Extended Data Fig. 1: Absorbance spectra as a function of pressure.

a, f–f transitions in Cm-1 spectra show large bathochromic shifts as pressure is applied; however, the pydtc⁻ ligand-based broadband absorption quickly obscures the Cm³⁺ transitions. b, In Cm-2, these transitions are not competing with any broadband ligand-based transitions; however, the f–f transitions show much smaller shifts up to high pressures than those observed for Cm-1. c, The shifts observed in Nd-1, the Nd³⁺ analogue of Cm-1, are more similar to those of Cm-2 than those of Cm-1.