Optical properties of nanoplasmon excitations in clusters of endometallofullerenes

The optical properties of solutions of endometallofullerenes with lanthanides (Gd@C₈₂, Ce@C₈₂, La@C₈₂, Y@C₈₂) in dimethylformamide are studied. It is found that these solutions luminesce in the visible region. This luminescence is accompanied by enhanced Raman scattering. It is suggested that these processes are related to nanoplasmon excitations in clusters of endometallofullerenes. It is shown that the luminescence spectrum is described by a superposition of three to four Gaussian spectral profiles, whose energy positions and intensities nonmonotonically depend on the energy of excitation quanta. A detailed quantitative dependence of the intensity and shape of the Raman scattering signal on the concentration of endometallofullerenes in the solutions is determined. Comparative measurements are performed for the emission spectra of solutions of simple fullerenes and chromatographically pure endometallofullerenes. Complex investigations show that the visible luminescence and Raman scattering enhancement are only observed in the case of the formation of nanosized anionic complexes of endometallofullerenes in the solution.