Optical properties of endohedral Li@C60

UV–VIS, IR and Raman investigations have been carried out on purified Li@C60 produced by low energy ion implantation of C60. Two endohedral fractions can be isolated that have very different optical properties and stabilities. Here we show that the first endohedral fraction is a dimer species and the second fraction is the monomer. The IR spectra of sublimed monomer films show a prominent peak at around 1.1 μm corresponding to the first electronic transition of the C60− anion. Raman spectra show the vibrational–rotational movement of the Li inside the carbon cage.