Hua Qu

Synthesis and characterization of the water-soluble silica-coated ZnS:Mn nanoparticles as fluorescent sensor for Cu2+ ions

Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core-shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core-shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40nm). Photoluminescence (PL) spectroscopy and UV-vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu(2+) ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu(2+) concentrations as low as 7.3x10(-9)molL(-1), thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed.

Synthesis and Luminescence Properties of Core/Shell ZnS:Mn/ZnO Nanoparticles

In this paper the influence of ZnO shell thickness on the luminescence properties of Mn-doped ZnS nanoparticles is studied. Transmission electron microscopy (TEM) images showed that the average diameter of ZnS:Mn nanoparticles is around 14 nm. The formation of ZnO shells on the surface of ZnS:Mn nanoparticles was confirmed by X-ray diffraction (XRD) patterns, high-resolution TEM (HRTEM) images, and X-ray photoelectron spectroscopy (XPS) measurements. A strong increase followed by a gradual decline was observed in the room temperature photoluminescence (PL) spectra with the thickening of the ZnO shell. The photoluminescence excitation (PLE) spectra exhibited a blue shift in ZnO-coated ZnS:Mn nanoparticles compared with the uncoated ones. It is shown that the PL enhancement and the blue shift of optimum excitation wavelength are led by the ZnO-induced surface passivation and compressive stress on the ZnS:Mn cores.

Effect of ultraviolet irradiation on luminescence properties of undoped ZnS and ZnS:Ag nanoparticles

Undoped ZnS and ZnS:Ag nanoparticles have been prepared through hydrothemal synthesis. The changes of luminescence properties induced by ultraviolet irradiation have been investigated. For both samples, the initial slight increase in luminescence is ascribed to the fast electron filling, while the succedent decrease is supposed to be caused by nonradiative pathways originating from some unknown photochemical products. The more remarkable decrease in ZnS:Ag is put down to the segregation of Ag on the surfaces of ZnS:Ag nanoparticles. Multipeaks Gaussian fitting is applied to the emission spectra. The fitting peaks around 490 nm in both samples are related with the surface states emission and the fitting peaks around 456 nm in ZnS nanoparticles and 443 nm in ZnS:Ag nanoparticles are attributed to the type of donor-acceptor pair luminescence, which corresponds to the transition between different donor levels and acceptor levels in different samples. A model of stretched exponential function is used to fit th...

ZnS:Ag Luminescent Nanoparticles Synthesized with Different Molar Ratio of S/Zn

ZnS:Ag (Ag+-doped ZnS) nanoparticles have been synthesized through the hydrothermal route, and the effects of the molar ratio of S/Zn in reagents have been studied. The products are all cubic sphalerite structure, and the crystallinity is generally increased as this ratio rises. The ratio less than 1 leads to small particles less than 10 nm, and the ratio more than 1 leads to large particles between 20~30 nm. Luminescence properties of samples show significant dependence on the ratio. The sample synthesized using stoichiometric reagents during hydrothermal preparation exhibits the strongest blue emission in this series. There is significant defect luminescence in samples synthesized using nonstoichiometric reagents and the Ag-related luminescence is quenched in them.