E-Mail IMAGE: Schematic illustration of the synthetic protocol of the self-assembly induced luminescence (SAIL) of Eu-complex and its bioimaging application. view more Credit: @Science China Press The unique properties of rare earth (RE) complexes including ligand-sensitized energy transfer, fingerprint-like emissions and long-lived emissions, make them promising materials for many applications, such as optical encoding, luminescence imaging/sensing and time-resolved luminescence detection. In particularly, the use of RE luminescent materials for in vitro and in vivo imaging can easily eliminate the autofluorescence of organisms and any interference from background fluorescence. However, most RE complexes have poor solubility and stability in aqueous solution and their luminescence can be easily quenched by nearby X-H (X = O, N, C) oscillators, which limits their further applications in aqueous solutions and bioimaging. Consequently, improving luminescence performance as well as dispersibility has become a key issue to expand the application of RE complexes. Till now, extensive efforts have been devoted to increasing the luminescence intensity of RE complexes, such as increasing structural rigidity, adjusting coordination numbers, replacing ligand C-H bonds with C-F bonds and changing the electron-donating or electron-withdrawing characteristics of substituents.