Hydrothermal Synthesis, Crystal Structure, and Spectroscopic Properties of Pure and Eu3+-Doped NaY[SO4]2 ∙ H2O and Its Anhydrate NaY[SO4

Constantin Buyer,Thomas Schleid,Thomas Jüstel,David Enseling

doi:10.3390/cryst11060575

Constantin Buyer, Thomas Schleid + Show 2 more

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https://doi.org/10.3390/cryst11060575

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Abstract

The water-soluble colorless compound NaY[SO4]2 ∙ H2O was synthesized with wet methods in a Teflon autoclave by adding a mixture of Na2[SO4] and Y2[SO4]3 ∙ 8 H2O to a small amount of water and heating it up to 190 °C. By slow cooling, single crystals could be obtained and the trigonal crystal structure of NaY[SO4]2 ∙ H2O was refined based on X-ray diffraction data in space group P3221 (a = 682.24(5) pm, c = 1270.65(9) pm, Z = 3). After its thermal decomposition starting at 180 °C, the anhydrate NaY[SO4]2 can be obtained with a monoclinic crystal structure refined from powder X-ray diffraction data in space group P21/m (a = 467.697(5) pm, b = 686.380(6) pm, c = 956.597(9) pm, β = 96.8079(5), Z = 2). Both compounds display unique Y3+-cation sites with eightfold oxygen coordination (d(Y–Os = 220–277 pm)) from tetrahedral [SO4]2− anions (d(S–O = 141–151 pm)) and a ninth oxygen ligand from an H2O molecule (d(Y–Ow = 238 pm) in the hydrate case. In both compounds, the Na+ cations are atoms (d(Na–Os = 224–290 pm) from six independent [SO4]2− tetrahedra each. Thermogravimetry and temperature-dependent PXRD experiments were performed as well as IR and Raman spectroscopic studies. Eu3+-doped samples were investigated for their photoluminescence properties in both cases. The quantum yield of the red luminescence for the anhydrate NaY[SO4]2:Eu3+ was found to be almost 20 times higher than the one of the hydrate NaY[SO4]2 ∙ H2O:Eu3+. The anhydrate NaY[SO4]2:Eu3+ exhibits a decay time of about τ1/e = 2.3 µm almost independent of the temperature between 100 and 500 K, while the CIE1931 color coordinates at x = 0.65 and y = 0.35 are very temperature-consistent too. Due to these findings, the anhydrate is suitable as a red emitter in lighting for emissive displays.

Highlights

Eu3+-doped luminescence materials based on complex oxides are very important in application [1,2] and show a red emission with typical 5D0 → 7FJ transitions between 610 and 620 nm [3]
We report on the preparation of NaY[SO4]2 · H2O via wet synthesis, its trigonal crystal structure, and the red luminescence of Eu3+-doped samples
Sodium yttrium oxosulfate monohydrate NaY[SO4]2 · H2O was obtained from a wet synthesis by adding 6.6 mmol Na2[SO4] (ChemPur, 99.9%) and 5.5 mmol Y2[SO4]3 · 8 H2O, which means an excess of Na2[SO4], to about 4 ml demineralized water and heated the obtained wet powder to 190 ◦C in a 25 ml Teflon autoclave overnight, with a yield only limited by the solubility of the monohydrate

Summary

Introduction

Eu3+-doped luminescence materials based on complex oxides are very important in application [1,2] and show a red emission with typical 5D0 → 7FJ transitions between 610 and 620 nm [3] They could be prepared on “classic” solid-state routes at high temperatures, as has been done for the examples of Y2[MoO4]3:Eu3+ and Y2[MoO4]2[Mo2O7]:Eu3+ [4], GdSb2O4Br:Eu3+ [5], as well as YNbO4:Eu3+ and YTaO4:Eu3+ [6]. Another energy-saving synthesis route to get Eu3+-doped luminescence materials without heating uses wet synthesis strategies.

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