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.