Near Infrared-Emitting Cr/Eu Co-doped Zinc Gallogermanate Persistence Luminescent Nanoparticles for Cell Imaging.

Near infrared (NIR)-emitting persistent luminescent nanoparticles have been developed as potential agents for bioimaging. However, synthesizing uniform nanoparticles with long afterglow for long-term imaging is lacking. Here, we demonstrated the synthesis of spinel structured ZnGaGeO:Cr (ZGGO:Cr) and ZnGaGeO:Cr,Eu (ZGGO:Cr,Eu) nanoparticles by a sol-gel method in combination with a subsequent reducing atmosphere-free calcination. The samples were investigated via detailed characterizations by combined techniques of XRD, TEM, STEM, selected area electron diffraction, photoluminescence excitation (PLE)/photoluminescence (PL) spectroscopy, and temperature-dependent PL analysis. The single-crystalline nanoparticles are homogeneous solid solution, possessing uniform cubic shape and lateral size of ~ 80-100 nm. Upon UV excitation at 273 nm, ZGGO:Cr,Eu exhibited a NIR emission band at 697 nm (E → A transition of distorted Cr ions in gallogermanate), in the absence of Eu emission. NIR persistent luminescence of the sample can last longer than 7200 s and still hold intense intensity. Eu incorporation increased the persistent luminescence intensity and the afterglow time of ZGGO:Cr, but it did not significantly affect the thermal stability. The obtained ZGGO:Cr,Eu-NH nanoparticles possessed an excellent imaging capacity for cells in vitro.