Crystal structure re‐determination, spectroscopy, and photoluminescence of π‐YBO3:Eu3+.

To unambiguously clarify the long‐debated crystal structure of the low‐temperature orthoborate π‐YBO3, single‐crystals of the europium‐doped π‐YBO3:Eu3+ were prepared via a high‐pressure/high‐temperature route at 7.5 GPa and 1400 °C. The structure was solved and refined in the monoclinic space group C2/c (no. 15) in the pseudowollastonite structure type, with the lattice parameters a=11.3407(5), b=6.5501(3), c=9.5798(4) Å, and β=113.08(2)°. This structure determination was corroborated by powder X‐ray diffraction and vibrational spectroscopy. 11B as well as 89Y MAS NMR spectroscopy was used to verify that our results are also accurate for the undoped π‐YBO3 and samples with varying europium content prepared under ambient pressure conditions. Additionally, the luminescence properties of the Eu3+ doped π‐orthoborate were determined in comparison with these ambient‐pressure samples. [ABSTRACT FROM AUTHOR]