Gold Doping of Silver Nanoclusters: A 26-Fold Enhancement in the Luminescence Quantum Yield (original) (raw)
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Gold-doped silver nanoclusters with enhanced photophysical properties
Physical chemistry chemical physics : PCCP, 2018
We detail the characterization of atomically precise, luminescent silver and gold bimetallic nanoclusters (Ag and AgAuNCs) grown in the presence of bidentate lipoic acid (LA, the oxidized form) and dihydrolipoic acid (DHLA, the reduced form) ligands. We found that while doping AuNCs with Ag or Cu precursors using up to a 50% molar fraction (during growth) did not lead to any photoluminescence enhancement, doping of AgNCs with Au resulted in a six-fold enhancement of the PL emission compared to undoped AgNCs. The effect of doping is also reflected in the optical absorption and PL excitation spectra of the gold-doped NCs (AgAuNCs), where a clear blue shift in the absorbance features with respect to the pure AgNCs has been measured. Mass spectrometry measurements using ESI-MS showed that the AgNCs and Au-doped AgNCs had the compositions Ag29(DHLA)12 and Ag28Au(DHLA)12, respectively. The bimetallic nature of the AgAuNC cores was further supported by X-ray Photoelectron Spectroscopy (XPS...
Materials Research Express, 2020
Bimetallic noble metal nanoclusters (NCs) are an emerging topic of metal clusters due to their distinguishing characteristics compared to monometallic clusters. Doping of different noble atoms in other clusters is an effective strategy for tailoring their functionalities for specific applications and synergistic effects. Obtaining single-heteroatom doping is desirable but still very challenging to date. Herein, 2,4-dimethylbenzenthiol (2,4-DMBT) protected Ag/Au alloy NCs (ca. 2-3 nm) were synthesized via a wet chemical one-pot process. The effect of the number of Au atoms in Ag NCs on their optical properties and bandgap was investigated. We found that the change of the absorption peak positions of the Ag NCs was influenced by the presence of Au atoms. Besides, we found that the HOMO-LUMO peak has appeared without a significant change in cluster size during synthesis. Ag/ Au alloy NCs are characterized by UV-visible spectroscopy, transmission electron microscopy (TEM) and scanning electron transmission microscopy (STEM).
Optical Properties and Structural Relationships of the Silver Nanoclusters Ag32(SG)19 and Ag15(SG)11
The Journal of Physical Chemistry C, 2017
The recent discovery of stable Ag nanoclusters presents new opportunities to understand the detail electronic and optical properties of the metal core and the ligands using ultrafast spectroscopy. This paper focuses on Ag 32 and Ag 15 (with thiolate ligands), which are stable in solution. The steady state absorption spectra of Ag nanoclusters show interesting quantum size effects, expected for this size regime. Using a simple model for Ag 32 , TDDFT calculations identified the absorption at 480 nm is associated with the metal core. While the broad absorption feature near 680 nm is assigned to metal-ligand excitations. Ag 32 (SG) 19 and Ag 15 (SG) 11 have quantum yields up to 2 orders of magnitude higher than Au nanoclusters of similar sizes, with an emission maximum at 650 nm, identified as the metal-ligand state. The emission from both Ag nanoclusters have a common lifetime of about 130 ps and a common energy transfer rate of K EET ≥ 9.7•10 9 s-1. A "dark state" competing with the emission process was also observed and was found to be directly related to the difference in QY for the two Ag clusters. Two-photon excited emission was observed for Ag 15 (SG) 11, with a cross-section of 34 GM under 800 nm excitation. Femtosecond transient absorption measurements for Ag 32 recorded a possible metal core state at 530 nm, a metal-ligand state at 651 nm, and ground state bleaches at 485 nm and 600 nm. The ground state bleach signals in the transient spectrum for Ag 32 are 100 nm blue shifted in comparison to Au 25. The transient spectrum for Ag 15 shows a weak ground state bleach at ~480 nm and a broad excited state centered at 610 nm. TDDFT calculations indicate that the electronic and optical properties of Ag nanoclusters can be divided into core states and metal-ligand states, and photoexcitation generally involves a ligand to metal core transition. Subsequent relaxation leaves the electron in a
Isomerization-induced enhancement of luminescence in Au28(SR)20 nanoclusters†
2020
Understanding the origin and structural basis of the photoluminescence (PL) phenomenon in thiolate-protected metal nanoclusters is of paramount importance for both fundamental science and practical applications. It remains a major challenge to correlate the PL properties with the atomic-level structure due to the complex interplay of the metal core (i.e. the inner kernel) and the exterior shell (i.e. surface Au(i)-thiolate staple motifs). Decoupling these two intertwined structural factors is critical in order to understand the PL origin. Herein, we utilize two Au28(SR)20 nanoclusters with different –R groups, which possess the same core but different shell structures and thus provide an ideal system for the PL study. We discover that the Au28(CHT)20 (CHT: cyclohexanethiolate) nanocluster exhibits a more than 15-fold higher PL quantum yield than the Au28(TBBT)20 nanocluster (TBBT: p-tert-butylbenzenethiolate). Such an enhancement is found to originate from the different structural a...
Ultrabright Luminescence from Gold Nanoclusters: Rigidifying the Au(I)−Thiolate Shell
Luminescent nanomaterials have captured the imagination of scientists for a long time and offer great promise for applications in organic/inorganic light-emitting displays, optoelectronics, optical sensors, biomedical imaging, and diagnostics. Atomically precise gold clusters with well-defined core−shell structures present bright prospects to achieve high photoluminescence efficiencies. In this study, gold clusters with a luminescence quantum yield greater than 60% were synthesized based on the Au 22 (SG) 18 cluster, where SG is glutathione, by rigidifying its gold shell with tetraoctylammonium (TOA) cations. Time-resolved and temperature-dependent optical measurements on Au 22 (SG) 18 have shown the presence of high quantum yield visible luminescence below freezing, indicating that shell rigidity enhances the luminescence quantum efficiency. To achieve high rigidity of the gold shell, Au 22 (SG) 18 was bound to bulky TOA that resulted in greater than 60% quantum yield luminescence at room temperature. Optical measurements have confirmed that the rigidity of gold shell was responsible for the luminescence enhancement. This work presents an effective strategy to enhance the photoluminescence efficiencies of gold clusters by rigidifying the Au(I)− thiolate shell.
Enhanced luminescence of Ag nanoclusters via surface modification
Nanotechnology, 2013
In this work we present a detailed study on the influence of surface modifications for luminescent silver (Ag) clusters. Ag clusters (25 atoms) capped with dihydrolipoic acid show a distinct absorbance spectrum with several sharp transitions, and relative broad deep red luminescence with a quantum yield of 5% combined with a remarkably long luminescence lifetime of ∼3 µs at room temperature. Both pH and the presence of coordinating ligands influence the absorbance spectra and fluorescence intensity. A strong increase in luminescence intensity up to 45% quantum yield could be induced by coordination with PEG ligands. Conclusion: the surface coordination of the Ag clusters strongly influences the optical properties.
High photostability and enhanced fluorescence of gold nanoclusters by silver doping
Nanoscale, 2012
Gold nanoclusters prepared with a controlled amount of Ag exhibit intense fluorescence with a quantum yield of $16% and a "quasimonoexponential" long lifetime of >200 ns. Characterization of the luminescent probes indicates high photostability and easy detection in cells. Additionally, fluorescence enhancement in the presence of proteins was found.
Templated Atom-Precise Galvanic Synthesis and Structure Elucidation of a Ag24 Au(SR)18 Nanocluster
Angewandte Chemie (International ed. in English), 2015
Synthesis of atom-precise alloy nanoclusters with uniform composition is challenging when the alloying atoms are similar in size (for example, Ag and Au). A galvanic exchange strategy has been devised to produce a compositionally uniform [Ag24 Au(SR)18 ](-) cluster (SR: thiolate) using a pure [Ag25 (SR)18 ](-) cluster as a template. Conversely, the direct synthesis of Ag24 Au cluster leads to a mixture of [Ag25-x Aux (SR)18 ](-) , x=1-8. Mass spectrometry and crystallography of [Ag24 Au(SR)18 ](-) reveal the presence of the Au heteroatom at the Ag25 center, forming Ag24 Au. The successful exchange of the central Ag of Ag25 with Au causes perturbations in the Ag25 crystal structure, which are reflected in the absorption, luminescence, and ambient stability of the particle. These properties are compared with those of Ag25 and Ag24 Pd clusters with same ligand and structural framework, providing new insights into the modulation of cluster properties with dopants at the single-atom level.
2008
Ligand exchange offers an effective way to modify the properties of the recently prepared quantum clusters of gold. To tune optical and photoluminescence properties of one of the most stable quantum clusters of gold, Au 25 SG 18 (SG-glutathione thiolate), we functionalized it by the exchange of-SG with functionalized-SG and with an altogether different ligand, namely, 3-mercapto-2-butanol (MB). The products were characterized by various techniques such as optical absorption (UV-vis), Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron (XPS), and luminescence spectroscopies, mass spectrometry, and thermogravimetry (TG). Analyses of the TG data helped to establish the molecular composition of the products. Ligand exchange reaction was monitored by NMR spectroscopy, and it was found that the exchange reaction follows a first order kinetics. The XPS study showed that after the exchange reaction there was no change in the chemical nature of the metal core and binding energy values of Au 4f 7/2 and 4f 5/2 , which are similar in both the parent and the exchanged products. Photoluminescence studies of these clusters, done in the aerated conditions, showed that the excitation spectrum of the MB-exchanged product is entirely different from the acetyl-and formyl-glutathione exchanged products. The inherent fluorescence and solid-state emission of these clusters were observed. This intense emission allows optical imaging of the material in the solid state. The emission is strongly temperature dependent. The synthesis of a diverse variety of clusters and their chemical stability and intense luminescence offer numerous applications in areas such as energy transfer, sensors, biolabeling, and drug delivery.