A new barium-containing alkali metal silicate fluoride NaBa3Si2O7F with deep-UV optical property

A new silicate fluoride, NaBa3Si2O7F, has been successfully synthesized by a high-temperature solution method. It crystallizes in the orthorhombic space group Cmcm (No. 63). NaBa3Si2O7F is the first barium-containing alkali metal silicate fluoride with the [NaO6] polyhedra, the [BaO8F] polyhedra and isolated [Si2O7] units. The optical characterizations indicate that NaBa3Si2O7F possesses wide transparent window and available luminescence properties. To confirm the coordination surroundings of anionic groups and its thermostability, infrared spectroscopy and thermal behaviors were also analyzed, which proved the existence of tetrahedronly coordinated silicium atoms and the good stability of NaBa3Si2O7F at high temperature. First-principles calculation was also implemented for better understanding the relationship between the structure of NaBa3Si2O7F and its property. Additionally, to further explore the structural novelty of NaBa3Si2O7F, the comparison of the anionic structures was carried out in mixed alkali and alkaline-earth metal silicate fluorides. Interestingly, the result indicates the isolated [Si2O7] dimer is rare among the above systems, which enriches the structural chemistry of silicate fluorides.