Synthesis and Characterization of Long-Afterglow Eu2+, Dy3+-Doped Strontium Aluminates

Strontium aluminate-based phosphors activated by Eu2+ (0.5–4.0 at %) and Dy3+ (1.0–8.0 at %) were prepared by solution combustion synthesis (SCS) followed by reduction annealing at 1000° under CO atmosphere. The optimal dopant concentrations that provided the highest afterglow intensity and duration were 1.0 at % Eu2+ and 2.0 at % Dy3+. The K+ and Na+ (1.0 at % each) charge-compensator ions increased the afterglow time up to 10 min due to their efficient incorporation into the strontium sublattice. The substitution of boron for aluminum (8–30 at %) did not change the phase composition, but significantly increased the afterglow duration: for a 15 at % boron sample, the afterglow time amounted to 60 min, which exceeds the documented values for similar compositions. The phase composition of the samples was a mixture of luminescent phases (Sr4Al14O25, SrAl2O4, and SrAl12O19) and nonluminescent compounds; a single-phase product was not a prerequisite for long-lasting afterglow to be achieved. The photoluminescence spectra featured a broad band in the range 450–600 nm with a peak at about 520 nm, corresponding to 4f 65d1 → 4f 7 (8S7/2) transitions in Eu2+ ions in various crystal environments. The luminescence was excited by 365-nm UV radiation.