Reverse saturable absorption in C60-doped porous glasses studied by single- and double-pulse pump-probe experiments

We investigate the nonlinear absorption of C-60-doped porous sol-gel glasses by single- and double-pulse pump-probe experiments. We find that the reverse saturable absorption (RSA) of these samples can be explained in the frame of a five level system as it is commonly used for C-60 solutions. We observe a strong saturation of the RSA at high fluences, especially if the molecules are prepared in the triplet state. In a double-pulse pump-probe experiment we measure the triplet quantum yield for C-60 solutions (0.8) and doped glasses (0.25) and the singlet and triplet absorption cross sections. In the first excited singlet state (S-1) lifetimes of 1 ns and 65 ps are determined in solutions and glasses, respectively. We find that the dynamics of both depopulation processes, direct S-1-S-0 relaxation, and intersystem crossing is faster in glasses than in the case where C-60 is in solution in a liquid aromatic solvent. We tentatively explain these findings by the absence of a stabilizing solvent and a perturbation of the molecular energy levels due to interaction with the solid glass matrix. We finally determine the lifetime of the triplet states in our glass samples to 2 mu s. (C) 1999 American Institute of Physics. [S0021-9606(99)00537-1].