Crystal Structure and Eu ²⁺ Luminescence of the Lithium Alkaline‐Earth Silicate Fluoride LiBa ₂ SiO ₄

A high‐temperature solid‐state synthesis in weld‐shut tantalum ampoules yielded a new alkaline‐earth silicate fluoride, LiBa ₂ SiO ₄ F. The compound crystallizes isotypically to LiSr ₂ SiO ₄ F in the monoclinic space group P 2 ₁ / m (no. 11) with cell parameters of a  = 6.8840(3) Å, b  = 5.5998(2) Å, c  = 7.2670(2) Å, β  = 112.60(1)°, and a cell volume of V  = 258.62(2) Å ³ . When Eu ²⁺ as an activator is provided in the synthesis, the resulting product exhibits strong photoluminescence in the blue spectral region with λ _max  = 465 nm (2.67 eV, 21 505 cm ⁻¹ ) and a bandwidth of FWHM = 95 nm (0.54 eV, 4336 cm ⁻¹ ) under irradiation with UV‐light. The single‐crystal and powder X‐ray diffraction data as well as the photoluminescence spectroscopy measurements are complemented with scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), and experiments to determine the thermal quenching resistance of the luminescence intensity. Structure and luminescence properties are compared to those of the isotypic strontium compound.