Optical Absorption Studies on CdI2Crystals in the Region near the Absorption Edge

Optical absorption measurements were made on single crystals of CdI 2 , in the region near the absorption edge. The intrinsic absorption edge of Cdl 2 is dominated by the well-defined structures due to indirect excitonic absorption below 30 K. With raising the temperature, these structures are smeared out into an exponential absorption tail with relatively large steepness. Another exponential component with small steepness appears on the low energy side above 100 K and grows up to surpass the former above 130 K. Absorption measurements were also made on very thin crystals. A prominent peak and a shoulder were found at 3.693 and 3.80 eV. The small steepness component is considered as the low energy tail of the 3.693 eV absorption band. Discussions are made on the excitonic states responsible for these absorption structures and tails as well as on the exciton relaxation in the CdI 2 crystal.