Colloidal synthesis of emission-tunable Cu-doped Zn–In–Se/ZnSe core/shell nanocrystals for lighting and bioimaging applications†

Abstract

Herein, environmentally benign Cu^I:Zn–In–Se/ZnSe core/shell luminescent inorganic nanocrystals (NCs) were synthesized via a phosphine-free one-pot, two-step organometallic approach with good colloidal quality. Firstly, Cu^I ion-doped Zn–In–Se colloidal NCs were synthesized via a one-pot heating chemical method using phosphine-free, highly reactive alkylammonium selenide as a Se source. The resulting Cu^I-doped Zn–In–Se colloidal NCs exhibited a doping concentration-dependent colour tunable emission in the range of 450–800 nm with a poor emission intensity. Consequently, in the second, to improve the stability and emission intensity of the doped colloidal NCs, a ZnSe shell was grown over their core via a hot-injection chemical route. The shell growth, performed at a relatively high temperature of ∼240 °C with zinc precursor injection, initially leads to the diffusion of Zn^II ions into the core lattice, followed by the partial substitution with Cu^I and In^III ions close to the surface of NCs and formation of a shell layer over the core. In addition, a continuous blue shift with an increase in the intensity of the emission peak of core Cu^I:Zn–In–Se NCs, caused by partial cation exchange, was observed after sequential Zn precursor injections at specified intervals. The prolonged radiative lifetime of the NCs was observed with the successive injection of the shell precursor, reaching the highest value of 348.7 ns. Subsequently, the potential application of these Cu^I:Zn–In–Se/ZnSe core–shell NCs in flexible electronics and live-cell imaging was tested. Flexible nanocomposite films of polymer–NCs were prepared via the solution drop-casting technique. The composite films showed a good level of optical transmission in the visible region and good PL emission intensity. Moreover, cytotoxicity and optical live-cell imaging studies were carried out and the results revealed that the 11-mercaptoundecanoic acid-capped Cu^I:Zn–In–Se/ZnSe core–shell NCs are biocompatible with the potential for use in the bio-imaging application as a luminescent agent.