Persistent luminescence excitation spectroscopy of BaAl₂O₄:Eu²⁺,Dy³⁺

BaAl₂O₄:Eu²⁺,Dy³⁺ is related, both by structure and luminescence, to one of the best persistent luminescent phosphors, SrAl₂O₄:Eu²⁺,Dy³⁺. At room temperature (RT), the green persistent emission of BaAl₂O₄:Eu²⁺,Dy³⁺ remains visible for hours after ceasing irradiation. Similar to SrAl₂O₄, BaAl₂O₄ with hexagonal P6₃ structure, has two M²⁺ sites, but, limited optical activity from the 2nd site is observed in the emission of BaAl₂O₄:Eu²⁺,Dy³⁺ - even at 77 K. Using combined approach of photoluminescence, thermoluminescence (TL), and persistent (excitation) luminescence measurements, the origin and properties of persistent luminescence of BaAl₂O₄:Eu²⁺,Dy³⁺ were studied in detail. Ultraviolet (UV) excited and persistent emission are identical and no contribution from the Eu²⁺ in the high-symmetry Ba site was observed. TL excitation spectra clarified the unstructured conventional excitation spectrum; now it is evident that defects or the Dy³⁺ co-dopant do not contribute to persistent luminescence via direct energy absorption. Mechanisms for persistent luminescence should thus be revised.