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

Effect of sample dimensions on observed photoluminescence from Er³⁺ ions in GeGaS and LaGaS glass hosts

The 4I9/2 - 4I13/2 emission band of trivalent Er3+ is potentially interesting light source for methane (CH4) detection because of its closeness to CH4 absorption band at 1.67 µm. In the present paper we report the influence of glass sample geometry on the shape of spectra and relative emission intensity of 4I9/2 - 4I13/2 band as well as three main 4I13/2 - 4I15/2 , 4I11/2 - 4I15/2 and 4I9/2 - 4I15/2 emission bands in sulfide glasses (GeGaS and LaGaS) doped with 0.5 at.% of Er. We show that the increase of sample size leads to a significant broadening of emission spectra as well as to the substantial suppression of 4I13/2 - 4I15/2 and 4I11/2 - 4I15/2 bands. The observed effects are explained by excitation diffusion or photon trapping (consecutive absorption and emission of light by Er3+ ions [1,2]) which turns out to be more effective in large samples. We present the results of Monte-Carlo simulations supporting our considerations and we discuss the possibility of increasing the 4I9/2 - 4I13/2 emission by controlling photon trapping

Emission from a bismuth doped chalcogenide glass spanning from 1µm to 2.7µm

We report emission from a bismuth doped chalcogenide glass with a full width half maximum of 850 nm. The quantum efficiency and lifetime were 32% and 175 µs. We report two new bismuth emission bands at 2000 and 2600 nm

Fabrication of thin film solar cell materials by APCVD

Thin film solar cells are currently being implemented commercially as they reduce the amount of semiconductor material required for each cell when compared to silicon wafers, thereby lowering the cost of production. Currently two direct band gap chalcogenide thin-film technologies, CdTe and CuInGa(S,Se)2 (CIGS), yield the highest reported power conversion efficiencies of 16.5% and 20.3%, respectively. In addition, Cu2ZnSnS4 (CZTS) is one of the most promising chalcogenide thin film photovoltaic absorber materials; with an optimal band gap of about 1.5 eV. More importantly, CZTS consists of abundant and non-toxic elements, so research on CZTS thin-film solar cells has been increasing significantly in recent years. Moreover, Sb2S3 based chalcogenide thin films have been proposed for use in photovoltaic applications. The preparation of chalcogenide thin films solar cells commonly use physical vapour deposition methods including thermal/e-beam evaporation, sputtering, and pulsed laser deposition, electrochemical deposition, spray pyrolysis, solution-based synthesis, followed by the sulfurization or selenization annealing process. In this paper, we report a non-vacuum process, using atmospheric pressure chemical vapour deposition (APCVD), to fabricate chalcogenide thin film solar cell materials as well as transparent conductive oxide (TCO) thin films. The optical, electrical, and structural properties of these materials were characterized by UV-VIS-NIR, four-point probes, SEM, EDX, XRD, Micro-Raman

Quantum efficiency measurements in oxygen-containing gallium lanthanum sulphide glasses and fibers doped with Pr³⁺

The quantum efficiency of Pr3+ emission at 1.3µm from the 1G4 - 3H5 transition is measured in Gallium Lanthanum Sulphide (GLS) glass containing varying quantities of lanthanum oxide. The variation of quantum efficiency with host composition is described, and the variation of quantum efficiency with pump wavelength in oxide-containing hosts is compared to a model of the effect of the addition of oxygen on the spectroscopy of the Pr ion. Oxide-containing GLS glasses can show quantum efficiencies of up to 84% of that of pure GLS, while retaining considerably better thermal and glass-forming properties. No degradation of quantum efficiency is seen when GLS glass is pulled into fiber form

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

Laser-induced forward transfer of thermoelectric materials on polymer and glass substrates

Laser-induced forward transfer (LIFT) is a laser-assisted direct write method that has been used to print a range of solids and rheological fluids. The donor that is to be printed is previously deposited onto a transparent support substrate that is usually referred to as a carrier. A highly energetic short-pulsed laser beam imaged through the transparent carrier onto the donor results in the forward transfer of a donor pixel onto a receiver substrate placed either in contact or a few microns apart. Solid films can be transferred with minimal change in their crystal and domain structure via LIFT

Electrical phase change of CVD-grown Ge-Sb-Te thin film device

A prototype Ge-Sb-Te thin film phase-change memory device has been fabricated and reversible threshold and phase change switching demonstrated electrically, with a threshold voltage of 1.5 – 1.7 V. The Ge-Sb-Te thin film was fabricated by chemical vapour deposition (CVD) at atmospheric pressure using GeCl4, SbCl5, and Te precursors with reactive gas H2 at reaction temperature 780 °C and substrate temperature 250 °C. The surface morphology and composition of the CVD-grown Ge-Sb-Te thin film has been characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The CVD-grown Ge-Sb-Te thin film shows promise for the phase change memory applications

Manufacturing high purity chalcogenide glass

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-linearity's 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 the range of materials we synthesize highlighting high purity sulphide bulk glass and transition metal di-chalcogenides for electronic applications, crystalline semiconductors for solar cell applications, low power phase change memory devices, switchable metamaterial devices as well as traditional chalcogenides glass and optical fibre

New glasses for active fibre devices

Through a series of case studies based on current research topics in Southampton, we describe optoelectronic devices whose realization is entirely dependent on new materials. The first is a practical optical fibre amplifier for the second telecommunications window at 1.3µm. Such a device based on rare-earth-doped fibres simply does not work in a silica host, where all useful emission is dissipated as heat in the glass. The second is a planar waveguide device, the lossless splitter. In this important component for fibre to the home, fibres with lengths of several metres would normally be required. New glasses allow greater concentrations of the active rare-earth dopant to be incorporated, thereby shrinking the size of the device to dimensions of a few centimetres. Thirdly, new glasses and fibres for fibre-based acousto-optic modulators will be described. These devices have the potential to allow direct modulation of the light within the fibre. Through these three case studies, we highlight the potential role of new materials in three key waveguide devices for telecommunications; amplifiers, splitters and modulators. The paper will conclude by reviewing overall efforts in Southampton in new glasses for optoelectronics, identifying key materials, their properties and applications in a global telecommunications network