In metal nanoparticles absorption is strong while luminescence (emission) is weak unlike in semiconductors nanoparticles. Why is this the case?

01 January 2015 1 10K Report

Thanks in advance for your replies.

I am not a physicist but I will try my best:

- We know that the surface plasmons become dominant in metal nanoparticles. Actually all the nanoparticles having free charge carriers (metal and semiconductors) have a surface plasmon absorption band and it depends on the free charge carrier concentration of the material. The higher the concentration, the higher the plasmon frequency and the stronger the absorption. The surface plasmon frequency is high in metals because there is at least one charge carrier (electron) for each atom in the nanoparticle and the corresponding absortion band is in the visible region. On the other hand, charge carrier density in semiconductors is low and the band appears in the IR or microwave region depending on the doping level. Because less free charge carrier is involved in the process, the absorption is also lower in semiconductors than in metals.

-As for the emission, it is in the nature of semiconductors to make electron-hole recombination, a process which leads to emission. This mechanism does not exist in metals because all the valence electrons are already delocalized.

I hope it helped.

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