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.