Method of removing ultra fine phosphor particles of a (zn,mg){11 (si,ge){11 {11 : mn phosphor

Claim 1

The method of sizing finely divided particles of a zinc-magnesium silico-germanate phosphor to remove ultra fine particle sizes having a diameter less than one micron to improve the performance of a discharges lamp, comprising: a. after said phosphor is prepared in finely divided form having a range of particle sizes such that all particles will pass through a standard 400 mesh screen and including ultrafine particles having a diameter less than about one micron, but before incorporation in a discharge lamp, twice suspending said phosphor in a solution of aqueous vehicle having a pH from about 2.5 to 6 and having dissolved therein a predetermined amount of one of ionizable aluminum compound or diethylenetriamine pentaacetic acid (DTPA); b. twice settling said phosphor in said solution for a predetermined period sufficient to leave only a substantial portion of the ultrafine phosphor particles remaining suspended therein; c. twice separating said settled phosphor from phosphor remaining suspended in said solution; in the first said suspension, settling and separation, said solution is said DTPA; and in the second said suspension, settling and separation, said solution is said aluminum compound; and intermediate said first suspension and said second suspension, said phosphor is water washed to remove residual solute; and d. resuspending said separated phosphor in aqueous medium, resettling and then separating settled phosphor, and repeating this procedure as required to separate substantially all ultrafine phosphor particles from residual settled phosphor as well as to remove from residual settled phosphor substantially all solute remaining from said solution.