Optical properties of atomically mono-dispersed gold clusters have received vast research attention in recent years as they show properties of a transition region in metal and molecule. To understand the influence of cluster’s structure and symmetry on the optical properties, temperature-dependent absorption and ultrafast luminescence dynamics of hexane thiol protected Au67, Au102 were studied and compared with Au­144. Interesting absorption spectral features were observed with decreasing temperature. These changes in the absorption spectra were modeled with electron-phonon and exciton-phonon interactions and they found to differ significantly from one cluster to another. Earlier we studied smaller clusters such as Au25 (sphere and bi-icosahedral) and Au38, and in this study we focused on bigger clusters such as Au67 Au102 and Au144. In low symmetry clusters, optical information is not rich even at low temperatures due to overlapping transitions as in the case of Au67 and Au102 clusters. However, in higher symmetry cluster like Au144 optical information is rich at low temperatures with discrete electronic states. In principle, optical information should diminish with cluster size. But, we observed a different scenario that we can assign to the symmetry of cluster. In addition, the oscillator strength of transitions has increased with decrease in temperature that was modeled with electron-phonon interactions. Also for Au144 cluster staple motifs that protect are quite similar, making the strength of electron phonon larger than Au67 and Au102. Ultrafast luminescence measurements have shown fast relaxation from core-gold to shell-gold.

Ultrafast and temperature-dependent optical properties of Au67, Au102 and Au144 clusters

249th National Meeting (2015)

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