Evaluating Conditions for Strong Coupling between Nanoparticle Plasmons and Organic Dyes Using Scattering and Absorption Spectroscopy

Zengin, Gülis; Gschneidtner, Tina; Verre, Ruggero; Shao, Lei; Antosiewicz, Tomasz J.; Moth‐Poulsen, Kasper; Käll, Mikael; Shegai, Timur

doi:10.1021/acs.jpcc.6b00219

Cited by 66 publications

(80 citation statements)

References 45 publications

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“…Several hybrid nanoparticles that allegedly show strong coupling have been presented in recent literature [14][15][16][17][18]. In several cases these claims have however been challenged [19,20], as an unambiguous determination of the coupling regime for hybrid nanoparticles is difficult. A clear prove for the presence of strong coupling would be obtained by comparing Ω to the spectral line-width of both the uncoupled plasmon and the molecules.…”

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confidence: 99%

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Signatures of Strong Coupling on Nanoparticles: Revealing Absorption Anticrossing by Tuning the Dielectric Environment

2017

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Strongly coupled plasmon-exciton systems offer promising applications in nanooptics. The classification of the coupling regime is currently debated both from experimental and theoretical perspectives. We present a method to unambiguously identify strong coupling in plasmon-exciton core-shell nanoparticles by measuring true absorption spectra of the system. We investigate the coupling of excitons in J-aggregates to the localized surface plasmon polaritons on gold nanospheres and nanorods by fine-tuning the plasmon resonance via layer-by-layer deposition of polyelectrolytes. While both structures show a characteristic anticrossing in extinction and scattering experiments, the careful assessment of the systems' light absorption reveals that strong coupling of the plasmon to the exciton is only present in the nanorod system. In a phenomenological model of two classical coupled oscillators, intermediate coupling strengths split up only the resonance frequency of the light-driven oscillator, while the other one still dissipates energy at its original frequency. Only in the strong-coupling limit, both oscillators split up the frequencies at which they dissipate energy, qualitatively explaining our experimental finding.The electromagnetic coupling of molecular excitations to plasmonic nanoparticles offers a promising method to manipulate the light-matter interaction at the nanoscale. This approach is frequently used to enhance the optical cross-section of molecules, e.g. in surface enhanced Raman scattering (SERS) [1], enhancement of fluorescence [2] and infrared absorption [3,4], plasmonenhanced light-harvesting in dye-sensitized solar cells [5] or plasmon-enhanced dye-lasers [6].The coupling strength between molecular excitations and plasmons is given by the rate of energy-exchange between the two components Ω = E · µ/h [7]. Here µ describes the transition dipole moment of the emitter and E the electric-field strength of the light at the emitter-location. Plasmonic nanoparticles foster exceptionally high coupling strengths, due to their capacity to strongly concentrate the light-field to sub-wavelength mode volumes and hence to generate very high electrical field-strengths in their vicinity. A particularly interesting coupling regime occurs, if the coupling increases to a level such that Ω surpasses all damping rates in the system. In this socalled strong coupling regime hybrid light-matter states emerge, which cannot be divided into separate light and matter components. The new resonances of the coupled system emerge from the plasmon resonance ω p and the exciton resonance ω ex as [8,9] where g is the coupling parameter.Hence, the presence of the new hybrid-states can be de- The most frequently used approach for achieving strong light-matter coupling on nanoparticles, is the fabrication of hybrid core-shell particles with a noble-metal core and a molecular shell. Several hybrid nanoparticles that allegedly show strong coupling have been presented in recent literature [14][15][16][17][18]. In several cases these claim...

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“…This brings up the question, how to prove the presence of strong coupling for an ensemble of hybrid nanoparticles. Several authors discussed that absorption and fluorescence are the only reliable quantities to determine the presence of strong light-matter coupling [19,20]. However, both quantities are not regularly determined for nanoparticle ensembles.…”

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Signatures of Strong Coupling on Nanoparticles: Revealing Absorption Anticrossing by Tuning the Dielectric Environment

2017

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“…It was found that the deposited light‐absorbing molecules induce transparency windows in the plasmonic spectra of the arrays of gold and silver nanodisks (Table , sketch e) . Moreover, it was shown that the density of the dye coating on Ag nanodisks ( Figure a) plays an important role in the light–matter interaction leading to IT . In the case of R6G dissolved in methanol (Figure b, sketch S1), the scattering spectra turned out to be almost identical for the coated and uncoated samples, which was caused by low density of the coating.…”

Section: The Geometries and Morphologies Of Plasmon–exciton Nanostrucmentioning

confidence: 95%

“…Apart from single‐particle core–shell systems, an array of metal structures coated with a layer of an absorber is another plasmonic structure that was proposed and used to reach the IT regime. It was found that the deposited light‐absorbing molecules induce transparency windows in the plasmonic spectra of the arrays of gold and silver nanodisks (Table , sketch e) . Moreover, it was shown that the density of the dye coating on Ag nanodisks ( Figure a) plays an important role in the light–matter interaction leading to IT .…”

Section: The Geometries and Morphologies Of Plasmon–exciton Nanostrucmentioning

confidence: 98%

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Induced Transparency in Plasmon–Exciton Nanostructures for Sensing Applications

Krivenkov

Goncharov

Nabiev

et al. 2018

Laser & Photonics Reviews

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The effect of induced transparency, which is related to photoinduced bleaching of photoabsorbers, is being intensely studied and has many applications in the field of sensing. Along with this classical effect, numerous studies on induced transparency in coupled plasmon-exciton systems, which is accompanied by the formation of hybrid states, have been recently published. The formation of a new coupled system results in various spectral modifications. For example, induced transparency manifests itself as a narrow dip in the absorption spectrum of a coupled system. This effect can be used in sensing, the feasibility of which is the main objective here, where a variety of materials and methods for obtaining the induced transparency are considered. Various morphologies and geometries of plasmonic nanoparticles are discussed as well as types of molecular absorbers to assess the most favorable combinations for the evolvement of induced transparency. The potential applications of the induced transparency effect in sensing and molecular diagnostics are summarized.As shown above, the IT effect is highly sensitive to several parameters of the composite system: the distance between the absorber and the plasmonic structure, their mutual arrangement, and the type and properties of the absorber itself. At the same time, the

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Probing Vibrational Strong Coupling of Molecules with Wavelength‐Modulated Raman Spectroscopy

Menghrajani

Chen

Dholakia

et al. 2021

Advanced Optical Materials

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that are shifted from that of the incident laser light. In particular, peaks appear in the spectrum of the scattered light that correspond to vibrational resonances of the molecules/materials of which the sample is composed. These spectral peaks form the characteristic fingerprints of the molecules/materials under investigation; the study of such spectra is known as Raman spectroscopy and has become a well-established and powerful analytic technique. [5] Unfortunately, Raman signals are very weak with cross-sections of order 10 −30 cm 2 for non-resonant Raman and 10 −24 cm 2 for resonant Raman. [6] In many situations, these very weak signals are swamped by light produced by other processes, notably fluorescence, which can be many orders of magnitude stronger than the Raman signal. Background fluorescence is particularly problematic when the samples to be investigated are dyes/pigments, [3] for example, resonant Raman, [6] and also when they involve metals. [7] In both cases, fluorescence can be so significant as to mask the desired Raman signals.Various approaches have been adopted to try and deal with the background problem, [8,9] and they fall into three broad categories. First, post-processing can be used to try and subtract the background. [10,11] Although appealing and commonly used, this approach has its drawbacks, especially in that it does not overcome the problem of noise in the background signal. Second, one can move to the time-domain. Raman scattering is an instantaneous process, whereas fluorescence occurs over a protracted time-scale; however, this approach comes at a very significant increase in complexity. [12] Third, a differential approach can be adopted. Here, the idea is to modify the way the data are acquired so as to directly filter out the background and its associated noise. A number of such approaches have been successfully deployed. One technique is based on acquiring spectra for slightly different grating settings in the spectrometer. [7] Another approach is to subtract two Raman spectra obtained with different polarization configurations. [13] Then, there are techniques that make use of the fact that if the pump wavelength is shifted the Raman peaks will also move in wavelength, but the fluorescence will not. Spectra acquired at two or more closely spaced pump wavelengths can thus be processed to provide a differential signal that largely eliminates the background; [14] this technique is known as shifted excitation Raman difference spectroscopy (SERDS). We make use of one variant of this approach here, that of wavelength-modulated Raman spectroscopy (WMRS). WMRS [15] is a significant improvement on Raman spectroscopy is a powerful technique that enables fingerprinting of materials, molecules, and chemical environments by probing vibrational resonances. In many applications, the desired Raman signals are masked by fluorescence, either from the molecular system being studied, or from adjacent metallic nanostructures. Here, it is shown that wavelength-modulated Raman spectroscopy provides...

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Evaluating Conditions for Strong Coupling between Nanoparticle Plasmons and Organic Dyes Using Scattering and Absorption Spectroscopy

Cited by 66 publications

References 45 publications

Signatures of Strong Coupling on Nanoparticles: Revealing Absorption Anticrossing by Tuning the Dielectric Environment

Signatures of Strong Coupling on Nanoparticles: Revealing Absorption Anticrossing by Tuning the Dielectric Environment

Induced Transparency in Plasmon–Exciton Nanostructures for Sensing Applications

Probing Vibrational Strong Coupling of Molecules with Wavelength‐Modulated Raman Spectroscopy

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