Nonlinear optical spectra of confined and localized excitons in mesoscopic domain and quasi-2D stacking fault interface in BiI₃ crystals

Abstract
Saturation spectra of the excitons confined and localized at several kinds of stacking disorders in layered crystal BiI₃ are studied. The quasi-two dimensional exciton localized at the stacking fault interface does not saturate its absorption strength below the density of 10⁵W/cm² due to the large binding energy and the lateral center-of-mass motion along the interface. On the exciton system associated with some polytypic structures contained in a very small region, an obvious absorption saturation is observed. The behaviour of absorption saturation is well described by a saturation effect on a simplified two-level system having a homogeneous line broadening. An absorption saturation is also observed on the confined excitons in mesoscopic domains induced by the external deformation of the crystal. The pumping-laser photon-energy dependence of the saturation density characterizes this exciton system to be inhomogeneous.