White afterglow observed in Ce3+, Eu2+ and Dy3+ Co-activated Sr3Al2O5Cl2 phosphor

A white phosphor, Sr3Al2O5Cl2: Ce3+, Eu2+ and Dy3+, was synthesized successfully through high temperature solid state process. XRD refinement revealed that all the doping cations replaced the original Sr2+ site in the phosphor lattice. Upon ultraviolet excitation, the phosphor displayed a blue emission from the 5 d-4f Ce3+ transition centered at 441 nm, as well as a broad orange emission from the 5 d-4f Eu2+ transition centered at 636 nm. By adjusting the concentrations of Eu2+, a white emission was achieved with the formula Sr3Al2O5Cl2: 0.005Eu2+, 0.02Dy3+, 0.005Ce3+. After the removal of excitation, a persistent white afterglow was observed due to the presence of Dy3+ electron traps in the lattice with optimal trap depth. The mechanism proposed suggests that the recombination between thermally released electrons originating from the trap center and existing holes at the emission centers of Ce3+ and Eu2+ drives the observed white afterglow phenomenon. These findings highlight the potential of Sr3Al2O5Cl2: Ce3+, Eu2+ and Dy3+ phosphors in solid-state lighting applications.