Plasma display panels (PDPs) are regarded as a promising technology for large and flat TV displays. But much improvement is needed concerning luminous efficiency, lifetime, and color purity. $BaMaAl_10O_17$ : $Eu^{2+}(BAM)$ is an important blue phosphor for PDP application. However, the luminance decrease and color shift of this material are the most important problems to be solved. The degradation of BAM is known and much researcher has tried to improve its stability. It is found that the degradation process is caused by thermal treatment of the PDP manufacturing, irradiation by VUV photons (＜200nm), and ion sputtering. The thermal degradation during the manufacturing process is a particularly serious problem. In this study, the thermal degradation during a paste-baking process was focused on, and also their optical property and various surface analysis et al. were performed to study the degradation mechanism of BAM phosphor paste.
To investigate the cause of the thermal degradation, the phosphor paste was made by mixing the phosphor powder with an organic binder, then the paste was baked in air at 500℃. And after baking a paste at various process condition such as baking temperature, baking time, and baking atmosphere, the changes in the emission and excitation spectra, EPR, XPS, TG-DSC, FT-IR, and XRD were measured.
First, the VUV emission spectra showed that the luminance was significantly reduced after the baking and only after baking at 500℃ for 30 min. the color shift toward green was observed. Moreover, the ESR spectra showed that the $Eu^{2+}$ emission decreased after the baking. And the XPS spectrum showed that the Oxygen peak and Europium peak changed when the phosphor paste heated at 500℃. The XPS spectra of O1s showed that only after baking at 500℃ for 30 min. additional 531.85eV peak was observed. This peak was assigned the OH peak of $H_2O$. And the XPS spectra of Eu3d showed that the $Eu^{2+}$ ion changed $Eu^{3+}$ ion after the baking. These results suggest that the cause of luminance decrease be related with the oxidation of $Eu^{2+}$.
Thermo gravimetric analysis gave a loss in weight after the baking. From this result, it is found that a decomposition occurred near 450℃. And From FT-IR spectrum, OH-related peaks increased after baking a paste. From X-ray diffraction measurements, c lattice parameter expanded as Ba β-alumina was hydrated. These results suggest that the cause of luminance decrease be related with intercalation of water molecules in the conduction plane of Ba β-alumina.
