Enhancing and Quenching Functions of Silver Nanoparticles on the Luminescent Properties of Europium Complex in the Solution Phase

Luminescent properties of the Eu(dinic) complex, where dinic is dinicotinic acid, were examined in the presence of silver nanoparticles in N,N-dimethylformamide. The formation of particle aggregates was observed upon mixing the particle solution with the complex solution, in which the complexes behaved like linker molecules. Luminescent intensity of the complexes was enhanced in the presence of silver nanoparticles, but at only a limited particle concentration region. The observed particle concentration dependences of the luminescent intensity were regarded as the result of a delicate balance between an enhancing and a quenching effect of the silver nanoparticles. In addition to the change in intensity, silver nanoparticles also affected the asymmetric ratio (or monochromaticity) of the europium luminescence. These changes in the luminescent properties of the complex were discussed in terms of the effects of particle aggregates and consequent modifications of the local electromagnetic field, refractive index, and the ligand field around europium ion.