Concentration dependence of the fluorescence decay profile in transition metal doped chalcogenide glass

In this paper we present the fluorescence decay profiles of vanadium and titanium doped gallium lanthanum sulphide (GLS) glass at various doping concentrations between 0.01 and 1% (molar). We demonstrate that below a critical doping concentration the fluorescence decay profile can be fitted with the stretched exponential function: exp[-(t/τ)β], where τ is the fluorescence lifetime and β is the stretch factor. At low concentrations the lifetime for vanadium and titanium doped GLS was 30µs and 67µs respectively. We validate the use of the stretched exponential model and discuss the possible microscopic phenomenon it arises from. We also demonstrate that above a critical doping concentration of around 0.1% (molar) the fluorescence decay profile can be fitted with the double exponential function: a*exp-(t/τ1)+ b*exp-(t/τ2), where τ1 and τ2 are characteristic fast and slow components of the fluorescence decay profile, for vanadium the fast and slow components are 5µs and 30µs respectively and for titanium they are 15µs and 67µs respectively. We also show that the fluorescence lifetime of vanadium and titanium at low concentrations in the oxide rich host; gallium lanthanum oxy-sulphide (GLSO) is 43µs and 97µs respectively, which is longer than that in GLS. From this we deduce that vanadium and titanium fluorescing ions preferentially substitute into high efficiency oxide sites until at a critical concentration they become saturated and low efficiency sulphide sites start to be filled

Experiments on Direct Dark Matter Search with Two-phase Emission Detectors

AbstractEmission detectors, invented 45 years ago in MEPhI, found their unique application in modern experiments searching for cold dark matter in the form of weakly ionizing massive particles (WIMPs). The current best limits for the interaction cross sections of supersymmetric WIMPs having a mass of 100GeV/c2 with nucleons were measured with emission detector LUX containing 360kg of liquid xenon as detector medium installed in Davis’ cave at Homestake mine in South Dakota. Emission detectors of the next generation G2, with an active detector mass of about 10 tons, will either unambiguously detect WIMPs or rule out all current theoretical predictions for WIMP existence. Detectors of the G3 generation will be used for multiple purposes including detection of double beta neutrinoless decay and low-energy neutrino

Near-field blast loading and transient target response : a collaboration between Sheffield and Cape Town

Near-field blast loads are high in magnitude, short in duration, and non-uniformly distributed across the loaded face of a structural element. Experimental characterisation of near-field blast loading and the resulting deformation of a blast loaded target is made difficult by conflicting requirements, namely: robustness to survive the extreme loading conditions; and sensitivity to accurately measure transient behaviour at high sampling frequencies. As such, there is little definitive experimental data in the literature, and the deformation behaviour of plates subjected to non-uniform impulsive loading is yet to be properly quantified. This paper presents an update on the ongoing collaborative research effort between the University of Sheffield, UK, and the University of Cape Town, South Africa. Direct experimental measurements of blast pressure and impulse using an array of Hopkinson pressure bars (Sheffield), and high-fidelity transient plate deformation measurements using digital image correlation (Cape Town) are jointly-used to assess, and develop predictive methods for, the response of blast loaded plates. Simplified predictive methods, based on knowledge of the applied load rather than an assumed distribution, have been developed which show very good correlation with the experiments and physics-based numerical models

Predicting the response of plates subjected to near-field explosions using an energy equivalent impulse

Recent experimental work by the current authors has provided highly spatially and temporally resolved measurements of the loading imparted to, and the subsequent dynamic response of, structures subjected to near-field explosive loading [1]. In this article we validate finite element models of plates subjected to near-field blast loads and perform a parametric study into the relationship between imparted load and peak and residual plate deformation. The energy equivalent impulse is derived, based on the theory of upper bound kinetic energy uptake introduced herein, which accounts for the additional energy imparted to a structure from a spatially non-uniform blast load. Whilst plate deflection is weakly correlated to total impulse, there is shown to be a strong positive correlation between deflection and energy equivalent impulse. The strength of this correlation is insensitive to loading distribution and mode of response. The method developed in this article has clear applications for the generation of fast-running engineering tools for the prediction of structural response to near-field explosions

Chalcogenide glasses for photonics device applications

Chalcogenides are compounds formed predominately from one or more of the chalcogen elements; sulphur, selenium and tellurium. Although first studied over fifty years ago, interest in chalcogenide glasses has, over the past few years, increased significantly as glasses, crystals and alloys find new life in a wide range of photonic devices. This chapter begins with an overview of chalcogenide glass compositions, their purification, synthesis and fabrication. Focussing on more novel gallium lanthanum sulphide based chalcogenides, as well as reviewing more established materials such as arsenic trisulphide based glasses we then explore the purification and synthesis of these materials, along with their basic optical and thermal properties. Next the fabrication of these versatile glasses into a variety of forms; including thin films, microspheres and optical fibers is explained. This chapter ends with an overview of representative applications of these exciting optoelectronic materials

Improved diagnostics for structural response and impulse transfer in blast experiments

This paper describes collaboration into experimental techniques for measuring spatial impulse distribution across target plates subjected to air-blast. In South Africa, the transient responses were obtained from digital image correlation and stereo-imaging of a flexible target plate. Specific impulse distributions were inferred from the velocity profiles. At the University of Sheffield, scaled blast tests employed a Hopkinson pressure bar array to obtain directly measured values at discrete locations across a rigid target. The findings demonstrate the usefulness of improved diagnostics and techniques in blast experiments, and demonstrate the potential of high speed imaging and DIC for determining impulse profiles

Optical diagnostics in near-field blast measurements

The understanding of structural and material response to air-blast loading is a necessary prerequisite to the development of effective blast protection and mitigation systems. Computational tools have advanced significantly, enabling extensive simulations of the loading and ensuing structural response that occur as the result of an explosive detonation. Experimental techniques, however, have lagged behind in providing robust, high fidelity measurements regarding the transient response and spatial distribution of specific impulse across a structure. This article discusses recent advances in these techniques at the University of Sheffield and describes the results that can be obtained. It details proof of concept testing via a bilateral collaboration between the UK and South Africa involving single-blind experimentation using high-speed imaging, digital image correlation and comparisons with results from near-field blast experiments performed at the University of Sheffield CoBL facility. Secondly, it describes some of the continued developments since the success of those early trials, resulting in a new optical diagnostics for blast capability at the University of Sheffield. This article demonstrates the usefulness of improved diagnostics and techniques in blast experiments and shows the efficacy and versatility of high-speed imaging and DIC for determining impulse profiles and transient structural behaviour. Ultra-high speed imaging is also shown to be a useful tool for visualising detonation fronts in explosive charges and the expanding fireball

Preparation of chalcogenide materials for next generation optoelectronic devices

Chalcogenide materials are finding increasing interest as an active material in next generation optical and electronic devices. There wide range of properties, ranging from photosensitivity, ability to host rare earth ions, electrical conductivity, phase change, exceptional optical non-linearities to name only a few are fueling this interest. Moreover, the ability to synthesize these materials in numerous forms as diverse as 2D monolayers, microspheres, optical fibres, nanowires, thin films as well as bulk glass ingots of over a kilogram in size ensures their application space is vast. We began preparation of chalcogenides, largely based on sulphides, in 1992 and since then have built up an extensive capability for their purification, synthesis and fabrication in various forms. A key aspect of this facility is the ability to process in a flowing atmosphere of hydrogen sulphide which provided the capability of synthesis from elemental, oxide or halide precursors, processing through various chemical vapour deposition reactions as well as post purification.In this talk we describe recent additions to the range of materials we synthesize highlighting transition metal di-chalcogenides for electronic applications, an example of which is shown below, crystalline semiconductors for solar cell applications, ion implanted thin films which provide carrier type reversal, low power phase change memory devices, switchable metamaterial devices as well as traditional chalcogenides glass and optical fibre