Structural and photoluminescence properties of Eu 3+ doped α-Ag 2 WO 4 synthesized by the green coprecipitation methodology

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 44; no. 40; pp. 17673 - 17685
• Main Authors: Pinatti, Ivo M., Nogueira, Içamira C., Pereira, Wyllamanney S., Pereira, Paula F. S., Gonçalves, Rosana F., Varela, José A., Longo, Elson, Rosa, Ieda L. V.
• Format: Journal Article
• Language: English
• Published: 2015
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/C5DT01997D

Europium doped silver tungstates α-Ag 2−3x Eu x WO 4 ( x = 0, 0.0025, 0.005, 0.0075 and 0.01 mol) were synthesized by the coprecipitation method at 90 °C for 30 minutes. These crystals were structurally characterized by means of X-ray diffraction (XRD), Rietveld refinement, and micro-Raman (MR) and Fourier transformed infrared (FT-IR) spectroscopies. Field emission scanning electron microscopy (FE-SEM) images were employed to observe the shape of the crystals. The optical properties were investigated by ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) measurements. The XRD pattern indicated structural organization at a long range for all undoped and Eu-doped samples, while MR and FT-IR revealed that the presence of the Eu 3+ ions favors the structural organization at a short range. The Rietveld refinement showed that all the crystals are monophasic with an orthorhombic structure and the Pn 2̄ n space group. The refined lattice parameters and atomic positions were employed to model the WO 6 and AgO n ( n = 2, 4, 6 and 7) polyhedra in the unit cell. FE-SEM analysis revealed nanorod-like microcrystals with growth of metallic silver on the surface. Further, the UV-vis absorption spectra indicated the existence of intermediary energy levels within the band gap. PL spectra showed a broad band related to the [WO 6 ] group and characteristic narrow peaks due to the f–f transitions of Eu 3+ as a result of efficient energy transfer from the matrix. Also, the emission line shape transitions from 5 D 0 to 7 F J ( J = 0–4) levels of the Eu 3+ were noticed. Among the samples, the most intense photoluminescence results were observed for the α-Ag 2−3x Eu x WO 4 ( x = 0.0075) sample. Lifetime decays support that the Eu 3+ ions occupy at least two crystallographic sites. CIE coordinates confirmed the colors of the emission spectra which classify this material as a potential phosphor in the visible range.