DIRECT OBSERVATION OF ELECTRON SELF-TRAPPING IN PBCL2 CRYSTALS

Direct experimental evidence is reported for the self-trapping of electrons produced at 80 K by x-ray irradiation or by UV illumination above the band gap in pure, orthorhombic (D2h16) PbCl2 crystals. The ESR analysis demonstrates that the electron is trapped at a pair of nearest-neighbor substitutional Pb2+ ions along the a direction, resulting in a paramagnetic Pb-2(3+) molecular ion with electronic configuration complementary to that of the (halogen)2- self-trapped hole center in the alkali halides. The results of this paper suggest that the self-trapped exciton in PbCl2 consists of a hole trapped in an excited orbital around the Pb-2(3+) center.