Origin of the photoabsorption responsible for the long-lasting phosphorescence in SrAl2O4:Eu2+,Dy3+ phosphors

The emission and excitation spectra for long-lasting phosphorescence (LLP) from Eu2+ ions in SrAl2O4 : Eu2+, Dy3+ phosphors have been measured at 300 K using a xenon lamp and synchrotron radiation. The emission spectrum for LLP is composed of a prominent band peaking at 2.38 eV. This band is similarly observed in the emission spectrum for photoluminescence (PL). The LIP is strongly excited around 6.3 eV below the fundamental absorption edge of the host SrAl2O4. However, it is weakly excited in the photoabsorption due to the 4f -> 5d transition of Eu2+ ions and the fundamental absorption, where the PL is strongly excited. The origin of the photoabsorption responsible for the LLP is discussed on the basis of a comparison of experimental results with DV-X alpha calculation.