Ultrafast Relaxation Dynamics of Luminescent Rod-Shaped, Silver-Doped Ag_xAu_25–x Clusters

Abstract

The luminescent ligand protected metal clusters have attracted considerable attentions while the origin of the emission still remains elusive. As recently reported in our previous work, the rod-shaped Au 25 cluster possesses a low photoluminescence quantum yield (QY=0.1%), whereas substituting silver atoms for central gold atom in the rod-shaped Au 25 cluster can drastically enhance the photoluminescence with high quantum yield (QY=40.1%). To explore the enhancement mechanism of fluorescence, femtosecond transient absorption spectroscopy is performed to determine the electronic structure and ultrafast relaxation dynamics of the highly luminescent silver-doped Ag x Au 25-x cluster by comparing the excited state dynamics of doped and un-doped Au 25 rod cluster, it is found that the excited state relaxation in Ag x Au 25-x , is proceeded with an ultrafast (~0.58 ps) internal conversion and a subsequent nuclear relaxation (~20.7 ps) followed by slow (7.4 µs) decay back to the ground state. Meanwhile, the observed nuclear relaxation is much faster in Ag x Au 25-x (~20.7 ps) compared to that in un-doped Au 25 rod (~52 ps). We conclude that it is the central Ag atom which stabilizes the charges on LUMO orbital and enhances the rigidity of Ag x Au 25-x cluster that leads to strong fluorescence.Meanwhile, coherent oscillations around ~ 0.8 THz were observed in both clusters, indicating the symmetry preservation from Au cluster to Ag alloying Au clusters. The present results provide new insights for the structure-related excited state behaviors of luminescent ligand protected Ag alloying Au clusters.

Templated Atom‐Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18]− Nanocluster

“…25 compared to that of pure Ag 25 ( Figure 4B); this may be attributed to the stabilization of the charges in the LUMO of the alloy cluster akin to Au 25Àn Ag n cluster. [8,22] Conversely,w ef ound al ittle change in the luminescence of Ag 24 Pd cluster.…”

Templated Atom‐Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18]− Nanocluster

“…Thes ignificant blue-shift (ca. [8,22] Conversely,w ef ound al ittle change in the luminescence of Ag 24 Pd cluster. [9,11] Thep eaks at 390 and 334 nm in the Ag 24 Au are less pronounced compared to those of the parent Ag 25 and Ag 24 Pd;t his may be due to the mixing of the Ag and Au electronic states, [16b] rendering these optical transitions forbidden in the Ag 24 Au cluster.T he overall optical features of Additionally,w ef ound that the photoluminescence of Ag 24 Au clusters was blue-shifted relative to those of pure Ag 25 ( Figure 4B inset), which are likely due to significant modulation in the HOMO-LUMO gap and/or in the surface states [21] after alloying.I nterestingly,t he luminescence of the Au-doped clusters was enhanced by afactor of !…”

The Origin of the Photoluminescence Enhancement of Gold‐Doped Silver Nanoclusters: The Importance of Relativistic Effects and Heteronuclear Gold–Silver Bonds

“…[1][2][3][4][5][6][7][8][9] Over the past decades,t heir spectroscopic properties,e xcited-state relaxation, and photoluminescence dynamics have been studied both experimentally and computationally. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Luminescent nanoclusters offer great promise for applications in optoelectronics and optical sensors.H owever, atomically precise Ag nanoclusters with well-defined coreshell structures usually have weak photoluminescence,which limits their utility as luminescent nanomaterials.R ecently, Bakr and co-workers [29,30] systematically explored the photoluminescence properties of [Ag 29 (BDT) 12 (TPP) 4 ] 3À (BDT = 1,3-benzenedithiol, TPP = triphenylphosphine;a bbreviated as Ag 29 hereinafter;F igure 1) and its Au-doped nanoclusters by single-crystal X-ray diffraction, mass spectrometry,aswell as optical and NMR spectroscopy.Byvarying the Au amount in the Ag and Au precursors,as eries of [Ag 29Àx Au x (BDT) 12 -(TPP) 4 ] 3À (x = 1-5;A g 29Àx Au x )n anoclusters have been produced. Interestingly,u pon increasing the amount of the Au precursor from 0t o4 0mmol %, significantly enhanced luminescence was observed.…”