RELAXATION OF C-60 IN SOLUTIONS AND FILMS - RESULTS OF FEMTOSECOND MEASUREMENTS

Femtosecond laser spectroscopy has revealed a substantial difference b etween the relaxation properties of C60 in solutions and in films at e xcitation intensities 10(10)-10(11) W/cm2. An absorption increase with a time scale of 1.2 ps is observed in the solution. This increase is attributed to a restructuring of the molecule after the absorption of a photon. In the film, the induced absorption undergoes a nonexponenti al decay, at a rate which increases with increasing excitation intensi ty. This effect is attributed to singlet-singlet annihilation.