GB426789A - Improvements in and relating to fluorescent screens - Google Patents

Abstract

426,789. Fluorescent screens. SIEMENS-REINIGER-WERKE AKT.-GES., 31, Karlstrasse, Berlin. Oct. 5, 1933, No. 27454. Convention date, July 6. [Class 98 (i)] [See also Group XL] A fluorescent screen has the active layer protected by a light filter, which transmits the light issued by the screen but is opaque to light which diminishes the power of luminescence of the active layer, as by chemical change or discolouration. The filter may also modify the spectral composition of the light issued by the screen. A screen comprising a layer of zinccadmium sulphide protected by a filter, transparent to the yellow light emitted by the sulphide and opaque to green light, may be used in daylight. Suitable filters for a particular luminescent material are selected by a long exposure of the material covered by strips of different coloured filters to daylight, and afterwards noting under what filters the material has lost the power of response to the radiation to be employed; another screen under a series of filters is exposed to the exciting rays to ascertain the absorption of the emitted light by the filters used. From the two sets of results a filter is selected, which excludes such light as diminishes the power of luminescence but does not absorb the light emitted under radiation. The light filter may be a layer applied to the screen ; or a colouring material may be added to the binding medium (for example cellulose ester or cellulose ether). Lead glass plates used on screens for Rontgen ray examination may constitute the filter. Screens in a container, e.g. in a Braun tube, may have the filter supplied by tinting or coating the container wall with a coloured coating, for instance a glass flux of low melting point. Specifications 372,827 and 396,601 are referred to. The Specification as open to inspection under Sect. 91 also describes filters for use with materials which are phosphorescent under daylight, the filters being opaque to those rays which cause the phosphorescence. A filter opaque to blue light may be used with a screen coated with zinc sulphide as the fluorescent material, the blue rays being those which would cause phosphorescence in daylight. This subject-matter does not appear in the Specification as accepted.