Role of Redox Reaction and Electrostatics in Transition-Metal Impurity-Promoted Photoluminescence Evolution of Water-Soluble ZnSe Nanocrystals

Abstract

In this article, the experimental variable-dependent photoluminescence (PL) evolution of transition-metal-doped ZnSe nanocrystals (NCs) is analyzed by combining the redox reaction and the electrostatics of aqueous NCs. Bulk doping of NCs involves two steps − surface adsorption of the metal impurities and the followed internal doping. The former relates to the electrostatics of aqueous NCs, whereas the latter relates to a redox reaction between the impurities and mercapto-ligands. Both of them occur on the NC surface. In this context, aqueous NCs are essentially charge-stabilized particles. The electrostatic factors that weaken the electrostatic repulsion will facilitate the adsorption of metal impurities on NC surfaces, thus benefiting the surface redox reaction. It furthermore promotes the internal doping of the metal impurities. Consequently, the trap emission and the PL evolution of NCs are facilitated. Besides, the internal doping is favored for the metal impurities with high reduction potential because they are easily reduced by mercapto-ligands. Furthermore, because the presence of metal impurities in NC solution both promotes the oxidation of mercapto-ligands and weakens the interparticle electrostatic repulsion, the colloidal solution of doped aqueous NCs is theoretically proved unstable.

Fast Doping of Cu into ZnSe NCs by Hydrazine Promoted Cation Exchange in Aqueous Solution at Room Temperature

“…For PL peak around 480 nm, the stokes shift is as large as 100 nm, which indicated surface defect related emission. This PL characteristic of water soluble ZnSe NCs and ZnSe:Cu was reported by earlier publications [28,31]. Once addition of Cu stock solution into ZnSe solution, the emission of ZnSe NCs changed immediately, indicating the extremely fast cation exchange reaction.…”

“…Since Cu stock solution was prepared by mixing CuCl 2 with MPA, Cu 2+ ions were probably reduced to Cu + by MPA in aqueous solution [31]. Interestingly, the product of complete cation exchange reaction was not Cu 2 Se.…”

“…Aqueous ZnSe NCs were synthesized according to the reference method [30,31]. Namely, the mixture of Zn(NO 3 ) 2 and MPA was adjusted to pH 11.4 by drop wise addition of 5.0 mol/L NaOH solution.…”

Aqueous Synthesis of Nontoxic Ag2Se/ZnSe Quantum Dots Designing as Fluorescence Sensors for Detection of Ag(I) and Cu(II) Ions

“…3-Mercaptopropionic acid (MPA), 1-thiolglycerol (TG), and Se powder were purchased from Aldrich. NaHSe solution was prepared by using Se with NaBH 4 according to the reference methods [7][8][9].…”

Aqueous phase synthesis and fluorescence properties of inverted core/shell ZnSe/CdSe nanocrystals

“…3(a)). The fluorescence peak at 403 nm is attributed to the bandgap emission of nanometer-sized ZnSe crystals, and the emission peak over 461 nm is assigned to the trap emission [30] . Fig.…”