Patent GB-1257194-A (GB)
IPC: H01J29/14
Filed: 1968-07-06
Abstract: 1,257,194. Luminescent and tenebiescent materials and uses thereof. FERRANTI Ltd. 30 June, 1969 [6 July, 19'68], No. 32364/68. Heading C4S. [Also in Divisions H1 and H4] An information display system (e.g. for radar or sonar applications) has an initially transparent or translucent layer of a Groups II and VI compound (e.g. ZnS) and includes means for rendering at least parts of the screen opaque to radiation of two separated parts of the spectrum by absorption centre development, in the visible, U.V., or infra-red for instance (e.g. by electron or radiation incidence), means for causing information input signals to apply a clearing beam of radiation of one the two. separated spectrum partsselectively to opaque regions and means for irradiating the non-displayed face with radiation of the other of thetwo separated parts the arrangement being such that the latter radiation is transmitted by screen regions also irradiated by the clearing beam.. A high pressure Hg lamp 20 with filter 21 may produce U.V. and green radiations, 3650 Š and 5460 Š wavelengths respectively, which are. transmitted through window 12 and silicate phosphor. layer 14 to layer 13 of ZnS not contaminated: with. halogens or Al but with excess Zn ions, the material having been formed by heating, in. Zn vapour or bombarding with neutrons. The U.V. radiation forms uniformly distributed absorption centres in layer 13 and a blue. clearing beam (4300 Š) produced by the electron beam on the phosphor 14 selectively erases, the green light being transmitted at the erasure points. Rapid heat removal is required to reduce thermal bleaching such. as occurs at 300‹ C. The ratio. of the darkening intensity to transmitted light intensity may be altered by units 19 and/or 23. Viewing may be direct or by projection. The.screen.may alternatively be darkened by electrons. (Fig. 2, not shown), the blue erasure beam being from a second c.r.t. (35) with a calcium magnesium silicate phosphor (36) activated with Ti and projected by a Schmidt optical system. Green light (5450 Š) is transmitted through the image from phosphor layer 33 (e.g. ZnCdS:Ag) with. U.V. radiation (3130 Š). The whole screen may be initially darkened or areas 41 may be completely darkened prior to selective erasure and dark information traces may be formed directly on light areas 42. Alternatively in Fig. 2, darkening may be by U.V. radiation (3650 Š) from a barium silicate phosphor layer activated by lead on electron beam excitation. In a further modification, the. darkening: radiation is from a barium silicate layer activated with Pb in c.r.t. (35), the clearing radiation being from layer (33) of calcium magnesium silicate activated by titanium. In a two-gun c.r.t., one electron beam may darken directly and the other produce clearing radiation from a silicate phosphor. Selective and other removal of traces on a long persistence screen may be by using darkening: radiation for light traces- and vice versa, as produced by torches or. mechanical filters to theabove sources. The intensity and/or rate of decay of light portions of the screenmay be controlledby selective electron or U.V. incidence, and relative control of light and dark beams if superposed. Contrast may be controlled by gating information input signals to apply parts to the clearing and darkening means respectively, or alternatively by illuminating the screen face with light of the background colour. The current end of a track may be displayed by partial transmission of the blue clearing beam, and moving objects distinguished from permanent echoes by a dotted light-dark track, and successive shortening or lengthening of the dotted' portions determines object movement direction.