Doped or Not Doped: Ionic Impurities for Influencing the Phase and Growth of Semiconductor Nanocrystals

Dimension, phase, and shape tunable architectures of nanostructures are of interest due to morphology-dependent modulation of the properties of materials. However, the manipulation of specific structures of nanomaterials, in order to achieve unique physical and chemical properties by modulating the synthesis parameters, remains challenging. Wet chemistry has proven to be quite efficient for such shape- and size-controlled synthesis. Recent architectural progress with different nanostructures suggests that dopants or impurities present in the reaction system can affect the crystal growth and tune the shapes of crystals in ways that go beyond the classical approach where the nature of the precursors, ligands, and reaction conditions dependent facets controlling crystal growth mostly determined the shape. These foreign atoms or ions may or may not be retained in the crystal lattice and may or may not become incorporated into the crystal. This is a new era of current research on the architecture of nanostructures and involves deep fundamental insights that are unsolved or unknown to date. This review presents several reports where foreign ions or impurities influence the crystal growth, tune shapes of nanostructures, and unveil the chemistry involved in their synthesis processes. The ability of those species, either from inside the crystal (as dopants) or from bulk solution, to affect the growth and even the nucleation itself, is discussed. Furthermore, the specific roles of some of these impurities either alone or in combination with other synthesis parameters like surfactants, solvents, temperature, and precursors in forming nanostructures using a variety of inorganic compounds as precursors are also summarized. Finally, the challenges and future perspectives of these novel impurity-driven strategies are presented.