Luminescent calcium carbonate micro ‘bow ties’

Calcium carbonate (CaCO₃) is a ubiquitous material which has been studied for centuries due to its integral nature across various fields and its vast range of applications. Here we report, for the first time, a low temperature dry ice carbonation method for the production of unique rare earth-doped calcium carbonate ‘bow ties’. CaCO₃ exhibits retrograde solubility, an interesting property in which its solubility increases with decreasing temperature. In this synthesis, dry ice acts not only as a CO₂ source, but as a coolant, increasing the solubility of CaCO₃ and CO₂ and allowing specific growth to occur. The incorporation of trivalent lanthanide ions Eu³⁺ and Tb³⁺ into the CaCO₃ synthesis results in the formation of these unique luminescent calcite ‘bow tie’ microstructures which cannot be produced using either standard gaseous CO₂ carbonation, or chemical precipitation methods. This new method and materials might find potential applications including, but not limited to, radionuclide sequestration, imaging and photonics.