GB763744A - Method of making a photo-conductive sheet for a radiation amplifier - Google Patents

Abstract

763,744. Photo-conductors. STANDARD TELEPHONES & CABLES, Ltd. June 11, 1954 [June 17, 1953], No. 17287/54. Class 37. [Also in Group XL (a)] A photo-conductive sheet for a radiation amplifier, is produced by embedding a plurality of elongated photo-conductive particles in a film of sticky substance, the longitudinal axes of the particles being normal to the plane of the film. In Fig. 1, the sticky substance 3, such as cellulose acetate or wax, is applied to a baseplate 1, and a quantity of photo-conductive particles such as cadmium sulphide is spread over a plate 2. A high potential is applied between plates 1 and 2 so that the particles are oriented into alignment with the electric field, and propelled towards plate 1 to become embedded in layer 3. A layer 9 of an insulating liquid binder such as wax or plastic, is applied to layer 3, as shown in Fig. 3. Layers 3 and 9 are removed as an assembly, and the surface may be lightly ground to provide a smooth surface containing the exposed ends of the particles. This assembly may then form the photo-conductive layer 10 (Fig. 4) of a radiation amplifier comprising electro-luminescent layer 13, transparent metallic electrodes 12 and 14, and glass sheets 11 and 15. When potential is applied between electrodes 12 and 14, the electric field across any part of the electroluminescent layer 13 is proportional to conductivity of the corresponding part of layer 10, and hence an image projected on layer 10 appears in intensified form on layer 13, as described, for example, in Specification 749,798, [Group XL (a)]. The luminescent layer may be a mixture of zinc oxide and zinc sulphide activated by copper. The photo-conductive particles may be produced by evaporation of metallic cadmium in an atmosphere of hydrogen sulphide and hydrogen. In an alternative method of producing the photo-conductive layer, the crystals are suspended on a fine mesh screen placed above the base-plate with the sticky layer, the whole being suspended in an insulating liquid. Alternatively the screen may be placed on the base-plate, or may be left in place in the finished sheet. This method ensures that the individual crystals are spaced apart and thus eliminates any conductivity along the film.