Aggregation of Gold Nanoparticles for Controlling Emission Polarization: Implications for Applications in Photonics

Manipulating the light polarization properties of gold nanoparticle aggregates can facilitate their applications in sensing and imaging. However, control of the intrinsic light polarization on demand at the nanoscale is hindered by the lack of a fundamental understanding of the structure-dependent plasmon coupling in the aggregates. Here, the polarization properties of intrinsic photoluminescence (PL) and scattering of gold nanoparticle dimers and trimers are studied experimentally and computationally at the single-aggregate level. We find that the PL excitation and emission polarization degrees of the aggregates are highly correlated to the shift of their PL and scattering spectra. The results suggest that the degree of PL polarization is dominated by the strength of the longitudinal plasmon resonance mode arising from the plasmon coupling between the two closest particles in the aggregate. While the PL direction is always along the two most strongly interacting particles in the trimers, changing the arrangement can modify the PL polarization degree. This work provides further insights into the mechanism of the plasmon coupling-induced polarized optical response of aggregated metal nanoparticles and suggests routes to achieve on-demand control of the PL light polarization. This paves the way to using the polarized optical response of plasmonic nanostructures for applications in photonics including sensing and imaging.