Copper cluster energy dependencies

Noble or semi-noble metals colloids from copper, silver or gold exhibit both free electron and inter-band transition behavior. As a clear consequence from the band model of molecular and cluster excitation the deterioration is depending on the frequency range. Ofien the IR and red part of the spectrum exhibits ideal behavior whereas at the interband level (higher energy) spectra a dominated by inter-band excitation and plasmons are quenched rapidly. For theoretical studies alkali metals are ideal, but due to their instability in an ambient environment, only noble metal clusters are applicable in air and under aqueous solvents. 

---