Calibration of ruby’s luminescence shift from the bismuth I-II transition: constraints on the initial slope of ruby gauge

We have measured the luminescence shift of the ruby’s R1-line corresponding to the transition pressure of bismuth (Bi) I-II. The Bi sample was loaded in a diamond anvil cell using neon as pressure medium, with small ruby spheres positioned near the Bi sample. Fine compression and decompression were controlled by a double-sided membrane system. Synchrotron x-ray diffraction measurements on Bi and luminescence measurements on ruby were simultaneously collected using an in-line ruby system at the 16-ID-B beamline at the Advanced Photon Source. The Bi I-II transformation is signified by the distinct diffraction patterns, associated with discontinuities in the luminescence shift as a function of time. The determined ruby’s R1-shift is 0.9311 ± 0.007 nm at the Bi I-II transition at 25.8 ± 0.1°C. Together with the previously determined R1-shift relative to the melting pressure of mercury, the calibrations constrain the initial slope of ruby gauge to 1860 ± 3 GPa, compared to 1870 ± 10 GPa in the Ruby2020 gauge.