Cu(3-x)P Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions

[Image: see text] Synthesis approaches to colloidal Cu(3)P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump–probe measurements on platelet-shaped Cu(3-x)P NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu(3)P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu(3-x)P NCs. It is likely that both the LSPR and the p-type character of our Cu(3-x)P NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu(3-x)P NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu(3-x)P NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu(3-x)P is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu(3-x)P/InP heterostructures, as a consequence of the fact that the exchange between Cu(+) and In(3+) ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu(3-x)P NCs an interesting material platform from which to access other metal phosphides by cation exchange.