Patent GB-601593-A (GB)
Title: Improvements relating to methods of preparing luminescent materials
IPC: C09K11/08
Filed: 1944-09-11
Abstract: 601,593. Luminescent materials.- MARCONI'S WIRELESS TELEGRAPH CO.. Ltd. Sept. 11, 1944, No. 17349. Convention date, Jan. 31, 1942. [Class 39 (i)] A method of preparing a luminescent material comprising a metal and sulphur and/or selenium includes the step of firing the constituents of the material in the presence of at least three fluxes consisting of an alkali metal halide, an alkaline earth metal halide and a hydrogencontaining halide. One or more of copper, silver and gold may be used as activator. The ratio of the hydrogen-containing halide flux to the total amount of the three fluxes during the initial stage of the firing is between onethird and one-tenth for a total flux content of between 0. 1 per cent and approximately 5 per cent by weight of the constituents and is between one-tenth and one-twentienth for a total flux content of approximately 5 per cent to 20 per cent by weight of the constituents. In one example the total amount of said fluxes is substantially 3 per cent by weight of the constituents, the hydrogen-containing halide flux being about one-third by weight of the total flux. and in another example the total amount of the fluxes is substantially 4.3 per cent by weight of the constituents and the hydrogencontaining halide is about one-ninth by weight of the total flux. The proportions of the fluxes govern the crystal size of the material. The constituents are fired at a temperature between 700‹ C. and1500‹ C. in a neutral, oxidizing or reducing atmosphere. The pressure to which the material is subjected during firing may vary from 0.0001 to 20 atmospheres. The material may be provided with additions of elements or compounds which have relatively large atoms or ionic radii in order to improve the secondary electron emission properties of the material. In one example 86 grams of pure zinc sulphide are mixed with 14 grams of pure cadmium sulphide, 1 gram of an alkali metal halide flux, e.g. sodium chloride, 1 gram of a hydrogen containing halide flux, e.g. ammonium chloride, and 1 gram of an alkaline earth metal halide flux, e.g. barium chloride. The materials are ground and mixed and moistened with a concentrated aqueous solution of copper chloride to the equivalent of .007 grams of copper. Pure water is added to make a paste which is stirred thoroughly and evaporated to dryness at a temperature of from 90‹ C. to 160‹ C. The material is then broken up, mildly ground, mixed and fired in a covered quartz crucible in an electric resistance furnace raised to a temperature of about 1250‹ C. in about one to one-and-a-half hours. After firing the crucible and contents are removed from the furnace and allowed to cool rapidly. The material may be quenched in water immediately upon removal from the furnace. The material is then preferably washed vigorously in alternate washings of hot doublydistilled water and hot doubly-distilled water containing, or saturated with, hydrogen sulphide to remove the fluxes and is then dried or placed in a ball mill and rolled with small balls of material known under the Registered Trade Mark "Pyrex " preferably in an aqueous solution containing hydrogen sulphide. In another example the initial ingredient proportions may be zinc sulphide, 100 grams, potassium bromide 3 grams, barium chloride 1 gram, ammonium chloride 0.5 grams with an activator such as silver nitrate to the equivalent of 0.015 grams of silver, the firing taking place at 1270‹ C.