BaAl2O4:Eu2+, Dy3+ Nanotube Synthesis by Heating Conversion of Homogeneous Coprecipitates and Afterglow Characteristics

Hexagonal BaAl2O4:Eu2+, Dy3+ polynary complex nanotubes with long-lasting phosphorescence were obtained through a facile coprecipitation approach followed by a postcalcining reaction in a weak reducing atmosphere. In the case of low annealing temperature, anion vacancies and surface stress can induce lattice contraction due to poor crystallininty; moreover, Eu2+ ions can occupy two different crystallo-graphic Ba2+ sites due to low symmetry, resulting in an appearance of double emission peaks. For the sample annealed at higher temperature, however, Eu2+ ions only occupy substitutedly the Ba2+ sites with lowest energy due to high crystallinity; moreover, as compared to the sample annealed at low temperature, its emission band redshifts as the results of both high crystal symmetry around Eu2+ ions and large average optical path. Additionally, Eu2+ and Dy3+ ions substitute incompletely for Ba2+ sites in nanostructures, leading to the decrease of effective electron trap densities and depths, and therefore tubular nanostructures show fast afterglow decay rate in comparison with the bulk counterpart.