EXCITONS IN PBI2 CLUSTERS INCORPORATED INTO ZEOLITE CAGES

The absorption spectra are reported for PbI2 clusters incorporated into zeolite cages. At 3.0 ∼ 3.6 eV, there appear absorption bands whose energies depend on the size of the cage. These energies are considerably blue-shifted compared with the bulk exciton energy of 2.5 eV, and shift to the higher energy with decreasing the size of the cage. The absorption band is attributed to the exciton generated at an isolated cluster stabilized in the cage, where the diameter of cluster is expected to be 1 ∼ 1.3 nm. The remarkable blue-shift is qualitatively interpreted in terms of the quantum size effect on excitons, but does not coincide quantitatively with the value calculated by the effective mass approximation. © 1990.