Crystal Structure and Luminescent Properties of R2- xEux(MoO4)3 (R = Gd, Sm) Red Phosphors

Vladimir A. Morozov, Maria V. Raskina, Bogdan I. Lazoryak, Katrien W. Meert, Katleen Korthout, Philippe F. Smet, Dirk Poelman, Nicolas Gauquelin, Johan Verbeeck, Artem M. Abakumov, Joke Hadermann

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22 Citations (Scopus)

Abstract

The R2(MoO4)3 (R = rare earth elements) molybdates doped with Eu3+ cations are interesting red-emitting materials for display and solid-state lighting applications. The structure and luminescent properties of the R2-xEux(MoO4)3 (R = Gd, Sm) solid solutions have been investigated as a function of chemical composition and preparation conditions. Monoclinic (α) and orthorhombic (β′) R2-xEux(MoO4)3 (R = Gd, Sm; 0 ≤ x ≤ 2) modifications were prepared by solid-state reaction, and their structures were investigated using synchrotron powder X-ray diffraction and transmission electron microscopy. The pure orthorhombic β′-phases could be synthesized only by quenching from high temperature to room temperature for Gd2-xEux(MoO4)3 in the Eu3+-rich part (x > 1) and for all Sm2-xEux(MoO4)3 solid solutions. The transformation from the α-phase to the β′-phase results in a notable increase (∼24%) of the unit cell volume for all R2-xEux(MoO4)3 (R = Sm, Gd) solid solutions. The luminescent properties of all R2-xEux(MoO4)3 (R = Gd, Sm; 0 ≤ x ≤ 2) solid solutions were measured, and their optical properties were related to their structural properties. All R2-xEux(MoO4)3 (R = Gd, Sm; 0 ≤ x ≤ 2) phosphors emit intense red light dominated by the 5D07F2 transition at ∼616 nm. However, a change in the multiplet splitting is observed when switching from the monoclinic to the orthorhombic structure, as a consequence of the change in coordination polyhedron of the luminescent ion from RO8 to RO7 for the α- and β′-modification, respectively. The Gd2-xEux(MoO4)3 solid solutions are the most efficient emitters in the range of 0 < x < 1.5, but their emission intensity is comparable to or even significantly lower than that of Sm2-xEux(MoO4)3 for higher Eu3+ concentrations (1.5 ≤ x ≤ 1.75). Electron energy loss spectroscopy (EELS) measurements revealed the influence of the structure and element content on the number and positions of bands in the ultraviolet-visible-infrared regions of the EELS spectrum.

Original languageEnglish
Pages (from-to)7124-7136
Number of pages13
JournalChemistry of Materials
Volume26
Issue number24
DOIs
Publication statusPublished - 23 Dec 2014
Externally publishedYes

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