Temperature-Dependent Absorption and Ultrafast Exciton Relaxation Dynamics in MAu24(SR)18 Clusters (M = Pt, Hg)

Role of the Central Metal Atom

Viraj Dhanushka Thanthirige, Minseok Kim, Woojun Choi, Kyuju Kwak, Dongil Lee, Guda Ramakrishna

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Temperature-dependent and ultrafast transient absorption measurements were carried out to probe the optical properties and exciton relaxation dynamics in metal-doped (Pt and Hg) Au25 clusters. Optical absorption and electrochemistry results have shown that the Pt-doped cluster has a distinctly different HOMO-LUMO gap than that of Au25, while the gap did not change much for Hg-doped Au25. A decrease in temperature had resulted in much sharper absorption features as well as an increased number of absorption peaks, enhanced oscillator strength, and a shift in the energy maximum to higher energies for all metal-doped Au25 clusters. Interestingly, the peaks observed for Pt and Hg-doped clusters are very different from that of undoped Au25 cluster, suggesting that the altered structures play a crucial role on their optical properties. From the analysis of absorption peak shifts, higher phonon energies of 67 ± 8 meV were determined for Pt- and Hg-doped Au25 clusters when compared to 43 ± 6 meV for undoped Au25. The larger phonon energies suggest stronger coupling of core-gold and shell-gold and are explained by contraction of metal-doped clusters. Ultrafast transient absorption results have shown that Pt-doping lead to faster excited state relaxation, where more than 70% of the created electron-hole pairs recombine within 20 ps. However, Hg-doping and undoped Au25 relax to shell gold and recombination takes a much longer time. The results are consistent with energy gap law, where the smaller energy gap for PtAu24 led to faster exciton relaxation. An interesting correlation between the spin-orbit coupled transitions and bleach maximum was observed, which can be ascribed to exciton localization in Au12-icosahedron.

Original languageEnglish
Pages (from-to)23180-23188
Number of pages9
JournalJournal of Physical Chemistry C
Volume120
Issue number40
DOIs
Publication statusPublished - 2016 Oct 13

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Excitons
Gold
Metals
excitons
Atoms
Energy gap
Optical properties
Doping (additives)
metals
atoms
Electrochemistry
Excited states
Temperature
Light absorption
gold
temperature
Orbits
Electrons
optical properties
energy

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Surfaces, Coatings and Films
  • Physical and Theoretical Chemistry

Cite this

Thanthirige, Viraj Dhanushka ; Kim, Minseok ; Choi, Woojun ; Kwak, Kyuju ; Lee, Dongil ; Ramakrishna, Guda. / Temperature-Dependent Absorption and Ultrafast Exciton Relaxation Dynamics in MAu24(SR)18 Clusters (M = Pt, Hg) : Role of the Central Metal Atom. In: Journal of Physical Chemistry C. 2016 ; Vol. 120, No. 40. pp. 23180-23188.
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title = "Temperature-Dependent Absorption and Ultrafast Exciton Relaxation Dynamics in MAu24(SR)18 Clusters (M = Pt, Hg): Role of the Central Metal Atom",
abstract = "Temperature-dependent and ultrafast transient absorption measurements were carried out to probe the optical properties and exciton relaxation dynamics in metal-doped (Pt and Hg) Au25 clusters. Optical absorption and electrochemistry results have shown that the Pt-doped cluster has a distinctly different HOMO-LUMO gap than that of Au25, while the gap did not change much for Hg-doped Au25. A decrease in temperature had resulted in much sharper absorption features as well as an increased number of absorption peaks, enhanced oscillator strength, and a shift in the energy maximum to higher energies for all metal-doped Au25 clusters. Interestingly, the peaks observed for Pt and Hg-doped clusters are very different from that of undoped Au25 cluster, suggesting that the altered structures play a crucial role on their optical properties. From the analysis of absorption peak shifts, higher phonon energies of 67 ± 8 meV were determined for Pt- and Hg-doped Au25 clusters when compared to 43 ± 6 meV for undoped Au25. The larger phonon energies suggest stronger coupling of core-gold and shell-gold and are explained by contraction of metal-doped clusters. Ultrafast transient absorption results have shown that Pt-doping lead to faster excited state relaxation, where more than 70{\%} of the created electron-hole pairs recombine within 20 ps. However, Hg-doping and undoped Au25 relax to shell gold and recombination takes a much longer time. The results are consistent with energy gap law, where the smaller energy gap for PtAu24 led to faster exciton relaxation. An interesting correlation between the spin-orbit coupled transitions and bleach maximum was observed, which can be ascribed to exciton localization in Au12-icosahedron.",
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Temperature-Dependent Absorption and Ultrafast Exciton Relaxation Dynamics in MAu24(SR)18 Clusters (M = Pt, Hg) : Role of the Central Metal Atom. / Thanthirige, Viraj Dhanushka; Kim, Minseok; Choi, Woojun; Kwak, Kyuju; Lee, Dongil; Ramakrishna, Guda.

In: Journal of Physical Chemistry C, Vol. 120, No. 40, 13.10.2016, p. 23180-23188.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Temperature-Dependent Absorption and Ultrafast Exciton Relaxation Dynamics in MAu24(SR)18 Clusters (M = Pt, Hg)

T2 - Role of the Central Metal Atom

AU - Thanthirige, Viraj Dhanushka

AU - Kim, Minseok

AU - Choi, Woojun

AU - Kwak, Kyuju

AU - Lee, Dongil

AU - Ramakrishna, Guda

PY - 2016/10/13

Y1 - 2016/10/13

N2 - Temperature-dependent and ultrafast transient absorption measurements were carried out to probe the optical properties and exciton relaxation dynamics in metal-doped (Pt and Hg) Au25 clusters. Optical absorption and electrochemistry results have shown that the Pt-doped cluster has a distinctly different HOMO-LUMO gap than that of Au25, while the gap did not change much for Hg-doped Au25. A decrease in temperature had resulted in much sharper absorption features as well as an increased number of absorption peaks, enhanced oscillator strength, and a shift in the energy maximum to higher energies for all metal-doped Au25 clusters. Interestingly, the peaks observed for Pt and Hg-doped clusters are very different from that of undoped Au25 cluster, suggesting that the altered structures play a crucial role on their optical properties. From the analysis of absorption peak shifts, higher phonon energies of 67 ± 8 meV were determined for Pt- and Hg-doped Au25 clusters when compared to 43 ± 6 meV for undoped Au25. The larger phonon energies suggest stronger coupling of core-gold and shell-gold and are explained by contraction of metal-doped clusters. Ultrafast transient absorption results have shown that Pt-doping lead to faster excited state relaxation, where more than 70% of the created electron-hole pairs recombine within 20 ps. However, Hg-doping and undoped Au25 relax to shell gold and recombination takes a much longer time. The results are consistent with energy gap law, where the smaller energy gap for PtAu24 led to faster exciton relaxation. An interesting correlation between the spin-orbit coupled transitions and bleach maximum was observed, which can be ascribed to exciton localization in Au12-icosahedron.

AB - Temperature-dependent and ultrafast transient absorption measurements were carried out to probe the optical properties and exciton relaxation dynamics in metal-doped (Pt and Hg) Au25 clusters. Optical absorption and electrochemistry results have shown that the Pt-doped cluster has a distinctly different HOMO-LUMO gap than that of Au25, while the gap did not change much for Hg-doped Au25. A decrease in temperature had resulted in much sharper absorption features as well as an increased number of absorption peaks, enhanced oscillator strength, and a shift in the energy maximum to higher energies for all metal-doped Au25 clusters. Interestingly, the peaks observed for Pt and Hg-doped clusters are very different from that of undoped Au25 cluster, suggesting that the altered structures play a crucial role on their optical properties. From the analysis of absorption peak shifts, higher phonon energies of 67 ± 8 meV were determined for Pt- and Hg-doped Au25 clusters when compared to 43 ± 6 meV for undoped Au25. The larger phonon energies suggest stronger coupling of core-gold and shell-gold and are explained by contraction of metal-doped clusters. Ultrafast transient absorption results have shown that Pt-doping lead to faster excited state relaxation, where more than 70% of the created electron-hole pairs recombine within 20 ps. However, Hg-doping and undoped Au25 relax to shell gold and recombination takes a much longer time. The results are consistent with energy gap law, where the smaller energy gap for PtAu24 led to faster exciton relaxation. An interesting correlation between the spin-orbit coupled transitions and bleach maximum was observed, which can be ascribed to exciton localization in Au12-icosahedron.

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