The frequency and temperature dependences of the dielectric response of monocrystalline specimens were measured before and after ultra-violet irradiation. The irradiated crystals, but not as-grown samples, exhibited dielectric relaxation characteristics with an activation energy of 0.3eV and a frequency factor of about 108Hz. This was attributed to the dipoles of complex colour centres which formed in the W-O tetrahedra of the lattice. Infra-red spectroscopy confirmed that radiation affected the W-O bonds. However, irradiated crystals did not undergo dielectric relaxation if they had been previously annealed in O at a temperature at which O diffused readily; as indicated by thermogravimetry. It was concluded that reducing the O-vacancy concentration effectively enhanced the radiation hardness.

Complex Color Centers in Ultraviolet-Light Irradiated PbWO4 Single Crystal. W.Li, T.B.Tang, X.Feng: Journal of Applied Physics, 2000, 87[11], 7692-5