A 200‐fold Quantum Yield Boost in the Photoluminescence of Silver‐Doped Ag_xAu_25−x Nanoclusters: The 13 th Silver Atom Matters

Abstract

The rod-shaped Au25 nanocluster possesses a low photoluminescence quantum yield (QY=0.1%) and hence is not of practical use in bioimaging and related applications. Herein, we show that substituting silver atoms for gold in the 25-atom matrix can drastically enhance the photoluminescence. The obtained Ag(x)Au(25-x) (x=1-13) nanoclusters exhibit high quantum yield (QY=40.1%), which is in striking contrast with the normally weakly luminescent Ag(x)Au(25-x) species (x=1-12, QY=0.21%). X-ray crystallography further determines the substitution sites of Ag atoms in the Ag(x)Au(25-x) cluster through partial occupancy analysis, which provides further insight into the mechanism of photoluminescence enhancement.

Intense fluorescence of Au20

“…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.…”

Microwave-assisted synthesis of photoluminescent glutathione-capped Au/Ag nanoclusters: A unique sensor-on-a-nanoparticle for metal ions, anions, and small molecules

“…All of the absorption spectra exhibit onsets at 500 nm and shoulder peaks at ~400 nm. Neither stepwise multiple bands nor localized surface plasmon resonance (LSPR) bands that are characteristic of plasmonic gold or silver nanocrystals appear in the absorption spectra, suggesting that the obtained clusters are not conventional (AuAg) n (SR) m [22,26,31] clusters and that the core sizes in metallic regime are less than 2 nm [32]. Corresponding to the optical bands, the photoluminescent spectra show well-defined emission peaks between 610 and 620 nm, when excited at 380 nm.…”

“…Moreover, doping Au 25 (SC 2 H 4 Ph) 18 clusters with a single platinum atom greatly enhances cluster stability against oxidation treatment and its catalytic activity [21], whereas doping Au 25 (SC 12 H 25 ) 18 clusters with silver atoms shifts the optical spectra and fluorescence peaks by modulating the electronic structure [22]. Of such bimetallic clusters, Au/Ag alloy clusters [23][24][25][26] are especially fascinating because they often manifest significantly enhanced luminescence, which is beneficial for sensing and bioimaging.…”

Identification of an Eight-Electron Superatomic Cluster and Its Alloy in One Co-crystal Structure

“…Prominent silver/gold alloy examples being structurally characterized include Au 25-x Ag x [10], Au 38-x Ag x [11], Au 24 Ag 20 [12], Au 24 Ag 46 [13], Au 12 Ag 32 [3b], Au 25 Ag 2 [14], Ag 28 Au [15], Au 12 Ag 13 [16], Au 80 Ag 30 [17], Au 3 Ag 38 [18], Au 7 Ag 8 [19], and Au x Ag y [20] + via a galvanic replacement method [22]. Despite the tremendous progresses in their synthesis and characterization, the mechanistic studies for the formation of Ag alloy NCs are lagged significantly behind.…”