Ultrafast carrier relaxation in GaN, In_(0.05)Ga_(0.95)N and an In_(0.05)Ga_(0.95)/In_(0.15)Ga_(0.85)N Multiple Quantum Well

Room temperature, wavelength non-degenerate ultrafast pump/probe measurements were performed on GaN and InGaN epilayers and an InGaN multiple quantum well structure. Carrier relaxation dynamics were investigated as a function of excitation wavelength and intensity. Spectrally-resolved sub-picosecond relaxation due to carrier redistribution and QW capture was found to depend sensitively on the wavelength of pump excitation. Moreover, for pump intensities above a threshold of 100 microJ/cm2, all samples demonstrated an additional emission feature arising from stimulated emission (SE). SE is evidenced as accelerated relaxation (< 10 ps) in the pump-probe data, fundamentally altering the re-distribution of carriers. Once SE and carrier redistribution is completed, a slower relaxation of up to 1 ns for GaN and InGaN epilayers, and 660 ps for the MQW sample, indicates carrier recombination through spontaneous emission.Comment: submitted to Phys. Rev.

Алгоритм выбора точки интерконнекции распределенной генерации и ее интеграция в работу энергосистемы

В статье представлен алгоритм выбора точки интерконнекции распределенной генерации с учетом поставленных критериев. Рассмотрены основные факторы, влияющие на режимы работы энергосистемы в зависимости от точки интерконнекции источников распределенной генерации

Luminescence decay in highly excited GaN grown by hydride vapor-phase epitaxy

Contains fulltext : 112521.pdf (publisher's version ) (Open Access

Luminescence transients in highly excited GaN grown by hydride vapor-phase epitaxy

Contains fulltext : 60520.pdf (publisher's version ) (Closed access

Excitation relaxation in films of dipolar N,N-Dimethylaminobenzylidene 1,3-indandione (DMABI) molecules

International audienceUltrafast relaxation of self-trapped (ST) excitons in polycrystalline film of N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) molecules, which possess pronounced donor–acceptor properties, is studied by using femtosecond luminescence up-conversion spectroscopy. Exciton relaxation dynamics is compared to excitation decay obtained for DMABI molecules embedded in a rigid transparent matrix. Excitons in the film undergo rapid self-trapping on the time scale below 100 fs. A strong nonradiative recombination of ST excitons is observed on the subpicosecond time scale, which is shown to occur concurrently with their final localization. This final localization is attributed to the cooling of locally heated (up to 600 K) ST excitons, that occurs with the time constant τc=800 fs. The fast nonradiative relaxation is assigned to the thermally activated transition of the hot excitons to the ground state during their thermalization. After the fast relaxation stage is completed, the second, slow exciton relaxation stage emerges, which is attributed to one-dimensional migration of excitons and their nonradiative decay on structural defects

Concentration effects on emission of bay-substituted perylene diimide derivatives in a polymer matrix

10.1016/j.dyepig.2011.09.017Dyes and Pigments9231285-1291DYPI

Associations of job, living conditions and lifestyle with occupational injury in working population: a population-based study

International audienceObjectives To assess the roles of job demands, living conditions and lifestyle in occupational injury. Mehods The sample included 2,888 workers, aged >= 15 years, randomly selected from the north-eastern France. The subjects completed a mailed questionnaire. Data were analyzed with adjusted odds ratios (ORa) computed with the logistic model. Results In total, 9.2% of workers had an injury during the previous 2 years. The high job demands: tasks at height, handling objects, pneumatic tools, other vibrating hand tools, work in adverse climate, physical workload, vibrating platform, machine tools, cold, heat, awkward posture, noise, hammer, and pace had crude odds ratios between 1.81 and 5.25 for injury. A strong exposure-response relationship was found between the cumulated job demands (CJD, defined by their number) and injury: OR 1.88 (95% CI 1.23-2.87) for CJD1, 4.39 (2.98-4.46) for CJD2-3, and 9.93 (6.70-14.7) for CJD >= 4, versus CJD0. These ORs decreased to 1.68, 3.70, and 7.15 respectively, when adjusted for sex, age, and living conditions/lifestyle confounders; and to 1.54, 2.99, and 5.45 respectively when also adjusted for job category. The following factors had significant ORa: age = 40 or with frequent drug use for fatigue compared with the others. Obesity had ORa 2.05 (1.11-3.78) among the subjects aged >= 40, and excess alcohol use had ORa 2.44 (1.26-4.72) among those free of disease. Conclusions This study identified a wide range of job demands and living conditions/lifestyle which predicted injury. Preventive measures should be conducted to reduce job demands and to help workers to be aware of the risk and to improve their living conditions/lifestyle

Synthesis, photophysical and photoelectrical properties of glass-forming phenothiazinyl- and carbazolyl-substituted ethylenes

Phenothiazinyl- and carbazolyl-substituted ethylenes have been synthesized and found to constitute electro-active materials with high thermal stability as characterised by thermo-gravimetric analysis. Steady state absorption and luminescence spectra of the synthesized derivatives were examined in detail revealing green-blue emission with efficiency ranging from 13 % to 28 %. Based on the emission spectra of the synthesized compounds Commission Internationale d’Eclairage (CIE) chromaticity coordinates have been obtained. Major luminescence decay time component of ~2.5 ns was determined in dilute solutions of the compounds, whereas significantly shorter one has been estimated in thin films. Electron photoemission spectra of the materials have been recorded and the ionisation potentials of 5.3-5.4 eV have been established. Room temperature hole drift mobilities of the diarylethylenes dispersed in polymeric host approached 10-5 cm2/Vs at high electric fields

Hyper-Rayleigh Scattering and Two-Photon Luminescence of Phenylamine- Indandione Chromophores

Based on results of quantum chemical (QC) screening, we put under research several phenylamine indane-1,3-dione derivatives including octupolar NLO chromophore A3BI. According to these calculations, molecular first hyperpolarizability (βHRS) should be enhanced upon replacement of methyl substituents with phenyl groups. Surprisingly, βHRS values obtained in our measurements by hyper-Rayleigh scattering (HRS) are much higher than one could expect from QC. Bearing in mind that two-photon luminescence (TPL) is usual cause for overestimation of βHRS in HRS measurements, we have accomplished investigations of TPL properties of these compounds. All investigated triphenylamine derivatives exhibit strong TPL. In case of DANS and DMABI captured simultaneously, TPL spectra and HRS signal, reveal the least as clearly distinct on TPL background, thus TPL-free βHRS values can be defined. Concurrently, sharp HRS signal of DPABI is sinking in TPL and background noise along with increase in concentration. Due to fairly intensive TPL for other investigated triphenylamino compounds, the HRS signal was rather indistinguishable and therefore correct βHRS values could not be extracted

Characterization of as-grown and heavily irradiated GaN epitaxial structures by photoconductivity and photoluminescence

The influence of radiation defects on photoconductivity transients and photoluminescence (PL) spectra have been examined in semi-insulating GaN epitaxial layers grown on bulk n-GaN/sapphire substrates. Defects induced by 10-keV X-ray irradiation with a dose of 600 Mrad and 100-keV neutrons with fluences of 5×1014 and 1016 cm−2 have been revealed through contact photoconductivity and microwave absorption transients. The amplitude of the initial photoconductivity decay is significantly reduced by the radiation defect density. A simultaneous decrease with radiation-induced defect density is also observed in the steady-state PL intensity of yellow, blue and ultraviolet bands peaked at 2.18, 2.85, and 3.42 eV, respectively. The decrease of the PL intensity is accompanied by an increase of asymptotic decay lifetime, which is due to excess carrier multi-trapping. The decay can be described by the stretched exponential approximation exp[-(t/τ)α] with different values of α in as-grown material (α≈0.7) and irradiated samples (α≈0.3). The value of the fracton dimension ds of the disordered structure, evaluated as ds=2α/(1-α), changes from 4.7 to 0.86 for as-grown and irradiated material, respectively, implying percolative carrier motion on an infinite cluster of dislocations net in the as-grown material and cluster fragmentation into finite fractons after irradiation