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

Cr³⁺ activated red (694 nm) long persistent phosphorescence originating from ²E-⁴A₂ transition is observed in 4SrO·7Al₂O₃: Cr³⁺, Eu²⁺, Dy³⁺ system. It is demonstrated that the red phosphorescence is resulted from the conversion of Eu²⁺ activated blue phosphorescence through persistence energy transfer from Eu²⁺ to Cr³⁺. The excitation spectra of the 694 nm emission exhibit strong f-d band of Eu ²⁺, indicating the existence of the energy transfer. The dependence of lifetimes and intensities of the red and blue emissions on Cr³⁺ concentrations are studied. The intensity ratio of the red to blue emission bands obtained from photoluminescence spectra is in good agreement with that obtained from fluorescence lifetime measurements. The decay curves of the red phosphorescence at 694nm are also studied.