GB628308A - Improvements in or relating to luminescent materials - Google Patents

Abstract

628,308. Luminescent materials. PHILIPS ELECTRICAL, Ltd., (formerly PHILIPS LAMPS, Ltd.), and ROTHSCHILD, S. June 25, 1947, No. 16740. [Class 39 (i)] A luminescent material of high stability in respect of heat and chemical action, and particularly suitable for use as an internal coating material for fluorescent lamps, comprises a matrix consisting of an alkaline earth metal arsenate and an activator. One or more alkaline earth halides may be added to alter the colour of the luminescence, in such quantities that the material exhibits an apatite or wagnerite structure. The arsenate is prepared by precipitation or by heating the dry ingredients and is activated by mixing with manganese arsenate or antimony phosphate or arsenate, or both, and firing at 800‹ C. for half an hour in air. Calcium fluoride or strontium fluoride may also be added. The manganese arsenate may be prepared by dissolving manganese sulphate in boiling water, adding ammonium arsenate in solution, and filtering off the precipitate. Instead of being introduced as arsenates, the activating metals may be introduced as oxides, and the deficiency of arsenious oxide made up by an addition of ammonium arsenates. The activating metals which may include cerium may be incorporated in the materials to start with. Improved results may be obtained by firing in nitrogen instead of in air, provided that after firing the phosphors are allowed to cool to about 300‹ C. before coming into contact with air. Two stages of firing may be necessary to obtain a uniform product.