Doping PbWO4 with different ions to increase the light yield

To search for a possibility to utilize PbWO4-based scintillators in inexpensive positron emission computed tomography, we have studied the effects of doping PbWO4 with different ions on the light yield (LY). The LY in PbWO4, which is undoped except a small concentration of rare-earth 3+ ions to improve the radiation hardness, decay time, mechanical quality, etc., is 25–35 photoelectrons/MeV (pe/MeV) (about 3–4% of LY in BGO) with bialkali photomultiplier for a fixed condition of the crsytal size of 10×10×(20–30) mm3 and the gate width of 1 μs. For doping with single dopant, the maximum LY obtained was about 49 pe/MeV for Mo6+. For co-doping with two dopants, the maximum LY of 58 pe/MeV was obtained for Mo6++Nb5+. For co-doping with three dopants, we have recently obtained 77 pe/MeV for Mo6++Cd2++Sb5+,3+. The dependence of LY on the gate width indicates creation of medium-speed component in μs range in the samples doped with Mo6++Cd2++Sb5+,3+ or Mo6++Nb5+. Their radioluminescence spectra are similar in shape to PWO:Mo6+.