Optical Spectra of SnI₂ Crystal

Abstract

The polarized reflectivity spectra of monoclinic SnI₂ crystals were measured at 13K for polarization parallel and perpendicular to the crystal b-axis. The direct exciton band was found at 2.57eV. The dichroism of the exciton band indicates a strong axial crystal field along the b-axis.The exciton transition is discussed in terms of the cationic 5s→ 5p excitation in Sn²⁺ ions. The fundamental absorption tail was measured at various temperatures. The Urbach rule holds for the tail. The high temperature steepness parameter σ ₀=0.70 indicates the strong exciton-phonon coupling in SnI₂ crystals.