CA1270892A - Projection television display with multilayer interference filter - Google Patents
Projection television display with multilayer interference filterInfo
- Publication number
- CA1270892A CA1270892A CA000509662A CA509662A CA1270892A CA 1270892 A CA1270892 A CA 1270892A CA 000509662 A CA000509662 A CA 000509662A CA 509662 A CA509662 A CA 509662A CA 1270892 A CA1270892 A CA 1270892A
- Authority
- CA
- Canada
- Prior art keywords
- filter
- lambda
- display tube
- display
- luminescent material
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/74—Projection arrangements for image reproduction, e.g. using eidophor
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/28—Interference filters
- G02B5/285—Interference filters comprising deposited thin solid films
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
- H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
- H01J29/18—Luminescent screens
- H01J29/185—Luminescent screens measures against halo-phenomena
Abstract
PHQ 85.007 18 1985-4-22 Abstract:
"Projection television display tube and projection television device having at least one such tube".
A projection television display tube comprising in an evacuated envelope (1) a display screen (7) which is provided on the inside of a curved display window (2) in the wall of the envelope (1), which display screen (7) comprises luminescent material (13) and a multilayer interference filter (12) is provided between said material and the display window, and comprises a number of layers (HL) which are manufactured alternately from a material having a high refractive index (H) and a material having a low refractive index (L). If the filter (12) is composed of at least 6 layers, each having an optical thickness nd, wherein n is the refractive index of the material of the layer and d is the thickness, which optical thickness is between 0.2 .lambda.f and 0.3 f and preferably is between 0.23 .lambda.f and 0.27 .lambda.f, wherein .lambda.f is equal to p x .lambda. , wherein .lambda. is the desired central wavelength which is selected from the spectrum emitted by the luminescent material (13) and p is a number between 1.18 and 1.32, a display tube is obtained in which the luminous efficiency on the projection screen and in particular at the edge of the projection screen has proved to be considerably larger than the sum of the effects of the individual measures, namely the curved display window and the provision of an interference filter, would give.
"Projection television display tube and projection television device having at least one such tube".
A projection television display tube comprising in an evacuated envelope (1) a display screen (7) which is provided on the inside of a curved display window (2) in the wall of the envelope (1), which display screen (7) comprises luminescent material (13) and a multilayer interference filter (12) is provided between said material and the display window, and comprises a number of layers (HL) which are manufactured alternately from a material having a high refractive index (H) and a material having a low refractive index (L). If the filter (12) is composed of at least 6 layers, each having an optical thickness nd, wherein n is the refractive index of the material of the layer and d is the thickness, which optical thickness is between 0.2 .lambda.f and 0.3 f and preferably is between 0.23 .lambda.f and 0.27 .lambda.f, wherein .lambda.f is equal to p x .lambda. , wherein .lambda. is the desired central wavelength which is selected from the spectrum emitted by the luminescent material (13) and p is a number between 1.18 and 1.32, a display tube is obtained in which the luminous efficiency on the projection screen and in particular at the edge of the projection screen has proved to be considerably larger than the sum of the effects of the individual measures, namely the curved display window and the provision of an interference filter, would give.
Description
lZ7C~ 2 PHQ 85.007 The inven-tinn relates to a projection television d:isplay tube compris.ing in an evacuated enve].ope a d.isplay screen which is provided on the inside of a display window in the wall of the envelope, said display screen comprising a liminescent material, ~etween said luminescent material and the display wi.ndow a multilayer interference filter being provided, which comprises a number of layers which are manufactured alternately from a material having a high refractive index and a material having a low refractive index.
From ~erman Patent Appli.cation 23 30 898 laid open to public inspection a display tube is known in which a multilayer interference filter is used hetween the luminescent material (the phosphor) and the display window. For the thicknesses of the layers of the filter of a material having a high refractive index an optical thickness smaller than 0.25 A or between 0.5 A and 0.75 ~ is chosen, wherein A is the wavelength of the light emitted hy the luminescent material. For the layers of the filter of a material having a low refractive index an optical thickness of 0.25 A is chosen or an odd multiple thereof. The light emission characteristic of the display screen of the tube is varied hy the filter in such manner that the quantity of liyht emitted within a restricted angular aperture increases hy 25% compared with a tube without a filter. The contrast in the produced picture is also increased by a reduction of the background brightness.
A similar display tube is disclosed in ~ritish Patent Specification 1,306,335 in which a so-called passband interference filter is provided between the phosphor and the display screen. This filter consists of layers having an optical thickness of 0.25 A and appears as follows:
S L H L L L I. L I, H L H L L L L L L H L H L L L L L L H, wherein S is the display wi.ndow, L are layers of a material having a low refractice index, and H are layers of a material having a high r,efractive index. Such a filter may also be represented as follows:
S L H (L) H L H (L)6 H L H (L)6 H.
~s a result of the presence of the six ].ayers placed against each other -089~
PHQ 85.007 ~;~ 2 10-e~-1r~r and having a low refractive index (L)~, a Fabry-Perot filter is formed. This filter, with a given choice of the optical layer thickness, has a desired transmission band for light rays which enclose an angle smaller than 25 to 40 to the normal on the filter. In addition, however, there is a non-desired wide transmission band for light rays which enclose an angle between 55 and 90. All the light which is passed in this band is lost or contributes to so-called halo and hence to lnss of contrast in the displayed picture. This will be explained hereinaft~r. Moreover, the cryolite layers used in said filter are hygroscopic and remain soft so that damage of the filter can easily occur. The zinc sulphide t%nS) layers used in said filters easily oxidize during firing the tube at ayproximately 460C, so that they are not so suitable for use in display tubes.
In the article "Anti-halo coatings for cathode ray tubes face-plates", J.D. Rancourt, Proceedings of the SID, Vol. 25/1, 1984, an 11-layer edge-filter and an 8-layer pass-band-interference filter for suppressing halo effects is described. It is also suggested to use one of these filters for projection T.V. (page 47, right-hand top). An 11-layer filter, however, for projection T.V. still gives much loss because too much light is passed at large angles.
In projection television display tubes a number of problems occur, for example:
a) The display of a flat display screen on a flat projection screen requires a very complicated system of lenses. In order to reach a "Hi-Fi" (optical) quality, for example, a five or eight element lens is necessary.
b) A luminous decline to approximately 20% occurs from the centre of the projection screen towards the corners, caused by reduction of the acceptance angles of the lens (including vignetting). This decline in brightness becomes the worse accordiny as the focal distance of the lens is smaller. At the moment there is a clear trend towards smaller focal distances so as to reduce the size of the housing of the projection television device.
It is an object of the invention to provide a projection television display tube having a multilayer interference filter in which these problems are lessened.
A projection television display tube of the kind .~, ; .
~27~92 - 8 - ~9~9 PHQ ~5.007 C~ 3 1~ 0~ 1~0~
described in the opening paragraph is characterized according to the invention in that the displaY window on the vacuum side is inwardly curved having an angle of curvature ~, wherein ~ is the angle between a line at right angles to the centre of the display window and a line at 5 right angles to the part of the display window farthest remote from the centre, said angle ~ being between 5 and 25.
3y providiny the projection television display tube with both a curved display screen and with a multilayer interference filter, the above problems are solved for the greater part. The display quality is improved and at the same time the number ~f required lens elements in a projection telèvision device is reduced. Less light decline towards the corners also occurs.
Surprisingly the light gain in the corners of the display screen has proved to be considerably larger than the sum of the effects of the individual measures, namely the curved display window and the provision of an interference filter, would produce.
Display tubes having inwardly curved display windows are known Per se from British Patent Specification 2,091,898.
A preferred embodiment of a projection television display tube according to the invention is characterized in that-the curved display window is substantially spherical having a radius of curvature between 150 mm and 730 mm, for example, for a 127 mm diagonal display screen.
Further problems that occur are:
c) Projection television display tubes having green phosphors with Terbium as an activator have a less good colour rendition by too great contribution of orange and red spectral lines.
d) In tubes with the green Tb phosphors and with the wide band blue 2nS:Ag-phosphor, chromatic aberration occurs.
e) The brightness on the projection screen generally is on the low side.
f) The contrast also requires some improvement.
A second preferred embodiment of a projection television display according to the invention is characterized in that the filter is composed of at least 6 layers each having an optical thickness nd, wherein n is the refractive index of the material of the layer and _ is the thickness, said optical thickness being between 0.2~f and 0.3~fl -9 ~9 PHQ 85.007 cA 4 .l4~ .19G9 wherein ~f is equal to p ~ ~, wherein ~ is the desired central wavelength which is selected from the spectrum emitted by the luminescent material and P is a number between 1.18 and 1.32. The average optical thickness is 0.25 ~f and ~f is the central wavelength of the filter. On a frequency scale, 1/~f corresponds to the centre of the reflection band with perpendicular incidence of the - light.
By using a suitable multilayer optical interference filter between the phosphor and the display screen:
1) The colour point in the green for the usual Tb-phosphors in improved (solution problem c).
From ~erman Patent Appli.cation 23 30 898 laid open to public inspection a display tube is known in which a multilayer interference filter is used hetween the luminescent material (the phosphor) and the display window. For the thicknesses of the layers of the filter of a material having a high refractive index an optical thickness smaller than 0.25 A or between 0.5 A and 0.75 ~ is chosen, wherein A is the wavelength of the light emitted hy the luminescent material. For the layers of the filter of a material having a low refractive index an optical thickness of 0.25 A is chosen or an odd multiple thereof. The light emission characteristic of the display screen of the tube is varied hy the filter in such manner that the quantity of liyht emitted within a restricted angular aperture increases hy 25% compared with a tube without a filter. The contrast in the produced picture is also increased by a reduction of the background brightness.
A similar display tube is disclosed in ~ritish Patent Specification 1,306,335 in which a so-called passband interference filter is provided between the phosphor and the display screen. This filter consists of layers having an optical thickness of 0.25 A and appears as follows:
S L H L L L I. L I, H L H L L L L L L H L H L L L L L L H, wherein S is the display wi.ndow, L are layers of a material having a low refractice index, and H are layers of a material having a high r,efractive index. Such a filter may also be represented as follows:
S L H (L) H L H (L)6 H L H (L)6 H.
~s a result of the presence of the six ].ayers placed against each other -089~
PHQ 85.007 ~;~ 2 10-e~-1r~r and having a low refractive index (L)~, a Fabry-Perot filter is formed. This filter, with a given choice of the optical layer thickness, has a desired transmission band for light rays which enclose an angle smaller than 25 to 40 to the normal on the filter. In addition, however, there is a non-desired wide transmission band for light rays which enclose an angle between 55 and 90. All the light which is passed in this band is lost or contributes to so-called halo and hence to lnss of contrast in the displayed picture. This will be explained hereinaft~r. Moreover, the cryolite layers used in said filter are hygroscopic and remain soft so that damage of the filter can easily occur. The zinc sulphide t%nS) layers used in said filters easily oxidize during firing the tube at ayproximately 460C, so that they are not so suitable for use in display tubes.
In the article "Anti-halo coatings for cathode ray tubes face-plates", J.D. Rancourt, Proceedings of the SID, Vol. 25/1, 1984, an 11-layer edge-filter and an 8-layer pass-band-interference filter for suppressing halo effects is described. It is also suggested to use one of these filters for projection T.V. (page 47, right-hand top). An 11-layer filter, however, for projection T.V. still gives much loss because too much light is passed at large angles.
In projection television display tubes a number of problems occur, for example:
a) The display of a flat display screen on a flat projection screen requires a very complicated system of lenses. In order to reach a "Hi-Fi" (optical) quality, for example, a five or eight element lens is necessary.
b) A luminous decline to approximately 20% occurs from the centre of the projection screen towards the corners, caused by reduction of the acceptance angles of the lens (including vignetting). This decline in brightness becomes the worse accordiny as the focal distance of the lens is smaller. At the moment there is a clear trend towards smaller focal distances so as to reduce the size of the housing of the projection television device.
It is an object of the invention to provide a projection television display tube having a multilayer interference filter in which these problems are lessened.
A projection television display tube of the kind .~, ; .
~27~92 - 8 - ~9~9 PHQ ~5.007 C~ 3 1~ 0~ 1~0~
described in the opening paragraph is characterized according to the invention in that the displaY window on the vacuum side is inwardly curved having an angle of curvature ~, wherein ~ is the angle between a line at right angles to the centre of the display window and a line at 5 right angles to the part of the display window farthest remote from the centre, said angle ~ being between 5 and 25.
3y providiny the projection television display tube with both a curved display screen and with a multilayer interference filter, the above problems are solved for the greater part. The display quality is improved and at the same time the number ~f required lens elements in a projection telèvision device is reduced. Less light decline towards the corners also occurs.
Surprisingly the light gain in the corners of the display screen has proved to be considerably larger than the sum of the effects of the individual measures, namely the curved display window and the provision of an interference filter, would produce.
Display tubes having inwardly curved display windows are known Per se from British Patent Specification 2,091,898.
A preferred embodiment of a projection television display tube according to the invention is characterized in that-the curved display window is substantially spherical having a radius of curvature between 150 mm and 730 mm, for example, for a 127 mm diagonal display screen.
Further problems that occur are:
c) Projection television display tubes having green phosphors with Terbium as an activator have a less good colour rendition by too great contribution of orange and red spectral lines.
d) In tubes with the green Tb phosphors and with the wide band blue 2nS:Ag-phosphor, chromatic aberration occurs.
e) The brightness on the projection screen generally is on the low side.
f) The contrast also requires some improvement.
A second preferred embodiment of a projection television display according to the invention is characterized in that the filter is composed of at least 6 layers each having an optical thickness nd, wherein n is the refractive index of the material of the layer and _ is the thickness, said optical thickness being between 0.2~f and 0.3~fl -9 ~9 PHQ 85.007 cA 4 .l4~ .19G9 wherein ~f is equal to p ~ ~, wherein ~ is the desired central wavelength which is selected from the spectrum emitted by the luminescent material and P is a number between 1.18 and 1.32. The average optical thickness is 0.25 ~f and ~f is the central wavelength of the filter. On a frequency scale, 1/~f corresponds to the centre of the reflection band with perpendicular incidence of the - light.
By using a suitable multilayer optical interference filter between the phosphor and the display screen:
1) The colour point in the green for the usual Tb-phosphors in improved (solution problem c).
2) The chromatic aberration, in particular in the green, is reduced (solution problem d).
3) The brightness for all central colours is increased (solution problem e).
4) The contrast is improved (solution problem f).
The filter in the projection tube according to the second preferred embodi.ment hence consists exclusively or substantially exclusively of layers having an optical thickness of approximately 0,25 ~f. Herefrom the filter derives the special property of the very wide reflection band (no transmission) for light rays which enclose an angle between approximately 30 and 80 to 90 to the normal on the filter.
For example, in 0,75 ~f and 1.25 Af filters the width of the reflection band is reduced by factors 3 and 5, respectively, and undesired transmission occurs at large angles. As a result of this the gain in luminous efficiency with such filters in the forward direction, hence for light rays which enclose small angles to the normal on the filter, as described in German Patent Application 2,330,898 is restricted to 25%. There is also less gain in contrast. The Fabry-Perot filter according to ~3ritish Patent Specification 1,306,335 comprises three 1.5 ~ layers (each consisting of six 0.25 ~ layers of a material havinq a low refractive index) and also has an undesired wide transmission band for light rays which enclose large angles to the normal on the filter.
In the above article "Proceedings of the SID", Vol. 25l1, 1984 fllters for halo-suppression have been described as already ,;
.., _8, lZ7~8~Z
3 ~~ 9 PHQ 85.007 ~ 5 ~-92-t1~g--mentioned above. Even absorbing fi.lters are suggested. Due to theirsmall number of layers said filters are less critical as regards the angle within which the reflection strongly decreases (the acceptance angle). Characteristic of the second preferred embodiment present S invention is that the position of the "edge" of the filter (hence P and Af in ~f=pA) is exactly defined and the acceptance angle i5 c-o~npdratively small. This leads to a great gain in brightness at small angles. As d result of this the filter is very sensitive to losses at large angles and therefore filters having many layers (> 14) are des.ired.
The layer thicknesses in the filter are hence chosen to be so that at a desired wavelength the reflection begins to increase considerably for light rays of a luminescent material which enclose an angle exceeding 18 to 30 to the normal on the filter. The wide reflection band ensures that light rays having angles exceeding 25 to 35'~ are reflected as much as possible and after scattering in the luminescent material again obtain a chance to emanate from the tube within an angle of 18 to 30 to the normal on the filter. As a result of this a maximum luminous efficiency in the forward direction occurs and at small angles which for the central wavelength A of the phosphor is at least 50~O larger than without the use of the filter.
Moreover, the wide reflection band ensures a strongly reduced halo effect and a reduced emanation of light at large angLes. The optical thickness nd of the layers of the filter preferably is not equal for all layers but varies between 0.2 Af and 0.3 ~f~ and preferably between 0.23 Af and 0.27 ~f~ as will be explained in greater detail with reference to an embodiment. As a result of this variation of the thickness a flatter transmission characteristic of the filter is obtained. ~ecause the transmission characteristic of the filter is dependent on the wavelength, it is possible by d combination of a phosphor and an adapted filter to improve the colour point of the light rays which pass through the filter within an angle of 20 to 30 to the normal.
The value of the numeral ~ is between 1.18 and 1.32 dependent on the refractive indices of the layers used and on the width of the selected wavelength range, which will be explained inter alia with reference to the embod.iments. For a TiO2 - SiO2 filter P =Af/A is bet.ween 1.21 and 1.32.
Z
PHQ 85.007 h 12.04.1989 A third preFer.red embodiment of a projection television display tube according to the invention is characteri~ed in that the filter is composed substantially of 14 to 30 layers.
A follrth preferred embodiment of a tuhe according to the invention is characteri.zed in that the said optical thickness nd are between 0.23 ~f and 0.27 Af.
A fi.fth preferred emhodiment is characterized in that the layers of the filter having a hitJh refractive index consist of titanium oxide (Tio2) or tantalum oxide (Ta205) and the layers having a low re~ractive index consi.st of silicon oxide (siO2) or magnesium fluoride (MgF2). The optimum ~ values for a Ta205-SiO2 filter are approximately 0.04 to 0.05 lower than for a Tio2-SiO2 filter. In this case the reflection band is less wide. Furthermore, the magnesium fluoride is preferably provided at approximately 300C to thus ohtain a sufficiently hard layer.
A sixth preferred embodiment is characterized in that the luminescent material comprises a termbium-activated substantially green-luminescing phosphor and A = 545 nm and P is a number between 1.21 and 1.25 for a TiO2-SiO2 filter. Terbium-activated substantially green-luminescing phosphors are, for example, yttrium aluminium garnet-terhium (YAG:Tb), yttrium-sili.cate-terbium (Y25iO5:Tb), lanthanum-oxybromide-terbium (LaOBr:Tb), lanthanum oxychloride-terbium (LaOCl:Tb), and indium : horate-terbium (InBo3:Tb). For all these Tb-activated green phosphors the central wavelength is A = 545 nm. By choosing for the filter according to the invention p to be between 1.21 and 1.25, hence Af between 660 nm and 680 nm, a filter is obtained having a high transmission (exceeding 90%) for light rays which enclose an angle smaller than 20-30 to the normal on the filter. For light rays which enclose an angle greater than 25 to 35 to the normal on the filter the transmission rapidly reduces and reflection occurs up to 80-90.
This filter has a particularly good operation for these Tb-activated phosphors which have emission li.nes in the blue, green, orange-red and red. By using the filter a gain occurs .in the green, a much smaller gain i.n the blue and suhstanti.ally complete reduction of the quantity of light.emitted by the tube occurs in the red, which is favourable for the colour point. All thi.s provides a gai.n in luminous efficiency, colour improvement (closer to the EBU-standards) and gain in contrast. Tn an P~Q ~5 QnT 7 12.04.1989 optimum fi1ter the overal gain in luminous effici.ency for all colours together in these Tb-activated phosphors is 30-60%. The ga;n in the green is fiO to 120~. The coordinates x and ~ in the CIE olour triang1.e are then n 25 tl~ 0.30 ~nd 0.60 to 0.64, respectively Without a filter these coordinates are x = 0.3.~ to 0.36 and y - 0.54 to 0.59, respectively. The gain in contrast is approximately a fact~r 2. For opt;cal display with lenses, as in -the case of projection television, this presents considerable advantages, much less chromatic aberration (little~ or no red and proportiona1.1y l.ess blue with respect to the green).
A seventh preferred embodiment of a tube according to the invention i.s characterized in that the luminescent material comprises a terbium-activaled blue-luniinescing phosphor and ~ = 490 nm and p is a number between 1.21 and 1.25 for a TiQ2-Sio2 filter. By using for the doping a small quantity of Tb a predominantly b].ue-luminescing phosphor is obtained with A = 490 nm. By choosing ~ to be between 1.21 and 1.25, hence ~f hetween S90 nm and fi15 nm, a filter is obtained in which the reflection increases comparatively steeply for light rays which enclose an angle yreater than 25-35 to the normal on the filter. Then there is a gain in contrast of 70 to 100% and a gain in luminous efficiency in the hlue of 60-100. In this case a considerable improvement of the colour point occurs because the green spectral lines are Li.ltered out by the multil.ayer filter.
An eight preferred embodiment of a tube in accordance with the inventi.on is characterized in that ths luminescent material is europium-activated yttrium oxide (Y203:EIu) and ~ = 612 nm and ~ is a number betweerl 1.21 and 1.25 for a Tio2-Sio2 filter. As a result of this choice of P between 1.21 and 1.25, hence ~f hetween 740 nm and 765 nm, the reflection of the filter for lig31t ~ays which enclose an angle greater than 25 and 35 to the normal on the filter increases considerably. Now there is a gain of 60 and 120% in total luminous efficiency. The gain in contrast is approxi.mately 100%. In this case there is a small colour point imprs)vement. The red components in the spectrlJm of the generated light are as a matter of fact more strongly ~S intensified than the componerlts of shorter wavelength.
The i.nvention may also be used ln wide-band phosphors, fs)r example willemite (Zn~S104), zinc sulphide si.lver (ZnS:Ag) PHQ 85.007 8 12.04.1989 and str~ntium alum:inate-europium (SrAl305 5:Eu) with central wavelengths ~ of 530 nm, 460 nm and 460 nm, respecti.vely. The value of P
ls now chosen to be between 1.21 and 1.32.
~ ninth preferred embodiment of a tube in accort1ance with the invention is character;zed in that the luminescent material is zinc sulphide-silver (ZnS:Ag) and ~ = 460 nm and P i.s a number hetween 1.24 and 1.32 for a Ti.02-SiO2 filter.
As a result of this choice of P between 1.24 and 1.32, hence Af hetween 570 nm and 610 nm, the reflection of the filter for light rays which enclose an angle greater than 25 to 35 to the normal on the filter increases considerably. Now there is a gain of 30 to 80% in the luminous efficiency for wavelengths between approximately 440 nm and 500 nm. The gain in contrast is 80 to 100~o. In this case the longwave (green) part of the ~nS:Ag spectrum is filtered c)ut.
Chromatic aberration caused by the displaying lens is hence reduced.
A tenth preferred embodiment of a tube in accordance with the invention is characterized in that the luminescent material comprises a terbi.um-activated substantially green-luminescing phosphor 20 and A = 545 nm and P is a number between 1.18 and 1.22 for a Ta205-sio2 filter.
An eleventh preferred embodiment of a tube in accordance with the invention is characterized in that the luminescent material comprises a termbium-activated blue-luminescing phosphor and ~ = 490 nm 25 and P is a number between 1.18 and 1.22 for a Ta205-SiO2 filter.
An twelfth preferred embodiment of a tube in accordance with the lnvention is characterized in that the luminescent material is europium-activated yttrium oxyde (Y203:Eu) and ~ = 612 nm and P is a number between 1.18 and 1.22 for a Ta205-SiO2 filter.
A thirteenth preferred embodiment of a tube in accordance with the invention is characterized in that the luminescent material is zinc sulphide-silver (~nS:Ag) and ~ = 460 nm and P is a number between 1.21 and 1.28 for a Ta205-SiO2 filter.
For a Ta205-SiO2 filter the optimum P-values are 35 approximately 0.04 to 0.05 lower than for Tio2-Sio2 filter. The reflection band in this case is less wide.
: A fourteenth preferred embodiment of a display tube in lZ7Q1~12 PHQ 85.007 9 12.04.1989 accordance with the invention is characteri~ed in that the outermost approxi.mately 0.25 ~-thick layer of the filter which faces the lumi.nescent material consists of a material having a high refractive index and is covered with a terminating layer having an optical thickness of approximately 0.125 ~f of a material having a low refractive index, on which terminating layer the luminescent material is provided.
A fifteenth preferred embodiment of a display tube in accordance with the invention is characterized in that the outermost approximately 0.25 ~f-thi.ck layer of the filter facing the display window consists of a material having a high refractive i.ndex and is covered with an intermediate layer having an optical thickness of approximately 0.125 Af of a material having a lower refractive index.
By providing a terminating layer and/or intermediate layer having an optical thickness of approximately 0.125 ~f on the phophor si.de and/or the display window side, respectively, the transmission in the forward direction for light rays which enclose small angles to the normal is increased and the oscillations in the transmissions are reduced. The transmi.ssion characteristic becomes flatter.
A sixteenth preferred emhodiment of a display tube in accordance with the invention is characterized in that the outmost approximately 0.25 ~f-thick layer of the filter facing the luminescent material is composed of a mixture of metal oxide, said mi.xture comprising titanium oxide (Tio2) and a metal oxide from the group beryllium oxide (BeO), magnesium oxide (MgO) and calci.um oxide (CaO), in which mixture the quantity of titanium oxide is 70 to ~0% by weight.
By using such an extra smooth hence less porous coating layer on the phosphor side of the filter the optical contact with the phosphor is reduced so that the gain in contrast and luminous efficiency are extra increased.
Tubes accordiny to the invention are preferably coupled optically via liquid to a system of lenses or are provided with liquid cooling in which the likewise curved cover glass is provided on its outside with an anti-reflection layer. Said cover glass may also serve as the first lens element (the so-called "field-flattener").
~ isplay tubes according to the invention can advantageously be used in projection television dev.ices. The very bright picture transmitted in the forward direction is received substantially without losses by a system of lenses having a limited acceptance anyle of, J
- . , :
r 12~38~2 3~ a~5 / PHQ 85.007 ~ 10 _1a85-44_~2 / for example, 25-30 . As a result of this a brighter picture with more / contrast and an improved colour rendition is obtained.
/ The invention will ncw be descri ed in greater detail, by way ~/ of example, with reference to a drawinq, in which / 5 Figure 1 is an elevation of a projection television display ~ tu~e partly broken away having an inwardly curved display window, - l Figure 2 is a partial sectional view of the curved display screen, the filter and the curved display window, Figure 3 shcws diagrammatically the composition of a filter as used in a display tuke according to the invention, Figure 4 shcws a spectrum of LaOCl:Tb, Figure 5 shcws the transmission T as a function of the angle C- with respect to the normal for light rays through a filter as shown in Figure 3 for a display tu~e according to the invention, Figure 6 shcws the transmission T for perpendicularly incident light rays (O) as a function of the spectral wavelength ~ s for the Figure 3 filter, Figure 7 shows the angular distribution of the emitted quantity of light d0~ as a function of the angle ~ , measured at a projection television display tube, and ; Figure 8 shows the brightness on the projection screen as a function of the distance to the centre.
Figure 1 is a perspective view partly broken away of a projection television display tube according to the invention. The tube comprises in a glass envelope 1 which consists of an inwardly curved display window 2, a cone 3, and a neck 4, in said neck an electron gun 5 for generating an electron beam 6. Said electron beam is focused on a likewise curved display screen 7 to form a spot 8.
The display screen 7 is provided on the inside of the display window 2.
The electron beam is deflected over the display screen 7 in two mutually perpendicular directions x, y by means of the system of deflection coils 9. The tu~e has a base 10 with connection pins 11.
Figure 2 is a dia~rammatic partial sectional view of the curved display window 2 and of a part of said curved display window 2, the multilayer interferen oe filter 12, and the curved display screen 7.
The display screen 7 consists of a layer of lumines oe nt material (phosphor) 13 and a thin aluminium film 14 (the so-called "aluminium-backing"). The display window has an angle of curvature ~ and is Z
PHQ ~5.007 11 12.04.1989 preferably sperical having a radius of curvature ~.
Figure 3 shows diagrammatically a 20-layer filter 12 hetween a display screen 7, consisting of a layer of phosphor 13 ~Ph) and an aluminium fi.lm 14, and the display window 2 (~). Said diagrammatic representation is f:lat. Of course, the filter in the tube is curved just like the display window and the display screen. The fi.lter cons.i.sts of layers of SiO2 indicated by a letter I. and L' (refracti.ve index n = 1 47) and layers of TiO2 (g = 2.35) indicated by a letter H. The layers have a thickness of approximately 0.25 Af.
The last approximately 0.25 Af-thicX layer 15 on the side of the display screen 7 is covered by an approximately 0.125 Af-thick termlnating layer 16 (L').
The phosphor 13 is a Th-phosphor with A = 545 nm. At P =
1.22 Af becomes equal to 665 nm. The composition of the filter with this Af is indicated in the table hereinafter.
~27~2 PHQ 85.007 12 1985-04-22 Layer No. n n.d/
_ phosphor 1 L 0.131 2 H 0.260 3 L 0.257 4 H 0.254 L 0.251 10 6 H 0.249 7 L 0.247 8 H 0.246 9 L 0.245 H 0.245 1511 L 0.244 12 H 0.245 13 L 0.245 14 H 0.246 L 0.247 2016 H 0.249 17 L 0.251 18 H 0.254 19 L 0.257 H 0.260 25 display window 1.57 Figure 4 shows the spectrum (the intensity standardized at the highest peak (Ip) in % as a function f ~ s) of lanthanumoKychloride-terbium. m is spectrum is representative of all green terbium phosphors, 0 such as yttrium-aluminium garnet-terbium (YAG:Tb) yttriumrsilicate-terbium (Y2SiO5:Tb) lanthanum oxybromide-terbium (LaOBr:Tb) and indium korate-terbium (InBo3:Tb).
Figure 5 shows the tran~smission T (the solid line) of the filter 35 shown in Figure 3 as a function of the angle c~ with respect to the normal on the filter for ~ = 545 nm. The angle ~ 50% at which the transmission of the filter has decreased to 50% is apprcximately 24. For comparison, this Figure shows the transnLssion (the broken line) as a function of the 1~ 9~
F~IQ 85.007 13 1985-4-22 angle ~ for the Fabry-Perot filter according to the said British Patent Specification 1,306,335. In order to make this filter comparable to the filter shown according to the invention, C~ 50 for this filter has also keen chosen to ke 24. Moreover, the materials have keen chosen to s be equal, namely TiO2 and SiO2. Due to the different character of the filter, ~ = 0.99 hence ~ f = 0.99 x 545 = 540 nm. A great disadvantage of this filter is the wide transmission band between 55 and 90. All the ]ight which is transmitted in said transmission band is lost or after reflection contributes to halo and thus gives loss of contrast.
This disadvantage also applies to 0.75 ~f and 1.25~ f filters.
Figure 6 shows the transmission T for light rays which are incident perpendicularly on the filter (0) as a function of the spectral wavelength ~ s for the Figure 3 filter. The low-pass character of the filter (short-wave-pass filter) and also the wide reflection band between 565 and 780 nm are obvious.
Figure 7 shows the ]ight flux 0 as a function of the angle (d~) in arbitrary units as measured at a projection television display tuke having a 20-layer filter as shown in Figures 3, 5 and 6. For o~
smaller than 24 there is a clear gain in luminous efficiency (curve I) 20 as compared with a projection television display tuke without a filter (curve II).
Figure 8 shows the brightness L ~in arbitrary units) on the projection screen as a function of the distance r (in cm) to the centre a) for a flat display screen without a filter (the solid line A), 25 b) for a curved display screen without a filter (the dot-and-dash line B), c) for a flat display screen with filter (the dash line C), and d) for the same curved display window with the same filter (the dot line D).
For the curves shown in Figure 8 holds a p-value of the twenty-layer 30 filter of 1.25 (~ = 1.25), i.e. a transmission of 50% for an angle of 32, an angle of curvature ~ = 10.5 in a spherical display window and screen having a 127 mm diagonal and a 350 mm radius of curvature ~ (g = 350 mm), with a numerical aperture of the lens equal to 0.375 and a focal distan oe of 95 mm. From comparison of these curves it 35 follows that the sum of the effects as a result of curvature and filters (curve D)gives a much larger gain in the corners and at the edge of the display screen than the sum of the effects individually. As a matter of fact there is a small gain in curve B and even a loss in cur~e C.
1~7085~Z
PHQ 85.007 14 1985-4-22 Finally the table belc~ gives a numker of clifferent embodiments and their results. Column 1 gives the type of phosphor which is used for the display screen, column 2 shcws the central wavelength of said phosphor, column 3 gives a few values of ~. Column 4 gives the value of ~ for which the transmission T = 50~. Column 5 shows the number of layers of the filter used.
Type of ~(nm) C~ (50~)number of layers phosphor (in degrees) filter lO _ ~ ~ ~2 ~ .
~S 9 -en~1~ 544 1 21 8 20 23 Y~ e~ 1 612 1 21 13 20 ~illemite 528 1.30 48 14 Y203 EU 612 1.25 31 14 Upon vapour-depositing interference filters on in particular strongly curved display windows a small thickness variation may occur in which the layers beccme slightly thinner towards the corners and the 3D edge of the display screen. This variation in thickness, c.q. the variation in ~ and ~ f values, however, always falls within the range claimed in this Application. Such a small thickness variation may even have a favourable effect on the light decline towards the corners and the edge of the display screen.
The filter in the projection tube according to the second preferred embodi.ment hence consists exclusively or substantially exclusively of layers having an optical thickness of approximately 0,25 ~f. Herefrom the filter derives the special property of the very wide reflection band (no transmission) for light rays which enclose an angle between approximately 30 and 80 to 90 to the normal on the filter.
For example, in 0,75 ~f and 1.25 Af filters the width of the reflection band is reduced by factors 3 and 5, respectively, and undesired transmission occurs at large angles. As a result of this the gain in luminous efficiency with such filters in the forward direction, hence for light rays which enclose small angles to the normal on the filter, as described in German Patent Application 2,330,898 is restricted to 25%. There is also less gain in contrast. The Fabry-Perot filter according to ~3ritish Patent Specification 1,306,335 comprises three 1.5 ~ layers (each consisting of six 0.25 ~ layers of a material havinq a low refractive index) and also has an undesired wide transmission band for light rays which enclose large angles to the normal on the filter.
In the above article "Proceedings of the SID", Vol. 25l1, 1984 fllters for halo-suppression have been described as already ,;
.., _8, lZ7~8~Z
3 ~~ 9 PHQ 85.007 ~ 5 ~-92-t1~g--mentioned above. Even absorbing fi.lters are suggested. Due to theirsmall number of layers said filters are less critical as regards the angle within which the reflection strongly decreases (the acceptance angle). Characteristic of the second preferred embodiment present S invention is that the position of the "edge" of the filter (hence P and Af in ~f=pA) is exactly defined and the acceptance angle i5 c-o~npdratively small. This leads to a great gain in brightness at small angles. As d result of this the filter is very sensitive to losses at large angles and therefore filters having many layers (> 14) are des.ired.
The layer thicknesses in the filter are hence chosen to be so that at a desired wavelength the reflection begins to increase considerably for light rays of a luminescent material which enclose an angle exceeding 18 to 30 to the normal on the filter. The wide reflection band ensures that light rays having angles exceeding 25 to 35'~ are reflected as much as possible and after scattering in the luminescent material again obtain a chance to emanate from the tube within an angle of 18 to 30 to the normal on the filter. As a result of this a maximum luminous efficiency in the forward direction occurs and at small angles which for the central wavelength A of the phosphor is at least 50~O larger than without the use of the filter.
Moreover, the wide reflection band ensures a strongly reduced halo effect and a reduced emanation of light at large angLes. The optical thickness nd of the layers of the filter preferably is not equal for all layers but varies between 0.2 Af and 0.3 ~f~ and preferably between 0.23 Af and 0.27 ~f~ as will be explained in greater detail with reference to an embodiment. As a result of this variation of the thickness a flatter transmission characteristic of the filter is obtained. ~ecause the transmission characteristic of the filter is dependent on the wavelength, it is possible by d combination of a phosphor and an adapted filter to improve the colour point of the light rays which pass through the filter within an angle of 20 to 30 to the normal.
The value of the numeral ~ is between 1.18 and 1.32 dependent on the refractive indices of the layers used and on the width of the selected wavelength range, which will be explained inter alia with reference to the embod.iments. For a TiO2 - SiO2 filter P =Af/A is bet.ween 1.21 and 1.32.
Z
PHQ 85.007 h 12.04.1989 A third preFer.red embodiment of a projection television display tube according to the invention is characteri~ed in that the filter is composed substantially of 14 to 30 layers.
A follrth preferred embodiment of a tuhe according to the invention is characteri.zed in that the said optical thickness nd are between 0.23 ~f and 0.27 Af.
A fi.fth preferred emhodiment is characterized in that the layers of the filter having a hitJh refractive index consist of titanium oxide (Tio2) or tantalum oxide (Ta205) and the layers having a low re~ractive index consi.st of silicon oxide (siO2) or magnesium fluoride (MgF2). The optimum ~ values for a Ta205-SiO2 filter are approximately 0.04 to 0.05 lower than for a Tio2-SiO2 filter. In this case the reflection band is less wide. Furthermore, the magnesium fluoride is preferably provided at approximately 300C to thus ohtain a sufficiently hard layer.
A sixth preferred embodiment is characterized in that the luminescent material comprises a termbium-activated substantially green-luminescing phosphor and A = 545 nm and P is a number between 1.21 and 1.25 for a TiO2-SiO2 filter. Terbium-activated substantially green-luminescing phosphors are, for example, yttrium aluminium garnet-terhium (YAG:Tb), yttrium-sili.cate-terbium (Y25iO5:Tb), lanthanum-oxybromide-terbium (LaOBr:Tb), lanthanum oxychloride-terbium (LaOCl:Tb), and indium : horate-terbium (InBo3:Tb). For all these Tb-activated green phosphors the central wavelength is A = 545 nm. By choosing for the filter according to the invention p to be between 1.21 and 1.25, hence Af between 660 nm and 680 nm, a filter is obtained having a high transmission (exceeding 90%) for light rays which enclose an angle smaller than 20-30 to the normal on the filter. For light rays which enclose an angle greater than 25 to 35 to the normal on the filter the transmission rapidly reduces and reflection occurs up to 80-90.
This filter has a particularly good operation for these Tb-activated phosphors which have emission li.nes in the blue, green, orange-red and red. By using the filter a gain occurs .in the green, a much smaller gain i.n the blue and suhstanti.ally complete reduction of the quantity of light.emitted by the tube occurs in the red, which is favourable for the colour point. All thi.s provides a gai.n in luminous efficiency, colour improvement (closer to the EBU-standards) and gain in contrast. Tn an P~Q ~5 QnT 7 12.04.1989 optimum fi1ter the overal gain in luminous effici.ency for all colours together in these Tb-activated phosphors is 30-60%. The ga;n in the green is fiO to 120~. The coordinates x and ~ in the CIE olour triang1.e are then n 25 tl~ 0.30 ~nd 0.60 to 0.64, respectively Without a filter these coordinates are x = 0.3.~ to 0.36 and y - 0.54 to 0.59, respectively. The gain in contrast is approximately a fact~r 2. For opt;cal display with lenses, as in -the case of projection television, this presents considerable advantages, much less chromatic aberration (little~ or no red and proportiona1.1y l.ess blue with respect to the green).
A seventh preferred embodiment of a tube according to the invention i.s characterized in that the luminescent material comprises a terbium-activaled blue-luniinescing phosphor and ~ = 490 nm and p is a number between 1.21 and 1.25 for a TiQ2-Sio2 filter. By using for the doping a small quantity of Tb a predominantly b].ue-luminescing phosphor is obtained with A = 490 nm. By choosing ~ to be between 1.21 and 1.25, hence ~f hetween S90 nm and fi15 nm, a filter is obtained in which the reflection increases comparatively steeply for light rays which enclose an angle yreater than 25-35 to the normal on the filter. Then there is a gain in contrast of 70 to 100% and a gain in luminous efficiency in the hlue of 60-100. In this case a considerable improvement of the colour point occurs because the green spectral lines are Li.ltered out by the multil.ayer filter.
An eight preferred embodiment of a tube in accordance with the inventi.on is characterized in that ths luminescent material is europium-activated yttrium oxide (Y203:EIu) and ~ = 612 nm and ~ is a number betweerl 1.21 and 1.25 for a Tio2-Sio2 filter. As a result of this choice of P between 1.21 and 1.25, hence ~f hetween 740 nm and 765 nm, the reflection of the filter for lig31t ~ays which enclose an angle greater than 25 and 35 to the normal on the filter increases considerably. Now there is a gain of 60 and 120% in total luminous efficiency. The gain in contrast is approxi.mately 100%. In this case there is a small colour point imprs)vement. The red components in the spectrlJm of the generated light are as a matter of fact more strongly ~S intensified than the componerlts of shorter wavelength.
The i.nvention may also be used ln wide-band phosphors, fs)r example willemite (Zn~S104), zinc sulphide si.lver (ZnS:Ag) PHQ 85.007 8 12.04.1989 and str~ntium alum:inate-europium (SrAl305 5:Eu) with central wavelengths ~ of 530 nm, 460 nm and 460 nm, respecti.vely. The value of P
ls now chosen to be between 1.21 and 1.32.
~ ninth preferred embodiment of a tube in accort1ance with the invention is character;zed in that the luminescent material is zinc sulphide-silver (ZnS:Ag) and ~ = 460 nm and P i.s a number hetween 1.24 and 1.32 for a Ti.02-SiO2 filter.
As a result of this choice of P between 1.24 and 1.32, hence Af hetween 570 nm and 610 nm, the reflection of the filter for light rays which enclose an angle greater than 25 to 35 to the normal on the filter increases considerably. Now there is a gain of 30 to 80% in the luminous efficiency for wavelengths between approximately 440 nm and 500 nm. The gain in contrast is 80 to 100~o. In this case the longwave (green) part of the ~nS:Ag spectrum is filtered c)ut.
Chromatic aberration caused by the displaying lens is hence reduced.
A tenth preferred embodiment of a tube in accordance with the invention is characterized in that the luminescent material comprises a terbi.um-activated substantially green-luminescing phosphor 20 and A = 545 nm and P is a number between 1.18 and 1.22 for a Ta205-sio2 filter.
An eleventh preferred embodiment of a tube in accordance with the invention is characterized in that the luminescent material comprises a termbium-activated blue-luminescing phosphor and ~ = 490 nm 25 and P is a number between 1.18 and 1.22 for a Ta205-SiO2 filter.
An twelfth preferred embodiment of a tube in accordance with the lnvention is characterized in that the luminescent material is europium-activated yttrium oxyde (Y203:Eu) and ~ = 612 nm and P is a number between 1.18 and 1.22 for a Ta205-SiO2 filter.
A thirteenth preferred embodiment of a tube in accordance with the invention is characterized in that the luminescent material is zinc sulphide-silver (~nS:Ag) and ~ = 460 nm and P is a number between 1.21 and 1.28 for a Ta205-SiO2 filter.
For a Ta205-SiO2 filter the optimum P-values are 35 approximately 0.04 to 0.05 lower than for Tio2-Sio2 filter. The reflection band in this case is less wide.
: A fourteenth preferred embodiment of a display tube in lZ7Q1~12 PHQ 85.007 9 12.04.1989 accordance with the invention is characteri~ed in that the outermost approxi.mately 0.25 ~-thick layer of the filter which faces the lumi.nescent material consists of a material having a high refractive index and is covered with a terminating layer having an optical thickness of approximately 0.125 ~f of a material having a low refractive index, on which terminating layer the luminescent material is provided.
A fifteenth preferred embodiment of a display tube in accordance with the invention is characterized in that the outermost approximately 0.25 ~f-thi.ck layer of the filter facing the display window consists of a material having a high refractive i.ndex and is covered with an intermediate layer having an optical thickness of approximately 0.125 Af of a material having a lower refractive index.
By providing a terminating layer and/or intermediate layer having an optical thickness of approximately 0.125 ~f on the phophor si.de and/or the display window side, respectively, the transmission in the forward direction for light rays which enclose small angles to the normal is increased and the oscillations in the transmissions are reduced. The transmi.ssion characteristic becomes flatter.
A sixteenth preferred emhodiment of a display tube in accordance with the invention is characterized in that the outmost approximately 0.25 ~f-thick layer of the filter facing the luminescent material is composed of a mixture of metal oxide, said mi.xture comprising titanium oxide (Tio2) and a metal oxide from the group beryllium oxide (BeO), magnesium oxide (MgO) and calci.um oxide (CaO), in which mixture the quantity of titanium oxide is 70 to ~0% by weight.
By using such an extra smooth hence less porous coating layer on the phosphor side of the filter the optical contact with the phosphor is reduced so that the gain in contrast and luminous efficiency are extra increased.
Tubes accordiny to the invention are preferably coupled optically via liquid to a system of lenses or are provided with liquid cooling in which the likewise curved cover glass is provided on its outside with an anti-reflection layer. Said cover glass may also serve as the first lens element (the so-called "field-flattener").
~ isplay tubes according to the invention can advantageously be used in projection television dev.ices. The very bright picture transmitted in the forward direction is received substantially without losses by a system of lenses having a limited acceptance anyle of, J
- . , :
r 12~38~2 3~ a~5 / PHQ 85.007 ~ 10 _1a85-44_~2 / for example, 25-30 . As a result of this a brighter picture with more / contrast and an improved colour rendition is obtained.
/ The invention will ncw be descri ed in greater detail, by way ~/ of example, with reference to a drawinq, in which / 5 Figure 1 is an elevation of a projection television display ~ tu~e partly broken away having an inwardly curved display window, - l Figure 2 is a partial sectional view of the curved display screen, the filter and the curved display window, Figure 3 shcws diagrammatically the composition of a filter as used in a display tuke according to the invention, Figure 4 shcws a spectrum of LaOCl:Tb, Figure 5 shcws the transmission T as a function of the angle C- with respect to the normal for light rays through a filter as shown in Figure 3 for a display tu~e according to the invention, Figure 6 shcws the transmission T for perpendicularly incident light rays (O) as a function of the spectral wavelength ~ s for the Figure 3 filter, Figure 7 shows the angular distribution of the emitted quantity of light d0~ as a function of the angle ~ , measured at a projection television display tube, and ; Figure 8 shows the brightness on the projection screen as a function of the distance to the centre.
Figure 1 is a perspective view partly broken away of a projection television display tube according to the invention. The tube comprises in a glass envelope 1 which consists of an inwardly curved display window 2, a cone 3, and a neck 4, in said neck an electron gun 5 for generating an electron beam 6. Said electron beam is focused on a likewise curved display screen 7 to form a spot 8.
The display screen 7 is provided on the inside of the display window 2.
The electron beam is deflected over the display screen 7 in two mutually perpendicular directions x, y by means of the system of deflection coils 9. The tu~e has a base 10 with connection pins 11.
Figure 2 is a dia~rammatic partial sectional view of the curved display window 2 and of a part of said curved display window 2, the multilayer interferen oe filter 12, and the curved display screen 7.
The display screen 7 consists of a layer of lumines oe nt material (phosphor) 13 and a thin aluminium film 14 (the so-called "aluminium-backing"). The display window has an angle of curvature ~ and is Z
PHQ ~5.007 11 12.04.1989 preferably sperical having a radius of curvature ~.
Figure 3 shows diagrammatically a 20-layer filter 12 hetween a display screen 7, consisting of a layer of phosphor 13 ~Ph) and an aluminium fi.lm 14, and the display window 2 (~). Said diagrammatic representation is f:lat. Of course, the filter in the tube is curved just like the display window and the display screen. The fi.lter cons.i.sts of layers of SiO2 indicated by a letter I. and L' (refracti.ve index n = 1 47) and layers of TiO2 (g = 2.35) indicated by a letter H. The layers have a thickness of approximately 0.25 Af.
The last approximately 0.25 Af-thicX layer 15 on the side of the display screen 7 is covered by an approximately 0.125 Af-thick termlnating layer 16 (L').
The phosphor 13 is a Th-phosphor with A = 545 nm. At P =
1.22 Af becomes equal to 665 nm. The composition of the filter with this Af is indicated in the table hereinafter.
~27~2 PHQ 85.007 12 1985-04-22 Layer No. n n.d/
_ phosphor 1 L 0.131 2 H 0.260 3 L 0.257 4 H 0.254 L 0.251 10 6 H 0.249 7 L 0.247 8 H 0.246 9 L 0.245 H 0.245 1511 L 0.244 12 H 0.245 13 L 0.245 14 H 0.246 L 0.247 2016 H 0.249 17 L 0.251 18 H 0.254 19 L 0.257 H 0.260 25 display window 1.57 Figure 4 shows the spectrum (the intensity standardized at the highest peak (Ip) in % as a function f ~ s) of lanthanumoKychloride-terbium. m is spectrum is representative of all green terbium phosphors, 0 such as yttrium-aluminium garnet-terbium (YAG:Tb) yttriumrsilicate-terbium (Y2SiO5:Tb) lanthanum oxybromide-terbium (LaOBr:Tb) and indium korate-terbium (InBo3:Tb).
Figure 5 shows the tran~smission T (the solid line) of the filter 35 shown in Figure 3 as a function of the angle c~ with respect to the normal on the filter for ~ = 545 nm. The angle ~ 50% at which the transmission of the filter has decreased to 50% is apprcximately 24. For comparison, this Figure shows the transnLssion (the broken line) as a function of the 1~ 9~
F~IQ 85.007 13 1985-4-22 angle ~ for the Fabry-Perot filter according to the said British Patent Specification 1,306,335. In order to make this filter comparable to the filter shown according to the invention, C~ 50 for this filter has also keen chosen to ke 24. Moreover, the materials have keen chosen to s be equal, namely TiO2 and SiO2. Due to the different character of the filter, ~ = 0.99 hence ~ f = 0.99 x 545 = 540 nm. A great disadvantage of this filter is the wide transmission band between 55 and 90. All the ]ight which is transmitted in said transmission band is lost or after reflection contributes to halo and thus gives loss of contrast.
This disadvantage also applies to 0.75 ~f and 1.25~ f filters.
Figure 6 shows the transmission T for light rays which are incident perpendicularly on the filter (0) as a function of the spectral wavelength ~ s for the Figure 3 filter. The low-pass character of the filter (short-wave-pass filter) and also the wide reflection band between 565 and 780 nm are obvious.
Figure 7 shows the ]ight flux 0 as a function of the angle (d~) in arbitrary units as measured at a projection television display tuke having a 20-layer filter as shown in Figures 3, 5 and 6. For o~
smaller than 24 there is a clear gain in luminous efficiency (curve I) 20 as compared with a projection television display tuke without a filter (curve II).
Figure 8 shows the brightness L ~in arbitrary units) on the projection screen as a function of the distance r (in cm) to the centre a) for a flat display screen without a filter (the solid line A), 25 b) for a curved display screen without a filter (the dot-and-dash line B), c) for a flat display screen with filter (the dash line C), and d) for the same curved display window with the same filter (the dot line D).
For the curves shown in Figure 8 holds a p-value of the twenty-layer 30 filter of 1.25 (~ = 1.25), i.e. a transmission of 50% for an angle of 32, an angle of curvature ~ = 10.5 in a spherical display window and screen having a 127 mm diagonal and a 350 mm radius of curvature ~ (g = 350 mm), with a numerical aperture of the lens equal to 0.375 and a focal distan oe of 95 mm. From comparison of these curves it 35 follows that the sum of the effects as a result of curvature and filters (curve D)gives a much larger gain in the corners and at the edge of the display screen than the sum of the effects individually. As a matter of fact there is a small gain in curve B and even a loss in cur~e C.
1~7085~Z
PHQ 85.007 14 1985-4-22 Finally the table belc~ gives a numker of clifferent embodiments and their results. Column 1 gives the type of phosphor which is used for the display screen, column 2 shcws the central wavelength of said phosphor, column 3 gives a few values of ~. Column 4 gives the value of ~ for which the transmission T = 50~. Column 5 shows the number of layers of the filter used.
Type of ~(nm) C~ (50~)number of layers phosphor (in degrees) filter lO _ ~ ~ ~2 ~ .
~S 9 -en~1~ 544 1 21 8 20 23 Y~ e~ 1 612 1 21 13 20 ~illemite 528 1.30 48 14 Y203 EU 612 1.25 31 14 Upon vapour-depositing interference filters on in particular strongly curved display windows a small thickness variation may occur in which the layers beccme slightly thinner towards the corners and the 3D edge of the display screen. This variation in thickness, c.q. the variation in ~ and ~ f values, however, always falls within the range claimed in this Application. Such a small thickness variation may even have a favourable effect on the light decline towards the corners and the edge of the display screen.
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A projection television display tube comprising in an evacuated envelope a display screen which is provided on the inside of a display window in the wall of the envelope, said display screen comprising a luminescent material, between said luminescent material and the display window a multilayer inter-ference filter being provided, which filter comprises a number of layers which are manufactured alternately from a material having a high refractive index and a material having a low refractive index, characterized in that the display window on the vacuum side is inwardly curved having an angle of curvature ? wherein ? is the angle between a line at right angles to the centre of the display window and a line at right angles to the part of the display window farthest remote from the centre, said angle ? being between 5° and 25°.
2. A display tube as claimed in claim 1, characterized in that the inwardly curved display window is substantially spherical and has a radius or curvature ? between 150 mm and 730 mm.
3. A display tube as claimed in claim 1, characterized in that the filter is composed of at least 6 layers each having an optical thickness nd, wherein n is the refractive index of the material of the layer and d is the thickness, said optical thickness being between 0.2 .lambda.f and 0.3 .lambda.f, wherein .lambda.f is equal to p x .lambda., wherein .lambda. is the desired central wavelength which is selected from the spectrum emitted by the luminescent material and p is a number between 1.18 and 1.32.
4. A display tube as claimed in claim 3, characterized in that the filter is composed substantially of 14 to 30 layers.
5. A display tube as claimed in claim 3, characterized in that the optical thickness nd is between 0.23 .lambda.f and 0.27 .lambda.f.
6. A display tube as claimed in claim 3, characterized in that the layers of the filter having a high refractive index consist of titanium oxide (TiO2) or tantalum oxide (Ta2O5) and the layers having a low refractive index consist of silicon oxide (SiO2) or magnesium fluoride (MgF2).
7. A display tube as claimed in claim 6, characterized in that the magnesium fluoride is provided at approximately 300°C.
8. A display tube as claimed in claim 3, characterized in that the luminescent material comprises a terbium-activated substantially green-luminescing phosphor and .lambda.=545 nm and p is a number between 1.21 and 1.25 for a TiO2-SiO2 filter.
9. A display tube as claimed in claim 6, characterized in that the luminescent material comprises terbium-activated blue-luminescing phosphor and .lambda.=490 nm and p is a number between 1.21 and 1.25 for a TiO2-SiO2 filter.
10. A display tube as claimed in claim 6, characterized in that the luminescent material is europium-activated yttrium oxide (Y2O3:Eu) and .lambda.=612 nm and p is a number between 1.21 and 1.25 for a TiO2-SiO2 filter.
11. A display tube as claimed in claim 6, characterized in that the luminescent material is zinc sulphide-silver (ZnS:Ag) and .lambda.=460 nm and p is a number between 1.24 and 1.32 for a TiO2-SiO2 filter.
12. A display tube as claimed in claim 6, characterized in that the luminescent material comprises a terbium-activated substantially green-luminescing phosphor and .lambda.=545 nm and p is a number between 1.18 and 1.22 for a Ta2O5-SiO2 filter.
13. A display tube as claimed in claim 6, characterized in that the luminescent material comprises a terbium-activated blue-luminescing phosphor and .lambda.=490 nm and p is a number between 1.18 and 1.22 for a Ta2O5-SiO2 filter.
14. A display tube as claimed in claim 6, characterized in that the luminescent material is europium-activated yttrium oxide (Y2O3:Eu) and .lambda.=613 nm and p is a number between 1.18 and 1.22 for a Ta2O5-SiO2 filter.
15. A display tube as claimed in claim 6, characterized in that the luminescent material is zinc sulphide-silver (ZnS:Ag) and .lambda.=460 nm and p is a number 1.21 and 1.28 for a Ta2O5-SiO2 filter.
16. A display tube as claimed in claim 3, characterized in that the outermost approximately 0.25 .lambda.f-thick layer of the filter which faces the luminescent material consists of a material having a high refractive index and is covered with a terminating layer having an optical thickness of approximately 0.125 .lambda.f of a material having a lower refractive index.
17. A display tube as claimed in claim 16, characterized in that the luminescent layer is provided on the terminating layer.
18. A display tube as claimed in claim 8, 9 or 10, characterized in that the outermost approximately 0.25 .lambda.f thick layer of the filter facing the luminescent material is composed of a mixture of metal oxides, which mixture comprises titanium oxide (TiO2) and a metal oxide from the group beryllium oxide (BeO), magnesium oxide (MgO) and calcium oxide (CaO), in which mixture the quantity of titanium oxide is 70-99% by weight.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8513558A GB2176048B (en) | 1985-05-29 | 1985-05-29 | Projection television display tube and projection television device comprising at least one such tube |
| GB8513558 | 1985-05-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1270892A true CA1270892A (en) | 1990-06-26 |
Family
ID=10579857
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000509662A Expired - Lifetime CA1270892A (en) | 1985-05-25 | 1986-05-21 | Projection television display with multilayer interference filter |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4683398A (en) |
| EP (1) | EP0206381B1 (en) |
| JP (2) | JPH0734353B2 (en) |
| KR (1) | KR950000822B1 (en) |
| CA (1) | CA1270892A (en) |
| DE (1) | DE3674648D1 (en) |
| ES (1) | ES8707629A1 (en) |
| GB (1) | GB2176048B (en) |
Families Citing this family (38)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8502226A (en) * | 1985-08-12 | 1987-03-02 | Philips Nv | PROJECTION TELEVISION EQUIPMENT. |
| JPH0724197B2 (en) * | 1986-03-19 | 1995-03-15 | 株式会社日立製作所 | Projection color imager |
| GB8612358D0 (en) * | 1986-05-21 | 1986-06-25 | Philips Nv | Cathode ray tube |
| WO1988001824A1 (en) * | 1986-08-26 | 1988-03-10 | Tds Patent Management, Inc. | Cathode ray tube with integral mirror optics for three-tube projection television systems having increased light output |
| GB8623822D0 (en) * | 1986-10-03 | 1986-11-05 | Philips Nv | Colour cathode ray tube |
| GB8629552D0 (en) * | 1986-12-10 | 1987-01-21 | Philips Nv | Television system & display tubes |
| USRE34131E (en) * | 1986-12-10 | 1992-11-24 | U.S. Philips Corporation | Display tube having improved brightness distribution |
| DE3642321A1 (en) * | 1986-12-11 | 1988-06-23 | Standard Elektrik Lorenz Ag | PROJECTION TUBES |
| GB8707975D0 (en) * | 1987-04-03 | 1987-05-07 | Philips Nv | Colour cathode ray tube |
| US4904899A (en) * | 1987-06-26 | 1990-02-27 | Asahi Glass Company Ltd. | Projection cathode ray tube |
| US4896218A (en) * | 1987-09-04 | 1990-01-23 | Rockwell International Corporation | Circularly polarized multi-bandpass interference contrast enhancement filter |
| US4937661A (en) * | 1988-07-11 | 1990-06-26 | North American Philips Corporation | Projection television display tube and device having band pass interference filter |
| FR2634562B1 (en) * | 1988-07-22 | 1990-09-07 | Thomson Csf | METHOD FOR MANUFACTURING A SCINTILLATOR AND SCINTILLATOR THUS OBTAINED |
| NL8802210A (en) * | 1988-09-08 | 1990-04-02 | Koninkl Philips Electronics Nv | METHOD FOR VAPORATING AN INTERFERENCE FILTER COATING ON THE INSIDE OF AN IMAGE WINDOW, AN IMAGE WINDOW, A PROJECTION CATHODIC TUBE AND A PROJECTION TELEVISION DEVICE. |
| US5209690A (en) * | 1988-09-08 | 1993-05-11 | U.S. Philips Corporation | Method of vapor depositing an interference filter layer on the inside of a display window, a display window, a projection cathode ray tube and a projection television apparatus |
| FR2640425A1 (en) * | 1988-12-09 | 1990-06-15 | Malifaud Pierre | Process for the spectral selection of radiation and device for implementation, especially video image television projector |
| US4914511A (en) * | 1988-12-23 | 1990-04-03 | North American Philips Corporation | Projection color TV using CRTs having interference filters with different number of layers |
| EP0375064A3 (en) * | 1988-12-23 | 1991-04-03 | North American Philips Corporation | Projection color television display devices with improved white field uniformity |
| JPH0834596B2 (en) * | 1989-02-20 | 1996-03-29 | 三菱電機株式会社 | Projection television |
| JPH0722004B2 (en) * | 1989-05-15 | 1995-03-08 | 三菱電機株式会社 | Method of manufacturing projection cathode ray tube |
| EP0400565A3 (en) * | 1989-05-30 | 1991-09-11 | Hitachi, Ltd. | Projection cathode-ray tube |
| JPH0744688B2 (en) * | 1989-06-08 | 1995-05-15 | 三菱電機株式会社 | Projection-type television system |
| US5248518A (en) * | 1989-06-27 | 1993-09-28 | Mitsubishi Denki Kabushiki Kaisha | Projection cathode ray tube |
| JPH0817084B2 (en) * | 1989-06-27 | 1996-02-21 | 三菱電機株式会社 | Projection type cathode ray tube |
| US5138222A (en) * | 1989-06-27 | 1992-08-11 | Mitsubishi Denki Kabushiki Kaisha | Projection cathode ray tube having an interference filter |
| US5179318A (en) * | 1989-07-05 | 1993-01-12 | Nippon Sheet Glass Co., Ltd. | Cathode-ray tube with interference filter |
| JPH03127436A (en) * | 1989-10-11 | 1991-05-30 | Mitsubishi Electric Corp | Projection-type television apparatus |
| JPH03133034A (en) * | 1989-10-16 | 1991-06-06 | Mitsubishi Electric Corp | Projection-type cathode-ray tube |
| JPH03138838A (en) * | 1989-10-24 | 1991-06-13 | Mitsubishi Electric Corp | Projection type cathode-ray tube |
| JPH03198492A (en) * | 1989-12-26 | 1991-08-29 | Mitsubishi Electric Corp | Projector type television unit |
| US5065071A (en) * | 1990-01-02 | 1991-11-12 | North American Philips Corporation | Monochrome CRT with interference filter having filter layer with reduced transmission and projection color TV incorporating same |
| JP2650458B2 (en) * | 1990-03-29 | 1997-09-03 | 三菱電機株式会社 | Projection type cathode ray tube |
| JP2512204B2 (en) * | 1990-05-09 | 1996-07-03 | 三菱電機株式会社 | Projection type cathode ray tube |
| JP2714995B2 (en) * | 1990-05-29 | 1998-02-16 | 三菱電機株式会社 | Projection type cathode ray tube |
| JPH081791B2 (en) * | 1990-08-20 | 1996-01-10 | 三菱電機株式会社 | Projection type cathode ray tube |
| JPH0554804A (en) * | 1991-08-26 | 1993-03-05 | Mitsubishi Electric Corp | Method for salvaging glass panel for use in projection type cathode-ray tube equipped with multiple interference film |
| US6441550B1 (en) * | 1998-10-12 | 2002-08-27 | Extreme Devices Inc. | Carbon-based field emission electron device for high current density applications |
| FR2843204B1 (en) * | 2002-08-05 | 2004-09-17 | Saint Gobain | OPTICAL FILTERING AND ELECTROMAGNETIC SHIELDING STRUCTURE |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1306335A (en) * | 1971-07-01 | 1973-02-07 | ||
| DE2330898A1 (en) * | 1973-06-18 | 1975-01-09 | Siemens Ag | Luminescent screen for X-ray appts. etc. - has transparent support with several layers of different refractors of thickness effecting interference |
| US4365183A (en) * | 1978-02-06 | 1982-12-21 | Kloss Henry E | Projection televison tube and process for forming same |
| US4310783A (en) * | 1979-05-07 | 1982-01-12 | Temple Michael D | Cathode ray tube face plate construction for suppressing the halo having a low reflection and method |
| US4310784A (en) * | 1979-05-07 | 1982-01-12 | Anthon Erik W | Cathode ray tube face plate construction for suppressing the halo and method |
| JPS60100347A (en) * | 1983-11-04 | 1985-06-04 | Mitsubishi Electric Corp | Projection type cathode ray tube |
| NL8402304A (en) * | 1984-07-20 | 1986-02-17 | Philips Nv | PICTURE TUBE. |
-
1985
- 1985-05-29 GB GB8513558A patent/GB2176048B/en not_active Expired
- 1985-11-04 US US06/794,862 patent/US4683398A/en not_active Expired - Lifetime
-
1986
- 1986-05-21 CA CA000509662A patent/CA1270892A/en not_active Expired - Lifetime
- 1986-05-22 EP EP86200892A patent/EP0206381B1/en not_active Expired - Lifetime
- 1986-05-22 DE DE8686200892T patent/DE3674648D1/en not_active Expired - Lifetime
- 1986-05-26 ES ES555319A patent/ES8707629A1/en not_active Expired
- 1986-05-27 KR KR1019860004146A patent/KR950000822B1/en not_active IP Right Cessation
- 1986-05-28 JP JP61121358A patent/JPH0734353B2/en not_active Expired - Fee Related
-
1993
- 1993-05-20 JP JP5118215A patent/JPH0744018B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| ES555319A0 (en) | 1987-08-01 |
| GB2176048A (en) | 1986-12-10 |
| KR950000822B1 (en) | 1995-02-02 |
| EP0206381A1 (en) | 1986-12-30 |
| GB2176048B (en) | 1989-07-05 |
| JPS61273837A (en) | 1986-12-04 |
| EP0206381B1 (en) | 1990-10-03 |
| US4683398A (en) | 1987-07-28 |
| JPH0744018B2 (en) | 1995-05-15 |
| ES8707629A1 (en) | 1987-08-01 |
| KR860009589A (en) | 1986-12-23 |
| DE3674648D1 (en) | 1990-11-08 |
| JPH0734353B2 (en) | 1995-04-12 |
| GB8513558D0 (en) | 1985-07-03 |
| JPH0696701A (en) | 1994-04-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |