Exploring the role of the surface states in the luminescence of gold Exploring the role of the surface states in the luminescence of gold

摘要

Here we report on the two-photon excited visible luminescence, emitted by small gold spheres dispersed in water. The study was performed at the single particle level in order to determine if two-photon luminescence could be an alternative to fluorescently labeled particles for particle tracking. Unexpectedly, the single molecule approach demonstrates that the luminescence is anisotropic at low excitation powers, allowing for the observation of the Brownian rotation of nearly spherical objects. The combined observations of a multi parameter approach suggest that the anisotropy, as well as the power threshold effect, result from the interaction between the capping ligands and the particle surface. The latter interaction favors new radiative deexcitation channels at some very specific sites, in line with the hot spots observed in Surface Enhanced Raman Scattering. The dynamics of the process depends on the excitation power. If the study demonstrates that an increase of the excitation power results in switching on the luminescence of nearly all particles in the sample, it also suggests that the use of two-photon excited gold particles as biolabels will require preliminary characterization of the emission depending on the real system particle and ligands.