Green photoluminescence and afterglow of Tb-doped SrAl₂O₄

Trivalent terbium-doped strontium aluminate (SrAl₂O₄:Tb³⁺) nanoparticles were synthesized via the sol–gel combustion technique, and the green photoluminescence (PL) and afterglow were evaluated to clarify the afterglow mechanism of SrAl₂O₄:Tb³⁺. The green PL of SrAl₂O₄:Tb³⁺ with characteristic emissions at 488, 543, 586, and 622 nm indicated that Tb dopant acts as the luminescent center of the PL. Contrarily, the green afterglow of SrAl₂O₄:Tb³⁺ was a broadband spectrum with its peak centered at around 520 nm, but no traces of Eu were found in SrAl₂O₄:Tb³⁺ phosphors within the detection limit of 1 μg/g. The band structures and density of states of SrAl₂O₄:Tb³⁺ were calculated within the framework of density functional theory. Both the ground state of Tb³⁺ dopant and the trap levels of oxygen vacancy were quantitatively determined in the band gap of SrAl₂O₄. Our results suggest that the deep electron trap of oxygen vacancy in the host acts as the luminescent center of the green afterglow from SrAl₂O₄:Tb³⁺. A possible afterglow mechanism is proposed to shed fresh light on the green afterglow of SrAl₂O₄:Tb³⁺.