Persistent luminescence excitation spectroscopy of BaAl2O4:Eu2+,Dy3+
Marja Malkamäki (University of Turku)
A. J.J. Bos (TU Delft - RST/Luminescence Materials)
P Dorenbos (TU Delft - RST/Luminescence Materials)
Mika Lastusaari (University of Turku)
Lucas C.V. Rodrigues (Universidade de São Paulo)
Hendrik C. Swart (University of the Free State)
Jorma Hölsä (Universidade de São Paulo, University of Turku, Polish Academy of Sciences, University of the Free State)
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Abstract
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.