Surface modified EuxLa1-xF3 nanoparticles as luminescent biomarkers: Still plenty of room at the bottom

Investigation of the formation and luminescent properties of surface modified bimetallic lanthanide fluorides and their use in bioimaging is described. We have shown that the solvent during the wet synthesis of EuF3 nanoparticles affects the nanoparticle morphology, which in turn influences the conditions of its phase transition from hexagonal to orthorhombic. The morphology of bimetallic EuxLa1-xF3 depends on the europium fraction x, allowing nanoparticles of ca. 50 nm to be obtained. Surface modification with aromatic carboxylates (L) allowed luminescence intensity increase by two orders magnitude, while luminescence quantum yield (PLQY) dependence on Eu fraction was shown to be affected by the ligand L: so, when L = 2,6-naphtalenedicarboxylate, PLQY reached its maximum of 70% at x = 0.3, while when L = terephthalate, almost no quantum yield decrease was observed for 0.01 < x < 0.3 (PLQY = 70 ± 5%). Nanoparticles solubilized in water were obtained by different polymer immobilization of the particle surface, and the use of poly(vinylpyrrolidone) (PVP) resulted in the formation of non-toxic nanoparticles PVP@L@Eu0.3La0.7F3, which uniformly distributed in cell cytoplasm and exhibited intensive luminescence in cells.