Borate polyanions tuning persistent luminescence in Eu and Dy co-doped strontium aluminate

Abstract

Although the longest duration of persistent luminescence in Eu and Dy co-doped strontium aluminate (S4A7ED) is obtained by processing with 30 mol% B₂O₃ (S4A7EDB), this composition does not contain the highest amount of the long persistence phase. To elucidate how the structural arrangement of atoms in S4A7EDB induced by synthesis using 30–40 mol% B₂O₃ yields the longest persistence, the crystal environment of B in S4A7ED is evaluated by using micro-Raman and FTIR spectroscopy. Polyatomic vibration modes containing B–O are revealed, in forms of metaborate and other borate polyanions. Based on these results, we propose a structural model for S4A7EDB, in which B introduces non-bridging oxygen, which offers excess negative charge and enlarged adjacent Sr sites, both of which enable Eu and Dy dopant clustering that yields extreme persistent luminescence.