Patent GB-901367-A (GB)
Title: Method of making luminescent screens and systems for producing coloured images therewith
IPC: H01J29/18
Filed: 1958-04-19
Abstract: 901,367. Colour television tubes; luminescent screens; electroluminescence. DAVOHN CORPORATION. April 19, 1958 [April 19, 1957], No. 9005/58. Class 39 (1). [Also in Group II] Method of making a luminescent screen, for use in colour television tubes or electronic display tubes, or for excitation by U.V. rays, X-rays or gamma rays, or for electroluminescent devices with or without photo-conductive layers, comprises the steps of condensing in a high vacuum vaporized solid components of a first luminescent material on a transparent base, e.g. of glass, to form a first thin transparent or translucent film thereon, and then subjecting the film and base to a baking temperature between 500‹ C. and 1200‹ C., further condensing in a high vacuum vaporized solid components of a second luminescent material on top of the first film to form a second thin transparent or translucent film thereon, and then subjecting the base, the first film and second film to a baking temperature between 500‹ C. and 1200‹ C. The second luminescent material can produce light of a different colour when excited than the light produced by the first material. The baking temperature of the first luminescent material should be equal to or greater than that of the second luminescent material. Electrically conducting or non-conducting layers of transparent non-luminescent material can separate the luminescent films from each other and from the base. Light-absorbing means can be placed behind the screen, e.g. in a C.R.T. the interior of the tube can be made black. The luminescent films can be of the materials and formed by the method described in Specification 900,582. In one specific example, Fig. 2, a three-layer screen of zinc silicate 15, magnesium silicate 14 and calcium tungstate 13, each activated by manganese, is described, and the magnesium silicate can be formed in two layers. A conducting transparent layer 18 is formed on top of the last film or next to the base 11 and can be of a metal, tin oxide or copper iodide. The non-luminescent, transparent layers 16, 17, 12 separating the luminescent layers from each other and from the base 11 can be formed by evaporating and depositing layers of non-conducting silicon dioxide, siliconmonoxide or titanium dioxide. A grid 20 is spaced a short distance from the conducting layer 18. To produce differently coloured images the depth of penetration of a scanning electron beam into the layers is varied by varying the potential difference between the layer 18 and the grid 20. Two depths of penetration of the electron beam to the various layers are used to produce combined colours. The conducting layer 18 is about 500 Š thick, the luminescent layer 13 is between 2000 and 5000 Š thick, the luminescent layer 14 is between about 5000 Š and 2 microns thick and the luminescent layer 15 is between I and 3 microns thick. Each of the non-luminescent layers 12, 16 and 17 is between 2000 and 5000 Š thick. The layers 13, 14 and 15 luminesce in blue, red and green, respectively. Layers luminescing in other than the primary colours can be additionally provided. In a modified construction an additional redluminescing layer is provided and the blueluminescing layer is titanium activated calciummagnesium silicate. Combined colours are obtained by causing the electron beam to penetrate to positions between the luminescent layers. A circuit system for controlling the depth of penetration of the electron beam in the screen of Fig. 2 is referred to and is as described in U.S.A. Specification 2,580,073, a separate field scan being used for each colour. A modification of this system for the modified screen referred to above is also referred to, one single scan being used. A method of varying the depth of penetration of the electron beam in the screen by varying the angle at which the electron beam enters the screen as described in Specification 901,368 is also referred to. Another method of controlling the depth of penetration of the electron beam into the luminescent screen is shown in Fig. 5, in which transparent conducting layers 56 and 57 of titanium oxide or copper iodide, instead of non conducting layers, separate the luminescent layers 13, 14 and 15, a non-conducting layer 12 separating the luminescent layer 15 from the base 11. Leads 44, 45, 46 and 47 connect the layers 56, 57, the conducting layer 18 and the grid 20 to the colour control circuit 25 for varying the potentials thereto.