Improved Low-Temperature Aqueous Synthesis of ZnO Nanorods and Their Use in SERS Detection of 4-ABT and RDX

The growth-controlled synthesis of zinc oxide nanorods (ZnO NR) in the aqueous phase has been investigated. The rods were grown on ZnO films previously deposited onto Si(100) and indium tin oxide (ITO) substrates by RF magnetron sputtering. The formation of the rods took place in the presence of hexamethylenetetramine (HMT) as habit-control reagent. The grains in the base ZnO film acted as seeds that promoted the longitudinal growth of the oxide. As-synthesized base films and rods were characterized by X-ray diffraction, scanning electron microscopy (SEM), field emission SEM, optical absorption and photoluminescence spectroscopy techniques. Subsequently, a wet chemistry procedure was performed to achieve ZnO NR growth. This methodology was conducive to the formation of rods of a relatively narrow distribution of diameters (60 - 70 nm) with lengths in the 1 - 3 μm range. Photoluminescence spectra were characterized by a dominant near-band-edge (NBE) peak followed by a green luminescence (GL) broad band, indicative of higher oxygen vacancy concentration in the ZnO NR grown on ZnO/ITO in comparison with those grown on ZnO/Si(100). A UV process was used for coating the ZnO NR with gold (Au). Au coating on ZnO NR was used to evaluate the detection capability by SERS of different analytes such as: 4-aminobenzenethiol (4-ABT) and 1,3,5-trinitroperhydro-1,3,5- triazine (RDX) at low levels. A strong SERS Raman spectrum was observed for 4-ABT. A limit of detection (LOD) of 1 × 10-8M for 4-ABT was achieved corresponding to a minimum of 5.4 × 105molecules detected under the experimental conditions at excitation wavelength of 785 nm with a sensitivity of the ZnO NR in the range of 1.1 × 10-16g under the laser spot.

Origin of light emission and enhanced Eu^(3+) photoluminescence in tin-containing glass

A barium-phosphate glass matrix was co-doped with Sn O and Eu2O3 for investigating on material luminescent properties. Optical absorption and X-ray photoelectron spectroscopy（XPS） were employed in the characterization of tin species. The prevalence of divalent tin was indicated by the XPS data in accord with a conspicuous absorption band detected around 285 nm ascribed to twofold-coordinated Sn centers（isoelectronic with Sn^2＋）. Photoluminescence（PL） excitation spectra obtained by monitoring Eu^3＋ emission from the 5D0 state revealed a broad excitation band from about 250 to 340 nm, characteristic of donor/acceptor energy transfer. Under excitation of such at 290 nm, the co-doped material exhibited a bright whitish luminescence, and a four-fold enhanced Eu3＋ emission relative to a purely Eu-doped reference. Time-resolved PL spectra recorded under the excitation at 290 nm exposed a broad band characteristic of the twofold-coordinated Sn centers and emission bands of Eu^3＋ ions, which appeared well separated in time in accord with their emission decay dynamics. The data suggested that light absorption took place at the Sn centers（donors） followed by energy transfer to Eu^3＋ ions（acceptors） which resulted in populating the 5D0 emitting state. Energy transfer pathways likely resulting in the enhanced Eu3＋ photoluminescence and the consequential light emission were discussed.