Absorption-spectral-shape analysis of the band-edge exciton in aBiI3crystal based on the exciton-phonon interaction

Abstract
We have observed optical absorption spectra of the band-edge direct-exciton absorption line at temperatures from 4.2 to 293 K in BiI3 thin-film single crystals grown by the hot-wall crystal growth technique. The absorption spectral shape has been calculated by use of the weak-coupling exciton-phonon interaction theory. At low temperatures, the calculated results are in good agreement with the experimental measurements in the spectral regions of both the indirect-exciton edge and the direct-exciton peak.