Structural, Optical, and UVA-Emitting Persistent Luminescence Features of Ba1–xAl2Si2O8:(x = 0–0.05)Eu2+ and Its Anticounterfeiting Application
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 Eu2+-doped BaAl2Si2O8 phosphors synthesized using the solution combustion method with varying Eu concentrations from 1 to 5 mol %. Structural analysis confirms that the undoped and Eu2+-doped samples crystallize in a hexagonal crystal structure with the p63mcm space group of BaAl2Si2O8. An X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of a Eu2+ 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 Eu2+-doped samples give UVA emission with a peak centered at around 372 nm. The UVA emission of the doped samples is attributed to the 4f65d1 → 4f7 transition of the Eu2+ 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.