Extended investigations on the pressure stability of AlB₄O₆N:Cr³⁺

Abstract Recently, we discovered the aluminium oxonitridoborate AlB 4 O 6 N:Cr 3+ , whose high-pressure/high-temperature synthesis could be optimized in the last months. This compound shows extraordinary luminescence properties, that closely resemble the famous compound ruby, whose luminescence is characterized by two narrow R emission lines close to each other. Apart from a slight blue shift, the main difference of the luminescence of the title compound is the presence of a single R line due to nearly perfect [(Al/Cr)O 6 ] octahedra in the structure. Ruby plays a crucial role as gold standard for pressure calibration in diamond anvil cells by measuring the shift of one of these R lines with increasing pressure. However, the accuracy is limited at elevated pressure, since the two R lines broaden and eventually merge. Since the compound AlB 4 O 6 N:Cr 3+ showed only one single R line up to a pressure of at least 52 GPa, it could provide improved accuracy for the calibration of diamond anvil cells. This raises the question as to how the material behaves at even higher pressures. Therefore, we performed luminescence measurements of AlB 4 O 6 N:Cr 3+ up to 78(1) GPa in a diamond anvil cell and complemented our findings with single-crystal diffraction data (synchrotron) at elevated pressure to detect possible structural changes.