LONG-LIVED EXCITED-STATES AND PHOTOLUMINESCENCE EXCITATION-SPECTRA INSINGLE-CRYSTALS OF FULLERENE C-60

Photoluminescence, optical absorption spectra, and photoluminescence e xcitation spectra were measured on large (2-3 mm), very pure crystals of fullerene C-60 at 5 K. It is shown that the main contribution to th e photoluminescence of these crystals is from singlet and triplet exci tons captured on crystal defects. The concentration of these defects d oes not exceed 10(18) cm(-3) and the lifetime of triplet excitons on t hese defects is about 3 ms. It is shown that the symmetry distortion o f the C-60 molecules at the defects is rather large and causes the osc illator strength of the zero-phonon optical transitions to be comparab le to the most intense optical transitions with the participation of i ntramolecular vibrations. (C) 1998 American Institute of Physics.