Energy transfer and depolarization in the photoluminescence of a plasmonic molecule

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Light emission from plasmonic nanostructures

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.

Selectively enhanced Raman/fluorescence spectra in photonic-plasmonic hybrid structures

The manipulation of the interaction between molecules and photonic-plasmonic hybrid structures is critical for the application of surface-enhanced spectroscopy (SES). Herein, we report a study on the mode coupling mechanism and SES performance in a typical optoplasmonic system constructed with a polystyrene microsphere (PS MS) resonator and gold nanoparticles (Au NPs). The mode coupling mechanism was found to be closely dependent on the relative positions of PS MS, Au NPs, and molecules in the optoplasmonic system, based on which selectively enhanced Raman and fluorescence signals of molecules can be realized via the collaboration of enhancement and quenching channels of the PS MS and Au NPs. We demonstrate two arrangements of the photonic-plasmonic hybrid structure, which can support fluorescence signals with sharp whispering-gallery modes and apparently enhanced Raman signals with relatively low detection limits and good robustness, respectively.

Optimal geometry parameter for plasmonic sensitivities of individual Au nanopoarticle sensors

The shape, aspect ratio and size are key parameters governing the plasmon sensitivities of individual Au nanoparticle bio/chemical sensors.