Intense fluorescence of Au₂₀

Area of Science:

• Nanotechnology
• Quantum Chemistry
• Materials Science

Background:

• Ligand-protected gold clusters are utilized as non-bleaching fluorescence markers in biological and medical fields.
• The origin of fluorescence in these clusters has been attributed to the protecting ligands.

Purpose of the Study:

• To investigate whether fluorescence is an intrinsic property of gold clusters themselves.
• To characterize the optical absorption and fluorescence of gold nanoclusters (Au20).

Main Methods:

• Experimental measurement of fluorescence spectra for Au20 clusters in a Neon matrix at 6 K.
• Theoretical calculations using Density-Functional Theory (DFT) and time-dependent DFT (TD-DFT).

Main Results:

• A sharp and intense fluorescence peak was observed at 739.2 nm (1.68 eV) for Au20 clusters.
• The observed fluorescence directly correlates with the Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) diabatic bandgap.
• Au20 clusters exhibit molecule-like quantum levels due to their monodisperse nature (single stable tetrahedral isomer).
• DFT and TD-DFT calculations accurately predicted the main absorption peaks and intrinsic fluorescence, showing good agreement with experimental data.

Conclusions:

• The fluorescence of Au20 clusters is an intrinsic property of the gold cluster core, not solely dependent on ligands.
• The study clarifies the nature of optical absorption and fluorescence in gold nanoclusters.
• This finding opens new avenues for designing intrinsic fluorescent gold-based nanomaterials for various applications.