The Synthesis, Structure, and Luminescent Properties of TmMgB₅O₁₀ Crystals

TmMgB₅O₁₀ spontaneous crystals were synthesized via the flux-growth technique from a K₂Mo₃O₁₀-based solvent. The crystal structure of the compound was solved and refined within the space group P2₁/n. The first principles calculations of the electronic structure reveal that TmMg-pentaborate with an ideal not defected crystal structure is an insulator with an indirect energy band gap of approximately 6.37 eV. Differential scanning calorimetry measurements and powder X-ray diffraction studies of heat-treated solids show that TmMgB₅O₁₀ is an incongruent melting compound. A characteristic band of the Tm³⁺ cation corresponding to the ³H₆ → ¹D₂ transition is observed in the photoluminescence excitation spectra of TmMg-borate. The as-obtained crystals exhibit intense blue emission with the emission peaks centered at 455, 479, 667, and 753 nm. The most intensive band corresponds to the ¹D₂ → ³F₄ transition. TmMgB₅O₁₀ solids demonstrate the thermal stability of photoluminescence.