described in NL 7314464.
It is needed in devices for optically scanning information tracks and in film scanners used to convert film images into television images, such as those described in Dutch Patent No. 6,706,095.

In addition, such a bright moving light source can also be used as a scanning light source for two microscopes. Very bright images are required in projection television picture tubes. In order to obtain a sufficiently bright image, conventional displays of considerably large dimensions (
A luminescent) screen was required. For example, in order to sufficiently enlarge (enlarge) and project an image, it was necessary to generate a very bright image on a display (emitting) screen with a diameter of 13 (1771 mm).The cathode ray tube of the present invention has good heat dissipation. , it is possible to draw a very bright image on a small screen, and is therefore very suitable for use in projection television equipment. A screen can be made (preferably less than 5d).In this case, the average power density of the synchrotron radiation is certainly more than 0.1W/G.In most cases it is more than 0.5W/C77l2.Drawings The present invention will be explained below.

FIG. 1 is a cross-sectional view of a portion of a single crystal luminescent screen of known construction.

The substrate 31 is made of rock salt (mineral salt), and about 17
After heating to 5° C., a zinc sulfide layer 32 is deposited. This zinc sulfide layer 32 is then activated with lead or copper at about 350°C and further annealed at this same temperature. However, for many applications, this known structure of the luminescent screen has insufficient heat conduction from the zinc sulfide layer 32 to the rock salt substrate 31, and furthermore, the interface 33 between the zinc sulfide layer 32 and the rock salt substrate 31
It has the disadvantage that the generated light is diffusely reflected. In contrast, FIG. 2 is a cross-sectional view of a portion of a monocrystalline luminescent screen according to the invention.

Here, the substrate 34 is made of yttrium-aluminum garnet (Y3Al5Ol2). A cerium active layer 35 (of yttrium-aluminum garnet) is deposited on this substrate 34 by liquid phase epitaxial growth (LPE).
Y2. ,,CeO. O3Al5Ol2) is grown.
A single crystal is thus formed, but this surface layer will contain some cerium atoms. Since there is no crystallographic interface between the active layer (above the dashed line) and the inactive substrate (below the dashed line) in this case, no diffuse reflection occurs. In this case, an aluminum film 36 with a thickness of 0.08 μm is provided on the active layer 35 to reflect light generated within the active layer 35. Note that the Y3Al5Ol2 substrate used here and the Y2. ,,CeO. Some properties of the O3Al5Ol2 layer are shown in the table below. The brightness of the luminescent screen of the present invention shown in FIG. 2 is plotted in FIG. ) is plotted as a graph.For this measurement, the energy of the electron beam colliding with the luminescent screen was set at 15kV) and the current strength was set at 100kV.
nA. Changing the value of W/m'' was done by changing the degree of focusing of the electron beam and changing the area of the spot. If a high power electron beam is used, the fluorescent material will be overheated.

In addition, as the supplied power is increased, the powder phosphor becomes saturated and no longer emits any more intense light. Furthermore, the radiance values of known powder phosphors are outside the range shown in FIG. In contrast, it has been found that according to the invention, the fluorescent screen is not overheated.

In the fluorescent screen of the present invention, the active layer 35 serves as a light emitting layer.
Since the light emitting layer and the substrate 34 are integrated into one single crystal, thermal contact between the two is extremely good, so the light emitting layer does not overheat. FIG. 4 is an exploded perspective view of a cathode ray tube (CRT) having a luminescent screen according to the present invention.

Conductive coating 2 on the inside of the aluminum oxide cylindrical container 1
is provided and connected to the anode contact 3. Then, an electron gun 4 is mounted inside this cylindrical container 1. This electron gun has a cathode (
), but this cathode is a Wehnelt electrode 5
The grids 6, T, and 8 are housed within each other to prevent the plurality of grids 6, T, and 8 from being short-circuited by the electron beam. The electrodes of the electron gun 4 are attached using glass assembly rods 9 in the usual manner.
A centering spring 10 is provided at one end of the electron gun 4.
The other end of the electron gun 4 is fixed to a substrate 11.
A hole 12 for an outlet wire and an exhaust pipe line 13 are provided for electrical connection with the outside. The other end of the cylindrical container 1 is . It is closed with a luminescent screen 14, which is made of gadolinium-gallium garnet and whose side facing the electron gun 4 is activated with europium. The luminescent screen 14 has a thickness of 500 μm and a diameter of 251 μm. The luminescent screen 14 is coated with an aluminum film (not shown). This luminescent screen 14
is connected to the aluminum oxide cylindrical container 1 using a heat-shrinkable adhesive. For this purpose, an aluminum ring 15 is used as a connecting member between the end face of the cylindrical container 1 and the luminescent screen 14. The thermal expansion coefficients of the aluminum oxide of the cylindrical container 1 and those of the luminescent screen differ only slightly, so that no undesired stresses occur as a result of thermal expansion. The electron beam produced by the electron gun 4 is normally deflected by a deflection magnetic field, but it is also possible to deflect it electrostatically instead. The reason for this is that the deflection can be small with a small display (light-emitting) screen as mentioned above. FIG. 5 is a partially cutaway perspective view of the electron tube of FIG. 4 as a component of a projection television apparatus.

A deflection coil 16 is mounted around the cylindrical container 1. A very bright image on the luminescent screen 14 is projected onto a projection screen (not shown) by a lens system IT. 6th
The figure is a schematic representation of a device for optically scanning an information track 18 on an information carrier 19 with a beam of light 20 generated by a cathode ray tube 21 equipped with a luminescent screen according to the invention.

How this optical scanning is carried out is specified in Dutch Patent Publication No. 7314464. The great advantage of using a cathode ray tube equipped with a luminescent screen according to the invention is that the image on the luminescent screen is bright, so that losses caused by the optical elements are not a problem. A bright bright spot 23 created on a luminescent screen 22 by a cathode ray tube 21
can be moved over the entire surface of the luminescent screen 22 by changing the voltage applied to the deflection plate 24. Lenses 25 and 26 project this bright spot (light spot) onto the rotating disc-shaped record carrier 19. The light reflected by the information carrier 19 is received by a photocell 29 via a lens 26 and mirrors 2T and 28. The mirror 28 is a semi-transparent mirror. The light reflected by the rotating disc-shaped record carrier 19 is intensity-modulated with the information stored therein, and thus contains the information of the disc-shaped record carrier 19. To change the position of the light spot on the disk, the bright spot on the luminescent screen 23 can be moved. In the above-described optical system as shown in FIG. 6, the intensity of the light decreases when it passes through various optical components, such as the semi-transparent mirror 28. Therefore, it is necessary to increase the brightness of the light source as much as possible. In such cases, the cathode ray tube equipped with the luminescent screen of the present invention is very useful.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a part of a prior art luminescent screen, FIG. 2 is a schematic sectional diagram of a part of a luminescent screen of the present invention,
FIG. 3 is a graph showing that the brightness of the luminescent screen of the present invention is high; FIG. 4 is an exploded perspective view of the cathode ray tube of the present invention; and FIG. 5 is a partially cutaway perspective view of the cathode ray tube shown in FIG. 4 assembled. , FIG. 6 is a schematic diagram of an optical scanning device for a record carrier. 1...Cylindrical container, ``...End face, 2...
...Conductive film, 3...Anode contact, 4...
...Electron gun, 5...Wehnelt electrode, 6
, 7, 8...grid, 9...glass assembly rod, 10...spring, 11...
・Board, 12... Hole for lead wire, 13...
... Exhaust pipe line, 14 ... Luminous screen, 15
... Aluminum ring, 16 ... Deflection coil, 17 ... Lens system, 18 ...
・Information truck, 19...Information carrier, 20...
... Luminous flux, 21 ... Cathode ray tube, 22 ...
...Luminous screen, 23... Bright spot (light spot)
, 24... Deflection plate, 25... Luns, 2
6...Luns, 27...Mirror, 28...
...Semi-transparent mirror, 29...Photo cell, 31.
...Rock salt substrate, 32...Zinc sulfide layer, 3
3...Boundary surface, 34...Substrate, 35.
...Active layer, 36...Coating.

Claims (1)

[Scope of Claims] 1. A luminescent screen comprising a substrate having a luminescent layer having a single crystal structure and containing at least one activator, in which the luminescent layer and the substrate are combined into one self-supporting monocrystalline body. A luminescent screen characterized by being integrally constructed with. 2. The luminescent screen according to claim 1, characterized in that the single crystal body has a garnet crystal structure. 3. The single crystal body is made of yttrium-gallium garnet, and at least one activator selected from the group consisting of terebrium and thulium is added to the portion constituting the internal luminescent layer.
The luminescent screen according to claim 2, characterized in that the luminescent screen contains 2 to 5% by weight. 4. The light emitting device according to claim 2, wherein the single crystal main body is gadolinium-gallium garnet, and the portion constituting the luminescent layer contains 0.5 to 15% by weight of trivalent europium. screen. 5. The single crystal body is yttrium-aluminum garnet, and the portion constituting the internal luminescent layer contains 0.2 to 3% by weight of at least one type of activator selected from the group consisting of cerium, neodymium, and terbium. A luminescent screen according to claim 2, characterized in that: 6. The luminescent screen according to any one of claims 1 to 5, wherein the thickness of the substrate is between 0.3 mm and 2 mm. 7. The luminescent screen according to any one of claims 1 to 6, characterized in that the luminescent layer has a thickness of 1 to 6 μm. 8. A luminescent screen according to any one of claims 1 to 7, characterized in that it comprises a luminescent layer epitaxially grown (LPE) from a liquid, often called flux. 9 In a projection television device in which an image displayed by irradiating an electron beam onto a display screen of a cathode ray tube is displayed as a bright image on the projection screen using an optical device, the display screen of the cathode ray tube has a single crystal structure. A light-emitting layer containing at least one type of activator and a substrate are combined into one
The display screen comprises a luminescent screen integrally constructed of two self-supporting monocrystalline bodies, with a surface area of 20
cm^2 or less, and the average radiance on the display screen is 0.1 W/cm^2 or more. 10 The surface area of the display screen is 5 cm^2 or less, and the average radiance on the display screen is 0.5 W/cm.
10. The projection television apparatus according to claim 9, characterized in that the projection television set is ^2 or more.