Influence of Silver Doping on the Photoluminescence of Protected Ag_nAu_25–n Nanoclusters: A Time-Dependent Density Functional Theory Investigation

Abstract

The effect of silver doping on the electronic properties and photoluminescence of a class of structurally similar AgnAu25–n2+ nanoclusters (0 ≤ n ≤ 13) has been investigated here by means of time-dependent density functional calculations. As very recently reported in the literature, a mixture of these clusters showed an unexpected 200-fold fluorescence quantum yield boost with respect to Au252+, but no mechanism has been proposed to date to explain this phenomenon. The results presented here suggest that the origin of this boost lies in the nature of the first excited state (S1), which is affected differently by the increasing presence of Ag atoms into the network of Au atoms. In fact, doping the cluster with silver atoms has the effect of shifting the lowest-energy “dark” excited states to higher energy, leaving a very “bright” highest occupied molecular orbital → lowest unoccupied molecular orbital (HOMO → LUMO) transition as the lowest-energy excitation. We propose that when fluorescence occurs from “bright” S1 states, it receives a boost in the quantum yield because of the high oscillator strength of these HOMO → LUMO transitions

Ultrafast Relaxation Dynamics of Luminescent Rod-Shaped, Silver-Doped AgxAu25–x Clusters

“…These results indicate that the luminescence enhancement in Au 12 Ag 13 rod is due to the doped Ag atoms at the central position. All these theoretical results obtained here agree with the recently published theoretical investigation on Au 12 Ag 13 rod cluster 43. To further reveal the excited state relaxation dynamics, femtosecond broadband transient absorption experiment was carried out as follows.…”

“…Furthermore, the rigidity may have been enhanced due to doping of the central Ag atom, which largely increases the fluorescence quantum yield. Ag doping has led to the elongation of the cluster along the vertex axis by ~0.5 Å (the distance between central atom and icosahedral centers has been increased),43 which proved the rigidity enhancement. The analysis mentioned above…”

“…25 and43 . These results indicate that the luminescence enhancement in Au 12 Ag 13 rod is due to the doped Ag atoms at the central position.…”

Thiolated Au18 cluster: preferred Ag sites for doping, structures, and optical and chiroptical properties

“…On the other hand, a recent study of the enhancement in the fluorescence of a silver-doped rod-shaped Au 25 cluster has been reported by Muniz-Miranda et al 28 They have attributed the enhancement to an intense lower energy peak (large oscillator strength) that is shifted toward high energies in the adsorption spectrum after silver doping. Moreover, they proposed that the fluorescence occurs due to the high oscillator strength of the HOMO 4 LUMO transitions.…”

Structure-conserving spontaneous transformations between nanoparticles

“…Atomically precise nanoparticles of noble metals12345678910, often called nanoclusters, which constitute an exploding discipline in nanomaterials, are promising candidates to explore such transformations because of their well-defined structures and drastic changes in their properties, in comparison to their bulk form, arising due to electronic confinement. Most intensely explored of these properties are optical absorption and emission1112131415; near infrared emission of some of the clusters and their large quantum yields have resulted in new applications1617181920. Nanoparticles are generally considered stable and are expected to preserve their structural integrity in solution.…”