Optical probes of crystal growth mechanisms: Intrasectoral zoning

Impurities present in crystallizing solutions may become segregated within regions of the resulting crystals that correspond to specific slopes of growth hillocks. When the impurities are dyes or luminophores, chemical zoning of this sort results in distinct patterns of color or light that serve to identify growth active surface structures and crystal growth mechanisms. Moreover, the optical probes reveal the specificity of non-covalent interactions between molecules and anisotropic hillocks. These phenomena are illustrated herein for three crystals, potassium dihydrogen phosphate, potassium sulfate, and α-lactose monohydrate, grown in the presence of an azo dye, a luminescent benzene derivative, and a naturally occurring anthraquinone, respectively.