Size effects in the optical properties of AunAgn embedded clusters

The optical properties of bimetallic silver-gold clusters are investigated in the size range 1.9-2.8 nm. Clusters, produced by laser vaporization of a n alloy target Au-Ag (50%-50% atomic composition) are embedded with a low c oncentration in an alumina matrix. The mixed particles have the same stoich iometry as the rod. Absorption spectra exhibit a plasmon resonance band bet ween those of pure Au and Ag embedded clusters, shifting towards higher ene rgies with decreasing cluster size. Theoretical calculations in the frame o f the time-dependent-local-density-approximation including an inner skin of ineffective screening and the porosity of the matrix, an in good agreement with experimental results.