Recent progress in the development of lead tungstate crystals

The investigation performed up to now on single crystals of PbWO4 (PWO) provides the evidence of the possibility to optimise the optical properties, of an intrinsic scintillator such as PWO: the control of essential requirements in the crystal preparation (raw material purity, growing methods and postgrowth annealing) as well as the introduction of selected dopants at suitable concentrations (particularly trivalent and pentavalent ions) were found to be very successful in lowering the concentration of point defects in the lattice which strongly affect scintillation properties and radiation hardness. The optical transmission as well as light yield before and after irradiation was measured. The systematic investigation effort to better understand the scintillation characteristics and to improve the quality of PWO crystals is due to their use for the CMS electromagnetic calorimeter.