Bluish-green afterglow and blue photoluminescence of undoped BaAl2O4

Abstract

Undoped BaAl₂O₄ was derived via sol–gel combustion technique. The afterglow and photoluminescence (PL) properties of undoped BaAl₂O₄ were explored with the combination of experiments and density functional theory (DFT) calculations. Undoped BaAl₂O₄ is found to display bluish-green afterglow that is discernible to naked eye in dark for about 20 s. The broad afterglow spectrum of undoped BaAl₂O₄ is peaked at around 495 nm. As a contrast, the broad PL spectrum of undoped BaAl₂O₄ can be decomposed into a bluish-green PL band peaking at about 2.53 eV (490 nm) and a blue PL band centered at about 3.08 eV (402.6 nm). DFT calculations indicate that the defect energy levels generated by oxygen and barium vacancies are critical to the afterglow and PL of undoped BaAl₂O₄. This work demonstrates that the oxygen and barium vacancies in undoped BaAl₂O₄ are liable for the bluish-green afterglow and blue PL of undoped BaAl₂O₄. The recorded bluish-green afterglow of BaAl₂O₄ is particularly important to understand the afterglow mechanisms of rare-earth doped BaAl₂O₄.