Long-lasting afterglow characteristics of Eu, Dy codoped SrO-Al2O3 phosphor

By codoping Dy3+ into the SrAl2O4:Eu2+ phosphor, long persistent phosphorescence was observed and its afterglow characteristics were investigated. The excitation wavelength suitable for long persistent phosphorescence was 200-250 nm, much shorter than the wavelength of 4f(7)-4f(6)5d absorption of the Eu2+ ions, suggesting that the energy levels of electron traps are higher than the 4f(6)5d level. The phosphorescence intensity and its lifetime increased with increasing temperature. The depth of the electron traps was calculated from the Hoogenstraaten's plot of glow curves at about 0.3 and 0.6 eV. From the temperature dependence of decay curves, the deeper trap is considered to contribute to the long-lasting afterglow.