Enhancement mechanism of saturable absorption effect in graphene decorated with silver nanoparticles

Reduced graphene oxide (rGO) decorated with silver nanoparticles exhibits an enhanced nonlinear absorption effect compared with pure rGO. Using femtosecond time-resolved transient absorption spectroscopy, the enhancement mechanism and carrier dynamics of the composites are experimentally demonstrated. When the material is excited by laser pulses, the excited carriers in the conduction band of graphene will transfer to the d-band of silver before returning to the valence band. As the decay process (∼210 ps) is much longer than that of the relaxation time in pure graphene (∼fs), the bleaching effect of valence band is prolonged, resulting in enhanced saturable absorption effect.