GB820800A - Improvements in or relating to arrangements including electroluminescent and photoconductive elements - Google Patents

Abstract

820,800. Electroluminescence. GENERAL ELECTRIC CO. Ltd. April 8, 1957 [April 9, 1956], No. 10776/56. Class 39(1). In a photo-conductive electroluminescent combination, the electroluminescent element and the photoconductive elements are connected in parallel with each other, and the parallel combination is connected in series with a fixed impedance between input terminals across which the input fluctuating voltage is applied, whereby in operation the amplitude of the voltage applied across the electroluminescent element decreases as the conductivity of the photoconductive element increases. As shown in Fig. 3 the combination is formed as a unitary structure, comprising a photoconductive layer 16, an electroluminescent layer 18, a first electrode 17 between these layers and two transparent electrodes 15, 19 on the outer faces of the layers 16, 18, the first electrode 17 being connected via a capacitor 23 to one terminal 22 of the supply and the two transparent electrodes 15, 19 being connected to the other terminal 21 of the supply. The capacitor may form part of the unitary structure. The first electrode 17 may be partly transparent or in the form of a grid so that controlled feed-back between the electroluminescent and photoconductive elements may take place to achieve linearity of response of the device. An image intensifier may comprise a multiplicity of such arrangements in the form of a mosaic. In another embodiment, Fig. 4, a unitary device comprises a first transparent conducting coating 31, a dielectric layer 30, a conducting grid 27 with a conducting element 28 located in, but not in contact with, each grid aperture, a deposit of photoconductive material 29 in the interstice between each element 28 and the adjacent part of the grid, an electroluminescent layer 26, an opaque insulating layer 34 and a second transparent conducting coating 25. The arrangement and connections are such that each individual photoconductive element is provided by the material 29 between each element 28 and the adjacent part of the grid 27, the corresponding electroluminescent element between the conducting element 28 and the second coating 25 and the corresponding fixed impedance in series with these two elements is provided by the capacity between the conducting elements 28 and the first conducting coating 31. Feed back may be provided by making the layer 34 partly transparent or translucent. Two arrangements of either embodiment may be so disposed that radiations emitted by the electroluminescent element of one arrangement are incident on the photoconductive element of the second arrangement, so that a radiation image incident on the photoconductive element of the first arrangement is reproduced as a luminous display image by the electroluminescent element of the second arrangement. The electroluminescent material may be copper activated zinc sulphide.