Cr3+-activated Li5Zn8Al5Ge9O36: A near-infrared long-afterglow phosphor

Near-infrared long-afterglow (LAG) materials have attracted considerable attention owing to their high potential for invivo imaging applications. Here, we present a series of near-infrared LAG phosphors Li5Zn8Al5-xGe9O36:xCr(3+) (LZAG:Cr3+), which were synthesized using a solid-state reaction method. The pure LZAG host exhibits blue photoluminescence and LAG emission. We investigated the effect of the zinc vacancy contents on the photoluminescence and LAG performance by adjusting the zinc content and introducing Ga3+ ions to substitute the Zn2+ sites in LZAG host. When Cr3+ ions were introduced into the LZAG host, LZAG:Cr3+ produced a strong, broad blue emission band centered at 456nm and a near-infrared emission band at 700nm caused by the (2)E(4)A(2) transition of Cr3+. The energy transfer processes from the LZAG host to Cr3+ were identified in the photoluminescence and LAG process. After irradiation at 258nm for 10minutes, the LAG emission of LZAG:0.008Cr(3+) can last nearly 2.5hours. Moreover, the LAG intensity and duration of LZAG: 0.008Cr(3+) were significantly improved by introducing a small dose of Ga3+ ions. Finally, the traps and mechanism of LAG in LZAG, LZAG:Ga3+, and LZAG:Cr3+ were discussed in detail.