Near-infrared (NIR) persistent luminescence nanoparticles (PLNPs) with high brightness, small sizes, good hydro-dispersivity, and intrinsic surface-functional groups are desirable in biological applications. In this work, Cr3+-doped zinc gallogermanates Zn1+xGa2-2xGexO4:Cr (ZGGC) PLNPs were hydrothermally synthesized via 3-aminopropyltriethoxysilane (APTES) as an additive, or APTES and cetyltrimethylammonium bromide (CTAB) as two co-additives. Addition of APTES not only dramatically enhances the 696 nm NIR luminescence intensity, but also obviously decreases the particle size and introduces amino groups. In particular, thex= 0.1 series ZGGC (ZGGC0.1) with the addition of n moles equivalent APTES (ZGGC0.1-nA) had smaller particle sizes than thex= 0.2 counterpart (ZGGC0.2-nA). The NIR afterglow intensities increased with the APTES introduction. The ZGGC0.2-2.5A sample (also named as ZGGC, Si, -NH2) exhibited maximum luminescence intensities both in solid and aqueous states. With APTES, Si atom is doped and -NH2groups are modified, the trap depth and density become larger, and the afterglow intensities and decay time are significantly enhanced. More notably, co-addition of CTAB (ZGGC0.2-2.5A-C) (also named as ZGGC, Si, -NH2') further enhances hydro-dispersivity and luminescence intensity, decreases particle sizes, and results in more prominent amino groups. The trap density is drastically higher than that without CTAB (i.e. ZGGC0.2-2.5A). Change of Cr3+microenvironment in the crystal and more defects introduction contribute to the enhanced brightness. As expected, the ZGGC,Si,-NH2' PLNPs possess excellent biocompatibility, deep tissue penetration and distinguished bioimaging properties, and rechargeability with orange LED light. The ZGGC,Si,-NH2' PLNPs should provide to be an excellent nanomaterial for various functionalization and bioimaging applications.
Keywords: APTES; bioimaging; doping; mechanisms; near-infrared; persistent luminescence nanoparticles.
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