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

Two refractory phosphors, BaMg₂Al₁₆O₂₇: Eu²⁺ (BAM) and MgAl₁₁O_17.5: 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 °C in (a) steam and (b) steam + AlF₃. The phosphors were well crystallized with particle sizes in the range of 1–10 μm. The emission spectra showed the characteristic broad band blue emission of Eu²⁺ 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 °C and 1950 ± 20 °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 °C. Enhancement of the luminescent output by the steam treatment by some 25% was determined.