Thermally stimulated and photoinduced depolarization processes in PbI2 crystals

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Abstract
The thermally stimulated depolarization (TSD) of photo-, thermo-, and electroelectret states in undoped lead iodide crystals was studied in the temperature range 85–330 K. The results demonstrate that the centers responsible for the electret charge localization in PbI2 crystals are related to structural defects. The peak observed in the PbI2 thermoelectret TSD current at 170 K arises from the dipole relaxation of donor-acceptor pairs formed by Pb+ ions and anion vacancies V a, and the peak at 295–305 K is due to the formation of a space charge during poling owing to the displacement of anion vacancies. The electroelectret formation during poling of PbI2 near 85 K in the dark is probably associated with the electric-field ionization of Pb+ and Pb0 centers and the formation of electronic F-centers, responsible for the IR sensitivity of PbI2. The main peak (130–135 K), present in both the thermo-and electroelectret TSD current curves, arises from the thermal dissociation of those centers. IR irradiation of crystals photopolarized at 85 K leads to electron release from trapping centers, accompanied by electret field decay and an increase in V a concentration.

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