Ba₂BP₇N₁₄ – A Quaternary Alkaline Earth Nitridoborophosphate with a Mixed 3D Network Structure

Highly condensed alkaline earth nitridophosphates have attracted increasing scientific interest, due to their high thermal and chemical stability, as well as their promising luminescence behavior upon doping with Eu²⁺ for pc-LED applications. In particular, the barely explored mixed tetrahedra-based nitridophosphates offer a wide range of structural and compositional diversity, enabling new insights into structure-property relationships. Herein, we report on the first quaternary alkaline earth nitridoborophosphate Ba₂BP₇N₁₄, synthesized at 8 GPa and 1600 °C in a multianvil press, starting from Ba(N₃)₂, h-BN and P₃N₅. Ba₂BP₇N₁₄ crystallizes in the barylite-1O polytype and features a highly condensed mixed (B,P)-N anionic 3D network (κ≈0.57) built up of PN₄ and mixed occupied (P_0.75B_0.25)N₄ tetrahedra. The structure was characterized by a multi-step process involving single-crystal and powder X-ray diffraction (SCXRD, PXRD), elemental analysis, electron microscopy (STEM, EELS), and solid-state ³¹P and ¹¹B MAS NMR spectroscopy. The plausibility of the structural model was corroborated by low-cost crystallographic calculations. The optical band gap and the thermal behavior of an undoped sample of Ba₂BP₇N₁₄, were determined from diffuse reflectance spectroscopy and temperature-dependent powder X-ray diffraction, respectively. Irradiation of a Eu²⁺-doped sample with near-UV light results in a blue emission peaking at λ_em=422 nm.