Tb3+/Yb3+ heavily-doped tellurite glasses with efficient green light emission

Without introducing concentration quenching phenomenon, a few wt% of Tb3+ and Yb3+ ions were doped into a group of easily-fiberized tellurite glasses characterized by loose polyhedron structures and rich interstitial positions. Intense green upconversion emission from Tb3+ ions centered at 539 nm due to transition 5D4→7F5 was observed by direct excitation of Yb3+ ions with a laser diode at 976 nm. Optimizing the concentration ratio of Tb3+/Yb3+, a tellurite glass with composition of 80TeO2-10ZnO-10Na2O (mol%)+1.0wt% Tb2O3+3.0wt% Yb2O3 was found to present the highest green light intensity and therefore is especially suitable for efficient green fiber laser development.

Faraday Glasses with a Large Size and High Performance

A kind of Faraday glass with a size of 40 mm x 14 mm and 100-300 mm x 25 mm, respectively, was prepared by the melting and casting process, which had neither a Pt particulate nor a bubble or striation. The measurement results showed that the surface homogeneity of the samples was up to +/- 1 x 10-6, the laser threshold reached 10 J/cm2 (1 omega, 3 ns), and the Verdet constants of the glasses were -0.273 min/Oe/cm at 632.8 nm and -0.076 min/Oe/cm at 1064 nm, respectively.

Shear transformation zone volume determining ductile–brittle transition of bulk metallic glasses

Three-point bending experiments were performed on as-cast and annealed samples of Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) bulk metallic glasses over a wide range of temperatures varying from room temperature (293 K) to liquid nitrogen temperature (77 K). The results demonstrated that the free volume decrease due to annealing and/or cryogenic temperature can reduce the propensity for the formation of multiple shear bands and hence deteriorate plastic deformation ability. We clearly observed a sharp ductile-to-brittle transition (DBT), across which microscopic fracture feature transfers from micro-scale vein patterns to nano-scale periodic corrugations. Macroscopically, the corresponding fracture mode changes from ductile shear fracture to brittle tensile fracture. The shear transformation zone volume, taking into account free volume, temperature and strain rate, is proposed to quantitatively characterize the DBT behavior in fracture of metallic glasses.

Strain rate-dependent shear band behavior in bulk metallic glasses

In this article, we review our recent advances in understanding the deformation behavior of a typical tough Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit 1) bulk metallic glass (BMG), as a model material, under various loading modes and strain rates, focusing particularly on the rate-dependence and formation mechanism of shear-banding. Dynamic and quasi-static mechanical experiments, including plate shear, shear punch and spherical indentation, and continuum as well as atomistic modeling on shear-banding are discussed. The results demonstrate that higher strain rate slows down the annihilation process of free volume, but promotes the free-volume coalescence, which is responsible for the rate-dependent shear banding. The physical origin of shear bands, that is the free volume softening underpinned by irreversible rearrangements of atoms, is unveiled. Finally, some concluding remarks are given.

Flow-through room temperature phosphorescence optosensing for the determination of lead in sea water

The chelates formed between the heavy metal ion Pb(II) and the reagents 8-hydroxy-5-quinolinesulphonic acid, 8-hydroxy-7-quinolinesulphonic acid and 8-hydroxy-7-iodo-5-quinolinesulphonic acid exhibit strong room temperature phosphorescence (RTP) if retained on the surface of anion exchange resin beads. Based on the on-line formation, in a flow-injection system, of such RTP lead chelates and their transient immobilization on an anion exchange resin, three flow-through optosensing systems are investigated for lead in sea water. Optimum experimental conditions and the analytical performance characteristics of the three optosensors are discussed. Relative standard deviations (RSDs) of the order of 3% are typical at 100 ng ml−1 Pb(II) and the active sensing phases can easily be regenerated by passing 500 μl of 6 M hydrochloric acid. A lead(II) detection limit of 0.1 ng ml−1 (3×background SD, for 2 ml sample injection volumes) was achieved for the optosensor based on 8-hydroxy-7-quinolinesulphonic acid. Possible interferences present in sea water, including cations and anions which could affect the sensor response, are discussed in detail. Finally, the selected RTP flow-through optical sensor has been successfully tested for the determination of lead in sea water at a few ng ml−1.

Determination of lead using a poly(vinyl chloride)-based crown ether membrane

A poly(vinyl chloride)(PVC)-based membrane of 15-crown-5 exhibits a good response for lead(II) ions over a wide concentration range. The response time of the sensor is 30 s and the membrane can be used for more than four months without observing any divergence. The selectivity of the sensor is comparable with those reported for other such electrodes. It was possible to determine lead in polluted waters using this electrode assembly.

DNAzyme-based Colorimetric Sensing of Lead (Pb2+) Using Unmodified Gold Nanoparticle Probes

Novel functional oligonucleotides, especially DNAzymes with RNA-cleavage activity, have been intensively studied due to their potential applications in therapeutics and sensors. Taking advantage of the high specificity of 17E DNAzyme for Pb2+, highly sensitive and selective fluorescent, electrochemical and colorimetric sensors have been developed for Pb2+. In this work, we report a simple, sensitive and label-free 17E DNAzyme-based sensor for Pb2+ detection using unmodified gold nanoparticles (GNPs) based on the fact that unfolded single-stranded DNA could be adsorbed on the citrate protected GNPs while double-stranded DNA could not. By our method the substrate cleavage by the 17E DNAzyme in the presence of Pb2+ could be monitored by color change of GNPs, thereby Pb2+ detection was realized.