Time-resolved carrier relaxation in solidC60thin films

The time dependence of the carrier relaxation in undoped solid ${\mathrm{C}}_{60}$ thin films has been studied by monitoring changes in the optical transmission upon photoexcitation at the HOMO-LUMO band edge. The relaxation closely follows a Kohlrausch-Williams-Watts decay with an exponent of β=0.4. This functional form is typical of carrier relaxation associated with states of localized rather than extended character. In addition, we observe this relaxation behavior to be independent of temperature, which indicates that a hopping mechanism may be important in the carrier recombination process in solid ${\mathrm{C}}_{60}$.