One-Pot Synthesis of Monodisperse Colloidal Copper-Doped CdSe Nanocrystals Mediated by Ligand–Copper Interactions

Abstract

We report a one-pot synthesis of high-quality colloidal copper-doped cadmium selenide nanocrystals (Cu+:CdSe NCs) by injection of a mixture of copper iodide (CuI) and trioctylphosphine (TOP) into solutions containing preformed CdSe NCs. This method allows NC doping to be separated from nucleation and growth, thereby simultaneously achieving large size tunability, narrow size dispersion, and exclusively copper-based photoluminescence (PL). The copper doping level is affected by both the reaction time and the relative concentrations of the cadmium precursor, CuI, and TOP. A correlation is demonstrated between the copper dopant concentration and the intensities of the characteristic near-IR PL and midgap absorption bands, both associated with metal-to-ligand (conduction band) charge-transfer (MLCBCT) excitation of Cu+ dopants. Mechanistic studies reveal that Cu2–xSe NCs are easily formed as kinetic intermediates under reaction conditions involving substantial copper and that these NCs then act as a copper source for the subsequent formation of Cu+:CdSe NCs in the same reaction mixture. We also observe postsynthetic loss of copper from the doped NCs during shell growth or exposure to phosphines and amines, reflecting the high mobility of Cu+ ions in colloidal NCs.