Ultrafast Charge Transfer Dynamics in Photoexcited CdTe Quantum Dot Decorated on Graphene

We report synthesis and ultrafast charge transfer dynamics of photoexcited CdTe quantum dots (QDs) decorated on graphene. We have synthesized CdTe QD particles of 2.2 nm sizes with first exciton (1S(3/2)-1S(e)) band similar to 450 nm and then decorated the QD particles on graphene which has been confirmed by HRTEM studies. The CdTe QD decorated graphene has been named as G-CdTe. Steady state emission studies revealed that on the graphene surface CdTe emission gets quenched drastically which indicates the charge transfer from photoexcited CdTe to graphene. To unravel the charge transfer dynamics in ultrafast time scale we have carried out femtosecond transient absorption studies by exciting the CdTe QD particles and monitoring the transients in the visible to near-IR region. Transient absorption studies indicate that exciton recombination time (as monitored the exciton bleach) of, pure CdTe QD takes place within 50 ps; however, on graphene the surface exciton recombination time was found to be much longer (> 1 ns). Our studies clearly indicate that charge separation of G-CdTe composite materials drastically improves as compared to that CdTe QD.