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High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
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Exciting clusters, what does off-resonance actually mean?
Goonay Yousefalizadeh1, Shideh Ahmadi, Nicholas J Mosey
1Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario K7L 3N6, Canada. kevin.stamplecoskie@queensu.ca.
Nanoscale
|December 17, 2020
Summary
Noble metal clusters show promise for multiphoton biomedical imaging due to their large two-photon absorption. This study reveals the mechanisms behind this phenomenon, offering insights for optimizing their use in imaging applications.
Area of Science:
- Materials Science
- Nanotechnology
- Biomedical Imaging
Background:
- Noble metal clusters possess unique photophysical properties valuable for advanced applications like multiphoton biomedical imaging.
- The Au25SR18 cluster previously demonstrated exceptionally large two-photon absorbance cross-sections, sparking interest in understanding this phenomenon.
Purpose of the Study:
- To investigate the origins of large two-photon absorption in Au25SR18 and ten other gold (Au) and silver (Ag) clusters.
- To elucidate the influence of metal type, cluster size/structure, and ligand effects on multiphoton absorption capabilities.
- To analyze the impact of excitation wavelength on non-linear optical responses in these clusters.
Main Methods:
- Utilized femtosecond pump/probe transient absorption spectroscopy (fsTAS) to study 11 different Au and Ag clusters.
- Employed excited-state absorbance (ESA) as an optical signature for two-photon absorbances, independent of emission quantum yields.
- Investigated the effect of a 1028 nm excitation wavelength on cluster responses.
Main Results:
- Identified excited-state absorbance (ESA) as a consistent optical signature for two-photon absorption across various thiolated Au and Ag clusters.
- Demonstrated that metal type, cluster size, structure, and ligand environment significantly impact the ability to absorb multiple near-infrared (NIR) photons.
- Revealed the critical role of excitation wavelength in determining the observed non-linear optical responses, explaining previous experimental variances.
Conclusions:
- The double resonance mechanism is responsible for the giant two-photon absorbance cross-sections observed in noble metal clusters.
- Understanding these mechanisms allows for tailoring metal cluster properties to specific experimental conditions for enhanced multiphoton imaging signal and response.
- This research provides a foundation for optimizing noble metal clusters for efficient multiphoton biomedical applications.
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