Currently, a comprehensive understanding of the relationship between atomic structures and optical properties of ultrasmall metal nanoclusters with diameters between 1 and 3 nm is lacking. To address this challenge, it is necessary to develop tools for perturbing the atomic structure and modulating the optical properties of metal nanoclusters beyond what can be achieved using synthetic chemistry. Here, we present a systematic high-pressure study on a series of atomically precise ligand-protected metal nanoclusters. A diamond anvil cell is used as a high-pressure chamber to gradually compress the metal nanoclusters, while their optical properties are monitored in situ. Our experimental results show that the photoluminescence (PL) of these nanoclusters is enhanced by up to 2 orders of magnitude at pressures up to 7 GPa. The absorption onset red-shifts with increasing pressure up to ∼12 GPa. Density functional theory calculations reveal that the red-shift arises because of narrowing of the spacing between discrete energy levels of the cluster due to delocalization of the core electrons to the carbon ligands. The pressure-induced PL enhancement is ascribed to (i) the enhancement of the near-band-edge transition strength, (ii) suppression of the nonradiative vibrations, and (iii) hindrance of the excited-state structural distortions. Overall, our results demonstrate that high pressure is an effective tool for modulating the optical properties and improving the luminescence brightness of metal nanoclusters. The insights into structure–property relations obtained here also contribute to the rational design of metal nanoclusters for various optical applications.

As circuitry approaches single nanometer length scales, it is important to predict the stability of metals at these scales. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at single nanometer dimensions. Here, we report the formation of dislocations within individual 3.9 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell. We used a combination of x-2 ray diffraction, optical absorbance spectroscopy, and molecular dynamics simulation to characterize the defects that are formed, which were found to be surface-nucleated partial dislocations. These results indicate that dislocations are still active at single nanometer length scales and can lead to permanent plasticity. Main text:

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