The green emission of lead tungstate (PbWO4) is closely related to structure defects. For studying the mechanism of the green emission, the local structure of PbWO4 has been first investigated by extended X-ray absorption fine structure using synchrotron radiation. The results indicate that the excess oxygen in air-annealed PbWO4 exists and forms "WO4 + O-i" centers. The green emission of PbWO4 is not caused by (WO3 + F) centers, but probably originates from the centers Of "WO4 + O-i". (C) 2001 Elsevier Science B.V. All rights reserved.