title: Syntheses of the Water-Dispersible Glycolic Acid Capped ZnS:Mn Nanocrystals at Different pH Conditions, and Their Aggregation and Luminescence Quenching Effects in Aqueous Solution.
abstract: Water-dispersible ZnS:Mn nanocrystals were prepared by capping their surface with polar glycolic acid molecules at three different pH conditions. The produced ZnS:Mn-GA nanocrystals were characterized by XRD, HR-TEM, ICP-AES, and FT-IR spectroscopy. The optical properties were also measured by UV-Visible and room temperature photoluminescence (PL) spectroscopy. In the PL spectra, theses ZnS:Mn-GA nanocrystals showed broad emission peaks around 595 nm, and the calculated relative quantum efficiencies against an organic dye standard were in the range from 2.16 to 5.52%. The measured particle size from the HR-TEM images was about 3.7 nm on average, which were also supported by the calculations with the Debye-Scherrer methods. In addition, the surface charges of the nanocrystals were determined by an electrophoretic method, which showed pH dependent charge values of the nanocrytals: +0.88 mV (pH 2), +0.82 mV (pH 7), and -0.59 mV (pH 12) respectively. In addition, the degrees of aggregation of the nanocrystals in aqueous solutions were determined by a hydrodynamic light scattering method. As a result, formations of micrometer size agglomerates for all the ZnS:Mn-GA nanocrystals in water was observed at room temperature. This was probably caused by intermolecular attraction between the capping molecules. In addition, the ZnS:Mn-GA with the negative surface charge was presumed to be suitable for further coordination to a transition metal ion on the surface of the nanocrystal. As a result, fast luminescence quenching was observed after addition of aqueous solution containing Cu2+ ions.
authors.forename: Yu Jin
authors.initials: YJ
authors.lastname: Sim
authors.forename: Cheong-Soo
authors.initials: CS
authors.lastname: Hwang
mesh_terms: D003300:Copper / Q000737:chemistry; D006016:Glycolates / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008163:Luminescent Measurements; D008345:Manganese / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology; D010316:Particle Size; D012996:Solutions; D013440:Sulfides / Q000737:chemistry*; D014867:Water / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D006016:Glycolates; D012996:Solutions; D013440:Sulfides; D017967:Zinc Compounds; D014867:Water; C031149:glycolic acid; D008345:Manganese; D003300:Copper; C031238:zinc sulfide