BiI3 nanoclusters in melt-grown CdI2 crystals studied by optical absorption spectroscopy

Optical absorption spectroscopy of CdI2–BiI3 layered crystals has been performed in the temperature range of 77–300 K. The main absorption, observed in these crystals at 2.59 eV is related to quantum confined exciton absorption of bimolecular BiI3 cluster. Low energy absorption peaks at 2.38 eV, 2.06 eV and 1.94 eV can be tentatively assigned to larger clusters composed of 4, 6 or more BiI3 molecules. In ultra-thin samples of CdI2–BiI3 several bands at 2.84 eV, 3.03 eV and 3.27 eV were observed which are ascribed to higher excited states of the excitons in bimolecular BiI3 cluster.