• bipyramids;
  • nanoantennas;
  • orientation;
  • pattern imaging;
  • photoluminescence

Photoluminescence of single gold bipyramid due to the radiative decay of the longitudinal surface plasmon is used to determine its 3D orientation using a direct emission pattern imaging technique. The photoluminescence (PL) intensity from individual gold bipyramids is recorded at the objective's back focal plane, which directly maps the angular emission distribution. By correlating the PL spectra, dark-field scattering, emission pattern, and atomic force microscopy data, the spatial orientation and the radiation characteristics of an individual nanoantenna can be unambiguously determined. The PL emission pattern imaging can be used as a stand-alone technique for the fast and facile determination of nanoantenna orientations. The experimental data also agree well with a simple analytical model based on a far-field angular distribution of an isolated dipole emitter on the interface. In situ measurements are also performed on the PL pattern of a single gold bipyramid during optical heating to monitor the photothermal reshaping of the nanoantenna. The results show that the PL emission pattern imaging method is highly sensitive to changes of the geometry and orientation of the nanoparticle. The PL direct imaging technique offers great advantages, including a facile full-3D angle-resolved capability, free of photobleaching and photoblinking. Additionally, the results reveal that the gold bipyramids can generate efficient PL emission, and the unique features of gold bipyramids would be outstanding candidates for orientation sensing. These findings have great potential for characterizing optical nanoantennas, for optical imaging and sensing in materials science and biological applications.