What is an Extinction Spectrum? Plasmonic Gold Nanoparticles

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    Extinction Spectrum
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Discussion Overview

The discussion centers around the concept of an extinction spectrum, particularly in the context of plasmonic gold nanoparticles. Participants explore its relationship to reflection, absorption, and transmission spectra, as well as its implications for analyzing colloidal solutions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on whether an extinction spectrum is equivalent to reflection, absorption, or transmission spectra.
  • Another participant inquires about how to derive an absorption spectrum from reference extinction spectra for plain water and a colloid solution.
  • A participant explains that extinction is related to the damping of a wave in a medium and notes that for diluted solutions, extinction and absorption can be equivalent, referencing Lambert-Beer's law.
  • There is a question regarding whether the resonant frequency of a nanoparticle colloid corresponds to the peak of its extinction spectrum, along with an observation about the expected behavior of extinction spectra as particle size changes.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and interpretation regarding the relationship between extinction and absorption spectra, and there is uncertainty about the expected behavior of extinction spectra with changing particle size. No consensus is reached on these points.

Contextual Notes

Participants mention specific conditions under which extinction and absorption may differ, particularly in strongly absorbing or reflecting media, indicating that assumptions about particle size and concentration may affect the discussion.

Who May Find This Useful

Researchers and students interested in the optical properties of nanoparticles, particularly in the fields of plasmonics and materials science, may find this discussion relevant.

austinmw89
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Would someone please tell me what an extinction spectrum refers to? e.g. for plasmonic gold nanoparticles. Is it the same thing as reflection, absorption, or transmission spectrum? Something else?
 
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I have a reference extinction spectrum (plain water) and an extinction spectrum for a colloid solution. How do I use these to get the absorption spectrum for the colloid? Any help is greatly appreciated!
 
Extinction is the constant which determines the damping of a wave entering a medium. Absorption is the part of energy which is absorbed.
For diluted solutions (as may be the case with your gold particle solution) the two are basically equivalent, see Lambert Beers law. However, for strongly absorbing or reflecting media the two may be quite different. E.g. a metal has a high extinction constant but absorbs little of the light, as most of it is reflected.
 
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Thank you, that clarifies things a lot. Does this mean the resonant frequency for my nanoparticle colloid is just at the wavelength corresponding to the peak of its extinction spectrum? Also the extinction specta for my particles (5, 50, 100, 200nm) is moving toward smaller wavelengths as the particles get larger, but I thought they were supposed to red-shift?
 
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