Absorption, luminescence, and electret properties of CdI2:Sn2+ crystals

To elucidate the nature of emission and capture centers, the mechanism of luminescence excitation, and the nature of electret state, we studied the absorption, luminescence, and electret properties of Sn-, SnCl2-, and SnI2-doped CdI2 crystals. Sn ions in CdI2 were demonstrated to give rise to near-edge impurity absorption and activator-related bands in the excitation and photoconductivity spectra and in the range of photoelectret sensitivity. A luminescence band insensitive to the type of dopant was observed. The emission at 680-690 nm was attributed to electron-hole recombination on halogen vacancies, followed by energy transfer, via an Anger process, to emission centers involving interstitial Cd. Based on the luminescent properties of our crystals, relaxation behavior of CdI2 and CdI2:Cd2+, and reported data, we infer that Sn increases self-activated luminescence, characteristic of slightly Cd-doped CdI2 crystals, without producing emission centers.