New viewpoint about the persistent luminescence mechanism of Mn2+/Eu3+ co-doped Zn2GeO4

Abstract

In this work, Mn[Formula: see text]Eu[Formula: see text] co-doped Zn2GeO4 (Zn2GeO4:Mn[Formula: see text] was prepared by high-temperature solid phase method. Compared with common fluorescent materials Zn2GeO4:Mn[Formula: see text], Zn2GeO4:Mn[Formula: see text] could not only emit strong green fluorescence of 535 nm, but also maintain excellent persistent luminescence performance. Through Density Functional Theory calculation, we obtained the fine band structure of Zn2GeO4:Mn[Formula: see text]. The results of the band structure were consistent with the experimental spectral data. On this basis, we proposed a new luminescence mechanism model of Zn2GeO4:Mn[Formula: see text] to explain the phenomena observed in experiment reasonably, though which was not completely consistent with previous works. When Zn2GeO4:Mn[Formula: see text] was excited, electron–hole separation occurred in the valence band (VB), and the electron transitioned to the conduction band (CB) directly. Through CB, the electron was trapped by trap levels (7F[Formula: see text]F5 of Eu[Formula: see text] and maintained metastable for a long time. Under the action of thermal stimulation, electron returned to CB from the trap level slowly. The electron was captured again by the 4T2(D) level of Mn[Formula: see text]. Then the electron transitioned down toward VB and recombined with the previous hole and emitted a photon with 535 nm (afterglow). The samples were being irradiated, trap levels accommodated the excited electrons to saturation. More electrons excited into the CB could not be captured by the trap levels any more. They were captured directly by the 4T2(D) and transitioned directly to VB, then emitted green fluorescence.