A FLUORESCENT GAS DISCHARGE DISPLAY PANEL

Abstract: A fluorescent gas-discharge display panel, in which a fluorescent material (8) is excited by a gas discharge therein, contains a gas mixture of neon, argon and xenon as the discharge gas (9). Typically, the argon gas content is more than 5% by partial pressure, and the xenon gas less than 10%. The argon gas content contributes to produce a pure and high peak of green light spectrum and to reduce the orange light spectrum produced by the discharge of the neon gas. Other characteristics, such as operation voltages, brightness, luminous efficacy, and operation life, are kept satisfactory.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a fluorescent gas-discharge panel. More particularly, this invention relates to an improvement to the gas contents of the discharge gas, which is capable of producing a color display by exciting a fluorescent material. Description of the Related Art Various types of fluorescent gas-discharge panels utilizing an ultra violet light generated by a gas discharge, either DC (direct current) driven or AC (alternate current) driven, have been practically in application for displaying characters as well as images. It is also well known that a color display is achieved by providing plural kinds of fluorescent materials installed in the discharge panel, and each excited by an ultra violet light generated in respectively associated gas discharge. A typical configuration utilizing a surface discharge, such as shown in the accompanying FIGS. 1 and 2 or such as the one disclosed in U.S. Patent No. 4,638,218 by the inventor of the present invention, is considered of particular interest to realize a gas discharge color display panel by the use of plural fluorescent materials. Basically, in such a surface discharge type panel, the discharge electrodes (3, 4, 6 & 7 in FIG. 1) are provided on only one substrate 1 of a pair of substrates forming the panel envelope. On the inner side of the other facing substrate 2, a fluorescent material layer 8 is provided, which is excited by the ultra violet light generated by the gas discharge on the facing substrate. Thus, the color determined by the respective fluorescent material is emitted. The electrodes for the gas discharge are mutually isolated and arranged in mutually orthogonal X and Y directions on the substrate 1. Surfaces of these electrodes are covered with an insulation material 10 having high secondary-electron emissivity, such as magnesium oxide, MgO. This configuration allows the fluorescent material to be prevented from direct bombardment of the ions produced in the discharged gas, and has therefore been employed in order to achieve a long life operation of the fluorescent material. Discharge gases which emit an ultra violet light for exciting a fluorescent material to emit a visual light have been extensively studied as disclosed by Kagami et al in U.S. Patent No. 4,085,350. A two-composition gas, such as a mixture of helium gas and xenon gas (He + Xe) is well known and has been used for a multiple color display where purity of the emitted color is important. The xenon gas is used to lower the discharge firing voltage as well as the discharge sustain voltage known as Penning effect. With such a gas compostion, the heavy xenon ions bombard the MgO surface layer coated over the electrodes, causing the MgO layer to be rapidly deteriorated and, thus, the operating life to be shortened. Argon gas, which is heavier than helium, could be effectively added to form a three-composition gas mixture (He + Ar + Xe) in order to lower the energy of the xenon ions which bombard the MgO surface. However, such a three-composition gas shows a disadvantage in that the operation voltages are increased. A two-composition gas, e.g. Ne + 0.2% Xe, (where the percentage indicates the ratio of the partial pressure of the gas; this will also be the case in the remainder of the specification), has been also used for exciting a mono color display. One such display is disclosed in patent document GB-A-1559272. However, the orange visual light of the neon gas discharge deteriorates the color purity. In a gas discharge panel for practical use, a long operating life, a low operating voltage, a sufficient luminescent brightness, and a sufficient color purity are all naturally important requirements. However, none of the prior art devices can satisfy all these requirements at the same time. SUMMARY OF THE INVENTION It is therefore a general object of the invention to provide a flurorescent gas-discharge color display panel having a long operating life, a low operating voltage, an adequate luminescent brightness, and an adequate color purity as well, by improving the gas contents. It is another object of the present invention to provide a gas-discharge multiple-color display panel whose emission contains suppressed orange spectrum. The above objects are reached by a fluroescent gas-discharge display panel in which a discharge gas, composed of neon and xenon gases, radiates an ultra violet light to excite a fluorescent material to light, wherein according to the present invention argon gas is added to the discharge gas in a quantity exceeding 5% by partial pressure so as to suppress the visible light spectrum of neon gas dischage. Preferably, the content of the argon gas in the discharge gas is more than 5%. Due to the addition of argon gas, the orange spectrum of the neon gas discharge is suppressed. The above and other features and advantages of the present invention will become apparent from the following description made with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a cross-sectional view of a fluorescent gas-discharge panel of surface discharge type, Fig. 2 shows a plan view of the discharge electrodes configuration of the fluorescent gas-discharge panel of fig. 1, Fig. 3 shows the effect of argon gas content in neon on operation characteristics, Fig. 4 shows the effect of the invention on light spectrums, Fig. 5 shows changes in operational characteristics during operation of the panel, and Fig. 6 shows the effect of xenon gas content on the operation characteristics. DESCRIPTION OF PARTICULAR EMBODIMENTS The structure and operation of an embodiment of a panel according to the present invention is hereinafter described. It is to be noted that the structure and operation of surface discharge type display panels of the type of which the present invention relates to are well known as disclosed by T. Shinoda et al in "Green Surface-Discharge Plasma Decode Displays" at pages 51 to 54 of 1985 International Display Research Conference. A pair of glass substrates, i.e. a first substrate 1 and second substrate 2, form an envelope of a gas discharge panel (FIG. 1). A plurality of paired parallel display electrodes 3 and 4 are arranged on the first substrate 1 in a lateral direction (Y direction). A dielectric layer 5, made of a low melting point glass, is formed on the display electrodes 3 and 4 except in portions AC and DC shown by dashed circles in FIG. 2. Details of these portions AC and DC will be described later on. A plurality of insulation ribs 6 and address electrodes 7 are provided on the dielectric layer 5. Each address electrode extends along one side of a respective insulation rib 6; the insulation ribs 6 and address electrodes 7 extend in longitudinal direction (the X direction) for delineating the discharge cells. The surfaces of the address electrodes 7 and of the dielectric layer 5 are covered with a thin surface layer 10, as thin as several tenths of microns, made of magnesium oxide MgO. Facing the above-described first substrate, a layer 8 of fluorescent material is formed on the inner surface of the second substrate 2. In a case where the displayed color is monochromatic, the fluorescent layer 8 is formed of, for example, a fluorescent material emitting a green light, such as of Zn₂SiO₄ family, and covers uniformly all the substrate surface. In a case where multiple colors are displayed, a fluorescent material for each color is coated as a spot or a stripe on the second substrate 2 corresponding to a respective discharge cell or line of discharge cells (where "a line" means a row of cells along paired electrodes 3 and 4 or along an address electrode 7) on the first substrate 1. The substrates 1 and 2 are assembled in facing relationship, being separated by a predetermined distance, are vacuum-tightly sealed at their periphery, and a discharge gas 9 is filled therein. In the above-described configuration, an address discharge cell AC is formed at a location corresponding to an intersection between a display electrode 3 and an address electrode 7, and a display cell DC is formed on the display electrodes at a location closest to a corresponding address discharge cell AC. A pair constituted by an address cell AC and a display cell DC adjacent to each other forms a single pixel. For operation of the panel, a voltage higher than the firing voltage is first applied between paired display electrodes 3 and 4 to initiate gas discharge of all the cells on the line formed by the display electrodes. Next, the gas discharge of display cells DC of unnecessary pixels in the line is erased by discharging the associated addressing cell AC. Repetition of this operation on each line formed by paired display electrodes allows all the pixels on the panel to be written with display information. According to the present invention, the discharge gas 9 filled in the discharge gaps in the panel is modified to improve the characteristics of the display panel, the modification consisting in the addition of argon gas to the discharge gas composed of a mixture of neon gas and xenon gas. Effects of adding argon gas into (neon+xenon) gas are shown in FIG. 3 and FIG. 4. In FIG. 3, operating characteristics such as variations of chromaticity (X), chromaticity (Y), brightness B, minimum firing voltage Vf1, maximum firing voltage Vfn, minimum sustain voltage Vsm1, maximum sustain voltage VsmN and luminous efficacy are shown for variable contents ratio of argon in neon gas, in which xenon gas is present with a constant content of 0.2%, and the gas pressure being 80000 Pa (600 Torr). The fluorescent material 8 used therein is a widely used green fluorescent material P1G1 (Zn₂SiO₂: Mn) uniformly coated all over the surface of the second substrate 2. It is observed in this figure that the existence of the argon gas with a content of more than 5% cancels the visible orange emission from the neon gas discharge, and improves the brightness as well. In the range where the argon gas content is more than 80%, the operating voltages become so high as to increase the cost of the driving circuits, and the luminous efficacy. Therefore, this composition range is not suitable for practical use. Wave length spectrum of the emitting light is shown in FIG. 4, where the same fluorescent material P1G1 as mentioned hereinbefore with reference to FIG. 3 is used. Chain line I shows the spectrum obtained with a discharge gas whose composition is Ne + Ar (20%) + Xe (0.35%) at a pressure of 86500 Pa (650 Torr), whereas solid line II shows the spectrum obtained with a prior art discharge gas whose composition is Ne + Xe(0.2%), for comparison. It is evidently observed in the figure that the orange light components indicated by "OR" obtained with the prior art gas have disappeared in the spectrum I when adding argon gas to the discharge gas according to the present invention. Furthermore, the peak value of the spectrum component of green light whose wave length is approximately 540 nm is increased to be almost twice of that reached with the prior art discharge gas composition. FIG. 5 illustrates the operating life, i.e. the variations as a function of time of the characteristics of a panel according to the invention having a discharge gas whose composition is Ne + Ar(20%) + Xe(0.35%) at a pressure of 86500 Pa (650 Torr) (same as the one corresponding to spectrum I in FIG. 4). The notations given to each curve in FIG. 5 are the same as those appearing in FIG. 3. It is observed that each voltage characteristic shows almost a flat transition, except during the early stage of the life, and extends stably beyond 2000 hours at least. Curve B showing the brightness remains at a level above 100 cd/m², a practical requirement, for a long period. Chromaticity (X) and chromaticity (Y) show that there is no change in the chromaticity during the operation period. The function of the xenon gas in the three-composition gas mixture is not only for lowering the firing voltage as well as the sustain voltage of the gas discharge (Penning effect), which is the original purpose, but also for emitting by itself a light of ultra violet spectrum to excite the fluorescent material during the discharging, thus improving the luminous efficacy, and its ion gives a considerable effect on the memory effect as the wall charge for an AC (alternating current) drive type gas discharge panel. FIG. 6 illustrates the effects of the xenon gas content on the operation characteristics of the panel in the case where the gas mixture is composed of Ne + 20%Ar + Xe at a pressure of 5300 Pa (400 Torr). It can be observed that a xenon gas content below 10% is effective to achieve adequately low operation voltages. If low operation voltages are particularly desired, a xenon gas content of 8% maximum is preferred. Thus, the neon gas whose use has been avoided for multiple color display because of its orange spectrum can be used now in a three-composition gas including argon gas, achieving a long operating life, adequately low operation voltages, and pure fluorescent light emission of an adequate brightness. Although the above-described embodiment refers to fluorescent panel of a surface discharge type with an AC drive, it is apparent that this invention is applicable to a wide variety of gas discharge panels where the light generated by the gas discharge excites a fluorescent material to emit a display color regardless of the driving type.

Claims: 1. A fluorescent gas-discharge display panel having: first and second substrates (1, 2) positioned substantially parallel to each other, for defining a space (9) containing a discharge gas, a plurality of electrodes (3, 4, 7) for discharging said discharge gas, said electrodes being positioned on an inner surface of at least one of said substrates; and a layer (8) of a fluorescent material in said discharge gas space, said layer being so located as to be excited by ultra violet light generated by gas discharge in said discharge gas space, characterized in that: said discharge gas is composed of a mixture of neon and xenon gases further added with argon gas, the content by partial pressure of said argon gas in said discharge gas being more than 5% so as to suppress the visible light spectrum of neon gas discharge. 2. A fluorescent gas-discharge display panel according to claim 1, characterized in that the content by partial pressure of said xenon gas in said discharge gas is less than 10%. 3. A fluorescent gas-discharge display panel according to claim 2, characterized in that the content by partial pressure of said xenon gas in said discharge gas is less than 8%. 4. A fluorescent gas-discharge display panel according to any one of claims 1 to 3, characterized in that said fluorescent layer (8) is composed of plural kinds of fluorescent materials each of which is provided in a position corresponding to a respective discharge location defined by said electrodes (3, 4, 7) so as to emit different colors excited individually by said ultra violet light of said gas discharge.

Inventors: NANTO, TOSHIYUKI, SHINODA, TSUTAE
Applicants: FUJITSU LIMITED
Application year: 1988
Main classification: H01J17
IPC codes: H01J17, H01J11