Gamma or ultra-violet (254nm) irradiation of as-received crystals of Li-doped material, or ultra-violet (366nm) bleaching of reduced crystals, produced a W5+ paramagnetic defect for irradiation at 77K. The electron spin resonance spectra indicated a C1 symmetry for this center. It was characterized by a strong 183W hyperfine interaction as well as by weaker 183W, 1H and 67Zn superhyperfine interactions. The defect was deduced to be a W5+-H center. It was related to a Mo impurity center which had been reported for reduced ZnWO4 crystals, but its production and stability were different.

A.Watterich, O.R.Gilliam, L.A.Kappers, K.Raksányi: Solid State Communications, 1996, 97[6], 477-80