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

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.