M. P. Kalita, J.M. Kalita
Research concerning UVA-emitting persistent luminescence (PerL) phosphors is growing due to their potential applications in phototherapy, sterilization, photocatalytic activity, etc. We report the structural and optical properties of undoped and Eu 2+ -doped BaAl 2 Si 2 O 8 phosphors synthesized using the solution combustion method with varying Eu concentrations from 1 to 5 mol %. Structural analysis confirms that the undoped and Eu 2+ -doped samples crystallize in a hexagonal crystal structure with the p 63 mcm space group of BaAl 2 Si 2 O 8 . An X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of a Eu 2+ ion. An absorption spectroscopic analysis revealed that the undoped sample shows the maximum absorption at around 245 nm, along with two weaker absorption bands at around 355 and 530 nm. In contrast, all the doped samples show three distinct maxima at around 255, 314, and 348 nm. Under 348 nm excitation, the undoped sample gives emission in the visible region with distinct peaks at 432, 457, 480, and 557 nm, attributed to oxygen-related vacancy defects. The peak at 457 nm has the highest emission intensity with a lifetime of 1.68 ns. Under the same excitation, the Eu 2+ -doped samples give UVA emission with a peak centered at around 372 nm. The UVA emission of the doped samples is attributed to the 4f 6 5d 1 → 4f 7 transition of the Eu 2+ ion. The photoluminescence lifetime of the doped samples is found to decrease from 1.75 to 1.54 μs with an increase in the dopant concentration. The 2 mol % Eu-doped sample exhibits the highest persistent luminescence emission intensity under both 260 and 365 nm UV light. The potential application of the phosphor in anticounterfeiting applications under different illumination conditions is studied.