In high energy physics experiments

large arrays of scintillation crystals has been used in electromagnetic for precision measurements of photons and electrons. Lead tungstate is a fast and dense scintillating crystal and has been selected as scintillator for the construction of calorimeter in CMS experiment of Large Hadron Collider(LHC)at CERN(European Organization for Nuclear Research)this century. In the course of studying the effects of various heterovalent ions introduced into the PbWO

4

lattice

we have found that Y

3+

ions can significantly improve the optical transmittance in the short wavelength region. Correlated measurements of transmission

X-ray excited emission

positron annihilation lifetime and X-ray photoelectron spectrometers were performed on a selected set of undoped and Y-doped PbWO

4

single crystals. The samples were grown from 5N purity raw powders by modified Bridgman method and show the blue emission component only. The transmittance

luminescence and point defects of Y doped PbWO

4

crystal have been studied by these methods. The results show that Y dopants can improve the luminescence property of the crystal

i.e. it can increase the ratio of fast luminescent component

and suppress the concentrations of positron capture centers and low-valent oxygen ions. It was tentatively proposed that Y

3+

dopants would mainly occupy the sites of lead vacancies resulted from Pb volatilization but not replace the lattice Pb

2+

ions. This is the reason why the absorption edge of PbWO

4

:Y crystal slightly shifts to shorter wavelength. The low-valent oxygen ions suppression can lead to the decrease of green luminescence centers(WO

3

+O

-

)so as to result in higher ratio of fast luminescent component.