Broad distribution of crystal-field environments for Nd₃₊ in calcite

Calcite crystals were grown from solution with single-crystal dimensions up to 3 mm and doped up to ∼0.1 at% with Nd³⁺ ions. Phase purity was verified by powder X-ray diffraction. The concentration of Nd³⁺ was measured by energy-dispersive spectrometry and Rutherford backscattering spectrometry. Micro X-ray fluorescence mapping of the calcite grains indicates uniform Nd distribution in as-grown crystal grains X-ray absorption fine structure suggests that Nd³⁺ is substituted for Ca²⁺ with local lattice distortion. Temperature-dependent near-infrared spectroscopy of Nd³⁺ impurities in calcite reveals large inhomogeneous line-widths and smooth line profiles that are characteristic of glassy hosts, though the samples are well crystallized.