Confirmation of the resonance energy transfer between Rare Earth-DNA-Carbon Nanotube complex

We used the resonance excitation spectroscopy combined with the time-resolved study of the excited states following the 20ps laser excitation to investigate the energy transfer between rare earth (RE) ions and single wall nanotubes (SWNT). Selectively excited Tb$^{3+}$ and Eu$^{3+}$ ions in water solution containing a high concentration of DNA-wrapped SWNT showed a small systematic energy transfer from RE to SWNT. The measured value of the resonant energy transfer is consistent with our theoretical estimation based on the spectral overlap of the corresponding absorption and emission spectra of energy acceptors and donors. We performed additional characterization to prove the ionization states of the RE ions using the high-resolution X-ray Photoelectron Spectroscopy. The observed shift of the 4d -- line of Tb is a signature of Tb$^{2+}$ state which corroborates our assumption of Tb chemical bonding with the DNA-SWNT complex.