Peculiarities of manifestation of different forms of structure disordering in the exciton spectra of the PbI2

For an express reveal of defects of different nature in single crystals of PbI2 a method highly sensitive to structure changes, based on the measure of low-temperature (T = 4.5 K) exciton spectra of light reflection (RS) and photoluminescence (PL), has been used. The doping of PbI2 with impurities (In, Ga, Ag, Cu, Cd, Fe, Mn, Ni) promotes preferably the creation of the 4H-polytype in the process of growth and one-dimensional structure disordering. The high coefficient values of the concentration shift and broadening of substitutional solid solution (SSS) of Pb1-xMnxI2 and Pb1-xCdxI2 exciton band are explained by the realization of conditions for the creation of the 4H-PbI2-cluster phase. In the PL spectra of some samples representing joints of 2H+4H-polytypes, an additional D band (lambda = 499.2 nm, T = 5 K) has been revealed. The D band is characterized by the coefficient of temperature shift dE/dT = -0.25 x 10(-3) eV/K which is not proper to bands connected with defects.