RESUMO
We present Raman spectroscopic studies of the isostructural and isoelectronic Eu(6-x)Sr(x)C(60) (x = 0, 3, 5, 6) and Ba(6)C(60) compounds. The Raman spectra of the Eu-based fullerides show dramatic changes compared to the pure alkaline-earth systems, including significant broadening, splitting and frequency shifts of the fivefold degenerate H(g) intramolecular modes of C(60). Moreover, the A(g)(2) mode exhibits an even larger downshift and a remarkable broadening. These findings are consistent with distortions of the C(60) molecular cages and a considerable electron-phonon coupling strength-strongly enhanced in the Eu containing systems-originating from the strong orbital hybridization between the metal atom and the C(60) molecule.
RESUMO
Specific details of the electronic spectra of perfect crystalline polymers of C60 were studied by means of the photoluminescence spectra measurements at normal conditions and at high pressure up to 4 GPa. The structure of the photoluminescence spectra, the intensity distribution between the principal bands and the pressure-induced shift of the bands differ considerably among the pristine C60, linear orthorhombic and planar tetragonal and rhombohedral polymeric phases of C60. Unlike the planar polymers of C60, the linear orthorhombic polymer exhibits irreversible changes in the photoluminescence spectrum under simultaneous application of high pressure and laser irradiation. The changes observed in the photoluminescence spectra of the planar polymeric phases of C60, as compared to the pristine material, are discussed in relation to the corresponding changes in the calculated electronic structure of the pristine C60 and its polymeric phases. The observed photoluminescence spectral structure along with the pressure behavior of the photoluminescence spectra are very sensitive to the structure of the polymers as well as to the C60 cage deformations and can be used to effectively characterize the various polymeric phases of C60.
