Exciton Transition of SnI2 at the Fundamental Absorption Edge

Polarized absorption and reflection spectra of monoclinic SnI2 crystals have been measured in the fundamental absorption region at temperatures between 6 and 300 K. The square-root like structure at the fundamental absorption edge observed by Gorban et al. has been found not to appear in the absorption spectra for purified single crystals. The temperature dependence of the spectral lineshape has revealed that the lowest energy gap of SnI2 is of direct type, which is contrary to the expectation of the band calculation. The lowest exciton transition in SnI2 is discussed on the basis of the present results.