Reproduction of surface-enhanced resonant Raman scattering and fluorescence spectra of a strong coupling system composed of a single silver nanoparticle dimer and a few dye molecules

Abstract

The spectral changes in surface-enhanced resonant Raman scattering (SERRS) and surface enhanced fluorescence (SEF) of single silver nanoparticle dimers adsorbed by near-single dye molecules are reproduced under strong coupling regimes. For the reproduction, the enhancement and quenching factors in SERRS and SEF are derived from the Purcell factors including both radiative and nonradiative plasmon modes. The Purcell factors are estimated using the coupling energies obtained by analyzing the spectral changes in plasmon resonance during SERRS and SEF decay processes on the basis of a classical hybridization model. The model is composed of a plasmon and a molecular exciton with phonon replicas accurately representing the molecular multi-level system. The reproduced SERRS spectral changes are consistent with the experimental ones. Furthermore, the calculated SEF spectral changes can reproduce the experimental ones by phenomenologically assuming transitions from ultra-fast SEF to conventional SEF with decreasing coupling energies.

Absorption cross-section spectroscopy of a single strong-coupling system between plasmon and molecular exciton resonance using a single silver nanoparticle dimer generating surface-enhanced resonant Raman scattering

“…We applied the above conversion method to the plasmon resonance spectra from 14 silver NP dimers before and after SERRS quenching. with the disappearance of SERRS activity [7,9,12]. As the origin of SERRS is the EM coupling between a plasmon and a molecular exciton [3,4], these simultaneous blue-shifts are considered to be the result of a loss of EM coupling energy by SERRS quenching.…”

“…The values of fn are determined from the absorption spectrum of R6G molecules [4,12]: , where d (= 0.12 nm) is the dipole length of R6G [4], and 2 f -4 f are obtained by multiplying 1 f by the ratios of the peak intensity of the Lorentzian curves between 1 f and n f [12].…”

“…Therefore, by excluding such variations, the development of optical absorption spectroscopy for single strong coupling systems is an important step in correctly evaluating the relationships between these unique phenomena and strong coupling. The other intrinsic importance of investigating single strong coupling systems is the identification of the plasmon "resonance" that induces the strong coupling [9,12]. In the case of SERRS, the relationships between plasmon resonance and SERRS have been confirmed using single silver NP dimers [5,[20][21][22][23].…”

Anti-crossing property of strong coupling system of silver nanoparticle dimers coated with thin dye molecular films analyzed by electromagnetism

“…1(b)). 9 They also mean that the exchange rate of photons between plasmons and excitons is larger than their dephasing rates. 13 Such a fast coupling process occurring within the coherent times of both resonances is called "strong coupling", during which plasmon resonance couples with the molecular exciton resonance.…”

“…1(d)). 9 In the case of dimers, it is not easy to experimentally detect anti-crossing behavior by tuning plasmon resonance through the adjustment of various experimental parameters including NP sizes, shapes, and gap distances because the latter significantly change the coupling energy. Furthermore, the multi-level properties of molecules make anti-crossing characteristics very unclear.…”