Polychromatic luminescence of LiSr4(BO3)3:Eu2+, Dy3+persistent phosphors

A long persistent phosphor LiSr4(BO3)(3): Eu2+, Dy3+ shows a typical 5d-4f transition of Eu2+ under ultraviolet activation with an emission centered at 632 nm. Herein, the lattice site of Sr2+ is partially replaced with Mg2+ and Ba2+ and co-doping is performed using Eu2+ and Dy3+ to successfully synthesize several LiSr4_x- Bax(BO3)3:2% Eu2+, Dy3+ and LiSr4_yMgy(BO3)3:2% Eu2+, Dy3+ phosphors with multicolor luminescence using a high-temperature solid-phase approach. When x or y = 0.4, the samples exhibit bright yellow or orange-red luminescence under ultraviolet (UV) excitation, with the emission spectra showing blue (611-632 nm) or red (632-648 nm) shifts, respectively. Such shifts in the peak position are ascribed to the weakened or enhanced crystal field strength. Under UV excitation, an afterglow phenomenon is also observed. The afterglow profiles can be simulated using an empirical double decay model. The LiSr3.76Mg0.2(BO3)3: 2% Eu2+, Dy3+ sample exhibits the best afterglow phenomenon, which is potentially attributed to the formation of numerous electron traps with suitable trap depths after the incorporation of Mg2+ into the phosphor lattice.