Pressure-induced phase transition from calcite to aragonite detected by fluorescence spectroscopy

Pressure-induced structural changes in Eu-doped CaCO (sub 3) have been studied by time-resolved optical fluorescence spectroscopy and by total X-ray scattering combined with a pair distribution function analysis. Time-resolved fluorescence measurements are ideally suited to distinguish between calcitic and aragonitic local environments around the Eu-ions. We show that at ambient temperature calcite transforms at approximately 10 GPa into an amorphous phase which locally has an aragonitic structure. This local structure is maintained on pressure release. The decay times of aragonite and the amorphous phase with a locally aragonitic structure are substantially longer than those of calcite.