title: Synthesis and optoelectrochemical properties of ZnS:Mn nanocrystals.
abstract: Mn2+ ions doped ZnS semiconductor nanocrystals (ZnS:Mn NCs) were synthesized using colloidal chemical method at 70 degrees C without any capping agents. The as-prepared undoped ZnS and ZnS:Mn NCs were characterized by UV-Vis absorption spectra, fluorescent emission spectra, X-ray powder diffraction (XRD), inductively coupled plasma analysis (ICP), X-ray photoelectron spectroscopy (XPS), Dynamic light scattering (DLS), cyclic voltammogram and electronic transmission microscopy (TEM). The dependence of photoluminescence of ZnS:Mn NCs on dopant concentration was studied. The results show that Mn2+ ions mainly stay at ZnS nanocystal surface, and Mn2+-surface defect state complex was formed, as a result of which, surface defect emission of ZnS nanocrystals was substituted with Mn2+-related PL emission. The strongest fluorescent emission intensity was obtain at 1.85 at% Mn2+ doped ZnS:Mn NCs. The Mn2+ doped ZnS:Mn NCs are of 5 nm in diameter. The emission peak at 575 nm is attributed to d-d (4T1 --> 6A1) transition of Mn2+ ions. The existence of Mn2+-related photoluminescence could be well correlated with cyclic voltammogram of Mn2+-doped NCs, where pair of oxidation and reduction peaks were clearly observed due to the doped Mn2+ ions. The adsorbed Mn2+ ions on ZnS NCs produced neither Mn2+ emission nor redox peaks. For heavily doped ZnS:Mn NCs (4.87 at%), redox peaks gap in cyclic voltammogram became larger and new oxidation peak appeared. Correspondingly, when the Mn2+ doping concentration reached 4.87 at%, the Mn2+-related emission totally disappears due to the Mn-Mn interactions. This work implys that electrochemical technique is possibly an useful tool to probe the local structure of doped Mn2+ ions.
authors.affiliation: School of Chemistry & Chemical Engineering, Southeast University, Nanjing 211189, P.R. China.
authors.forename: Bin
authors.initials: B
authors.lastname: Shen
authors.forename: Hong
authors.initials: H
authors.lastname: Zhou
authors.forename: Zhiren
authors.initials: Z
authors.lastname: Chen
authors.forename: Zhifei
authors.initials: Z
authors.lastname: Wang
authors.forename: Yujie
authors.initials: Y
authors.lastname: Sheng
authors.forename: Jia
authors.initials: J
authors.lastname: Chen
authors.forename: Binbin
authors.initials: B
authors.lastname: Geng