MECHANISM OF LUMINANCE DECREASE IN BAMGAL10O17-EU2+ PHOSPHOR BY OXIDATION

The mechanism of luminance decrease in blue emitting BaMgAl10O17:Eu2phosphor after annealing has been studied. It was shown experimentally that annealing in air oxidizes BaMgAl10O17:Eu2+ and substantially cha nges the Eu2+ ion to an Eu3+ ion. This is also deactivates the Eu2+ lu minescent center, thus decreasing Eu2+ emission. Furthermore, the comp ound EuMgAl11O19, in which the valence of the Eu ion is trivalent, was detected in BaMgAl10O17:Eu2+ annealed at temperatures higher than 800 degrees C as a resulting product of oxidation. It was demonstrated th at BaMgAl10O17:Eu2+ was converted by oxidation into a mixture of the t wo compounds BaMgAl10O17 and EuMgAl11O19, and resulting in a further d ecrease in luminance. This suggests that obstructing the formation of Eu(III)MgAl11O19 during the annealing is essential for alleviating the decrease in luminance. Preparing BaMgAl10O17:Eu2+ having both superio r crystallinity and completely stoichiometric composition has been fou nd to be effective in alleviating the luminance decrease.