The paper describes and discusses the results of investigation of opti
cal properties of CdI2 depending on concentration of impurity overstoi
chiometric cadmium atoms Cd-i, localized in Van-der-Waals gaps of laye
red crystals. The experimental results are discussed within the scope
of phase transition in CdI2-Cd-i system, which take place when the con
centration of Cd-i atoms increases.