A NO-STOKES SHIFT MODEL FOR THE PHOTOLUMINESCENCE OF a-Si:H

From the close similarity of the absorption and excitation spectra below the gap, we deduce that there is no significant Stokes shift in the luminescence of a-Si:H. We propose a model for the zero-phonon states which accounts for the luminescence and the absorption spectrum in terms of disorder related fluctuations of the band-gap

RECOMBINAISON RADIATIVE ET EFFETS DE SPIN DANS LE SILICIUM MICROCRISTALLIN POST-HYDROGENE PLASMA

Nous présentons des résultats préliminaires sur la luminescence du silicium microcristallin obtenu par LPCVD sur saphir, à 620°C, et hydrogéné plasma à 400°C. Le spectre de luminescence obtenu à 5 K présente six bandes non résolues réparties entre 0,45 et 1 eV, et une bande plus large à plus haute énergie (1,4 eV). Les bandes à basses énergies proviennent vraisemblablement des défauts associés aux grains et aux joints de grains. Les bandes à 0,75 et 0,85 eV présentent un signal RMDO (Résonance Magnétique Détectée Optiquement) d'augmentation et de diminution respectivement. Le signal d'augmentation est la convolution de deux raies ; une étroite à g = 1,9997, de largeur 18 Gauss, une large à g = 2,016 et de largeur 100 Gauss. Le signal de diminution est constitué d'une seule raie à 2,0043 et de largeur 25 Gauss.We report preliminary results of photoluminescence and Optically Detected Magnetic Resonance (O.D.M.R.) studies in microcrystalline silicon elaborated on sapphire by LPCVD and plasma-hydrogenated at 400°C. The 5K luminescence spectrum shows 6 unresolved bands between 0.45 and 1 eV, and one broader band at higher energy (1.4 eV). The 0.75 and 0.85 eV bands show an ODMR enhancing and quenching signal, respectively. The enhancing spectrum is a convolution of two signals : a narrow signal at g = 1.9997, width 18 Gauss, and a broad signal at g = 2.016, width 100 Gauss. The quenching signal is at g = 2.0043 and of width = 25 Gauss

Gradient-based metamodel optimization for the design of 3F3 Ferrites Core in a WPT system

International audienceThis paper shows the useful combination of stochastic tools with 3D finite element analysis in order to build accurate predictor at a low computation cost in the case of human exposure for a high power wireless power transfer system. This surrogate model can be used to compute accurate sensitivity analysis regarding the various positions of the human body for the electromagnetic problem. Such an analysis enabled us to find the worst case scenario for the posture of the human body around the WPT3/Z3 system from SAE J2954

Breakdown of Kasha’s Rule in a Ubiquitous, Naturally Occurring, Wide Bandgap Aluminosilicate (Feldspar)

Excitation-energy-dependent emission (EDE) is well known from photoluminescence (PL) studies of polar solvents and carbon-based nanostructures. In polar solvents, this effect known as the 'red edge effect' (REE) is understood to arise from solute-solvent interactions, whereas, in case of carbon-based nanostructures, the origin is highly debated. Understanding this effect has important bearings on the potential applications of these materials. EDE has never been reported from large crystalline materials, except very recently by our group. Here, we make detailed investigations to understand the universality and the mechanism behind the EDE in a wide band gap aluminosilicate (feldspar), which comprises more than half of the Earth's crust, and is widely used in geophotonics (e.g., optical dating). We observe EDE up to 150 nm at room temperature in our samples, which is unprecedented in rigid macroscopic structures. Based on PL investigations at 295 K and 7 K, we present a novel model that is based on photoionisation of a deep lying defect and subsequent transport/relaxation of free electrons in the sub-conduction band tail states. Our model has important implications for potential photonic applications using feldspar, measurement of band tail width in wide bandgap materials, and understanding the EDE effect in other materials