Crystal Structure and Nontypical Deep-Red Luminescence of Ca₃Mg[Li₂Si₂N₆]:Eu²⁺

Rare-earth-doped nitridosilicates exhibit outstanding luminescence properties and have been intensively studied for solid-state lighting. Here, we describe the new nitridolithosilicate Ca₃Mg­[Li₂Si₂N₆]:Eu²⁺ with extraordinary luminescence characteristics. The compound was synthesized by the solid-state metathesis reaction in sealed Ta ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ca₃Mg­[Li₂Si₂N₆]:Eu²⁺ crystallizes in the monoclinic space group C2/m (no. 12) [Z = 4, a = 5.966(1), b = 9.806(2), c = 11.721(2) Å, β = 99.67(3)°, V = 675.9(2) ų] and exhibits a layered anionic network made up of edge- and corner-sharing LiN₄ tetrahedra and [Si₂N₆]^10– bow-tie units. The network charge is compensated by Ca²⁺ and Mg²⁺ ions. Upon irradiation with UV to blue light, red emission at exceptionally long wavelengths (λ_em = 734 nm, fwhm ≈2293 cm^–1) is observed. According to emission in the near-infrared, application in LEDs for horticultural lighting appears promising.