Self-trapped electrons and holes inPbBr2crystals

We have directly observed self-trapped electrons and holes in ${\mathrm{PbBr}}_2$ crystals with the electron-spin-resonance (ESR) technique. The self-trapped states are induced below 8 K by two-photon interband excitation with pulsed 120-fs-width laser light at 3.10 eV. Spin-Hamiltonian analyses of the ESR signals have revealed that the self-trapping electron centers are the dimer molecules of ${\mathrm{Pb}}_2^{3+}$ along the crystallographic a axis and the self-trapping hole centers are those of ${\mathrm{Br}}_2^{-}$ with two possible configurations in the unit cell of the crystal. Thermal stability of the self-trapped electrons and holes suggests that both of them are related to the blue-green luminescence band at 2.55 eV coming from recombination of spatially separated electron-hole pairs.