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–x Se 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.

Understanding the Journey of Dopant Copper Ions in Atomically Flat Colloidal Nanocrystals of CdSe Nanoplatelets Using Partial Cation Exchange Reactions

“…In the absorption spectra for the doped samples, there exists a weak tail along with e-hh transition (at the lower photon energy) as compared to the undoped NPLs (Figures 2a and 2d), which is attributed to the metal-to-ligand (conduction band) charge transfer (ML CB CT) absorption state for the Cu-doped CdSe CQDs. 3,36 Figures 2b and 2e show the PL emission spectra of Cu (0− 3.6%) and Cu (0−2.2%) doped NPLs with the use of copperacetate and -nitrate precursors, respectively. For both cases, an increase in the Cu-doping results in an increase in the dopantrelated Stokes-shift of the emission with respect to the BE emission.…”

Observation of a phonon bottleneck in copper-doped colloidal quantum dots

“…Here we show that, in Cu:CdSe QDs prepared by a recently-introduced, one-pot method 37 , hole capturing by Cu* occurs on a ≪390 fs timescale and hence competes favorably with the sub-ps Auger-type energy transfer. As a result, electrons are effectively decoupled from holes (Fig.…”

n-Type PbSe Quantum Dots via Post-Synthetic Indium Doping

“…A ligand-assisted dopant outdiffusion has been previously observed in Cu + -doped CdSe QDs. 41,42 Therefore, the surface chemistry of doped QDs plays a critical role in stabilizing electron impurity dopants, and extra 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 14 caution must be taken when characterizing the n-type nature of In:PbSe films. In fact, when ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) were performed on both PbSe and In:PbSe QDs to probe the shift of the QD Fermi-level, we were not able to gain any insightful results on the valence band maximum due to the high sensitivity of surface treatments on doped QDs (Fig.…”