Understanding the mechanism of the energy transfer process from non-plasmonic fluorescence bimetallic nanoparticles to plasmonic gold nanoparticles.

Understanding the fundamentals behind the photophysical response of a fluorescing species in the vicinity of plasmonic nanoparticles is of great interest due to the importance of this event in various applications. The present work has been carried out to throw light on how plasmonic nanoparticles electronically interact with non-plasmonic nanoparticles. Specifically, in this work, the excitation energy transfer (EET) from fluorescence bimetallic silver capped gold (F-AgAu) to gold nanoparticles (AuNPs) and how this process can be modulated by cetyltrimethylammonium bromide (CTAB) have been investigated at both ensemble average and single particle levels. Steady-state and time-resolved fluorescence studies have revealed that the fluorescence intensity and lifetime of F-AgAu in the presence of AuNPs are significantly quenched. Cyclic voltammetry (CV) and polarity-dependent studies have ruled out the possibility of an electron transfer mechanism. The increased non-radiative decay rate has substantiated that the photoluminescence quenching is due to excitation energy transfer from F-AgAu to AuNPs. Interestingly, investigations have revealed that the energy transfer efficiency is reduced from 87% to 28% in the presence of CTAB due to the formation of a CTAB bilayer over AuNPs. Analysis of the data by conventional EET, nano surface energy transfer (NSET), and stretched exponential models have firmly established that the EET process follows a 1/ distance dependence (NSET) rather than conventional 1/ distance dependence as predicted with the Förster resonance energy transfer model. Additionally, single particle level measurements through fluorescence lifetime imaging microscopy (FLIM) studies have clearly demonstrated that the surfactant (CTAB) can play an important role in controlling the EET process from non-plasmonic to plasmonic nanoparticles. The outcome of the present EET between two different classes of nanoparticles is expected to be useful in developing nanoscale systems for various optoelectronic applications.