Synthesis and characterization of sol-gel derived hexa-aluminate phosphors

Two refractory phosphors, BaMg2Al16O27:EU(2+) (BAM) and MgAl11O17.5 :Ce3+, Tb3+ (MAO), have been synthesized both by the conventional solid-state processing route (using oxides as the starting materials) and by reacting precursors made by the sol-gel process using organic precursors. The phases formed were reacted at 1000 degrees C in (a) steam and (b) steam + ALF(3). The phosphors were well. crystallized with particle sizes in the range of 1-10 mu m. The emission spectra showed the characteristic broad band blue emission of EU(2+) for BAM and a narrow band green luminescence of Tb3+ for MAO. The melting points of BAM and MAO were measured to be 1920 +/- 20 degrees C and 1950 +/- 20 degrees C, respectively, using an Ir-strip furnace and optical pyrometer. BAM and MAO phosphor materials are congruently and incongruently melting, respectively. Excellent crystallization via the sol-gel route was found even at 1220 degrees C. Enhancement of the luminescent output by the steam treatment by some 25% was determined.