Electron exchange between impurity centers of tin in lead chalcogenides

Electron exchange between neutral and doubly ionized U-minus centers of tin in partially compensated solid solutions Pb$_{0.96}$Sn$_{0.02}$Na$_{0.01}$Tl$_{0.01}$S, Pb$_{0.99}$Sn$_{0.005}$Na$_{0.005}$S, Pb$_{0.965}$Sn$_{0.015}$Na$_{0.01}$Tl$_{0.01}$Se, and Pb$_{0.988}$Sn$_{0.005}$Na$_{0.007}$Se has been investigated using $^{119mm}$Sn($^{119m}$Sn) emission Mössbauer spectroscopy. The activation energy of the process for PbS-based solid solutions is 0.11(2) eV and is comparable to the depth of energy levels of tin in the PbS band gap, while the activation energy of this process for PbSe-based solid solutions is comparable to the activation energy of donor $U$-minus centers of tin in PbSe being 0.05(1) eV. The exchange has been performed by the simultaneous transfer of two electrons with the use of the valence band states.