Patent GB-701033-A (GB)
Title: Improvements in or relating to phosphors for the colour modification of light sources
IPC: C09K11/66
Filed: 1949-09-02
Abstract: 701,033. Discharge lamps; luminescent materials. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Sept. 2, 1949 [Oct. 21, 1948], No. 22757/49. Class 39(1) A luminescent material for use in colour modifying the light from a discharge lamp has the approximate gram molecular composition wMgO. xBeO.yMgF 2 .GeO 2 .zMn in which w is between and including 2 and 4.5, x is between and including 1.9 and 0, y is between and including 2 and 0, the sum of x and y being at least 0.1 and the sum of w, x and y not exceeding 4.6, and z is between and including 0.001 and 0.1. In one composition x is between and including 1.9 and 0.1 and y is between and including 2 and 0.1. In other compositions MgF 2  or BeO may be absent. The starting materials may be oxides or compounds yielding the oxides on ignition, fluorine being added as MgF 2 . The starting materials of the composition may include a material having the sulphate radical, such as H 2 SO 4  or (NH 4 ) 2 SO 4 , to an amount of from 0.05 to 2 mols. of the radical SO 4  per mol of the luminescent material. Mixing is done wet or dry in a mortar with a pestle, or in a ballmill, after which the batch is dried, ground and sieved preparatory to firing in an oxygen-steam atmosphere. Be-substituted materials are fired for 12 hours at temperatures between 1000‹ and 1250‹C. F-substituted materials are usually fired from 1.5 to 2 hours in the same temperature range but can be fired for longer periods. The luminescent material is coated as a nitro-cellulose suspension on the inner surface 34, Fig. 1, of an envelope 22 surrounding the quartz high pressure mercury vapour lamp 12. The envelope 22 is baked out at approximately 500‹C in a stream of air or oxygen to remove the binder, the lamp sealed in and the annular space exhausted and sealed off at pressures less than 1 microns of mercury. The ends of the lamp 12 are supported by mica plates 13 and 14 through which pass supporting wires 15 and 16 welded to a lead 17 projecting from a press 19. Spring fingers 24 on the supporting wires 15 and 16 position the lamp 12 within the envelope 22. A mica disc 23 supported in the neck portion 32 on the leads 17 and 18 serves to protect the press from the heat of operation. The lamp has a main electrode 25 connected to the support wires 15 and 16 by a lead 26 and a main electrode 27 connected to the lead 18 by a flexible conductor 28. A starting electrode 29 is connected through a resistor 31 to lead 17. The ends of the lamp 12, the plates 13 and 14 and the support wires 15 and 16 are coated with a reflecting material such as magnesium oxide. The envelope 22 is such that its operating temperature coincides with the peak in the temperature-fluorescence curve of the luminescent material. The device shown in Fig. 1 is used horizontally and has an outer envelope of ellipsoidal form so that the device operates approximately isothermally. In a modification for vertical operation base-downwards the outer envelope is pear-shaped with its larger end uppermost so that currents of air passing up along the outside of the envelope cool it so as to result in approximately isothermal operation. In a further modification for vertical operation base-upwards the larger end of the pear-shaped envelope is uppermost adjacent the base. In a further modification the outer envelope is cylindrical. Dimensions are stated.