Source of Bright Near-Infrared Luminescence in Gold Nanoclusters

Abstract

Gold nanoclusters with near-infrared (NIR) photoluminescence (PL) have great potential as sensing and imaging materials in biomedical and bioimaging applications. In this work, Au21(S-Adm)15 and Au38S2(S-Adm)20 are used to unravel the underlying mechanisms for the improved quantum yields (QY), large Stokes shifts, and long PL lifetimes in gold nanoclusters. Both nanoclusters show decent PL QY. In particular, the Au38S2(S-Adm)20 nanocluster shows a bright NIR PL at 900 nm with QY up to 15% in normal solvents (such as toluene) at ambient conditions. The relatively lower QY for Au21(S-Adm)15 (4%) compared to that of Au38S2(S-Adm)20 is attributed to the lowest-lying excited state being symmetry-disallowed, as evidenced by the pressure-dependent antispectral shift of the absorption spectra compared to PL, yet Au21(S-Adm)15 maintains some emissive properties due to a nearby symmetry-allowed excited state. Furthermore, our results show that suppression of nonradiative decay due to the surface “lock rings”, which encircle the Au kernel and the surface “lock atoms” which bridge the fundamental Au kernel units (e.g., tetrahedra, icosahedra, etc.), is the key to obtaining high QYs in gold nanoclusters. The complicated excited-state processes and the small absorption coefficient of the band-edge transition lead to the large Stokes shifts and the long PL lifetimes that are widely observed in gold nanoclusters.

Origin of luminescence properties and synthetic methods for gold- and bimetallic gold-based nanomaterials

“…11,43,44,112,114,127,249,250 Recent advances in the synthesis of AuNCs enabled the development of NIR-photoluminescent (NIR PL) AuNCs functionalized with a variety of thiol-containing ligands. 251…”

“…11,43,44,112,114,127,249,250 Recent advances in the synthesis of AuNCs enabled the development of NIR-photoluminescent (NIR PL) AuNCs functionalized with a variety of thiol-containing ligands. 251 These ligands exhibit a significant enhancement in the emission efficiency of AuNCs, e.g., the optimized quantum yield (QY) of glutathione (GSH)-stabilized AuNCs reached about 15%, which can truly overcome the QY of less than 0.1% obtained from the classic Burst method for the synthesis of AuNCs. 252 The tunable emission of the protein-stabilized Au nanoclusters (AuNCs) over a large spectral range makes them a useful platform in biomedical studies.…”

Master key to coinage metal nanoclusters treasure chest: 38-metal clusters

“…16e). 104 This is so far the highest QY in Au–thiolate nanoclusters in normal solvents and ambient conditions. The photoluminescence lifetime of the Au 38 S 2 (S-Adm) 20 nanocluster is ∼3 μs, which is similar to the lifetime result of nanosecond transient absorption measurement (Fig.…”

Advances of gold nanoclusters for bioimaging

“…In previous studies, electron leaps between HOMO and LUMO in Au atoms were considered the primary source of FL production in AuNCs ( Li et al., 2021 ; Zhang and Wang, 2014 ). According to this concept, the FL properties change dramatically when the structure of AuNCs is changed.…”