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Thermal Quenching (thermal + quenching)
Selected AbstractsThermal quenching of luminescence and isovalent trap model for rare-earth-ion-doped AlNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007H. J. Lozykowski Abstract Investigations of the luminescent properties of Pr-, Eu-, Tb- and Tm-implanted AlN thin films at temperature in the range 9,830 K are reported. The temperature studies of photoluminescence and cathodoluminescence spectra revealed unexpectedly weak thermal quenching for all investigated rare earth (RE) ions. The maximum CL emission is observed from Eu (red) at 485 K, Tb (green) at 590 K and Tm (blue) at 530 K, respectively. For Tb- and Tm-doped AlN samples, temperature-dependent crossrelaxation processes were observed. Photoluminescence excitation spectra, obtained under UV excitation in the spectral range 200,400 nm, exhibit several bands. It is proposed that the RE ions exist in semiconductors as isolated ions (singlet), nearest-neighbor (nn) ion pairs (dimer), and three ions (trimer). The Koster,Slater and simple spherical potential-well models for RE-structured isovalent (RESI) hole trap are proposed. The exciton binding energies of RESI traps are calculated and compared with experimental thermal-quenching energies. The energy-transfer processes between the AlN host and the 4f-shell systems are emphasized as the main mechanisms for thermal-quenching processes rather than nonradiative decay of 4f transitions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature variation of radiative recombination rate of electron-hole pairs responsible for defect photoluminescence in a-Si:HPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009C. Ogihara Abstract Lifetime distribution and characteristic lifetime of the defect photoluminescence (PL) in a-Si:H have been obtained by means of frequency resolved spectroscopy at various temperatures in the range of 10-200 K. Temperature variation of the radiative recombination rate has been obtained from the intensities and the characteristic lifetimes. The results obtained for the a-Si:H films as grown and after prolonged illumination have been compared. Thermal quenching of the defect PL becomes more significant after illumination. However the decrease of lifetime with raising temperature becomes less significant after illumination. Increase of the radiative recombination rate with increasing temperature, which is significantly observed above 100 K, becomes less significant after the illumination, indicating that the illumination causes the increase of the density of strongly localised tail states. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Energy Release in Isothermally Stretched Silicate Glass fibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006Lasse Hornbøll Three types of silicate glass fibers are annealed, simultaneously stretched in the glass transition region for certain time lengths, then slowly cooled to room temperature under load, and subsequently scanned by differential scanning calorimetry (DSC). During the DSC scanning, a broad exothermic peak (representing energy release) occurs in the stretched fibers well below the glass transition temperature, while it does not occur in the non-stretched fibers. The peak indicates that mechanical stretching can result in an energy enhancement in the fibers. It also confirms that the energy released during reheating of the fibers formed using an industrial continuous fiber drawing process originates not only from thermal quenching but also from mechanical stretching. However, the mechanical stretching-induced energy is much lower than the thermal hyperquenching-induced energy in glass fibers. The effect of annealing temperature and time on the energy release behavior is discussed in terms of viscoelasticity. [source] Simulation of the influence of thermal quenching on thermoluminescence glow-peaksPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010B. Subedi Abstract The thermal quenching of luminescence efficiency is an effect which is present in many thermoluminescent (TL) materials. It causes a significant decrease of the luminescence signal and disturbs the shape of the glow-peaks. Therefore, in principle, the thermoluminescence kinetics theory cannot describe TL glow-peaks influenced by thermal quenching. In the present work a detailed simulation of the influence of the thermal quenching effect on thermoluminescence glow-peaks is presented. Specifically we study the shift of the quenched glow-peak with heating rate and the effect on the various heating rate methods, the influence on the symmetry factor and the kinetic order of the glow-peak, and the effect of thermal quenching on the initial rise and peak shape methods for evaluating kinetic parameters. Furthermore, the evaluation of the thermal quenching parameters using the quenched glow-peak and the possibility of using the conventional expression describing a single glow-peak to fit the quenched glow peaks are also investigated. [source] Thermal quenching of luminescence and isovalent trap model for rare-earth-ion-doped AlNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007H. J. Lozykowski Abstract Investigations of the luminescent properties of Pr-, Eu-, Tb- and Tm-implanted AlN thin films at temperature in the range 9,830 K are reported. The temperature studies of photoluminescence and cathodoluminescence spectra revealed unexpectedly weak thermal quenching for all investigated rare earth (RE) ions. The maximum CL emission is observed from Eu (red) at 485 K, Tb (green) at 590 K and Tm (blue) at 530 K, respectively. For Tb- and Tm-doped AlN samples, temperature-dependent crossrelaxation processes were observed. Photoluminescence excitation spectra, obtained under UV excitation in the spectral range 200,400 nm, exhibit several bands. It is proposed that the RE ions exist in semiconductors as isolated ions (singlet), nearest-neighbor (nn) ion pairs (dimer), and three ions (trimer). The Koster,Slater and simple spherical potential-well models for RE-structured isovalent (RESI) hole trap are proposed. The exciton binding energies of RESI traps are calculated and compared with experimental thermal-quenching energies. The energy-transfer processes between the AlN host and the 4f-shell systems are emphasized as the main mechanisms for thermal-quenching processes rather than nonradiative decay of 4f transitions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical Analysis of the Catalytic Combustion of Premixed Methane/Air Mixtures in MicrotubesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2008J. Zhong Abstract The combustion characteristics and extinction limits for the catalytic combustion of a methane/air mixture in a microtube are investigated computationally using the commercial CFD code FLUENT coupled to an external subroutine DETCHEM. The effects of the microtube dimensions, conductivities of wall materials, external heat losses and flow velocity on the combustion stability, are also studied. The numerical model is set as either adiabatic or non-adiabatic with a fixed exterior heat transfer coefficient. Numerical results indicate that thermal conductivity and wall thickness are vital to preheat the methane/air mixture through the conducting wall. Two types of extinction occur, i.e., thermal quenching and blow out. These extinction limits are characterized by wall surface temperature in the microtube and the ratio of Pt(s)/O(s). [source] | ||||||||||