Method of making alkaline earth metal halophosphate phosphor using metal phosphide reducing agent

A method of improving the brightness of a calcium chlorofluoroapatite phosphor activated with antimony and manganese, comprising the steps of:

• forming a uniform mixture of calcium hydrogen phosphate, calcium carbonate, calcium fluoride, a source of chloride, manganese carbonate, antimony trioxide, and from about 0.001 to about 0.0035 mole of zinc phosphide, said zinc phosphide being in an amount sufficient to reduce any pentavalent antimony to the trivalent state and any tetravalent manganese to the divalent state and to maintain antimony and manganese in the trivalent and divalent states, respectively;
• firing said mixture at 1150.degree. C. for two hours in a nitrogen atmosphere to obtain a phosphor cake;
• washing said phosphor cake in a weakly acidic solution and then in a weakly basic solution to obtain a washed phosphor;
• and drying and screening said phosphor, said phosphor exhibiting a higher brightness than the phosphor prepared as above, absent zinc phosphide.