Luminescence properties of Tm3+ co-doped Sr2Si5N8:Eu2+ red phosphor

The Sr2Si5N8:Eu2+ phosphors, both undoped and doped with Tm3+, were synthesized by high temperature solid-state method. The XRD pattern shows that only Sr2Si5N8 phase is formed whatever Tm3+ was doped or not. The peak positions of both phosphors are centered at 612 nm which is assigned to the 4f65d→4f7 transition of Eu2+. It implies that the crystal field, which affects the 5d electron states of Eu2+, is not changed dramatically after the phosphor is doped with Tm3+. The afterglow time is about 10 min after Tm3+ ion is introduced into the phosphor. The concentration of Tm3+ has little influence on the afterglow time of the phosphor. The depths of trap energy level of the two phosphors were calculated based on the TL spectra. The depths of Sr2Si5N8:Eu2+ and Sr2Si5N8:Eu2+, Tm3+ are 1.75 and 1.01 eV, respectively.