New triple molybdate and tungstate Na₅Rb₇Sc₂(XO₄)₉ (X = Mo, W)

Abstract

New compounds of the composition Na5Rb7Sc2(XO4)9 (X = Mo, W) were obtained via the ceramic technology. The sequences of chemical transformations occurring during the formation of these compounds were established, and their primary characterization was performed. Both Na5Rb7Sc2(XO4)9 (X = Mo, W) were found to melt incongruently at 857 K (X = Mo) and 889 K (X = W). They are isostructural to Ag5Rb7Sc2(XO4)9 (X = Mo, W), Na5Cs7Ln2(MoO4)9 (Ln = Tm, Yb, Lu) and crystallize in the trigonal crystal system (sp. gr. R32). The crystal structures were refined with the Rietveld method using the powder X-ray diffraction data. The thermal expansion of Na5Rb7Sc2(WO4)9 was studied by high-temperature powder X-ray diffraction; it was shown that this triple tungstate belongs to high thermal expansion materials.

Upconversion luminescence and temperature measurement performance of Ho3+/Yb3+ and Tm3+/Yb3+ codoped Na5Rb7Sc2(WO4)9 phosphors

“…R 32) triple tungstates and molybdates of the general formula (M′ = Ag, Na, M′′ = Rb, R = Sc, X = Mo, W; M′ = Ag, M′′ = Cs, R = Sc, X = Mo; M′ = Na, M′′ = Cs, R = Tm, Yb, Lu, Sc, X = Mo). 31–34 The crystal structure of this tungstate is shown in Fig. 1a.…”

“…gr. R32) triple tungstates and molybdates of the general formula M′ [31][32][33][34] The crystal structure of this tungstate is shown in Fig. 1a.…”

“…1b). 31 Ho 3+ /Yb 3+ and Tm 3+ /Yb 3+ codoped Na 5 Rb 7 Sc 2 (WO 4 ) 9 tungstates were synthesized using the conventional solid state reaction method by annealing the stoichiometric mixtures of Na 2 WO 4 , Rb 2 WO 4 , Sc 2 (WO 4 ) 3 , Yb 2 (WO 4 ) 3 , Ho 2 (WO 4 ) 3 or Tm 2 (WO 4 ) 3 at 773-823 K for 120-150 h. Note that at the first stage, solid solutions of Na 5 Rb 7 Sc 1.95 Yb 0.05−x Ln x (WO 4 ) 9 (Ln = Ho, Tm) with a fixed scandium content and a varied ytterbium to codopant ratio were obtained. According to the results of luminescence spectroscopy, the optimal Ho 3+ /Yb 3+ and Tm 3+ /Yb 3+ ratios were found to be 2/3 and 1/9, respectively.…”

“…Fig.1The crystal structure of Na 5 Rb 7 Sc 2 (WO 4 ) 9 : a general view (a) and layers of [Sc 2 (WO 4 ) 9 ] clusters (b) 31. …”