Intrinsic trapping and recombination centers in CdWO_4 investigated using thermally stimulated luminescence

摘要

An investigation of carrier trapping and recombination processes in CdWO_4 crystals undoped and Li doped has been performed by wavelength-resolved thermally stimulated luminescence (TSL) studies following x-ray irradiation at 10 K. Particular focus has been paid to the temperature region from 10 to 100 K where as many as five TSL peaks were detected, with trap depths from 0.07 up to 0.19 eV. Two of them (at 61 and at 75 K) could be ascribed to the thermal detrapping of self-trapped holes (STH) and their subsequent radiative recom-rnbination with electrons localized at intrinsic defect sites. This ascription derives from the strong similarity of their energies and frequency factors (E=0.07 eV and s=10~4 s~(-1), E=0.08 eV and s=10~4 s~(-1)) with those of recently studied STH paramagnetic defects. The TSL emission spectrum features both the intrinsic emission at 2.5 eV probably originating from the (WO_6)~(6-) group and a further band at 1.9 eV previously ascribed to arntransition within a (WO_6)~(6-) group lacking of an oxygen ion. Our findings allow a detailed discussion on the trapping-recombination processes in CdWO_4, also in comparison with those occurring in another tungstate like PbWO_4. Moreover, the possible role of the detected traps in the scintillation performance of the crystal is discussed.