Tunneling recombination processes in PWO4 crystals

Time-resolved emission and excitation spectra and luminescence decay kinetics were studied at 160-300 K for undoped and Mo-doped PbWO4 crystals under XeCl (4.02 eV), N2 (3.67 eV) and KrF (5.0 eV) pulsed excimer laser excitation. The G(II) emission was found to be responsible for the slow (µs-ms) luminescence decay. Under excitation or after irradiation in the exciton region (Eexc = 4.02 eV), this emission accompanies the monomolecular tunneling recombination in genetic pairs of electron and hole centers produced at the photo-thermally stimulated decay of localized excitons, which occurs without release of free charge carriers. Under excitation or after irradiation in the host lattice (Eexc = 5.0 eV) and defect-related (Eexc = 3.67 eV) regions, the bimolecular tunneling recombination takes place in chaotic pairs of the electron and hole centers created at the trapping of optically released free charge carriers.