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Near-infrared long-afterglow (LAG) materials have attracted considerable attention owing to their high potential for in vivo imaging applications. Here, we present a series of near-infrared LAG phosphors Li 5 Zn 8 Al 5Àx Ge 9 O 36 :xCr 3+ (LZAG:Cr 3+ ), 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 Ga 3+ ions to substitute the Zn 2+ sites in LZAG host. When Cr 3+ ions were introduced into the LZAG host, LZAG:Cr 3+ produced a strong, broad blue emission band centered at 456 nm and a near-infrared emission band at 700 nm caused by the 2 E ? 4 A 2 transition of Cr 3+ . The energy transfer processes from the LZAG host to Cr 3+ were identified in the photoluminescence and LAG process. After irradiation at 258 nm for 10 minutes, the LAG emission of LZAG:0.008Cr 3+ can last nearly 2.5 hours. Moreover, the LAG intensity and duration of LZAG: 0.008Cr 3+ were significantly improved by introducing a small dose of Ga 3+ ions. Finally, the traps and mechanism of LAG in LZAG, LZAG:Ga 3+ , and LZAG:Cr 3+ were discussed in detail. K E Y W O R D Sluminescence, phosphors, vacancies

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