Emergence of Intrinsic One-Dimensional Excitons in Colloidal Bi13S18I2 Nanocrystals

We present a synthesis method for colloidal nanocrystals exhibiting a one-dimensional Peierls-like distortion in the form of size-tunable colloidal and monodisperse Bi13S18I2 nanorods. The Bi13S18I2 nanorods exhibit an absorption onset around 1.6 eV and an excitonic transition around 1.1 eV. First-principles calculations demonstrate that this intrinsic excitonic transition originates from one-dimensional excitons localized in the Bi2+ columns formed within the Bi13S18I2 lattice. In these columns, a Peierls-like distortion results in Bi2+ dimerization and the formation of a Peierls bandgap, which is intrinsic to Bi13S18I2. This work demonstrates an exciting approach to induce excitonic properties in semiconductors without relying on traditional quantum confinement strategies, as well as opportunities to explore the spontaneous inherent symmetry breaking in nanocrystals. The Bi13S18I2 nanorods also highlight the important role of colloidal chemistry in the discovery of complex materials and their optical properties and motivate further exploration of metal chalcohalide nanocrystals.