Search results for "quenching"
showing 10 items of 275 documents
Structure development in poly(ethylene terephthalate) quenched from the melt at high cooling rates: X-ray scattering and microhardness study
2000
The structure and microhardness of poly(ethylene terephthalate) (PET) cooled from the melt, using a wide range of cooling rates, was studied. PET thin films rapidly cooled from the melt (cooling rates larger than 5°C/s) show a continuous variation of structure and properties depending on cooling rate. Results highlight differences in the micro-mechanical properties of the glass suggesting the occurrence of amorphous structures with different degrees of internal chain ordering. The comparative X-ray scattering study of two glassy PET samples (7500 and 17°C/s) reveals the occurrence of frozen-in electron density states giving rise to an excess of scattering for the amorphous sample solidified…
Exciton quenching by diffusion of 2,3,5,6-tetrafluoro-7,7’,8,8’-tetra cyano quino dimethane and its consequences on joule heating and lifetime of org…
2013
In this Letter, the effect of F(4)-TCNQ insertion at the anode/hole transport layer (HTL) interface was studied on joule heating and the lifetime of organic light-emitting diodes (OLEDs). Joule heating was found to reduce significantly (pixel temperature decrease by about 10 K at a current density of 40 mA/cm(2)) by this insertion. However, the lifetime was found to reduce significantly with a 1 nm thick F(4)-TCNQ layer, and it improved by increasing the thickness of this layer. Thermal diffusion of F(4)-TCNQ into HTL leads to F(4)-TCNQ ionization by charge transfer, and drift of these molecules into the emissive layer caused faster degradation of the OLEDs. This drift was found to reduce w…
Increasing the efficiency of light-emitting electrochemical cells by limiting the exciton quenching
2013
ABSTRACTLight-emitting electrochemical cells (LECs) are one of the simplest electroluminescent devices. The possibility to be processed from solution and to operate with air-stable materials makes them an attractive alternative to organic light emitting diodes (OLEDs). Still their efficiencies are below those obtained in OLEDs. Additionally the best efficiencies were reported at low luminances and sustained for a short period of time. Here we show that for a LEC employing an orange-emitting charged iridium complex that is driven using a pulsed driving scheme high efficiencies of up to 20.5 cd A-1 can be obtained at high luminance and sustained over the device lifetime. It is also shown that…
Luminescence of coesite
2015
Coesite is a polymorph modification of crystalline silicon dioxide with a tetrahedral structure. The luminescence of a single crystal of synthetic coesite was studied under excitation using x-rays, an electron beam, and excimer lasers KrF (248 nm), ArF (193 nm) and F2 (157 nm). Luminescence bands in the regions of 2.5 eV and 4.4 eV appear. The blue band is dependent on temperature and is composed of decay kinetics. Three main decay times are revealed, exhibiting luminescence of a different nature in the same range of the spectrum. One is in the ns range of time with a time constant of about 2 ns. The two other decay times are in the regions of 5 μs and 700 μs. The 5 μs component is also see…
Mesoscopic gels at low agarose concentration: perturbation effects of ethanol
1997
Aqueous agarose solutions at low concentrations (0.5 g/liter) were temperature quenched below the spinodal line to form mutually disconnected mesoscopic gels. In the presence of 6% ethanol, these solutions, obtained by quenching at the same temperature depth as in pure water, appear much more fluid, as determined by probe diffusion experiments. We show by static and dynamic light scattering that this can be explained by the solvent-mediated effects of ethanol, leading to a globular shape of mesoscopic agarose gels, rather than to an extended rodlike structure observed in pure water. Our findings show the significant effects of solvent perturbations on particle condensation and, therefore, m…
Particle size-related limitations of persistent phosphors based on the doped Y3Al2Ga3O12 system
2021
AbstractCo-doped Ce3+, Cr3+ and Pr3+ yttrium–aluminium–gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100 °C show …
Modeling and Characterization of SiPM Parameters at Temperatures between 95 K and 300 K
2017
The modeling and characterization of silicon photomultipliers (SiPMs) in a wide temperature range from 95 K to 300 K is presented. The devices under study had the distinctive feature of forward-biased p-n junctions situated under each pixel as active quenching resistors making them particularly appropriate to be operated at cryogenic temperatures. The voltage drop across the diode in a forward direction was measured for a series of injected currents in this temperature range. It was observed that the characteristics of different SiPM types influence the temperature dependence of the reverse saturation current. The devices were further characterized by low-level light-pulse measurements. The…
Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa
2014
Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300~fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via…
Luminescence of Eu3+-doped lanthanum titanate (La2TiO5), a system with one-dimensional energy migration
1992
Abstract The titanate and Eu 3+ luminescence of a composition La 2 TiO 5 -Eu are reported as a function of temperature. At 4.2 K the quantum efficiency is very high, because the titanate excitation energy is localized. At 300 K there is delocalization and quenching centres are easily reached, so that the quantum efficiency becomes low. This is discussed in terms of the crystal structure, as are the peculiarities of the Eu 3+ spectra.
Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films
2020
Abstract In this paper we present critical analysis of different points of view on interpretation of the photoluminescence (PL) decay kinetics in lead halide perovskites prepared in the form of well passivated nanocrystals (PNCs) or thin polycrystalline layers. In addition to the literature data, our own measurements are also considered. For PNCs, a strong dependence of the PL lifetimes on the type of passivating ligand was observed with a consistently high PL quantum yield. It is shown that such ligand effects, as well as a decrease in the PL lifetime with decreasing temperature, are well qualitatively explained by the phenomenological model of thermally activated delayed luminescence, in …