Improvement in transmittance and decay time of PbWO4 scintillating crystals by La-doping

The optical transparency of PbWO4 single crystals in the short wavelength region between 320 nm (cutoff) and 450 nm is significantly improved by doping with a small amount of La. This result indicates the possibility that the light yield detected by photomultipliers in actual detectors could be significantly increased for the fast blue emission which peaks around 420 nm. The improvement in transmittance was compared for different amounts of La doping. La-doping also shortens the decay time; the best fit of the decay spectrum is a sum of three exponentials for undoped PbWO4, while it is a sum of two exponentials for La-doped PbWO4 with the absence of the next to the fastest component. GDMS analysis was carried out for the grown crystals to evaluate any other impurities.