GB1223153A - Solid-state energy-responsive luminescent devices - Google Patents

Abstract

1,223,153. Electroluminescence. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 23 Feb., 1968 [24 Feb., 1967], No. 9032/68. Heading C4S. An electroluminescent device comprises a semi-conductive electroluminescent layer 103 comprising electroluminescent powder and resistive metal oxide powder (e.g. SnO 2 , TiO 2 , WO 3 , Sb 2 O 5 ), which reflects the luminescent light, the two powders being mixed in a vitreous medium, photoconductive layer 106, electrodes 102, 107 and A.C. and D.C. sources 110, 111 for applying superimposed voltages, the structure constituting a single series circuit (Fig. 1, not shown). The photo-conductive sensitivity of layer 106 under an A.C. voltage increases as the D.C. voltage increases and the D.C: resistance of the electroluminescent layer is lower than the D.C. resistance of the photo-conductive layer in the dark state. The electroluminescent layer may be 30 to 60 micron thick ZnS: CuAl mixed with varying amounts of semi-conductive and reflective metal oxide bound in a vitreous material, to control the resistivity. Relative gradings, softening points, expansion coefficients, and vitreous material examples are considered and electroluminescent layer resistivities in the range 10<SP>7</SP> to 10<SP>9</SP> ohm. cms. disclosed. 10 micron layer 104 may be of light reflective ferroelectric BaTiO 3 and SnO 2 or TiO 2 in a vitreous on plastic material, for ohmic and non- ohmic layers respectively and 10 micron semiconductive layer 105 may be black paint mixed with non-linear resistivity powder CdS: Cl or linear resistivity carbon black powder, these layers preventing breakdown and facilitating resistance matching. Also the raised dielectric constant reduces A.C. voltage losses in the intermediate layers. Photoconductive layer 106 may be 200 to 500 micron thick including plastics binder and sensitive to visible light X-rays, infra-red and ultra-violet rays. Photoconductive material may be CdS activated with a Group IB element (e.g. Cu, Ag) and a Group VII B element (e.g. Cl) or a Group IIIB element (e.g. Al, Ga). To improve X-radiation sensitivity, ZnCdS:Ag phosphor may be added to photo-conduct ve CdS: Cu, Cl in a plastic binder the additions also increasing resistivity and dielectric strength. Al electrode 107 may be a parallel line mesh or lattice pattern. For feedback operation, layers 104 and 105 may be omitted and electroluminescent layer 103 a composite layer including a semi-conductive non-pervious layer, while for maximum sensitivity the electrode adjacent the electroluminescent layer is positive.