Crystal structure re‐determination, spectroscopy, and photoluminescence of π ‐YBO 3 :Eu 3+

To unambiguously clarify the long‐debated crystal structure of the low‐temperature orthoborate π ‐YBO 3 , single‐crystals of the europium‐doped π ‐YBO 3 :Eu 3+ 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 C 2/ 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. 11 B as well as 89 Y MAS NMR spectroscopy was used to verify that our results are also accurate for the undoped π ‐YBO 3 and samples with varying europium content prepared under ambient pressure conditions. Additionally, the luminescence properties of the Eu 3+ doped π ‐orthoborate were determined in comparison with these ambient‐pressure samples.