Resonant excitation energy transfer from carbon dots to different sized silver nanoparticles

The influence of size on the efficiency of the nanometal surface energy transfer (NSET) process between excited donors and different sized metal nanoparticles (NPs) is poorly explored in the literature. Here we present a systematic study by correlating the size of silver nanoparticles (Ag NPs) with the efficiency of excitation energy transfer (EET) from carbon dots (CDs) to Ag NPs. Three different sized citrate-capped Ag NPs with a mean hydrodynamic diameter of 39.91 ± 1.03, 53.12 ± 0.31 and 61.84 ± 0.77 nm have been synthesized for the present study. The estimated zeta potential of the synthesized CD is -25.45 ± 1.23 mV while that for the smallest, medium and largest sized Ag NPs are -76.24 ± 3.92, -67.60 ± 4.40, and -58.01 ± 3.10 mV, respectively. The steady-state and time-resolved PL measurements reveal a significant PL quenching of CDs as a function of Ag NP size. A control experiment with Ag NPs having a LSPR at 398 nm shows a negligible amount of PL quenching of CDs as a consequence of inadequate spectral overlap. The origin behind this PL quenching of CDs has been rationalized on the basis of the increased nonradiative decay rate due to NSET from the CDs to the Ag NP surface. Various energy transfer related parameters have been estimated from the NSET theory and it has been observed that the NSET efficiency increases with the increase in the size of Ag NPs. This phenomenon has been explained by considering a larger spectral overlap and a shorter separation distance between the CDs and larger sized Ag NPs due to reduced electrostatic repulsion. Our present results reveal that the size of NPs plays an important role in the NSET process and this phenomenon can be easily utilized to tune the efficiency of energy transfer for various applications.