D. Thangaraju

Single-step synthesis and catalytic activity of structure-controlled nickel sulfide nanoparticles

Nanoparticle single-phase nickel sulfides such as NiS, NiS2, Ni3S4, and Ni7S6 were prepared from elemental sulfur and nickel nitrate hexahydrate, using a temperature-controlled precursor injection method. The initial ratio of the concentrations of the sources was used to control the size and phase of the final product. Phase control was confirmed using X-ray diffraction and transmission electron microscopy. The synthesized nickel sulfide phases, which had metallic characteristics, were used to study the catalytic reduction of 4-nitrophenol. The results showed that the catalytic activity of the NiS nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol was higher than those of the other nickel sulfide phases. In addition, the nanocrystals showed good separation ability and reusability for reduction of 4-nitrophenol.

Multi-modal imaging of HeLa cells using a luminescent ZnS:Mn/NaGdF4:Yb:Er nanocomposite with enhanced upconversion red emission

The multi-modal luminescence properties of the ZnS:Mn/NaGdF4:Yb:Er nanocomposite were investigated. The ZnS:Mn/NaGdF4:Yb:Er nanocomposite was synthesized using a single-step hot injection method. Its crystallinity was confirmed using X-ray diffraction, and was compared with the crystallinities of NaGdF4:Yb:Er nanoparticles and ZnS:Mn quantum dots synthesized by thermal decomposition. Composite formation and morphology changes were investigated by transmission electron microscopy. Enhanced upconversion red emission (654 nm, 4F9/2–4I15/2) was observed for NaGdF4:Yb:Er in the presence of ZnS:Mn. Analysis of the excitation and downconversion emission spectra of ZnS:Mn/NaGdF4:Yb:Er indicated modified emission at lower wavelengths. Cathodoluminescence measurements indicated that the ZnS:Mn/NaGdF4:Yb:Er nanocomposite had a broad visible emission from green to red wavelengths. Cytotoxicity and stability measurements were executed to ensure the toxicity of the synthesized composite and their luminescence stability in water as well as phosphate buffered solution. The nanocomposite had multi-modal characteristics, and was used in the upconversion and downconversion optical imaging of living He–La cells. The multi-modal luminescence capability of the nanocomposite was suitable for upconversion and downconversion imaging.

Effect of Erbium on the Photocatalytic Activity of TiO2/Ag Nanocomposites under Visible Light Irradiation

Erbium co-doped TiO2 /Ag catalysts are synthesized by using a simple, one-step solvothermal method and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman analysis, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The catalysts exhibit anatase crystal structures with increased visible light absorption compared with pure TiO2 . Enhanced photocatalytic activity is observed with Er co-doped TiO2 /Ag nanocomposites for Rhodamine B degradation under visible light irradiation. The photocatalytic activity of 1 % Er co-doped TiO2 /Ag is much higher than that of TiO2 /Ag, TiO2 /Er, pure TiO2 , and commercial Degussa P25. The kinetics of the degradation process are studied and the pseudo-first-order rate constant (k) and half-life time (t1/2 ) of the reaction are calculated. The enhanced activity might be accredited to the efficient separation of electron-hole pairs by silver and higher visible light absorption of TiO2 induced by Er.

UV-visible and near-infrared active NaGdF4:Yb:Er/Ag/TiO2 nanocomposite for enhanced photocatalytic applications

A near infra-red (NIR) active NaGdF4:Yb:Er/Ag/TiO2 nanocomposite photocatalyst was successfully synthesized by a one-pot thermal decomposition method. The composite structure, morphology and elemental mapping of the synthesized NaGdF4:Yb:Er/Ag/TiO2 nanocomposite were characterized by X-ray diffraction and transmission electron microscopy analysis. The energy transfer among NaGdF4:Yb:Er, Ag, and TiO2 was revealed by upconversion photoluminescence measurements at 980 nm. The Ag and NaGdF4 nanoparticles enhanced the visible and NIR light absorption property of the NaGdF4:Yb:Er/Ag/TiO2 nanocomposite. The NIR and UV-visible light induced photocatalytic study of the NaGdF4:Yb:Er/Ag/TiO2 composite was examined by rhodamine B degradation. The energy transfer among NaGdF4:Yb:Er, Ag, and TiO2 significantly influenced the photocatalytic activity under NIR irradiation. The catalysts produced oxidative species during NIR irradiation, which are responsible for the photocatalytic degradation of rhodamine B. NaGdF4:Yb:Er/Ag/TiO2 showed photocatalytic activity under NIR and UV-visible radiation (full solar irradiation), which is superior to a UV or visible light active photocatalyst. The study provided a UV-visible and NIR-responsive photocatalyst and its energy transfer mechanism.

Synthesis structural and luminescence analysis of NaGd1−XTbx(WO4)2 solid solution for white LED application

NaGd1−xTbx(WO4)2 (Tb:NGW) green phosphor were synthesised by high temperature solid state reaction. Synthesised powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and spectroflorimeter analysis. The formation of NGW scheelite structure was conformed by XRD. FE-SEM images clearly show the surface morphology of synthesized powder. From excitation spectrum, the charge transfer band (CTB) of O-W elucidated at 270 nm and emission spectrum has shown green emission at 545 nm under 270 nm (UV light) excitation. The optimum dopant concentration of Tb has been found to be 15 at%.

Synthesis and characterization of Eu3+:YAG nanopowder by precipitation method

Eu3+:Y3Al5O12 (Eu3+:YAG) nanopowder has been synthesized by reverse co-precipitation method. Cubic YAG structure was obtained at 850 °C calcination. FE-SEM micrographs confirm that YAG:Eu3+ particles are homogeneous sphere like morphology with average particle size of 50-70 nm. The crystalline phosphors showed orange - red emission with magnetic dipole transition 5D0→7F1 (590 nm) as most prominent group than forced electric dipole transition 5D0→7F2 (610nm).