EP0412887A1 - High efficiency cathodoluminescent screen for high luminance cathode ray tube - Google Patents

High efficiency cathodoluminescent screen for high luminance cathode ray tube Download PDF

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Publication number
EP0412887A1
EP0412887A1 EP90402235A EP90402235A EP0412887A1 EP 0412887 A1 EP0412887 A1 EP 0412887A1 EP 90402235 A EP90402235 A EP 90402235A EP 90402235 A EP90402235 A EP 90402235A EP 0412887 A1 EP0412887 A1 EP 0412887A1
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EP
European Patent Office
Prior art keywords
substrate
layer
intermediate layer
refractive index
cathodoluminescent screen
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EP90402235A
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German (de)
French (fr)
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EP0412887B1 (en
Inventor
Daniel Gibilini
Bernard Courtan
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Thales Electron Devices SA
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Thomson Tubes Electroniques
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    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2229/00—Details of cathode ray tubes or electron beam tubes
    • H01J2229/89—Optical components associated with the vessel
    • H01J2229/8913—Anti-reflection, anti-glare, viewing angle and contrast improving treatments or devices
    • H01J2229/8916—Anti-reflection, anti-glare, viewing angle and contrast improving treatments or devices inside the vessel

Definitions

  • the invention relates to a cathodoluminescent screen for cathode ray tubes and particularly for high luminance tubes, such as for example tubes of the so-called "projection" type.
  • the object of the invention is to show a cathodoluminescent screen arranged in a new way which makes it possible, in particular to better concentrate the light emitted by this screen on axes perpendicular to the latter, that is to say which makes it possible to obtain , from each elementary image point on the screen, a more concentrated emission indicator on the axis.
  • One of the main aims, in the context of the so-called "projection" type of tube technique, is thus to improve the efficiency of capture, by projection optics, of the light emitted by the tube.
  • the cathodoluminescent screen generally comprises a glass slab serving as a substrate, on which is produced at least one luminescent layer which, most often, consists of grains of phosphors.
  • the cathode ray tube contains an electron source which makes it possible to produce a beam, which beam is accelerated and focused before bombarding the layer of phosphors. Under the effect of this bombardment, the phosphors emit light, and a bright image can be formed on the surface of the screen by deflecting the beam.
  • the resolution of the image depends in particular on the focusing of the beam, but it also depends on the characteristics of the cathodoluminescent screen, this screen having also effects on light output and luminance in general.
  • FIG. 1 shows partially and schematically in a sectional view, a conventional cathodoluminescent screen for cathode ray tubes.
  • This screen 1 comprises a glass slab 2 forming a substrate.
  • the substrate 2 carries a luminescent layer 3 formed for example from a plurality of phosphor grains L1, L2, ..., Ln.
  • the glass substrate 2 In a cathode ray tube, the glass substrate 2 generally has a thickness E of the order of 6 to 7 millimeters, and its refractive index n0 is of the order of 1.5. Under these conditions, the light emitted under the impact of an electron beam (symbolized by an arrow 13) by the layer 3 of phosphors, by a grain L1 for example which is in contact with an inner face 5 of the substrate 2 , can exit through a face 6 of the latter towards the outside of the tube, only for its part whose angle of incidence (in the substrate 2) is less than the limit angles ⁇ 0, ⁇ 0 ′ formed between rays R1, R1 ′ (Which represent the limit refraction) and an axis x normal to the plane of the external face 6 of the substrate 2.
  • this light undergoes a total reflection (as illustrated by the radius R1) by which it is returned towards the internal face 5 of the substrate 2, where it is again reflected towards opposite side 6, unless it meets a luminous grain ophore in touch with this inner face 5; in the latter case, this light can be re-emitted towards use as symbolized by arrows RD1, RD2, RD3.
  • This phenomenon which can be repeated several times, is at the base of the creation of a large halo which tends to degrade significantly the contrast of images, and in another way, the light energy of the peak central, that is to say the light energy emitted along the axis normal to the plane of the substrate 2.
  • FIG. 2 illustrates this situation and shows for this purpose the front of a conventional cathode ray tube T comprising a cathodoluminescent screen, such as for example the screen 1 of FIG. 1, and schematically shows the lens 7 of the optics of a conventional projection device also.
  • a light is produced, part of which is emitted with an angle of incidence equal to or greater than the limit angle ⁇ 0, as illustrated by the limit radius R1.
  • This light can undergo multiple reflections or be redistributed towards use according to rays RD1, RD2, R3, so that this light which is represented by the limit radius R1 generates the halo.
  • the use consists of the lens 7 which represents the optical means of a projection system.
  • the lens 7 has an opening 8 centered on an axis 9 of the tube T, the axis 9 being normal to the plane of the screen 1.
  • the light emitted with an angle of incidence less than the limit angle ⁇ 0 leaves the tube T, that is to say the substrate 2.
  • This light is captured by the use only for its part which passes through the aperture 8 of the lens 7, as illustrated by a useful radius RU which is emitted from point A.
  • the other part of this light is symbolized by a ray RP leaving the tube T but which does not pass not through opening 8, and which is therefore lost for use, which degrades the light output.
  • the rays re-broadcast towards the use and picked up by the latter can have a harmful effect, such as for example the re-broadcast ray RD2 which, although parallel to the axis 9, is re-broadcast from a point different from point A and tends to destroy the contrast.
  • the invention constitutes a solution to the problems set out above, a particularly advantageous solution in particular because the invention is simple to implement and, as a result, it constitutes an inexpensive solution making it possible in particular to obtain a maximum gain of luminance, to improve the contrast and to strongly decrease the halo.
  • a cathodoluminescent screen for cathode ray tubes comprising a substrate having a given thickness and a given refractive index, the substrate carrying a luminescent layer subjected to electronic bombardment and producing a light under the effect of said bombardment, characterized in that an intermediate layer is disposed between the luminescent layer and the substrate, the intermediate layer having on the one hand a second thickness much less than the thickness of the substrate, and on the other hand having a second refractive index higher than the refractive index of the substrate.
  • a refractive surface is created at the faces in contact with the intermediate layer and the substrate, a refractive surface which totally reflects the light coming from the luminescent layer when this light arrives with an angle of incidence more large than a limiting angle ⁇ l1 whose value is deduced from that of the refractive indices of the substrate and the middle layer.
  • the limit angle ⁇ l1 is less than another limit angle ⁇ 0 which causes total reflection of the light at the interface between the substrate and the air under conditions similar to those which have already been mentioned in the preamble to explain the faults of the prior art, and which lead to causing a large halo.
  • the interposition of the intermediate layer has the effect of diffusing a very large part of the light, beyond the limiting angle of refraction ⁇ l1, towards the cathodoluminescent layer, so that this light is retransmitted or redistributed towards the outside of the tube, that is to say towards use, with an emission indicator much more concentrated on the axis.
  • the light redistribution efficiency can be greatly promoted by the implantation of a compact monolayer of fine grains, between the intermediate layer and the luminescent layer or phosphor layer.
  • FIG. 3 partially shows a cathodoluminescent screen 10 according to the invention, intended to form the screen of a cathode ray tube.
  • the screen 10 comprises a substrate 11, constituted for example in a conventional manner by a glass slab having a thickness E1 of the order of 6 to 7 millimeters.
  • the substrate 11 carries a luminescent layer 12 exposed to an electron beam symbolized by an arrow 13.
  • the luminescent layer 12 is traditionally constituted by a plurality of phosphor grains L1, L2, ..., Ln.
  • a conductive layer 4, made of aluminum for example, is deposited on the luminescent layer 12, in particular for reflecting the light produced by the luminescent layer 12 towards use, that is to say towards an outer face 14 of the substrate 11, face outside which it is in contact with air.
  • an intermediate layer 15 is interposed between the luminescent layer 12 and the substrate 11.
  • the intermediate layer 15 is made for example of a dielectric material, transparent to the light emitted by the phosphors L1 to Ln and having a refractive index n1 greater than the refractive index n0 (n0 substantially equal to 1.5) of the substrate 11, and preferably much greater than this refractive index n0 of the substrate (for example n0 / n1 equal to or less than 0.75).
  • the intermediate layer 15 can be made of titanium oxide TiO2 or also of zinc sulfide ZnS, so as to have a refractive index n1 of the order of 2.35.
  • the intermediate layer 15 has a thickness E2 much less than the thickness E1 of the substrate 11.
  • the intermediate layer 15 constitutes a thin layer which can be carried out in a simple and inexpensive manner by evaporation, or even for example by a dip alcoholate method from a titanium alcoholate T i (OC2H5) 4.
  • the thickness E2 of the intermediate layer 15 is not really critical for operation, the important thing being that it is much smaller than the thickness E1 of the substrate 11; very satisfactory results have been obtained with values close to the micrometer for the thickness E2 of the intermediate layer 15. It note that in the figures the scale of dimensions is not respected.
  • the trajectory of the first photon p1 is such that it has an angle ⁇ 1 less than the limit angle ⁇ l1, which allows it to cross the interface between the intermediate layer and the substrate 15-11, then leave the substrate 11 by the external face 14 of the latter if its trajectory forms, with an axis x normal to the external face 14, an angle ⁇ 1 ′ smaller than a limit angle ⁇ 0 given by the indices of the substrate 11 and of the 'air; the limiting angle ⁇ 0 in the substrate 11 having a value similar to that mentioned in the preamble, namely of the order of 43 ° (the outer face 14 represents a refractive surface formed at the interface of the substrate 11 and the air).
  • this second photon p2 is reflected at a point marked c of this interface, towards the luminescent layer 12 and, if it encounters a grain of phosphor L1 to Ln in contact with an upper face 16 of the intermediate layer 15, at a point f for example, this photon p2 is rebroadcast in the direction of the substrate 11 into which it can penetrate or not depending on whether its angle of incidence is less than the limit angle ⁇ l1 or not.
  • this photon can be redistributed towards the substrate 11, that is to say towards the outside as symbolized by arrows marked RD; but if there are no phosphors at point f, the second p2 is reflected towards the interface 15-11 with an angle greater than the limit angle ⁇ l1, so that this photon will be reflected again by the interface 15-11 towards the luminescent layer 12.
  • this distance D2 is of the order of 2 micrometers.
  • the configuration of the invention induces this redistribution much closer to the point where the light was emitted. Consequently we suppress the intensity of the halo at long distance, and by combining this with the fact that in the intermediate layer 15 the amount of light which undergoes a total reflection is increased, an emission indicator more concentrated on the axis is obtained than in the prior art, that is to say that the intensity of the light emitted along the axis normal to the plane of the substrate 11.
  • FIG. 4 illustrates a preferred version of the invention, in which the efficiency of redistribution of the light which has been reflected by the interface intermediate layer-substrate 15-11 is improved.
  • a diffusing layer 20 is arranged between the intermediate layer 15 and the luminescent layer 12 or layer of phosphors.
  • the diffusing layer 20 is constituted by fine grains G1, G2, ..., GN which form a compact monolayer, and which make it possible to greatly improve the collection of light after total reflection by the interface 15-11.
  • the finer and closer the grains G1 to GN the more the contact points are numerous for the recovery of light above the intermediate layer 15.
  • fine grains we will define grains whose average diameter is less than the average diameter of phosphor grains L1 to Ln of the luminescent layer 12.
  • the grains G1 to GN can have an average diameter of the order of for example 1 micrometer, and according to another characteristic of the invention, they can be advantageously formed, themselves by phosphors of the same nature as the phosphors of the luminescent layer 12, so as to also participate in the light production.
  • monolayer we mean a layer whose thickness includes a single grain, this for the entire surface of the layer (although in practice there may remain locally some exceptions to this rule without degrading the resolution).
  • the screen 10 of the invention may further comprise a bonding layer 22 which is both in contact with the face upper 16 of the intermediate layer 15, and in contact with the grains G1 to GN of the diffusing monolayer 20.
  • the bonding layer 22 makes it possible to improve the collection of light by preventing, by its presence, that the light rays do not undergo a reflection total at the level of the upper face 16 of the intermediate layer 15, when these light rays reach this upper face 16 at a point located between two grains G1 with neighboring GN, as illustrated in FIG. 3 by way of example by a third photon p3.
  • the bonding layer 22 has a refractive index n2 greater than or equal to the refractive index n1 of the intermediate layer 15.
  • the bonding layer 22 can constitute a dielectric layer produced for example by titanium oxide TiO2 by the same method as the intermediate layer 15.
  • the photon p3 can be emitted in the intermediate layer 15 by a grain G2 for example of the diffusing layer 20.
  • the photon p3 undergoes reflection at the level of the intermediate layer-substrate interface 15-11, reflection which returns it to the upper face 16.
  • the photon p3 In the absence of the bonding layer 22, the photon p3 would be reflected at a point O2 of this upper face 16, as it is represented by an arrow in dotted lines marked p3 ′, except of course if the point O2 is sufficiently close to a grain G1 at GN so that the phenomenon of evanescent waves can manifest itself, and allows the photon p3 to exit from the intermediate layer 15 and penetrate into the grain. With the presence of the bonding layer 22, the photon p3, even if it arrives at the upper face 16 at a point of the latter relatively distant from a grain, this photon p3 leaves the intermediate layer 15, and the layer link 22 picks up this photon and channels it to a third grain G3, for example where it is diffused to the outside.
  • the bonding layer 22 also makes it possible to provide a particularly advantageous thermal junction function in the application to projection, a function which is also useful if the grains G1 to GN of the diffusing monolayer 20 are grains of phosphors.
  • FIG. 5 shows another version of the invention which makes it possible to reinforce the effect obtained by the interposition of the intermediate layer 15.
  • a second intermediate layer 25 is disposed between the substrate 11 and the first intermediate layer 15.
  • this second intermediate layer 25 has a refractive index n3 lower than the refractive index n0 of the substrate 11.
  • this second intermediate layer 25 has a thickness E3 of the same order of magnitude that the thickness E2 of the first intermediate layer 15, that is to say close to 1 micrometer; but it should be noted that this thickness E3 is not critical, the important thing being that it is very small compared to the thickness E1 of the substrate 11.
  • the second intermediate layer 25 can be produced for example from magnesium fluoride MgF2 of which the refractive index n3 is of the order of 1.35, by a conventional method of evaporation.
  • This new configuration makes it possible to reduce the value of the limit angle ⁇ l1 in the first intermediate layer 15.
  • the limit angle ⁇ 1 beyond which the photon p2 is reflected towards the upper face 16 of the first intermediate layer 15 this angle limits to a lower value in the case of this new version of the invention than in the case represented in FIG. 3.
  • the new value of the limit angle ⁇ l1 is of the order of 35 °, This is due to the fact that the difference in refractive index between the index n1 of the first layer intermediate 15 and the index n3 of the second intermediate layer 25 is greater than the difference in index between the intermediate layer 15 and the substrate 11 shown in FIG. 3. As mentioned above, this reinforces the effects produced by the intermediate layer 15, and makes it possible to increase the light emission indicator as much as possible and thus obtain the maximum luminance gain by a concentration of the angle (not shown) of the light indicator.
  • the second intermediate layer 25 can be an even lower refractive index n3, if this second intermediate layer 25 consists of a microporous layer.
  • the second intermediate layer 25 can be a microporous layer of silicon oxide SiO2, the refractive index of which can be close to 1.25, which makes it possible to obtain an even smaller limit angle ⁇ l1 of the order of 32 °.
  • This second intermediate layer formed of a porous layer of silicon oxide can be deposited on the substrate 11 in a conventional manner in itself, for example by an ultracentrifugation method whose implementation is easy, or also by a wet densification process which leads to a deposit, the degree of porosity of which depends on the conditions of use.
  • the nature of the materials capable of forming the different layers namely the first intermediate layer 15, the second intermediate layer 25, the diffusing layer 20, the bonding layer 22, the nature of these materials is indicated as in no way limiting example, and other materials can be chosen in particular according to the color of the light.
  • the use of such materials makes it possible to obtain luminance gains of the order of 40%, for green and blue in particular, and greater than 40% for red in the case of the use of Fe2O3.

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Abstract

The invention relates to a high efficiency cathodoluminescent screen for high luminance cathode ray tubes, the novel layout of which permits a significant improvement in luminance. …<??>The cathodoluminescent screen of the invention comprises a glass substrate (11) carrying a luminescent screen (12) consisting of luminophore grains. According to a characteristic of the invention, an intermediate screen (15) is interposed between the luminescent screen (12) and the substrate (11), the intermediate screen (15) having a refractive index n1 markedly greater than the refractive index n0 of the substrate (11). This arrangement results in a significant part of the light which penetrates into the intermediate layer (15) being reflected towards the luminescent layer (12), in such a way that this light can later be scattered back towards the substrate (11), that is to say towards the end-use, with an emission indicatrix which is much more strongly concentrated on the axis than in the prior art. …<??>The invention finds a particularly attractive application in so-called "projection" tubes. …<IMAGE>…

Description

L'invention concerne un écran cathodoluminescent pour tubes à rayons cathodiques et particulièrement pour tubes à haute luminance, comme par exemple les tubes du type dit "de projection".The invention relates to a cathodoluminescent screen for cathode ray tubes and particularly for high luminance tubes, such as for example tubes of the so-called "projection" type.

L'invention a pour objet de montrer un écran cathodoluminescent agencé d'une manière nouvelle qui permet, notamment de mieux concentrer la lumière émise par cet écran sur des axes perpendiculaires à ce dernier, c'est-à-dire qui permet d'obtenir, à partir de chaque point élémentaire d'image sur l'écran, une indicatrice d'émission plus concentrée sur l'axe. L'un des buts principaux, dans le cadre de la technique des tubes du type dit "de projection", est d'améliorer ainsi le rendement de captation, par l'optique de projection, de la lumière émise par le tube.The object of the invention is to show a cathodoluminescent screen arranged in a new way which makes it possible, in particular to better concentrate the light emitted by this screen on axes perpendicular to the latter, that is to say which makes it possible to obtain , from each elementary image point on the screen, a more concentrated emission indicator on the axis. One of the main aims, in the context of the so-called "projection" type of tube technique, is thus to improve the efficiency of capture, by projection optics, of the light emitted by the tube.

Dans un tube à rayons cathodiques, l'écran cathodoluminescent comporte généralement une dalle en verre servant de substrat, sur laquelle est réalisée au moins une couche luminescente qui, le plus souvent, est constituée de grains de luminophores. Le tube à rayons cathodiques contient une source d'électrons qui permet de produire un faisceau, lequel faisceau est accéléré et focalisé avant de bombarder la couche de luminophores. Sous l'effet de ce bombardement, les luminophores émettent de la lumière, et une image lumineuse peut être formée sur la surface de l'écran en déviant le faisceau.In a cathode ray tube, the cathodoluminescent screen generally comprises a glass slab serving as a substrate, on which is produced at least one luminescent layer which, most often, consists of grains of phosphors. The cathode ray tube contains an electron source which makes it possible to produce a beam, which beam is accelerated and focused before bombarding the layer of phosphors. Under the effect of this bombardment, the phosphors emit light, and a bright image can be formed on the surface of the screen by deflecting the beam.

La résolution de l'image dépend notamment de la focalisation du faisceau, mais elle dépend aussi des caractéristiques de l'écran cathodoluminescent, cet écran ayant également des effets sur le rendement lumineux et la luminance en général.The resolution of the image depends in particular on the focusing of the beam, but it also depends on the characteristics of the cathodoluminescent screen, this screen having also effects on light output and luminance in general.

La figure 1 montre partiellement et schématiquement par une vue en coupe, un écran cathodoluminescent classique pour tubes à rayons cathodiques. Cet écran 1 comporte une dalle de verre 2 formant un substrat. Le substrat 2 porte une couche 3 luminescente formée par exemple d'une pluralité de grains de luminophores L1, L2, ..., Ln. Sur la couche 3 de luminophores est déposée de manière classique, A l'opposé du substrat 2 c'est-à-dire vers l'intérieur du tube, une couche 4 en un matériau électriquement conducteur, en aluminium par exemple, formant un film qui permet d'une part, d'appliquer la tension accélératrice ainsi que d'écouler les charges, et d'autre part, de réfléchir vers le substrat 2 c'est-à-dire vers l'utilisation, la lumière produite dans la couche 3 de luminophore ou couche luminescente.Figure 1 shows partially and schematically in a sectional view, a conventional cathodoluminescent screen for cathode ray tubes. This screen 1 comprises a glass slab 2 forming a substrate. The substrate 2 carries a luminescent layer 3 formed for example from a plurality of phosphor grains L1, L2, ..., Ln. On the layer 3 of phosphors is deposited in a conventional manner, opposite to the substrate 2 that is to say towards the inside of the tube, a layer 4 of an electrically conductive material, aluminum for example, forming a film which allows on the one hand, to apply the accelerating voltage as well as to flow the charges, and on the other hand, to reflect towards the substrate 2 that is to say towards the use, the light produced in the layer 3 of phosphor or luminescent layer.

Dans un tube à rayons cathodiques, le substrat 2 en verre a généralement une épaisseur E de l'ordre de 6 à 7 millimètres, et son indice de réfraction n0 est de l'ordre de 1,5. Dans ces conditions, la lumière émise sous l'impact d'un faisceau d'électrons (symbolisé par une flèche 13) par la couche 3 de luminophores, par un grain L1 par exemple qui est en contact avec une face intérieure 5 du substrat 2, peut sortir par une face 6 de ce dernier vers l'extérieur du tube, seulement pour sa part dont l'angle d'incidence (dans le substrat 2) est inférieur aux angles limites Φ0, Φ0′ formés entre des rayons R1, R1′ (qui représentent la réfraction limite) et un axe x normal au plan de la face extérieure 6 du substrat 2. Ainsi pour la lumière émise à partir du grain L1, qui se propage en direction de la face extérieure 6 vers l'utilisation et qui n'est pas comprise dans les angles limites Φ0, Φ0′, cette lumière subit une réflexion totale (comme illustré par le rayon R1) par laquelle elle est renvoyée vers la face intérieure 5 du substrat 2, où elle est à nouveau réfléchie vers la face 6 opposée, sauf si elle rencontre un grain luminophore en contact avec cette face intérieure 5 ; dans ce dernier cas, cette lumière peut être rediffusée vers l'utilisation comme symbolisé par des flèches RD1, RD2, RD3. Ce phénomène, qui peut se renouveler plusieurs fois, est à la base de la création d'un halo de grande dimension qui tend à dégrader de manière importante le contraste d'images, et d'une autre façon, l'énergie lumineuse du pic central, c'est-à-dire l'énergie lumineuse émise selon l'axe normal au plan du substrat 2.In a cathode ray tube, the glass substrate 2 generally has a thickness E of the order of 6 to 7 millimeters, and its refractive index n0 is of the order of 1.5. Under these conditions, the light emitted under the impact of an electron beam (symbolized by an arrow 13) by the layer 3 of phosphors, by a grain L1 for example which is in contact with an inner face 5 of the substrate 2 , can exit through a face 6 of the latter towards the outside of the tube, only for its part whose angle of incidence (in the substrate 2) is less than the limit angles Φ0, Φ0 ′ formed between rays R1, R1 ′ (Which represent the limit refraction) and an axis x normal to the plane of the external face 6 of the substrate 2. Thus for the light emitted from the grain L1, which propagates in the direction of the external face 6 towards the use and which is not included in the limit angles Φ0, Φ0 ′, this light undergoes a total reflection (as illustrated by the radius R1) by which it is returned towards the internal face 5 of the substrate 2, where it is again reflected towards opposite side 6, unless it meets a luminous grain ophore in touch with this inner face 5; in the latter case, this light can be re-emitted towards use as symbolized by arrows RD1, RD2, RD3. This phenomenon, which can be repeated several times, is at the base of the creation of a large halo which tends to degrade significantly the contrast of images, and in another way, the light energy of the peak central, that is to say the light energy emitted along the axis normal to the plane of the substrate 2.

Une proportion importante de la lumière émise par la couche 3 de luminophore sort à l'extérieur du tube c'est-à-dire du substrat 2, avec des angles d'incidence tels qu'elle est perdue pour l'utilisation ; ceci particulièrement dans l'application à la projection, où des rayons de lumière sortant du substrat 2, ne sont pas captés dans une proportion importante par les moyens d'optique du système de projection.A significant proportion of the light emitted by the phosphor layer 3 exits outside the tube, that is to say the substrate 2, with angles of incidence such that it is lost for use; this particularly in the application to projection, where rays of light leaving the substrate 2, are not captured in a significant proportion by the optical means of the projection system.

La figure 2 illustre cette situation et montre à cet effet, l'avant d'un tube T à rayons cathodiques classique comprenant un écran cathodoluminescent, tel que par exemple l'écran 1 de la figure 1, et montre schématiquement la lentille 7 de l'optique d'un dispositif de projection classique également. Sous l'impact en un point A du faisceau d'électrons 13, une lumière est produite dont une partie est émise avec un angle d'incidence égal ou supérieur à l'angle limite Φ0, comme illustré par le rayon limite R1. Cette lumière peut subir de multiples réflexions ou être rediffusée vers l'utilisation selon des rayons RD1, RD2, R3, de telle sorte que cette lumière qui est représentée par le rayon limite R1 engendre le halo.FIG. 2 illustrates this situation and shows for this purpose the front of a conventional cathode ray tube T comprising a cathodoluminescent screen, such as for example the screen 1 of FIG. 1, and schematically shows the lens 7 of the optics of a conventional projection device also. Under the impact at a point A of the electron beam 13, a light is produced, part of which is emitted with an angle of incidence equal to or greater than the limit angle Φ0, as illustrated by the limit radius R1. This light can undergo multiple reflections or be redistributed towards use according to rays RD1, RD2, R3, so that this light which is represented by the limit radius R1 generates the halo.

Dans l'exemple représenté à la figure 2, l'utilisation est constituée par la lentille 7 qui représente les moyens d'optique d'un système de projection. La lentille 7 à une ouverture 8 centrée sur un axe 9 du tube T, l'axe 9 étant normal au plan de l'écran 1.In the example shown in Figure 2, the use consists of the lens 7 which represents the optical means of a projection system. The lens 7 has an opening 8 centered on an axis 9 of the tube T, the axis 9 being normal to the plane of the screen 1.

La lumière émise avec un angle d'incidence inférieur à l'angle limite Φ0 sort du tube T, c'est-à-dire du substrat 2. Cette lumière est captée par l'utilisation seulement pour sa part qui passe dans l'ouverture 8 de la lentille 7, comme illustré par un rayon utile RU qui est émis à partir du point A. L'autre part de cette lumière est symbolisée par un rayon RP sortant du tube T mais qui ne passe pas par l'ouverture 8, et qui est donc perdu pour l'utilisation, ce qui dégrade le rendement lumineux.The light emitted with an angle of incidence less than the limit angle Φ0 leaves the tube T, that is to say the substrate 2. This light is captured by the use only for its part which passes through the aperture 8 of the lens 7, as illustrated by a useful radius RU which is emitted from point A. The other part of this light is symbolized by a ray RP leaving the tube T but which does not pass not through opening 8, and which is therefore lost for use, which degrades the light output.

Il est à remarquer en outre que les rayons rediffusés vers l'utilisation et captés par cette dernière peuvent avoir un effet néfaste, comme par exemple le rayon rediffusé RD2 qui, bien que parallèle à l'axe 9, est rediffusé à partir d'un point différent du point A et tend à détruire le contraste.It should also be noted that the rays re-broadcast towards the use and picked up by the latter can have a harmful effect, such as for example the re-broadcast ray RD2 which, although parallel to the axis 9, is re-broadcast from a point different from point A and tends to destroy the contrast.

L'invention constitue une solution aux problèmes ci-dessus exposés, solution particulièrement intéressante du fait notamment que l'invention est simple à mettre en oeuvre et, qu'elle constitue par suite une solution peu onéreuse permettant notamment d'obtenir un gain maximum de luminance, d'améliorer le contraste et de diminuer fortement le halo.The invention constitutes a solution to the problems set out above, a particularly advantageous solution in particular because the invention is simple to implement and, as a result, it constitutes an inexpensive solution making it possible in particular to obtain a maximum gain of luminance, to improve the contrast and to strongly decrease the halo.

Selon l'invention, un écran cathodoluminescent pour tubes à rayons cathodiques, comportant un substrat ayant une épaisseur donnée et un indice de réfraction donné, le substrat portant une couche luminescente soumise à un bombardement électronique et produisant une lumière sous l'effet dudit bombardement, caractérisé en ce qu'une couche intermédiaire est disposée entre la couche luminescente et le substrat, la couche intermédiaire ayant d'une part, une seconde épaisseur largement inférieure à l'épaisseur du substrat, et ayant d'autre part un second indice de réfraction supérieur à l'indice de réfraction du substrat.According to the invention, a cathodoluminescent screen for cathode ray tubes, comprising a substrate having a given thickness and a given refractive index, the substrate carrying a luminescent layer subjected to electronic bombardment and producing a light under the effect of said bombardment, characterized in that an intermediate layer is disposed between the luminescent layer and the substrate, the intermediate layer having on the one hand a second thickness much less than the thickness of the substrate, and on the other hand having a second refractive index higher than the refractive index of the substrate.

En interposant ainsi une telle couche intermédiaire, on crée une surface réfringente au niveau des faces en contact de la couche intermédiaire et du substrat, surface réfringente qui réfléchit totalement la lumière provenant de la couche luminescente quand cette lumière arrive avec un angle d'incidence plus grand qu'un angle limite Φl1 dont la valeur est déduite de celle des indices de réfraction du substrat et de la couche intermédiaire. D'autre part, l'angle limite Φl1 est inférieur à un autre angle limite Φ0 qui provoque une réflexion totale de la lumière à l'interface entre le substrat et l'air dans des conditions semblables à celles qui ont déjà été mentionnées dans le préambule pour expliquer les défauts de l'art antérieur, et qui conduisent à provoquer un halo de grande dimension. Dans ces conditions, l'interposition de la couche intermédiaire a pour effet de rediffuser une part très importante de la lumière, au-delà de l'angle limite de réfraction Φl1, vers la couche cathodoluminescente, de manière que cette lumière soit retransmise ou redistribuée vers l'extérieur du tube c'est-à-dire vers l'utilisation, avec une indicatrice d'émission beaucoup plus concentrée sur l'axe.By thus interposing such an intermediate layer, a refractive surface is created at the faces in contact with the intermediate layer and the substrate, a refractive surface which totally reflects the light coming from the luminescent layer when this light arrives with an angle of incidence more large than a limiting angle Φl1 whose value is deduced from that of the refractive indices of the substrate and the middle layer. On the other hand, the limit angle Φl1 is less than another limit angle Φ0 which causes total reflection of the light at the interface between the substrate and the air under conditions similar to those which have already been mentioned in the preamble to explain the faults of the prior art, and which lead to causing a large halo. Under these conditions, the interposition of the intermediate layer has the effect of diffusing a very large part of the light, beyond the limiting angle of refraction Φl1, towards the cathodoluminescent layer, so that this light is retransmitted or redistributed towards the outside of the tube, that is to say towards use, with an emission indicator much more concentrated on the axis.

Le rendement de redistribution de la lumière peut être fortement favorisé par l'implantation d'une monocouche compacte de grains fins, entre la couche intermédiaire et la couche luminescente ou couche de luminophores.The light redistribution efficiency can be greatly promoted by the implantation of a compact monolayer of fine grains, between the intermediate layer and the luminescent layer or phosphor layer.

L'invention sera mieux comprise à l'aide de la description qui suit, faite à titre d'exemple non limitatif en référence aux figures annexées, parmi lesquelles :

  • - les figure 1 et 2 déjà décrites, montrent un écran cathodoluminescent de l'art antérieur ;
  • - la figure 3 est une vue schématique en coupe montrant un écran cathodoluminescent conforme à l'invention ;
  • - la figure 4 montre schématiquement par une vue en coupe, une version préférée d'un écran conforme à l'invention ;
  • - la figure 5 montre schématiquement par une vue en coupe, une variante de la version de l'invention montrée à la figure 4.
The invention will be better understood with the aid of the description which follows, given by way of nonlimiting example with reference to the appended figures, among which:
  • - Figures 1 and 2 already described, show a cathodoluminescent screen of the prior art;
  • - Figure 3 is a schematic sectional view showing a cathodoluminescent screen according to the invention;
  • - Figure 4 shows schematically in a sectional view, a preferred version of a screen according to the invention;
  • FIG. 5 schematically shows, in a sectional view, a variant of the version of the invention shown in FIG. 4.

La figure 3 montre partiellement un écran cathodoluminescent 10 selon l'invention, destiné à former l'écran d'un tube à rayon cathodique. L'écran 10 comporte un substrat 11, constitué par exemple de manière classique par une dalle en verre ayant une épaisseur E₁ de l'ordre de 6 à 7 millimètres. Le substrat 11 porte une couche luminescente 12 exposée à un faisceau d'électrons symbolisé par une flèche 13. Dans l'exemple non limitatif de la description, la couche luminescente 12 est constituée de manière traditionnelle par une pluralité de grains de luminophores L1, L2, ..., Ln. Une couche 4 conductrice, en aluminium par exemple, est déposée sur la couche luminescente 12, pour notamment réfléchir la lumière produite par la couche luminescente 12 vers l'utilisation c'est-à-dire vers une face extérieure 14 du substrat 11, face extérieure qui elle est au contact de l'air.FIG. 3 partially shows a cathodoluminescent screen 10 according to the invention, intended to form the screen of a cathode ray tube. The screen 10 comprises a substrate 11, constituted for example in a conventional manner by a glass slab having a thickness E₁ of the order of 6 to 7 millimeters. The substrate 11 carries a luminescent layer 12 exposed to an electron beam symbolized by an arrow 13. In the nonlimiting example of the description, the luminescent layer 12 is traditionally constituted by a plurality of phosphor grains L1, L2, ..., Ln. A conductive layer 4, made of aluminum for example, is deposited on the luminescent layer 12, in particular for reflecting the light produced by the luminescent layer 12 towards use, that is to say towards an outer face 14 of the substrate 11, face outside which it is in contact with air.

Selon une caractéristique de l'invention, une couche intermédiaire 15 est interposée entre la couche luminescente 12 et le substrat 11. La couche intermédiaire 15 est constituée par exemple en un matériau diélectrique, transparent à la lumière émise par les grains luminophores L1 à Ln et ayant un indice de réfraction n1 supérieur à l'indice de réfraction n0 (n0 sensiblement égal à 1,5) du substrat 11, et de préférence très supérieur à cet indice de réfraction n0 du substrat (par exemple n0/n1 égal ou inférieur à 0,75). Ainsi par exemple la couche intermédiaire 15 peut être réalisée en oxyde de titane TiO2 ou encore en sulfure de zinc ZnS, de manière à présenter un indice de réfraction n1 de l'ordre de 2,35.According to a characteristic of the invention, an intermediate layer 15 is interposed between the luminescent layer 12 and the substrate 11. The intermediate layer 15 is made for example of a dielectric material, transparent to the light emitted by the phosphors L1 to Ln and having a refractive index n1 greater than the refractive index n0 (n0 substantially equal to 1.5) of the substrate 11, and preferably much greater than this refractive index n0 of the substrate (for example n0 / n1 equal to or less than 0.75). Thus, for example, the intermediate layer 15 can be made of titanium oxide TiO2 or also of zinc sulfide ZnS, so as to have a refractive index n1 of the order of 2.35.

D'autre part, selon une autre caractéristique de l'invention, la couche intermédiaire 15 a une épaisseur E2 largement inférieure à l'épaisseur E1 du substrat 11. Par rapport au substrat 11, la couche intermédiaire 15 constitue une couche mince qui peut être réalisée d'une manière simple et peu onéreuse par évaporation, ou encore par exemple par une méthode au trempé d'alcoolate à partir d'un alcoolate de titane Ti(OC₂H₅)₄. Il est à remarquer que l'épaisseur E₂ de la couche intermédiaire 15 n'est pas vraiment critique pour le fonctionnement, l'important étant qu'elle soit beaucoup plus faible que l'épaisseur E1 du substrat 11 ; des résultats très satisfaisants ont été obtenus avec des valeurs voisines du micromètre pour l'épaisseur E2 de la couche intermédiaire 15. Il est à noter que sur les figures l'échelle des dimensions n'est pas respectée.On the other hand, according to another characteristic of the invention, the intermediate layer 15 has a thickness E2 much less than the thickness E1 of the substrate 11. Compared to the substrate 11, the intermediate layer 15 constitutes a thin layer which can be carried out in a simple and inexpensive manner by evaporation, or even for example by a dip alcoholate method from a titanium alcoholate T i (OC₂H₅) ₄. It should be noted that the thickness E₂ of the intermediate layer 15 is not really critical for operation, the important thing being that it is much smaller than the thickness E1 of the substrate 11; very satisfactory results have been obtained with values close to the micrometer for the thickness E2 of the intermediate layer 15. It note that in the figures the scale of dimensions is not respected.

Dans ces conditions, quand un électron pénètre dans la couche luminescente 12, et engendre dans cette dernière des photons p1, p2 (symbolisés par leur trajectoire), ces photons ne peuvent traverser la surface réfringente formée par l'interface couche intermédiaire-substrat 15-11 que si les angles Φ1, Φ2 que présente leur trajectoire par rapport à un axe x normal à la surface réfringente 15-11, sont inférieurs à l'angle limite Φl1 dont la valeur est donnée par les indices de réfraction n0 et n1 (cet angle limite Φl1 étant dans l'exemple de l'ordre de 38°). En conséquence dans l'exemple représenté, la trajectoire du premier photon p1 est telle qu'elle présente un angle Φ1 inférieur à l'angle limite Φl1, ce qui lui permet de traverser l'interface couche intermédiaire-substrat 15-11, puis de sortir du substrat 11 par la face extérieure 14 de ce dernier si sa trajectoire forme, avec un axe x normal à la face extérieure 14, un angle Φ1′ plus petit qu'un angle limite Φ0 donné par les indices du substrat 11 et de l'air; l'angle limite Φ0 dans le substrat 11 ayant une valeur semblable à celle mentionnée dans le préambule, à savoir de l'ordre de 43° (la face extérieure 14 représente une surface réfringente formée à l'interface du substrat 11 et de l'air).Under these conditions, when an electron enters the luminescent layer 12, and generates in the latter photons p1, p2 (symbolized by their trajectory), these photons cannot cross the refracting surface formed by the interface between the intermediate layer and the substrate 15- 11 that if the angles Φ1, Φ2 that their trajectory presents with respect to an axis x normal to the refractive surface 15-11, are less than the limit angle Φl1 whose value is given by the indices of refraction n0 and n1 (this limit angle Φl1 being in the example of the order of 38 °). Consequently in the example shown, the trajectory of the first photon p1 is such that it has an angle Φ1 less than the limit angle Φl1, which allows it to cross the interface between the intermediate layer and the substrate 15-11, then leave the substrate 11 by the external face 14 of the latter if its trajectory forms, with an axis x normal to the external face 14, an angle Φ1 ′ smaller than a limit angle Φ0 given by the indices of the substrate 11 and of the 'air; the limiting angle Φ0 in the substrate 11 having a value similar to that mentioned in the preamble, namely of the order of 43 ° (the outer face 14 represents a refractive surface formed at the interface of the substrate 11 and the air).

En supposant que la trajectoire, du second photon p2 présente, par rapport à l'axe normal x, un angle égal ou supérieur à l'angle limite Φl1 à l'interface couche intermédiaire-substrat 15-11, ce second photon p2 est réfléchi en un point repéré c de cette interface, vers la couche luminescente 12 et, s'il rencontre un grain de luminophore L1 à Ln en contact avec une face supérieure 16 de la couche intermédiaire 15, en un point f par exemple, ce photon p2 est rediffusé en direction du substrat 11 dans lequel il peut pénétrer ou non selon que son angle d'incidence est inférieur ou non à l'angle limite Φl1.Assuming that the trajectory of the second photon p2 has, with respect to the normal axis x, an angle equal to or greater than the limit angle Φl1 at the intermediate layer-substrate interface 15-11, this second photon p2 is reflected at a point marked c of this interface, towards the luminescent layer 12 and, if it encounters a grain of phosphor L1 to Ln in contact with an upper face 16 of the intermediate layer 15, at a point f for example, this photon p2 is rebroadcast in the direction of the substrate 11 into which it can penetrate or not depending on whether its angle of incidence is less than the limit angle Φl1 or not.

Ainsi, si le photon p2 rencontre un luminophore au point f, ce photon peut être redistribué vers le substrat 11, c'est-à-dire vers l'extérieur comme symbolisé par des flèches repérées RD ; mais s'il n'y a pas de luminophores au point f, le second p2 est réfléchi en direction de l'interface 15-11 avec un angle supérieur à l'angle limite Φl1, de telle sorte que ce photon sera à nouveau réfléchi par l'interface 15-11 en direction de la couche luminescente 12.Thus, if the photon p2 encounters a phosphor at point f, this photon can be redistributed towards the substrate 11, that is to say towards the outside as symbolized by arrows marked RD; but if there are no phosphors at point f, the second p2 is reflected towards the interface 15-11 with an angle greater than the limit angle Φl1, so that this photon will be reflected again by the interface 15-11 towards the luminescent layer 12.

Si l'on considère une distance D2, formée entre le point f qui marque le retour du second photon p2 à la face supérieure 16 de la couche intermédiaire 15, et un point O où cette face supérieure 16 est en contact avec le premier luminophore L1, point O qui marque le point où a été émis ce second photon p2 dans la couche intermédiaire 15, on constate que pour une épaisseur E2 de la couche intermédiaire 15 de l'ordre de 1 micromètre, et pour un angle limite Φl1 donné par les indices de réfraction n0 et n1 qui dans l'exemple ont pour valeur respectivement 2,35 et 1,5, cette distance D2 est de l'ordre de 2 micromètres. Ceci montre que tous les photons qui pénètrent dans la couche intermédiaire 15 avec un angle d'incidence supérieur à l'angle limite Φl1 auront la possibilité d'être redistribués vers le substrat 11, c'est-à-dire en direction de l'utilisation, à une distance D2 latérale de 16 micromètres du point où ils ont été émis, alors que dans l'art antérieur les photons qui pénètrent dans le substrat selon des angles plus grands que l'angle limite Φ0, sont éventuellement redistribués vers l'utilisation à une distance latérale de plusieurs millimètres du point où ils auront pénétrés dans le substrat.If we consider a distance D2, formed between the point f which marks the return of the second photon p2 to the upper face 16 of the intermediate layer 15, and a point O where this upper face 16 is in contact with the first phosphor L1 , point O which marks the point where this second photon p2 was emitted in the intermediate layer 15, it can be seen that for a thickness E2 of the intermediate layer 15 of the order of 1 micrometer, and for a limit angle Φl1 given by the refractive indices n0 and n1 which in the example have respectively 2.35 and 1.5, this distance D2 is of the order of 2 micrometers. This shows that all the photons which penetrate into the intermediate layer 15 with an angle of incidence greater than the limit angle Φl1 will have the possibility of being redistributed towards the substrate 11, that is to say in the direction of the use, at a lateral distance D2 of 16 micrometers from the point where they were emitted, whereas in the prior art the photons which penetrate into the substrate at angles larger than the limit angle Φ0, are possibly redistributed towards the use at a lateral distance of several millimeters from the point where they will have entered the substrate.

Aussi, pour une même probabilité dans les deux cas qu'un photon rencontre un grain luminophore qui assure sa redistribution vers l'extérieur, la configuration de l'invention induit cette redistribution beaucoup plus près du point où la lumière a été émise. En conséquence on supprime l'intensité du halo à grande distance, et en combinant ceci au fait que dans la couche intermédiaire 15 on augmente la quantité de lumière qui subit une réflexion totale, on obtient une indicatrice d'émission plus concentrée sur l'axe que dans l'art antérieur, c'est-à-dire qu'on renforce l'intensité de la lumière émise selon l'axe normal au plan du substrat 11.Also, for the same probability in the two cases that a photon encounters a luminophore grain which ensures its redistribution towards the outside, the configuration of the invention induces this redistribution much closer to the point where the light was emitted. Consequently we suppress the intensity of the halo at long distance, and by combining this with the fact that in the intermediate layer 15 the amount of light which undergoes a total reflection is increased, an emission indicator more concentrated on the axis is obtained than in the prior art, that is to say that the intensity of the light emitted along the axis normal to the plane of the substrate 11.

La figure 4 illustre une version préférée de l'invention, dans laquelle on améliore le rendement de redistribution de la lumière qui a été réfléchie par l'interface couche intermédiaire-substrat 15-11.FIG. 4 illustrates a preferred version of the invention, in which the efficiency of redistribution of the light which has been reflected by the interface intermediate layer-substrate 15-11 is improved.

A cet effet, une couche diffusante 20 est disposée entre la couche intermédiaire 15 et la couche luminescente 12 ou couche de luminophores.For this purpose, a diffusing layer 20 is arranged between the intermediate layer 15 and the luminescent layer 12 or layer of phosphors.

La couche diffusante 20 est constituée par des grains fins G1, G2, ..., GN qui forment une monocouche compacte, et qui permettent d'améliorer fortement la collection de lumière après la réflexion totale par l'interface 15-11. En effet, plus les grains G1 à GN sont fins et rapprochés, et plus les points de contacts sont nombreux pour la récupération de lumière au-dessus de la couche intermédiaire 15.The diffusing layer 20 is constituted by fine grains G1, G2, ..., GN which form a compact monolayer, and which make it possible to greatly improve the collection of light after total reflection by the interface 15-11. In fact, the finer and closer the grains G1 to GN, the more the contact points are numerous for the recovery of light above the intermediate layer 15.

Par le terme "grains fins" nous entendrons définir des grains dont le diamètre moyen est inférieur au diamètre moyen de grains luminophores L1 à Ln de la couche luminescente 12. Les grains G1 à GN peuvent avoir un diamètre moyen de l'ordre par exemple de 1 micromètre, et selon une autre caractéristique de l'invention, ils peuvent être formés de manière avantageuse, eux mêmes par des grains luminophores d'une même nature que les grains luminophores de la couche luminescente 12, de manière à participer eux aussi à la production de lumière.By the term "fine grains" we will define grains whose average diameter is less than the average diameter of phosphor grains L1 to Ln of the luminescent layer 12. The grains G1 to GN can have an average diameter of the order of for example 1 micrometer, and according to another characteristic of the invention, they can be advantageously formed, themselves by phosphors of the same nature as the phosphors of the luminescent layer 12, so as to also participate in the light production.

Il est à noter que par le terme monocouche, nous entendons définir une couche dont l'épaisseur comprend un unique grain, ceci pour toute la surface de la couche (même si en pratique il peut subsister localement quelques exceptions à cette règle sans trop dégrader la resolution).It should be noted that by the term monolayer, we mean a layer whose thickness includes a single grain, this for the entire surface of the layer (although in practice there may remain locally some exceptions to this rule without degrading the resolution).

L'écran 10 de l'invention peut comporter en outre, une couche de liaison 22 qui est à la fois en contact avec la face supérieure 16 de la couche intermédiaire 15, et en contact avec les grains G1 à GN de la monocouche diffusante 20. La couche de liaison 22 permet d'améliorer la collection de lumière en évitant par sa présence, que les rayons lumineux ne subissent une réflexion totale au niveau de la face supérieure 16 de la couche intermédiaire 15, quand ces rayons lumineux atteignent cette face supérieure 16 en un point situé entre deux grains G1 à GN voisins, comme il est illustré sur la figure 3 à titre d'exemple par un troisième photon p3. A cet effet, la couche de liaison 22 à un indice de réfraction n2 plus grand ou égal à l'indice de réfraction n1 de la couche intermédiaire 15. Dans cet esprit, la couche de liaison 22 peut constituer une couche diélectrique réalisée par exemple en oxyde de titane TiO2 par une même méthode que la couche intermédiaire 15.The screen 10 of the invention may further comprise a bonding layer 22 which is both in contact with the face upper 16 of the intermediate layer 15, and in contact with the grains G1 to GN of the diffusing monolayer 20. The bonding layer 22 makes it possible to improve the collection of light by preventing, by its presence, that the light rays do not undergo a reflection total at the level of the upper face 16 of the intermediate layer 15, when these light rays reach this upper face 16 at a point located between two grains G1 with neighboring GN, as illustrated in FIG. 3 by way of example by a third photon p3. To this end, the bonding layer 22 has a refractive index n2 greater than or equal to the refractive index n1 of the intermediate layer 15. In this spirit, the bonding layer 22 can constitute a dielectric layer produced for example by titanium oxide TiO2 by the same method as the intermediate layer 15.

En supposant que les grains G1 à GN de la couche diffusante 20 soient également des grains luminophores, le photon p3 peut être émis dans la couche intermédiaire 15 par un grain G2 par exemple de la couche diffusante 20. Le photon p3 subit une réflexion au niveau de l'interface couche intermédiaire-substrat 15-11, réflexion qui le renvoie vers la face supérieure 16. En l'absence de la couche de liaison 22, le photon p3 serait réfléchi en un point O2 de cette face supérieure 16, comme il est représenté par une flèche en traits pointillés repérée p3′, sauf bien entendu si le point O2 se trouve suffisamment proche d'un grain G1 à GN pour que le phénomène d'ondes évanescentes puisse se manifester, et permette au photon p3 de sortir de la couche intermédiaire 15 et de pénétrer dans le grain. Avec la présence de la couche de liaison 22, le photon p3, même s'il arrive à la face supérieure 16 en un point de cette dernière relativement éloignée d'un grain, ce photon p3 sort de la couche intermédiaire 15, et la couche de liaison 22 capte ce photon et le canalise vers un troisième grain G3 par exemple où il est diffusé vers l'extérieur.Assuming that the grains G1 to GN of the diffusing layer 20 are also phosphors, the photon p3 can be emitted in the intermediate layer 15 by a grain G2 for example of the diffusing layer 20. The photon p3 undergoes reflection at the level of the intermediate layer-substrate interface 15-11, reflection which returns it to the upper face 16. In the absence of the bonding layer 22, the photon p3 would be reflected at a point O2 of this upper face 16, as it is represented by an arrow in dotted lines marked p3 ′, except of course if the point O2 is sufficiently close to a grain G1 at GN so that the phenomenon of evanescent waves can manifest itself, and allows the photon p3 to exit from the intermediate layer 15 and penetrate into the grain. With the presence of the bonding layer 22, the photon p3, even if it arrives at the upper face 16 at a point of the latter relatively distant from a grain, this photon p3 leaves the intermediate layer 15, and the layer link 22 picks up this photon and channels it to a third grain G3, for example where it is diffused to the outside.

La couche de liaison 22 permet aussi d'assurer une fonction de jonction thermique particulièrement intéressante dans l'application à la projection, fonction qui est utile également si les grains G1 à GN de la monocouche diffusante 20 sont des grains de luminophores.The bonding layer 22 also makes it possible to provide a particularly advantageous thermal junction function in the application to projection, a function which is also useful if the grains G1 to GN of the diffusing monolayer 20 are grains of phosphors.

La figure 5 montre une autre version de l'invention qui permet de renforcer l'effet obtenu par l'interposition de la couche intermédiaire 15.FIG. 5 shows another version of the invention which makes it possible to reinforce the effect obtained by the interposition of the intermediate layer 15.

Dans cette nouvelle version de l'invention, une seconde couche intermédiaire 25 est disposée entre le substrat 11 et la première couche intermédiaire 15.In this new version of the invention, a second intermediate layer 25 is disposed between the substrate 11 and the first intermediate layer 15.

Selon une caractéristique de l'invention, cette seconde couche intermédiaire 25 a un indice de réfraction n3 inférieur à l'indice de réfraction n0 du substrat 11. D'autre part, cette seconde couche intermédiaire 25 a une épaisseur E3 du même ordre de grandeur que l'épaisseur E2 de la première couche intermédiaire 15, c'est-à-dire voisine de 1 micromètre ; mais il est à noter que cette épaisseur E3 n'est pas critique, l'important étant qu'elle soit très petite devant l'épaisseur E1 du substrat 11. La seconde couche intermédiaire 25 peut être réalisée par exemple en fluorure de magnésium MgF2 dont l'indice de réfraction n3 est de l'ordre de 1,35, par une méthode classique d'évaporation.According to a characteristic of the invention, this second intermediate layer 25 has a refractive index n3 lower than the refractive index n0 of the substrate 11. On the other hand, this second intermediate layer 25 has a thickness E3 of the same order of magnitude that the thickness E2 of the first intermediate layer 15, that is to say close to 1 micrometer; but it should be noted that this thickness E3 is not critical, the important thing being that it is very small compared to the thickness E1 of the substrate 11. The second intermediate layer 25 can be produced for example from magnesium fluoride MgF2 of which the refractive index n3 is of the order of 1.35, by a conventional method of evaporation.

Cette nouvelle configuration permet de diminuer la valeur de l'angle limite Φl1 dans la première couche intermédiaire 15. Ainsi par exemple, pour reprendre les mêmes éléments que dans l'exemple dans la figure 3, l'angle limite Φ1 au-delà duquel le photon p2 est réfléchi vers la face supérieure 16 de la première couche intermédiaire 15, cet angle limite à une valeur inférieure dans le cas de cette nouvelle version de l'invention que dans le cas représenté à la figure 3. En effet en supposant que la seconde couche intermédiaire 25 soit en fluorure de magnésium MgF2, la nouvelle valeur de l'angle limite Φl1 est de l'ordre de 35°, Ceci est dû au fait que la différence d'indice de réfraction entre l'indice n1 de la première couche intermédiaire 15 et l'indice n3 de la seconde couche intermédiaire 25 est plus importante que la différence d'indice entre la couche intermédiaire 15 et le substrat 11 montrés à la figure 3. Comme il a été dit plus haut, ceci renforce les effets produits par la couche intermédiaire 15, et permet d'augmenter au maximum l'indicatrice d'émission lumineuse et d'obtenir ainsi le gain maximum de luminance par une concentration de l'angle (non représenté) de l'indicatrice lumineuse.This new configuration makes it possible to reduce the value of the limit angle Φl1 in the first intermediate layer 15. Thus for example, to use the same elements as in the example in FIG. 3, the limit angle Φ1 beyond which the photon p2 is reflected towards the upper face 16 of the first intermediate layer 15, this angle limits to a lower value in the case of this new version of the invention than in the case represented in FIG. 3. In fact assuming that the second intermediate layer 25 is made of magnesium fluoride MgF2, the new value of the limit angle Φl1 is of the order of 35 °, This is due to the fact that the difference in refractive index between the index n1 of the first layer intermediate 15 and the index n3 of the second intermediate layer 25 is greater than the difference in index between the intermediate layer 15 and the substrate 11 shown in FIG. 3. As mentioned above, this reinforces the effects produced by the intermediate layer 15, and makes it possible to increase the light emission indicator as much as possible and thus obtain the maximum luminance gain by a concentration of the angle (not shown) of the light indicator.

Il est possible d'obtenir, pour la seconde couche intermédiaire 25, un indice de réfraction n3 encore plus faible, si cette seconde couche intermédiaire 25 est constituée d'une couche microporeuse. Ainsi par exemple, la seconde couche intermédiaire 25 peut être une couche microporeuse d'oxyde de silicium SiO2 dont l'indice de réfraction peut être voisin de 1,25, ce qui permet d'obtenir un angle limite Φl1 encore plus faible de l'ordre de 32°. Cette seconde couche intermédiaire formée d'une couche poreuse d'oxyde de silicium peut être déposée sur le substrat 11 d'une manière en elle-même classique par exemple par une méthode d'ultracentrifugation dont la mise en oeuvre est aisée, ou encore par un procédé de densification par voie humide qui conduit à obtenir un dépôt dont le degré de porosité dépend des conditions de mise en oeuvre.It is possible to obtain, for the second intermediate layer 25, an even lower refractive index n3, if this second intermediate layer 25 consists of a microporous layer. Thus, for example, the second intermediate layer 25 can be a microporous layer of silicon oxide SiO2, the refractive index of which can be close to 1.25, which makes it possible to obtain an even smaller limit angle Φl1 of the order of 32 °. This second intermediate layer formed of a porous layer of silicon oxide can be deposited on the substrate 11 in a conventional manner in itself, for example by an ultracentrifugation method whose implementation is easy, or also by a wet densification process which leads to a deposit, the degree of porosity of which depends on the conditions of use.

Il est à noter que la nature des matériaux susceptibles de former les différentes couches, à savoir la première couche intermédiaire 15, la seconde couche intermédiaire 25, la couche diffusante 20, la couche de liaison 22, la nature de ces matériaux est indiquée à titre d'exemple nullement limitatif, et d'autres matériaux peuvent être choisis notamment en fonction de la couleur de la lumière. Ainsi par exemple, les couches dont l'indice de réfraction est élevé peuvent être TiO2, ZnS, Ta2O5, CeO2, Fe2O3 (n = 2,6), ce dernier étant particulièrement intéressant dans le cas de la gamme de couleur orange-rouge. L'utilisation de tels matériaux, suivant le concept de l'invention, permet d'obtenir des gains de luminance de l'ordre de 40 % , pour le vert et le bleu notamment, et supérieur à 40 % pour le rouge dans le cas de l'utilisation de Fe2O3.It should be noted that the nature of the materials capable of forming the different layers, namely the first intermediate layer 15, the second intermediate layer 25, the diffusing layer 20, the bonding layer 22, the nature of these materials is indicated as in no way limiting example, and other materials can be chosen in particular according to the color of the light. Thus, for example, the layers with a high refractive index can be TiO2, ZnS, Ta2O5, CeO2, Fe2O3 (n = 2.6), the latter being particularly advantageous in the case of the orange-red color range. The use of such materials, according to the concept of the invention, makes it possible to obtain luminance gains of the order of 40%, for green and blue in particular, and greater than 40% for red in the case of the use of Fe2O3.

Claims (12)

1 - Ecran cathodoluminescent pour tubes à rayons cathodiques, comportant un substrat (11) ayant une épaisseur (E₁)donnée et un indice de réfraction donné, le substrat (11) portant une couche luminescente (12) soumise à un bombardement électronique et produisant une lumière sous l'effet dudit bombardement, caractérisé en ce qu'une couche intermédiaire (15) est disposée entre la couche luminescente (12) et le substrat (11), la couche intermédiaire (15) ayant d'une part, une seconde épaisseur (E₂) largement inférieure à l'épaisseur (E₁) du substrat (11), et ayant d'autre part un second indice de réfraction supérieur à l'indice de réfraction du substrat (11).1 - Cathodoluminescent screen for cathode ray tubes, comprising a substrate (11) having a given thickness (E₁) and a given refractive index, the substrate (11) carrying a luminescent layer (12) subjected to electronic bombardment and producing a light under the effect of said bombardment, characterized in that an intermediate layer (15) is disposed between the luminescent layer (12) and the substrate (11), the intermediate layer (15) having on the one hand, a second thickness (E₂) much less than the thickness (E₁) of the substrate (11), and having on the other hand a second refractive index greater than the refractive index of the substrate (11). 2 - Ecran cathodoluminescent selon la revendication 1, caractérisé en ce qu'il comporte une couche diffusante (20) formée d'une pluralité de grains fins (G1 à GN), la couche diffusante (20) étant interposée entre la couche luminescente (12) et la couche intermédiaire (15).2 - Cathodoluminescent screen according to claim 1, characterized in that it comprises a diffusing layer (20) formed of a plurality of fine grains (G1 to GN), the diffusing layer (20) being interposed between the luminescent layer (12 ) and the intermediate layer (15). 3 - Ecran cathodoluminescent selon la revendication 2, caractérisé en ce que la couche diffusante est une monocouche.3 - Cathodoluminescent screen according to claim 2, characterized in that the diffusing layer is a monolayer. 4 - Ecran cathodoluminescent selon l'une des revendications 2 ou 3, caractérisé en ce que les grains (G1 à GN) sont des grains de luminophores.4 - Cathodoluminescent screen according to one of claims 2 or 3, characterized in that the grains (G1 to GN) are phosphor grains. 5 - Ecran cathodoluminescent selon l'une quelconque des revendications 2 ou 3 ou 4, caractérisé en ce qu'il comporte en outre une couche de liaison (22) formée sur une face supérieure (16) de la couche intermédiaire (15) opposée au substrat (11), les grains (G1 à GN) de la couche diffusante (20) étant partiellement enrobés dans ladite couche de liaison (22), la couche de liaison ayant un indice de réfraction dont la valeur est égale ou supérieure à celle de l'indice de réfraction de la couche intermédiaire (15).5 - Cathodoluminescent screen according to any one of claims 2 or 3 or 4, characterized in that it further comprises a bonding layer (22) formed on an upper face (16) of the intermediate layer (15) opposite to the substrate (11), the grains (G1 to GN) of the diffusing layer (20) being partially coated in said bonding layer (22), the bonding layer having a refractive index whose value is equal to or greater than that of the refractive index of the intermediate layer (15). 6 - Ecran cathodoluminescent selon l'une des revendications précédentes, caractérisé en ce qu une seconde couche intermédiaire (25) est disposée entre la première couche intermédiaire (15) et le substrat (11), la seconde couche intermédiaire (25) ayant un indice de réfraction de valeur inférieure à la valeur de l'indice de réfraction du substrat (11).6 - Cathodoluminescent screen according to one of the preceding claims, characterized in that a second intermediate layer (25) is disposed between the first intermediate layer (15) and the substrate (11), the second intermediate layer (25) having an index of refraction with a value lower than the value of the refractive index of the substrate (11). 7 - Ecran cathodoluminescent selon la revendication 6, caractérisé en ce que la deuxième couche intermédiaire (25) est constituée par une couche microporeuse.7 - Cathodoluminescent screen according to claim 6, characterized in that the second intermediate layer (25) consists of a microporous layer. 8 - Ecran cathodoluminescent selon la revendication 7 caractérisé en ce que la seconde couche intermédiaire (25) est formée d'une couche microporeuse d'oxyde de silicium SiO2.8 - Cathodoluminescent screen according to claim 7 characterized in that the second intermediate layer (25) is formed of a microporous layer of silicon oxide SiO2. 9 - Ecran cathodoluminescent selon la revendication 6, caractérisé en ce que la seconde couche intermédiaire est du fluorure de magnésium MgF2.9 - Cathodoluminescent screen according to claim 6, characterized in that the second intermediate layer is magnesium fluoride MgF2. 10 - Ecran cathodoluminescent selon la revendication 1 , caractérisé en ce que la première couche intermédiaire (15) est en oxyde de titane TiO2.10 - Cathodoluminescent screen according to claim 1, characterized in that the first intermediate layer (15) is made of titanium oxide TiO2. 11 - Ecran cathodoluminescent selon la revendication 1 , caractérisé en ce que la première couche intermédiaire (15) est un sulfure de zinc ZnS.11 - Cathodoluminescent screen according to claim 1, characterized in that the first intermediate layer (15) is a zinc sulfide ZnS. 12 - Ecran cathodoluminescent selon l'une des revendications précédentes, caractérisé en ce que le rapport de l'indice de réfraction (n0) du substrat (11) à l'indice de réfraction (n1) de la première couche intermédiaire (15) est égal ou inférieur à 0,75 (n0/n1 égal ou plus petit que 0,75).12 - Cathodoluminescent screen according to one of the preceding claims, characterized in that the ratio of the refractive index (n0) of the substrate (11) to the refractive index (n1) of the first intermediate layer (15) is 0.75 or less (n0 / n1 equal to or less than 0.75).
EP90402235A 1989-08-11 1990-08-03 High efficiency cathodoluminescent screen for high luminance cathode ray tube Expired - Lifetime EP0412887B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8910828A FR2650914A1 (en) 1989-08-11 1989-08-11 HIGH EFFICIENCY CATHODOLUMINESCENT SCREEN FOR HIGH LUMINANCE CATHODE RAY TUBES
FR8910828 1989-08-11

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EP0412887A1 true EP0412887A1 (en) 1991-02-13
EP0412887B1 EP0412887B1 (en) 1994-07-06

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EP (1) EP0412887B1 (en)
JP (1) JPH03129642A (en)
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JPH08129963A (en) * 1994-10-31 1996-05-21 Hitachi Ltd Color cathode-ray tube
DE69510170T2 (en) * 1994-12-26 1999-11-04 Toshiba Kawasaki Kk Screen and method of making the same
KR100315007B1 (en) * 1995-11-22 2002-02-28 이시다 아키라 Substrate detection and transfer apparatus in cassette and method thereof
US6812636B2 (en) * 2001-03-30 2004-11-02 Candescent Technologies Corporation Light-emitting device having light-emissive particles partially coated with light-reflective or/and getter material
JP2006228498A (en) * 2005-02-16 2006-08-31 Sonac Kk Fluorescent screen for display device and display device using the same

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EP0018667A1 (en) * 1979-05-07 1980-11-12 Optical Coating Laboratory, Inc. Cathode ray tube face plate construction for suppressing the halo having a low reflection
EP0018666A1 (en) * 1979-05-07 1980-11-12 Optical Coating Laboratory, Inc. Cathode ray tube face plate construction for suppressing the halo and method

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JPS6012650A (en) * 1983-07-01 1985-01-23 Mitsubishi Electric Corp Cathode-ray tube
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EP0018667A1 (en) * 1979-05-07 1980-11-12 Optical Coating Laboratory, Inc. Cathode ray tube face plate construction for suppressing the halo having a low reflection
EP0018666A1 (en) * 1979-05-07 1980-11-12 Optical Coating Laboratory, Inc. Cathode ray tube face plate construction for suppressing the halo and method

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FR2650914A1 (en) 1991-02-15
EP0412887B1 (en) 1994-07-06
DE69010423D1 (en) 1994-08-11
DE69010423T2 (en) 1994-10-20
US5101136A (en) 1992-03-31
JPH03129642A (en) 1991-06-03

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