Abstract
The mechanism of light emission from metallic nanoparticles has been a subject of debate in recent years. Photoluminescence and electronic Raman scattering mechanisms have both been proposed to explain the observed emission from plasmonic nanostructures. Recent results from Stokes and anti-Stokes emission spectroscopy of single gold nanorods using continuous wave laser excitation carried out in our laboratory are summarized here. We show that varying excitation wavelength and power change the energy distribution of hot carriers and impact the emission spectral lineshape. We then examine the role of interband and intraband transitions in the emission lineshape by varying the particle size. We establish a relationship between the single particle emission quantum yield and its corresponding plasmonic resonance quality factor, which we also tune through nanorod crystallinity. Finally, based on anti-Stokes emission, we extract electron temperatures that further suggest a hot carrier based mechanism. The central role of hot carriers in our systematic study on gold nanorods as a model system supports a Purcell effect enhanced hot carrier photoluminescence mechanism. We end with a discussion on the impact of understanding the light emission mechanism on fields utilizing hot carrier distributions, such as photocatalysis and nanothermometry.
Highlights
We show the effects that varying excitation wavelength and power as well as the AuNR size have on the PL and relate quantitative single particle PL quantum yields (QYs) to their corresponding Purcell factors and electromagnetic local density of states (LDOS)[94–96] by analyzing darkfield scattering (DFS) quality factors (Q-factors)
The wavelength, excitation power, and size dependence of inter- and intraband emission efficiencies highlight the effect of confinement and the band structure of gold in determining the spectral lineshape and QY of the emission
The slight changes in observed emission indicate different hot carrier energy distributions and suggest that it should be possible through further theoretical studies to determine hot carrier distributions from emission spectroscopy using cw excitation, which more accurately mimics low level and solar irradiation
Summary
Light emission from plasmonic nanoparticles can be applied in imaging[1,2,3,4,5,6,7] and sensing,[8,9,10,11,12] accurately probing local temperature[13,14,15,16,17] and chemical reactions at the nanoscale.[18,19,20,21] It contributes to the background of surface-enhanced Raman scattering (SERS)[22,23,24,25] and plasmon enhanced fluorescence.[26,27,28,29] the emission mechanism is a critical area of study.
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