Time-resolved fluorescence spectra for C-60 molecules embedded in Ne and Ar matrices and C-70 in Ne matrices were recorded using a synchroscan streak camera. In the case of C-60, the decay times of the S-1 state are identical for all fluorescence bands confirming that it is a state of mixed T-1g, T-2g, and G(g) characters. Its lifetime is determined by the intersystem crossing rate to the triplet manifold which increases in going from Ar to Ne matrices. This is attributed to a change of the dominant symmetry character of S-1 in the two matrices. A transient, short-lived (similar to 170 ps in Ne, similar to 70 ps in Ar), S-3 fluorescence of dominant G(g) symmetry is also observed, which feeds the S-2/S-1 population (of dominant T-2g and T-1g symmetry). Using the Energy Gap Law, a change of the S-3 --> S-2/S-1 decay rate from Ne to Ar matrices is attributed to the different number of phonons needed to bridge the gap between these states and/or to an environment-dependent change of the coupling matrix element. In C-70, the fluorescence from both S-1 and S-2 are populated at the same rate despite the 165 cm(-1) energy gap between them. This is explained in terms of an intersystem crossing from the triplet state manifold. Finally, S-2 decays predominantly to S-1, while the latter decays to the triplet states by reversible intersystem crossing. These conclusions are confirmed by a simple kinetic model.