kao Shi

Controlled synthesis and optimum luminescence of Sm3+-activated nano/submicroscale ceria particles by a facile approach

Rare-earth Sm3+-activated nano/submicroscale ceria particles were prepared by a rapid combustion reaction. Characterized with X-ray diffraction patterns and Raman spectra, the formation of solid solution was confirmed after Sm3+ doping into ceria, and the concentration of oxygen vacancies in the host was gradually increased with the increase of Sm3+ doping content. Assisted by polyvinyl alcohol (PVA) in the combustion reaction process, the morphology of the particles was well distributed and the particle size was controlled from nano (10 nm) to submicro (∼250 nm), depending on the post-sintering temperature. More interesting was that the samples could be effectively excited with 370 nm and emitted strong orange-red light after optimization, which was suitable for the demands of high-efficiency UV LEDs. Without the addition of PVA, the samples showed very weak luminescence even after lengthy sintering. However, the samples prepared by PVA-assisted combustion synthesis exhibited remarkably enhanced emission after an appropriate heat treatment. The quenching concentration of activator Sm3+ was 1.5 mol%, and the optimal luminescence intensity reached nearly 10-fold in comparison with that of samples prepared by conventional solid state reaction. The Sm3+-activated nano/submicroscale ceria materials have potential for use in solid state lighting.

Kinetically controlled seed-mediated growth of narrow dispersed silver nanoparticles up to 120 nm: secondary nucleation, size focusing, and Ostwald ripening

A facile synthesis method was developed based on the seed-mediated growth to get the narrow dispersed silver nanoparticles with controllable sizes ranging from 20 nm to larger than 120 nm. Environmentally friendly glucose acts as a reducing agent. Because of its weak reducing ability, the secondary nucleation is prevented in the seed-mediated growth, and the size of silver nanoparticles can be tuned continuously by the continuous addition of reactants. Controlling the supersaturation level is critical to suppress both the nucleation and Ostwald ripening, which can be realized by carefully controlling the addition rate of the reactants. We also set up a convenient method to determine the size and size-distribution of silver nanoparticles from the size-dependent absorption spectra of the colloids, and optimize the growth parameters using this method to get narrow dispersed silver nanoparticles.

Lanthanide complexes with 3,4,5-triethoxybenzoic acid and 1,10-phenanthroline: synthesis, crystal structures, thermal decomposition mechanism and phase transformation kinetics

Three novel lanthanide complexes [Ln(3,4,5-TEOBA)3phen]2 (Ln = La(1), Pr(2), Eu(3); 3,4,5-TEOBA = 3,4,5-triethoxybenzoate; phen = 1,10-phenanthroline) were synthesized and characterized. Single crystal X-ray diffraction showed that the complexes are isostructural. Each complex has two center metals and each center is coordinated with seven oxygen atoms and two nitrogen atoms to form a distorted monocapped square antiprism geometry. A carboxylic group adopts three modes coordinated with center metal: bidentate chelate, bridging bidentate and bridging tridentate. The luminescence of complex 3 showed the characteristic emission of Eu3+ (5D0 → 7F0–3). The thermal decomposition mechanism of title complexes was studied by TG/DSC-FTIR technology. The heat capacities of complexes 1–3 were measured by DSC over the temperature range from 263.15 to 463.15 K. In the temperature range from 280 to 350 K, there was a solid-to-solid phase transition for each complex, which was further evidenced by four thermal circulating processes with the scanning rate of 10 K min−1. A study of the phase transition of four thermal circulating processes under different heating rates revealed a fine linear relationship between the activation energy (E) and the percent conversion (α). In the heating and cooling runs, supercooling was observed and the endothermic and exothermic enthalpies behaved differently.

A series of lanthanide complexes with different N-donor ligands: synthesis, structures, thermal properties and luminescence behaviors

Four novel lanthanide complexes, [Ln(2,4-DClBA)3(terpy)(H2O)]·H2O (Ln = Eu(1), Tb(2)); [Ln(2,4-DClBA)3(5,5′-DM-2,2′-bipy)(C2H5OH)]2 (Ln = Eu(3), Tb(4); 2,4-DClBA: 2,4-dichlorobenzoate; terpy: 2,2′:6′,2′′-terpyridine; 5,5′-DM-2,2′-bipy: 5,5′-dimethyl-2,2′-bipyridine) have been synthesized via a conventional solution method at room temperature and structurally characterized by single crystal and powder X-ray diffraction. Complexes 1–2 exhibit mononuclear lanthanide architectures and each Ln3+ ion is nine-coordinated adopting a distorted monocapped square antiprismatic molecular geometry, while complexes 3–4 exhibit binuclear lanthanide architectures in which each Ln3+ ion is eight-coordinated adopting a distorted square antiprismatic molecular geometry. Mononuclear complexes 1–2 are stitched together via Cl–π and hydrogen bonding interactions to form the 1D, 2D, 3D supramolecular structures. While complexes 3–4 are packed together through Cl–Cl, π–π, and hydrogen bonding interactions to form 1D, 2D supramolecular structures. Luminescence investigation reveals that complexes 1, 3 and 2, 4 display strong red and green emission respectively, showing that terpy and 5,5′-DM-2,2′-bipy can act as sensitizing chromophores, but the former is more effective. The IR, TG-DTG, and the heat capacities of complexes 1–4 were also measured.

Structural characterization and enhanced luminescence of Eu-doped 2CeO2–0.5La2O3 composite phosphor powders by a facile solution combustion synthesis

The cerium lanthanum composite 2CeO2–0.5La2O3 and rare earth Eu3+-doped composite phosphor powders were synthesized by a facile solution combustion reaction. X-ray diffraction patterns suggested Ce2LaO5.5 with a cubic fluorite structure which was the same as pure CeO2 except for the lattice parameter a. After the activator Eu3+ was doped to the composite, Eu3+ could locate at either La3+ or Ce4+ sites due to their close ionic radius. It was found that the lattice parameter a gradually decreased with increasing Eu concentration as Eu3+ occupied the La3+ site. However, the lattice parameter a obviously increased with increasing Eu concentration if Eu3+ occupied the Ce4+ site. All of the phosphor powders showed red-light emission from the dominant 5D0 → 7F2 characteristic transition of Eu3+ under excitation with 466 nm blue light. In particular, the system displayed remarkably enhanced luminescence as Eu3+ occupied the Ce4+ site rather than the La3+ site. The reason for this should be ascribed to the change in the amount of O vacancies in the host, which was confirmed from their Raman spectra. The results might be beneficial for the system potentially used in solid state lighting as well as other optoelectronic fields.

Ultrasensitive and reproducible surface-enhanced Raman scattering detection via an optimized adsorption process and filter-based substrate

Wih a view to improve the surface-enhanced Raman scattering (SERS) properties, including the sensitivity and uniformity, a simple and practical pretreatment method via optimizing the adsorption process of probe molecules and the morphology of SERS-active nanostructures was studied. Excellent SERS performances were obtained using this method such as high sensitivity (5 × 10−14 M rhodamine 6G, 1 × 10−8 M melamine), remarkable uniformity (∼9% relative standard deviation (RSD)) and reproducibility (∼10% RSD). Uniform and repeatable silver nanoparticle arrays were fabricated by an optimized filter-based method, which guaranteed the reliability of SERS detection. The SERS intensity was greatly improved by adjusting the adsorption capacity of the noble metal nanostructures, which has a linear relationship with the pH value of silver solution below 10. An accurate and reliable enhancement factor (EF) of 3.28 × 108 was calculated through the quantification of the adsorbed probe molecules. It is worth noting that the lifetime of the substrates prepared by this method could be prolonged to two months, which was definitely longer than other ordinary silver SERS substrates. The pretreatment method not only provided perfect SERS properties, but also made SERS a practical analysis tool because of its good homogeneity and ultralow detection limit.

Microwave memristive behavior in split-ring resonator metamaterials

Photonic memristors, which behave as memristors operating with electromagnetic fields, present an effective means to achieve all-optical networking, and can promote the development of optical communications and computer technology. In this paper, we report a microwave memristive phenomenon at room temperature in metamaterials consisting of negative temperature coefficient thermistor ceramic disk and split-ring resonator (SRR). Hysteretic transmission-incident field power loops, the area of which varies with the scan rate of power, (similar to the fingerprint of memristors) were observed in the metamaterials. These effects are attributed to the increasing conductivity of the ceramic disk with increasing temperature generated by the interaction between electromagnetic waves and metamaterials. This work offers new opportunities for the development of photonic memristors.