GB1332743A - Electroluminescent devices - Google Patents

Abstract

1332743 Radiographic screens THORN ELECTRICAL INDUSTRIES Ltd 16 April 1971 9684/71 Addition to 1185832 Heading H5R [Also in Division C4] An EL device comprises a device as in parent Specification 1,185,832, with a further layer 16 comprising a flexible and resilient metallic sheet. The device such as a radiographic screen of flexible laminated construction includes first transparent electrode 11, EL phosphor layer 12, dielectric layer 14, a second electrode 15 and strengthening backing sheet 16 adjacent or in contact with electrode 15. The first electrode may be a plastics sheet bearing a conductive film obtained by vapour or solution deposition process, the phosphor may be dispersed in an organic resin or lacquer, the dielectric is dispersed in a resin layer and the second electrode a thin metal foil or a deposited coating which may be transparent. The metallic backing sheet may be of stainless or spring steel of thickness 0À001 to 0À010 inches, preferably stainless steel 0À002 to 0À005 inches. Excitation may be X-rays, U.V., or cathode rays. The layer 13 of irradiation responsive material includes ZnO for instance, whose electrical characteristics are altered when irradiated, such that after irradiation light emission occurs on electrical field application, emission ceases on removal of field, and recommences on field reimposition. Eradication may be by heat or infra-red radiation, the metallic backing sheet ensuring that during heating the device retains its resiliency, and promotes uniformity of heating, ensuring more even image eradication and also absorbs X-rays. Encapsulation of the device is preferred, and may be wholly or partially enveloped in a plastics material 17, and is preferably omitted on the face of the first transparent electrode for photographic contact printing. The envelope material overlying layer 18 may be transparent and the remainder opaque. Film 11 can be applied to plastics sheet 18 by evaporation of Au, Ni, Cr alloys or indium compounds or as described in Specification 1,129,816. Phosphor 12 may be of green emitting ZnS in a plastics material layer 14, a dielectric material, e.g. barium or barium strontium titanate in a plastics material, electrode 14, a metal foil, evaporated metal film or a conducting paint, and contacts may be metal ribbons or eyelets entering envelope 17. Features as in Specification 1,190,421 may be included, such as a dye-stuff or other colouring material in the phosphor layer or in the path of light passing to the outside of the device to increase contrast.