Synthesis, properties and applications of colloidal germanium and germanium-based nanomaterials

Germanium nanoparticles have excited scientists and engineers because of their size-dependent optical properties and their potential applications in optoelectronics, biological imaging and therapeutics, flash memories, and lithium-ion batteries. In order to further develop these applications and to gain deeper insights into their size-dependent properties, robust and facile synthetic methods are needed to controllably synthesize Ge nanoparticles. However, when compared to other II-VI, IV-VI, and III-V semiconductor systems, colloidal routes to Ge NPs with uniform sizes and shapes are much less mature. In this Review Article, we highlight the progress that has been made in this field and provide insights into the strategies used for the colloidal synthesis of size and shape-controlled germanium nanomaterials. We also survey some of the potential applications of these materials in optoelectronics, biological imaging, and energy conversion and storage. Finally, we discuss the colloidal synthesis of other germanium-containing compounds, emphasizing technologically relevant germanium chalcogenides that include GeS, GeSe, and GeTe.