Rietveld refinement, cluster modelling, growth mechanism and photoluminescence properties of CaWO sub(4):Eu super(3+) microcrystals

• Published in: CrystEngComm 2015-02, Vol.17 (7), p.1654-1666
• Main Authors: Goncalves, R F, Cavalcante, L S, Nogueira, I C, Longo, E, Godinho, MJ, Sczancoski, J C, Mastelaro, V R, Pinatti, I M, Rosa, ILV, Marques, APA
• Format: Article
• Language: English
• Subjects: Chromaticity; Clusters; Coprecipitation; Field emission; Microcrystals; Photoluminescence; Spectra; Spectroscopy; X-rays
• ISSN: 1466-8033
• DOI: 10.1039/c4ce02279c

CaWO sub(4):Eu super(3+) microcrystals (with 0, 1, 2 and 4 mol% Eu super(3+)) were synthesized by a co-precipitation (CP) method and grown in a microwave-assisted hydrothermal (MAH) system at 130 degree C for 30 min. X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near edge spectroscopy (XANES), Fourier-transform Raman (FT-Raman) and Fourier-transform infrared (FT-IR) spectroscopy indicated that all of the microcrystals have a scheelite-type tetragonal structure without deleterious phases. Structural refinement data were employed to model the [CaO sub(8)], [EuO sub(8)] and [WO sub(4)] clusters. XANES spectra confirmed that the presence of deltahedral [EuO sub(8)] clusters promotes small distortions of neighbouring tetrahedral [WO sub(4)] clusters in a global tetragonal lattice. Field emission scanning electron microcopy (FE-SEM) images revealed that the replacement of Ca super(2+) by Eu super(3+) ions changed the particles' shapes, resulting in the different morphologies of the microcrystals. UV-vis diffuse reflectance spectra indicated a reduction in the optical band gap with the replacement of Ca super(2+) by Eu super(3+) ions. The photoluminescence (PL) properties of the Eu super(3+) ions in CaWO sub(4) were studied as well as the chromaticity coordinates and lifetimes of these compounds.