Semiconducting optical properties of silver/silica mesoporous composite

The optical absorption properties were investigated for mesoporous silica loaded with different amounts (up to 5% in weight) of silver (Ag) nanoparticles (less than 4 nm in diameter) into its pores. In contrast to the previously reported glasses containing Ag particles, in this Ag particle-loaded silica no apparent surface plasmon resonance peak of Ag particle, other than an absorption edge, was observed. This composite exhibits the optical features of a semiconductor with direct band gap. The absorption edge shifts in the range from about 200 to about 700 nm with an increasing Ag loading amount up to 5% in weight, and hence, is controllable. Adsorption of oxygen in air on the surface of Ag particles within the pores, and scattering inside the porous structure were used to explain these results.