Synthesis, crystal structure analysis, and photoluminescence of Ti ⁴⁺-doped Mg₅SnB₂O₁₀

Single crystals of magnesium tin oxyborate, Mg₅SnB ₂O₁₀ (Mg₅SnO₄(BO₃) ₂), were prepared at 1350 °C in air, using B₂O ₃ as a flux. They were colorless and transparent with needlelike or columnar shapes. X-ray diffraction analysis of the single crystals revealed that Mg₅SnB₂O₁₀ crystallizes in the triclinic space group F1̄ (No. 2) with Z = 16, a = 6.1295(8), b = 18.714(3), c = 24.719(3) Å, α = 90.021(5)°, β = 90.032(4)°, γ = 90.041(5)°, and V = 2835.4(7) ų (R1 = 0.0168, wR2 = 0.0459, and S = 1.297 for all data). The crystal structure of Mg ₅SnB₂O₁₀ is a ludwigite-type superstructure. Mg and Sn atoms are ordered and coordinated by six O atoms, and the edges of MO₆ (where M = Mg and Sn) octahedra are connected along the a-axis and form zigzag walls. B atoms are in the spaces surrounded by the walls and are coordinated by three O atoms. Polycrystals of titanium(IV)-doped solid solutions, Mg₅Sn_1-xTi_xB₂O ₁₀ (0 < x ≤ 0.50), were also prepared by solid state reaction at 1300 °C in air. The refined unit cell volumes decreased with increasing titanium content (x), indicating partial substitution of Ti for Sn atoms. A broad blue emission with a peak wavelength of ∼430 nm was observed from the solid solutions under 265-nm ultraviolet excitation. A quantum efficiency of 0.81 was measured at room temperature for Mg₅Sn_0.80Ti _0.20B₂O₁₀.