Studies On The Synthesis And Thermal Stability Of BaMgAl₁₀O₁₇:Eu～(2+) Phosphor

BaMgAl₁₀O₁₇:Eu²⁺ (BAM) has been regarded as the preferred blue-emitting phosphor for fluorescent lamp, plasma display panel (PDP) and Hg-free lamp applications because of its high luminance efficiency and good color purity under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. However, it still remains two main problems on BAM, one is the high temperature of its conventional synthesis and another is its degradation on luminance efficiency and color quality.To avoid the high temperature and agglomeration in the conventional solid-state reaction, we exploited co-precipitation method which is a commercially available process to synthesize BAM. Using ammonium salt co-precipitation method, single phase of BAM was obtained at 1350°C which was 250°C lower than the temperature of solid-state reaction. The as-prepared phosphor had non-agglomerated particles with regular shape and uniform distribution, and exhibited stronger emission intensity and better thermal stability than the sample prepared by solid-state reaction. When using oxalic acid and ammonia as precipitants, single phase of BAM can be obtained at 1300°C by "direct strike" or "reverse strike" of precipitants, but the products have agglomerated particles and worse photoluminescence performances than the phosphor prepared by ammonium salt co-precipitation method.The key to overcome the degradation lies in making clear the mysterious degradation mechanism. Therefore, we detailedly investigated the effects of the annealing time and temperature on the luminescent properties of BAM. A distinct green emission was detected in the emission spectra of annealed BAM, and could be assigned to the emission of Eu²⁺ within the spinel block. Then a new and full-scale thermal degradation mechanism was proposed. It was confirmed that the oxidation and the migration of Eu²⁺ both contributed to the thermal degradation of BAM. This mechanism can well explain all the degradation phenomenons, such as luminescent decrease and color shift.Basing on the clarification of the thermal degradation mechanism, a simple method was designed to improve the thermal stability of BAM. Utilizing the interstitial cations derived from the substitution of Mg²⁺ for Al³⁺ within spinel block, the migration of Eu²⁺ from mirror plane to spinel block was prevented, thereby, the thermal stability of BAM was efficiently improved.