Non‐aqueous Sol—Gel Synthesis of Ultra Small Persistent Luminescence Nanoparticles for Near‐Infrared in vivo Imaging.

ZnGa2O4:Cr3+ (5 mol%) nanoparticles of 6 nm are prepared by a microwave-assisted non-aqueous sol-gel method starting with microwave heating of ZnII-, GaIII, and CrIII-2,4-pentanedionate monohydrates in BnOH in the presence of Cr (270 °C, 30 min) followed by grafting of the as-prepared precipitate with a phosphonate-PEG (MW 2000) aqueous solution leading to a highly stable dispersion (pH 2-10) under physiological conditions.