Electronic structure of oxygen-related defects inPbWO4andCaMoO4

Abstract

Several types of defect structures in PbWO 4 and CaMoO 4 are studied within the framework of density functional theory. While PbWO 4 is currently of greater technological interest, we were able to carry out more extensive calculations for CaMoO 4 , including lattice relaxation, large simulation cells, and more complicated defects. The structural and chemical similarity of the two materials suggests that their defect properties may also be similar. The electronic structure of isolated oxygen vacancies, oxygen and Pb or Ca double vacancies, and substitutional Y are modeled using a supercell approximation. We find that the main effect of oxygen vacancies in PbWO 4 and CaMoO 4 is the introduction of states of W or Mo d character into the band gap. The energies of these defect states are very sensitive to their occupancy. An isolated O vacancy produces a doubly occupied defect state below the conduction band. Removing charge from this defect state lowers its energy and causes additional states of W or Mo d character to move into the band gap. Large supercell simulations for the Ca and O double vacancy in an unrelaxed or slightly relaxed structure produce an unstable electronic structure suggesting the possibility of more extensive lattice distortion. In addition, we also present preliminary results of simulations of interstitial oxygen atoms in CaMoO 4 , finding a relatively stable configuration with the interstitial O forming a weak bond between two MoO 4 clusters.

Contribution of structural order-disorder to the green photoluminescence ofPbWO4

“…At this stage, it has to be noted that Abraham et al also presented density-functional theory calculations of irregular PWO, 63 but their results are difficult to compare with ours because they created oxygen vacancies in a supercell while we only displaced some atoms, keeping their total number constant. Figure 9 illustrates the PL spectra recorded at room temperature for the PWO thin films heat treated at 200, 300, 400, and 500°C.…”

Synthesis and Performance of BaAl2O4 with a Wide Spectral Range of Optical Absorption

“…[7][8][9] Defect-related properties have been widely investigated in semiconductors, such as Si, [10] TiO 2 , [11] ZnO, [12] and PbWO 4 . [13] The first-principle calculation, electron-spin resonance (ESR) spectroscopy, and temperature-programmed reduction (TPR) analysis show that photoabsorption in the visible region of the reduced TiO 2 can be attributed to oxygen vacancies caused by the reduction. [13][14][15][16] However, these semiconductors usually have a simple defect structure, while the optical absorption of insulating metal oxides has seldom been reported.…”

“…[13] The first-principle calculation, electron-spin resonance (ESR) spectroscopy, and temperature-programmed reduction (TPR) analysis show that photoabsorption in the visible region of the reduced TiO 2 can be attributed to oxygen vacancies caused by the reduction. [13][14][15][16] However, these semiconductors usually have a simple defect structure, while the optical absorption of insulating metal oxides has seldom been reported. The highly ionic nature of some materials, especially MgO, BaO, and Al 2 O 3 , allows the formation of many stable defect sites, including edges, corners, and anion/cation vacancies.…”

Electronic structure and luminescence mechanisms in ZnMoO4crystals

“…It was shown that oxide crystals of this family have many congenial features in their electronic structures that are preconditioned by the presence of similar molecular oxyanions XO 2− 4 in anionic positions of their lattice. The full-potential linear-augmented-plane-wave (FLAPW) method has been applied to studies of the electronic structures of perfect ZnWO 4 [6], PbWO 4 , CaWO 4 , CaMoO 4 and PbMoO 4 [7], CdWO 4 and CdMoO 4 [8], as well as of AXO 4 with several point defects [9,10]. Also the electronic structures of PbWO 4 , CdWO 4 and ZnWO 4 with point defects and impurities have been studied in the quantum chemical cluster approach [11][12][13][14].…”