Electronic structure of pure and defective PbWO4, CaWO4, and CdWO4

Lead tungstate (PbWO4) and cadmium tungstate (CdWO4) are dense, fast scintillator crystals which have achieved technological importance for high energy radiation detectors and medical imaging, respectively. Calcium tungstate (CaWO4, the mineral scheelite) is an important phosphor for lighting and displays. We recently compared the electronic structures of the four scheelite-structure materials CaWO4, PbWO4, CaMoO4 , and PbMoO4 [1]. The present paper discusses further aspects of the electronic properties of the first two of these crystals and presents new electronic structure results for CdWO4 using the same calculation method. Furthermore, a supercell adaptation of the method has been employed to study chemical impurities and vacancies at effective 50% concentrations. Results for Pb impurities in CaWO4 were reported in Ref. [2]. Additional results on Pb vacancies, La impurities, and Bi impurities in PbWO4 are reported here. Comparisons to experimental data on photoelectron spectroscopy, reflectivity [3], electronic transport, EPR, and luminescence spectroscopy will be discussed.