Optical Properties of Extrinsic Two-Dimensional Excitons in BiI₃Single Crystals

Abstract

Interface excitons caused by stacking faults in BiI 3 , crystals have been investigated on absorption, photoluminescence and its excitation spectra. Characteristic three sharp absorption lines (called R , S and T ), appear close to the fundamental absorption edge. The temperature dependence of the line shape shows a typical feature of exciton-phonon interaction in the case that K =0 at the bottom of the exciton band. Resonant luminescences of these lines have also very narrow line widths, and no Stokes shifts can be detected. The luminescence line shape of phonon side band shows Maxwellian-like having the line width proportional to thermal energy but accompanied by a fine structure which reflects a quasi two-dimensional band nature of this exciton system. The high density excitation effects of these states reveal a specific interaction among the R , S and T excitons.