By using electron paramagnetic resonance, and electron nuclear double resonance, new trapped electron and hole centers were characterized in single crystals. In undoped and Al-doped material, a new W5+-type defect was produced by UV- or X-irradiation at 77K. The center was stabilized by a nearby Al3+ impurity that substituted for Zn2+. In ZnWO4:Al, in addition to the above electron-type defect, 3 kinds of hole-type center created by X-irradiation at 77K were also studied. One of these was attributed to an O- ion near to a VZn–AlZn3+ complex. The second was attributed to an O- ion near to a VZn–OH- pair. Due to the higher concentration in the Al-doped crystal, SHF tensors of two W neighbors could also be determined. The third hole-type defect exhibited quartet SHF (I = 3/2) with a 100% abundant nucleus. Therefore, the O- in this center was thought to be likely to be stabilized by an Na+ impurity.

Al- and OH-Related Paramagnetic Impurity Centres in UV- or X-Irradiated ZnWO4 Single Crystals. A.Watterich, A.Hofstaetter, A.Scharmann, O.Szakács: Journal of Physics - Condensed Matter, 2003, 15[41], 7073-84