Patent GB-900582-A (GB)
Title: Luminescent screens and methods of making same
IPC: H01J9/22
Filed: 1958-04-02
Abstract: 900,582. Luminescent screens. DAVOHN CORPORATION. April 2, 1958 [April 5, 1957 (2) ; April 8, 1957], No. 8680/58. Class 39 (1). [Also in Group II] Method of making a luminescent screen for use in cathode-ray tubes comprises the steps carried out within a high vacuum of evaporating an oxygen-containing phosphor matrix or the components thereof, and an activator, either separately or together, and condensing the resulting vapours on a smooth surface of a refractory non-oxidizing base to form a thin film thereon, and then subjecting the film and base to baking in the presence of oxygen, e.g. air, at a temperature, e.g. between 500‹ C. and 1200‹ C., and for a time up to 3 hours sufficient to form a transparent or translucent activated crystalline oxygen-containing phosphor film. The longer the period of baking the more translucent the film becomes. Preferably the baking temperature is maintained within a range of 750‹ to 1100‹ C. for a period of 5 minutes to 1 hour. The phosphor matrix can be zinc phosphate with 1-10 mols. per cent of manganese as activator as described in Specification 900,584 and the baking can be at a temperature between 500‹ C. and 800‹ C., or the phosphor matrix can be a metal silicate or silicates, e.g. of zinc, calcium or magnesium with manganese or titanium as the activator, and the baking can be at a temperature between 1000‹ C. and 1200‹ C., preferably at about 1100‹ C. for between 15 minutes and 1 hour. Other luminescent materials referred to are cadmium and zinc beryllium silicates, magnesium, calcium and cadmium tungstates, calcium and cadmium phosphates, zinc and cadmium sulphates, zinc oxide and zinc borate, with activators of manganese, manganese in combination with lead, titanium, and the rare earth metals. Commercial activated phosphors can be vaporized to form the film. The base on which the luminescent film is deposited can be transparent, e.g. of glass, silica glass such as quartz glass, or " Vycor " (Registered Trade Mark) glass, or opaque, e.g. of platinum or a ceramic metal oxide such as aluminium oxide. Screens with a transparent base can be used in cathode-ray tubes for daylight viewing, the inner surface of the wall of the tube being covered with a light absorbing coating, e.g. of " Aquadag " (Registered Trade Mark). Apparatus for carrying out the method is shown in Figs. 1 and 2 and comprises a glass vessel 1 arranged in vacuum-tight relationship on a polished steel platform 2 by means of a gasket 3 of heat-resistant rubber (Neoprene), a conduit 4 being used for evacuation to a pressure of the order of 10<SP>-4</SP> to 5 X 10<SP>-5</SP> mm. A tantalum boat-shaped vessel 5 for containing the materials to be vaporized is supported by brass standards 6 and clamping pieces, electrical leads 7 and 8 being connected to the standards. A metal standard 9 carries a steel ring 10 adjustably mounted thereon by a slidable clamping arm 11, the base 12 to be coated with the luminescent film resting upon the ring 10. A radiant heater 13 is adjustably mounted on the standard 9 by a slidable clamping arm 14, is connected to electrical leads 15 and 16 and is used for outgassing the base 12 prior to the coating operation. In order to effect baking of the film after deposition on the base 12, the base is inverted as shown in Fig. 2 to present the film directly to the heater 13, a plate of tantalum being placed between the base and the ring support 10 and a thermocouple being placed on the plate. Alternatively, the baking in air can be carried out in a conventional electrical furnace.