Patent ID: 7875466

Claim:
A process of preparing a nanoparticle comprising a magnetic particle coated with a phosphor fluoride, which process comprises: a) dispersing a nanometer-sized magnetic particle and an aqueous fluoride-containing compound in de-ionized water; b) contacting the mixture of step a) with an aqueous solution containing soluble salts of a phosphor host, an absorber-emitter pair, and a rare-earth metal chelator by stirring for a sufficient time to allow formation of a phosphor fluoride precipitate which forms a coating around the magnetic particle; and c) heating the magnetic particle with the phosphor fluoride coating of step b) at a temperature ranging from about 300° C. to about 450° C. for a period of time ranging from about 1 hour to about 10 hours to obtain the phosphor fluoride coated magnetic particle that emits light in the visible wavelength range when excited by long wavelength light.