On the phosphors Na5M(WO4)4 (M = Y, La–Nd, Sm–Lu, Bi) – crystal structures, thermal decomposition, and optical and magnetic properties. Issue 24 (5th June 2020)

• Record Type: Journal Article
• Authors: Hämmer, Matthias; Janka, Oliver; Bönnighausen, Judith; Klenner, Steffen; Pöttgen, Rainer; Höppe, Henning A.
• Is Part Of: Dalton transactions. Volume 49:Issue 24(2020)
• Page Start: 8209
• Page End: 8225
• Publication Date: 2020-06-05
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt00782j
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : An exploration of the crystal chemistry of exciting luminescent title compounds – possible phosphors – is discussed also employing magnetic measurements. Abstract : The pentasodium rare-earth tungstates Na5 M(WO4 )4 are closely related to the sodium rare-earth double tungstates Na5 M(WO4 )2 both adopting the scheelite structure type (space group I 41 / a, no. 88). After the preparation of polycrystalline powders via flux syntheses improving the phase purity significantly, the crystal structures of Na5 M(WO4 )4 (M = Y, La–Nd, Sm–Lu, Bi) were determined by single crystal XRD and Rietveld analysis. Na5 M(WO4 )4 is a promising phosphor material both as a host and as a 100% phosphor due to the possible charge transfer of the tungstate group and the absence of any concentration quenching. Na5 M(WO4 )4 incongruently melts to Na5 M(WO4 )2 and Na2 WO4 . After the clarification of the crystallographic relationship of Na5 M(WO4 )4 and Na5 M(WO4 )2 based on a rare isomorphic transition of index 5 ( i 5) the non-linear trend of the decomposition temperature within the row of rare earth ions is explained systematically taking into account the existence of domains within the crystal structure predetermining the posterior decomposition. A miscibility gap for solid solutions of Na5 Y(WO4 )4 and Na5 Eu(WO4 )4 or Na5 Tb(WO4 )4 is identified and its temperature dependence is investigated. Furthermore, the investigation of the fluorescent properties of Na5 M(WO4 )4 (M = Pr, Sm, Eu, Tb, Tm, Bi), Na5 Y1− x Eu x (WO4 )4 and Na5 Y1− y Tb y (WO4 )4 provided insights into the weak ligand field and the energy transfer from WO4 2− to M 3+ governed by the emission of the sensitiser within Na5 M(WO4 )4 . Additionally, the compounds were characterised by magnetic measurements and vibrational, UV/Vis and 151 Eu Mössbauer spectroscopy.