OPTICAL-PROPERTIES OF SMALL SI-SKELETON SHEETS - LADDER POLYSILANES

We have studied optical properties of confined excitons in ladder polysilanes regarded as small Si sheets. With a decrease in the size of Si sheets, the blueshift of the lowest exciton energy was observed. Broad photoluminescence spectra with large Stokes shifts were observed in the visible region of 2-3 eV. Optical properties of small Si sheets are different from those of linear Si chains. Spectroscopic analyses and ab initio molecular orbital calculations suggest that excitons strongly bound to the lattice and are localized on 1-2 Si atoms and the large Stokes shift is due to the significant structural difference between the ground and excited states.