Structural, morphological and optical properties of new Eu-doped and vacancied lead molybdato-tungstates

Abstract

A new tetragonal, scheelite-type Pb1–3x▯xEu2x(MoO4)1–3x(WO4)3x (0 < x ≤ 0.1970 and ▯ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results confirm the formation of single, tetragonal scheelite-type phases (space group I41/a) with the average crystallite size in the range of ∼20–100 μm. Substitution of Pb2+ with Eu3+ is relatively easy despite the large difference in ionic radii, and the formation of vacancies is necessary to compensate the excess positive charge in PbMoO4 framework. A change in lattice parameters (both a and c as well as lattice parameter ratio c/a) and progressive deformation of MoO4 and WO4 tetrahedra with increasing Eu concentration are observed. Thermal stability of Eu-doped materials strongly depends on the concentration of Eu3+ ions. The Pb1–3x▯xEu2x(MoO4)1–3x(WO4)3x solid solution for x = 0.0098 shows the highest melting point (1057 °C) which is slightly higher than that of pure PbMoO4 (1040 °C). The UV-vis diffuse reflectance spectroscopy (DRS) and the Tauc plots were used to extrapolate the optical indirect band gap (Eg) of doped materials. Eu-doped ceramics are insulators (Eg > 3 eV) and their band gap nonlinearly decreases with increasing dopant concentration.