Why is there a red shift in UV-vis absorbance of (gold) nanoparticles when reducing air pressure from atmospheric to high-vacuum?

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Mohammad Kooti

I also think that the red shift in UV-vis spectrum of gold NPs can be attributed to the grow in the size of these NPs. Perhaps any left surfactant is removed under vacuum and this will cause the NPs to aggregate.

Omar M S

One of the main reason is the enlargement of the particle, there may also be the reason of refracting index changing from thick air to a vacuum that is if the light passes a distance from the sample

Amarjeet Bisla

It is due to increase in the particle size. This phenomenon is also observed in iron oxide nanoparticles. I also observed that subsequent conjugation of IONPs leads to red shift in UV Visible spectrum.