Scintillation and phosphorescence of PbWO4 crystals

There are two types of crystals with respect to luminescence. In de measurement, type A gives a primary emission at 410-430 nm (blue) with a second one at around 500 nm. Type B gives only dominant emission at 480-500 nm (green). This apparent difference can be interpreted as follows; the characteristic scintillation of PbWO4 is dominantly blue and subdominantly green. Intense phosphorescence with a decay constant of about 15 ms exists only in Type B at about 500 nm with one to two orders of magnitude larger intensity than scintillation, hiding the blue scintillation in its tail. The cause of the phosphorescence may be Mo.