Information on quantum states pervades the visible spectrum of the ubiquitous Au144(SR)60 gold nanocluster

Abstract

Absorption spectra of very small metal clusters exhibit individual peaks that reflect the discreteness of their localized electronic states. With increasing size, these states develop into bands and the discrete absorption peaks give way to smooth spectra with, at most, a broad localized surface-plasmon resonance band. The widely accepted view over the last decades has been that clusters of more than a few dozen atoms are large enough to have necessarily smooth spectra. Here we show through theory and experiment that for the ubiquitous thiolate cluster compound Au 144 (SR) 60 this view has to be revised: clearly visible individual peaks pervade the full near-IR, VIS and near-UV ranges of low-temperature spectra, conveying information on quantum states in the cluster. The peaks develop well reproducibly with decreasing temperature, thereby highlighting the importance of temperature effects. Calculations using time-dependent density-functional theory indicate the contributions of different parts of the cluster-ligand compound to the spectra.

Intense fluorescence of Au20

“…We present first-principles calculations that trace the origin of fluorescence back to molecule-like single particle excitations that are appreciably intermixed by Coulomb and spin-orbit effects. Our results prove that fluorescence is an intrinsic property of Au 20 suggesting that in many of the above mentioned studies, the fluorescence can go back to the Au core itself rather than to the ligands.…”

“…This setup selects cluster ions up to 16 000 amu with an electronically controllable mass resolution. We created a flux of Au 20 cations with a kinetic energy of 20 eV and directed it onto a super polished aluminum mirror held at 6 K while dosing Ne that condenses onto the mirror and 0021-9606/2017/147(7)/074301/6/$30.00…”

“…Here we report fluorescence and absorption measurements of Au 20 . For this size, the tetrahedral structure is by far the most favorable one 27 such that only this single conformer exists at our measurement temperature of 6 K. We use Ne matrices that exhibit weak van der Waals interactions with the clusters leading to a known offset in energies, but leaving the cluster properties unchanged with respect to the gas phase.…”

“…Since all previous studies were either performed on ligand-protected or protein-encapsulated Au clusters, [12][13][14][15][16] it has remained unclear whether the fluorescence is intrinsic to the Au cluster or emerging from its interaction with ligands, and the considerable theoretical effort dedicated to the simulation of absorption spectra [17][18][19][20][21] and fluorescence 22 has not answered this question. For bare Au clusters, experiments were limited to cluster sizes below the relevant one.…”

Thin films of size-selected Mo clusters: growth modes and structures

“…5 For example, Au nanoparticles smaller than 3-4 nm are active catalysts for various reactions such as the CO oxidation, whereas the bulk counterpart is inert. [5][6][7][8][9] In addition, quantum confinement effects and unique geometric structures dissimilar to the bulk counterparts result in unexpected electronic properties, [8][9][10][11][12][13][14] which make clusters interesting for future nano-electronics.…”