Excitation Energy Transfer between Non-Spherical Metal Nanoparticles: Effects of Shape and Orientation on Distance Dependence of Transfer Rate

Surface plasmon mediated excitation energy transfer (EET) between two nonspherical metal nanoparticles (MNP) is studied through a microscopic theoretical formulation that provides quantitative information about the distance, size, shape, and orientation dependence of the transfer rate. At constant separation, the EET rate increases with increase in the size of the nanoparticle and decreases with increase in the aspect ratio of the particle. The relative orientation of the nanoparticles is found to markedly influence the center-to-center distance (r) dependence of the excitation energy transfer rate. At intermediate separations, we find a significant deviation from $1/r^6$ dependence (which is robust for spherical particles at these separations), and it becomes more pronounced with increase in the aspect ratio of the particles. Interestingly, the relative orientation of the nanoparticles effect the surface-to-surface distance (d) dependence of the rate to lesser extend in comparison to the r-dependence of the rate. Our results suggest that for nonspherical particles studying EET rate as a function of d (not r) provides more conclusive results