| abstract |
A surface modified phosphor powder exhibiting increased lumen maintenance. At the outer surface of each phosphor particle, the cations of the phosphor material have been replaced by other cations, e.g., a metal or metalloid cation such as aluminum, barium, calcium, lanthanum, magnesium, strontium, yttrium, zinc, titanium, tantalum, boron, or silicon. The phosphor powder is chemically modified by forming a suspension of phosphor particles in a liquid medium including the metal or metalloid ions in solution. The phosphor suspension is stirred for a time sufficient to permit an ion exchange reaction in which the metal or metalloid ions are substituted for cations of the phosphor to form a layer of the desired metal or metalloid compound at the phosphor outer surface. |