Nonlinear luminescence of stacking-fault excitons inBiI3induced by the exciton-exciton Auger process

We have studied the optical nonlinearities of stacking-fault excitons in layered crystals of BiI3 by means of luminescence spectroscopy. From a measurement of the excitation density dependence of the luminescence we find a saturation of the intensity and an increase in the decay rate. Especially at high excitation densities, the decay curve of the T exciton shows a clear nonexponential decay which is well fitted by a nonlinear differential equation. We have also observed the time correlation signal of the nonlinear luminescence. These experimental findings show that an Auger exciton-exciton annihilation process is dominant over that of optical nonlinearity of the stacking-fault excitons