Method of making electroluminescent devices

Claim 1

A process for making an electroluminescent device which comprises producing phosphor particles made of at least one compound each of an element of Group IIb with an element of the group consisting of sulphur and selenium intermixed with an activator, coating said phosphor particles with an element of Group Ib, embedding said coated particles in a translucent matrix, arranging the particle-bearing matrix as a single phosphor layer in contact with and between two electrodes, forming the interface between a selected one of the electrodes and the phosphor layer to conform to a desired configuration of shape, and increasing the electrical resistance in the phosphor layer in a localised predetermined region which is relatively near to the interface with the positive electrode by passing a forming direct electrical current between the two electrodes and through said localised region with the selected electrode functioning as the positive electrode, whereby when an electrical current is subsequently passed between the electrodes when the electroluminescent device is used in service, the luminescence of the predetermined region of the phosphor layer is at least 100 times what it would have been if uncoated phosphor particles as aforesaid had been used.