Enhanced Cu emission in ZnS : Cu,Cl/ZnS core–shell nanocrystals

Abstract

ZnS : Cu,Cl/ZnS core-shell nanocrystals (NCs) have been synthesized via a facile aqueous synthesis method. The shell growth of the NCs was observed via a red-shift in the UV-Vis absorption spectra with increasing NC size. The Cu photoluminescence (PL) emission was enhanced by capping with a thin ZnS shell. The ZnS : Cu (0.2%) and ZnS : Cu (0.5%) show a more pronounced red-shift in the apparent PL peak position as well as a 37% and 67% increase in emission intensity, respectively, in comparison to the undoped NCs. The observed red-shift is mainly due to an increase in intensity of the Cu PL emission. The 1% Cu-doped NCs exhibit very little red-shift because the observed emission is dominated by the Cu-dopant and thus nearly independent of the size of the NCs. The increase in Cu emission is evidence that Cu atoms occupying non-emissive surface sites in doped ZnS NCs were encapsulated by the ZnS shell. Extended X-Ray Absorption Fine Structure (EXAFS) data also suggests that the Cu had slightly more neighbors upon growth of a ZnS shell, indicating its encapsulation into the core of the NCs. The EXAFS Zn edge data also indicate greater disorder in the ZnS structure when the shell is grown, which may be attributed to the ZnS shell being more amorphous than the core NCs. This study demonstrates that core-shell structures can be used as a simple and yet powerful strategy to enhance PL properties of doped semiconductor NCs.

Effect of capping on the mechanoluminescence of γ-irradiated ZnS:Cu nanophosphors

“…Generally speaking, the emission spectra of Cu-doped ZnS were reported quite different by different authors because of different quantum particle sizes and surface or impurity defect levels in the band gap caused by different synthesis techniques. In this paper, we observe the emission peaks of Cu-doped sample at about 460 nm, which was close to the value reported by Corrado et al [25]. It is attributed to the transition between conduction band of ZnS host and the acceptor like t 2 (d 9 ) state of Cu [26].…”

Preparation of photoluminescence tunable Cu-doped AgInS2 and AgInS2/ZnS nanocrystals and their application as cellular imaging probes

“…11–25 For instance, Cu doped ZnS NCs show a pronounced red-shift in the PL peak position compared to the undoped ZnS host and present a blue-green emission depending on the doped Cu levels. 12 For CdS NCs, their green emission can be more extended to orange-red by Cu doping. 15 Green to red emissions have been achieved for Cu doped Zn-In-Se NCs.…”

Effects of Cu Dopant on Lattice and Optical Properties of ZnS Quantum Dots

“…12 14 15 That is, CuS commonly exhibits hexagonal structure, while ZnS exist in a solid cubic structure at low temperatures. 12 The solubility of CuS (K sp = 2 5 × 10 −48 is 10 −26 less than that (K sp = 2 2 × 10 −22 of ZnS, making their co-precipitation difficult. 14 15 Furthermore, their optical properties are intricate.…”

“…18 It is worth mentioning that Cu incorporation will not 19 20 Therefore there are fewer studies on Cu doped ZnS nanocrystals than on Mn doped ZnS. 12 However, doping with Cu leads to a wider range of tunable emissions that depend on the size and nature of the host than doping with Mn does. 9 Consequently, in order to resolve the dopant difficulty, Cu 2+ ions were effectively introduced into the ZnS host via a double doping strategy of growing ZnS:Cu/ZnS core/shell structures.…”

“…However it has been reported that there is no significant luminescence when the Mn dopant locates at the surface of the host. 12 Therefore, the nuclei doped method has been employed to prepare the Mn dopant ZnS nanostructures. Zhang et al 13 used the nucleation doping method to prepare highly luminous Mn:ZnS nanocrystals via a hot injection approach, and the fluorescence quantum yield reached up to 55-65%.…”