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Published on: September 13, 2024
Polymorphism and polymorph-dependent luminescence properties of the first lithium oxonitridolithosilicate
Kilian M Rießbeck1, Daniel S Wimmer1, Markus Seibald2
1Department of General, Inorganic and Theoretical Chemistry, Universität Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria. Hubert.Huppertz@uibk.ac.at.
Abstract:
Building on studies of monoclinic Li3SiNO2, a polymorph, β-Li3SiNO2, with a previously unknown structure type was synthesized. The β-phase crystallizes in the orthorhombic space group Pbca (no. 61) with lattice parameters of a = 18.736(2), b = 11.1267(5), c = 5.0897(3) Å, and a cell volume of V = 1057.2(1) Å3. Using high-temperature solid-state reactions in sealed tantalum tubes, it was possible to obtain high purity samples (<5 wt% of side phase LiSi2N3 according to Rietveld analysis) containing exclusively one or the other polymorph, depending solely on the cooling rate. In contrast to the monoclinic phase, orthorhombic β-Li3SiNO2 additionally contains a third layer and shows a layer-sequence of the type ABCB. Doped with the activator ion Eu2+, the new polymorph exhibits an intense yellow emission (λmax = 586 nm, fwhm = 89 nm, 0.33 eV, 2650 cm-1) under irradiation with UV to blue light. Hence, the structural difference between the two polymorphs goes along with a significant blue-shift of 16 nm. The results from single-crystal diffraction and single-grain luminescence measurements were confirmed by Rietveld analysis of bulk samples and powder luminescence data.
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