Nonlinear absorption and scattering of C₆₀ colloids in water with Triton X-100 surfactant

New synthesis techniques for highly concentrated colloidal C₆₀ suspensions were developed. The nonlinear absorption and nonlinear scattering behavior of colloidal C₆₀ suspensions and benchmark materials (carbon black suspension and C₆₀ solution) were studied with an apparatus that simultaneously measured the total scattered and transmitted energy, inferring absorbance. These experimental results were compared to simple thermodynamic and reverse saturable absorption models, as well as a hybridized model proposed for the nonlinear optical behavior of C₆₀ colloids. All samples followed an attenuation pattern in the nonlinear scattering regime that was fit by a single extinction coefficient, indicating that the energy in excess of that required to reach the sublimation threshold does not significantly affect the size of the induced scattering centers. C₆₀ colloids evidenced strong quenching of the first excited singlet band, leading to weak intersystem-crossing to the triplet manifold. The degree of quenching was morphology dependent. Tighter crystalline packing led to stronger quenching. Samples with higher triplet quantum yield evidenced less efficient heating of the particles. Consequently, for otherwise similar C₆₀ colloids, stronger nonlinear absorption response was found to diminish the nonlinear scattering response. Large, crystalline C₆₀ colloids had a stronger nonlinear optical response than benchmarks.