Spectroscopic investigations of the photo-induced structural transformation of C60 single crystals under high pressure

Photo-induced structural transformations of C60 single crystals under pressures up to 30 GPa were investigated by means of optical transmittance and photoluminescence. We found that the band gap energy shifts toward lower energies at a rate of −16 meV/GPa with an increase in the pressure applied during photo-irradiation. The activation energy of the photo-induced structural transformation at 3 GPa was estimated to be 0.23 eV. Analysis of the optical spectra estimates the number of [2 + 2] cycloadditional bonds created by photo-irradiation under pressure, and indicates that the intermolecular bonds expand to three dimensions to sustain highly contracted structure.