Green photoluminescence, but blue afterglow of Tb3+ activated Sr4Al14O25

Tb3+ activated Sr4Al14O25 phosphors were synthesized by the high temperature solid-state reaction. For the sample, the color of the photoluminescence (PL) was green, but that of the afterglow was blue. The spectral results indicated that the photoluminescence was mainly due to the transitions from 5D4 to the ground energy levels of Tb3+ and obeyed the cross-relaxation mechanism; however, the afterglow was derived from the transitions from 5D3 and independent with the concentration of Tb3+. This difference was attributed to the reason that the energy transfer process of cross-relaxation was halted by the traps during the period of afterglow.