Ligand-capped gold nanoparticles were synthesized by capping monothiol derivatives of 2,2'dipyridyl onto the surface of Au nanoparticles (Au-BT). The average size of the metal core is around 4 nm, with a shell of similar to 340 bipyridine ligands around the Au nanoparticle. The high local concentration of the chelating ligands (similar to 5 M) around the Au nanoparticle makes these particles excellent ion sponges, and their complexation with Eu-lll/Tb-lll ions yields phosphorescent nanomaterials. Absorption spectral studies confirm a 1:3 complexation between Eul(lll)/Tb-lll ions and bipyridines, functionalized on the surface of Au nanoparticles. The red-emitting Au-BT:Eu-lll complex exhibits a long lifetime of 0.36 ms with six line-like emission peaks, whereas the green-emitting Au-BT:Tb-lll complex exhibits a lifetime of 0.7 ms with four line-like emission peaks. These phosphorescent nanomaterials, designed by linking BT:Eu-lll complexes to Au nanoparticles, were further utilized as sensors for metal cations. A dramatic decrease in the luminescence was observed upon addition of alkaline earth metal ions (Ca2+, Mg2+) and transition metal ions (Cu2+, Zn2+, Ni2+), resulting from an isomorphous substitution of Eu-lll ions, whereas the luminescence intensity was not influenced by the addition of Na+ and K+ ions. Direct interaction of bipyridine-capped Au nanoparticles with Cu2+ ions brings the nanohybrid systems closer, leading to the formation of three-dimensional superstructures. Strong interparticle plasmon interactions were observed in these closely spaced Au nanoparticles.