Model simulations of zeolite supralattices: Semiconductor Si clusters in sodalite

Periodic three-dimensional arrays of uniform nanosize clusters can be synthesized in the cages and channels of open framework materials. The aluminosilicate frameworks of zeolites have wide electronic band gaps. In addition, they are optically transparent, which opens up the possibility of forming new guest electronic states within the gap, similar to the rare-earth doping of garnets and other insulating matrices. Here we investigate theoretically the atomic geometries, energetics and electronic properties of small semiconducting Si clusters encapsulated in the all-silica sodalite {β} cages. The {β} cage of sodalite is a building block common to the structure of many zeolites. We find that introducing ``native'' semiconductor clusters within the cages of the host materials gives rise to extremely flat molecular electronic bands in the band gap of the host. The band gaps of the cluster can be altered by the silica potential, geometrical alteration of the cluster, and by quantum confinement.