Influence of a three-dimensional photonic crystal on the plasmonic properties of gold nanorods.

The influence of a three-dimensional (3D) photonic crystal (PC) on the plasmonic properties of gold nanorods (GNRs), which are placed on the surface of the PC, was investigated both numerically and experimentally. The 3D PC formed by closely packed polystyrene spheres was fabricated by using a pressure controlled isothermal heating vertical deposition technique. For a GNR whose longitudinal surface plasmon resonance (LSPR) is located at the bandgap edges of the PC, a dramatic narrowing of the absorption spectrum as well as an enhancement in electric field and thus the absorption was observed. It was suggested that the small group velocities at the bandgap edges of the PC are responsible for the slow decay of the plasmonic mode in the GNR. To confirm the enhancement in the absorption of the GNRs induced by the nearby PC, we examined the two-photon-induced luminescence (TPL) of an assembly of GNRs dispersed on the surface of the PC. Under the excitation of femtosecond laser pulses which was resonant with the LSPR of GNRs, it was found that the excitation intensity necessary for melting GNRs placed on the surface of the PC was nearly one order of magnitude smaller than that for GNRs placed on the surface of a glass slide, in good agreement with the results predicted by the numerical simulations. Our findings indicate the possibility of using PCs to modify the plasmonic and optical properties of GNRs which are quite useful for the practical applications of GNRs such as nanoscale sensors and optical data storage.