Effect of Bi Doping on the Optical Properties of CdI2

The effect of Bi impurity on the optical absorption and roentgeno-, photo-, and thermoluminescence spectra of CdI2 crystals grown by the Bridgman-Stockbarger method is studied. CdI2 activation with BiI3 produces a number of absorption bands related to electronic transitions of Bi3+. Bi produces no emission centers in CdI2. The 550- to 560-nm luminescence of CdI2 is due to the radiative recombination of self-trapped anion excitons. The observed changes in spectral distribution and the reduction in light yield upon CdI2 activation with Bi3+ are mainly due to the reabsorption of emission from native centers by activator centers. Under x-ray excitation, CdI2: Bi3+ accumulates a small light sum at shallow trap levels related to native defects.