Long-Range Resonance Coupling-Induced Surface Energy Transfer from CdTe Quantum Dot to Plasmonic Nanoparticle

Abstract

Fundamental understanding and precise control of complex nonradiative processes in nanoscale system finds significant interest in recent times due to their importance in various nanophotonics applications. Here we have systematically investigated the mechanism behind photoluminescence (PL) quenching of mercaptosuccinic acid (MSA) capped CdTe QDs in the near field of gold and silver nanoparticles (Au and Ag NPs) by using steady-state and time-resolved photoluminescence (PL) spectroscopy. Resonance coupling between excitonic emission and localized surface plasmon resonance (LSPR) of Au NPs has been tuned by varying the size of QDs. Herein, three differently sized MSA-capped CdTe QDs have been synthesized namely, 2.1 ± 0.7, 3.1 ± 0.4, and 3.9 ± 0.3 nm with emission in green, yellow and red region of the electromagnetic spectrum, respectively. It has been observed that both the luminescence intensity and lifetime of green QDs quench significantly in the near field of 20 nm sized Au NPs. In contrast, the luminescent intensity and lifetime of yellow and red QDs remain unaltered in the presence of Au NPs. Moreover, it has been observed that ligand exchange at the surface of Au NPs with Poly(ethylene glycol) methyl ether thiol (PEG-SH) decreases the quenching efficiency of the green QD-Au NP pair significantly. In addition, the extent of quenching strongly depends on excitation wavelength. The observed quenching is more efficient at the excitation wavelength close to the LSPR of Au NP. These results have been explained on the basis of a size-dependent nanometal surface energy transfer (NSET) model by incorporating the changes in the complex dielectric function and the absorptivity of the Au NP. On the contrary, irrespective of the sizes of QDs, significant PL quenching has been observed in the presence of 10 nm sized citrate-capped Ag NPs as a consequence of photoinduced electron transfer (PET). The present findings of size and wavelength-dependent long-range nonradiative electromagnetic coupling in hybrid QD-metal NP system can be useful to understand and optimize the performance of various nanophotonic devices. © 2018 American Chemical Society.