Ultrafast Relaxation Dynamics in Graphene Oxide: Evidence of Electron Trapping

We have employed ultrafast optical pump-probe spectroscopy to study excited dynamics of graphene oxide (GO) and reduced graphene oxide (RGO) dispersed in water by exciting the samples at 400 nm laser light. We have observed multiexponential relaxation dynamics of nonequilibrium photo-generated carriers for both GO and RGO with time constants varying from 0.8 to > 400 Ps. Our analysis on excited dynamics of charge carriers revealed the involvement of phonon and trap states in relaxation dynamics. Transient absorption in the visible region on the longer time scale is attributed mainly due to the electron trap states which have been confirmed by quenching studies. Dynamics of RGO after chemical reduction was found to have reduced trap state contributions. Although the reduction procedure was found to be effective, still we have observed minor contribution due the trap states of charge carriers in transient absorption.