Energy transfer and red phosphorescence in strontium aluminates co-doped with Cr3+, Eu2+ and Dy3+

Cr3+ activated red long persistent phosphorescence through persistence energy transfer from Eu2+ to Cr3+ has been reported in strontium aluminates co-doped with Cr3+, Eu2+ and Dy3+. The decay processes of the red long persistent phosphorescence at 693 nm emission exhibit strong behavior of f-d band of Eu2+, indicating the occurrence of energy transfer from Eu2+ to Cr3+. Lifetime measurements of the blue band show that the energy transfer rates increase with the increase of the Cr3+ concentration. There are several phases observed in the strontium aluminates. Energy transfer occurs only for the Eu2+ and Cr3+ ions that located in the same phase in the host. In SrAl12O19 phase, the Eu2+ ions emit blue light centered at 400 nm and prefer to transferring energy to the Cr3+ that yields 688 nm emission, while in the Sr2Al6O11 and Sr4Al14O25 phases, the Eu2+ ions emit at 460 and 490 nm, respectively, and transfer the energy to the Cr3+ ions that give emission at 693 nm. It is found that the persistent phosphorescence only consists of the 490 and 693 nm bands, indicating the dominant contribution to the phosphorescence is from the ions in the Sr4Al14O25 phase.