Photoluminescence and afterglow behavior of a new orange long-lasting borate phosphor Eu2+, Dy3+: NaSr4(BO3)3

A new long-lasting phosphor Eu2+, Dy3+: NaSr4(BO3)3 was obtained by high temperature solid state process. The phosphor displays typical 5 dd-4f transition of Eu2+ upon UV illumination with a broad emission centering around 588 nm, which is orange visible to the naked eye. Such an emission can be divided into 2 single emissions since the Eu2+ cations are located in two different crystallographic sites in the forms of [EuO6] and [EuO8]. An optimal doping concentration for Eu2+ cation is determined as 2 at% due to the quenching effect with increasing Eu2+ concentration. The critical distance between the luminescence center is determined around 14 Å. Afterglow behaviors are further observed for the prepared phosphors, which can be expressed by an empirical double exponential decay model. The sample 2% Eu/Dy: NaSr4(BO3)3 displays the best afterglow performance. The reason for such an afterglow performance is revealed by thermal stimulated luminescence (TSL) that the co-doped Dy cations offer large numbers of electron traps with suitable trap depth.