We can create semiconductor quantum dots like Si quantum dots but it is quite impossible to create metallic quantum dots.
As oppose to semiconductor nanoparticles where quantum confinement is responsible for quantization of electron and hole energy states that is manifested in changes in optical spectra, metal nanoparticles exhibit changes in their spectra that can be explained by a classical dielectric picture.
The density of states is so how high and the energy levels are so close to each other in metals, that when reducing a size of particle one obtains ... familiar metal nanoparticles with a localized surface plasmon resonance.
The quantum confinement does affect energy spacing of various levels in the conduction band of metal nanoparticles, but this effect affects conductive properties of metal nanoparticles and is used to describe metal-to-insulator transition as a particle size reduces. This is similar to a particle in the box problem with energy spacing more or less the the thermal energy, kT. However, the energy level separations are still too small to affect optical properties of metals in UV to IR range.
In a semiconductor, the carrier density is low and can be adjusted. That means, a semiconductor quantum dot behaves like an artificial atom with few electrons and single-particle approximations are applicable. In a metal, every atoms provides at least one electron. That means, a “metal quantum dot” would have carriers with density close to the atom density of some 10 to 6. Here, rather collective excitations like plasmons are relevant.
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