Extra Silver Atom Sparks Breakthrough in Photoluminescence of Silver Nanoclusters

Structural architectures of anion-templated (a) Ag78 and (b) Ag79 NCs. Hydrogen atoms are omitted for clarity.
Image Credit: ©Yuichi Negishi et al.

A team of researchers from Tohoku University, Tokyo University of Science, and the Institute for Molecular Science have uncovered how the precise addition of a single silver (Ag) atom can dramatically transform the light-emitting properties of high-nuclear Ag nanoclusters (NCs). The study reports a remarkable 77-fold increase in photoluminescence (PL) quantum yield (QY) at room temperature - a milestone that paves the way for practical applications in optoelectronics and sensing technologies. The findings were published in the Journal of the American Chemical Society.

Photoluminescence quantum yield is an important metric used to evaluate the efficiency of photoluminescence, which is how well a material can absorb energy and convert it into light. Improving PLQY positively impacts technology such as OLEDs in TV screens.

Metal atoms in the outer shell and the associated surface protecting ligands in (a) Ag78 and (b) Ag79 NCs. Hydrogen atoms are omitted for the clarity.
Image Credit: ©Yuichi Negishi et al.

However, choosing materials with high PLQY alone is not enough. For example, Ag NCs have inherently low PL efficiency that has long limited practical applications, but there is immense promise held in their unique optical properties. To probe the structure-property relationship in greater detail, the team synthesized and compared two closely related anion-templated Ag NCs: [SO4@Ag78S15(CpS)27(CF3COO)18]+: Ag78 NC (CpS: cyclopentatethiolate), [SO4@Ag79S15(iPrS)28(iPrSO3)15(CF3COO)4]: Ag79 NC (iPrS: iso-propyl thiolate). Both NCs share a common structural framework, with the key distinction being a single additional Ag atom in the outermost shell of Ag79 NC.

(a) Room-temperature PL emission for both Ag78 and Ag79 NC in the solution medium. Inset showing the excitation of the solutions from both NCs under UV-light irradiation, (b) schematic representation of PL emission enhancement Ag79 NC through the synergistic effect.
Image Credit: ©Yuichi Negishi et al.

This addition was achieved through subtle modifications of the surface-protecting ligands, particularly the in-situ generated iPrSO3- group, which created a void within the NC framework that enabled the extra atom's incorporation. While the core structures remained largely unchanged, the shell modification had profound effects.

In Ag79 NC, the added silver atom enhanced radiative decay rates and a more rigid cluster. The rigidity effectively suppressed non-radiative decay pathways that typically diminish luminescence efficiency.

The combination of these factors - enhanced radiative decay from symmetry reduction and reduced non-radiative losses from structural rigidity - enabled the Ag79 NC to exhibit a remarkable 77-fold improvement in PL quantum yield over Ag78 NC at room temperature.

Illustration of the synergistic mechanism by which an additional silver atom enhances the PL quantum yield of high-nuclear Ag NCs.
Image Credit: ©Yuichi Negishi et al.

"This is the first clear evidence that the incorporation of just one extra silver atom, guided by ligand design, can drastically boost performance," Professor Negishi explained. "Our findings open a pathway to rationally engineer efficient light-emitting nanoclusters through atomic-level structural modifications."

With this new advancement, researchers anticipate new opportunities for deploying silver nanoclusters in high-performance light-emitting devices, bioimaging, and catalytic systems, where efficient luminescence at room temperature is critical.

Published in journal: Journal of the American Chemical Society

Title: Triggering Photoluminescence in High-Nuclear Silver Nanoclusters via Extra Silver Atom Incorporation

Authors: Aoi Akiyama, Sakiat Hossain, Sourav Biswas, Takafumi Shiraogawa, Pei Zhao, Mana Nakamoto, Daiji Ogata, Tokuhisa Kawawaki, Yoshiki Niihori, Junpei Yuasa, Masahiro Ehara, and Yuichi Negishi

Source/Credit: Tohoku University

Reference Number: chm101425_01

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