Luminescence of europium(III) and terbium(III) complexes incorporated in poly(vinyl pyrrolidone) matrix

Lanthanide complexes of europium and terbium ions with hydrogen phthalate [Eu(Hphth)(3) and Tb(Hphth)(3), respectively, Hphth = hydrogen phthalate] were incorporated into poly(vinyl pyrrolidone) (PVP) matrix. Transmission electron microscopy (TEM) results showed that the lanthanide complexes, with a mean diameter about 8.0 nm, were dispersed homogeneously in the PVP matrix. The excitation of the Ln(Hphth)(3)-PVP system by UV light resulted in a ligand-to-metal energy transfer and the emission spectra of the complexes displayed characteristic luminescence of the central ions. PVP significantly affected the strength of the hypersensitive transitions (D-5(0) --> F-7(2) for EU3+, and D-5(4) --> F-7(5) for Tb3+) of the complexes. For the mixed complexes containing both EU3+ and Tb3+ as central ions, the luminescent intensity was strongly dependent upon the ratio of the lanthanide ions. Trace amount of EU3+ quenched the luminescence of the Tb3+, whereas the presence of Tb3+ enhanced the luminescence of the EU3+, thus demonstrating an important feature of energy transfer from terbium to europium in the mixed complexes.