Take for example a 20 nm Ag NP with its LSPR in air at 400 nm. Now when this nanoparticle will be in water, light will refract from air to water to interact with it. Since the wavelength of all the light will now be changed as : Wavelength/1.33. So 532 nm wavelength in air now will be converted to 400 nm in air (400 nm in air will be converted to 300 nm). So as of now, if we exclude the effect of dielectric medium on the plasmons, then the LSPR should be at 532 (because the nanoparticle is actually experiencing 400 nm wavelength).

But then of course, the effect of the dielectric medium on the polarizability comes into the picture. And we have an LSPR at around 420 (Not 532!).

So it looks like, the dielectric medium actually blue shifted the LSPR from 532 to 420. In the absence of the effect of the dielectric medium on the plasmonics, the peak would actually be at 532.

Is this argument correct?

Thanks a lot in advance for your response!

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