FEMTOSECOND TO NANOSECOND DYNAMICS IN FULLERENES - IMPLICATIONS FOR EXCITED-STATE OPTICAL NONLINEARITIES

We compared detailed dynamics of the excited-state absorption for C-60 in solution, thin films, and entrapped in an inorganic sol-gel glass matrix. Our results demonstrate that the microscopic morphology of the C-60 molecules plays a crucial role in determining the relaxation dyn amics. This is a key factor for applications in optical limiting for n anosecond pulses using reverse saturable absorption. We find that the dynamics of our C-60-glass composites occur on long (ns) timescales, c omparable to those in solution; thin film samples, by contrast, show r apid decay (<20 picoseconds). These results demonstrate that C-60-sol- gel glass composites contain C-60 in a molecular dispersion, and are s uitable candidates for solid-state optical limiting. Multispectral ana lysis of the decay dynamics in solution allows accurate determination of both the intersystem crossing time (600 +/- 100 ps) and the relativ e strengths of the singlet and triplet excited-state cross sections as a function of wavelength from 450-950 nm. The triplet excited-state c ross section is greater than that for the singlet excited-state over t he range from 620-810 nm.