GB353394A - Improvements in light sensitive electric discharge devices - Google Patents

Abstract

353,394. Photo-electric cells. ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Bush House, Aldwych, London.-(Assignees of Knowles, D. D.; 194, Castlegate Road, Wilkinsburg, Pennsylvania, U.S.A.) Jan. 17, 1930, No. 1744. Convention date, Jan. 18, 1929. Void Published under Sect. 91 of the Acts]. [Class 39 (i).] A photo-electric cell has a cathode consisting of a thin layer of an alkali metal or barium on a layer of magnesium, an alkalineearth metal, misch metal, silver, or silver oxide, and a filling of a noble gas such as helium. A cathode consisting of a layer of barium on magnesium has maximum sensitivity in the red region of the spectrum ; by substituting caesium for barium the maximum is displaced towards the blue-green region, and by using rubidium, potassium or sodium as the surface layer the maximum is moved towards the ultra-violet region. Lithium or two or more alkali metals may be used. The lead 2 for the cathode 8 has an extension carrying a disc 4 on which a piece of magnesium 5 is welded. After evacuation of the envelope, the disc is treated by high frequency current and the magnesium is vaporized and deposited on the wall. Alkali metal may be introduced by heating a tube containing the metal; or caesium trinitride may be painted on a part of the disc 4 removed from the magnesium ; or a salt of the alkali metal may be heated by bombardment. The anode 3 consists of a wire enclosed by a glass sleeve 6, the area of the cathode being at least 10 times the active area of the anode.