What is an Extinction Spectrum? Plasmonic Gold Nanoparticles

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    Extinction Spectrum
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SUMMARY

An extinction spectrum refers to the measure of the attenuation of light as it passes through a medium, specifically for plasmonic gold nanoparticles. It is distinct from reflection and transmission spectra, although for diluted solutions, extinction and absorption can be considered equivalent according to Lambert-Beer's law. The resonant frequency of nanoparticle colloids corresponds to the peak of their extinction spectrum. Interestingly, the extinction spectra for gold nanoparticles (5, 50, 100, 200 nm) shift toward smaller wavelengths with increasing particle size, contrary to the expected red-shift.

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  • Understanding of extinction spectra in optical physics
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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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