An EPR study of the Tl${}^{+}$-doped PbCl${}_2$ crystals x-ray irradiated at low temperature reveals the presence, besides known spectra attributed to hole-trapped Tl${}^{2+}$ centers and ${\mathrm{Pb}}_2^{3+}$ self-trapped-electron (STEL) centers, of an additional strongly anisotropic set of lines consisting of an intense doublet and several weaker satellite lines spread over a large magnetic-field range. The quantitative analysis of the EPR spectrum shows the corresponding paramagnetic center to be a bent molecular ion (PbTl)${}^{2+}$ resulting from electron trapping at a pair of substitutional ${\mathrm{Pb}}^{2+}$ and Tl${}^{+}$ ions. Its formation suggests the electron trapping at pairs of neighboring cations is a more general characteristic of this material, with possible relevance in photolysis and exciton localization properties.

• Received 19 June 1997

DOI:https://doi.org/10.1103/PhysRevB.57.1