Photo-initiated energy transfer in nanostructured complexes observed by near-field optical microscopy

We report an apertureless near-field optical study on nanostructured objects formed by J-aggregates adsorbed on silver (Ag) nanoparticles. Near-field images reveal that the enhanced near-field from the dressed particle's (DP) resonantly excited plasmon oscillation is efficiently absorbed by the J-aggregates. The sensitivity of the near-field images recorded at the harmonics of the probe vibration frequency suggests that the DP is releasing part of the absorbed energy radiatively upon interaction with the probe. The role of the probe in providing this new radiative relaxation channel is further confirmed as fluorescence from the J-aggregates on the particle is detected on the particle location only. We based the interpretation of our results on the near-field optical response from a bare Ag particle excited at the plasmon resonance as well as on far-field emission and transient absorption experiments.