ESR OF W5-H CENTERS IN GAMMA-IRRADIATED ZNWO4 SINGLE-CRYSTALS DOPED BY LI()

Gamma or UV (254 nm) irradiation of an ''as-received'' ZnWO4:Li crysta l, or, UV (366 nm) bleaching of a reduced crystal, produces a W5+ para magnetic defect for irradiation at 77 K. The ESR spectra indicate Ct s ymmetry for this center. It is characterized by a strong W-183 hyperfi ne interaction as well as weaker W-183, H-1 and Zn-67 superhyperfine i nteractions, permitting the development of a defect model. The defect is designated as the W5+-H center. It is related to a Mo impurity cent er reported in reduced ZnWO4 crystals, although both its production an d stability are different.