Polaronic WO43- centres in PbWO4 single crystals

The autolocalization of free electrons at PbWO4 regular lattice sites, namely at WO42- complex anions, has been demonstrated by ESR measurements. It has been shown that the WO43- centre is a shallow donor; its energy level is situated approximate to 50 meV below the bottom of the PbWO4 conduction band. At temperatures of 50-60 K the captured electrons are detrapped and the formation of other paramagnetic centres occurs. In La-doped PbWO4, an enhanced cross-section for electron trapping by MoO(4)(2-)impurity centres with respect to that for undoped samples is found. In contrast to the case for other tungstates, no intrinsic oxygen hole and/or Pb3+ centres were revealed in PbWO4. The role of the WO43- centres in the processes of transport and recombination of nonequilibrium carriers in the PbWO4 lattice is discussed.