Search results for "ELECTRONICS"
showing 10 items of 4340 documents
Efficient excitation of photoluminescence in a two-dimensional waveguide consisting of a quantum dot-polymer sandwich-type structure
2014
International audience; In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10–50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is develo…
<title>Formation of deep acceptor centers in AlGaN alloys</title>
2008
AlGaN alloy thin film materials are of high interest for light emitting diodes (LED of the ultraviolet (UV) spectral region. Origin of the deep intrinsic and impurity Si states in the AlxGa1-xN (0 < x < 0.35) epilayer structures grown by metalorganic chemical vapor deposition (MOCVD) technique have been considered. Effects of the lattice mismatch and Si-doping in the heterostructures of epilayers with different alloy composition are investigated using time resolved photoluminescence (PL) of donor – deep acceptor (DA) pairs. It is shown that the undoped AlGaN alloys, grown on a GaN buffer layer, due to the lattice mismatch contain the increased concentration of cation vacancy (Vcation) defec…
Optical properties of ultrathin Al2O3/ZnO nanolaminates
2015
Abstract Because of their high resistance against ultraviolet and high energy particles, ultrathin amorphous nanolaminates can be very attractive for aerospace application. Here we report on the optical and structural properties of ultrathin Al2O3/ZnO nanolaminates deposited by Atomic Layer Deposition. Structural properties of nanolaminates were studied by GIXRD and AFM. Optical characterization was performed by transmittance, spectroscopic ellipsometry and photoluminescence (PL) spectroscopy. Regression analysis of ellipsometric spectra has shown that absorption peak decreases and blue shifted with the decrease of bilayer thickness in the stack. On the basis of the analysis of structural a…
Nature of the blue luminescence bands in PbWO4
1997
Abstract The photoluminescence spectrum of PbWO 4 is composed of blue and green bands, previously attributed to the regular WO 4 group and to the defect-related WO 3 group, respectively. Untill now only green emission was observed in the thermostimulated luminescence (TSL) above 77 K. Investigation of the TSL spectra starting from 20 K indicates that the blue band, being definitely present at least in the 28 K TSL peak, is also due to recombination emission at defect sites.
Comparison of &#x03B3; and &#x03B2;-ray irradiation effects in sol-gel Ge-doped SiO<inf>2</inf>
2009
We report an experimental study on the comparison between the γ or β ray induced Ge related point defects in Ge doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol-gel technique have been irradiated. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E'Ge, Germanium Lone Pair Center (GLPC) and H(II) point defects. No relevant differences between the concentrations of γ or β ray induced Ge(1) and E'Ge point defects have been observed. In addition, it is found that both irradiations are able t…
Dynamic doping in planar ionic transition metal complex-based light-emitting electrochemical cells
2013
Using a planar electrode geometry, the operational mechanism of iridium(III) ionic transition metal complex (iTMC)-based light-emitting electrochemical cells (LECs) is studied by a combination of fluorescence miscroscopy and scanning Kelvin probe microscopy (SKPM). Applying a bias to the LECs leads to the quenching of the photoluminescence (PL) in between the electrodes and to a sharp drop of the electrostatic potential in the middle of the device, far away from the contacts. The results shed light on the operational mechanism of iTMC-LECs and demonstrate that these devices work essentially the same as LECs based on conjugated polymers do, i.e., according to an electrochemical doping mechan…
The influence of localized plasmons on the optical properties of Au/ZnO nanostructures
2015
Optical and structural experiments have been carried out on Si/ZnO thin films modified with ultra-thin gold layers of different thicknesses. ZnO was produced via Atomic Layer Deposition (ALD) and Au via Physical Vapor Deposition (sputtering). The structural properties of nanostructures were studied by XRD and AFM. Optical characterization was performed by absorbance, photoluminescence (PL) and spectroscopic ellipsometry (SE). A transition from cluster-to-thin films with the increase of Au thickness has been revealed from an analysis of optical and structural parameters. The analysis of optical features of the system has shown that slight changes of the localized plasmon absorption peaks in …
Green light-emitting devices based on soluble oligo(phenylenevinylenes)
2005
In this work, we report our investigations on the film-forming properties as well as the optical and electroluminescent characterisations of a series of lateral-substituted soluble oligo(phenylenevinylenes) of various conjugation length. Preliminary investigations show that these materials are potential candidates for use in organic light-emitting devices (OLEDs). Two types of OLEDs were fabricated: single layer (SL) and single heterostructure (SHS), with poly(p-phenylenevinylene) (PPV) as hole transporting layer. Our best results were obtained with single layer device emitting green light with a luminance of 0.18 cd m(-2) and 0.24 cd m(-2) at a driving voltage of 10 V. (c) 2004 Elsevier B.…
γ-ray-induced bleaching in silica: Conversion from optical to paramagnetic defects
2000
We report experimental results on optical and ESR measurements performed in $\ensuremath{\gamma}$-irradiated natural silica samples having different content of OH groups. A partial bleaching of the optical absorption band ${B}_{2\ensuremath{\beta}}$ at 5.15 eV and the related photoluminescence emissions at 3.1 eV and 4.2 eV is observed together with the growth of an ESR doublet split by 11.8 mT. The kinetics of the two processes as a function of the $\ensuremath{\gamma}$ dose are correlated and depend on the OH content. Our experiments indicate the occurrence of a $\ensuremath{\gamma}$-ray-induced conversion, from optically active centers to paramagnetic ones and vice versa, changing the re…
Inhomogeneous Broadening of Photoluminescence Spectra and Kinetics of Nanometer-Thick (Phenethylammonium)2PbI4 Perovskite Thin Films: Implications fo…
2021
An outstanding potentiality of layered two-dimensional (2D) organic–inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundament…