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 Eu ²⁺ to Cr³⁺. Lifetime measurements of the blue band show that the energy transfer rates increase with the increase of the Cr ³⁺ concentration. There are several phases observed in the strontium aluminates. Energy transfer occurs only for the Eu²⁺ and Cr ³⁺ ions that located in the same phase in the host. In SrAl ₁₂O₁₉ 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 Sr₂Al₆O ₁₁ 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.