Figure 2.

Schematic of the anti-Stokes luminescence arising from a single gold nanorod. After excitation with a photon, a collective oscillation of electrons is generated. Once the coherence is lost, the state can be described as an electron-hole pair. Three scenarios are possible: electron and hole may recombine radiatively after one of more interactions with the thermal baths of lattice phonons and charge carrier thermal excitations: 1) if the energy difference between electron and hole states is lower than the initial one after excitation we obtain Stokes emission upon a radiative recombination; 2) if electron and hole transiently increase their energy difference at the bath’s expense before recombining radiatively, we observe anti-Stokes emission; and 3) if electron and hole recombine nonradiatively, their energy difference is transferred to the baths and no photon is emitted. (The latter process is the most probable one.) To see this figure in color, go online.