Size and Emission Control of Wurtzite InP Nanocrystals Synthesized from Cu_3-xP by Cation Exchange

Phosphide-based nanocrystals (NCs), including InP and Cu_3-xP, are relevant for applications in light-emitting devices and catalysis, yet their synthetic design is limited in terms of size range and homogeneity. We report the synthesis of uniform and size-controlled emissive wurtzite-phase InP NCs formed via cation exchange from Cu_3-xP. First, size-controlled Cu_3-xP NCs are synthesized by the formation of metallic Cu⁰ NCs and their phosphidation to Cu_3-xP. By changing the ligands and precursor concentrations, the NC size is varied between 5 and 13 nm. Using cation exchange, InP NCs are then generated. As the surface of InP NCs is prone to oxidation and defects that decrease their emission, we performed a reaction with NOBF₄. This yields InP NCs with resolved absorption features and efficient band-gap emission as a result of impurity removal and surface passivation. The effect of water, acid, and halides on the balance of NC etching and surface passivation is studied. With this approach, high-quality wurtzite InP NCs are obtained while the emission is tuned between 810 and 600 nm. The obtained NCs are potential building blocks for catalytic and optoelectronic applications.