Temperature variation of the ESR parameters of the self-trapped-electron center inPbCl2

The self-trapped-electron center in ${\mathrm{PbCl}}_2$ crystals, i.e., the ${\mathrm{Pb}}_2^{3+}$ molecular ion resulting from the trapping of a conduction electron by a pair of ${\mathrm{Pb}}^{2+}$ lattice cations along the a direction, exhibits in the 10–78 K temperature range a strong temperature dependence in both g and hyperfine tensors of the ESR spectrum. Such an unusual large variation, which is not observed for the isoelectronic ${\mathrm{Tl}}_2^{+}$ and ${\mathrm{Pb}}_2^{3+}$ impurity centers in alkali chlorides, seems to be related to the anisotropic thermal expansion of the layered ${\mathrm{PbCl}}_2$ lattice.