GB809380A - Improvements in and relating to combined electro-luminescent and photo-conductive devices - Google Patents

Abstract

809,380. Photo-conductive devices. THORN ELECTRICAL INDUSTRIES Ltd. Aug. 1, 1957 [Aug. 28, 1956], No. 26317/56. Class 37. [Also in Group XL (a)] A combined electroluminescent and photoconductive device comprises a super-linear resistor and a circuit connecting an electroluminescent element, a photo-conductive element, the super-linear resistor and sources of alternating and direct voltage so that at least part of the alternating current is prevented from traversing the photo-conductive element and at least part of the direct current is prevented from traversing the electroluminescent element. The two sources 12, 14, Fig. 2, the photo-conductive element 10, the superlinear resistor 11 and the electroluminescent element 13 may be arranged in series as shown, the alternating current by-passing the element 10 by a capacitance 15 and the direct current by-passing the element 13 by a resistance 16. The elements and super-linear resistor may be arranged in layers 10<SP>1</SP>, 13<SP>1</SP> and 11<SP>1</SP>, Fig. 3, respectively, the photo-conductive layer 10<SP>1</SP> containing material of high permittivity forming the capacitance 15, and the electroluminescent layer conductive material forming the resistor 16, the layers being arranged between transparent electrodes 18, 19 and supported on a transparent base 20, an opaque layer 17 being provided to eliminate feed-back. In another circuit arrangement the direct voltage is applied across the photo-conductive element and the super-linear resistor in series and the alternating voltage is applied across the electroluminescent element in series with the same resistor. A super-linear resistor is defined as a resistor in which the current varies as a power greater than unity of the voltage applied thereto, e.g. silicon carbide.