EP0014156A1 - Electroluminescent chromatic transducer with additive synthesis - Google Patents

Abstract

1. Apparatus for generating images in at least two colors comprising an image reproduction screen, means for directing an energizing electronic beam over the entire surface of said screen, the intensity of which beam is dependent on the amplitude of a brightness control signal, and means for imparting a scanning movement to the said energizing beam so that its point of impact on the surface of the screen moves according to two dimensions, the said image generating apparatus being characterized in that it further comprises : a) a superimposition of at least two layers (23-25) each one produced in a luminescent material radiating light of a predetermined wavelength, different from the wavelength of the light radiated by the other layers, the luminescent materials used, radiating light under the action of an electronic bombardment and adapting to an amplification of the light intensity thus radiated by superposition of an electroluminescent effect, b) an appropriate control device, associated to each luminescent layer to generate therein a pulsating electric field, the frequency and amplitude of which are dependent on the amplitude of a corresponding color signal so as to ensure the restitution of the different chromatic components, and c) generators (31, 32) supplying the said signals controlling the color and brightness.

Description

The invention relates to a current-light translating device for a special image tube.

It more particularly relates to the production of a color image generator, characterized in that, in a "single-channel" cathode ray tube, electroluminescent capacitors are irradiated with a single electron beam, respectively emitting light d '' a specific wavelength (red, blue, green). These electroluminescent capacitors (whose metallic armatures exit outside the tube) are stacked, and constitute the front face of the tube and become control parameters for the "chrominance" signals. The subject of the invention is also the selection and the colorometric mixing of colors. To do this, a specific physical property of electroluminescent capacitors is used, namely: the amplification of

shine.

Simultaneously with cathodic bombardment, the light spot of the irradiated point is amplified when a variable electric field is applied in the considered capacitor.

Another object of the invention is that, in addition to the preponderant color obtained, a colorometric mixture is possible. The addition of "luminances" ensures a succession of colored points, without side effects, and fully restores the shades and shades in their exact brilliance.

For 25 years, all of the color T.V. receivers have been fitted with a "tri-channel" image tube, which has a mechanical focusing system for color selection. This set concentrates the 3 electron beams to obtain an impact point on a luminescent deposit (arranged in triplets or in lines) giving red, blue, green light points.

• 1/ au niveau des couleurs, convergence et pureté. (en dépit des progrès technologiques - a/ autoconvergence, b/ Précision In Ligne P.I.L.),
• 2/défauts de géométrie de l'image, (corrigés par des circuits complexes et onéreux),
• 3/ sensibilité au champ magnétique terrestre (obligation de blindages et de circuits de démagnétisation, impossibilité de déplacer un T.V. couleurs en fonctionnement sans perturber l'image).

These image tubes of a delicate industrial manufacture, require for their construction important investments, expensive specific tools, and their cost price are very high. In addition, the reconstruction of a colored image by these tubes has several shortcomings, namely:

• 1 / in terms of colors, convergence and purity. (despite technological progress - a / autoconvergence, b / Precision In Line PIL),
• 2 / image geometry faults, (corrected by complex and expensive circuits),
• 3 / sensitivity to the earth's magnetic field (obligation of shields and demagnetization circuits, inability to move a color TV in operation without disturbing the image).

In addition, in a color receiver, the image tube represents more than 50% of the cost price, and the supply of the tube and its supply circuits are large consumers of energy (80% of the electrons emitted by the cathode are intercepted by the focusing system - 20 to 30 watts are dissipated unnecessarily in heat).

The present technological innovation aims to remedy these drawbacks. The invention as characterized in the claims makes it possible to increase the number of colored dots visible to the observer and the resolution (confusion in current TVs, in the reproduction of texts in "telematics" B with 8, D with 0, S with 8, etc ...) giving a perfect reproduction of the texts, the colors and the nuances. The number of points reproduced without "parasitic effects" is almost double that of a current picture tube. Each point of light in the image is reconstituted in its natural color and its brilliance in the visual space. As the eye has no effort to synthesize, visual comfort is felt. The mixing of the colors is done point by point on the receiver on the one hand by the cathode current for the luminance, and on the other hand by the transducers for the chroma.

• 1/ une plus grande facilité de fabrication,
• 2/ une fiabilité incontestable,
• 3/ une consommation de matière première moins importante (1 canon au lieu de 3),
• ,4/ une consommation d'énergie inférieure de plus de 50% pour l'alimentation du tube et de ses accessoires,
• 5/ une augmentation de la définition de l'image et une restitution plus complète des couleurs.

Thus, the invention makes it possible to use a "single-channel" television tube which is entirely identical electronically for the "electron gun" part to that of a tube used for reception of black and white television. Only the front side is different. This single-channel tube technology is known and the results obtained are:

• 1 / greater ease of manufacture,
• 2 / undeniable reliability,
• 3 / less consumption of raw material (1 barrel instead of 3),
• , 4 / more than 50% lower energy consumption for feeding the tube and its accessories,
• 5 / an increase in the definition of the image and a more complete restitution of the colors.

The image tube "monocanon with chromatic electroluminescent transducers", according to the invention is based for the translation of current-light energy on the physical phenomena of electroluminescence of "thin film" solids associated with those of cathodoluminescence, physiology of the eye and colorometry. In summary, electroluminescence is the sustained emission of light from substances when they are irradiated by X-rays or ultraviolet rays, an electron beam or an external excitation energy. The phenomenon mainly resides in the direct excitation, luminescent centers by accelerated electrons, in a high electric field.

• 1/ un produit de base formé de cristaux à haut point de fusion, tel que le sulfure de zinc, l'oxyde de zinc, le sulfure de strontium, le tungstate de calcium, le silicate de zinc, le fluorure de calcium, le germanate de magnésium, le sulfure de cadmium, le fluorure de cadmium,
• 2/ des traces d'un élément étranger, dit "activateur", en proportion très faible (10^-2 à 10^-4 en poids) tels que le cuivre, l'or, l'argent, le manganèse, le plomb, le chrome, le bismuth et différentes terres rares. Ces éléments constituent les centres "luminogènes" du composé électroluminescent.

A material such as zinc sulfide (ZnS) can emit light under the action of an electric field. A solid electroluminescent compound comprises:

• 1 / a basic product formed of crystals with high melting point, such as zinc sulfide, zinc oxide, strontium sulfide, calcium tungstate, zinc silicate, calcium fluoride, germanate magnesium, cadmium sulfide, cadmium fluoride,
• 2 / traces of a foreign element, called "activator", in very small proportion (10 ^-2 to 10 ^-4 by weight) such as copper, gold, silver, manganese, lead, chromium, bismuth and various rare earths. These elements constitute the "luminogenic" centers of the electroluminescent compound.

A thin film of the above-mentioned luminescent compound coated in an insulator is placed between two plates which are both transparent and conductive, generally two glass plates on which an invisible but conductive layer of antimony chloride or oxide has been sprayed. of tin. The electroluminescent cell thus produced constitutes a capacitor. If we connect the two conductive strips of this capacitor to a periodic voltage generator we see, through the glass slides, shine the luminescent compound. This brightness increases both with the value of the applied voltage and with its frequency. The light emitted is blue, green, yellow or red, depending on the nature of the basic product and the activator.

A new effect, "the shine boosting effect", was discovered in 1953 by DESTRIAU. Certain materials which are luminescent under the action of an external excitation have an increased sensitivity, that is to say become much brighter when they are subjected simultaneously to the action of external excitation and to that of the alternating electric field produced. by a periodic voltage, applied between the armatures of the capacitor. The enhancement of the gloss depends on the luminogenic products used, and especially on the voltage and the frequency of the applied electric field. These cells measured from 20 to 50 J-.

. Pour augmenter l'efficacité lumineuse un recuit à 500° durant 20 à 30 minutes sous atmosphère d'argon est conseillé. Ces couches minces possèdent une grande fiabilité chimique, des caractéristiques stables et homogènes sur toutes leurs surfaces et leurs épaisseurs. Elles fonctionnent avec des tensions d'excitation relativement faibles et leur durée de vie est de 10⁴ heures.For more than a decade, the average diameter of the light-generating centers has been less than a micron. The production of thin films (structure in "thin layers") is achievable by implementing a process falling within the radiofrequency sputtering technique in a vacuum chamber (residual gas pressure less than 10- ⁵ torr) in the presence of an inert gas (argon). The whole of a cell is in the form of a thin layer having a thickness of 0.4 to 1

. To increase the luminous efficiency, annealing at 500 ° for 20 to 30 minutes under an argon atmosphere is recommended. These thin layers have high chemical reliability, stable and homogeneous characteristics over all their surfaces and thicknesses. They operate with relatively low excitation voltages and their lifespan is 10 ⁴ hours.

Cathodoluminescence, the conversion of the kinetic energy of electrons into light energy, has an extremely high light output when the luminogen is a Zinc sulfide (ZnS) and the activator is in the molecular form of a rare earth fluoride ( TbF ₃ -EuF ₃ -TmF ₃ ) and most of the trivalent lanthanides (Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm).

These centers are known as the "LUMOCEN effect" (Luminescence from Molecular Centers).

The association of the physical phenomena of electroluminescence and cathodoluminescence does not necessarily give the expected result with any phosphor. The response of ZnS is very fast, but cathodoluminescence ZnS doped only with earth fluorides uncommon not working properly (lifetime Lumino ^g enes too short) afterglow is below the threshold sensitivity of the human eye ( retina inertia). A change in light signal of less than 20 milliseconds is not visible. But by using as matrix ZnS associated with an oxysulfide doped by a rare earth fluoride, the phenomenon of cathodoluminescence approaches that of electroluminescence.

• 1/ le ZnS agit immédiatement, sous l'action du bombardement cathodique, mais très brièvement (rémanence équivalente au temps du bombardement),
• 2/ à l'extinction du ZnS, les oxysulfures dopés par les terres rares prennent le relais, et la continuité du phénomène de brillance dans les différents spectres chromatiques rend le résultat applicable à l'oscillographie et la T.V couleurs.

A possible explanation of the phenomenon is as follows:

• 1 / ZnS acts immediately, under the action of cathodic bombardment, but very briefly (persistence equivalent to the time of bombardment),
• 2 / at the extinction of ZnS, the oxysulfides doped by rare earths take over, and the continuity of phenomenon of brightness in the different chromatic spectra makes the result applicable to oscillography and color TV.

• 0 1/ deux couches tampons d'oxyde d'yttrium (Y₂0₃) de 2000 A d'épaisseur, ces deux couches étant sensiblement transparentes, le coté extérieur de ces couches est rendu conducteur par un dépôt d'oxyde d'étain (Sn0₂) ou d'oxyde d'indium (In0₃) ; o
• 2/ une couche électroluminescente de 6000 A composée de sulfure de zinc associé à un oxysulfure dopé par un fluorure de terre rare, est intercalé entre les couches tampons. On applique aux bornes des parties conductrices des impulsions de tension.

A chromogenic electroluminescent transducer, according to an embodiment of the invention, is in the form of an electroluminescent cell with a total thickness of the order of a micron. This transducer includes:

• 0 1 / two buffer layers of yttrium oxide (Y ₂ 0 ₃ ) of 2000 A thickness, these two layers being substantially transparent, the outside of these layers is made conductive by a deposit of tin oxide (Sn0 ₂ ) or indium oxide (In0 ₃ ); o
• 2 / an electroluminescent layer of 6000 A composed of zinc sulphide associated with an oxysulphide doped with a rare earth fluoride, is interposed between the buffer layers. Voltage pulses are applied across the terminals of the conductive parts.

If we direct an electron beam with a post-acceleration voltage of 5KV on this transducer, a fine spot of light appears, at the point of impact of the beam on the luminescent layer. This light emission is amplified localement.lorsau ^the voltage pulse (less than full illumination of the light emitting capacitor) is applied across the transducer.

The invention is explained in more detail using drawings representing only one embodiment.

• FIG. 1 is a schematic view in cross section of an electroluminescent transducer,
• _- Figure 2 is a schematic sectional view of a display tube using the principle of the invention,
• FIG. 3 is a section along AA of the front panel of the image tube of FIG. 2,
• - Figure 4, is the block diagram of a color television receiver using the picture tube of Figure 2.

The electroluminescent transducer (Figure 1) comprises a luminescent layer 1 made of one material at a time cathodoluminescent and electroluminescent, on either side of this layer are arranged two conductive layers 2 and 3 each connected to a respective terminal of a pulse generator 4 9.

Means, not shown, maintain a fairly high vacuum in the space 5 located on one side of the stack of layers 1, 2, and 3. A threadlike beam of electrons 6 scans the surface 7, on the empty side. This electron beam 6 has sufficient energy to penetrate the luminescent layer 1, but this energy is low enough that in the absence of periodic voltage between the layers 2 and 3, the luminescent material 1 does not emit to the point impact 8 of the electron beam 6, than a low intensity spot.

If applied between the layers 2 and 3 a voltage pulse 9, 100 to 140 volts and of short duration, for example of 10- ⁴ seconds, a flash of light, schematically represented by the arrow 10, is issued at the point impact 8. The wavelength of this light depends on the nature of the impurity atoms constituting the luminogenic centers of the material 1.

It is advantageous to interpose between the luminescent layer 1 and each of the conductive layers 2 and 3, a so-called buffer layer 11 and 12 made of a good material insulating from electricity and having a high dielectric constant. These layers 11 and 12 make it possible to apply high voltages between the two conductive layers 2 and 3, in order to obtain a large electric field in the material 1.

The method illustrated in FIG. 1 can be applied to obtaining colored images from video-color signals. For this purpose, as shown in FIG. 2, a television picture tube with a single electron gun is used.

We can see on the schematic section in Figure 2, the filament 13 of the electron gun, the cathode 14 on which the luminance signal Y is applied, the wenehlt 15 of adjusting the brightness of the image, the accelerating grid 16 and the concentration grid 17. Electromagnetic deflection coils, not shown, ensure a suitable deflection movement of the electron beam ₁ 8, coming from the electron gun 13 to 17, so that this beam 18 scans in known manner the surface of the "slab" 19. This slab 19, being constituted by the outer wall of the image tube 20 located opposite the barrel 13 to 17. The result would be equivalent, if instead of 'an electromagnetic deflection tube an electrostatic deflection tube was used, the bulb would also have plates X1, X ₂ and Y,, Y ₂ to ensure the deflection of the electron beam in two dimensions.

As shown in FIG. 3, this glass slab 21 is provided on its inner face with a filtering layer (gray filter) 22, and with a stack of thin layers comprising three superimposed electroluminescent transducers. These three transducers consist of three luminescent layers 23, 24 and 25 and four conductive layers 26, 27, 28 and 29; the luminescent layers 23, 24 and 25 are made of a material which is both electroluminescent and cathodoluminescent, each containing a "doper" of different nature, allowing respectively the emission of green, red and blue light under the conditions described in FIG. 1. To this end, each electroluminescent layer 23, 24 and 25 is located between two conductive layers 26 and 27, 27 and 28, 28 and 29 respectively. As in the case of FIG. 1, buffer layers 30 are interposed between the luminescent layers 23 to 25 and the conductive layers 26 to 29.

The conductive layer 29 located on the inside of the tube 20 may be a thin layer of aluminum or copper, brought to a high positive potential. The purpose of this thin layer is to increase the conductivity of the screen and to act as a mirror for the light rays emitted by the luminescent layers, the light rays are all reflected forward.

• - pour 23 du terbium (Tb), donnant une lumière de longueur d'onde 545 nm (nanomètre) lumière verte,
• - pour 24 de l'europium (Eu), donnant une lumière de longueur d'onde 620 nm (rouge),
• - pour 25 du Thullium (Tm), donnant une lumière de longueur d'onde 450 nm (bleu)

Layers 23, 24 and 25 have as their matrices zinc sulphide, ZnS, associated with doped molecules, containing oxysulphides to limit the molecule-matrix interactions. The activators are:

• - for 23 terbium (Tb), giving a light of wavelength 545 nm (nanometer) green light,
• - for 24 of europium (Eu), giving a light of wavelength 620 nm (red),
• - for 25 Thullium (Tm), giving a light of wavelength 450 nm (blue)

The layers 26, 27 and 28 are layers of tin oxide Sn0 ₂ or indium oxide In ₂ 0 ₃ . The layers 30 are layers of yttrium oxide Y ₂ 0 ₃ . The conductive layer 29 is a 1000 A aluminum layer.

The brightness amplification coefficient, the main theme of this invention is 10 to 15% on each transducer. What allows for a brightness equivalent to a normal reception in color TV, to decrease the amplification video, it is even possible instead of using an analog amplifier with high supply voltage from + 150 V to + 180 V , to use a digital amplifier with voltages from + 15 V to + 25 V.

• Ey = 0,30 E_R + 0,59 E_V + 0,11 Eg

To respect the color laws that meet the equation:

• Ey = 0.30 E _R + 0.59 E _V + 0.11 Eg

• La première cellule vers l'observateur est la cellule verte, la seconde cellule qui subit une atténuation d'environ 40% pour traverser la cellule précédente, est la cellule rouge, la troisième cellule ayant deux cellules à traverser subit une atténuation de 60 à 80%, est la cellule bleue.

Conditioning the mixing of the electrical chrominance signals in addition to the matrixing of the signals inside the chrominance amplifiers, a mechanical arrangement of the stacking of the cells contributes to the same result, namely:

• The first cell towards the observer is the green cell, the second cell which undergoes an attenuation of approximately 40% to cross the previous cell, is the red cell, the third cell having two cells to cross undergoes an attenuation of 60 to 80 %, is here blue cell.

For reproduction in color television, the different light points to be reproduced are: yellow, cyan, purple, green, blue, red, white. The green, red, and blue transducers by their separate operation or simultaneously 2 by 2 determine the set of colors.

As shown in FIG. 4, the tube 20 reproduces the color images of a television program in the following manner: a reception and demodulation block 31 picks up the HF waves on its terminal 31 A, and delivers the video signal of luminance Y on terminal 31 B, this is applied to cathode 14 of tube 20. The chrominance video signal delivered on terminal 31 C is applied to input 32 A of the chrominance decoding block 32. This set of decoding elaborates the green, red and blue chrominance signals respectively on the output terminals 32 B, 32 C, 32 D. These voltages delivered in 32 B, 32 C and 32 D are proportional to the green, red, blue chromatic component of the emission and are applied respectively between layers 26 and 27, 27 and 28, 28 and 29.

For compatibility in all black and white standards, the chrominance signal decoder 32 does not deliver any signal at the output of the green, red, blue amplifiers at 32 B, 32 C, 32 D. The television works like a black television and plain white. At the point of impact of the cathodic bombardment, the kinetic energy of the electrons on the electroluminescent parts of the three transducers causes a white point of light to appear, with a brightness proportional to the voltage of the video-luminance signals applied to the tube cathode.

Starting from the block diagram in FIG. 4, a black and white receiver, to which a monochrome picture tube is replaced by a picture tube with chromatic electroluminescent transducers 20, and which a decoder stage 32 is added, will produce according to the characteristics of the invention, a color image for defining and restoring hues and optimal nuances. e

Another characteristic of the invention is that the brightness of the tube with transducers is very important, and by slightly increasing the supply voltages of the tube, a projection on a large screen by a SCHMITT optic is possible.

The detailed description of the use in color television is only an important application but not limiting. Applications in very diverse branches such as: data visualization, oscillography, radar, industrial and medical television, audiovisual, telematics, IT, advertising, should bring new industrial outlets .

The use of this technological innovation in the reception of television signals in all world standards, and the compatibility with black and white must give a rapid increase in color receivers, with great reliability, ease of construction. a significantly lower cost price.

Claims (9)

1. Apparatus for generating images, in at least two colors, characterized in that it comprises: a) a stack of at least two layers each made of a luminescent material emitting light, of a determined wavelength, different from that of the other luminescent layer. b) a particular control device associated with each luminescent layer to generate in this layer a variable electric field, the rate of change of which is a function of the amplitude of a corresponding color signal. c) means for directing an excitation beam over the entire surface of the stack, this beam having an intensity as a function of the amplitude of a luminence control signal and being associated with a scanning movement, such as its impact on the stacking surface moves in two dimensions. d) generators for supplying said color and luminance control signals. 2. Apparatus according to claim 1, each luminescent layer has a thickness between 0.4 and 2 µ and preferably between 0.4 and 0.8 µ. 3. Apparatus, according to claims 1 and 2 the material constituting the luminescent layers is chosen from the following materials: ZnS, ZnO, SrS, CaW0 ₄ , Zn ₂ SiO ₄ , CaF ₂ , MgGe0 ₄ , CdS, CdF ₂ , doped with using at least one of the following impurities: fluorides of Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm. 4. Apparatus according to one of claims 1 to 3, because to increase the electric field in the electroluminescent layer, one or two buffer layers, made of an insulating material with high dielectric factor are arranged on one side or on each side of the electroluminescent layer. 5. Apparatus according to claim 4, each buffer layer has a thickness between 0.2 to 0.8 µ and that the material used is Y ₂ 0 ₃ . 6. Apparatus according to claims 1 to 5, because in that the control device associated with an electroluminescent layer and the buffer layers comprises two conductive layers, semi transparent, arranged on either side and connected to the signal generator. color control. 7. Apparatus according to claim 6, because the conductive layers are made of a material such as Sn0 ₂ , or I ⁿ⁰ 3 ^. 8. Apparatus according to claims 1 to 7, characterized in that the excitation beam is an electron beam. 9. Apparatus according to claims 1 to 8, because the stack comprising three electroluminescent layers, radiating respectively in blue, red, green, allows the restitution of colors in their respective hue and shine with maximum definition.

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