GB1300548A - Improvements in or relating to electroluminescent devices - Google Patents

Abstract

1300548 Electroluminescence TECHNOLOGY MINISTER OF 27 Feb 1970 [28 Jan 1969] 4566/69 Heading C4S A process for making an electroluminescent device comprises producing phosphor particles 4 of a compound or compounds of an element of Group IIb (e.g. Zn) with an element of Group VIb (e.g. S or Se) with an admixture of an activator, coating the particles with an element of Group Ib (e.g. Cu, Ag or Au) so as to introduce atoms of the element into the external surface of the particles, embedding the coated particles in a translucent matrix 5 (e.g. 50Á thick) and arranging in contact with two electrodes 2a, 2b and passing a forming direct electrical current (e.g. 0À5 to 5 watts cm.<SP>2</SP>) between the electrodes until the electrical resistance is increased (e.g. x 10) in a localized and predetermined region 7 of the phosphor layer, whereby the electroluminescence, A.C. or D.C. of either polarity, of the localized region in subsequent use is at least 100 times what it would have been if uncoated particles had been used. The translucent matrix may be polymethylmethacrylate or nitrocellulose. The localized region may be letter or figure shapes, a groove 6 being cut or scribed in the surface, to locally constrict the cross-sectional area of the phosphor layer through which forming current is to pass, a conductor etched, or heat applied to or generated within by applied visible or near infra-red radiation through masks to subject regions to distinct physical conditions which give rise to local heating Alternatively, the electrodes themselves may determine the localized region, this forming near the positive electrode. Doubly illuminated letters may be formed by using a double gap with a narrow intermediate conducting strip. The compound is preferably ZnS or ZnSe or mixtures or solid solutions of same and the activator preferably Mn or Cu and Mn. The particle to binder weight proportions may be 10 to 25%. The device is preferably encapsulated in a translucent vessel (18) containing inert gas, e.g. N 2 , with a drying agent (20) to increase its life (Fig. 3, not shown). High resistance regions form corresponding to gaps 26a, 26b to outline the letter "A" (Fig. 4, not shown). A sand wich device (Fig. 5, not shown) includes tin or indium oxide electrode (31) and Al graphite or Cu strip electrode (32). With orthogonally arrayed strips (31A) (32A) the Group Ib element is usually present as part of a complex surface phase in which atoms of the host lattice may in part have been replaced by the Group Ib element. The Group Ib element can be coated on to the phosphor particles by the use of organometallic compounds or by reacting the particles with a salt of the Group Ib metal in solution. Cu may be present in the coating in amount 0À2% by wt. of the phosphor particles. Incorporation in battery and transistor circuits is instanced.