Synthesis, crystal structure, and characterization of DyMgB ₅ O ₁₀ : thermal behavior, band gap calculation, and luminescence

Abstract

A new member of the rare-earth magnesium pentaborate family, DyMgB ₅ O ₁₀ , was synthesized via solid-state reaction followed by flux growth in a K ₂ Mo ₃ O ₁₀ melt. Single crystals up to 0.5 mm were obtained and characterized by SEM, EDX, DSC, and XRD techniques. The crystal structure was refined in the monoclinic space group P 2 ₁ / n , confirming that it belongs to the same structural family as other R MgB ₅ O ₁₀ compounds. The structure consists of alternating anionic borate layers built from [B ₅ O ₁₂ ] ³⁻ clusters and cationic Dy–O–Mg layers. Dy ³⁺ ions are coordinated by ten oxygen atoms in distorted polyhedra, while Mg ²⁺ occupy edge-sharing octahedral dimers. Thermal analysis revealed incongruent melting with T _onset ∼ 1,072 °C. DFT calculations gave an indirect band gap of ∼6.06 eV, indicating a wide-bandgap dielectric. Photoluminescence and X-ray induced luminescence spectra exhibit characteristic Dy ³⁺ intra-4 f transitions, with dominant blue ( ⁴ F ₉ / ₂ → ⁶ H ₁₅ / ₂ ) and yellow ( ⁴ F ₉ / ₂ → ⁶ H ₁₃ / ₂ ) emissions. The intense yellow emission reflects the low symmetry of the DyO ₁₀ polyhedra. Characteristic luminescence under X-ray excitation confirms effective energy transfer from the borate matrix to Dy ³⁺ . The combination of high thermal stability, wide band gap, and favorable optical properties makes DyMgB ₅ O ₁₀ a promising candidate for phosphors and X-ray scintillators.