Nanoassembly of photoluminescent films containing rare earth complex nanoparticles on planar and microspherical supports

In this paper, we describe the fabrication of photoluminescent films containing rare earth complex nanoparticles on both planar and spherical supports by using the layer-by-layer (LBL) self-assembly technique. The rare earth complex nanoparticles are synthesized in aqueous solution, with trivalent europium as the metal center ion, dibenzoylmethane (DBM) as the ligand and poly(ethylenimine) (PEI) as the stabilizing agent. The particle size is about 2 nm as revealed by transmission electron microscopy (TEM) images. During the formation of Eu(DBM)₃ nanoparticles, PEI stabilize the nanoparticles and confer a well-defined positive surface, thus preventing the nanoparticles from aggregation and affording stable dispersion. These nanoparticles can be assembled to form ultrathin films by alternate deposition with poly(sodium 4-styrene sulfonate) (PSS) on planar supports. The resulting films show the same UV and fluorescence characteristics as the corresponding aqueous nanoparticle dispersion, which indicates that the deposition process is successful. In addition, atomic force microscopy (AFM) and TEM have been used to characterize the surface morphology of these films. Aggregations in the size range of 30-70 nm are found in the composite films. A strong and narrow emission peak at 612 nm can be found in the photoluminescence (PL) spectra of the LBL films, which is the characteristic emission of Eu³⁺. We have also extended the substrate of LBL assembly to microspherical surface, and obtained composite fluorescent shells on silica microspheres.