Two-electron exchange between neutral and ionized negative-U tin centers in lead chalcogenides

Abstract

Two-electron exchange between neutral and doubly ionized negative-U tin centers in PbS and PbSe has been studied by Mössbauer emission spectroscopy. The activation energy for this process in PbS is 0.11(2) eV, which is comparable to the depth of tin levels in the band gap of PbS, whereas the activation energy for this process in PbSe, 0.05(1) eV, is comparable to the correlation energy of negative-U donor tin centers in PbSe. The exchange occurs through simultaneous transfer of two electrons and involves valence band states.