Method for treating a phosphor

A method of treating a rare-earth-containing phosphor including copper or copper compound contaminants which comprises mixing the phosphor with an aqueous reagent solution comprising a chelating agent selected from the group consisting of ethylenediaminetetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, diethylenetriaminopentaacetic acid, and triethylenetetraaminehexaacetic acid, an oxidizing agent selected from the group consisting of hydrogen peroxide, sodium peroxide, alkali metal perchlorate, alkali metal periodate, alkali metal perbromate, periodic acid, hypochlorous acid, and alkali metal hypochlorite, and an alkali agent selected from the group consisting of aqueous ammonia, sodium hydroxide, potassium hydroxide, and lithium hydroxide, at a temperature of from 40.degree. to 85.degree. C., and

• recovering the phosphor therefrom to provide a recovered phosphor having a lower copper content than a phosphor treated according to the above-method when either the oxidizing agent or alkali agent or both are absent.