Electronic States of SnBr4 Single Crystal and of Its Clusters Inserted in the Molecular Vessel of Cyclodextrin

From the reflection spectra of SnI 4 single crystal, the exciton absorption band has been observed at peak energies, 3.13 eV (1.6 K) and 3.07 eV (room temperature). The binding energy of the exciton is estimated to be 350 meV (1.6 K) assuming the hydrogen-like series for the exciton energy levels. The novel idea of using a cyclodextrin molecule as a size-controlling vessel to make a SnI 4 cluster is proposed. The reflection spectra of SnI 4 clusters inserted in α-, β- and γ-cyclodextrins were measured. The first exciton absorption peak of the clusters shifts to the higher energy by nearly 0.3 eV (1.6 K) and 0.4 eV (room temperature) compared with that of the single crystals. The shift is due to the quantum size effect.