Structural refinement, growth mechanism, infrared/Raman spectroscopies and photoluminescence properties of PbMoO4crystals
Abstract: Lead molybdate (PbMoO4) crystals were synthesized by the co-precipitation method at room temperature and then processed in a conventional hydrothermal (CH) system at low temperature (70 C for different times). These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, micro-Raman (MR) and Fourier transformed infrared (FT-IR) spectroscopies. Field emission scanning electron microscopy images were employed to observe the shape and monitor the crystal growth process. The optical properties were investigated by ultraviolet–visible (UV–Vis) absorption and photoluminescence (PL) measurements. XRD patterns and MR spectra indicate that these crystals have a scheelite-type tetragonal structure. Rietveld refinement data possibilities the evaluation of distortions in the tetrahedral ½MoO4 clusters. MR and FT-IR spectra exhibited a high mode m1(Ag) ascribed to symmetric stretching vibrations as well as a large absorption band with two modes m3(Eu and Au) related to anti-symmetric stretching vibrations in ½MoO4 clusters. Growth mechanisms were proposed to explain the stages involved for the formation of octahedron-like PbMoO4 crystals. UV–Vis absorption spectra indicate a reduction in optical band gap with an increase in the CH processing time. PL properties of PbMoO4 crystals have been elucidated using a model based on distortions of tetrahedral ½MoO4 clusters due to medium-range intrinsic defects and intermediary energy levels (deep and shallow holes) within the band gap.
Author(s): Bomio, M. R. D.; Cavalcante, L. S.; Almeida, M. A. P.; et al.
Polyhedron
Volume: 50 Issue: 1 Pages: 532-545 Published: 2013
DOI: https://doi.org/10.1016/j.poly.2012.12.001
