The luminescence spectra of lanthanide ions bound to DNA or RNA are highly dependent on nucleic acid sequence and structure. For example, a simple DNA hairpin with the naturally occurring GCA loop is a binding site for europium ion. Direct excitation luminescence spectroscopy shows that europium ion luminescence intensity and lifetime increase upon addition of the DNA hairpin. These excitation spectra and time-resolved studies are consistent with loss of europium water ligands in the europium-DNA complex. The hairpin binding site is exquisitely sensitive to single nucleotide changes in both the loop and stem. The luminescence signature of lanthanides bound to various DNA and RNA oligonucleotides containing common structural motifs will be presented. The characterization of metal ion binding sites is important to the design of luminescent nucleic acid materials and toward the development of luminescent metal ions and complexes as sensors of RNA and DNA targets.