Colloidal Synthesis of Tunable Copper Phosphide Nanocrystals

Colloidal copper phosphide (Cu3–x P) nanocrystals are attractive materials because of their ability to support excess delocalized holes, leading to localized surface plasmon resonance (LSPR) absorption in the near-IR. We present a one-pot, colloidal synthesis of Cu3–x P nanoplatelets from copper halide salts and tris­(diethylamino)­phosphine [P­(NEt2)3] in the presence of oleylamine (OAm) and trioctylamine. Mass spectrometry and nuclear magnetic resonance spectroscopy reveal that the formation of Cu3–x P is accompanied by an aminophosphonium byproduct, suggesting that Cu3–x P synthesis proceeds through a mechanism similar to that of other metal phosphide nanocrystals. The in situ copper–phosphorus precursor is identified by mass spectrometry, providing an insight into the prenucleation chemistry that was not possible in other aminophosphine-based metal phosphide syntheses. The final nanocrystal ensemble can be tuned by varying the precursor ratios (OAm/P­(NEt2)3 or P­(NEt2)3/CuCl), copper halide (CuCl vs CuBr), or temperature, maintaining low polydispersity over a wide parameter space. By modulating the reactivity, the syntheses presented herein can be used to access nanocrystals with lateral sizes of 6.1–23 nm with LSPR energies of 709–861 meV. Overall, this synthesis presents a platform for systematic mechanistic investigations of the chemical processes underlying Cu3–x P nanocrystal formation. The low polydispersity, size- and LSPR-tunability, and colloidal stability make these nanocrystals promising candidates for further investigations into factors governing the LSPR energy in Cu3–x P nanomaterials.