Eu-Doped BaF2 Nanoparticles for Bioimaging Applications

摘要： Pure Eu3+ ion doped BaF2 nanoparticles with tunable properties or property combinations are accessible via an ionic liquid-assisted solvothermal method. Structural parameters such as cell parameters, lattice strain and especially morphology are judiciously tuned with calcination temperatures. For example, tensile strain is observed in samples calcined up to 400oC, however compressive strain appears in samples calcined at 600oC and beyond. Larger surface area up to the sample calcined at 400oC and observation of layer structure at higher calcinations temperature (650oC and beyond) have been rationalized based on secondary nucleation. 3-dimensional island-like morphology with step-like layer structure caused by secondary nucleation and self-assembly are visualized and explained by Scanning Electron Microscope analysis. Moreover, emission intensity, decay time, quantum yield and Judd-Ofelt parameter of the Eu3+ ions increase systematically with calcinations temperature to a maximum at 400oC, above which they decrease and finally vanish at 800oC. Our results suggest that, smaller sized nanoparticles with 3-dimensional island-like structures, generated due to secondary nucleation at higher calcinations temperature may cause the increase of surface defects and subsequent luminescence quenching. To the best of our knowledge, the interplay between calcinations and secondary nucleation followed by drastic changes in the luminescence properties is new and previously unreported for the nanopowders. In addition, to improve the dispersibility, as-prepared nanoparticles are coated with silica and solubility of nanoparticles is measured in different solvents so that it can be useful for bio-imaging applications also.