Optical absorption of divalent metal tungstates: Correlation between the band-gap energy and the cation ionic radius

Abstract

We have carried out optical-absorption and reflectance measurements at room temperature in single crystals of AWO4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr, and Zn). From the experimental results their band-gap energy has been determined to be 5.26 eV (BaWO4), 5.08 eV (SrWO4), 4.94 eV (CaWO4), 4.15 eV (CdWO4), 3.9-4.4 eV (ZnWO4), 3.8-4.2 eV (PbWO4), and 2.3 eV (CuWO4). The results are discussed in terms of the electronic structure of the studied tungstates. It has been found that those compounds where only the s electron states of the A2+ cation hybridize with the O 2p and W 5d states (e.g BaWO4) have larger band-gap energies than those where also p, d, and f states of the A2+ cation contribute to the top of the valence band and the bottom of the conduction band (e.g. PbWO4). The results are of importance in view of the large discrepancies existent in prevoiusly published data.

16 pages, 3 figures, 1 table

References in corpus (4)

• Pressure effects on the structural and electronic properties of ABX4 scintillating crystals
• Effects of high pressure on the optical absorption spectrum of scintillating PbWO4 crystals
• Landau theory applied to phase transitions in calcium orthotungstate and isostructural compounds
• High-pressure effects on the optical-absorption edge of CdIn2S4, MgIn2S4, and MnIn2S4 thiospinels

Cited by in corpus (2)

• Combined Raman scattering and ab initio investigation of pressure-induced structural phase transitions in the scintillator ZnWO4
• High-pressure Raman spectroscopy and lattice-dynamics calculations on scintillating MgWO4: A comparison with isomorphic compounds