Synthesis, Structural, and Optical Properties of Stable ZnS:Cu,Cl Nanocrystals

Abstract

Stable water-suspendable Cu+-doped ZnS nanocrystals (NCs) have been synthesized with mercaptopropionic acid (MPA) as a capping molecule. The nanocrystals have been characterized using a combination of experimental techniques including UV-vis and photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP), and extended X-ray absorption fine structure (EXAFS). The UV-vis electronic absorption spectrum shows an excitonic peak at 310 nm, characteristic of quantum-confined ZnS NCs. This excitonic peak does not change noticeably with Cu+ doping. XRD confirms the formation of ZnS nanocrystals, and the average size of the NCs has been determined to be around 6 nm by TEM. The incorporation of Cu+ into the ZnS is manifested as a substantial red-shift of the emission band in the PL spectra upon addition of Cu2+ that was reduced into Cu+ during the synthesis reaction. EXAFS data were obtained to confirm copper doping as well as determine the local structure about Cu+ and Zn2+ in the NCs. Fitting to the EXAFS data for Cu+ suggests that most Cu+ ions are located near the surface within the ZnS NCs and that a significant fraction may be in the form of CuS as found in bulk material. These combined optical and structural studies have provided important new insight into the relevant electronic energy levels and their correlation to the optical and structural properties of ZnS:Cu,Cl NCs. This has important implications in potential applications of this phosphor material for solid state lighting, imaging, and other photonic devices.

One-pot aqueous synthesis of composition-tunable near-infrared emitting Cu-doped CdS quantum dots as fluorescence imaging probes in living cells

“…Cu(II) may be reduced to Cu(I) by the sulfide ions during the diffusion of Cu into the host. 22,24,[34][35][36][37] Fig . 1c gives the mechanism of the emission broadening of the Cu:CdS d-dots, which has also been discussed in some literature for organic synthesis of the copper-doped d-dots.…”

Cadmium-free quantum dots in aqueous solution: Potential for fingermark detection, synthesis and an application to the detection of fingermarks in blood on non-porous surfaces

“…The synthesis of copper-doped zinc sulphide quantum dots (ZnS:Cu) stabilized with 3-mercaptopropionic acid (MPA) was based on a published protocol [45]. This protocol was optimized by varying several parameters in order to get the best results in terms of luminescence intensity, solution stability and narrowness of the size distribution.…”

“…indicated [45], the solution before the reflux is characterized by an UV absorption excitonic peak around 290 nm. After the reflux, this peak is broadened and red-shifted to around 310 nm.…”

“…Various protocols were tested according to these two parameters. Eventually, the synthetic protocol of Corrado et al [45] was found to give the best results in terms of luminescence intensity, solution stability and narrowness of the size distribution. This protocol was further optimized.…”

“…Adding more copper is possible, but a decrease in the solution stability has been observed for the higher concentration. The 1% doping was thus chosen, following the recommendations of Corrado et al [45].…”