Unveiling the effect of Eu2+ and Ce3+ activation on the first rare-earth oxonitridolithosilicate LiGd2Si3N5O2: Crystal structure and luminescence properties

This research article provides structural and luminescence information for the first rare-earth oxonitridolithosilicate LiGd₂Si₃N₅O₂, as determined by single-crystal X-ray diffraction, Rietveld refinement, and spectroscopic investigations. The compound LiGd₂Si₃N₅O₂ crystallizes with similarities to the mineral melilite but in a novel structure type in the tetragonal space group $P\bar{4}{2}_{1}m$ (no. 113) with lattice parameters of a = 7.7178(1) Å, c = 4.9324(1) Å and a cell volume of V = 293.80(2) ų. Upon activating with Eu²⁺, luminescence in the orange spectral region (λ_max = 644 nm, 1.93 eV, 15,528 cm⁻¹; fwhm = 225 nm, 0.66 eV, 5291 cm⁻¹) was observed. In addition, a blue emission (λ_max = 460 nm, 2.70 eV, 21,739 cm⁻¹; fwhm = 89 nm, 0.49 eV, 3912 cm⁻¹) could be measured on a single-crystal of LiGd₂Si₃N₅O₂:Ce³⁺. By comparison of LiGd₂Si₃N₅O₂:Ce³⁺ with literature known Ce³⁺ activated materials, this study investigates the hypothesis that the increase in size and distortion of the rare-earth coordination polyhedron within the distinct substance class correlates with a hypsochromic shift and a broadening of the emission band.