Indirect Transitions in Spectra of BiI 3 Crystals at Low Temperatures

Absorption and luminescence spectra of BiI 3 crystals have been studied in a temperature interval of 1.6 to 77°K. In the vicinity of the intrinsic absorption edge steps in the absorption contour have been detected (steps A, B, C, A T , B T ), having a positive coefficient of temperature shift. These steps can be related to indirect exciton transitions with phonon emission and absorption. Emission of the indirect exciton has been observed, which belongs to the spectral region where the inverse hydrogen‐like series lines of absorption and luminescence are located. The energy of the indirect exciton formation ( E ik = 16205 cm −1 ) and of phonons taking part in indirect transitions have been determined.