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 (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) Å3. Upon activating with Eu2+, luminescence in the orange spectral region (λmax = 644 nm, 1.93 eV, 15528 cm-1; fwhm = 225 nm, 0.66 eV, 5291 cm-1) was observed. In addition, a blue emission (λmax = 460 nm, 2.70 eV, 21739 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.