Structural and photoluminescence properties of Eu³⁺doped α-Ag₂WO₄synthesized by the green coprecipitation methodology

Abstract

Europium doped silver tungstates α-Ag2-3xEuxWO4 (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 Pn2[combining macron]n space group. The refined lattice parameters and atomic positions were employed to model the WO6 and AgOn (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 [WO6] 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)D0 to (7)FJ (J = 0-4) levels of the Eu(3+) were noticed. Among the samples, the most intense photoluminescence results were observed for the α-Ag2-3xEuxWO4 (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.

Low temperature micro Raman and laser induced upconversion and downconversion spectra of europium doped silver tungstate Ag2−3xEuxWO4 nanorods

“…Figures 3 and 4 present the room temperature Raman spectra of the a-(Ag 2-3x Eu x )WO 4 (x = 0-0.08 mol) samples excited at 532 and 633 nm, respectively. These spectra are very similar to those reported and assigned for the aAg 2-3x Eu x WO 4 (x = 0.0-0.01 mol) phosphor samples [21] The main features observed are for samples with x [ 2 mol% (k exc = 532 nm), in which the mode A 1g at 883 cm -1 appears to shifts to higher wavenumber because of the this is because of an underlying emission band that gets stronger and causes the apparent movement of the Raman band as the Eu 2? concentration increases in the aAg 2 WO 4 lattice.…”

“…As a-Ag 2 WO 4 belongs to the C 2v 10 point group and has two molecular formulas per unit cell (Z = 2). Group theory predicts that there are 21 different Raman modes [46], of these 14 modes have previously been identified [21]. Figures 3 and 4 present the room temperature Raman spectra of the a-(Ag 2-3x Eu x )WO 4 (x = 0-0.08 mol) samples excited at 532 and 633 nm, respectively.…”

“…The nanorods were synthesised via a low temperature (90°C) coprecipitation route [21]; the nanorods emitted red light without further heat treatments.…”

“…concentrations studied it was not bright enough for the application [21]. Thus in this work we report on attempts to increase the Eu 3?…”

Femtosecond-laser-irradiation-induced structural organization and crystallinity of Bi2WO6

“…Furthermore, this PL profile is typical of a multiphonon process, i.e., a system in which relaxation occurs by various paths, involving the participation of numerous energy levels within the band www.nature.com/scientificreports www.nature.com/scientificreports/ gap. Based on the molecular orbital theory, the emission bands can be ascribed to the transition from the low vibration level of 1 T 2 to the 1 A 1 ground state within the WO 6 excited moiety [96][97][98][99][100][101][102][103] . Figure 6(b) shows a schematic representation of the PL emissions related to the presence of the intermediate levels between the CB and the VB.…”