Broad-gain (Δλ/λ0

PubMed

Fujita, Kazuue; Furuta, Shinichi; Dougakiuchi, Tatsuo; Sugiyama, Atsushi; Edamura, Tadataka; Yamanishi, Masamichi

2011-01-31

Broad-gain operation of λ~8.7 μm quantum cascade lasers based on dual-upper-state to multiple-lower-state transition design is reported. The devices exhibit surprisingly wide (~500 cm(-1)) electroluminescence spectra which are very insensitive to voltage and temperature changes above room temperature. With recourse to the temperature-insensitivity of electroluminescence spectra, the lasers demonstrate an extremely-weak temperature-dependence of laser performances: T0-value of 510 K, associated with a room temperature threshold current density of 2.6 kA/cm2. In addition, despite such wide gain spectra, room temperature, continuous wave operation of the laser with buried hetero structure is achieved.

Semi-transparent all-oxide ultraviolet light-emitting diodes based on ZnO/NiO-core/shell nanowires

NASA Astrophysics Data System (ADS)

Shi, Zhi-Feng; Xu, Ting-Ting; Wu, Di; Zhang, Yuan-Tao; Zhang, Bao-Lin; Tian, Yong-Tao; Li, Xin-Jian; Du, Guo-Tong

2016-05-01

Semi-transparent all-oxide light-emitting diodes based on ZnO/NiO-core/shell nanowire structures were prepared on double-polished c-Al2O3 substrates. The entire heterojunction diode showed an average transparency of ~65% in the ultraviolet and visible regions. Under forward bias, the diode displayed an intense ultraviolet emission at ~382 nm, and its electroluminescence performance was remarkable in terms of a low emission onset, acceptable operating stability, and the ability to optically excite emissive semiconductor nanoparticle chromophores.Semi-transparent all-oxide light-emitting diodes based on ZnO/NiO-core/shell nanowire structures were prepared on double-polished c-Al2O3 substrates. The entire heterojunction diode showed an average transparency of ~65% in the ultraviolet and visible regions. Under forward bias, the diode displayed an intense ultraviolet emission at ~382 nm, and its electroluminescence performance was remarkable in terms of a low emission onset, acceptable operating stability, and the ability to optically excite emissive semiconductor nanoparticle chromophores. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07236k

Green-light-emitting electroluminescent device based on a new cadmium complex

NASA Astrophysics Data System (ADS)

Kumar, Rahul; Srivastava, Ritu; Kumar, Akshay; Kamalasanan, M. N.; Singh, K.

2010-06-01

A new cadmium complex is synthesized to investigate its stability and applicability for a luminescent device. The as-prepared Cd(Bpy)q sample is characterized by Fourier-transformed infra-red spectroscopy (FTIR), thermal gravimetric analyzer (TGA) and photoluminescence (PL). The prepared sample shows excellent thermal stability up to 380 °C. A maximum is observed at 240 nm in absorption spectra which is attributed to the π-π* transition. An organic-light-emitting diode (OLED) has been fabricated using this material. The fundamental structures of the device exhibit ITO/α-NPD/Cd(Bpy)q/BCP/Alq3/LiF/Al. The electroluminescence (EL) device emits bright green light with maximum luminescence 1683 cd/m2 at 20 V.

Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Qiushi; Zhang, Chao; Zhang, Yang, E-mail: zhyangnano@ustc.edu.cn, E-mail: zcdong@ustc.edu.cn

2015-07-27

We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within severalmore » molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism.« less

Large magneto-conductance and magneto-electroluminescence in exciplex-based organic light-emitting diodes at room temperature

NASA Astrophysics Data System (ADS)

Ling, Yongzhou; Lei, Yanlian; Zhang, Qiaoming; Chen, Lixiang; Song, Qunliang; Xiong, Zuhong

2015-11-01

In this work, we report on large magneto-conductance (MC) over 60% and magneto-electroluminescence (MEL) as high as 112% at room temperature in an exciplex-based organic light-emitting diode (OLED) with efficient reverse intersystem crossing (ISC). The large MC and MEL are individually confirmed by the current density-voltage characteristics and the electroluminescence spectra under various magnetic fields. We proposed that this type of magnetic field effect (MFE) is governed by the field-modulated reverse ISC between the singlet and triplet exciplex. The temperature-dependent MFEs reveal that the small activation energy of reverse ISC accounts for the large MFEs in the present exciplex-based OLEDs.

Magnetic tunnel spin injectors for spintronics

NASA Astrophysics Data System (ADS)

Wang, Roger

Research in spin-based electronics, or "spintronics", has a universal goal to develop applications for electron spin in a broad range of electronics and strives to produce low power nanoscale devices. Spin injection into semiconductors is an important initial step in the development of spintronic devices, with the goal to create a highly spin polarized population of electrons inside a semiconductor at room temperature for study, characterization, and manipulation. This dissertation investigates magnetic tunnel spin injectors that aim to meet the spin injection requirements needed for potential spintronic devices. Magnetism and spin are inherently related, and chapter 1 provides an introduction on magnetic tunneling and spintronics. Chapter 2 then describes the fabrication of the spin injector structures studied in this dissertation, and also illustrates the optical spin detection technique that correlates the measured electroluminescence polarization from quantum wells to the electron spin polarization inside the semiconductor. Chapter 3 reports the spin injection from the magnetic tunnel transistor (MTT) spin injector, which is capable of producing highly spin polarized tunneling currents by spin selective scattering in its multilayer structure. The MTT achieves ˜10% lower bound injected spin polarization in GaAs at 1.4 K. Chapter 4 reports the spin injection from CoFe-MgO(100) tunnel spin injectors, where spin dependent tunneling through MgO(100) produces highly spin polarized tunneling currents. These structures achieve lower bound spin polarizations exceeding 50% at 100 K and 30% in GaAs at 290 K. The CoFe-MgO spin injectors also demonstrate excellent thermal stability, maintaining high injection efficiencies even after exposure to temperatures of up to 400 C. Bias voltage and temperature dependent studies on these structures indicate a significant dependence of the electroluminescence polarization on the spin and carrier recombination lifetimes inside the semiconductor. Chapter 5 investigates these spin and carrier lifetime effects on the electroluminescence polarization using time resolved optical techniques. These studies suggest that a peak in the carrier lifetime with temperature is responsible for the nonmonotonic temperature dependence observed in the electroluminescence polarization, and that the initially injected spin polarization from CoFe-MgO spin injectors is a nearly temperature independent ˜70% from 10 K up to room temperature.

ZnO nanorods for electronic and photonic device applications

NASA Astrophysics Data System (ADS)

Yi, Gyu-Chul; Yoo, Jinkyoung; Park, Won Il; Jung, Sug Woo; An, Sung Jin; Kim, H. J.; Kim, D. W.

2005-11-01

We report on catalyst-free growth of ZnO nanorods and their nano-scale electrical and optical device applications. Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) enables fabrication of size-controlled high purity ZnO single crystal nanorods. Various high quality nanorod heterostructures and quantum structures based on ZnO nanorods were also prepared using the MOVPE method and characterized using scanning electron microscopy, transmission electron microscopy, and optical spectroscopy. From the photoluminescence spectra of ZnO/Zn 0.8Mg 0.2O nanorod multi-quantum-well structures, in particular, we observed a systematic blue-shift in their PL peak position due to quantum confinement effect of carriers in nanorod quantum structures. For ZnO/ZnMgO coaxial nanorod heterostructures, photoluminescence intensity was significantly increased presumably due to surface passivation and carrier confinement. In addition to the growth and characterizations of ZnO nanorods and their quantum structures, we fabricated nanoscale electronic devices based on ZnO nanorods. We report on fabrication and device characteristics of metal-oxidesemiconductor field effect transistors (MOSFETs), Schottky diodes, and metal-semiconductor field effect transistors (MESFETs) as examples of the nanodevices. In addition, electroluminescent devices were fabricated using vertically aligned ZnO nanorods grown p-type GaN substrates, exhibiting strong visible electroluminescence.

Electroluminescent devices formed using semiconductor nanocrystals as an electron transport media and method of making such electroluminescent devices

DOEpatents

Alivisatos, A. Paul; Colvin, Vickie

1996-01-01

An electroluminescent device is described, as well as a method of making same, wherein the device is characterized by a semiconductor nanocrystal electron transport layer capable of emitting visible light in response to a voltage applied to the device. The wavelength of the light emitted by the device may be changed by changing either the size or the type of semiconductor nanocrystals used in forming the electron transport layer. In a preferred embodiment the device is further characterized by the capability of emitting visible light of varying wavelengths in response to changes in the voltage applied to the device. The device comprises a hole processing structure capable of injecting and transporting holes, and usually comprising a hole injecting layer and a hole transporting layer; an electron transport layer in contact with the hole processing structure and comprising one or more layers of semiconductor nanocrystals; and an electron injecting layer in contact with the electron transport layer for injecting electrons into the electron transport layer. The capability of emitting visible light of various wavelengths is principally based on the variations in voltage applied thereto, but the type of semiconductor nanocrystals used and the size of the semiconductor nanocrystals in the layers of semiconductor nanometer crystals may also play a role in color change, in combination with the change in voltage.

High-performance planar green light-emitting diodes based on a PEDOT:PSS/CH3NH3PbBr3/ZnO sandwich structure

NASA Astrophysics Data System (ADS)

Shi, Zhi-Feng; Sun, Xu-Guang; Wu, Di; Xu, Ting-Ting; Zhuang, Shi-Wei; Tian, Yong-Tao; Li, Xin-Jian; Du, Guo-Tong

2016-05-01

Recently, perovskite-based light-emitting diodes based on organometal halide emitters have attracted much attention because of their excellent properties of high color purity, tunable emission wavelength and a low-temperature processing technique. As is well-known, organic light-emitting diodes have shown powerful capabilities in this field; however, the fabrication of these devices typically relies on high-temperature and high-vacuum processes, which increases the final cost of the product and renders them uneconomical for use in large-area displays. Organic/inorganic hybrid halide perovskites match with these material requirements, as it is possible to prepare such materials with high crystallinity through solution processing at low temperature. Herein, we demonstrated a high-brightness green light-emitting diode based on PEDOT:PSS/CH3NH3PbBr3/ZnO sandwich structures by a spin-coating method combined with a sputtering system. Under forward bias, a dominant emission peak at ~530 nm with a low full width of half-maximum (FWHM) of 30 nm can be achieved at room temperature. Owing to the high surface coverage of the CH3NH3PbBr3 layer and a device design based on carrier injection and a confinement configuration, the proposed diode exhibits good electroluminescence performance, with an external quantum efficiency of 0.0645%. More importantly, we investigated the working stability of the studied diode under continuous operation to verify the sensitivity of the electroluminescence performance to ambient atmosphere and to assess the suitability of the diode for practical applications. Moreover, the underlying reasons for the undesirable emission decay are tentatively discussed. This demonstration of an effective green electroluminescence based on CH3NH3PbBr3 provides valuable information for the design and development of perovskites as efficient emitters, thus facilitating their use in existing applications and suggesting new potential applications.

Pure white OLED based on an organic small molecule: 2,6-Di(1H-benzo[d]imidazol-2-yl)pyridine

NASA Astrophysics Data System (ADS)

Liu, Jian

2015-10-01

2,6-Di(1H-benzo[d]imidazol-2-yl)pyridine (DBIP) was synthesized. The single-crystal structure of DBIP was resolved. DBIP-based OLED was fabricated. The electroluminescence for the device corresponds to a pure white emission. In addition, thermal stability, UV-vis, photoluminescence and electrochemical behaviors of DBIP were investigated as well.

Low temperature transient response and electroluminescence characteristics of OLEDs based on Alq3

NASA Astrophysics Data System (ADS)

Yuan, Chao; Guan, Min; Zhang, Yang; Li, Yiyang; Liu, Shuangjie; Zeng, Yiping

2017-08-01

In this work, the organic light-emitting diodes (OLEDs) based on Alq3 are fabricated. In order to make clear the transport mechanism of carriers in organic light-emitting devices at low temperature, detailed electroluminescence transient response and the current-voltage-luminescence (I-V-L) characteristics under different temperatures in those OLEDs are investigated. It founds that the acceleration of brightness increases with increasing temperature is maximum when the temperature is 200 K and it is mainly affected by the electron transport layer (Alq3). The MoO3 injection layer and the electroluminescent layer have great influence on the delay time when the temperature is 200 K. Once the temperature is greater than 250 K, the delay time is mainly affected by the MoO3 injection layer. On the contrary, the fall time is mainly affected by the electroluminescent material. The Vf is the average growth rate of fall time when the temperature increases 1 K which represents the accumulation rate of carriers. The difference between Vf caused by the MoO3 injection layer is 0.52 us/K and caused by the electroluminescent material Ir(ppy)3 is 0.73 us/K.

Ag-Decorated Localized Surface Plasmon-Enhanced Ultraviolet Electroluminescence from ZnO Quantum Dot-Based/GaN Heterojunction Diodes by Optimizing MgO Interlayer Thickness.

PubMed

Chen, Cheng; Chen, Jingwen; Zhang, Jun; Wang, Shuai; Zhang, Wei; Liang, Renli; Dai, Jiangnan; Chen, Changqing

2016-12-01

We demonstrate the fabrication and characterization of localized surface plasmon (LSP)-enhanced n-ZnO quantum dot (QD)/MgO/p-GaN heterojunction light-emitting diodes (LEDs) by embedding Ag nanoparticles (Ag-NPs) into the ZnO/MgO interface. The maximum enhancement ration of the Ag-NP-decorated LEDs in electroluminescence (EL) is 4.3-fold by optimizing MgO electron-blocking layer thickness. The EL origination was investigated qualitatively in terms of photoluminescence (PL) results. Through analysis of the energy band structure of device and carrier transport mechanisms, it suggests that the EL enhancement is attributed to the increased rate of spontaneous emission and improved internal quantum efficiency induced by exciton-LSP coupling.

Ag-Decorated Localized Surface Plasmon-Enhanced Ultraviolet Electroluminescence from ZnO Quantum Dot-Based/GaN Heterojunction Diodes by Optimizing MgO Interlayer Thickness

NASA Astrophysics Data System (ADS)

Chen, Cheng; Chen, Jingwen; Zhang, Jun; Wang, Shuai; Zhang, Wei; Liang, Renli; Dai, Jiangnan; Chen, Changqing

2016-10-01

We demonstrate the fabrication and characterization of localized surface plasmon (LSP)-enhanced n-ZnO quantum dot (QD)/MgO/p-GaN heterojunction light-emitting diodes (LEDs) by embedding Ag nanoparticles (Ag-NPs) into the ZnO/MgO interface. The maximum enhancement ration of the Ag-NP-decorated LEDs in electroluminescence (EL) is 4.3-fold by optimizing MgO electron-blocking layer thickness. The EL origination was investigated qualitatively in terms of photoluminescence (PL) results. Through analysis of the energy band structure of device and carrier transport mechanisms, it suggests that the EL enhancement is attributed to the increased rate of spontaneous emission and improved internal quantum efficiency induced by exciton-LSP coupling.

A Piezoelectroluminescent Fiber-Optical Sensor for Diagnostics of the 3D Stress State in Composite Structures

NASA Astrophysics Data System (ADS)

Pan'kov, A. A.

2018-05-01

The mathematical model of a piezoelectroluminescent fiber-optical sensor is developed for diagnostics of the 3D stress state of composite structures. The sensor model is a coaxial sector-compound layered cylinder consisting of a central optical fiber with electroluminescent and piezoelectric layers and an external uniform elastic buffer layer. The electroluminescent and piezoelectric layers are separated by radial-longitudinal boundaries, common for both layers, into geometrically equal six "measuring elements" — cylindrical two-layered sectors. The directions of 3D polarization of the piezoelectric phases and the frequencies of luminous efficacy of the electroluminescent phases are different in each sector. In the sensor, a thin translucent "internal" controlling electrode is located between the optical fiber and the electroluminescent layer, and the piezoelectric layer is coated by a thin "external" controlling electrode. The results of numerical modeling of the nonuniform coupled electroelastic fields of the piezoelectroluminescent fiber-optical sensor in the loaded "representative volume" of a composite, taking into account the action of the controlling voltage on the internal and external electrodes, of a numerical calculation of "informative and controlling coefficients" of the sensor, and of testing of an arbitrary 3D stress of state of a unidirectional glass-fiber plastic by the finite-element method are presented.

Investigation of thioglycerol stabilized ZnS quantum dots in electroluminescent device performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ethiraj, Anita Sagadevan, E-mail: anita.ethiraj@vit.ac.in; Center for Nanotechnology Research, VIT University, Vellore, TamilNadu-632014; Rhen, Dani

2016-05-06

The present work is focused on the investigation of thioglycerol (TG) stabilized Zinc Sulfide Quantum dots (ZnS QDs) in the hybrid electroluminescence (EL) device. Optical absorption spectroscopy clearly indicates the formation of narrow size distributed ZnS in the quantum confinement regime. X-ray Diffraction (XRD), Photoluminescence (PL), Energy Dispersive X-ray Spectroscopy (EDS) data supports the same. The hybrid EL device with structure of ITO (indium tin oxide)//PEDOT:PSS ((poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)//HTL (α NPD- N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-phenyl)-4,4′-diamine// PVK:ZnS QDs//ETL(PBD- 2-tert-butylphenyl- 5-biphenyl-1,3,4-oxadiazole)//LiF:Al (Device 1) was fabricated. Reference device without the ZnS QDs were also prepared (Device 2). The results show that the ZnS QDs based device exhibitedmore » bright electroluminescence emission of 24 cd/m{sup 2} at a driving voltage of 16 Volts under the forward bias conditions as compared to the reference device without the ZnS QDs, which showed 6 cd/m{sup 2} at ∼22 Volts.« less

Polymer and small molecule based hybrid light source

DOEpatents

Choong, Vi-En; Choulis, Stelios; Krummacher, Benjamin Claus; Mathai, Mathew; So, Franky

2010-03-16

An organic electroluminescent device, includes: a substrate; a hole-injecting electrode (anode) coated over the substrate; a hole injection layer coated over the anode; a hole transporting layer coated over the hole injection layer; a polymer based light emitting layer, coated over the hole transporting layer; a small molecule based light emitting layer, thermally evaporated over the polymer based light emitting layer; and an electron-injecting electrode (cathode) deposited over the electroluminescent polymer layer.

Optimisation of GaN LEDs and the reduction of efficiency droop using active machine learning

DOE PAGES

Rouet-Leduc, Bertrand; Barros, Kipton Marcos; Lookman, Turab; ...

2016-04-26

A fundamental challenge in the design of LEDs is to maximise electro-luminescence efficiency at high current densities. We simulate GaN-based LED structures that delay the onset of efficiency droop by spreading carrier concentrations evenly across the active region. Statistical analysis and machine learning effectively guide the selection of the next LED structure to be examined based upon its expected efficiency as well as model uncertainty. This active learning strategy rapidly constructs a model that predicts Poisson-Schrödinger simulations of devices, and that simultaneously produces structures with higher simulated efficiencies.

Theoretical and material studies on thin-film electroluminescent devices

NASA Technical Reports Server (NTRS)

Summers, C. J.; Brennan, K. F.

1986-01-01

Electroluminescent materials and device technology were assessed. The evaluation strongly suggests the need for a comprehensive theoretical and experimental study of both materials and device structures, particularly in the following areas: carrier generation and multiplication; radiative and nonradiative processes of luminescent centers; device modeling; new device concepts; and single crystal materials growth and characterization. Modeling of transport properties of hot electrons in ZnSe and the generation of device concepts were initiated.

High-sensitivity strain visualization using electroluminescence technologies

NASA Astrophysics Data System (ADS)

Xu, Jian; Jo, Hongki

2016-04-01

Visualizing mechanical strain/stress changes is an emerging area in structural health monitoring. Several ways are available for strain change visualization through the color/brightness change of the materials subjected to the mechanical stresses, for example, using mechanoluminescence (ML) materials and mechanoresponsive polymers (MRP). However, these approaches were not effectively applicable for civil engineering system yet, due to insufficient sensitivity to low-level strain of typical civil structures and limitation in measuring both static and dynamic strain. In this study, design and validation for high-sensitivity strain visualization using electroluminescence technologies are presented. A high-sensitivity Wheatstone bridge, of which bridge balance is precisely controllable circuits, is used with a gain-adjustable amplifier. The monochrome electroluminescence (EL) technology is employed to convert both static and dynamic strain change into brightness/color change of the EL materials, through either brightness change mode (BCM) or color alternation mode (CAM). A prototype has been made and calibrated in lab, the linearity between strain and brightness change has been investigated.

D-A-D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies.

PubMed

Gan, Lin; Li, Xianglong; Cai, Xinyi; Liu, Kunkun; Li, Wei; Su, Shi-Jian

2018-01-01

The design of orange-light emitting, thermally activated, delayed fluorescence (TADF) materials is necessary and important for the development and application of organic light-emitting diodes (OLEDs). Herein, two donor-acceptor-donor (D-A-D)-type orange TADF materials based on fluorenone and acridine, namely 2,7-bis(9,9-dimethylacridin-10(9 H )-yl)-9 H -fluoren-9-one (27DACRFT, 1 ) and 3,6-bis(9,9-dimethylacridin-10(9 H )-yl)-9 H -fluoren-9-one (36DACRFT, 2 ), were successfully synthetized and characterized. The studies on their structure-property relationship show that the different configurations have a serious effect on the photoluminescence and electroluminescence performance according to the change in singlet-triplet splitting energy (Δ E ST ) and excited state geometry. This indicates that a better configuration design can reduce internal conversion and improve triplet exciton utilization of TADF materials. Importantly, OLEDs based on 2 exhibited a maximum external quantum efficiency of 8.9%, which is higher than the theoretical efficiency of the OLEDs based on conventional fluorescent materials.

Electroluminescence from single-wall carbon nanotube network transistors.

PubMed

Adam, E; Aguirre, C M; Marty, L; St-Antoine, B C; Meunier, F; Desjardins, P; Ménard, D; Martel, R

2008-08-01

The electroluminescence (EL) properties from single-wall carbon nanotube network field-effect transistors (NNFETs) and small bundle carbon nanotube field effect transistors (CNFETs) are studied using spectroscopy and imaging in the near-infrared (NIR). At room temperature, NNFETs produce broad (approximately 180 meV) and structured NIR spectra, while they are narrower (approximately 80 meV) for CNFETs. EL emission from NNFETs is located in the vicinity of the minority carrier injecting contact (drain) and the spectrum of the emission is red shifted with respect to the corresponding absorption spectrum. A phenomenological model based on a Fermi-Dirac distribution of carriers in the nanotube network reproduces the spectral features observed. This work supports bipolar (electron-hole) current recombination as the main mechanism of emission and highlights the drastic influence of carrier distribution on the optoelectronic properties of carbon nanotube films.

Unusual near-white electroluminescence of light emitting diodes based on saddle-shaped porphyrins.

PubMed

Shahroosvand, Hashem; Zakavi, Saeed; Sousaraei, Ahmad; Mohajerani, Ezeddin; Mahmoudi, Malek

2015-05-14

In contrast to the red electroluminescence emission frequently observed in porphyrins based OLED devices, the present devices exhibit a nearly white emission with greenish yellow, yellowish green and blue green hues in the case of Fe(II)(TCPPBr6) (TCPPBr6 = β-hexabromo-meso-tetrakis-(4-phenyl carboxyl) porphyrinato), Zn(II)(TPPBr6) and Co(II)(TPPBr6), respectively.

Advancements in the Quantification of the Crystal Structure of ZNS Materials Produced in Variable Gravity

NASA Astrophysics Data System (ADS)

Castillo, Martin

2016-07-01

Screens and displays consume tremendous amounts of power. Global trends to significantly consume less power and increase battery life have led to the reinvestigation of electroluminescent materials. The state of the art in ZnS materials has not been furthered in the past 30 years and there is much potential in improving electroluminescent properties of these materials with advanced processing techniques. Self-propagating high temperature synthesis (SHS) utilises a rapid exothermic process involving high energy and nonlinearity coupled with a high cooling rate to produce materials formed outside of normal equilibrium boundaries thus possessing unique properties. The elimination of gravity during this process allows capillary forces to dominate mixing of the reactants which results in a superior and enhanced homogeneity in the product materials. ZnS type materials have been previously conducted in reduced gravity and normal gravity. It has been claimed in literature that a near perfect phases of ZnS wurtzite was produced. Although, the SHS of this material is possible at high pressures, there has been no quantitative information on the actual crystal structures and lattice parameters that were produced in this work. Utilising this process with ZnS doped with Cu, Mn, or rare earth metals such as Eu and Pr leads to electroluminescence properties, thus making this an attractive electroluminescent material. The work described here will revisit the synthesis of ZnS via high pressure SHS and will re-examine the work performed in both normal gravity and in reduced gravity within the ZARM drop tower facility. Quantifications in the lattice parameters, crystal structures, and phases produced will be presented to further explore the unique structure-property performance relationships produced from the SHS of ZnS materials.

Microstructure and electroluminescent performance of chemical vapor deposited zinc sulfide doped with manganese films for integration in thin film electroluminescent devices

NASA Astrophysics Data System (ADS)

Topol, Anna Wanda

Zinc sulfide (ZnS) doped with manganese (Mn), ZnS:Mn, is widely recognized as the brightest and most effective electroluminescent (EL) phosphor used in current thin film electroluminescent (TFEL) devices. ZnS acts as a host lattice for the luminescent activator, Mn, leading to a highly efficient yellow-orange EL emission, and resulting in a wide array of applications in monochrome, multi-color and full color displays. Although this wide band dap (3.7 eV) material can be prepared by several deposition techniques, the chemical vapor deposition (CVD) is the most promising for TFEL applications in terms of viable deposition rates, high thickness and composition uniformity, and excellent yield over large area panels. This study describes the development and optimization of a CVD ZnS:Mn process using diethylzinc [(C2H5)2Zn, DEZ], di-pi-cyclopentadienylmanganese [(C5H5)2Mn, CPMn], and hydrogen sulfide [H2S] as the chemical sources for, respectively, Zn, Mn, and S. The effects of key deposition parameters on resulting Film microstructure and performance are discussed, primarily in the context of identifying an optimized process window for best electroluminescence behavior. In particular, substrate temperature was observed to play a key role in the formation of high quality crystalline ZnS:Mn films leading to improved brightness and EL efficiency. Further investigations of the influence of temperature treatment on the structural characteristics and EL performance of the CVD ZnS:Mn film were carried out. In this study, the influence of post-deposition annealing both in-situ and ex-situ annealing processes, on chemical, structural, and electroluminescent characteristics of the phosphor layer are described. The material properties of the employed dielectric are among the key factors determining the performance, stability and reliability of the TFEL display and therefore, the choice of dielectric material for use in ACTFEL displays is crucial. In addition, the luminous efficiency depends on the density of the interface states and their depth at the insulator-phosphor interfaces. Hence, critical integration issues are discussed in terms of the incorporation of ZnS:Mn films in dielectricsemiconductor-dielectric (DSD) structures with silicon nitride (SiNx) and aluminum titanium oxide (ATO) as top and bottom insulators.

Pure white OLED based on an organic small molecule: 2,6-Di(1H-benzo[d]imidazol-2-yl)pyridine.

PubMed

Liu, Jian

2015-10-05

2,6-Di(1H-benzo[d]imidazol-2-yl)pyridine (DBIP) was synthesized. The single-crystal structure of DBIP was resolved. DBIP-based OLED was fabricated. The electroluminescence for the device corresponds to a pure white emission. In addition, thermal stability, UV-vis, photoluminescence and electrochemical behaviors of DBIP were investigated as well. Copyright © 2015 Elsevier B.V. All rights reserved.

Multilayer organic based structures with enhanced hole transport

NASA Astrophysics Data System (ADS)

Mladenova, D.; Sinigersky, V.; Budurova, D.; Dobreva, T.; Karashanova, D.; Dimov, D.; Zhivkov, I.

2010-11-01

Multilayer Organic Based Devices (OBDs) were constructed by subsequent casting of organic films (from polymers, soluble in the same organic solvent). The problem with dissolution of the underlying layer was avoided by using electrophoretic deposition technique. Optimized conditions for electrophoretic deposition (EPD) of thin films with homogeneous and smooth surfaces, as confirmed by SEM, were found. The EPD, carried out at constant current, requires continuous increase of the voltage between the electrodes. In this way the decreased deposition rate caused by the decreased concentration of the material in the suspension and the increased thickness of the film deposited is compensated. The SEM images and the current voltage characteristics recorded, show that the hole transport polyvinylcarbazole (PVK) underlayer survive the treatment with the suspension used for the electrophoretic deposition of the active poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene vinylene] electroluminescent layer. The PVK hole transport layer increases the device current, as confirmed by the current-voltage measurements. The results obtained demonstrate the possibility of OBDs preparation for electroluminescent and photovoltaic applications.

Electroluminescence of ZnO-based semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Novodvorskii, O. A.; Lotin, A. A.; Panchenko, Vladislav Ya; Parshina, L. S.; Khaidukov, E. V.; Zuev, D. A.; Khramova, O. D.

2011-01-01

Using pulsed laser deposition, we have grown n-ZnO/p-GaN, n-ZnO/i-ZnO/p-GaN and n-ZnO/n-Mg0.2Zn0.8O/i-Cd0.2Zn0.8O/p-GaN light-emitting diode (LED) heterostructures with peak emission wavelengths of 495, 382 and 465 nm and threshold current densities (used in electroluminescence measurements) of 1.35, 2, and 0.48 A cm-2, respectively. Because of the spatial carrier confinement, the n-ZnO/n-Mg0.2Zn0.8O/i-Cd0.2Zn0.8O/p-GaN double heterostructure LED offers a higher electroluminescence intensity and lower electroluminescence threshold in comparison with the n-ZnO/p-GaN and n-ZnO/i-ZnO/p-GaN LEDs.

Effect of uniaxial stress on electroluminescence, valence band modification, optical gain, and polarization modes in tensile strained p-AlGaAs/GaAsP/n-AlGaAs laser diode structures: Numerical calculations and experimental results

NASA Astrophysics Data System (ADS)

Bogdanov, E. V.; Minina, N. Ya.; Tomm, J. W.; Kissel, H.

2012-11-01

The effects of uniaxial compression in [110] direction on energy-band structures, heavy and light hole mixing, optical matrix elements, and gain in laser diodes with "light hole up" configuration of valence band levels in GaAsP quantum wells with different widths and phosphorus contents are numerically calculated. The development of light and heavy hole mixing caused by symmetry lowering and converging behavior of light and heavy hole levels in such quantum wells under uniaxial compression is displayed. The light or heavy hole nature of each level is established for all considered values of uniaxial stress. The results of optical gain calculations for TM and TE polarization modes show that uniaxial compression leads to a significant increase of the TE mode and a minor decrease of the TM mode. Electroluminescence experiments were performed under uniaxial compression up to 5 kbar at 77 K on a model laser diode structure (p-AlxGa1-xAs/GaAs1-yPy/n-AlxGa1-xAs) with y = 0.16 and a quantum well width of 14 nm. They reveal a maximum blue shift of 27 meV of the electroluminescence spectra that is well described by the calculated change of the optical gap and the increase of the intensity being referred to a TE mode enhancement. Numerical calculations and electroluminescence data indicate that uniaxial compression may be used for a moderate wavelength and TM/TE intensity ratio tuning.

Luminescence studies of HgCdTe- and InAsSb-based quantum-well structures

NASA Astrophysics Data System (ADS)

Izhnin, I. I.; Izhnin, A. I.; Fitsych, O. I.; Voitsekhovskii, A. V.; Gorn, D. I.; Semakova, A. A.; Bazhenov, N. L.; Mynbaev, K. D.; Zegrya, G. G.

2018-04-01

Results of photoluminescence studies of single-quantum-well HgCdTe-based structures and electroluminescence studies of multiple-quantum-well InAsSb-based structures are reported. HgCdTe structures were grown with molecular beam epitaxy on GaAs substrates. InAsSb-based structures were grown with metal-organic chemical vapor deposition on InAs substrates. The common feature of luminescence spectra of all the structures was the presence of peaks with the energy much larger than that of calculated optical transitions between the first quantization levels for electrons and heavy holes. Possibility of observation of optical transitions between the quantization levels of electrons and first and/or second heavy and light hole levels is discussed in the paper in relation to the specifics of the electronic structure of the materials under consideration.

Single-layer electroluminescent devices based on fluorene-1H-pyrazolo[3,4-b]quinoxaline co-polymers

NASA Astrophysics Data System (ADS)

Pokladko-Kowar, Monika; Danel, Andrzej; Chacaga, Łukasz

2013-11-01

A fluorene based copolymer was synthesized for electroluminescent application. To the main chain of polymer the nitrogen heterocyclic, 1H-pyrazolo[3,4-b]quinoxaline, unit was introduced. The incorporation of this derivative tuned the emission from the blue to yellow-green one. A simple, single layered device was fabricated with the configuration ITO/PEDOT/co-poly-FLU-PQX/Ca/Mg.

Luminescence and related properties of nanocrystalline porous silicon

NASA Astrophysics Data System (ADS)

Koshida, N.

This document is part of subvolume C3 'Optical Properties' of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter, on the optical properties of quantum structures based on group IV semiconductors. It discusses luminescence and related properties of nanocrystalline porous silicon. Topics include an overview of nanostructured silicon, its fabrication technology, and properties of nanocrystalline porous silicon such as confinement effects, photoluminescence, electroluminesce, carrier charging effects, ballistic transport and emission, and thermally induced acoustic emission.

Photo- and electroluminescence of sulfide and silicate phosphors embedded in synthetic opal

NASA Astrophysics Data System (ADS)

Kaplan, S. F.; Kartenko, N. F.; Kurdyukov, D. A.; Medvedev, A. V.; Badalyan, A. G.; Golubev, V. G.

2007-02-01

The sulfide (ZnS:Mn, Zn xCd 1 -xS:Mn, Zn xCd 1- xS:Ag) and silicate (Zn 2SiO 4:Mn) phosphors were synthesized directly inside the pores of synthetic opal by chemical bath deposition. These composites are perfect three-dimensional photonic crystals, which produce effective photo- and electroluminescence at room temperature. The emission spectra are considerably modified by the photonic crystal structure to become anisotropic in accordance with the photonic band gap angular dispersion.

Pure circular polarization electroluminescence at room temperature with spin-polarized light-emitting diodes.

PubMed

Nishizawa, Nozomi; Nishibayashi, Kazuhiro; Munekata, Hiro

2017-02-21

We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spin-polarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation. There are two small schemes in the tested spin-LEDs: first, the stripe-laser-like structure that helps intensify the EL light at the cleaved side walls below the spin injector Fe slab, and second, the crystalline AlO x spin-tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density ( J ) region, whereas it increases steeply and reaches close to the pure CP when J > 100 A/cm 2 There, either right- or left-handed CP component is significantly suppressed depending on the direction of magnetization of the spin injector. Spin-dependent reabsorption, spin-induced birefringence, and optical spin-axis conversion are suggested to account for the observed experimental results.

Electroluminescence of ZnO-based semiconductor heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novodvorskii, O A; Lotin, A A; Panchenko, Vladislav Ya

2011-01-31

Using pulsed laser deposition, we have grown n-ZnO/p-GaN, n-ZnO/i-ZnO/p-GaN and n-ZnO/n-Mg{sub 0.2}Zn{sub 0.8}O/i-Cd{sub 0.2}Zn{sub 0.8}O/p-GaN light-emitting diode (LED) heterostructures with peak emission wavelengths of 495, 382 and 465 nm and threshold current densities (used in electroluminescence measurements) of 1.35, 2, and 0.48 A cm{sup -2}, respectively. Because of the spatial carrier confinement, the n-ZnO/n-Mg{sub 0.2}Zn{sub 0.8}O/i-Cd{sub 0.2}Zn{sub 0.8}O/p-GaN double heterostructure LED offers a higher electroluminescence intensity and lower electroluminescence threshold in comparison with the n-ZnO/p-GaN and n-ZnO/i-ZnO/p-GaN LEDs. (lasers)

Polarized electroluminescence from edge-emission organic light emitting devices

NASA Astrophysics Data System (ADS)

Ran, G. Z.; Jiang, D. F.

2011-01-01

We report the experimental observation and measurement of the polarized electroluminescence from an edge-emission Si based- organic light emitting device (OLED) with a Sm/Au or Sm/Ag cathode. Light collected from the OLED edge comes from the scattering of the surface plasmon polaritons (SPPs) at the device boundary. This experiment shows that such Si-OLED can be an electrically excited SPP source on a silicon chip for optical interconnect based on SPPs.

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

NASA Astrophysics Data System (ADS)

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

2016-12-01

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method of enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission.

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method ofmore » enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission« less

Low-voltage polariton electroluminescence from an ultrastrongly coupled organic light-emitting diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gubbin, Christopher R.; Maier, Stefan A.; Kéna-Cohen, Stéphane, E-mail: s.kena-cohen@polymtl.ca

2014-06-09

We demonstrate electroluminescence from Frenkel molecular excitons ultrastrongly coupled to photons of a metal-clad microcavity containing a 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene emissive layer. Thin layers of molybdenum oxide and 4,7-diphenyl-1,10-phenanthroline are used as hole and electron injection layers, respectively. The fabricated devices exhibit an electroluminescence threshold of 3.1 V, a value that is below the bare exciton energy. This result is found to be independent of detuning and consistent with a two-step process for polariton formation. Moreover, we investigate the quantum efficiency of carrier to polariton to photon conversion and obtain an external quantum efficiency of 0.1% for the fabricated structures, an improvement ofmore » 5 orders of magnitude over previous reports.« less

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

DOE PAGES

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

2016-12-12

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method ofmore » enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission« less

Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts.

PubMed

Cui, Lin-Song; Ruan, Shi-Bin; Bencheikh, Fatima; Nagata, Ryo; Zhang, Lei; Inada, Ko; Nakanotani, Hajime; Liao, Liang-Sheng; Adachi, Chihaya

2017-12-21

Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.

2-(2-Hydroxyphenyl)imidazole-based four-coordinate organoboron compounds with efficient deep blue photoluminescence and electroluminescence.

PubMed

Zhang, Zhenyu; Zhang, Zuolun; Zhang, Hongyu; Wang, Yue

2017-12-19

Two new four-coordinate organoboron compounds with 2-(2-hydroxyphenyl)imidazole derivatives as the chelating ligands have been synthesized. They possess high thermal stability and are able to form an amorphous glass state. Crystallographic analyses indicate that the differences in ligand structure cause the change of ππ stacking character. The CH 2 Cl 2 solutions and thin films of these compounds display bright blue emission, and these compounds have appropriate HOMO and LUMO energy levels for carrier injection in OLEDs. By utilizing the good thermal and luminescent properties, as well as the proper frontier orbital energy levels, bright non-doped OLEDs with a simple structure have been realized. Notably, these simple devices show deep blue electroluminescence with the Commission Internationale de l'Éclairage (CIE) coordinate of ca. (0.16, 0.08), which is close to the CIE coordinate of (0.14, 0.08) for standard blue defined by the National Television System Committee. In addition, one of the devices exhibits good performance, showing brightness, current efficiency, power efficiency and external quantum efficiency up to 2692 cd m -2 , 2.50 cd A -1 , 1.81 lm W -1 and 3.63%, respectively. This study not only provides good deep-blue emitting OLED materials that are rarely achieved by using four-coordinate organoboron compounds, but also allows a deeper understanding of the structure-property relationship of 2-(2-hydroxyphenyl)imidazole-based boron complexes, which benefits the further structural design of this type of material.

On the shift of the electroluminescence spectra of In{sub x}Ga{sub 1−x}N/GaN structures with various indium contents and various substrate materials caused by the stark effect and mechanical stresses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veleschuk, V. P., E-mail: vvvit@ukr.nd; Vlasenko, A. I.; Kisselyuk, M. P.

2015-08-15

The shift between the maxima of the electroluminescence spectra of In{sub x}Ga{sub 1−x}N/GaN structures is measured at forward and reverse bias depending on the indium content x in the quantum well and on the substrate material (SiC, AuSn/Si, and Al{sub 2}O{sub 3}). It is established that this shift increases as the indium concentration in the In{sub x}Ga{sub 1−x}N layer and mechanical stresses from the substrate increase.

Strain-free Ge/GeSiSn Quantum Cascade Lasers Based on L-Valley Intersubband Transitions

DTIC Science & Technology

2007-01-01

found in III-V quantum cascade lasers QCLs. Various groups have obtained electroluminescence from Si-rich Si/SiGe quantum cascade structures,2–4 but...Ge/GeSiSn quantum cascade lasers based on L-valley intersubband transitions 5c. PROGRAM ELEMENT NUMBER 612305 6. AUTHOR(S) 5d. PROJECT NUMBER...ABSTRACT The authors propose a Ge/Ge0.76Si0.19Sn0.05 quantum cascade laser using intersubband transitions at L valleys of the conduction band

Semiconductor Terahertz Technology

DTIC Science & Technology

2009-06-15

is found in IJI-V quantum cascade lasers (QCLs). 1.I Brief overview of 5i-based QCL development Various groups have obtained electroluminescence from...sources and detectors of far-IR radiation in the range of 12-30 flm. These devices, especially quantum cascade lasers (QCLs) require efficient ...elements and their alloys that can be developed on Si substrates. The design work focused on the structure of the so-called quantum cascade laser

Direct Integration of Dynamic Emissive Displays into Knitted Fabric Structures

NASA Astrophysics Data System (ADS)

Bellingham, Alyssa

Smart textiles are revolutionizing the textile industry by combining technology into fabric to give clothing new abilities including communication, transformation, and energy conduction. The advent of electroluminescent fibers, which emit light in response to an applied electric field, has opened the door for fabric-integrated emissive displays in textiles. This thesis focuses on the development of a flexible and scalable emissive fabric display with individually addressable pixels disposed within a fabric matrix. The pixels are formed in areas where a fiber supporting the dielectric and phosphor layers of an electroluminescent structure contacts a conductive surface. This conductive surface can be an external conductive fiber, yarn or wire, or a translucent conductive material layer deposited at set points along the electroluminescent fibers. Different contacting methods are introduced and the different ways the EL yarns can be incorporated into the knitted fabric are discussed. EL fibers were fabricated using a single yarn coating system with a custom, adjustable 3D printed slot die coater for even distribution of material onto the supporting fiber substrates. These fibers are mechanically characterized inside of and outside of a knitted fabric matrix to determine their potential for various applications, including wearables. A 4-pixel dynamic emissive display prototype is fabricated and characterized. This is the first demonstration of an all-knit emissive display with individually controllable pixels. The prototype is composed of a grid of fibers supporting the dielectric and phosphor layers of an electroluminescent (EL) device structure, called EL fibers, and conductive fibers acting as the top electrode. This grid is integrated into a biaxial weft knit structure where the EL fibers make up the rows and conductive fibers make up the columns of the reinforcement yarns inside the supporting weft knit. The pixels exist as individual segments of electroluminescence that occur where the conductive fibers contact the EL fibers. A passive matrix addressing scheme was used to apply a voltage to each pixel individually, creating a display capable of dynamically communicating information. Optical measurements of the intensity and color of emitted light were used to quantify the performance of the display and compare it to state-of-the-art display technologies. The charge-voltage (Q-V) electrical characterization technique is used to gain information about the ACPEL fiber device operation, and mechanical tests were performed to determine the effect everyday wear and tear would have on the performance of the display. The presented textile display structure and method of producing fibers with individual sections of electroluminescence addresses the shortcomings in existing textile display technology and provides a route to directly integrated communicative textiles for applications ranging from biomedical research and monitoring to fashion. An extensive discussion of the materials and methods of production needed to scale this textile display technology and incorporate it into wearable applications is presented.

2D Semiconductors for Valley-Polarized LEDs and Photodetectors

NASA Astrophysics Data System (ADS)

Yu, Ting

The recently discovered two-dimensional (2D) semiconductors, such as transitional-metal-dichalcogenide monolayers, have aroused great interest due to the underlying quantum physics and the appealing optoelectronic applications like atomically thin light-emitting diodes (LEDs) and photodetectors. On the one hand, valley-polarized electroluminescence and photocurrent from such monolayers have not caused enough attention but highly demanded as building blocks for the new generation valleytronic applications. On the other hand, most reports on these devices are based on the mechanically exfoliated small samples. Considering real applications, a strategy which could offer mass-product and high compatibility to the current planar processes is greatly demanded. Large-area samples prepared by chemical vapour deposition (CVD) are perfect candidates towards such a goal. Here, we report electrically tunable valley-polarized electroluminescence and the selective spin-valley-coupled photocurrent in optoelectronic devices based on monolayer WS2 and MoS2 grown by CVD, exhibiting large electroluminescence and photocurrent dichroisms of 81% and 60%, respectively. The controllable valley polarization and emission components of the electroluminescence have been realized by varying electrical injection of carriers. For the observed helicity-dependent photocurrent, the circular photogalvanic effect at resonant excitations has been found to take the dominant responsibility.

Poly[(arylene ethynylene)-alt-(arylene vinylene)]s Based on Anthanthrone and Its Derivatives: Synthesis and Photophysical, Electrochemical, Electroluminescent, and Photovoltaic Properties

PubMed Central

2017-01-01

Anthanthrone and its derivatives are large polycyclic aromatic compounds (PACs) that pose a number of challenges for incorporation into the structure of soluble conjugated polymers. For the first time, this group of PACs was employed as the building blocks for the synthesis of copolymers (P1–P5) based on poly[(arylene ethynylene)-alt-(arylene vinylene)]s backbone (−Ph–C≡C–Anth–C≡C–Ph–CH=CH–Ph–CH=CH−)n. During the synthesis of P1–P5, different alkyloxy side chains were incorporated in order to tune the properties of the polymers. Of the copolymer series only P1 (containing anthanthrone and branched 2-ethylhexyloxy side chains on phenylenes), P2 and P3 (for which the anthanthrones containing carbonyl groups were converted to anthanthrene containing alkyloxy substituents) were soluble. The photophysical, electrochemical, electroluminescent and photovoltaic properties of P1–P3 are reported, compared and discussed with respect to the effects of side chains. PMID:29151617

Effect of deep centers on the radiative characteristics of epitaxial structures in the Ga-As-P system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ermakov, O.P.

1986-08-01

This paper studies the radiative characteristics of structures not doped with nitrogen based on AgP and GaAs /SUB 1-y/ P /SUB y/ in a wide range of compositions, containing stoichiometry and radiation defects. The structures studied were obtained by the methods of liquid-phase and gas-phase epitaxy. Zn was used as the acceptor impurity in obtaining the p-n structures. The radiation defects were introduced by irradiation with a beam of fast 2.5-MeV electrons and the radiative characteristics were studied with the help of the method of electroluminescence (EL).

GaN-based light emitting diodes using p-type trench structure for improving internal quantum efficiency

NASA Astrophysics Data System (ADS)

Kim, Garam; Sun, Min-Chul; Kim, Jang Hyun; Park, Euyhwan; Park, Byung-Gook

2017-01-01

In order to improve the internal quantum efficiency of GaN-based LEDs, a LED structure featuring a p-type trench in the multi-quantum well (MQW) is proposed. This structure has effects on spreading holes into the MQW and reducing the quantum-confined stark effect (QCSE). In addition, two simple fabrication methods using electron-beam (e-beam) lithography or selective wet etching for manufacturing the p-type structure are also proposed. From the measurement results of the manufactured GaN-based LEDs, it is confirmed that the proposed structure using e-beam lithography or selective wet etching shows improved light output power compared to the conventional structure because of more uniform hole distribution. It is also confirmed that the proposed structure formed by e-beam lithography has a significant effect on strain relaxation and reduction in the QCSE from the electro-luminescence measurement.

Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands.

PubMed

Kaplunov, Mikhail G; Krasnikova, Svetlana S; Nikitenko, Sergey L; Sermakasheva, Natalia L; Yakushchenko, Igor K

2012-04-03

We have investigated the electroluminescence spectra of the electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and quinolines containing the C-N-M-N chains in their chelate cycles. The spectra exhibit strong exciplex bands in the green to yellow region 540 to 590 nm due to interaction of the excited states of zinc complexes and triaryl molecules of the hole-transporting layer. For some devices, the intrinsic luminescence band of 460 nm in the blue region is also observed along with the exciplex band giving rise to an almost white color of the device emission. The exciplex band can be eliminated if the material of the hole-transporting layer is not a triarylamine derivative. We have also found the exciplex emission in the photoluminescence spectra of the films containing blends of zinc complex and triphenylamine material.

Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands

PubMed Central

2012-01-01

We have investigated the electroluminescence spectra of the electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and quinolines containing the C-N-M-N chains in their chelate cycles. The spectra exhibit strong exciplex bands in the green to yellow region 540 to 590 nm due to interaction of the excited states of zinc complexes and triaryl molecules of the hole-transporting layer. For some devices, the intrinsic luminescence band of 460 nm in the blue region is also observed along with the exciplex band giving rise to an almost white color of the device emission. The exciplex band can be eliminated if the material of the hole-transporting layer is not a triarylamine derivative. We have also found the exciplex emission in the photoluminescence spectra of the films containing blends of zinc complex and triphenylamine material. PMID:22471942

Hole-exciton interaction induced high field decay of magneto-electroluminescence in Alq3-based organic light-emitting diodes at room temperature

NASA Astrophysics Data System (ADS)

Zhang, Tingting; Holford, D. F.; Gu, Hang; Kreouzis, T.; Zhang, Sijie; Gillin, W. P.

2016-01-01

The magnetic field effects on the electroluminescence of aluminium tris-(8-hydroxyqinoline) (Alq3) based organic light emitting diodes have been investigated by varying the electron/hole ratio in the emissive layer. Experimental results reveal that a negative high field effect in the magneto-electroluminescence (MEL) can be found in devices with very low triplet exciton concentration at room temperature. This suggests triplet-triplet annihilation cannot be used to explain the negative high field MEL in the Alq3 system. Our results suggest that hole-exciton interaction may be the origin of the negative high field MEL and also, in parallel with this interaction, there is also the more common positive high field process occurring which has been tentatively attributed to electron-exciton interactions. The competition between these different processes decides the final shape of the MEL at high fields.

Magnetically modulated electroluminescence from hybrid organic/inorganic light-emitting diodes based on electron donor-acceptor exciplex blends

NASA Astrophysics Data System (ADS)

Pang, Zhiyong; Baniya, Sangita; Zhang, Chuang; Sun, Dali; Vardeny, Z. Valy

2016-03-01

We report room temperature magnetically modulated electroluminescence from a hybrid organic/inorganic light-emitting diode (h-OLED), in which an inorganic magnetic tunnel junction (MTJ) with large room temperature magnetoresistance is coupled to an N,N,N ',N '-Tetrakis(4-methoxyphenyl)benzidine (MeO-TPD): tris-[3-(3-pyridyl)mesityl]borane (3TPYMB) [D-A] based OLED that shows thermally activated delayed luminescence. The exciplex-based OLED provides two spin-mixing channels: upper energy channel of polaron pairs and lower energy channel of exciplexes. In operation, the large resistance mismatch between the MTJ and OLED components is suppressed due to the non-linear I-V characteristic of the OLED. This leads to enhanced giant magneto-electroluminescence (MEL) at room temperature. We measured MEL of ~ 75% at ambient conditions. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

NCN-Coordinating Ligands based on Pyrene Structure with Potential Application in Organic Electronics.

PubMed

Zych, Dawid; Kurpanik, Aneta; Slodek, Aneta; Maroń, Anna; Pająk, Michał; Szafraniec-Gorol, Grażyna; Matussek, Marek; Krompiec, Stanisław; Schab-Balcerzak, Ewa; Kotowicz, Sonia; Siwy, Mariola; Smolarek, Karolina; Maćkowski, Sebastian; Danikiewicz, Witold

2017-11-07

Five novel derivatives of pyrene, substituted at positions 1,3,6,8 with 4-(2,2-dimethylpropyloxy)pyridine (P1), 4-decyloxypyridine (P2), 4-pentylpyridine (P3), 1-decyl-1,2,3-triazole (P4), and 1-benzyl-1,2,3-triazole (P5), are obtained through a Suzuki-Miyaura cross-coupling reaction or Cu I -catalyzed 1,3-dipolar cycloaddition reaction, respectively, and characterized thoroughly. TGA measurements reveal the high thermal stability of the compounds. Pyrene derivatives P1-P5 all show photoluminescence (PL) quantum yields (Φ) of approximately 75 % in solution. Solid-state photo- and electroluminescence characteristics of selected compounds as organic light-emitting diodes are tested. In the guest-host configuration, two matrixes, that is, poly(N-vinylcarbazole) (PVK) and a binary matrix consisting of PVK and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (50:50 wt %), are applied. The diodes show red, green, or blue electroluminescence, depending on both the compound chemical structure and the actual device architecture. In addition, theoretical studies (DFT and TD-DFT) provide a deeper understanding of the experimental results. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Luminescence in Sulfides: A Rich History and a Bright Future

PubMed Central

Smet, Philippe F.; Moreels, Iwan; Hens, Zeger; Poelman, Dirk

2010-01-01

Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles.

Transparent Conductive Ink for Additive Manufacturing

NASA Technical Reports Server (NTRS)

Patlan, X. J.; Rolin, T. D.

2017-01-01

NASA analyzes, tests, packages, and fabricates electrical, electronic, and electromechanical (EEE) parts. Nanotechnology is listed in NASA's Technology Roadmap as a key area to invest for further development.1 This research project focused on using nanotechnology to improve electroluminescent lighting in terms of additive manufacturing and to increase energy efficiency. Specifically, this project's goal was to produce a conductive but transparent printable ink that can be sprayed on any surface for use as one of the electrodes in electroluminescent device design. This innovative work is known as thick film dielectric electroluminescent (TDEL) technology. TDEL devices are used for "backlighting, illumination, and identification due to their tunable color output, scalability, and efficiency" (I.K. Small, T.D. Rolin, and A.D. Shields, "3D Printed Electroluminescent Light Panels," NASA Fiscal Year 2017 Center Innovation Fund Proposal, unpublished data, 2017). These devices use a 'front-to-back' printing method, where the substrate is the transparent layer, and the dielectric and phosphor are layered on top. This project is a first step in the process of creating a 3D printable 'back-to-front' electroluminescent device. Back-to-front 3D-printed devices are beneficial because they can be printed onto different substrates and embedded in different surfaces, and the substrate is not required to be transparent, all because the light is emitted from the top surface through the transparent conductor. Advances in this area will help further development of printing TDEL devices on an array of different surfaces. Figure 1 demonstrates the layering of the two electrodes that are aligned in a parallel plate capacitor structure (I.K. Small, T.D. Rolin, and A.D. Shields, "3D Printed Electroluminescent Light Panels," NASA Fiscal Year 2017 Center Innovation Fund Proposal, unpublished data, 2017). Voltage is applied across the device, and the subsequent electron excitation results in light emission at the top layer.

Manufacturing Methods and Engineering for TFT Addressed Display.

DTIC Science & Technology

1980-02-20

type required for the Army’s DMD (Digital Message Device), based on an active-matrix addressed electroluminescent display previously developed by...electroluminescent phosphor as the light emitter, and finally packaging or encapsulation. Because of size limitations of the pilot manufacturing facility, the DMD ...display was designed as two identical halves, which were then to be made individually in the auto- mated machine and later assembled into a single DMD

Highly efficient organic electroluminescent diodes realized by efficient charge balance with optimized electron and hole transport layers

NASA Astrophysics Data System (ADS)

Khan, M. A.; Xu, Wei; Wei, Fuxiang; Bai, Yu; Jiang, X. Y.; Zhang, Z. L.; Zhu, W. Q.

2007-11-01

Highly efficient organic electroluminescent devices (OLEDs) were developed based on 4,7-diphenyl-1, 10-phenanthroline (BPhen) as the electron transport layer (ETL), tris-(8-hydroxyquinoline) aluminum (Alq 3) as the emission layer (EML) and N,Ń-bis-[1-naphthy(-N,Ńdiphenyl-1,1'-biphenyl-4,4'-diamine)] (NPB) as the hole transport layer (HTL). The typical device structure was glass substrate/ ITO/ NPB/ Alq 3/ BPhen/ LiF/ Al. Since BPhen possesses a considerable high electron mobility of 5×10 -4 cm 2 V -1 s -1, devices with BPhen as ETL can realize an extremely high luminous efficiency. By optimizing the thickness of both HTL and ETL, we obtained a highly efficient OLED with a current efficiency of 6.80 cd/A and luminance of 1361 cd/m 2 at a current density of 20 mA/cm 2. This dramatic improvement in the current efficiency has been explained on the principle of charge balance.

Pure circular polarization electroluminescence at room temperature with spin-polarized light-emitting diodes

PubMed Central

Nishibayashi, Kazuhiro

2017-01-01

We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spin-polarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation. There are two small schemes in the tested spin-LEDs: first, the stripe-laser-like structure that helps intensify the EL light at the cleaved side walls below the spin injector Fe slab, and second, the crystalline AlOx spin-tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density (J) region, whereas it increases steeply and reaches close to the pure CP when J > 100 A/cm2. There, either right- or left-handed CP component is significantly suppressed depending on the direction of magnetization of the spin injector. Spin-dependent reabsorption, spin-induced birefringence, and optical spin-axis conversion are suggested to account for the observed experimental results. PMID:28174272

Planar electroluminescent panel techniques

NASA Technical Reports Server (NTRS)

Kerr, C.; Kell, R. E.

1973-01-01

Investigations of planar electroluminescent multipurpose displays with latch-in memory are described. An 18 x 24 in. flat, thin address panel with elements spacing of 0.100 in. was constructed which demonstrated essentially uniform luminosity of 3-5 foot lamberts for each of its 43200 EL cells. A working model of a 4-bit EL-PC (electroluminescent photoconductive) electrooptical decoder was made which demonstrated the feasibility of this concept. A single-diagram electroluminescent display device with photoconductive-electroluminescent latch-in memory was constructed which demonstrated the conceptual soundness of this principle. Attempts to combine these principles in a single PEL multipurpose display with latch-in memory were unsuccessful and were judged to exceed the state-of-the-art for close-packed (0.10 in. centers) photoconductor-electroluminescent cell assembly.

Electrical properties of III-Nitride LEDs: Recombination-based injection model and theoretical limits to electrical efficiency and electroluminescent cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

David, Aurelien, E-mail: adavid@soraa.com; Hurni, Christophe A.; Young, Nathan G.

The current-voltage characteristic and ideality factor of III-Nitride quantum well light-emitting diodes (LEDs) grown on bulk GaN substrates are investigated. At operating temperature, these electrical properties exhibit a simple behavior. A model in which only active-region recombinations have a contribution to the LED current is found to account for experimental results. The limit of LED electrical efficiency is discussed based on the model and on thermodynamic arguments, and implications for electroluminescent cooling are examined.

Detection of microstructural defects in chalcopyrite Cu(In,Ga)Se2 solar cells by spectrally-filtered electroluminescence

NASA Astrophysics Data System (ADS)

Skvarenina, L.; Gajdos, A.; Macku, R.; Skarvada, P.

2017-12-01

The aim of this research is to detect and localize microstructural defects by using an electrically excited light emission from a forward/reverse-bias stressed pn-junction in thin-film Cu(In; Ga)Se2 solar cells with metal wrap through architecture. A different origin of the local light emission from intrinsic/extrinsic imperfections in these chalcopyrite-based solar cells can be distinguished by a spectrally-filtered electroluminescence mapping. After a light emission mapping and localization of the defects in a macro scale is performed a micro scale exploration of the solar cell surface by a scanning electron microscope which follows the particular defects obtained by an electroluminescence. In particular, these macroscopic/microscopic examinations are performed independently, then the searching of the corresponding defects in the micro scale is rather difficult due to a diffused light emission obtained from the macro scale localization. Some of the defects accompanied by a highly intense light emission very often lead to a strong local overheating. Therefore, the lock-in infrared thermography is also performed along with an electroluminescence mapping.

Ultraviolet electroluminescence from hybrid inorganic/organic ZnO/GaN/poly(3-hexylthiophene) dual heterojunctions.

PubMed

Chen, Yungting; Shih, Hanyu; Wang, Chunhsiung; Hsieh, Chunyi; Chen, Chihwei; Chen, Yangfang; Lin, Taiyuan

2011-05-09

Based on hybrid inorganic/organic n-ZnO nanorods/p-GaN thin film/poly(3-hexylthiophene)(P3HT) dual heterojunctions, the light emitting diode (LED) emits ultraviolet (UV) radiation (370 nm - 400 nm) and the whole visible light (400 nm -700 nm) at the low injection current density. Meanwhile, under the high injection current density, the UV radiation overwhelmingly dominates the room-temperature electroluminescence spectra, exponentially increases with the injection current density and possesses a narrow full width at half maximum less than 16 nm. Comparing electroluminescence with photoluminescence spectra, an enormously enhanced transition probability of the UV luminescence in the electroluminescence spectra was found. The P3HT layer plays an essential role in helping the UV emission from p-GaN material because of its hole-conductive characteristic as well as the band alignment with respect to p-GaN. With our new finding, the result shown here may pave a new route for the development of high brightness LEDs derived from hybrid inorganic/organic heterojuctions.

Electroluminescence Efficiency Enhancement using Metal Nanoparticles

DTIC Science & Technology

2008-06-22

ABSTRACT We apply the “effective mode volume” theory to evaluate enhancement of the electroluminescence efficiency of semiconductor emitters placed in... Electroluminescence efficiency enhancement using metal nanoparticles J. B. Khurgin,1 G. Sun,2,a and R. A. Soref3 1Department of Electrical and Computer...published online 17 July 2008 We apply the “effective mode volume” theory to evaluate enhancement of the electroluminescence efficiency of semiconductor

Specific features of electroluminescence in heterostructures with InSb quantum dots in an InAs matrix

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parkhomenko, Ya. A.; Ivanov, E. V.; Moiseev, K. D., E-mail: mkd@iropt2.ioffe.rssi.ru

2013-11-15

The electrical and electroluminescence properties of a single narrow-gap heterostructure based on a p-n junction in indium arsenide, containing a single layer of InSb quantum dots in the InAs matrix, are studied. The presence of quantum dots has a significant effect on the shape of the reverse branch of the current-voltage characteristic of the heterostructure. Under reverse bias, the room-temperature electroluminescence spectra of the heterostructure with quantum dots, in addition to a negative-luminescence band with a maximum at the wavelength {lambda} = 3.5 {mu}m, contained a positive-luminescence emission band at 3.8 {mu}m, caused by radiative transitions involving localized states ofmore » quantum dots at the type-II InSb/InAs heterointerface.« less

Organic solution-processible electroluminescent molecular glasses for non-doped standard red OLEDs with electrically stable chromaticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bi, Xiaoman; Zuo, Weiwei; Liu, Yingliang, E-mail: liuylxn@sohu.com

Highlights: • The D–A–D electroluminescent molecular glasses are synthesized. • Non-doped red electroluminescent film is fabricated by spin-coating. • Red OLED shows stable wavelength, luminous efficiency and chromaticity. • CIE1931 coordinate is in accord with standard red light in PAL system. - Abstract: Organic light-emitting molecular glasses (OEMGs) are synthesized through the introduction of nonplanar donor and branched aliphatic chain into electroluminescent emitters. The target OEMGs are characterized by {sup 1}H NMR, {sup 13}C NMR, IR, UV–vis and fluorescent spectra as well as elemental analysis, TG and DSC. The results indicated that the optical, electrochemical and electroluminescent properties of OEMGsmore » are adjusted successfully by the replacement of electron-donating group. The non-doped OLED device with a standard red electroluminescent emission is achieved by spin-coating the THF solution of OEMG with a triphenylamine moiety. This non-doped red OLED device takes on an electrically stable electroluminescent performance, including the stable maximum electroluminescent wavelength of 640 nm, the stable luminous efficiency of 2.4 cd/A and the stable CIE1931 coordinate of (x, y) = (0.64, 0.35), which is basically in accord with the CIE1931 coordinate (x, y) = (0.64, 0.33) of standard red light in PAL system.« less

Charge transfer through amino groups-small molecules interface improving the performance of electroluminescent devices

NASA Astrophysics Data System (ADS)

Havare, Ali Kemal; Can, Mustafa; Tozlu, Cem; Kus, Mahmut; Okur, Salih; Demic, Şerafettin; Demirak, Kadir; Kurt, Mustafa; Icli, Sıddık

2016-05-01

A carboxylic group functioned charge transporting was synthesized and self-assembled on an indium tin oxide (ITO) anode. A typical electroluminescent device [modified ITO/TPD (50 nm)/Alq3 (60 nm)/LiF (2 nm)/(120 nm)] was fabricated to investigate the effect of the amino groups-small molecules interface on the characteristics of the device. The increase in the surface work function of ITO is expected to facilitate the hole injection from the ITO anode to the Hole Transport Layer (HTL) in electroluminescence. The modified electroluminescent device could endure a higher current and showed a much higher luminance than the nonmodified one. For the produced electroluminescent devices, the I-V characteristics, optical characterization and quantum yields were performed. The external quantum efficiency of the modified electroluminescent device is improved as the result of the presence of the amino groups-small molecules interface.

Fabrication of current confinement aperture structure by transforming a conductive GaN:Si epitaxial layer into an insulating GaOx layer.

PubMed

Lin, Chia-Feng; Lee, Wen-Che; Shieh, Bing-Cheng; Chen, Danti; Wang, Dili; Han, Jung

2014-12-24

We report here a simple and robust process to convert embedded conductive GaN epilayers into insulating GaOx and demonstrate its efficacy in vertical current blocking and lateral current steering in a working LED device. The fabrication processes consist of laser scribing, electrochemical (EC) wet-etching, photoelectrochemical (PEC) oxidation, and thermal oxidization of a sacrificial n(+)-GaN:Si layer. The conversion of GaN is made possible through an intermediate stage of porosification where the standard n-type GaN epilayers can be laterally and selectively anodized into a nanoporous (NP) texture while keeping the rest of the layers intact. The fibrous texture of NP GaN with an average wall thickness of less than 100 nm dramatically increases the surface-to-volume ratio and facilitates a rapid oxidation process of GaN into GaOX. The GaOX aperture was formed on the n-side of the LED between the active region and the n-type GaN layer. The wavelength blueshift phenomena of electroluminescence spectra is observed in the treated aperture-emission LED structure (441.5 nm) when compared to nontreated LED structure (443.7 nm) at 0.1 mA. The observation of aperture-confined electroluminescence from an InGaN LED structure suggests that the NP GaN based oxidation will play an enabling role in the design and fabrication of III-nitride photonic devices.

Electroluminescence of fluorescent-phosphorescent organic light-emitting diodes with regular, inverted, and symmetrical structures

NASA Astrophysics Data System (ADS)

Yang, Su-Hua; Shih, Po-Jen; Wu, Wen-Jie

2014-11-01

The influence of the device structure on the electroluminescence (EL) properties of fluorescent-phosphorescent organic light emitting diodes (OLEDs) was demonstrated. Four devices with regular-, inverted-, compensated- and symmetrical-emission layers (EMLs) were prepared. In regular-EML device, DCJTB emission increased when the phosphorescent sensitized EML was thickened. In inverted-EML device, low electron energy barrier at the Bphen/BCzVB interface resulted in weakened blue emission. The compensated-EML device, prepared with a red color-compensated layer, showed a color-tunable broadband white emission. Conversely, device with a quantum-like symmetrical-EML showed a narrow color-temperature range. Stable EL efficiency was obtained from regular, compensated, and symmetrical-EML devices. In contrast, EL efficiency of inverted-EML device rolled off significantly, though it had the highest EL efficiency of 11.4 cd/A.

Polymer matrix electroluminescent materials and devices

DOEpatents

Marrocco, III, Matthew L.; Motamedi, Farshad J [Claremont, CA; Abdelrazzaq, Feras Bashir [Covina, CA; Abdelrazzaq, legal representative, Bashir Twfiq

2012-06-26

Photoluminescent and electroluminescent compositions are provided which comprise a matrix comprising aromatic repeat units covalently coordinated to a phosphorescent or luminescent metal ion or metal ion complexes. Methods for producing such compositions, and the electroluminescent devices formed therefrom, are also disclosed.

Sub-bandgap Voltage Electroluminescence and Magneto-oscillations in a WSe2 Light-Emitting van der Waals Heterostructure.

PubMed

Binder, Johannes; Withers, Freddie; Molas, Maciej R; Faugeras, Clement; Nogajewski, Karol; Watanabe, Kenji; Taniguchi, Takashi; Kozikov, Aleksey; Geim, Andre K; Novoselov, Kostya S; Potemski, Marek

2017-03-08

We report on experimental investigations of an electrically driven WSe 2 based light-emitting van der Waals heterostructure. We observe a threshold voltage for electroluminescence significantly lower than the corresponding single particle band gap of monolayer WSe 2 . This observation can be interpreted by considering the Coulomb interaction and a tunneling process involving excitons, well beyond the picture of independent charge carriers. An applied magnetic field reveals pronounced magneto-oscillations in the electroluminescence of the free exciton emission intensity with a 1/B periodicity. This effect is ascribed to a modulation of the tunneling probability resulting from the Landau quantization in the graphene electrodes. A sharp feature in the differential conductance indicates that the Fermi level is pinned and allows for an estimation of the acceptor binding energy.

Quantifying Solar Cell Cracks in Photovoltaic Modules by Electroluminescence Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spataru, Sergiu; Hacke, Peter; Sera, Dezso

2015-06-14

This article proposes a method for quantifying the percentage of partially and totally disconnected solar cell cracks by analyzing electroluminescence images of the photovoltaic module taken under high- and low-current forward bias. The method is based on the analysis of the module's electroluminescence intensity distribution, applied at module and cell level. These concepts are demonstrated on a crystalline silicon photovoltaic module that was subjected to several rounds of mechanical loading and humidity-freeze cycling, causing increasing levels of solar cell cracks. The proposed method can be used as a diagnostic tool to rate cell damage or quality of modules after transportation.more » Moreover, the method can be automated and used in quality control for module manufacturers, installers, or as a diagnostic tool by plant operators and diagnostic service providers.« less

Polarization of edge emission from III-nitride light emitting diodes of emission wavelength from 395 to 455 nm

NASA Astrophysics Data System (ADS)

Jia, Chuanyu; Yu, Tongjun; Mu, Sen; Pan, Yaobo; Yang, Zhijian; Chen, Zhizhong; Qin, Zhixin; Zhang, Guoyi

2007-05-01

Polarization-resolved edge-emitting electroluminescence of InGaN /GaN multiple quantum well (MQW) light emitting diodes (LEDs) from 395to455nm was measured. Polarization ratio decreased from 3.2 of near-ultraviolet LEDs (395nm) to 1.9 of blue LEDs (455nm). Based on TE mode dominant emissions in InGaN /GaN MQWs, compressive strain in well region favors TE mode, indium induced quantum-dot-like behavior leads to an increased TM component. As wavelength increased, indium enhanced quantum-dot-like behavior became obvious and E ‖C electroluminescence signal increased thus lower polarization ratio. Electroluminescence spectrum shifts confirmed that quantum dotlike behaviors rather than strain might be dominant in modifying luminescence mode of InGaN /GaN MQWs from near ultraviolet to blue.

Spatial nonuniformity of current flow and its consideration in determination of characteristics of surface illuminated InAsSbP/InAs-based photodiodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zotova, N. V.; Karandashev, S. A.; Matveev, B. A., E-mail: Bmat@iropt3.ioffe.ru

Current-voltage characteristics of surface-irradiated photodiodes based on the InAsSbP/InAs structures are analyzed using experimental data on the distribution of electroluminescence intensity over the diode surface and taking into account thickening the current streamlines near the contacts. The influence of the potential barrier associated with the N-InAsSbP/n-InAs junction in double heterostructures on the differential resistance of diodes under zero bias, the value of the reverse current, and spreading of the forward current is discussed.

Electroluminescent apparatus having a structured luminescence conversion layer

DOEpatents

Krummacher, Benjamin Claus [Sunnyvale, CA

2008-09-02

An apparatus such as a light source is disclosed which has an OLED device and a structured luminescence conversion layer disposed on the substrate or transparent electrode of said OLED device and on the exterior of said OLED device. The structured luminescence conversion layer contains color-changing and non-color-changing regions arranged in a particular pattern.

Organic emitters: Light-emitting fabrics

NASA Astrophysics Data System (ADS)

Ortí, Enrique; Bolink, Henk J.

2015-04-01

Light-emitting fibres that suit integration with textiles are prepared by dip-coating a steel wire with an electroluminescent material and then cleverly wrapping the structure with a carbon nanotube sheet that functions as a transparent electrode.

Light emission in forward and reverse bias operation in OLED with amorphous silicon carbon nitride thin films

NASA Astrophysics Data System (ADS)

Reyes, R.; Cremona, M.; Achete, C. A.

2011-01-01

Amorphous silicon carbon nitride (a-SiC:N) thin films deposited by magnetron sputtering were used in the structure of an organic light emitting diode (OLED), obtaining an OLED operating in forward and reverse bias mode. The device consist of the heterojunction structure ITO/a-SiC:N/Hole Transport Layer (HTL)/ Electron Transport Layer (ETL)/a-SiC:N/Al. As hole transporting layer was used a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline - 6 - carboxyaldehyde - 1,1'- diphenylhydrazone (MTCD), while the tris(8-hydroxyquinoline aluminum) (Alq3) is used as electron transport and emitting layer. A significant increase in the voltage operation compared to the conventional ITO/MTCD/Alq3/Al structure was observed, so the onset of electroluminescence occurs at about 22 V in the forward and reverse bias mode of operation. The electroluminescence spectra is similar in both cases, only slightly shifted 0.14 eV to lower energies in relation to the conventional device.

Active polarisation control of a quantum cascade laser using tuneable birefringence in waveguides.

PubMed

Dhirhe, D; Slight, T J; Holmes, B M; Ironside, C N

2013-10-07

We discuss the design, modelling, fabrication and characterisation of an integrated tuneable birefringent waveguide for quantum cascade lasers. We have fabricated quantum cascade lasers operating at wavelengths around 4450 nm that include polarisation mode converters and a differential phase shift section. We employed below laser threshold electroluminescence to investigate the single pass operation of the integrated device. We use a theory based on the electro-optic properties of birefringence in quantum cascade laser waveguides combined with a Jones matrix based description to gain an understanding of the electroluminescence results. With the quantum cascade lasers operating above threshold we demonstrated polarisation control of the output.

New cyclometalated Iridium(III) beta-dicetone complex as phosphorescent dopant in Organic light emitting devices

NASA Astrophysics Data System (ADS)

Ivanov, P.; Petrova, P.; Stanimirov, S.; Tomova, R.

2017-01-01

A new Bis[4-(benzothiazolato-N,C2‧-2-yl)-N,N-dimethylaniline]Iridium(III) acetylacetonate (Me2N-bt) 2Ir(acac) was synthesized and identified by 1H NMR and elemental analysis. The application of the new compound as a dopant in the hole transporting layer (HTL) of Organic light emitting diode (OLED) structure: HTL/EL/ETL, where HTL was N,N’-bis(3-methylphenyl)-N,N’-diphenylbenzidine (TPD), incorporated in Poly(N-vinylcarbazole) (PVK) matrix, EL - electroluminescent layer of Bis(8-hydroxy-2-methylquinoline)-(4-phenylpheno-xy)aluminum (BAlq) and ETL - electron-transporting layer of Tris-(8-hydroxyquinoline) aluminum (Alq3) or Bis[2-(2-benzothiazoly) phenolato]zinc (Zn(btz)2). We established that the electroluminescent spectra of OLEDs at different concentrations of the dopant were basically the sum of the greenish-blue emission of BAlq and yellowish-green emission of Ir complex. It was found that with increasing of the dopant concentration the relative electroluminescent intensity of Iridium complex emission increased and this of BAlq decreased and as a result the fine tuning of OLED color was observed.

Efficient electroluminescent cooling with a light-emitting diode coupled to a photovoltaic cell (Conference Presentation)

NASA Astrophysics Data System (ADS)

Xiao, Tianyao P.; Chen, Kaifeng; Santhanam, Parthiban; Fan, Shanhui; Yablonovitch, Eli

2017-02-01

The new breakthrough in photovoltaics, exemplified by the slogan "A great solar cell has to be a great light-emitting diode (LED)", has led to all the major new solar cell records, while also leading to extraordinary LED efficiency. As an LED becomes very efficient in converting its electrical input into light, the device cools as it operates because the photons carry away entropy as well as energy. If these photons are absorbed in a photovoltaic (PV) cell, the generated electricity can be used to provide part of the electrical input that drives the LED. Indeed, the LED/PV cell combination forms a new type of heat engine with light as the working fluid. The electroluminescent refrigerator requires only a small amount of external electricity to provide cooling, leading to a high coefficient of performance. We present the theoretical performance of such a refrigerator, in which the cool side (LED) is radiatively coupled to the hot side (PV) across a vacuum gap. The coefficient of performance is maximized by using a highly luminescent material, such as GaAs, together with device structures that optimize extraction of the luminescence. We consider both a macroscopic vacuum gap and a sub-wavelength gap; the latter allows for evanescent coupling of photons between the devices, potentially providing a further enhancement to the efficiency of light extraction. Using device assumptions based on the current record-efficiency solar cells, we show that electroluminescent cooling can, in certain regimes of cooling power, achieve a higher coefficient of performance than thermoelectric cooling.

Electroluminescence of ordered ZnO nanorod array/p-GaN light-emitting diodes with graphene current spreading layer

PubMed Central

2014-01-01

Ordered ZnO nanorod array/p-GaN heterojunction light-emitting diodes (LEDs) have been fabricated by introducing graphene as the current spreading layer, which exhibit improved electroluminescence performance by comparison to the LED using a conventional structure (indium-tin-oxide as the current spreading layer). In addition, by adjusting the diameter of ZnO nanorod array in use, the light emission of the ZnO nanorod array/p-GaN heterojunction LEDs was enhanced further. This work has great potential applications in solid-state lighting, high performance optoelectronic devices, and so on. PACS 78.60.Fi; 85.60.Jb; 78.67.Lt; 81.10.Dn PMID:25489284

Electroluminescence of ordered ZnO nanorod array/p-GaN light-emitting diodes with graphene current spreading layer.

PubMed

Dong, Jing-Jing; Hao, Hui-Ying; Xing, Jie; Fan, Zhen-Jun; Zhang, Zi-Li

2014-01-01

Ordered ZnO nanorod array/p-GaN heterojunction light-emitting diodes (LEDs) have been fabricated by introducing graphene as the current spreading layer, which exhibit improved electroluminescence performance by comparison to the LED using a conventional structure (indium-tin-oxide as the current spreading layer). In addition, by adjusting the diameter of ZnO nanorod array in use, the light emission of the ZnO nanorod array/p-GaN heterojunction LEDs was enhanced further. This work has great potential applications in solid-state lighting, high performance optoelectronic devices, and so on. 78.60.Fi; 85.60.Jb; 78.67.Lt; 81.10.Dn.

Emission characteristics in solution-processed asymmetric white alternating current field-induced polymer electroluminescent devices

NASA Astrophysics Data System (ADS)

Chen, Yonghua; Xia, Yingdong; Smith, Gregory M.; Gu, Yu; Yang, Chuluo; Carroll, David L.

2013-01-01

In this work, the emission characteristics of a blue fluorophor poly(9, 9-dioctylfluorene) (PFO) combined with a red emitting dye: Bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate)iridium (III) [Ir(MDQ)2(acac)], are examined in two different asymmetric white alternating current field-induced polymer electroluminescent (FIPEL) device structures. The first is a top-contact device in which the triplet transfer is observed resulting in the concentration-dependence of the emission similar to the standard organic light-emitting diode (OLED) structure. The second is a bottom-contact device which, however, exhibits concentration-independence of emission. Specifically, both dye emission and polymer emission are found for the concentrations as high as 10% by weight of the dye in the emitter. We attribute this to the significant different carrier injection characteristics of the two FIPEL devices. Our results suggest a simple and easy way to realize high-quality white emission.

Advances in display technology III; Proceedings of the Meeting, Los Angeles, CA, January 18, 19, 1983

NASA Astrophysics Data System (ADS)

Schlam, E.

1983-01-01

Human factors in visible displays are discussed, taking into account an introduction to color vision, a laser optometric assessment of visual display viewability, the quantification of color contrast, human performance evaluations of digital image quality, visual problems of office video display terminals, and contemporary problems in airborne displays. Other topics considered are related to electroluminescent technology, liquid crystal and related technologies, plasma technology, and display terminal and systems. Attention is given to the application of electroluminescent technology to personal computers, electroluminescent driving techniques, thin film electroluminescent devices with memory, the fabrication of very large electroluminescent displays, the operating properties of thermally addressed dye switching liquid crystal display, light field dichroic liquid crystal displays for very large area displays, and hardening military plasma displays for a nuclear environment.

Unveiling the composite structures of emissive consolidated p-i-n junction nanocells for white light emission.

PubMed

Lee, Kyu Seung; Shim, Jaeho; Lee, Hyunbok; Yim, Sang-Youp; Angadi, Basavaraj; Lim, Byungkwon; Son, Dong Ick

2018-06-08

Hybrid organic-Red-Green-Blue (RGB) color quantum dots were incorporated into consolidated p(polymer)-i(RGB quantum dots)-n(small molecules) junction structures to fabricate a single active layer for a light emitting diode device for white electroluminescence. The semiconductor RGB quantum dots, as an intrinsic material, were electrostatically bonded between functional groups of the p-type polymer organic material core surface and the n-type small molecular organic material shell surface. The ZnCdSe/ZnS and CdSe/ZnS quantum dots distributed uniformly and isotropically surrounding the polymer core which in turn was surrounded by small molecular organic materials. In the present study, we have identified the mechanisms of chemical synthesis and interactions of the p-i-n junction nanocell structure through modeling studies by DFT calculations. We have also investigated optical, structural and electrical properties along with the carrier transport mechanism of the light emitting diodes which have a single active layer of consolidated p-i-n junction nanocells for white electroluminescence.

Flexible, polymer gated, AC-driven organic electroluminescence devices

NASA Astrophysics Data System (ADS)

Xu, Junwei; Carroll, David L.

2017-08-01

Comparing rigid inorganic layer, polymeric semiconducting gate layer exhibits superior flexibility as well as efficient carrier manipulation in high frequency AC cycles. Mechanism of the carrier manipulation at the gate in forward and reversed bias of AC cycle is studied. The flexible PET-based AC-OEL device with poly[(9,9-bis(3'-((N,N-dimethyl)-Nethylammonium)- propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN-Br) gate shows a stable electroluminescent performance in frequency sweep with a color rendering index (CRI) over 81 at 2800K color temperature.

Characterizations of low-temperature electroluminescence from ZnO nanowire light-emitting arrays on the p-GaN layer.

PubMed

Lu, Tzu-Chun; Ke, Min-Yung; Yang, Sheng-Chieh; Cheng, Yun-Wei; Chen, Liang-Yi; Lin, Guan-Jhong; Lu, Yu-Hsin; He, Jr-Hau; Kuo, Hao-Chung; Huang, JianJang

2010-12-15

Low-temperature electroluminescence from ZnO nanowire light-emitting arrays is reported. By inserting a thin MgO current blocking layer in between ZnO nanowire and p-GaN, high-purity UV light emission at wavelength 398 nm was obtained. As the temperature is decreased, contrary to the typical GaN-based light emitting diodes, our device shows a decrease of optical output intensity. The results are associated with various carrier tunneling processes and frozen MgO defects.

Control of circular polarization of electroluminescence in spin light-emitting diodes based on InGaAs/GaAs/δ〈Mn〉 heterostructures

NASA Astrophysics Data System (ADS)

Malysheva, E. I.; Dorokhin, M. V.; Demina, P. B.; Zdoroveyshchev, A. V.; Rykov, A. V.; Ved', M. V.; Danilov, Yu. A.

2017-11-01

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.

Power generation by thermally assisted electroluminescence: like optical cooling, but different

NASA Astrophysics Data System (ADS)

Buckner, Benjamin D.; Heeg, Bauke

2008-02-01

Thermally assisted electro-luminescence may provide a means to convert heat into electricity. In this process, radiation from a hot light-emitting diode (LED) is converted to electricity by a photovoltaic (PV) cell, which is termed thermophotonics. Novel analytical solutions to the equations governing such a system show that this system combines physical characteristics of thermophotovoltaics (TPV) and the inverse process of laser cooling. The flexibility of having both adjustable bias and load parameters may allow an optimized power generation system based on this concept to exceed the power throughput and efficiency of TPV systems. Such devices could function as efficient solar thermal, waste heat, and fuel-based generators.

Methods and apparatus of spatially resolved electroluminescence of operating organic light-emitting diodes using conductive atomic force microscopy

NASA Technical Reports Server (NTRS)

Hersam, Mark C. (Inventor); Pingree, Liam S. C. (Inventor)

2008-01-01

A conductive atomic force microscopy (cAFM) technique which can concurrently monitor topography, charge transport, and electroluminescence with nanometer spatial resolution. This cAFM approach is particularly well suited for probing the electroluminescent response characteristics of operating organic light-emitting diodes (OLEDs) over short length scales.

Exciton-dominant electroluminescence from a diode of monolayer MoS{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Yu; Ye, Ziliang; Gharghi, Majid

2014-05-12

In two-dimensional monolayer MoS{sub 2}, excitons dominate the absorption and emission properties. However, the low electroluminescent efficiency and signal-to-noise ratio limit our understanding of the excitonic behavior of electroluminescence. Here, we study the microscopic origin of the electroluminescence from a diode of monolayer MoS{sub 2} fabricated on a heavily p-type doped silicon substrate. Direct and bound-exciton related recombination processes are identified from the electroluminescence. At a high electron-hole pair injection rate, Auger recombination of the exciton-exciton annihilation of the bound exciton emission is observed at room temperature. Moreover, the efficient electrical injection demonstrated here allows for the observation of amore » higher energy exciton peak of 2.255 eV in the monolayer MoS{sub 2} diode, attributed to the excited exciton state of a direct-exciton transition.« less

Electroluminescence Properties of IrQ(ppy)2 Dual-Emitter Organometallic Compound in Organic Light-Emitting Devices

NASA Astrophysics Data System (ADS)

Ciobotaru, Constantin Claudiu; Polosan, Silviu; Ciobotaru, Iulia Corina

2018-02-01

This paper reports the influence of the charge carrier mobility on the electroluminescent properties of a dual-emitter organometallic compound dispersed in two conjugated organic small-molecule host materials and embedded in organic light-emitting devices (OLEDs). The electroluminescent processes in OLEDs are strongly influenced by the host-guest interaction. The charge carrier mobility in the host material plays an important role in the electroluminescent processes but also depends on the triplet-triplet interaction with the organometallic compound. The low charge carrier mobility in 4,4'-bis( N-carbazolyl)-1,1'-biphenyl (CBP) host material reduces the electroluminescent processes, but they are slightly enhanced by the triplet-triplet exothermic charge transfer. The higher charge carrier mobility in the case of N, N'-bis(3-methylphenyl)- N, N'-diphenylbenzidine (TPD) host material influences the electroluminescent processes by the endothermic energy transfer at room temperature, which facilitates the triplet-triplet harvesting in the host-guest system. The excitation is transferred to the guest molecules by triplet-triplet interaction as a Dexter transfer, which occurs by endothermic transfer from the triplet exciton in the host to the triplet exciton in the guest.

Preparation, characterization and electroluminescence studies of ZnO nanorods for optoelectronic device applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Anju, E-mail: singh-nk24@yahoo.com; Vishwakarma, H. L., E-mail: horilal5@yahoo.com

2015-07-31

In this work, ZnO nanorods were achieved by a simple chemical precipitation method in the presence of capping agent Poly Vinyl Pyrrolidone (PVP) at room temperature. X-Ray Diffraction (XRD) result indicates that the synthesized undoped ZnO nanorods have wurtzite hexagonal structure without any impurities. It has been seen that the growth orientation of the prepared ZnO nanorods were (101). XRD analysis revealed that the nanorods having the crystallite size 49 nm. The Scanning Electron Microscopy (SEM) image confirmed the size and shape of these nanorods. The diameter of nanorods has been found that 1.52 µm to 1.61 µm and the lengthmore » of about 4.89 µm. It has also been found that at room temperature Ultra Violet Visible (UV-VIS) absorption band is around 355 nm (blue shifted as compared to bulk). Electroluminescence (EL) studies show that emission of light is possible at very small threshold voltage and increases rapidly with increasing applied voltage. It is seen that smaller ZnO nanoparticles give higher electroluminescence brightness starting at lower threshold voltage. The brightness is also affected by increasing the frequency of AC signal.« less

A novel electroluminescent PPV copolymer and silsesquioxane nanocomposite film for the preparation of efficient PLED devices.

PubMed

Venegoni, Ivan; Carniato, Fabio; Olivero, Francesco; Bisio, Chiara; Pira, Nello Li; Lambertini, Vito Guido; Marchese, Leonardo

2012-11-02

Polymer light-emitting diodes (PLEDs) have attracted growing interest in recent years for their potential use in displays and lighting fields. Nevertheless, PLED devices have some disadvantages in terms of low optoelectronic efficiency, high cost, short lifetimes and low thermal stability, which limit their final applications. Huge efforts have been made recently to improve the performances of these devices. The addition of inorganic or hybrid organic-inorganic nanoparticles to the light-emitting polymers, for example, allows their thermal stability and electroluminescent efficiency to be increased. Following this approach, novel PLED devices based on composite films of PPV-derivative copolymer (commercial name Super Yellow, SY) and octaisobutil POSS, were developed in this study. The device containing Super Yellow loaded with 1 wt% of POSS showed higher efficiency (ca. +30%) and improved lifetime in comparison to PLED prepared with the pure electroluminescent polymer. The PLED devices developed in this study are suitable candidates for automotive dashboards and, in general, for lighting applications.

Guest concentration, bias current, and temperature-dependent sign inversion of magneto-electroluminescence in thermally activated delayed fluorescence devices

NASA Astrophysics Data System (ADS)

Deng, Junquan; Jia, Weiyao; Chen, Yingbing; Liu, Dongyu; Hu, Yeqian; Xiong, Zuhong

2017-03-01

Non-emissive triplet excited states in devices that undergo thermally activated delayed fluorescence (TADF) can be up-converted to singlet excited states via reverse intersystem crossing (RISC), which leads to an enhanced electroluminescence efficiency. Exciton-based fluorescence devices always exhibit a positive magneto-electroluminescence (MEL) because intersystem crossing (ISC) can be suppressed effectively by an external magnetic field. Conversely, TADF devices should exhibit a negative MEL because RISC is suppressed by the external magnetic field. Intriguingly, we observed a positive MEL in TADF devices. Moreover, the sign of the MEL was either positive or negative, and depended on experimental conditions, including doping concentration, current density and temperature. The MEL observed from our TADF devices demonstrated that ISC in the host material and RISC in the guest material coexisted. These competing processes were affected by the experimental conditions, which led to the sign change of the MEL. This work gives important insight into the energy transfer processes and the evolution of excited states in TADF devices.

High-efficiency electroluminescence and amplified spontaneous emission from a thermally activated delayed fluorescent near-infrared emitter

NASA Astrophysics Data System (ADS)

Kim, Dae-Hyeon; D'Aléo, Anthony; Chen, Xian-Kai; Sandanayaka, Atula D. S.; Yao, Dandan; Zhao, Li; Komino, Takeshi; Zaborova, Elena; Canard, Gabriel; Tsuchiya, Youichi; Choi, Eunyoung; Wu, Jeong Weon; Fages, Frédéric; Brédas, Jean-Luc; Ribierre, Jean-Charles; Adachi, Chihaya

2018-02-01

Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10% using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor-acceptor-donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.

Electroluminescence and Photoluminescence from a Fluorescent Cobalt Porphyrin Grafted on Graphene Oxide

NASA Astrophysics Data System (ADS)

Janghouri, Mohammad

2017-10-01

A new graphene oxide-cobalt porphyrin (GO-CoTPP) hybrid material has been used as an emissive layer in organic light-emitting diodes (OLEDs). Devices with fundamental structure of indium-doped tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, 45 nm)/polyvinylcarbazole (PVK):2-(4-biphenyl)-5-(4- t-butylphenyl)-1,3,4-oxadiazole (PBD):GO-CoTPP (70 nm)/1,3,5-tris( N-phenylbenzimidazol-2-yl)-benzene (TPBI, 20 nm)/Al (150 nm) were fabricated. A red electroluminescence (EL) was obtained from thin-film PVK:PBD:CoTPP at 70 nm thickness. When CoTPP was covalently grafted on graphene oxide (GO) sheets, near-white EL was obtained. The white emission, which was composed of bluish green and red, is attributed to electroplex formation at the GO-CoTPP/PBD interface. Such electroplex emission between electrons and holes is a reason for the low turn-on voltage of the GO-CoTPP-based OLED. Maximum luminance efficiency of 1.43 cd/A with Commission International de l'Eclairage coordinates of 0.33 and 0.40 was achieved at current of 0.02 mA and voltage of 14 V.

Correlating electroluminescence characterization and physics-based models of InGaN/GaN LEDs: Pitfalls and open issues

NASA Astrophysics Data System (ADS)

Calciati, Marco; Goano, Michele; Bertazzi, Francesco; Vallone, Marco; Zhou, Xiangyu; Ghione, Giovanni; Meneghini, Matteo; Meneghesso, Gaudenzio; Zanoni, Enrico; Bellotti, Enrico; Verzellesi, Giovanni; Zhu, Dandan; Humphreys, Colin

2014-06-01

Electroluminescence (EL) characterization of InGaN/GaN light-emitting diodes (LEDs), coupled with numerical device models of different sophistication, is routinely adopted not only to establish correlations between device efficiency and structural features, but also to make inferences about the loss mechanisms responsible for LED efficiency droop at high driving currents. The limits of this investigative approach are discussed here in a case study based on a comprehensive set of current- and temperature-dependent EL data from blue LEDs with low and high densities of threading dislocations (TDs). First, the effects limiting the applicability of simpler (closed-form and/or one-dimensional) classes of models are addressed, like lateral current crowding, vertical carrier distribution nonuniformity, and interband transition broadening. Then, the major sources of uncertainty affecting state-of-the-art numerical device simulation are reviewed and discussed, including (i) the approximations in the transport description through the multi-quantum-well active region, (ii) the alternative valence band parametrizations proposed to calculate the spontaneous emission rate, (iii) the difficulties in defining the Auger coefficients due to inadequacies in the microscopic quantum well description and the possible presence of extra, non-Auger high-current-density recombination mechanisms and/or Auger-induced leakage. In the case of the present LED structures, the application of three-dimensional numerical-simulation-based analysis to the EL data leads to an explanation of efficiency droop in terms of TD-related and Auger-like nonradiative losses, with a C coefficient in the 10-30 cm6/s range at room temperature, close to the larger theoretical calculations reported so far. However, a study of the combined effects of structural and model uncertainties suggests that the C values thus determined could be overestimated by about an order of magnitude. This preliminary attempt at uncertainty quantification confirms, beyond the present case, the need for an improved description of carrier transport and microscopic radiative and nonradiative recombination mechanisms in device-level LED numerical models.

Intrinsic Polarization and Tunable Color of Electroluminescence from Organic Single Crystal-based Light-Emitting Devices

PubMed Central

Ding, Ran; Feng, Jing; Zhou, Wei; Zhang, Xu-Lin; Fang, Hong-Hua; Yang, Tong; Wang, Hai-Yu; Hotta, Shu; Sun, Hong-Bo

2015-01-01

A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment. The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained. The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle. The polarized EL and the polarization-induced color tunability can be attributed to the anisotropic microcavity formed by the BP3T crystal with uniaxial alignment of the molecules. PMID:26207723

Single-Layer Halide Perovskite Light-Emitting Diodes with Sub-Band Gap Turn-On Voltage and High Brightness.

PubMed

Li, Junqiang; Shan, Xin; Bade, Sri Ganesh R; Geske, Thomas; Jiang, Qinglong; Yang, Xin; Yu, Zhibin

2016-10-03

Charge-carrier injection into an emissive semiconductor thin film can result in electroluminescence and is generally achieved by using a multilayer device structure, which requires an electron-injection layer (EIL) between the cathode and the emissive layer and a hole-injection layer (HIL) between the anode and the emissive layer. The recent advancement of halide perovskite semiconductors opens up a new path to electroluminescent devices with a greatly simplified device structure. We report cesium lead tribromide light-emitting diodes (LEDs) without the aid of an EIL or HIL. These so-called single-layer LEDs have exhibited a sub-band gap turn-on voltage. The devices obtained a brightness of 591 197 cd m -2 at 4.8 V, with an external quantum efficiency of 5.7% and a power efficiency of 14.1 lm W -1 . Such an advancement demonstrates that very high efficiency of electron and hole injection can be obtained in perovskite LEDs even without using an EIL or HIL.

Photoluminescence and electroluminescence from Ge/strained GeSn/Ge quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Chung-Yi; Chang, Chih-Chiang; Huang, Chih-Hsiung

2016-08-29

Ge/strained GeSn/Ge quantum wells are grown on a 300 mm Si substrate by chemical vapor deposition. The direct bandgap emission from strained GeSn is observed in the photoluminescence spectra and is enhanced by Al{sub 2}O{sub 3}/SiO{sub 2} passivation due to the field effect. The electroluminescence of the direct bandgap emission of strained GeSn is also observed from the Ni/Al{sub 2}O{sub 3}/GeSn metal-insulator-semiconductor tunneling diodes. Electroluminescence is a good indicator of GeSn material quality, since defects in GeSn layers degrade the electroluminescence intensity significantly. At the accumulation bias, the holes in the Ni gate electrode tunnel to the strained n-type GeSn layermore » through the ultrathin Al{sub 2}O{sub 3} and recombine radiatively with electrons. The emission wavelength of photoluminescence and electroluminescence can be tuned by the Sn content.« less

High Performance Organic Materials and Devices

DTIC Science & Technology

2006-03-31

on this material exhibited external quantum efficiency of 2.48% and electroluminescence efficiency as high as 3.33 cd/A. 15. SUBJECT TERMS 16...International de L’Eclairage coordinate at (0.164, 0.188). The external quantum efficiency of 2.48% and electroluminescence efficiency as high as 3.33 cd...more than 90% absorption in active layer, and highly balanced carrier transport. 4 5. High efficient blue- electroluminescence device shows maximum

Role of the inversion layer on the charge injection in silicon nanocrystal multilayered light emitting devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tondini, S.; Dipartimento di Fisica, Informatica e Matematica, Università di Modena e Reggio Emilia, Via Campi 213/a, 41125 Modena; Pucker, G.

2016-09-07

The role of the inversion layer on injection and recombination phenomena in light emitting diodes (LEDs) is here studied on a multilayer (ML) structure of silicon nanocrystals (Si-NCs) embedded in SiO{sub 2}. Two Si-NC LEDs, which are similar for the active material but different in the fabrication process, elucidate the role of the non-radiative recombination rates at the ML/substrate interface. By studying current- and capacitance-voltage characteristics as well as electroluminescence spectra and time-resolved electroluminescence under pulsed and alternating bias pumping scheme in both the devices, we are able to ascribe the different experimental results to an efficient or inefficient minoritymore » carrier (electron) supply by the p-type substrate in the metal oxide semiconductor LEDs.« less

Degradation of Bilayer Organic Light-Emitting Diodes Studied by Impedance Spectroscopy.

PubMed

Sato, Shuri; Takata, Masashi; Takada, Makoto; Naito, Hiroyoshi

2016-04-01

The degradation of bilayer organic light-emitting diodes (OLEDs) with a device structure of N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) (hole transport layer) and tris-(8-hydroxyquinolate)aluminum (Alq3) (emissive layer and electron transport layer) has been studied by impedance spectroscopy and device simulation. Two modulus peaks are found in the modulus spectra of the OLEDs below the electroluminescence threshold. After aging of the OLEDs, the intensity of electroluminescence is degraded and the modulus peak due to the Alq3 layer is shifted to lower frequency, indicating that the resistance of the Alq3 layer is increased. Device simulation reveals that the increase in the resistance of the Alq3 layer is due to the decrease in the electron mobility in the Alq3 layer.

Single-crystal perovskite CH3NH3PbBr3 prepared by cast capping method for light-emitting diodes

NASA Astrophysics Data System (ADS)

Nguyen, Van-Cao; Katsuki, Hiroyuki; Sasaki, Fumio; Yanagi, Hisao

2018-04-01

In this study, electroluminescence from single crystals of CH3NH3PbBr3 perovskite is explored. The cast capping method was applied to fabricate simple devices with an ITO/CH3NH3PbBr3/ITO structure. The devices showed a low operation voltage of 2 V and a pure green luminescence with full width at half maximum of ∼20 nm. However, the emission occurring at the crystal edges demonstrated blinking with a subsecond time interval, which is similar to the previously reported photoluminescence behavior of nanocrystal perovskites. This electroluminescence blinking may provide new insight into the recombination processes depending on the carrier traps and defects of emission layers in perovskite light-emitting devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xin, Yunzi; Nishio, Kazuyuki; Saitow, Ken-ichi, E-mail: saitow@hiroshima-u.ac.jp

A silicon (Si) quantum dot (QD)-based hybrid inorganic/organic light-emitting diode (LED) was fabricated via solution processing. This device exhibited white-blue electroluminescence at a low applied voltage of 6 V, with 78% of the effective emission obtained from the Si QDs. This hybrid LED produced current and optical power densities 280 and 350 times greater than those previously reported for such device. The superior performance of this hybrid device was obtained by both the prepared Si QDs and the optimized layer structure and thereby improving carrier migration through the hybrid LED and carrier recombination in the homogeneous Si QD layer.

The circular polarization inversion in δ〈Mn〉/InGaAs/GaAs light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorokhin, M. V., E-mail: dorokhin@nifti.unn.ru; Danilov, Yu. A.; Zvonkov, B. N.

We investigated light-emitting diodes consisting of an InGaAs/GaAs quantum well adjacent to a ferromagnetic δ〈Mn〉-layer. The magnetic field-dependent circular polarization obtained from both photo- and electroluminescence shows an unusual sign inversion depending on the growth parameters that can be explained by an interplay of the Zeeman splitting and Mn-hole interaction effects. Our results can help to understand the origin and control of the spin polarization on Mn doped GaAs structures, a fundamental step for the development of Mn-based spintronic devices.

Microscopic Perspective on Photovoltaic Reciprocity in Ultrathin Solar Cells

NASA Astrophysics Data System (ADS)

Aeberhard, Urs; Rau, Uwe

2017-06-01

The photovoltaic reciprocity theory relates the electroluminescence spectrum of a solar cell under applied bias to the external photovoltaic quantum efficiency of the device as measured at short circuit conditions. Its derivation is based on detailed balance relations between local absorption and emission rates in optically isotropic media with nondegenerate quasiequilibrium carrier distributions. In many cases, the dependence of density and spatial variation of electronic and optical device states on the point of operation is modest and the reciprocity relation holds. In nanostructure-based photovoltaic devices exploiting confined modes, however, the underlying assumptions are no longer justifiable. In the case of ultrathin absorber solar cells, the modification of the electronic structure with applied bias is significant due to the large variation of the built-in field. Straightforward use of the external quantum efficiency as measured at short circuit conditions in the photovoltaic reciprocity theory thus fails to reproduce the electroluminescence spectrum at large forward bias voltage. This failure is demonstrated here by numerical simulation of both spectral quantities at normal incidence and emission for an ultrathin GaAs p -i -n solar cell using an advanced quantum kinetic formalism based on nonequilibrium Green's functions of coupled photons and charge carriers. While coinciding with the semiclassical relations under the conditions of their validity, the theory provides a consistent microscopic relationship between absorption, emission, and charge carrier transport in photovoltaic devices at arbitrary operating conditions and for any shape of optical and electronic density of states.

Microscopic Perspective on Photovoltaic Reciprocity in Ultrathin Solar Cells.

PubMed

Aeberhard, Urs; Rau, Uwe

2017-06-16

The photovoltaic reciprocity theory relates the electroluminescence spectrum of a solar cell under applied bias to the external photovoltaic quantum efficiency of the device as measured at short circuit conditions. Its derivation is based on detailed balance relations between local absorption and emission rates in optically isotropic media with nondegenerate quasiequilibrium carrier distributions. In many cases, the dependence of density and spatial variation of electronic and optical device states on the point of operation is modest and the reciprocity relation holds. In nanostructure-based photovoltaic devices exploiting confined modes, however, the underlying assumptions are no longer justifiable. In the case of ultrathin absorber solar cells, the modification of the electronic structure with applied bias is significant due to the large variation of the built-in field. Straightforward use of the external quantum efficiency as measured at short circuit conditions in the photovoltaic reciprocity theory thus fails to reproduce the electroluminescence spectrum at large forward bias voltage. This failure is demonstrated here by numerical simulation of both spectral quantities at normal incidence and emission for an ultrathin GaAs p-i-n solar cell using an advanced quantum kinetic formalism based on nonequilibrium Green's functions of coupled photons and charge carriers. While coinciding with the semiclassical relations under the conditions of their validity, the theory provides a consistent microscopic relationship between absorption, emission, and charge carrier transport in photovoltaic devices at arbitrary operating conditions and for any shape of optical and electronic density of states.

Bias-polarity-dependent UV/visible transferable electroluminescence from ZnO nanorod array LED with graphene oxide electrode supporting layer

NASA Astrophysics Data System (ADS)

Liu, Weizhen; Wang, Wei; Xu, Haiyang; Li, Xinghua; Yang, Liu; Ma, Jiangang; Liu, Yichun

2015-09-01

A simple top electrode preparation process, employing continuous graphene oxide films as electrode supporting layers, was adopted to fabricate a ZnO nanorod array/p-GaN heterojunction LED. The achieved LED demonstrated different electroluminescence behaviors under forward and reverse biases: a yellow-red emission band was observed under forward bias, whereas a blue-UV emission peak was obtained under reverse bias. Electroluminescence spectra under different currents and temperatures, as well as heterojunction energy-band alignments, reveal that the yellow-red emission under forward bias originates from recombinations related to heterointerface defects, whereas the blue-UV electroluminescence under reverse bias is ascribed to transitions from near-band-edge and Mg-acceptor levels in p-GaN.

Exciplex emission and decay of co-deposited 4,4',4″-tris[3-methylphenyl(phenyl)amino]triphenylamine:tris-[3-(3-pyridyl)mesityl]borane organic light-emitting devices with different electron transporting layer thicknesses

NASA Astrophysics Data System (ADS)

Huang, Qingyu; Zhao, Suling; Xu, Zheng; Fan, Xing; Shen, Chongyu; Yang, Qianqian

2014-04-01

Highly efficient fluorescence organic light-emitting diodes (OLEDs) based on the mixed 4,4',4″-tris[3-methylphenyl(phenyl)amino]triphenylamine:tris-[3-(3-pyridyl)mesityl]borane (1:1) system are reported. The electroluminescence due to the exciplex emission is red shifted when the thickness of the electron-transporting layer increases. The prepared OLEDs achieve a low turn-on voltage of 2.1 V, a high current efficiency of 36.79 cd/A, and a very high luminescence of 17 100 cd/m2, as well as a low efficiency roll-off. The current efficiency of the optimized OLED is maintained at more than 28.33 cd/A up to 10 000 cd m-2. The detailed recombination mechanism of the prepared OLEDs is investigated by the transient electroluminescence method. It is concluded that there are no contributions from trapped charges and annihilations of triplet-triplet excitons to the detected electroluminescence.

Efficient Blue Electroluminescence Using Quantum-Confined Two-Dimensional Perovskites.

PubMed

Kumar, Sudhir; Jagielski, Jakub; Yakunin, Sergii; Rice, Peter; Chiu, Yu-Cheng; Wang, Mingchao; Nedelcu, Georgian; Kim, Yeongin; Lin, Shangchao; Santos, Elton J G; Kovalenko, Maksym V; Shih, Chih-Jen

2016-10-03

Solution-processed hybrid organic-inorganic lead halide perovskites are emerging as one of the most promising candidates for low-cost light-emitting diodes (LEDs). However, due to a small exciton binding energy, it is not yet possible to achieve an efficient electroluminescence within the blue wavelength region at room temperature, as is necessary for full-spectrum light sources. Here, we demonstrate efficient blue LEDs based on the colloidal, quantum-confined 2D perovskites, with precisely controlled stacking down to one-unit-cell thickness (n = 1). A variety of low-k organic host compounds are used to disperse the 2D perovskites, effectively creating a matrix of the dielectric quantum wells, which significantly boosts the exciton binding energy by the dielectric confinement effect. Through the Förster resonance energy transfer, the excitons down-convert and recombine radiatively in the 2D perovskites. We report room-temperature pure green (n = 7-10), sky blue (n = 5), pure blue (n = 3), and deep blue (n = 1) electroluminescence, with record-high external quantum efficiencies in the green-to-blue wavelength region.

Development of electroluminescence based pressure-sensitive paint system.

PubMed

Iijima, Yoshimi; Sakaue, Hirotaka

2011-01-01

We introduce a pressure-sensitive paint (PSP) measurement system based on an electroluminescence (EL) as a surface illumination. This consists of an inorganic EL as the illumination, a short-pass filter, and a platinum-porphyrin based PSP. The short-pass filter, which passes below 500 nm, was used to separate an overlay of the EL illumination and the PSP emission. The EL shows an opposite temperature dependency to that of the PSP. It gives a uniform illumination compared to that of a point illumination source such as a xenon lamp. Under atmospheric conditions, the resultant EL-PSP system reduces the temperature dependency by 54% compared to that of a conventional PSP system. An application of the EL-PSP system to a sonic jet impingement shows that the system demonstrated its reduction of the temperature dependency by 75% in a pressure measurement and reduces an image misalignment error.

Dielectric relaxation in AC powder electroluminescent devices

NASA Astrophysics Data System (ADS)

Zhang, Shuai; Su, Haibin; Tan, Chuan Seng; Wong, Terence Kin Shun; Teo, Ronnie Jin Wah

2017-01-01

The dielectric properties of AC powder electroluminescent devices were measured and analyzed using complex impedance spectroscopy to determine the relaxation processes occurring within the devices. The relaxation processes identified were ascribed to the electrode polarization caused by ion accumulation at the electrode/resin interfaces, the Maxwell-Wagner-Sillars effects at the (ZnS or BaTiO3) particle/resin interfaces, and the dipolar reorientation of polymer chains in the resin matrix. Each relaxation process was represented by its corresponding equivalent circuit component. Space charge polarization at the electrodes were represented by a Warburg element, a resistor, and a constant phase element. The resin matrix, ZnS/resin and BaTiO3/resin interfaces could each be modeled by a resistor and a capacitor in parallel. The simulated equivalent circuits for three different printed structures showed good fitting with their experimental impedance results.

M-plane core-shell InGaN/GaN multiple-quantum-wells on GaN wires for electroluminescent devices.

PubMed

Koester, Robert; Hwang, Jun-Seok; Salomon, Damien; Chen, Xiaojun; Bougerol, Catherine; Barnes, Jean-Paul; Dang, Daniel Le Si; Rigutti, Lorenzo; de Luna Bugallo, Andres; Jacopin, Gwénolé; Tchernycheva, Maria; Durand, Christophe; Eymery, Joël

2011-11-09

Nonpolar InGaN/GaN multiple quantum wells (MQWs) grown on the {11-00} sidewalls of c-axis GaN wires have been grown by organometallic vapor phase epitaxy on c-sapphire substrates. The structural properties of single wires are studied in detail by scanning transmission electron microscopy and in a more original way by secondary ion mass spectroscopy to quantify defects, thickness (1-8 nm) and In-composition in the wells (∼16%). The core-shell MQW light emission characteristics (390-420 nm at 5 K) were investigated by cathodo- and photoluminescence demonstrating the absence of the quantum Stark effect as expected due to the nonpolar orientation. Finally, these radial nonpolar quantum wells were used in room-temperature single-wire electroluminescent devices emitting at 392 nm by exploiting sidewall emission.

Fabrication of DC inorganic electroluminescent thin-film devices with novel n-p-n type structure

NASA Astrophysics Data System (ADS)

Ishimura, Takuyoshi; Matsumoto, Hironaga

2014-04-01

Inorganic electroluminescent (iEL) thin films are used in light-emitting devices and are functional under alternating current conditions only. Stable luminescent light has yet to be obtained under direct current conditions. We postulated that thin-film iEL light emission occurs when an injected electron occupies the excited state of a luminescent center and then recombines radiatively. From this perspective, we fabricated a novel stacked n-p-n type thin-film iEL device composed of indium tin oxide (ITO)-ZnO-CuAlO2-ZnS-ZnS:TbF3-Al thin films and obtained stable luminescence using a low-voltage DC power supply. The overall luminescent color of the device depended on only the dopant in the luminescent layer, not the band gap or thin-film material.

Quantum Dots and Their Multimodal Applications: A Review

PubMed Central

Bera, Debasis; Qian, Lei; Tseng, Teng-Kuan; Holloway, Paul H.

2010-01-01

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

Study of microstructure and electroluminescence of zinc sulfide thin film

NASA Astrophysics Data System (ADS)

Zhao-hong, Liu; Yu-jiang, Wang; Mou-zhi, Chen; Zhen-xiang, Chen; Shu-nong, Sun; Mei-chun, Huang

1998-03-01

The electroluminscent zinc sulfide thin film doped with erbium, fabricated by thermal evaporation with two boats, are examined. The surface and internal electronic states of ZnS thin film are measured by means of x-ray diffraction and x-ray photoemission spectroscopy. The information on the relations between electroluminescent characteristics and internal electronic states of the film is obtained. And the effects of the microstructure of thin film doped with rare earth erbium on electroluminescence are discussed as well.

Influence of photo-generated carriers on current spreading in double diode structures for electroluminescent cooling

NASA Astrophysics Data System (ADS)

Radevici, Ivan; Tiira, Jonna; Sadi, Toufik; Oksanen, Jani

2018-05-01

Current crowding close to electrical contacts is a common challenge in all optoelectronic devices containing thin current spreading layers (CSLs). We analyze the effects of current spreading on the operation of the so-called double diode structure (DDS), consisting of a light emitting diode (LED) and a photodiode (PD) fabricated within the same epitaxial growth process, and providing an attractive platform for studying electroluminescent (EL) cooling under high bias conditions. We show that current spreading in the common n-type layer between the LED and the PD can be dramatically improved by the strong optical coupling between the diodes, as the coupling enables a photo-generated current through the PD. This reduces the current in the DDS CSL and enables the study of EL cooling using structures that are not limited by the conventional light extraction challenges encountered in normal LEDs. The current spreading in the structures is studied using optical imaging techniques, electrical measurements, simulations, as well as simple equivalent circuit models developed for this purpose. The improved current spreading leads further to a mutual dependence with the coupling efficiency, which is expected to facilitate the process of optimizing the DDS. We also report a new improved value of 63% for the DDS coupling quantum efficiency.

The electroluminescence mechanism of Er³⁺ in different silicon oxide and silicon nitride environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rebohle, L., E-mail: l.rebohle@hzdr.de; Wutzler, R.; Braun, M.

Rare earth doped metal-oxide-semiconductor (MOS) structures are of great interest for Si-based light emission. However, several physical limitations make it difficult to achieve the performance of light emitters based on compound semiconductors. To address this point, in this work the electroluminescence (EL) excitation and quenching mechanism of Er-implanted MOS structures with different designs of the dielectric stack are investigated. The devices usually consist of an injection layer made of SiO₂ and an Er-implanted layer made of SiO₂, Si-rich SiO₂, silicon nitride, or Si-rich silicon nitride. All structures implanted with Er show intense EL around 1540 nm with EL power efficienciesmore » in the order of 2 × 10⁻³ (for SiO₂:Er) or 2 × 10⁻⁴(all other matrices) for lower current densities. The EL is excited by the impact of hot electrons with an excitation cross section in the range of 0.5–1.5 × 10⁻¹⁵cm⁻². Whereas the fraction of potentially excitable Er ions in SiO₂ can reach values up to 50%, five times lower values were observed for other matrices. The decrease of the EL decay time for devices with Si-rich SiO₂ or Si nitride compared to SiO₂ as host matrix implies an increase of the number of defects adding additional non-radiative de-excitation paths for Er³⁺. For all investigated devices, EL quenching cross sections in the 10⁻²⁰ cm² range and charge-to-breakdown values in the range of 1–10 C cm⁻² were measured. For the present design with a SiO₂ acceleration layer, thickness reduction and the use of different host matrices did not improve the EL power efficiency or the operation lifetime, but strongly lowered the operation voltage needed to achieve intense EL.« less

Performance evaluation of multi-junction solar cells by spatially resolved electroluminescence microscopy.

PubMed

Kong, Lijing; Wu, Zhiming; Chen, Shanshan; Cao, Yiyan; Zhang, Yong; Li, Heng; Kang, Junyong

2015-01-01

An electroluminescence microscopy combined with a spectroscopy was developed to visually analyze multi-junction solar cells. Triple-junction solar cells with different conversion efficiencies were characterized by using this system. The results showed that the mechanical damages and material defects in solar cells can be clearly distinguished, indicating a high-resolution imaging. The external quantum efficiency (EQE) measurements demonstrated that different types of defects or damages impacted cell performance in various degrees and the electric leakage mostly degraded the EQE. Meanwhile, we analyzed the relationship between electroluminescence intensity and short-circuit current density J SC. The results indicated that the gray value of the electroluminescence image corresponding to the intensity was almost proportional to J SC. This technology provides a potential way to evaluate the current matching status of multi-junction solar cells.

Electroluminescence from ZnCuInS/ZnS quantum dots/poly(9-vinylcarbazole) multilayer films with different thicknesses of quantum dot layer

NASA Astrophysics Data System (ADS)

Dong, Xiaofei; Xu, Jianping; Shi, Shaobo; Zhang, Xiaosong; Li, Lan; Yin, Shougen

2017-05-01

We report tunable electroluminescence (EL) from solution-processed ZnCuInS/ZnS (ZCIS/ZnS) quantum dots (QDs)/poly(9-vinlycarbazole) multilayer films. The EL spectra exhibit a red shift as the QD layer thickness increases. By analyzing the dependence of the applied voltage and the ZCIS/ZnS QD layer thickness on the EL spectra, the origin of the red shift is associated with the increased trap density of QDs that induces the injected electrons to be trapped in the deep donor level. The current conduction mechanism based on the current density-voltage curves at different voltage regions was discussed.

Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Junseok; Choi, Ji Eun; Hong, Young Joon, E-mail: yjhong@sejong.ac.kr

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p–n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunnelingmore » probability determined by wire/film junction geometry and size.« less

Bluish-white-light-emitting diodes based on two-dimensional lead halide perovskite (C6H5C2H4NH3)2PbCl2Br2

NASA Astrophysics Data System (ADS)

Cai, Peiqing; Wang, Xiangfu; Seo, Hyo Jin; Yan, Xiaohong

2018-04-01

Bluish-white-light-emitting diodes (BWLEDs) are designed based on the two-dimensional mixed halide perovskite (C6H5C2H4NH3)2PbCl2Br2 at room temperature. Bluish-white electroluminescence devices were fabricated by a spin-coating method. The BWLEDs can be turned on at 4.9 V and depict a maximum luminance of ˜70 cd/m2 at 7 V. Low and room temperature photoluminescence spectra show the coexistence of free exciton and self-trapped exciton luminescence in a deformable lattice. The strategy of achieving white electroluminescence (EL) from mixed halide perovskite reported here can be applied to other two-dimensional perovskites to increase the optoelectronic efficiency of the device in the future.

Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Jeong, Junseok; Choi, Ji Eun; Kim, Yong-Jin; Hwang, Sunyong; Kim, Sung Kyu; Kim, Jong Kyu; Jeong, Hu Young; Hong, Young Joon

2016-09-01

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p-n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunneling probability determined by wire/film junction geometry and size.

Two-band superlinear electroluminescence in GaSb based nanoheterostructures with AlSb/InAs{sub 1−x} Sb{sub x}/AlSb deep quantum well

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mikhailova, M. P.; Ivanov, E. V.; Danilov, L. V.

2014-06-14

We report on superlinear electroluminescent structures based on AlSb/InAs{sub 1−x}Sb{sub x}/AlSb deep quantum wells grown by MOVPE on n-GaSb:Te substrates. Dependence of the electroluminescence (EL) spectra and optical power on the drive current in nanoheterostructures with AlSb/InAs{sub 1−x}Sb{sub x}/AlSb quantum well at 77–300 K temperature range was studied. Intensive two-band superlinear EL in the 0.5–0.8 eV photon energy range was observed. Optical power enhancement with the increasing drive current at room temperature is caused by the contribution of the additional electron-hole pairs due to the impact ionization by the electrons heated at the high energy difference between AlSb and the first electronmore » level E{sub e1} in the InAsSb QW. Study of the EL temperature dependence at 90–300 K range enabled us to define the role of the first and second heavy hole levels in the radiative recombination process. It was shown that with the temperature decrease, the relation between the energies of the valence band offset and the second heavy hole energy level changes due to the temperature transformation of the energy band diagram. That is the reason why the EL spectrum revealed radiative transitions from the first electron level E{sub e1} to the first hole level E{sub h1} in the whole temperature range (90–300 K), while the emission band related with the transitions to the second hole level occurred only at T > 200 K. Comparative examination of the nanostructures with high band offsets and different interface types (AlAs-like and InSb-like) reveals more intense EL and optical power enhancement at room temperature in the case of AlAs-like interface that could be explained by the better quality of the heterointerface and more efficient hole localization.« less

A New Kind of Blue Hybrid Electroluminescent Device.

PubMed

Wang, Junling; Li, Zhuan; Liu, Chunmei

2016-04-01

Bright blue Electroluminescence come from a ITO/BBOT doped silica (6 x 10(-3) M) made by a sol-gel method/Al driven by AC with 500 Hz at different voltages and Gaussian analysis under 55 V showed that blue emission coincidenced with typical triple emission from BBOT. This kind of device take advantage of organics (BBOT) and inorganics (silica). Electroluminescence from a single-layered sandwiched device consisting of blue fluorescent dye 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene (BBOT) doped silica made by sol-gel method was investigated. A number of concentrations of hybrid devices were prepared and the maxium concentration was 6 x 10(-3) M. Blue electroluminescent (EL) always occurred above a threshold field 8.57 x 10(5) V/cm (30 V) at alternating voltage at 500 HZ. The luminance of the devices increased with the concentration of doped BBOT, but electroluminescence characteristics were different from a single molecule's photoluminescence properties of triple peaks. When analyzing in detail direct-current electroluminescence devices of pure BBOT, a single peak centered at 2.82 eV appeared with the driven voltage increase, which is similar to the hybrid devices. Comparing Gaussian decomposition date between two kinds of devices, the triple peak characteristic of BBOT was consistent. It is inferred that BBOT contributed EL of the hybrid devices mainly and silica may account for a very small part. Meanwhile the thermal stability of matrix silica was measured by Thermal Gravity-Mass Spectroscopy (TG-MS). There is 12 percent weight loss from room temperature to 1000 °C and silica has about 95% transmittance. So the matric silica played an important role in thermal stability and optical stability for BBOT. In addition, this kind of blue electroluminescence device can take advantages of organic materials BBOT and inorganic materials silica. This is a promising way to enrich EL devices, especially enriching inorganic EL color at a low cost.

Establishing Dual Electrogenerated Chemiluminescence and Multi-Color Electrochromism in Functional Ionic Transition Metal Complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puodziukynaite, Egle; Oberst, Justin L.; Dyer, Aubrey L.

A combination of electrochromism and electroluminescence in functional materials could lead to single-layer dual electrochromic/electroluminescent (EC/EL) display devices, capable of simultaneous operation in emissive and reflective modes. Whereas such next generation displays could provide optimal visibility in any ambient lighting situation, materials available that exhibit such characteristics in the active layer are limited due to the required intrinsic multifunctionality (i.e., redox activity, electroluminescence, electrochromism, and ion conductivity) and to date can only be achieved via the rational design of ionic transition-metal complexes. Reported herein is the synthesis and characterization of a new family of acrylate-containing ruthenium (tris)bipyridine-based coordination complexes withmore » multifunctional characteristics. Potential use of the presented compounds in EC/EL devices is established, as they are applied as cross-linked electrochromic films and electrochemiluminescent layers in light-emitting electrochemical cell devices. Electrochromic switching of the polymeric networks between yellow, orange, green, brown and transmissive states is demonstrated, and electrochemiluminescent devices based on the complexes synthesized show red-orange to deep red emission with λ{sub max} ranging from 680 to 722 nm and luminance up to 135 cd/m{sup 2}. Additionally, a dual EC/EL device prototype is presented where light emission and multicolor electrochromism occur from the same pixel comprised of a single active layer, demonstrating a true combination of these properties in ionic transition-metal complexes.« less

Establishing Dual Electrogenerated Chemiluminescence and Multicolor Electrochromism in Functional Ionic Transition-Metal Complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puodziukynaite, Egle; Oberst, Justin L.; Dyer, Aubrey L.

A combination of electrochromism and electroluminescence in functional materials could lead to single-layer dual electrochromic/electroluminescent (EC/EL) display devices, capable of simultaneous operation in emissive and reflective modes. Whereas such next generation displays could provide optimal visibility in any ambient lighting situation, materials available that exhibit such characteristics in the active layer are limited due to the required intrinsic multifunctionality (i.e., redox activity, electroluminescence, electrochromism, and ion conductivity) and to date can only be achieved via the rational design of ionic transition-metal complexes. Reported herein is the synthesis and characterization of a new family of acrylate-containing ruthenium (tris)bipyridine-based coordination complexes withmore » multifunctional characteristics. Potential use of the presented compounds in EC/EL devices is established, as they are applied as cross-linked electrochromic films and electrochemiluminescent layers in light-emitting electrochemical cell devices. Electrochromic switching of the polymeric networks between yellow, orange, green, brown and transmissive states is demonstrated, and electrochemiluminescent devices based on the complexes synthesized show red-orange to deep red emission with λmax ranging from 680 to 722 nm and luminance up to 135 cd/m². Additionally, a dual EC/EL device prototype is presented where light emission and multicolor electrochromism occur from the same pixel comprised of a single active layer, demonstrating a true combination of these properties in ionic transition-metal complexes.« less

Electroluminescence analysis for spatial characterization of parasitic optical losses in silicon heterojunction solar cells

NASA Astrophysics Data System (ADS)

Ahmed, Nuha; Zhang, Lei; Sriramagiri, Gowri; Das, Ujjwal; Hegedus, Steven

2018-04-01

Electroluminescence (EL) coupled with reflection measurements are used to spatially quantify optical losses in silicon heterojunction solar cells due to plasmonic absorption in the metal back contacts. The effect of indium tin oxide back reflector in decreasing this plasmonic absorption is found to increase the reflection from the back nickel (Ni)-aluminum (Al) and Al metals by ˜12% and ˜41%, respectively, in both bifacial and front junction silicon solar cells. Losses due to back reflection are calculated by comparison between the EL emission signals in high and low back reflection samples and are shown to be in agreement with standard reflection measurements. We conclude that the optical properties of the back contact can significantly influence the EL intensity which complicates the interpretation of EL as being primarily due to recombination especially when comparing two different devices with spatially varying back surface structures.

Synthesis, structures, and electroluminescent properties of scandium N,O-chelated complexes toward near-white organic light-emitting diodes.

PubMed

Katkova, Marina A; Balashova, Tatyana V; Ilichev, Vasilii A; Konev, Alexey N; Isachenkov, Nikolai A; Fukin, Georgy K; Ketkov, Sergey Yu; Bochkarev, Mikhail N

2010-06-07

Three members of a new class of electroluminescent, neutral, and monomeric scandium N,O-chelate complexes, namely, Sc(III)-tris-2-(2-benzoimidazol-2-yl)phenolate (1), Sc(III)-tris-2-(2-benzoxyazol-2-yl)phenolate (2), and Sc(III)-tris-2-(2-benzothiazol-2-yl)phenolate (3), have been prepared and X-ray characterized. DFT calculations have been performed. In contrast to the most frequently applied dual or multiple dopants in multilayer white OLED devices, all our simpler devices with the configuration of indium tin oxide/N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine/neat scandium complex/Yb exhibit close to near-white emission with a blue hue (CIE(x,y) = 0.2147, 0.2379) in the case of 1, a cyan hue (0.2702, 0.3524) in the case of 2, and a yellowish hue (0.3468; 0.4284) in the case of 3.

Analysis of power supply circuits for electroluminescent panels

NASA Astrophysics Data System (ADS)

Drumea, Andrei; Dobre, Robert Alexandru

2016-12-01

The electroluminescent panel is a light emitting device that requires for normal operations alternative voltages with peak to peak amplitudes in 100V… 300V range and frequencies in 100Hz … 2 kHz range. Its advantages, when compared with standard light sources like incandescent lamps, gas-discharge lamps or light emitting diodes (LEDs), are lower power consumption, flexible substrate and uniform light without observable luminous points. One disadvantage of electroluminescent panels is the complex power supply required to drive them, but the continuous improvement in passive and active integrated devices for switched mode power supplies will eventually solve this issue. The present paper studies different topologies for these power supplies and the effect of the electric parameters like the amplitude, frequency, waveform of the supplying voltage on the light emission and on power consumption for electroluminescent panels with different size and colors.

Optical properties of p–i–n structures based on amorphous hydrogenated silicon with silicon nanocrystals formed via nanosecond laser annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krivyakin, G. K.; Volodin, V. A., E-mail: volodin@isp.nsc.ru; Kochubei, S. A.

Silicon nanocrystals are formed in the i layers of p–i–n structures based on a-Si:H using pulsed laser annealing. An excimer XeCl laser with a wavelength of 308 nm and a pulse duration of 15 ns is used. The laser fluence is varied from 100 (below the melting threshold) to 250 mJ/cm{sup 2} (above the threshold). The nanocrystal sizes are estimated by analyzing Raman spectra using the phonon confinement model. The average is from 2.5 to 3.5 nm, depending on the laser-annealing parameters. Current–voltage measurements show that the fabricated p–i–n structures possess diode characteristics. An electroluminescence signal in the infrared (IR)more » range is detected for the p–i–n structures with Si nanocrystals; the peak position (0.9–1 eV) varies with the laser-annealing parameters. Radiative transitions are presumably related to the nanocrystal–amorphous-matrix interface states. The proposed approach can be used to produce light-emitting diodes on non-refractory substrates.« less

Correlating electroluminescence characterization and physics-based models of InGaN/GaN LEDs: Pitfalls and open issues

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calciati, Marco; Vallone, Marco; Zhou, Xiangyu

2014-06-15

Electroluminescence (EL) characterization of InGaN/GaN light-emitting diodes (LEDs), coupled with numerical device models of different sophistication, is routinely adopted not only to establish correlations between device efficiency and structural features, but also to make inferences about the loss mechanisms responsible for LED efficiency droop at high driving currents. The limits of this investigative approach are discussed here in a case study based on a comprehensive set of current- and temperature-dependent EL data from blue LEDs with low and high densities of threading dislocations (TDs). First, the effects limiting the applicability of simpler (closed-form and/or one-dimensional) classes of models are addressed,more » like lateral current crowding, vertical carrier distribution nonuniformity, and interband transition broadening. Then, the major sources of uncertainty affecting state-of-the-art numerical device simulation are reviewed and discussed, including (i) the approximations in the transport description through the multi-quantum-well active region, (ii) the alternative valence band parametrizations proposed to calculate the spontaneous emission rate, (iii) the difficulties in defining the Auger coefficients due to inadequacies in the microscopic quantum well description and the possible presence of extra, non-Auger high-current-density recombination mechanisms and/or Auger-induced leakage. In the case of the present LED structures, the application of three-dimensional numerical-simulation-based analysis to the EL data leads to an explanation of efficiency droop in terms of TD-related and Auger-like nonradiative losses, with a C coefficient in the 10{sup −30} cm{sup 6}/s range at room temperature, close to the larger theoretical calculations reported so far. However, a study of the combined effects of structural and model uncertainties suggests that the C values thus determined could be overestimated by about an order of magnitude. This preliminary attempt at uncertainty quantification confirms, beyond the present case, the need for an improved description of carrier transport and microscopic radiative and nonradiative recombination mechanisms in device-level LED numerical models.« less

Efficient red organic electroluminescent devices by doping platinum(II) Schiff base emitter into two host materials with stepwise energy levels.

PubMed

Zhou, Liang; Kwok, Chi-Chung; Cheng, Gang; Zhang, Hongjie; Che, Chi-Ming

2013-07-15

In this work, organic electroluminescent (EL) devices with double light-emitting layers (EMLs) having stepwise energy levels were designed to improve the EL performance of a red-light-emitting platinum(II) Schiff base complex. A series of devices with single or double EML(s) were fabricated and characterized. Compared with single-EML devices, double-EML devices showed improved EL efficiency and brightness, attributed to better balance in carriers. In addition, the stepwise distribution in energy levels of host materials is instrumental in broadening the recombination zone, thus delaying the roll-off of EL efficiency. The highest EL current efficiency and power efficiency of 17.36 cd/A and 14.73 lm/W, respectively, were achieved with the optimized double-EML devices. At high brightness of 1000 cd/m², EL efficiency as high as 8.89 cd/A was retained.

A Laboratory-Based Course in Display Technology

ERIC Educational Resources Information Center

Sarik, J.; Akinwande, A. I.; Kymissis, I.

2011-01-01

A laboratory-based class in flat-panel display technology is presented. The course introduces fundamental concepts of display systems and reinforces these concepts through the fabrication of three display devices--an inorganic electroluminescent seven-segment display, a dot-matrix organic light-emitting diode (OLED) display, and a dot-matrix…

Light-emitting block copolymers composition, process and use

DOEpatents

Ferraris, John P.; Gutierrez, Jose J.

2006-11-14

Generally, and in one form, the present invention is a composition of light-emitting block copolymer. In another form, the present invention is a process producing a light-emitting block copolymers that intends polymerizing a first di(halo-methyl) aromatic monomer compound in the presence of an anionic initiator and a base to form a polymer and contacting a second di(halo-methyl) aromatic monomer compound with the polymer to form a homopolymer or block copolymer wherein the block copolymer is a diblock, triblock, or star polymer. In yet another form, the present invention is an electroluminescent device comprising a light-emitting block copolymer, wherein the electroluminescent device is to be used in the manufacturing of optical and electrical devices.

Single n-GaN microwire/p-Silicon thin film heterojunction light-emitting diode.

PubMed

Ahn, Jaehui; Mastro, Michael A; Klein, Paul B; Hite, Jennifer K; Feigelson, Boris; Eddy, Charles R; Kim, Jihyun

2011-10-24

The emission and waveguiding properties of individual GaN microwires as well as devices based on an n-GaN microwire/p-Si (100) junction were studied for relevance in optoelectronics and optical circuits. Pulsed photoluminescence of the GaN microwire excited in the transverse or longitudinal direction demonstrated gain. These n-type GaN microwires were positioned mechanically or by dielectrophoretic force onto pre-patterned electrodes on a p-type Si (100) substrate. Electroluminescence from this p-n point junction was characteristic of a heterostructure light-emitting diode. Additionally, waveguiding was observed along the length of the microwire for light originating from photoluminescence as well as from electroluminescence generated at the p-n junction. © 2011 Optical Society of America

Density-matrix approach for the electroluminescence of molecules in a scanning tunneling microscope.

PubMed

Tian, Guangjun; Liu, Ji-Cai; Luo, Yi

2011-04-29

The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices.

Low injection losses in InGaN/GaN LEDs: The correlation of photoluminescence, electroluminescence, and photocurrent measurements

NASA Astrophysics Data System (ADS)

Quitsch, Wolf-Alexander; Sager, Daniel; Loewenich, Moritz; Meyer, Tobias; Hahn, Berthold; Bacher, Gerd

2018-06-01

Time-resolved photoluminescence spectroscopy and photocurrent measurements at quasi-resonant laser excitation are combined with electroluminescence studies to get access to low injection losses in high power InGaN/GaN LEDs. A direct relation between electroluminescence and photoluminescence efficiencies with photocurrent is found, indicating that tunneling losses play a key role in the low injection regime. This assertion is confirmed by comparing photoluminescence efficiencies under open and closed circuit conditions. Experiments under various excitation wavelengths hint at the role of resonant tunneling processes in the efficiency losses.

Red Light Emitting Schottky Diodes on p-TYPE GaN/AlN/Si(111) Substrate

NASA Astrophysics Data System (ADS)

Chuah, L. S.; Hassan, Z.; Abu Hassan, H.

High quality GaN layers doped with Mg were grown on Si(111) substrates using high temperature AlN as buffer layer by radio-frequency molecular beam epitaxy. From the Hall measurements, fairly uniform high hole concentration as high as (4-5) × 1020 cm-3 throughout the GaN was achieved. The fabrication of the device is very simple. Nickel ohmic contacts and Schottky contacts using indium were fabricated on Mg-doped p-GaN films. The light emission has been obtained from these thin film electroluminescent devices. Thin film electroluminescent devices were operated under direct current bias. Schottky and ohmic contacts used as cathode and anode were employed in these investigations. Alternatively, two Schottky contacts could be probed as cathode and anode. Thin film electroluminescent devices were able to emit light. However, electrical and optical differences could be observed from the two different probing methods. The red light color could be observed when the potential between the electrodes was increased gradually under forward bias of 8 V at room temperature. Electrical properties of these thin film electroluminescent devices were characterized by current-voltage (I-V) system, the heights of barriers determined from the I-V measurements were found to be related to the electroluminescence.

Quantum confinement-induced tunable exciton states in graphene oxide.

PubMed

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology.

Electrically induced spontaneous emission in open electronic system

NASA Astrophysics Data System (ADS)

Wang, Rulin; Zhang, Yu; Yam, Chiyung; Computation Algorithms Division (CSRC) Team; Theoretical; Computational Chemistry (HKU) Collaboration

A quantum mechanical approach is formulated for simulation of electroluminescence process in open electronic system. Based on nonequilibrium Green's function quantum transport equations and combining with photon-electron interaction, this method is used to describe electrically induced spontaneous emission caused by electron-hole recombination. The accuracy and reliability of simulation depends critically on correct description of the electronic band structure and the electron occupancy in the system. In this work, instead of considering electron-hole recombination in discrete states in the previous work, we take continuous states into account to simulate the spontaneous emission in open electronic system, and discover that the polarization of emitted photon is closely related to its propagation direction. Numerical studies have been performed to silicon nanowire-based P-N junction with different bias voltage.

Effects of two-step Mg doping in p-GaN on efficiency characteristics of InGaN blue light-emitting diodes without AlGaN electron-blocking layers

NASA Astrophysics Data System (ADS)

Ryu, Han-Youl; Lee, Jong-Moo

2013-05-01

A light-emitting diode (LED) structure containing p-type GaN layers with two-step Mg doping profiles is proposed to achieve high-efficiency performance in InGaN-based blue LEDs without any AlGaN electron-blocking-layer structures. Photoluminescence and electroluminescence (EL) measurement results show that, as the hole concentration in the p-GaN interlayer between active region and the p-GaN layer increases, defect-related nonradiative recombination increases, while the electron current leakage decreases. Under a certain hole-concentration condition in the p-GaN interlayer, the electron leakage and active region degradation are optimized so that high EL efficiency can be achieved. The measured efficiency characteristics are analyzed and interpreted using numerical simulations.

Ex post manipulation of barriers in InGaAs tunnel injection devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talalaev, Vadim G.; Fock Institute of Physics, St. Petersburg State University, St. Petersburg 198504; Cirlin, George E.

Ex post manipulation of ∼1.1 μm emitting InGaAs/GaAs-based quantum dot–quantum well tunnel injection light emitting devices is demonstrated experimentally. The devices were operated at elevated forward currents until irreversible alterations were observed. As a result, changes in the steady-state optical spectra (electroluminescence, photoluminescence, and photocurrent), in carrier kinetics, in transport properties, and real structure are found. Except for degradation effects, e.g., of larger quantum dots, also restoration/annealing effects such as increased tunnel barriers are observed. The results furnish evidence for a generic degradation mode of nanostructures. We qualitatively interpret the mechanisms involved on both the nanoscopic and the device scales.

A fluorescent stilbenoid dendrimer for solution-processed blue light emitting diodes

NASA Astrophysics Data System (ADS)

Coya, C.; Álvarez, A. L.; Ramos, M.; de Andrés, A.; Zaldo, C.; Gómez, R.; Segura, J. L.; Seoane, C.

2008-04-01

We report a solution processed blue stilbenoid dendrimer based on a 1, 3, 5 - benzene core and endowed with a periphery of electron donating and solubilizing alkoxy chains. Raman analysis it is revealed as a helpful tool to investigate changes from the pristine material to the material in the OLED structure, explaining the differences between the dendrimer single layer thin film photoluminescence (PL) and the electroluminescence (EL) dendrimer active layer emission in the device. We report a blue EL emission (439 nm) and a very promising effective mobility value of 2.55 × 10 -5 cm2/(V•s) suggesting good transport properties for non doped blue OLEDs that use air stable Al as the cathode.

Improvement of light extraction for a target wavelength in InGaN/GaN LEDs with an indium tin oxide dual layer by oblique angle deposition

NASA Astrophysics Data System (ADS)

Seo, Dong-Ju; Lee, Dong-Seon

2016-08-01

GaN-based blue LEDs were fabricated and studied with porous, dense, and dual-layer indium tin oxide (ITO) structures as transparent top electrodes to enhance light extraction. The electroluminescence intensity of the LED with a thickness-optimized and refractive-index-tuned ITO dual layer at I = 20 mA was higher by 19.7% than that of the conventional LED with a 200 nm planar ITO. This study confirmed that an ITO dual layer can be made with a single material by optimizing the thickness and tuning the refractive index, which improves the power output without any electrical property degradation.

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs

NASA Astrophysics Data System (ADS)

Puchert, Robin P.; Steiner, Florian; Plechinger, Gerd; Hofmann, Felix J.; Caspers, Ines; Kirschner, Johanna; Nagler, Philipp; Chernikov, Alexey; Schüller, Christian; Korn, Tobias; Vogelsang, Jan; Bange, Sebastian; Lupton, John M.

2017-07-01

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit 'cold' electroluminescence in percolation films, tunnel diodes, electromigrated nanoparticle aggregates, optical antennas or scanning tunnelling microscopy. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET-light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes in on-chip optical interconnects.

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs.

PubMed

Puchert, Robin P; Steiner, Florian; Plechinger, Gerd; Hofmann, Felix J; Caspers, Ines; Kirschner, Johanna; Nagler, Philipp; Chernikov, Alexey; Schüller, Christian; Korn, Tobias; Vogelsang, Jan; Bange, Sebastian; Lupton, John M

2017-07-01

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit 'cold' electroluminescence in percolation films, tunnel diodes, electromigrated nanoparticle aggregates, optical antennas or scanning tunnelling microscopy. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET-light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes in on-chip optical interconnects.

Tunable Optical Polymer Systems (TOPS)

DTIC Science & Technology

2001-05-01

pixelation o1 displays is done. One team member has combined this work with self-assembling layers so that it is possible to make three-dimensional...I THERMOCHROMISM I ELECTROCHEMILUMINESCENCE (ECL) I MAGNETOCHROMISM I TUNABLE ELECTROLUMINESCENCE (EL) PROTONIC BAND GAP (PBG) SELECTIVE...via Selective Reflection • Chiral-nematic liquid crystalline film as a helical stack of quasinematic layers , illustrated below with a LH structure

European Science Notes Information Bulletin. Reports on Current European and Middle Eastern Science

DTIC Science & Technology

1993-01-01

network. Mechanical properties of ormolytes can tion of TiO2 to "open-up" the structure tb.r Li be modified by altering the structure of the silicate...Cambridge es. The group from the University of California, group has demonstrated that the color (wavelength) Santa Barbara, and Uniax Corporation...A.J. of the electroluminescence can be tuned over a Heeger, F. Wudi, P. Smith) reported on their work range of colors . with polymer 12 in several talks

Electroluminescence and transport properties in amorphous silicon nanostructures

NASA Astrophysics Data System (ADS)

Irrera, Alessia; Iacona, Fabio; Crupi, Isodiana; Presti, Calogero D.; Franzò, Giorgia; Bongiorno, Corrado; Sanfilippo, Delfo; Di Stefano, Gianfranco; Piana, Angelo; Fallica, Pier Giorgio; Canino, Andrea; Priolo, Francesco

2006-03-01

We report the results of a detailed study on the structural, electrical and optical properties of light emitting devices based on amorphous Si nanostructures. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature electroluminescence (EL), with the advantage of being formed at a temperature of 900 °C, while at least 1100 °C is needed for the formation of Si nanocrystals. Optical and electrical properties of amorphous Si nanocluster devices have been studied in the temperature range between 30 and 300 K. The EL is seen to have a bell-shaped trend as a function of temperature with a maximum at around 60 K. The efficiency of these devices is comparable to that found in devices based on Si nanocrystals, although amorphous nanostructures exhibit peculiar working conditions (very high current densities and low applied voltages). Time resolved EL measurements demonstrate the presence of a short lifetime, only partially due to the occurrence of non-radiative phenomena, since the very small amorphous clusters formed at 900 °C are characterized by a short radiative lifetime. By forcing a current through the device a phenomenon of charge trapping in the Si nanostructures has been observed. Trapped charges affect luminescence through an Auger-type non-radiative recombination of excitons. Indeed, it is shown that unbalanced injection of carriers (electrons versus holes) is one of the main processes limiting luminescence efficiency. These data will be reported and the advantages and limitations of this approach will be discussed.

Theoretical and material studies on thin-film electroluminescent devices

NASA Technical Reports Server (NTRS)

Summers, C. J.; Brennan, K. F.

1986-01-01

A theoretical study of resonant tunneling in multilayered heterostructures is presented based on an exact solution of the Schroedinger equation under the application of a constant electric field. By use of the transfer matrix approach, the transmissivity of the structure is determined as a function of the incident electron energy. The approach presented is easily extended to many layer structures where it is more accurate than other existing transfer matrix or WKB models. The transmission resonances are compared to the bound state energies calculated for a finite square well under bias using either an asymmetric square well model or the exact solution of an infinite square well under the application of an electric field. The results show good agreement with other existing models as well as with the bound state energies. The calculations were then applied to a new superlattice structure, the variablly spaced superlattice energy filter, (VSSEP) which is designed such that under bias the spatial quantization levels fully align. Based on these calculations, a new class of resonant tunneling superlattice devices can be designed.

Highly Luminescent 2D-Type Slab Crystals Based on a Molecular Charge-Transfer Complex as Promising Organic Light-Emitting Transistor Materials.

PubMed

Park, Sang Kyu; Kim, Jin Hong; Ohto, Tatsuhiko; Yamada, Ryo; Jones, Andrew O F; Whang, Dong Ryeol; Cho, Illhun; Oh, Sangyoon; Hong, Seung Hwa; Kwon, Ji Eon; Kim, Jong H; Olivier, Yoann; Fischer, Roland; Resel, Roland; Gierschner, Johannes; Tada, Hirokazu; Park, Soo Young

2017-09-01

A new 2:1 donor (D):acceptor (A) mixed-stacked charge-transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene-based D and A molecules is designed and synthesized. Uniform 2D-type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique optoelectronic properties are unveiled. Exceptionally high photoluminescence quantum yield (Φ F ≈ 60%) is realized by non-negligible oscillator strength of the S 1 transition, and rigidified 2D-type structure. Moreover, this luminescent 2D-type CT crystal exhibits balanced ambipolar transport (µ h and µ e of ≈10 -4 cm 2 V -1 s -1 ). As a consequence of such unique optoelectronic characteristics, the first CT electroluminescence is demonstrated in a single active-layered organic light-emitting transistor (OLET) device. The external quantum efficiency of this OLET is as high as 1.5% to suggest a promising potential of luminescent mixed-stacked CT cocrystals in OLET applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Organic electroluminescent devices having improved light extraction

DOEpatents

Shiang, Joseph John [Niskayuna, NY

2007-07-17

Organic electroluminescent devices having improved light extraction include a light-scattering medium disposed adjacent thereto. The light-scattering medium has a light scattering anisotropy parameter g in the range from greater than zero to about 0.99, and a scatterance parameter S less than about 0.22 or greater than about 3.

Dual functions of a new n-type conjugated dendrimer: light-emitting material and additive for polymer electroluminescent devices

NASA Astrophysics Data System (ADS)

Hyeok Park, Jong; Kim, Chulhee; Kim, Young Chul

2009-02-01

We demonstrate a novel light-emitting diode (LED) of a graded bilayer structure that comprises poly(N-vinylcarbazole) (PVK) with good hole transport ability as the energy donor and a new distyrylanthracene-triazine-based dendrimer with enhanced electron transport ability as the light-emitting molecule. The device contains a graded bilayer structure of the PVK film covered with the dendrimer film prepared by sequential spin-casting of the dendrimer layer from a solvent that only swells the PVK layer. The bilayer device demonstrated a significantly enhanced electoluminescence quantum efficiency compared with the dendrimer single layer device or the PVK : dendrimer blend device with optimized composition. We also prepared composite LEDs with an MEH-PPV : emissive dendrimer blend. By doping the electron-deficient MEH-PPV layer with a small amount of the distyrylanthracene-triazine-based dendrimer, we could not only enhance the device performance but also depress the long-wavelength emission of MEH-PPV.

Separation of effects of InGaN/GaN superlattice on performance of light-emitting diodes using mid-temperature-grown GaN layer

NASA Astrophysics Data System (ADS)

Sugimoto, Kohei; Okada, Narihito; Kurai, Satoshi; Yamada, Yoichi; Tadatomo, Kazuyuki

2018-06-01

We evaluated the electrical properties of InGaN-based light-emitting diodes (LEDs) with a superlattice (SL) layer or a mid-temperature-grown GaN (MT-GaN) layer just beneath the multiple quantum wells (MQWs). Both the SL layer and the MT-GaN layer were effective in improving the electroluminescence (EL) intensity. However, the SL layer had a more pronounced effect on the EL intensity than did the MT-GaN layer. Based on a comparison with devices with an MT-GaN layer, the overall effects of the SL could be separated into the effect of the V-pits and the structural or compositional effect of the SL. It was observed that the V-pits formed account for 30% of the improvement in the LED performance while the remaining 70% can be attributed to the structural or compositional effect of the SL.

Electrical spin injection from an n-type ferromagnetic semiconductor into a III-V device heterostructure

NASA Astrophysics Data System (ADS)

Kioseoglou, George; Hanbicki, Aubrey T.; Sullivan, James M.; van't Erve, Olaf M. J.; Li, Connie H.; Erwin, Steven C.; Mallory, Robert; Yasar, Mesut; Petrou, Athos; Jonker, Berend T.

2004-11-01

The use of carrier spin in semiconductors is a promising route towards new device functionality and performance. Ferromagnetic semiconductors (FMSs) are promising materials in this effort. An n-type FMS that can be epitaxially grown on a common device substrate is especially attractive. Here, we report electrical injection of spin-polarized electrons from an n-type FMS, CdCr2Se4, into an AlGaAs/GaAs-based light-emitting diode structure. An analysis of the electroluminescence polarization based on quantum selection rules provides a direct measure of the sign and magnitude of the injected electron spin polarization. The sign reflects minority rather than majority spin injection, consistent with our density-functional-theory calculations of the CdCr2Se4 conduction-band edge. This approach confirms the exchange-split band structure and spin-polarized carrier population of an FMS, and demonstrates a litmus test for these FMS hallmarks that discriminates against spurious contributions from magnetic precipitates.

Exciplex formation and electroluminescent absorption in ultraviolet organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Qi; Zhang, Hao; Zhang, Xiao-Wen; Xu, Tao; Wei, Bin

2015-02-01

We investigated the formation of exciplex and electroluminescent absorption in ultraviolet organic light-emitting diodes (UV OLEDs) using different heterojunction structures. It is found that an energy barrier of over 0.3 eV between the emissive layer (EML) and adjacent transport layer facilitates exciplex formation. The electron blocking layer effectively confines electrons in the EML, which contributes to pure UV emission and enhances efficiency. The change in EML thickness generates tunable UV emission from 376 nm to 406 nm. In addition, the UV emission excites low-energy organic function layers and produces photoluminescent emission. In UV OLED, avoiding the exciplex formation and averting light absorption can effectively improve the purity and efficiency. A maximum external quantum efficiency of 1.2% with a UV emission peak of 376 nm is realized. Project supported by the National Natural Science Foundation of China (Grant Nos. 61136003 and 61275041) and the Guangxi Provincial Natural Science Foundation, China (Grant No. 2012GXNSFBA053168).

Electroluminescence from InGaN/GaN multi-quantum-wells nanorods light-emitting diodes positioned by non-uniform electric fields.

PubMed

Park, Hyunik; Kim, Byung-Jae; Kim, Jihyun

2012-11-05

We report that the nanorod light-emitting diodes (LEDs) with InGaN/GaN multi-quantum-wells (MQWs) emitted bright electroluminescence (EL) after they were positioned and aligned by non-uniform electric fields. Firstly, thin film LED structures with MQWs on sapphire substrate were coated with SiO(2) nanospheres, followed by inductively-coupled plasma etch to create nanorod-shapes with MQWs, which were transferred to the pre-patterned SiO(2)/Si wafer. This method allowed us to obtain nanorod LEDs with uniform length, diameter and qualities. Dielectrophoretic force created by non-uniform electric field was very effective at positioning the processed nanorods on the pre-patterned contacts. After aligned by non-uniform electric field, we observed bright EL from many nanorods, which had both cases (p-GaN/MQWs/n-GaN or n-GaN/MQWs/p-GaN). Therefore, bright ELs at different locations were observed under the various bias conditions.

Quantum confinement-induced tunable exciton states in graphene oxide

PubMed Central

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M.; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology. PMID:23872608

Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence

PubMed Central

Xing, Guichuan; Wu, Bo; Wu, Xiangyang; Li, Mingjie; Du, Bin; Wei, Qi; Guo, Jia; Yeow, Edwin K. L.; Sum, Tze Chien; Huang, Wei

2017-01-01

The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 1015 cm−3, defect-states trapping in three-dimensional perovskites competes effectively with the bimolecular radiative recombination. Herein, we overcome this limitation using van-der-Waals-coupled Ruddlesden-Popper perovskite multi-quantum-wells. Injected charge carriers are rapidly localized from adjacent thin few layer (n≤4) multi-quantum-wells to the thick (n≥5) multi-quantum-wells with extremely high efficiency (over 85%) through quantum coupling. Light emission originates from excitonic recombination in the thick multi-quantum-wells at much higher decay rate and efficiency than bimolecular recombination in three-dimensional perovskites. These multi-quantum-wells retain the simple solution processability and high charge carrier mobility of two-dimensional lead-halide perovskites. Importantly, these Ruddlesden-Popper perovskites offer new functionalities unavailable in single phase constituents, permitting the transcendence of the slow bimolecular recombination bottleneck in lead-halide perovskites for efficient electroluminescence. PMID:28239146

Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence.

PubMed

Xing, Guichuan; Wu, Bo; Wu, Xiangyang; Li, Mingjie; Du, Bin; Wei, Qi; Guo, Jia; Yeow, Edwin K L; Sum, Tze Chien; Huang, Wei

2017-02-27

The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 10 15  cm -3 , defect-states trapping in three-dimensional perovskites competes effectively with the bimolecular radiative recombination. Herein, we overcome this limitation using van-der-Waals-coupled Ruddlesden-Popper perovskite multi-quantum-wells. Injected charge carriers are rapidly localized from adjacent thin few layer (n≤4) multi-quantum-wells to the thick (n≥5) multi-quantum-wells with extremely high efficiency (over 85%) through quantum coupling. Light emission originates from excitonic recombination in the thick multi-quantum-wells at much higher decay rate and efficiency than bimolecular recombination in three-dimensional perovskites. These multi-quantum-wells retain the simple solution processability and high charge carrier mobility of two-dimensional lead-halide perovskites. Importantly, these Ruddlesden-Popper perovskites offer new functionalities unavailable in single phase constituents, permitting the transcendence of the slow bimolecular recombination bottleneck in lead-halide perovskites for efficient electroluminescence.

Broadly continuously tunable slot waveguide quantum cascade lasers based on a continuum-to-continuum active region design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Bo; Zeng, Yong Quan; Liang, Guozhen

2015-09-14

We report our progress in the development of broadly tunable single-mode slot waveguide quantum cascade lasers based on a continuum-to-continuum active region design. The electroluminescence spectrum of the continuum-to-continuum active region design has a full width at half maximum of 440 cm{sup −1} at center wavelength ∼10 μm at room temperature (300 K). Devices using the optimized slot waveguide structure and the continuum-to-continuum design can be tuned continuously with a lasing emission over 42 cm{sup −1}, from 9.74 to 10.16 μm, at room temperature by using only current tuning scheme, together with a side mode suppression ratio of above 15 dB within the whole tuning range.

Light-emitting self-assembled peptide nucleic acids exhibit both stacking interactions and Watson-Crick base pairing.

PubMed

Berger, Or; Adler-Abramovich, Lihi; Levy-Sakin, Michal; Grunwald, Assaf; Liebes-Peer, Yael; Bachar, Mor; Buzhansky, Ludmila; Mossou, Estelle; Forsyth, V Trevor; Schwartz, Tal; Ebenstein, Yuval; Frolow, Felix; Shimon, Linda J W; Patolsky, Fernando; Gazit, Ehud

2015-04-01

The two main branches of bionanotechnology involve the self-assembly of either peptides or DNA. Peptide scaffolds offer chemical versatility, architectural flexibility and structural complexity, but they lack the precise base pairing and molecular recognition available with nucleic acid assemblies. Here, inspired by the ability of aromatic dipeptides to form ordered nanostructures with unique physical properties, we explore the assembly of peptide nucleic acids (PNAs), which are short DNA mimics that have an amide backbone. All 16 combinations of the very short di-PNA building blocks were synthesized and assayed for their ability to self-associate. Only three guanine-containing di-PNAs-CG, GC and GG-could form ordered assemblies, as observed by electron microscopy, and these di-PNAs efficiently assembled into discrete architectures within a few minutes. The X-ray crystal structure of the GC di-PNA showed the occurrence of both stacking interactions and Watson-Crick base pairing. The assemblies were also found to exhibit optical properties including voltage-dependent electroluminescence and wide-range excitation-dependent fluorescence in the visible region.

New Molecular Design Concurrently Providing Superior Pure Blue, Thermally Activated Delayed Fluorescence and Optical Out-Coupling Efficiencies.

PubMed

Rajamalli, P; Senthilkumar, N; Huang, P-Y; Ren-Wu, C-C; Lin, H-W; Cheng, C-H

2017-08-16

Simultaneous enhancement of out-coupling efficiency, internal quantum efficiency, and color purity in thermally activated delayed fluorescence (TADF) emitters is highly desired for the practical application of these materials. We designed and synthesized two isomeric TADF emitters, 2DPyM-mDTC and 3DPyM-pDTC, based on di(pyridinyl)methanone (DPyM) cores as the new electron-accepting units and di(tert-butyl)carbazole (DTC) as the electron-donating units. 3DPyM-pDTC, which is structurally nearly planar with a very small ΔE ST , shows higher color purity, horizontal ratio, and quantum yield than 2DPyM-mDTC, which has a more flexible structure. An electroluminescence device based on 3DPyM-pDTC as the dopant emitter can reach an extremely high external quantum efficiency of 31.9% with a pure blue emission. This work also demonstrates a way to design materials with a high portion of horizontal molecular orientation to realize a highly efficient pure-blue device based on TADF emitters.

Pyrimidine-based twisted donor-acceptor delayed fluorescence molecules: a new universal platform for highly efficient blue electroluminescence.

PubMed

Park, In Seob; Komiyama, Hideaki; Yasuda, Takuma

2017-02-01

Deep-blue emitters that can harvest both singlet and triplet excited states to give high electron-to-photon conversion efficiencies are highly desired for applications in full-color displays and white lighting devices based on organic light-emitting diodes (OLEDs). Thermally activated delayed fluorescence (TADF) molecules based on highly twisted donor-acceptor (D-A) configurations are promising emitting dopants for the construction of efficient deep-blue OLEDs. In this study, a simple and versatile D-A system combining acridan-based donors and pyrimidine-based acceptors has been developed as a new platform for high-efficiency deep-blue TADF emitters. The designed pre-twisted acridan-pyrimidine D-A molecules exhibit small singlet-triplet energy splitting and high photoluminescence quantum yields, functioning as efficient deep-blue TADF emitters. The OLEDs utilizing these TADF emitters display bright blue electroluminescence with external quantum efficiencies of up to 20.4%, maximum current efficiencies of 41.7 cd A -1 , maximum power efficiencies of 37.2 lm W -1 , and color coordinates of (0.16, 0.23). The design strategy featuring such acridan-pyrimidine D-A motifs can offer great prospects for further developing high-performance deep-blue TADF emitters and TADF-OLEDs.

Luminescence and Electroluminescence of Nd, Tm and Yb Doped GaAs and some II-Vi Compounds

DTIC Science & Technology

1994-02-28

from the bandgap discontinuity (as was proposed in my publications [1,2]). Also, by using superlattice structure A1GaAs / GaAs: Er / AlGaAs, we could...n ipact ightemiting evic 10 3. The AlGaAs/GaAs: Er/A1GaAs superlattice structure. For the first time we designed the unipolar n’ - superlattice - n...structure as shown in Figure 5. The GaAs: Er/Alo.45Gao.55As superlattice was grown by MBE on an n’ GaAs: Si substrate. It consisted of 60 periods of

Emission spectra of a laser based on an In(Ga)As/GaAs quantum-dot superlattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sobolev, M. M., E-mail: m.sobolev@mail.ioffe.ru; Buyalo, M. S.; Nevedomskiy, V. N.

2015-10-15

The spectral characteristics of a laser with an active region based on a ten-layer system of In(Ga)As/GaAs vertically correlated quantum dots with 4.5-nm GaAs spacer layers between InAs quantum dots are studied under the conditions of spontaneous and stimulated emission, depending on the current and the duration of pump pulses. Data obtained by transmission electron microscopy and electroluminescence and absorption polarization anisotropy measurements make it possible to demonstrate that the investigated system of tunnel-coupled InAs quantum dots separated by thin GaAs barriers represents a quantum-dot superlattice. With an increase in the laser pump current, the electroluminescence intensity increases linearly andmore » the spectral position of the electroluminescence maximum shifts to higher energies, which is caused by the dependence of the miniband density-of-states distribution on the pump current. Upon exceeding the threshold current, multimode lasing via the miniband ground state is observed. One of the lasing modes can be attributed to the zero-phonon line, and the other is determined by the longitudinal-optical phonon replica of quantum-dot emission. The results obtained give evidence that, under conditions of the laser pumping of an In(Ga)As/GaAs quantum-dot superlattice, strong coupling between the discrete electron states in the miniband and optical phonons takes place. This leads to the formation of quantum-dot polarons, resulting from the resonant mixing of electronic states whose energy separation is comparable to the optical-phonon energy.« less

Localized surface plasmon-enhanced ultraviolet electroluminescence from n-ZnO/i-ZnO/p-GaN heterojunction light-emitting diodes via optimizing the thickness of MgO spacer layer

NASA Astrophysics Data System (ADS)

Liu, W. Z.; Xu, H. Y.; Zhang, L. X.; Zhang, C.; Ma, J. G.; Wang, J. N.; Liu, Y. C.

2012-10-01

Localized surface plasmon (LSP)-enhanced ultraviolet light-emitting diodes were manufactured by introducing Ag nanoparticles and MgO spacer layer into n-ZnO/i-ZnO/p-GaN heterostructures. By optimizing the MgO thickness, which can suppress the undesired charge transfer and nonradiative Förster resonant energy transfer between Ag and ZnO, a 7-fold electroluminescence enhancement was achieved. Time-resolved and temperature-dependent photoluminescence measurements reveal that both spontaneous emission rate and internal quantum efficiency are increased as a result of coupling between ZnO excitons and Ag LSPs, and simple calculations, based on experimental data, also indicate that most of LSP's energy can be converted into the photon energy.

White Electroluminescence Using ZnO Nanotubes/GaN Heterostructure Light-Emitting Diode

PubMed Central

2010-01-01

We report the fabrication of heterostructure white light–emitting diode (LED) comprised of n-ZnO nanotubes (NTs) aqueous chemically synthesized on p-GaN substrate. Room temperature electroluminescence (EL) of the LED demonstrates strong broadband white emission spectrum consisting of predominating peak centred at 560 nm and relatively weak violet–blue emission peak at 450 nm under forward bias. The broadband EL emission covering the whole visible spectrum has been attributed to the large surface area and high surface states of ZnO NTs produced during the etching process. In addition, comparison of the EL emission colour quality shows that ZnO nanotubes have much better quality than that of the ZnO nanorods. The colour-rendering index of the white light obtained from the nanotubes was 87, while the nanorods-based LED emit yellowish colour. PMID:20672120

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Tingting; Holford, D. F.; Gu, Hang

The magnetic field effects on the electroluminescence of aluminium tris-(8-hydroxyqinoline) (Alq{sub 3}) based organic light emitting diodes have been investigated by varying the electron/hole ratio in the emissive layer. Experimental results reveal that a negative high field effect in the magneto-electroluminescence (MEL) can be found in devices with very low triplet exciton concentration at room temperature. This suggests triplet-triplet annihilation cannot be used to explain the negative high field MEL in the Alq{sub 3} system. Our results suggest that hole-exciton interaction may be the origin of the negative high field MEL and also, in parallel with this interaction, there ismore » also the more common positive high field process occurring which has been tentatively attributed to electron-exciton interactions. The competition between these different processes decides the final shape of the MEL at high fields.« less

D–A–D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies

PubMed Central

Gan, Lin; Li, Xianglong; Cai, Xinyi; Liu, Kunkun; Li, Wei

2018-01-01

The design of orange-light emitting, thermally activated, delayed fluorescence (TADF) materials is necessary and important for the development and application of organic light-emitting diodes (OLEDs). Herein, two donor–acceptor–donor (D–A–D)-type orange TADF materials based on fluorenone and acridine, namely 2,7-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (27DACRFT, 1) and 3,6-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (36DACRFT, 2), were successfully synthetized and characterized. The studies on their structure–property relationship show that the different configurations have a serious effect on the photoluminescence and electroluminescence performance according to the change in singlet–triplet splitting energy (ΔE ST) and excited state geometry. This indicates that a better configuration design can reduce internal conversion and improve triplet exciton utilization of TADF materials. Importantly, OLEDs based on 2 exhibited a maximum external quantum efficiency of 8.9%, which is higher than the theoretical efficiency of the OLEDs based on conventional fluorescent materials. PMID:29623130

Quantum-Dot Light-Emitting Diodes with Nitrogen-Doped Carbon Nanodot Hole Transport and Electronic Energy Transfer Layer.

PubMed

Park, Young Ran; Jeong, Hu Young; Seo, Young Soo; Choi, Won Kook; Hong, Young Joon

2017-04-12

Electroluminescence efficiency is crucial for the application of quantum-dot light-emitting diodes (QD-LEDs) in practical devices. We demonstrate that nitrogen-doped carbon nanodot (N-CD) interlayer improves electrical and luminescent properties of QD-LEDs. The N-CDs were prepared by solution-based bottom up synthesis and were inserted as a hole transport layer (HTL) between other multilayer HTL heterojunction and the red-QD layer. The QD-LEDs with N-CD interlayer represented superior electrical rectification and electroluminescent efficiency than those without the N-CD interlayer. The insertion of N-CD layer was found to provoke the Förster resonance energy transfer (FRET) from N-CD to QD layer, as confirmed by time-integrated and -resolved photoluminescence spectroscopy. Moreover, hole-only devices (HODs) with N-CD interlayer presented high hole transport capability, and ultraviolet photoelectron spectroscopy also revealed that the N-CD interlayer reduced the highest hole barrier height. Thus, more balanced carrier injection with sufficient hole carrier transport feasibly lead to the superior electrical and electroluminescent properties of the QD-LEDs with N-CD interlayer. We further studied effect of N-CD interlayer thickness on electrical and luminescent performances for high-brightness QD-LEDs. The ability of the N-CD interlayer to improve both the electrical and luminescent characteristics of the QD-LEDs would be readily exploited as an emerging photoactive material for high-efficiency optoelectronic devices.

Spin-polarized light-emitting diodes based on organic bipolar spin valves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vardeny, Zeev Valentine; Nguyen, Tho Duc; Ehrenfreund, Eitan Avraham

Spin-polarized organic light-emitting diodes are provided. Such spin-polarized organic light-emitting diodes incorporate ferromagnetic electrodes and show considerable spin-valve magneto-electroluminescence and magneto-conductivity responses, with voltage and temperature dependencies that originate from the bipolar spin-polarized space charge limited current.

Tentative anatomy of ZnS-type electroluminescence

NASA Astrophysics Data System (ADS)

Bringuier, E.

1994-05-01

The paper reviews the electrical and optical mechanisms at work in sulfide-based thin-film electroluminescence display devices within the framework of general semiconductor physics. The electrical problem is twofold: (i) charge carriers are sourced at high electric field in a nominally insulating material, the carrier density increasing by almost eight orders of magnitude; (ii) the carriers are transported at high field, with an average energy largely exceeding the thermal one. (i) Carrier sourcing is best understood from direct-current-driven ZnS films, and is ascribed to partly filled deep donors transferring electrons to the conduction band by Fowler-Nordheim tunneling. The deep donors also act as carrier sinkers, and evidence for space charge is afforded by small-signal impedance analysis disclosing a markedly inductive behavior. The conduction picture obtained from dc-driven films is then used to clarify the operation of alternating-current electroluminescence structures where the sulfide is sandwiched between two blocking oxide layers. The electrostatics of the ac structure is investigated in detail including space charge and field nonuniformity, and external observables are related to internal quantities. The simple model of interfacial carrier sourcing and sinking is examined. (ii) High-field electronic transport is controlled by the electron-phonon interaction, and the modeling resorts to numerical simulations or the lucky-drift concept. At low electron energies the interaction with phonons is predominantly polar, while at optical energies it proceeds via deformation potential scattering. In spite of the uncertainties in transport models in that range, it is likely that ˜50% of the electrons overtake 2 eV at the usual operating fields in ZnS. Light emission is associated with impurity luminescence centers embedded in the sulfide host. They are excited while current is flowing, and the ensuing relaxation is partly radiative. We describe the two ways in which an impurity may be excited electrically, namely, impact excitation (internal promotion of the center to a state of higher energy) or impact ionization (with an electron released to the host conduction band). The actual excitation mechanism depends on the position of the impurity excited level relative to the host energy bands. A calculation of the excitation yield (number of excited centers per transferred electron) is detailed in the case of impact excitation. Lastly, a phenomenological description of the various relaxation channels is given in terms of formal kinetics, and the relative importance of radiative relaxation is assessed by means of the deexcitation yield (fraction of centers decaying radiatively), which is defined in the case of the impulse response.

The electroluminescence of Xe-Ne gas mixtures: A Monte Carol simulation study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santos, F.P.; Dias, T.H.V.T.; Rachinhas, P.J.B.M.

1998-04-01

The authors have performed a Monte Carlo simulation of the drift of electrons through a mixture of gaseous xenon with the lighter noble gas neon at a total pressure of 1 atm. The electroluminescence characteristics and other transport parameters are investigated as a function of the reduced electric field and composition of the mixture. For Xe-Ne mixtures with 5, 10, 20, 40, 70, 90, and 100% of Xe, they present results for electroluminescence yield and excitation efficiency, average electron energy, electron drift velocity, reduced mobility, reduced diffusion coefficients, and characteristic energies over a range of reduced electric fields which excludemore » electron multiplication. For the 5% Xe mixture, they also assess the influence of electron multiplication on the electroluminescence yield. The present study of Xe-Ne mixtures was motivated by an interest in using them as a filling for gas proportional scintillation counters in low-energy X-ray applications. In this energy range, the X rays will penetrate further into the detector due to the presence of Ne, and this will lead to an improvement in the collection of primary electrons originating near the detector window and may represent an advantage over the use of pure Xe.« less

Broadband light sources based on InAs/InGaAs metamorphic quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seravalli, L.; Trevisi, G.; Frigeri, P.

We propose a design for a semiconductor structure emitting broadband light in the infrared, based on InAs quantum dots (QDs) embedded into a metamorphic step-graded In{sub x}Ga{sub 1−x}As buffer. We developed a model to calculate the metamorphic QD energy levels based on the realistic QD parameters and on the strain-dependent material properties; we validated the results of simulations by comparison with the experimental values. On this basis, we designed a p-i-n heterostructure with a graded index profile toward the realization of an electrically pumped guided wave device. This has been done by adding layers where QDs are embedded in In{submore » x}Al{sub y}Ga{sub 1−x−y}As layers, to obtain a symmetric structure from a band profile point of view. To assess the room temperature electro-luminescence emission spectrum under realistic electrical injection conditions, we performed device-level simulations based on a coupled drift-diffusion and QD rate equation model. On the basis of the device simulation results, we conclude that the present proposal is a viable option to realize broadband light-emitting devices.« less

Study on the structural, optical, and electrical properties of the yellow light-emitting diode grown on free-standing (0001) GaN substrate

NASA Astrophysics Data System (ADS)

Deng, Gaoqiang; Zhang, Yuantao; Yu, Ye; Yan, Long; Li, Pengchong; Han, Xu; Chen, Liang; Zhao, Degang; Du, Guotong

2018-04-01

In this paper, GaN-based yellow light-emitting diodes (LEDs) were homoepitaxially grown on free-standing (0001) GaN substrates by metal-organic chemical vapor deposition. X-ray diffraction (XRD), photoluminescence (PL), and electroluminescence (EL) measurements were conducted to investigate the structural, optical, and electrical properties of the yellow LED. The XRD measurement results showed that the InGaN/GaN multiple quantum wells (MQWs) in the LED structure have good periodicity because the distinct MQWs related higher order satellite peaks can be clearly observed from the profile of 2θ-ω XRD scan. The low temperature (10 K) and room temperature PL measurement results yield an internal quantum efficiency of 16% for the yellow LED. The EL spectra of the yellow LED present well Gaussian distribution with relatively low linewidth (47-55 nm), indicating the homogeneous In-content in the InGaN quantum well layers in the yellow LED structure. It is believed that this work will aid in the future development of GaN on GaN LEDs with long emission wavelength.

Deep centers in AlGaN-based light emitting diode structures

NASA Astrophysics Data System (ADS)

Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Mil'vidskii, M. G.; Usikov, A. S.; Pushnyi, B. V.; Lundin, W. V.

1999-10-01

Deep traps were studied in GaN homojunction and AlGaN/GaN heterojunction light emitting diode (LED) p-i-n structures by means of deep levels transient spectroscopy (DLTS), admittance and electroluminescence (EL) spectra measurements. It is shown that, in homojunction LED structures, the EL spectra comes from recombination involving Mg acceptors in-diffusing into the active i-layer. This Mg in-diffusion is strongly suppressed in heterostructures with the upper p-type layer containing about 5% of Al. As a result the main peak in the EL spectra of heterostructures is shifted toward higher energy compared to homojunctions. Joint doping of the i-layer with Zn and Si allows to shift the main EL peak to longer wavelength. The dominant electron traps observed in the studied LED structures had ionization energies of 0.55 and 0.85 eV. The dominant hole traps had apparent ionization energies of 0.85 and 0.4 eV. The latter traps were shown to be metastable and it is argued that they could be at least in part responsible for the persistent photoconductivity observed in p-GaN.

Ultraviolet electroluminescence from hetero p-n junction between a single ZnO microsphere and p-GaN thin film.

PubMed

Tetsuyama, Norihiro; Fusazaki, Koshi; Mizokami, Yasuaki; Shimogaki, Tetsuya; Higashihata, Mitsuhiro; Nakamura, Daisuke; Okada, Tatsuo

2014-04-21

We report ultraviolet electroluminescence from a hetero p-n junction between a single ZnO microsphere and p-GaN thin film. ZnO microspheres, which have high crystalline quality, have been synthesized by ablating a ZnO sintered target. It was found that synthesized ZnO microspheres had a high-optical property and exhibit the laser action in the whispering gallery mode under pulsed optical pumping. A hetero p-n junction was formed between the single ZnO microsphere/ p-GaN thin film, and a good rectifying property with a turn-on voltage of approximately 6 V was observed in I-V characteristic across the junction. Ultraviolet and visible electroluminescence were observed under forward bias.

High performance organic integrated device with ultraviolet photodetective and electroluminescent properties consisting of a charge-transfer-featured naphthalimide derivative

NASA Astrophysics Data System (ADS)

Wang, Hanyu; Zhou, Jie; Wang, Xu; Lu, Zhiyun; Yu, Junsheng

2014-08-01

A high performance organic integrated device (OID) with ultraviolet photodetective and electroluminescent (EL) properties was fabricated by using a charge-transfer-featured naphthalimide derivative of 6-{3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy}-2-(4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione (CzPhONI) as the active layer. The results showed that the OID had a high detectivity of 1.5 × 1011 Jones at -3 V under the UV-350 nm illumination with an intensity of 0.6 mW/cm2, and yielded an exciplex EL light emission with a maximum brightness of 1437 cd/m2. Based on the energy band diagram, both the charge transfer feature of CzPhONI and matched energy level alignment were responsible for the dual ultraviolet photodetective and EL functions of OID.

Tuning emission color of electroluminescence from two organic interfacial exciplexes by modulating the thickness of middle gadolinium complex layer

NASA Astrophysics Data System (ADS)

Li, Mingtao; Li, Wenlian; Chen, Lili; Kong, Zhiguo; Chu, Bei; Li, Bin; Hu, Zhizhi; Zhang, Zhiqiang

2006-02-01

Electroluminescent colors of organic light-emitting diodes (OLEDs) can be tuned by modulating the thickness of gadolinium (Gd) complex layer sandwiched between an electron-transporting layer (ETL) and a hole-transporting layer (HTL). The emission colors, which originate from the two interfacial exciplexes simultaneously, can be tuned from green to orange by increasing the thickness of the Gd-complex layer. The atom force microscope images have proved that there are many gaps in the thinner Gd-complex layers. Therefore, besides the exciplex formation between Gd complex and HTL, the exciplex between ETL and HTL is also formed. The results demonstrate that a simple way of color tuning can be realized by inserting a thin layer of color tuning material between HTL with lower ionization potentials and ETL with higher electron affinities. Moreover, photovoltaic device and white OLED based on the two exciplexes are also discussed.

Thorough subcells diagnosis in a multi-junction solar cell via absolute electroluminescence-efficiency measurements

PubMed Central

Chen, Shaoqiang; Zhu, Lin; Yoshita, Masahiro; Mochizuki, Toshimitsu; Kim, Changsu; Akiyama, Hidefumi; Imaizumi, Mitsuru; Kanemitsu, Yoshihiko

2015-01-01

World-wide studies on multi-junction (tandem) solar cells have led to record-breaking improvements in conversion efficiencies year after year. To obtain detailed and proper feedback for solar-cell design and fabrication, it is necessary to establish standard methods for diagnosing subcells in fabricated tandem devices. Here, we propose a potential standard method to quantify the detailed subcell properties of multi-junction solar cells based on absolute measurements of electroluminescence (EL) external quantum efficiency in addition to the conventional solar-cell external-quantum-efficiency measurements. We demonstrate that the absolute-EL-quantum-efficiency measurements provide I–V relations of individual subcells without the need for referencing measured I–V data, which is in stark contrast to previous works. Moreover, our measurements quantify the absolute rates of junction loss, non-radiative loss, radiative loss, and luminescence coupling in the subcells, which constitute the “balance sheets” of tandem solar cells. PMID:25592484

Ultraviolet electroluminescence from nitrogen-doped ZnO-based heterojuntion light-emitting diodes prepared by remote plasma in situ atomic layer-doping technique.

PubMed

Chien, Jui-Fen; Liao, Hua-Yang; Yu, Sheng-Fu; Lin, Ray-Ming; Shiojiri, Makoto; Shyue, Jing-Jong; Chen, Miin-Jang

2013-01-23

Remote plasma in situ atomic layer doping technique was applied to prepare an n-type nitrogen-doped ZnO (n-ZnO:N) layer upon p-type magnesium-doped GaN (p-GaN:Mg) to fabricate the n-ZnO:N/p-GaN:Mg heterojuntion light-emitting diodes. The room-temperature electroluminescence exhibits a dominant ultraviolet peak at λ ≈ 370 nm from ZnO band-edge emission and suppressed luminescence from GaN, as a result of the decrease in electron concentration in ZnO and reduced electron injection from n-ZnO:N to p-GaN:Mg because of the nitrogen incorporation. The result indicates that the in situ atomic layer doping technique is an effective approach to tailoring the electrical properties of materials in device applications.

Enhancement of green electroluminescence from nanocrystalline silicon by wet and dry processes.

PubMed

Sato, Keisuke; Hirakuri, Kenji

2006-01-01

Correlation between defects and luminescence property from electroluminescent (EL) device composed of nanocrystalline silicon (nc-Si) prepared by wet and dry processes such as hydrofluoric (HF) acid solution treatment and annealing have investigated using electron spin resonance and EL measurements. The EL device using HF-treated nc-Si emitted strong red light, because of existence of only P'ce-centers (radiative recombination centers) on the surface vicinity. On the other hand, the EL device using annealed nc-Si above 400 degrees C exhibited green luminescence by the reduction of particle size due to surface oxidation. When the annealing temperature was risen from 400 degrees C up to 600 degrees C, the green luminescence strengthened with increasing the P'ce-centers. These results indicate that the formation of many radiative recombination centers onto the nc-Si surface vicinity lead to the enhancement of green luminescence from the nc-Si based EL device.

A spectrally tunable all-graphene-based flexible field-effect light-emitting device

NASA Astrophysics Data System (ADS)

Wang, Xiaomu; Tian, He; Mohammad, Mohammad Ali; Li, Cheng; Wu, Can; Yang, Yi; Ren, Tian-Ling

2015-07-01

The continuous tuning of the emission spectrum of a single light-emitting diode (LED) by an external electrical bias is of great technological significance as a crucial property in high-quality displays, yet this capability has not been demonstrated in existing LEDs. Graphene, a tunable optical platform, is a promising medium to achieve this goal. Here we demonstrate a bright spectrally tunable electroluminescence from blue (~450 nm) to red (~750 nm) at the graphene oxide/reduced-graphene oxide interface. We explain the electroluminescence results from the recombination of Poole-Frenkel emission ionized electrons at the localized energy levels arising from semi-reduced graphene oxide, and holes from the top of the π band. Tuning of the emission wavelength is achieved by gate modulation of the participating localized energy levels. Our demonstration of current-driven tunable LEDs not only represents a method for emission wavelength tuning but also may find applications in high-quality displays.

Diffusion lengths of silicon solar cells from luminescence images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wuerfel, P.; Trupke, T.; Puzzer, T.

A method for spatially resolved measurement of the minority carrier diffusion length in silicon wafers and in silicon solar cells is introduced. The method, which is based on measuring the ratio of two luminescence images taken with two different spectral filters, is applicable, in principle, to both photoluminescence and electroluminescence measurements and is demonstrated experimentally by electroluminescence measurements on a multicrystalline silicon solar cell. Good agreement is observed with the diffusion length distribution obtained from a spectrally resolved light beam induced current map. In contrast to the determination of diffusion lengths from one single luminescence image, the method proposed heremore » gives absolute values of the diffusion length and, in comparison, it is much less sensitive to lateral voltage variations across the cell area as caused by local variations of the series resistance. It is also shown that measuring the ratio of two luminescence images allows distinguishing shunts or surface defects from bulk defects.« less

Color tunable electroluminescence and resistance switching from a ZnO-nanorod-TaOx-p-GaN heterojunction.

PubMed

Zhao, J L; Teo, K L; Zheng, K; Sun, X W

2016-03-18

Well-aligned ZnO nanorods have been prepared on p-GaN-sapphire using a vapor phase transport (VPT) technique. A thin sputtered layer of TaOx is employed as the intermediate layer and an n-ZnO-TaOx-p-GaN heterojunction device has been achieved. The current transport of the heterojunction exhibited a typical resistance switching behavior, which originated from the filament forming and breaking in the TaOx layer. Color controllable electroluminescence (EL) was observed from the biased heterojunction at room temperature. Bluish-white wide band emission is achieved from the forward biased device in both the high resistance and low resistance states, while red emission can only be observed for the reverse biased device in the low resistance state. The correlation between the EL and resistance switching has been analyzed in-depth based on the interface band diagram of the heterojunction.

Enhanced luminescence efficiency by surface plasmon coupling of Ag nanoparticles in a polymer light-emitting diode

NASA Astrophysics Data System (ADS)

Chen, Sy-Hann; Jhong, Jhen-Yu

2011-08-01

This study achieved a substantial enhancement in electroluminescence by coupling localized surface plasmons in a single layer of Ag nanoparticles. Thermal evaporation was used to fabricate 20-nm Ag particles sandwiched between a gallium-doped zinc oxide film and a glass substrate to form novel window materials for use in polymer light-emitting diodes (PLEDs). The PLEDs discussed herein are single-layer devices based on a poly(9,9-di-n-octyl-2,7-fluorene) (PFO) emissive layer. In addition to low cost, this novel fabrication method can effectively prevent interruption or degradation of the charge transport properties of the active layer to meet the high performance requirements of PLEDs. Due to the surface-plasmon-enhanced emission, the electroluminescence intensity was increased by nearly 1-fold, compared to that of the same PLED without the interlayer of Ag nanoparticles.

Defect-related electroluminescence from metal-oxide-semiconductor devices with ZrO2 films on silicon

NASA Astrophysics Data System (ADS)

Lv, Chunyan; Zhu, Chen; Wang, Canxing; Li, Dongsheng; Ma, Xiangyang; Yang, Deren

2016-11-01

Defect-related electroluminescence (EL) from ZrO2 films annealed under different atmosphere has been realized by means of electrical pumping scheme of metal-oxide-semiconductor (MOS) devices. At the same injection current, the acquired EL from the MOS device with the vacuum-annealed ZrO2 film is much stronger than that from the counterpart with the oxygen-annealed ZrO2 film. This is because the vacuum-annealed ZrO2 film contains more oxygen vacancies and Zr3+ ions. Analysis on the current-voltage characteristic of the ZrO2-based MOS devices indicates the P-F conduction mechanism dominates the electron transportation at the EL-enabling voltages under forward bias. It is tentatively proposed that the recombination of the electrons trapped in multiple oxygen-vacancy-related states with the holes in the defect level pertaining to Zr3+ ions brings about the EL emissions.

Effects of electrode modification using calcium on the performance of alternating current field-induced polymer electroluminescent devices

NASA Astrophysics Data System (ADS)

Xia, Yingdong; Chen, Yonghua; Smith, Gregory M.; Li, Yuan; Huang, Wenxiao; Carroll, David L.

2013-06-01

In this work, the effects of electrode modification by calcium (Ca) on the performance of AC field induced polymer electroluminescence (FIPEL) devices are studied. The FIPEL device with Ca/Al electrode exhibits 550 cd m-2, which is 27.5 times higher than that of the device with only an Al electrode (20 cd m-2). Both holes and electrons are injected from one electrode in our FIPEL device. We found that the electron injection can be significantly enhanced by a Ca modification on the Al electrode without greatly affecting the hole injection. Therefore, the electrons and holes can be effectively recombined in the emissive layer to form more excitons under the AC voltage, leading to effective light emission. The device emitted much brighter light than other AC-based organic EL devices. This result provides an easy and effective way to improve FIPEL performance.

Toward blue emission in ZnO based LED

NASA Astrophysics Data System (ADS)

Viana, Bruno; Pauporté, Thierry; Lupan, Oleg; Le Bahers, Tangui; Ciofini, Ilaria

2012-03-01

The bandgap engineering of ZnO nanowires by doping is of great importance for tunable light emitting diode (LED) applications. We present a combined experimental and computational study of ZnO doping with Cd or Cu atoms in the nanomaterial. Zn1-xTMxO (TM=Cu, Cd) nanowires have been epitaxially grown on magnesium-doped p-GaN by electrochemical deposition. The Zn1-xTMxO/p-GaN heterojunction was integrated in a LED structure. Nanowires act as the light emitters and waveguides. At room temperature, TM-doped ZnO based LEDs exhibit low-threshold emission voltage and electroluminescence emission shifted from ultraviolet to violet-blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the transition metal (TM) content in the ZnO nanomaterial and the shift is discussed, including insights from DFT computational investigations.

Sb2O3/Ag/Sb2O3 Multilayer Transparent Conducting Films For Ultraviolet Organic Light-emitting Diode

NASA Astrophysics Data System (ADS)

Song, Chunyan; Zhang, Nan; Lin, Jie; Guo, Xiaoyang; Liu, Xingyuan

2017-01-01

A novel UV transparent conducting films based on Sb2O3/Ag/Sb2O3 (SAS) structure, which were prepared by an electron-beam thermal evaporation at room temperature. This SAS exhibits excellent electrical, optical and stable properties. Especially for UV region, the SAS has high transmittance of 80% at 306 nm and 92% at 335 nm, meanwhile achieving low sheet resistance ( ≤ 10 Ω sq-1). The UV OLED based on the SAS show competitive device performance. The UV OLED obtains the peak of UV electroluminescence at 376 nm and shows a very high maximum EQE of 4.1% with the maximum output power density of 5.18 mW cm-2. These results indicate that the potential of SAS applications in deep UV transparent electrodes and large-scale flexible transparent electronics.

Sb2O3/Ag/Sb2O3 Multilayer Transparent Conducting Films For Ultraviolet Organic Light-emitting Diode.

PubMed

Song, Chunyan; Zhang, Nan; Lin, Jie; Guo, Xiaoyang; Liu, Xingyuan

2017-01-25

A novel UV transparent conducting films based on Sb 2 O 3 /Ag/Sb 2 O 3 (SAS) structure, which were prepared by an electron-beam thermal evaporation at room temperature. This SAS exhibits excellent electrical, optical and stable properties. Especially for UV region, the SAS has high transmittance of 80% at 306 nm and 92% at 335 nm, meanwhile achieving low sheet resistance ( ≤ 10 Ω sq -1 ). The UV OLED based on the SAS show competitive device performance. The UV OLED obtains the peak of UV electroluminescence at 376 nm and shows a very high maximum EQE of 4.1% with the maximum output power density of 5.18 mW cm -2 . These results indicate that the potential of SAS applications in deep UV transparent electrodes and large-scale flexible transparent electronics.

Sb2O3/Ag/Sb2O3 Multilayer Transparent Conducting Films For Ultraviolet Organic Light-emitting Diode

PubMed Central

Song, Chunyan; Zhang, Nan; Lin, Jie; Guo, Xiaoyang; Liu, Xingyuan

2017-01-01

A novel UV transparent conducting films based on Sb2O3/Ag/Sb2O3 (SAS) structure, which were prepared by an electron-beam thermal evaporation at room temperature. This SAS exhibits excellent electrical, optical and stable properties. Especially for UV region, the SAS has high transmittance of 80% at 306 nm and 92% at 335 nm, meanwhile achieving low sheet resistance ( ≤ 10 Ω sq−1). The UV OLED based on the SAS show competitive device performance. The UV OLED obtains the peak of UV electroluminescence at 376 nm and shows a very high maximum EQE of 4.1% with the maximum output power density of 5.18 mW cm−2. These results indicate that the potential of SAS applications in deep UV transparent electrodes and large-scale flexible transparent electronics. PMID:28120888

GMAG Dissertation Award: Tunnel spin injectors for semiconductor spintronics

NASA Astrophysics Data System (ADS)

Jiang, Xin

2004-03-01

Spin-based electronics aims to develop novel sensor, memory and logic devices by manipulating the spin states of carriers in semiconducting materials. This talk will focus on electrical spin injection into semiconductors, which is a prerequisite for spintronics and, in particular, on tunnel based spin injectors that are potentially operable above room temperature. The magneto-transport properties of two families of tunnel spin injectors will be discussed. The spin polarization of the electron current within the semiconductor is detected by measuring the circular polarization of the electroluminescence (EL) from a quantum well light emitting diode structure. The temperature and bias dependence of the EL polarization provides insight into the mechanism of spin relaxation within the semiconductor heterostructure. Collaborators: Roger Wang^1,2, Sebastiaan van Dijken^1,*, Robert Shelby^1, Roger Macfarlane^1, Seth Bank^2, Glenn Solomon^2, James Harris^2, and Stuart S. P. Parkin^1 * Currently at Trinity College, Dublin, Ireland

Versatile Molecular Functionalization for Inhibiting Concentration Quenching of Thermally Activated Delayed Fluorescence.

PubMed

Lee, Jiyoung; Aizawa, Naoya; Numata, Masaki; Adachi, Chihaya; Yasuda, Takuma

2017-01-01

Concentration quenching of thermally activated delayed fluorescence is found to be dominated by electron-exchange interactions, as described by the Dexter energy-transfer model. Owing to the short-range nature of the electron-exchange interactions, even a small modulation in the molecular geometric structure drastically affects the concentration-quenching, leading to enhanced solid-state photoluminescence and electroluminescence quantum efficiencies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrically driven nanopillars for THz quantum cascade lasers.

PubMed

Amanti, M I; Bismuto, A; Beck, M; Isa, L; Kumar, K; Reimhult, E; Faist, J

2013-05-06

In this work we present a rapid and parallel process for the fabrication of large scale arrays of electrically driven nanopillars for THz quantum cascade active media. We demonstrate electrical injection of pillars of 200 nm diameter and 2 µm height, over a surface of 1 mm(2). THz electroluminescence from the nanopillars is reported. This result is a promising step toward the realization of zero-dimensional structure for terahertz quantum cascade lasers.

PECASE: Nanostructure Hybrid Organic/Inorganic Materials for Active Opto-Electronic Devices

DTIC Science & Technology

2011-01-03

FWHM= 30 nm), green-emitting core–shell material ( 4 nm in diameter) suitable for QD- LED display applications (Figure 1b). An alloyed material for...electroluminescence (EL) that can be of use in fields as diverse as optical communications, spectroscopy, and environmental and industrial sensing. The RC structure...variety of QD size distributions (of Gaussian size profile). Such QD monoalyers have already been utilized in a number of thin-film applications , QD

Hybrid electroluminescent devices

DOEpatents

Shiang, Joseph John; Duggal, Anil Raj; Michael, Joseph Darryl

2010-08-03

A hybrid electroluminescent (EL) device comprises at least one inorganic diode element and at least one organic EL element that are electrically connected in series. The absolute value of the breakdown voltage of the inorganic diode element is greater than the absolute value of the maximum reverse bias voltage across the series. The inorganic diode element can be a power diode, a Schottky barrier diode, or a light-emitting diode.

1000 X Difference Between Current Displays and Capability of Human Visual System: Payoff Potential for Affordable Defense Systems

DTIC Science & Technology

2000-01-01

second tier technologies: digital micromirror devices (DMD); alternating current gas plasma (ACGP); inorganic electroluminescent (EL, TFEL, AMEL... Micromirror Device (DMD) - Alternating Current Gas Plasma (ACGP) - Electroluminescent (EL, TFEL, AMEL) - Vacuum Fluorescent Display (VFD) - Inorganic Light...Instruments Digital Micromirror Device (DMD) Digital Light Processing technology and another, the Qualcomm/Hughes-JVC CRT/Liquid Crystal Light Valve

Optical sensors and multisensor arrays containing thin film electroluminescent devices

DOEpatents

Aylott, Jonathan W.; Chen-Esterlit, Zoe; Friedl, Jon H.; Kopelman, Raoul; Savvateev, Vadim N.; Shinar, Joseph

2001-12-18

Optical sensor, probe and array devices for detecting chemical biological, and physical analytes. The devices include an analyte-sensitive layer optically coupled to a thin film electroluminescent layer which activates the analyte-sensitive layer to provide an optical response. The optical response varies depending upon the presence of an analyte and is detected by a photodetector and analyzed to determine the properties of the analyte.

Electroluminescence and electrical degradation of insulating polymers at electrode interfaces under divergent fields

NASA Astrophysics Data System (ADS)

Zhang, Shuai; Li, Qi; Hu, Jun; Zhang, Bo; He, Jinliang

2018-04-01

Electrical degradation of insulating polymers at electrode interfaces is an essential factor in determining long-term reliability. A critical challenge is that the exact mechanism of degradation is not fully understood, either experimentally or theoretically, due to the inherent complex processes. Consequently, in this study, we investigate electroluminescence (EL) at the interface of an electrode and insulator, and determine the relationship between EL and electrical degradation. Using a tip-plate electrode structure, the unique features of EL under a highly divergent field are investigated. The voltage type (alternating or direct current), the polymer matrix, and the time of pressing are also investigated separately. A study of EL from insulators under a divergent field is provided, and the relationship between EL spectra and degradation is discussed. It is shown that EL spectra under a divergent field have unique characteristics compared with EL spectra from polymer films under a uniform field and the most obvious one is the UV emission. The results obtained in the current investigation bring us a step closer to understanding the process of electrical degradation and provide a potential way to diagnose insulator defects.

Temperature quenching of spontaneous emission in tunnel-injection nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talalaev, V. G., E-mail: vadimtalalaev@yandex.com; Novikov, B. V.; Cirlin, G. E.

2015-11-15

The spontaneous-emission spectra in the near-IR range (0.8–1.3 μm) from inverted tunnel-injection nanostructures are measured. These structures contain an InAs quantum-dot layer and an InGaAs quantum-well layer, separated by GaAs barrier spacer whose thickness varies in the range 3–9 nm. The temperature dependence of this emission in the range 5–295 K is investigated, both for optical excitation (photoluminescence) and for current injection in p–n junction (electroluminescence). At room temperature, current pumping proves more effective for inverted tunnel-injection nanostructures with a thin barrier (<6 nm), when the apexes of the quantum dots connect with the quantum well by narrow InGaAs strapsmore » (nanobridges). In that case, the quenching of the electroluminescence by heating from 5 to 295 K is slight. The quenching factor S{sub T} of the integrated intensity I is S{sub T} = I{sub 5}/I{sub 295} ≈ 3. The temperature stability of the emission from inverted tunnel-injection nanostructures is discussed on the basis of extended Arrhenius analysis.« less

Synthesis and electroluminescence characterization of a new aluminum complex, [8-hydroxyquinoline] bis [2, 2'bipyridine] aluminum Al(Bpy)2q

NASA Astrophysics Data System (ADS)

Rahul, Kumar; Ritu, Srivastava; Punita, Singh

2016-01-01

We have synthesized and characterized a new electroluminescent material, [8-hydroxyquinoline] bis [2,2'bipyridine] aluminum. A solution of this material Al(Bpy)2q in toluene showed absorption maxima at 380 nm, which was attributed to the moderate energy (π-π*) transitions of the aromatic rings. The photoluminescence spectrum of Al(Bpy)2q in the toluene solution showed a peak at 518 nm. This material shows thermal stability up to 300 °C. The structure of the device is ITO/F4-TCNQ (1 nm)/α-NPD (35 nm)/Al(Bpy)2q (35 nm)/ BCP (6 nm)/Alq3 (28 nm)/LiF (1 nm)/Al (150 nm). This device exhibited a luminescence peak at 515 nm (CIE coordinates, x = 0.32, y = 0.49). The maximum luminescence of the device was 214 cd/m2 at 21 V. The maximum current efficiency of OLED was 0.12 cd/A at 13 V and the maximum power efficiency was 0.03 lm/W at 10 V.

Study on copper phthalocyanine and perylene-based ambipolar organic light-emitting field-effect transistors produced using neutral beam deposition method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Dae-Kyu; Oh, Jeong-Do; Shin, Eun-Sol

2014-04-28

The neutral cluster beam deposition (NCBD) method has been applied to the production and characterization of ambipolar, heterojunction-based organic light-emitting field-effect transistors (OLEFETs) with a top-contact, multi-digitated, long-channel geometry. Organic thin films of n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and p-type copper phthalocyanine were successively deposited on the hydroxyl-free polymethyl-methacrylate (PMMA)-coated SiO{sub 2} dielectrics using the NCBD method. Characterization of the morphological and structural properties of the organic active layers was performed using atomic force microscopy and X-ray diffraction. Various device parameters such as hole- and electron-carrier mobilities, threshold voltages, and electroluminescence (EL) were derived from the fits of the observed current-voltage andmore » current-voltage-light emission characteristics of OLEFETs. The OLEFETs demonstrated good field-effect characteristics, well-balanced ambipolarity, and substantial EL under ambient conditions. The device performance, which is strongly correlated with the surface morphology and the structural properties of the organic active layers, is discussed along with the operating conduction mechanism.« less

Short-wavelength light beam in situ monitoring growth of InGaN/GaN green LEDs by MOCVD

PubMed Central

2012-01-01

In this paper, five-period InGaN/GaN multiple quantum well green light-emitting diodes (LEDs) were grown by metal organic chemical vapor deposition with 405-nm light beam in situ monitoring system. Based on the signal of 405-nm in situ monitoring system, the related information of growth rate, indium composition and interfacial quality of each InGaN/GaN QW were obtained, and thus, the growth conditions and structural parameters were optimized to grow high-quality InGaN/GaN green LED structure. Finally, a green LED with a wavelength of 509 nm was fabricated under the optimal parameters, which was also proved by ex situ characterization such as high-resolution X-ray diffraction, photoluminescence, and electroluminescence. The results demonstrated that short-wavelength in situ monitoring system was a quick and non-destroyed tool to provide the growth information on InGaN/GaN, which would accelerate the research and development of GaN-based green LEDs. PMID:22650991

Polarized emission from light-emitting electrochemical cells using uniaxially oriented polymer thin films of poly(9,9-dioctylfluorene-co-bithiophene)

NASA Astrophysics Data System (ADS)

Miyazaki, Masumi; Sakanoue, Tomo; Takenobu, Taishi

2018-03-01

Uniaxially oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) films were prepared on rubbed polyimide substrates and applied to emitting layers of light-emitting electrochemical cells (LECs). The layered structure of the uniaxially oriented F8T2 film and ionic liquid electrolytes enabled us to demonstrate LEC operations with high anisotropic characteristics both in emission and charge transport. Polarized electroluminescence (EL) from electrochemically induced p-n junctions in the uniaxially oriented F8T2 was obtained. The dichroic ratios of EL were the same as those of photoluminescence, suggesting that the doping process into the oriented F8T2 did not interrupt the polymer ordering. This indicates the usefulness of the layered structure of the polymer/electrolyte for the fabrication of LECs based on highly oriented polymer films. In addition, uniaxially oriented F8T2 was found to show reduced threshold energy in optically pumped amplified spontaneous emission. These demonstrations suggest the advantage of uniaxially oriented polymer-based LECs for potential application in future electrically pumped lasers.

A Stable Room-Temperature Luminescent Biphenylmethyl Radical.

PubMed

Ai, Xin; Chen, Yingxin; Feng, Yuting; Li, Feng

2018-03-05

There is only one family of room-temperature luminescent radicals, the triphenylmethyl radicals, to date. Herein, we synthesize a new stable room-temperature luminescent radical, (N-carbazolyl)bis(2,4,6-tirchlorophenyl)methyl radical (CzBTM), which has improved properties compared to the triphenylmethyl radicals. X-ray crystallography, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements confirmed the radical structure. CzBTM shows room-temperature deep-red to near-infrared emission in various solutions. Both thermal and photo stability were significantly enhanced by the replacement of trichlorobenzene by the carbazole moiety. The electroluminescence results of CzBTM verify its potential application to circumvent the problem of triplet harvesting in traditional fluorescent OLEDs. A new family of stable luminescent radicals based on CzBTM is anticipated. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photovoltaic reciprocity and quasi-Fermi level splitting in nanostructure-based solar cells (Conference Presentation)

NASA Astrophysics Data System (ADS)

Aeberhard, Urs

2017-04-01

The photovoltaic reciprocity theory relates the electroluminescence spectrum of a solar cell under applied bias to the external photovoltaic quantum efficiency of the device as measured at short circuit conditions [1]. So far, the theory has been verified for a wide range of devices and material systems and forms the basis of a growing number of luminesecence imaging techniques used in the characterization of photovoltaic materials, cells and modules [2-5]. However, there are also some examples where the theory fails, such as in the case of amorphous silicon. In our contribution, we critically assess the assumptions made in the derivation of the theory and compare its predictions with rigorous formal relations as well as numerical computations in the framework of a comprehensive quantum-kinetic theory of photovoltaics [6] as applied to ultra-thin absorber architectures [7]. One of the main applications of the photovoltaic reciprocity relation is the determination of quasi-Fermi level splittings (QFLS) in solar cells from the measurement of luminescence. In nanostructure-based photovoltaic architectures, the determination of QFLS is challenging, but instrumental to assess the performance potential of the concepts. Here, we use our quasi-Fermi level-free theory to investigate existence and size of QFLS in quantum well and quantum dot solar cells. [1] Uwe Rau. Reciprocity relation between photovoltaic quantum efficiency and electrolumines- cent emission of solar cells. Phys. Rev. B, 76(8):085303, 2007. [2] Thomas Kirchartz and Uwe Rau. Electroluminescence analysis of high efficiency cu(in,ga)se2 solar cells. J. Appl. Phys., 102(10), 2007. [3] Thomas Kirchartz, Uwe Rau, Martin Hermle, Andreas W. Bett, Anke Helbig, and Jrgen H. Werner. Internal voltages in GaInP-GaInAs-Ge multijunction solar cells determined by electro- luminescence measurements. Appl. Phys. Lett., 92(12), 2008. [4] Thomas Kirchartz, Anke Helbig, Wilfried Reetz, Michael Reuter, Jürgen H. Werner, and Uwe Rau. Reciprocity between electroluminescence and quantum efficiency used for the characterization of silicon solar cells. Prog. Photovolt: Res. Appl., 17(6):394-402, 2009. [5] U. Hoyer, M. Wagner, Th. Swonke, J. Bachmann, R. Auer, A. Osvet, and C. J. Brabec. Electroluminescence imaging of organic photovoltaic modules. Appl. Phys. Lett., 97(23), 2010. [6] U. Aeberhard. Theory and simulation of quantum photovoltaic devices based on the non-equilibrium Greens function formalism. J. Comput. Electron., 10:394-413, 2011. [7] U. Aeberhard. Simulation of ultrathin solar cells beyond the limits of the semiclassical bulk picture. IEEE J. Photovolt., 6(3):654-660, 2016.

Effect of defects on the electrical/optical performance of gallium nitride based junction devices

NASA Astrophysics Data System (ADS)

Ferdous, Mohammad Shahriar

Commercial GaN based electronic and optoelectronic devices possess a high density (107-109 cm-2) of threading dislocations (TDs) because of the large mismatch in the lattice constant and the thermal expansion coefficient between the epitaxial layer structure and the substrate. In spite of these dislocations, high brightness light emitting diodes (LEDs) utilizing InGaN or AlGaN multiple quantum wells (MQWs) and with an external quantum efficiency of more than 40%, have already been achieved. This high external quantum efficiency in the presence of a high density of dislocations has been explained by carrier localization induced by indium fluctuations in the quantum well. TDs have been found to increase the reverse leakage current in InGaN based LEDs and to shorten the operating lifetime of InGaN MQW/GaN/AlGaN laser diodes. Thus it is important that the TD density is further reduced. It remains unclear how the TDs interact with the device to cause the effects mentioned above, hence the careful and precise characterization of threading defects and their effects on the electrical and optical performances of InGaN/GaN MQW LEDs is needed. This investigation will be useful not only from the point of view of device optimization but also to develop a clear understanding of the physical processes associated with TDs and especially with their effect on leakage current. We have employed photoelectrochemical (PEC) etching to accurately measure the dislocation density initially in home-grown GaN-based epitaxial structures and recently in InGaN/GaN MQW LEDs fabricated from commercial grade epitaxial structures that were supplied by our industrial collaborators. Measuring the electrical and electroluminescence (EL) characteristics of these devices has revealed correlations between some aspects of the LED behavior and the TD density, and promises to allow a deeper understanding of the role of threading dislocations to be elucidated. We observed that the LED reverse leakage current increased exponentially, and electroluminescence intensity decreased by 22%, as the TD density in the LEDs increased from 1.7 x 107 cm-2 to 2 x 108 cm-2. Forward voltage remained almost constant with the increase of TD density. A model of carrier conduction via hopping through defect related states, was found to provide an excellent fit to the experimental I-V data and provides a useful basis for understanding carrier conduction in the presence of TDs.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Determination of the quantum efficiency of InGaAsP/InP double heterostructures from spontaneous emission measurements

NASA Astrophysics Data System (ADS)

Rheinländer, B.; Anton, A.; Heilmann, R.; Oelgart, G.; Gottschalch, V.

1988-11-01

A method was developed for determination of the suitability of epitaxial InGaAsP/InP double heterostructures in fabrication of ridge-waveguide lasers. The method is based on determination of the quantum efficiency of electroluminescence.

Molecularly "engineered" anode adsorbates for probing OLED interfacial structure-charge injection/luminance relationships: large, structure-dependent effects.

PubMed

Huang, Qinglan; Evmenenko, Guennadi; Dutta, Pulak; Marks, Tobin J

2003-12-03

Molecule-scale structure effects at organic light-emitting diodes (OLED) anode-organic transport layer interfaces are probed via a self-assembly approach. A series of ITO anode-linked silyltriarylamine molecules differing in aryl group and linker density are synthesized for this purpose and used to probe the relationship between nanoscale interfacial chemical structure, charge injection and electroluminescence properties. Dramatic variations in hole injection magnitude and OLED performance can be correlated with the molecular structures and electrochemically derived heterogeneous electron-transfer rates of such triarylamine fragments, placed precisely at the anode-hole transport layer interface. Very bright and efficient ( approximately 70 000 cd/m2 and approximately 2.5% forward external quantum efficiency) OLEDs have thereby been fabricated.

Multifunctional Device based on phosphor-piezoelectric PZT: lighting, speaking, and mechanical energy harvesting.

PubMed

Lee, Sunghoon; Kang, Taewook; Lee, Wunho; Afandi, Mohammad M; Ryu, Jongho; Kim, Jongsu

2018-01-10

We demonstrated the tri-functional device based on all powder-processing methods by using ZnS powder as phosphor layer and piezoelectric material as dielectric layer. The fabricated device generated the electroluminescent (EL) light from phosphor and the sound from piezoelectric sheet under a supply of external electric power, and additionally harvested the reverse-piezoelectric energy to be converted into EL light. Under sinusoidal applied voltage, EL luminances were exponentially increased with a maximum luminous efficiency of 1.3 lm/W at 40 V and 1,000 Hz, and sound pressure levels (SPLs) were linearly increased. The EL luminances were linearly dependent on applied frequency while the SPLs showed the parabolic increase behavior below 1,000 Hz and then the flat response. The temperature dependence on EL luminances and SPLs was demonstrated; the former was drastically increased and the latter was slightly decreased with the increase of temperature. Finally, as an energy harvesting application, the piezoelectric-induced electroluminescence effect was demonstrated by applying only mechanical pressure to the device without any external electric power.

Interface-Free Area-Scalable Self-Powered Electroluminescent System Driven by Triboelectric Generator

PubMed Central

Yan Wei, Xiao; Kuang, Shuang Yang; Yang Li, Hua; Pan, Caofeng; Zhu, Guang; Wang, Zhong Lin

2015-01-01

Self-powered system that is interface-free is greatly desired for area-scalable application. Here we report a self-powered electroluminescent system that consists of a triboelectric generator (TEG) and a thin-film electroluminescent (TFEL) lamp. The TEG provides high-voltage alternating electric output, which fits in well with the needs of the TFEL lamp. Induced charges pumped onto the lamp by the TEG generate an electric field that is sufficient to excite luminescence without an electrical interface circuit. Through rational serial connection of multiple TFEL lamps, effective and area-scalable luminescence is realized. It is demonstrated that multiple types of TEGs are applicable to the self-powered system, indicating that the system can make use of diverse mechanical sources and thus has potentially broad applications in illumination, display, entertainment, indication, surveillance and many others. PMID:26338365

The intensive terahertz electroluminescence induced by Bloch oscillations in SiC natural superlattices

PubMed Central

2012-01-01

We report on efficient terahertz (THz) emission from high-electric-field-biased SiC structures with a natural superlattice at liquid helium temperatures. The emission spectrum demonstrates a single line, the maximum of which shifts linearly with increases in bias field. We attribute this emission to steady-state Bloch oscillations of electrons in the SiC natural superlattice. The properties of the THz emission agree fairly with the parameters of the Bloch oscillator regime, which have been proven by high-field electron transport studies of SiC structures with natural superlattices. PMID:23043773

Improved Emergency Egress Lighting System for the ISS

NASA Technical Reports Server (NTRS)

Eaton, Leslie L.; Barr, Don A.

2005-01-01

Emergency lights provide illumination in corridors, stairwells, ramps, escalators, aisles, and exit passageways during power failures. Safety and visibility are critical during a power outage. If emergency lights fail to operate properly, the building occupants can become disoriented. Four documents in a collection discuss different topics relating to a proposed improved emergency egress lighting system (EELS) for the International Space Station (ISS). While the present EELS is designed around rows of green-light-emitting diodes, the proposed system contains strips of electroluminescent tape using different colors for each egress path. The proposed EELS can be powered by the same battery currently used by the present EELS, but would require an inverter because electroluminescent devices require AC. Electroluminescent devices also require significantly less current and, depending on the color, would emit 3 to 8 times the light of the present EELS. In addition, they could operate for up to 75 hours (versus .20 minutes for the present system). The first document contains a one-page summary of the proposal and an evaluation of technical merit. The second document summarizes the motivation for, and the design of, the proposed EELS. The third document addresses relevant aspects of the measurement of spectral sensitivity and the psychophysics of perception of light. The fourth document presents additional background information and technical specifications for the electroluminescent tapes.

White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates.

PubMed

Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

2017-06-02

We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates

NASA Astrophysics Data System (ADS)

Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

2017-06-01

We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

Plasmonic enhancement of electroluminescence

NASA Astrophysics Data System (ADS)

Guzatov, D. V.; Gaponenko, S. V.; Demir, H. V.

2018-01-01

Here plasmonic effect specifically on electroluminescence (EL) is studied in terms of radiative and nonradiative decay rates for a dipole near a metal spherical nanoparticle (NP). Contribution from scattering is taken into account and is shown to play a decisive role in EL enhancement owing to pronounced size-dependent radiative decay enhancement and weak size effect on non-radiative counterpart. Unlike photoluminescence where local incident field factor mainly determines the enhancement possibility and level, EL enhancement is only possible by means of quantum yield rise, EL enhancement being feasible only for an intrinsic quantum yield Q0 < 1. The resulting plasmonic effect is independent of intrinsic emitter lifetime but is exclusively defined by the value of Q0, emission spectrum, NP diameter and emitter-metal spacing. For 0.1< Q0 < 0.25, Ag nanoparticles are shown to enhance LED/OLED intensity by several times over the whole visible whereas Au particles feature lower effect within the red-orange range only. Independently of positive effect on quantum yield, metal nanoparticles embedded in an electroluminescent device will improve its efficiency at high currents owing to enhanced overall recombination rate which will diminish manifestation of Auger processes. The latter are believed to be responsible for the known undesirable efficiency droop in semiconductor commercial quantum well based LEDs at higher current. For the same reason plasmonics can diminish quantum dot photodegradation from Auger process induced non-radiative recombination and photoionization thus opening a way to avoid negative Auger effects in emerging colloidal semiconductor LEDs.

Photofunctional triplet excited states of cyclometalated Ir(III) complexes: beyond electroluminescence.

PubMed

You, Youngmin; Nam, Wonwoo

2012-11-07

The development of cyclometalated Ir(III) complexes has enabled important breakthroughs in electroluminescence because such complexes permit the efficient population of triplet excited states that give rise to luminescent transitions. The triplet states of Ir(III) complexes are advantageous over those of other transition metal complexes in that their electronic transitions and charge-transfer characteristics are tunable over wide ranges. These favorable properties suggest that Ir(III) complexes have significant potential in a variety of photofunctions other than electroluminescence. In this critical review, we describe recent photonic applications of novel Ir(III) complexes. Ir(III) complexes have been shown to affect the exciton statistics in the active layers of organic photovoltaic cells, thereby improving the photon-to-current conversion efficiencies. Nonlinear optical applications that take advantage of the strong charge-transfer properties of triplet transitions are also discussed. The tunability of the electrochemical potentials facilitates the development of efficient photocatalysis in the context of water photolysis or organic syntheses. The photoredox reactivities of Ir(III) complexes have been employed in studies of charge migration along DNA chains. The photoinduced cytotoxicity of Ir(III) complexes on live cells suggests that the complexes may be useful in photodynamic therapy. Potential biological applications of the complexes include phosphorescence labeling and sensing. Intriguing platforms based on cyclometalated Ir(III) complexes potentially provide novel protein tagging and ratiometric detection. We envision that future research into the photofunctionality of Ir(III) complexes will provide important breakthroughs in a variety of photonic applications.

Tetradentate Schiff base platinum(II) complexes as new class of phosphorescent materials for high-efficiency and white-light electroluminescent devices.

PubMed

Che, Chi-Ming; Chan, Siu-Chung; Xiang, Hai-Feng; Chan, Michael C W; Liu, Yu; Wang, Yue

2004-07-07

The capabilities of readily prepared and sublimable Pt(II) Schiff base triplet emitters as OLED dopants have been examined; maximum luminous and power efficiencies and luminance of 31 cd A(-1), 14 lm W(-1), and 23,000 cd m(-2), respectively, and white EL (CIE: 0.33, 0.35) by simultaneous host/dopant emission, have been achieved.

Organic electroluminescent devices and method for improving energy efficiency and optical stability thereof

DOEpatents

Heller, Christian Maria

2004-04-27

An organic electroluminescent device ("OELD") has a controllable brightness, an improved energy efficiency, and stable optical output at low brightness. The OELD is activated with a series of voltage pulses, each of which has a maximum voltage value that corresponds to the maximum power efficiency when the OELD is activated. The frequency of the pulses, or the duty cycle, or both are chosen to provide the desired average brightness.

Electroluminescence Caused by the Transport of Interacting Electrons through Parallel Quantum Dots in a Photon Cavity

NASA Astrophysics Data System (ADS)

Gudmundsson, Vidar; Abdulla, Nzar Rauf; Sitek, Anna; Goan, Hsi-Sheng; Tang, Chi-Shung; Manolescu, Andrei

2018-02-01

We show that a Rabi-splitting of the states of strongly interacting electrons in parallel quantum dots embedded in a short quantum wire placed in a photon cavity can be produced by either the para- or the dia-magnetic electron-photon interactions when the geometry of the system is properly accounted for and the photon field is tuned close to a resonance with the electron system. We use these two resonances to explore the electroluminescence caused by the transport of electrons through the one- and two-electron ground states of the system and their corresponding conventional and vacuum electroluminescense as the central system is opened up by coupling it to external leads acting as electron reservoirs. Our analysis indicates that high-order electron-photon processes are necessary to adequately construct the cavity-photon dressed electron states needed to describe both types of electroluminescence.

Enhancing light emission in flexible AC electroluminescent devices by tetrapod-like zinc oxide whiskers.

PubMed

Wen, Li; Liu, Nishuang; Wang, Siliang; Zhang, Hui; Zhao, Wanqiu; Yang, Zhichun; Wang, Yumei; Su, Jun; Li, Luying; Long, Fei; Zou, Zhengguang; Gao, Yihua

2016-10-03

Flexible alternating current electroluminescent devices (ACEL) are more and more popular and widely used in liquid-crystal display back-lighting, large-scale architectural and decorative lighting due to their uniform light emission, low power consumption and high resolution. However, presently how to acquire high brightness under a certain voltage are confronted with challenges. Here, we demonstrate an electroluminescence (EL) enhancing strategy that tetrapod-like ZnO whiskers (T-ZnOw) are added into the bottom electrode of carbon nanotubes (CNTs) instead of phosphor layer in flexible ACEL devices emitting blue, green and orange lights, and the brightness is greatly enhanced due to the coupling between the T-ZnOw and ZnS phosphor dispersed in the flexible polydimethylsiloxane (PDMS) layer. This strategy provides a new routine for the development of high performance, flexible and large-area ACEL devices.

High-efficiency white OLEDs based on small molecules

NASA Astrophysics Data System (ADS)

Hatwar, Tukaram K.; Spindler, Jeffrey P.; Ricks, M. L.; Young, Ralph H.; Hamada, Yuuhiko; Saito, N.; Mameno, Kazunobu; Nishikawa, Ryuji; Takahashi, Hisakazu; Rajeswaran, G.

2004-02-01

Eastman Kodak Company and SANYO Electric Co., Ltd. recently demonstrated a 15" full-color, organic light-emitting diode display (OLED) using a high-efficiency white emitter combined with a color-filter array. Although useful for display applications, white emission from organic structures is also under consideration for other applications, such as solid-state lighting, where high efficiency and good color rendition are important. By incorporating adjacent blue and orange emitting layers in a multi-layer structure, highly efficient, stable white emission has been attained. With suitable host and dopant combinations, a luminance yield of 20 cd/A and efficiency of 8 lm/W have been achieved at a drive voltage of less than 8 volts and luminance level of 1000 cd/m2. The estimated external efficiency of this device is 6.3% and a high level of operational stability is observed. To our knowledge, this is the highest performance reported so far for white organic electroluminescent devices. We will review white OLED technology and discuss the fabrication and operating characteristics of these devices.

Solid state carbon nanotube device for controllable trion electroluminescence emission

NASA Astrophysics Data System (ADS)

Liang, Shuang; Ma, Ze; Wei, Nan; Liu, Huaping; Wang, Sheng; Peng, Lian-Mao

2016-03-01

Semiconducting carbon nanotubes (CNTs) have a direct chirality-dependent bandgap and reduced dimensionality-related quantum confinement effects, which are closely related to the performance of optoelectronic devices. Here, taking advantage of the large energy separations between neutral singlet excitons and charged excitons, i.e. trions in CNTs, we have achieved for the first time all trion electroluminescence (EL) emission from chirality-sorted (8,3) and (8,4) CNT-based solid state devices. We showed that strong trion emission can be obtained as a result of localized impact excitation and electrically injected holes, with an estimated efficiency of ~5 × 10-4 photons per injected hole. The importance of contact-controlled carrier injection (including symmetric and asymmetric contact configurations) and EL spectral stability for gradually increasing bias were also investigated. The realization of electrically induced pure trion emission opens up a new opportunity for CNT film-based optoelectronic devices, providing a new degree of freedom in controlling the devices to extend potential applications in spin or magnetic optoelectronics fields.Semiconducting carbon nanotubes (CNTs) have a direct chirality-dependent bandgap and reduced dimensionality-related quantum confinement effects, which are closely related to the performance of optoelectronic devices. Here, taking advantage of the large energy separations between neutral singlet excitons and charged excitons, i.e. trions in CNTs, we have achieved for the first time all trion electroluminescence (EL) emission from chirality-sorted (8,3) and (8,4) CNT-based solid state devices. We showed that strong trion emission can be obtained as a result of localized impact excitation and electrically injected holes, with an estimated efficiency of ~5 × 10-4 photons per injected hole. The importance of contact-controlled carrier injection (including symmetric and asymmetric contact configurations) and EL spectral stability for gradually increasing bias were also investigated. The realization of electrically induced pure trion emission opens up a new opportunity for CNT film-based optoelectronic devices, providing a new degree of freedom in controlling the devices to extend potential applications in spin or magnetic optoelectronics fields. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07468a

Rare-earth Doped GaN - An Innovative Path Toward Area-scalable Solid-state High Energy Lasers Without Thermal Distortion (2nd year)

DTIC Science & Technology

2010-06-01

heat removal technique and its efficiency , the gain medium itself is the bottleneck for non-distortive heat removal―simply due to low thermal...dysprosium (Dy) has been demonstrated by photoluminescence (PL), electroluminescence (EL), and/or cathodoluminescence (CL) (2, 3). As the RE dopant...provides the highest level of laser efficiency due to the pump and signal mode confinement within a crystalline-guided structure) has been designed. The

Rare-Earth Doped Gallium Nitride (GaN)- An Innovative Path Toward Area-scalable Solid-state High Energy Lasers Without Thermal Distortion

DTIC Science & Technology

2009-04-01

technique and its efficiency , the gain medium itself is the bottleneck for non-distortive heat removal—due to the low thermal conductivity of known gain...photoluminescence (PL), electroluminescence (EL), and/or cathodoluminescence (CL) (2,3). As the RE dopant, Nd is an excellent candidate due to its success...highest level of laser efficiency due to the pump and signal mode confinement within a crystalline-guided structure). The successful implementation of

Novel red phosphorescent polymers bearing both ambipolar and functionalized Ir(III) phosphorescent moieties for highly efficient organic light-emitting diodes.

PubMed

Zhao, Jiang; Lian, Meng; Yu, Yue; Yan, Xiaogang; Xu, Xianbin; Yang, Xiaolong; Zhou, Guijiang; Wu, Zhaoxin

2015-01-01

A series of novel red phosphorescent polymers is successfully developed through Suzuki cross-coupling among ambipolar units, functionalized Ir(III) phosphorescent blocks, and fluorene-based silane moieties. The photophysical and electrochemical investigations indicate not only highly efficient energy-transfer from the organic segments to the phosphorescent units in the polymer backbone but also the ambipolar character of the copolymers. Benefiting from all these merits, the phosphorescent polymers can furnish organic light-emitting diodes (OLEDs) with exceptional high electroluminescent (EL) efficiencies with a current efficiency (η L ) of 8.31 cd A(-1) , external quantum efficiency (η ext ) of 16.07%, and power efficiency (η P ) of 2.95 lm W(-1) , representing the state-of-the-art electroluminescent performances ever achieved by red phosphorescent polymers. This work here might represent a new pathway to design and synthesize highly efficient phosphorescent polymers. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A spectrally tunable all-graphene-based flexible field-effect light-emitting device

PubMed Central

Wang, Xiaomu; Tian, He; Mohammad, Mohammad Ali; Li, Cheng; Wu, Can; Yang, Yi; Ren, Tian-Ling

2015-01-01

The continuous tuning of the emission spectrum of a single light-emitting diode (LED) by an external electrical bias is of great technological significance as a crucial property in high-quality displays, yet this capability has not been demonstrated in existing LEDs. Graphene, a tunable optical platform, is a promising medium to achieve this goal. Here we demonstrate a bright spectrally tunable electroluminescence from blue (∼450 nm) to red (∼750 nm) at the graphene oxide/reduced-graphene oxide interface. We explain the electroluminescence results from the recombination of Poole–Frenkel emission ionized electrons at the localized energy levels arising from semi-reduced graphene oxide, and holes from the top of the π band. Tuning of the emission wavelength is achieved by gate modulation of the participating localized energy levels. Our demonstration of current-driven tunable LEDs not only represents a method for emission wavelength tuning but also may find applications in high-quality displays. PMID:26178323

Kinetics of transient electroluminescence in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Shukla, Manju; Kumar, Pankaj; Chand, Suresh; Brahme, Nameeta; Kher, R. S.; Khokhar, M. S. K.

2008-08-01

Mathematical simulation on the rise and decay kinetics of transient electroluminescence (EL) in organic light emitting diodes (OLEDs) is presented. The transient EL is studied with respect to a step voltage pulse. While rising, for lower values of time, the EL intensity shows a quadratic dependence on (t - tdel), where tdel is the time delay observed in the onset of EL, and finally attains saturation at a sufficiently large time. When the applied voltage is switched off, the initial EL decay shows an exponential dependence on (t - tdec), where tdec is the time when the voltage is switched off. The simulated results are compared with the transient EL performance of a bilayer OLED based on small molecular bis(2-methyl 8-hydroxyquinoline)(triphenyl siloxy) aluminium (SAlq). Transient EL studies have been carried out at different voltage pulse amplitudes. The simulated results show good agreement with experimental data. Using these simulated results the lifetime of the excitons in SAlq has also been calculated.

Nonequilibrium transport of charge carriers and transient electroluminescence in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Nikitenko, V. R.; von Seggern, H.

2007-11-01

An analytic theory of nonequilibrium hopping charge transport in disordered organic materials includes quasiequilibrium (normal) and extremely nonequilibrium (dispersive) regimes as limiting cases at long and short times, respectively. In the intermediate interval of time quasiequilibrium value of mobility is nearly established while the coefficient of field-assisted diffusion continues to increase (quasidispersive regime). Therefore, normalized time dependencies of transient current in time-of-flight (TOF) conditions are practically independent of field strength and sample thickness, in good agreement both with data of TOF experiments for molecularly doped polymers and results of numerical simulations of Gaussian disorder model. An analytic model of transient electroluminescence (TEL) is developed on the base of the mentioned theory. Strong asymmetry of mobilities is presumed. In analogy with TOF transients, dispersion parameter of normalized TEL intensity is anomalously large and almost field independent in the quasidispersive regime of transport. The method for determination of mobility from TEL data is proposed.

Secondary scintillation yield from GEM and THGEM gaseous electron multipliers for direct dark matter search

NASA Astrophysics Data System (ADS)

Monteiro, C. M. B.; Fernandes, L. M. P.; Veloso, J. F. C. A.; Oliveira, C. A. B.; dos Santos, J. M. F.

2012-07-01

The search for alternatives to PMTs as photosensors in optical TPCs for rare event detection has significantly increased in the last few years. In particular, in view of the next generation large volume detectors, the use of photosensors with lower natural radioactivity, such as large area APDs or GM-APDs, with the additional possibility of sparse surface coverage, triggered the intense study of secondary scintillation production in micropattern electron multipliers, such as GEMs and THGEMs, as alternatives to the commonly used uniform electric field region between two parallel meshes. The much higher scintillation output obtained from the electron avalanches in such microstructures presents an advantage in those situations. The accurate knowledge of the amount of such scintillation is important for correct detector simulation and optimization. It will also serve as a benchmark for software tools developed and/or under development for the calculation of the amount of such scintillation.The secondary scintillation yield, or electroluminescence yield, in the electron avalanches of GEMs and THGEMs operating in gaseous xenon and argon has been determined for different gas pressures. At 1 bar, THGEMs deliver electroluminescence yields that are more than one order of magnitude higher when compared to those achieved in GEMs and two orders of magnitude when compared to those achieved in a uniform field gap. The THGEM electroluminescence yield presents a faster decrease with pressure when comparing to the GEM electroluminescence yield, reaching similar values to what is achieved in GEMs for xenon pressures of 2.5 bar, but still one order of magnitude higher than that produced in a uniform field gap. Another exception is the GEM operating in argon, which presents an electroluminescence yield similar to that produced in a uniform electric field gap, while the THGEM achieves yields that are more than one order of magnitude higher.

Color-Pure Violet-Light-Emitting Diodes Based on Layered Lead Halide Perovskite Nanoplates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Dong; Peng, Yuelin; Fu, Yongping

Violet electroluminescence is rare in both inorganic and organic light-emitting diodes (LEDs). Low-cost and room- temperature solution-processed lead halide perovskites with high- efficiency and color-tunable photoluminescence are promising for LEDs. Here, we report room-temperature color-pure violet LEDs based on a two-dimensional lead halide perovskite material, namely, 2-phenylethylammonium (C 6H 5CH 2CH 2NH 3 +, PEA) lead bromide [(PEA) 2PbBr 4]. The natural quantum confinement of two-dimen- sional layered perovskite (PEA) 2PbBr 4 allows for photoluminescence of shorter wavelength (410 nm) than its three-dimensional counterpart. By converting as-deposited polycrystalline thin films to micrometer-sized (PEA) 2PbBr 4 nanoplates using solvent vapor annealing,more » we successfully integrated this layered perovskite material into LEDs and achieved efficient room-temperature violet electroluminescence at 410 nm with a narrow bandwidth. This conversion to nanoplates significantly enhanced the crystallinity and photophysical properties of the (PEA) 2PbBr 4 samples and the external quantum efficiency of the violet LED. Finally, the solvent vapor annealing method reported herein can be generally applied to other perovskite materials to increase their grain size and, ultimately, improve the performance of optoelectronic devices based on perovskite materials.« less

Color-Pure Violet-Light-Emitting Diodes Based on Layered Lead Halide Perovskite Nanoplates

DOE PAGES

Liang, Dong; Peng, Yuelin; Fu, Yongping; ...

2016-06-23

Violet electroluminescence is rare in both inorganic and organic light-emitting diodes (LEDs). Low-cost and room- temperature solution-processed lead halide perovskites with high- efficiency and color-tunable photoluminescence are promising for LEDs. Here, we report room-temperature color-pure violet LEDs based on a two-dimensional lead halide perovskite material, namely, 2-phenylethylammonium (C 6H 5CH 2CH 2NH 3 +, PEA) lead bromide [(PEA) 2PbBr 4]. The natural quantum confinement of two-dimen- sional layered perovskite (PEA) 2PbBr 4 allows for photoluminescence of shorter wavelength (410 nm) than its three-dimensional counterpart. By converting as-deposited polycrystalline thin films to micrometer-sized (PEA) 2PbBr 4 nanoplates using solvent vapor annealing,more » we successfully integrated this layered perovskite material into LEDs and achieved efficient room-temperature violet electroluminescence at 410 nm with a narrow bandwidth. This conversion to nanoplates significantly enhanced the crystallinity and photophysical properties of the (PEA) 2PbBr 4 samples and the external quantum efficiency of the violet LED. Finally, the solvent vapor annealing method reported herein can be generally applied to other perovskite materials to increase their grain size and, ultimately, improve the performance of optoelectronic devices based on perovskite materials.« less

Fabrication and evaluation of plasmonic light-emitting diodes with thin p-type layer and localized Ag particles embedded by ITO

NASA Astrophysics Data System (ADS)

Okada, N.; Morishita, N.; Mori, A.; Tsukada, T.; Tateishi, K.; Okamoto, K.; Tadatomo, K.

2017-04-01

Light-emitting diodes (LEDs) have been demonstrated with a thin p-type layer using the plasmonic effect. Optimal LED device operation was found when using a 20-nm-thick p+-GaN layer. Ag of different thicknesses was deposited on the thin p-type layer and annealed to form the localized Ag particles. The localized Ag particles were embedded by indium tin oxide to form a p-type electrode in the LED structure. By optimization of the plasmonic LED, the significant electroluminescence enhancement was observed when the thickness of Ag was 9.5 nm. Both upward and downward electroluminescence intensities were improved, and the external quantum efficiency was approximately double that of LEDs without the localized Ag particles. The time-resolved photoluminescence (PL) decay time for the LED with the localized Ag particles was shorter than that without the localized Ag particles. The faster PL decay time should cause the increase in internal quantum efficiency by adopting the localized Ag particles. To validate the localized surface plasmon resonance coupling effect, the absorption of the LEDs was investigated experimentally and using simulations.

Study of the electroluminescence of highly stereoregular poly(N-pentenyl-carbazole) for blue and white OLEDs

NASA Astrophysics Data System (ADS)

Liguori, R.; Botta, A.; Pragliola, S.; Rubino, A.; Venditto, V.; Velardo, A.; Aprano, S.; Maglione, M. G.; Prontera, C. T.; De Girolamo Del Mauro, A.; Fasolino, T.; Minarini, C.

2017-06-01

The electroluminescence (EL) of isotactic and syndiotactic poly(N-pentenyl-carbazole) (PPK), achieved by coordination polymerization, is studied in order to investigate the interrelation between the polymer tacticity and their physical-chemical properties. The use of these polymers in organic light-emitting diode (OLED) fabrication is also explored. Thermal and x-ray diffraction analyses of PPKs show that the isotactic stereoisomer is semicrystalline, whereas the syndiotactic one is amorphous. Optical analysis of both stereoisomers, carried out on film samples, reveals the presence of two different excimers: ‘sandwich-like’ and ‘partially overlapping’. Nevertheless, the emission intensity ratio between ‘sandwich-like’ and ‘partially overlapping’ excimers is higher in the isotactic than in the syndiotactic stereoisomer. Using the synthesized polymers as OLED emitting layers, the influence of the polymer tacticity on the EL properties of the device is highlighted. In detail, while blue OLEDs are obtained by using the syndiotactic stereoisomer, OLEDs with a multilayer structure fabricated with the isotactic stereoisomer emit white light. The contribution of three different emissions (fluorescence, phosphorescence and electromer emissions) with comparable intensities to the detected white light is discussed.

Phosphorescent Iridium(III) Complexes Bearing Fluorinated Aromatic Sulfonyl Group with Nearly Unity Phosphorescent Quantum Yields and Outstanding Electroluminescent Properties.

PubMed

Zhao, Jiang; Yu, Yue; Yang, Xiaolong; Yan, Xiaogang; Zhang, Huiming; Xu, Xianbin; Zhou, Guijiang; Wu, Zhaoxin; Ren, Yixia; Wong, Wai-Yeung

2015-11-11

A series of heteroleptic functional Ir(III) complexes bearing different fluorinated aromatic sulfonyl groups has been synthesized. Their photophysical features, electrochemical behaviors, and electroluminescent (EL) properties have been characterized in detail. These complexes emit intense yellow phosphorescence with exceptionally high quantum yields (ΦP > 0.9) at room temperature, and the emission maxima of these complexes can be finely tuned depending upon the number of the fluorine substituents on the pendant phenyl ring of the sulfonyl group. Furthermore, the electrochemical properties and electron injection/transporting (EI/ET) abilities of these Ir(III) phosphors can also be effectively tuned by the fluorinated aromatic sulfonyl group to furnish some desired characters for enhancing the EL performance. Hence, the maximum luminance efficiency (ηL) of 81.2 cd A(-1), corresponding to power efficiency (ηP) of 64.5 lm W(-1) and external quantum efficiency (ηext) of 19.3%, has been achieved, indicating the great potential of these novel phosphors in the field of organic light-emitting diodes (OLEDs). Furthermore, a clear picture has been drawn for the relationship between their optoelectronic properties and chemical structures. These results should provide important information for developing highly efficient phosphors.

The role of thin MgO(100) epilayer for polarized charge injection into top-emitting OLED

NASA Astrophysics Data System (ADS)

Kim, Tae Hee; Jong Lee, Nyun; Bae, Yu Jeong; Cho, Hyunduck; Lee, Changhee; Ito, Eisuke

2012-02-01

A new top-emitting OLED (TOLED) structure, which is formed on an Si(100) substrate and an epitaxial MgO(100)/Fe(100)/MgO(100) bottom electrode, was investigated. Our TOLED design included a semi-transparent cathode Al, a stack of conventional organic electroluminescent layers (α-NPD/Alq3/LiF) and a thin Cu-Phthalocyanine (CuPc) film to enhance the hole injection into the luminescent layers. At room temperature (RT), magnetoluminescence of ˜5 % was observed in low magnetic field up to 1 Tesla , which is obviously larger than that of the OLEDs with epitaxial and polycrystalline Fe anodes without MgO(100) covering layer. Our results indicate that the magnetic field effect on the electroluminescence could be strongly related to the magnetic properties of bottom electrode, more precisely the interfacial properties between CuPc layer and the anode. Therefore, we focused on understanding interface electronic states and energy alignment by using x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. Our results showed that the use of appropriate oxide layers could represent a new interface engineering technique for improving reliability and functionality in organic semiconductor devices.

Green-Yellow Electroluminescence from a host-dopant blended system as the active layer in a bilayer polymer light emitting diode: Poly(n-vinyl carbazole) as the host and a new soluble thiophene based copolymer [poly(2,2‧-BT)-co-(3-DDT)] as the dopant

NASA Astrophysics Data System (ADS)

Shahalizad, Afshin; Ahmadi-Kandjani, Sohrab; Movla, Hossein; Omidi, Hafez; Massoumi, Bakhshali; Zakerhamidi, Mohammad Sadegh; Entezami, Ali Akbar

2014-11-01

A new type of bilayer Polymer Light Emitting Diode (PLED) which emits green-yellow light is reported. In this PLED, a novel thiophene-based copolymer [poly(2,2‧-BT)-co-(3-DDT)] with an excellent electron transporting property has been doped in hole transporting and electron blocking poly(n-vinylcarbazole) (PVK). Formation of type-II heterojunctions among nm-size features in PVK:poly(2,2‧-BT)-co-(3-DDT) blended system makes exciplex and electroplex emissions would be dominant in the Electroluminescence (EL) spectrum of the device. These cross recombinations between electrons in the LUMO of poly(2,2‧-BT)-co-(3-DDT) and holes in the HOMO of PVK is a reason for the low driving voltage of the PLED because there is no need for the charge carriers to hop or tunnel to the adjacent polymer. Morphological investigations demonstrate that the mixing degree between the components is high, favoring formation of exciplexes and electroplexes at the interface of the components.

Large Size Color-tunable Electroluminescence from Cationic Iridium Complexes-based Light-emitting Electrochemical Cells

PubMed Central

Zeng, Qunying; Li, Fushan; Guo, Tailiang; Shan, Guogang; Su, Zhongmin

2016-01-01

Solution-processable light-emitting electrochemical cells (LECs) with simple device architecture have become an attractive candidate for application in next generation lighting and flat-panel displays. Herein, single layer LECs employing two cationic Ir(III) complexes showing highly efficient blue-green and yellow electroluminescence with peak current efficiency of 31.6 cd A−1 and 40.6 cd A−1, respectively, have been reported. By using both complexes in the device, color-tunable LECs with a single spectral peak in the wavelength range from 499 to 570 nm were obtained by varying their rations. In addition, the fabrication of efficient LECs was demonstrated based on low cost doctor-blade coating technique, which was compatible with the roll to roll fabrication process for the large size production. In this work, for the first time, 4 inch LEC devices by doctor-blade coating were fabricated, which exhibit the efficiencies of 23.4 cd A−1 and 25.4 cd A−1 for the blue-green and yellow emission, respectively. The exciting results indicated that highly efficient LECs with controllable color could be realized and find practical application in large size lighting and displays. PMID:27278527

All-solution-processed, multilayered CuInS₂/ZnS colloidal quantum-dot-based electroluminescent device.

PubMed

Kim, Jong-Hoon; Yang, Heesun

2014-09-01

While significant progress of electroluminescent (EL) quantum dot light-emitting diodes (QD-LEDs) that rely exclusively on Cd-containing II-VI quantum dots (QDs) has been reported over the past two decades with respect to device processing and performance, devices based on non-Cd QDs as an active emissive layer (EML) remain at the early stage of development. In this work, utilizing highly luminescent colloidal CuInS2 (CIS)/ZnS QDs, all-solution-processed multilayered QD-LEDs are fabricated by sequentially spin depositing a hole transport layer of poly(9-vinlycarbazole), an EML of CIS/ZnS QDs, and an electron transport layer of ZnO nanoparticles. Our focus in device fabrication is to vary the thickness of the QD EML, which is one of the primary determinants in EL performance but has not been addressed in earlier reports. The device with an optimal EML thickness exhibits a peak luminance of 1564  cd/m2 and current efficiency of 2.52  cd/A. This record value in efficiency is higher by 3-4 times that of CIS QD-LEDs reported previously.

Exciton-Induced Degradation of Carbazole-Based Host Materials and Its Role in the Electroluminescence Spectral Changes in Phosphorescent Organic Light Emitting Devices with Electrical Aging.

PubMed

Yu, Hyeonghwa; Zhang, Yingjie; Cho, Yong Joo; Aziz, Hany

2017-04-26

We investigate the origins of the long-wavelength bands that appear in the emission spectra of carbazole-based host materials and play a role in the electroluminescence (EL) spectral changes of phosphorescent organic light emitting devices (PhOLEDs) with electrical aging. 4,4'-Bis(carbazol-9-yl)biphenyl (CBP) is used as a model carbazole host material and is studied using photoluminescence, EL, and atomic force microscopy measurements under various stress scenarios in both single and bilayer devices and in combination with various electron transport layer (ETL) materials. Results show that exciton-induced morphological aggregation of CBP is behind the appearance of those long-wavelength bands and that complexation between the aggregated CBP molecules and ETL molecules plays a role in this phenomenon. Comparisons between the effects of exciton and thermal stress suggest that exciton-induced aggregation may be limited to short-range molecular ordering or pairing (e.g., dimer or trimer species formation) versus longer-range ordering (crystallization) in the case of thermal stress. The findings provide new insights into exciton-induced degradation in wide band gap host materials and its role in limiting the stability of PhOLEDs.

Electroluminescence from metal-oxide-semiconductor devices with erbium-doped CeO{sub 2} films on silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lv, Chunyan; Department of Chemistry, Huzhou University, Zhejiang, Huzhou 313000; Zhu, Chen

2015-04-06

We report on erbium (Er)-related electroluminescence (EL) in the visible and near-infrared (NIR) from metal-oxide-semiconductor (MOS) devices with Er-doped CeO{sub 2} (CeO{sub 2}:Er) films on silicon. The onset voltage of such EL under either forward or reverse bias is smaller than 10 V. Moreover, the EL quenching can be avoidable for the CeO{sub 2}:Er-based MOS devices. Analysis on the current-voltage characteristic of the device indicates that the electron transportation at the EL-enabling voltages under either forward or reverse bias is dominated by trap-assisted tunneling mechanism. Namely, electrons in n{sup +}-Si/ITO can tunnel into the conduction band of CeO{sub 2} host viamore » defect states at sufficiently high forward/reverse bias voltages. Then, a fraction of such electrons are accelerated by electric field to become hot electrons, which impact-excite the Er{sup 3+} ions, thus leading to characteristic emissions. It is believed that this work has laid the foundation for developing viable silicon-based emitters using CeO{sub 2}:Er films.« less

Molding resonant energy transfer by colloidal crystal: Dexter transfer and electroluminescence

NASA Astrophysics Data System (ADS)

González-Urbina, Luis; Kolaric, Branko; Libaers, Wim; Clays, Koen

2010-05-01

Building photonic crystals by combination of colloidal ordering and metal sputtering we were able to construct a system sensitive to an electrical field. In corresponding crystals we embedded the Dexter pair (Ir(ppy3) and BAlq) and investigated the influence of the band gap on the resonant energy transfer when the system is excited by light and by an electric field respectively. Our investigations extend applications of photonic crystals into the field of electroluminescence and LED technologies.

Optical and electrical properties of GaN-based light emitting diodes grown on micro- and nano-scale patterned Si substrate

NASA Astrophysics Data System (ADS)

Chiu, Ching-Hsueh; Lin, Chien-Chung; Deng, Dongmei; Kuo, Hao-Chung; Lau, Kei-May

2011-10-01

We investigate the optical and electrical characteristics of the GaN-based light emitting diodes (LEDs) grown on Micro and Nano-scale Patterned silicon substrate (MPLEDs and NPLEDs). The transmission electron microscopy (TEM) images reveal the suppression of threading dislocation density in InGaN/GaN structure on nano-pattern substrate due to nanoscale epitaxial lateral overgrowth (NELOG). The plan-view and cross-section cathodoluminescence (CL) mappings show less defective and more homogeneous active quantum well region growth on nano-porous substrates. From temperature dependent photoluminescence (PL) and low temperature time-resolved photoluminescence (TRPL) measurement, NPLEDs has better carrier confinement and higher radiative recombination rate than MPLEDs. In terms of device performance, NPLEDs exhibits smaller electroluminescence (EL) peak wavelength blue shift, lower reverse leakage current and decreases efficiency droop compared with the MPLEDs. These results suggest the feasibility of using NPSi for the growth of high quality and power LEDs on Si substrates.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shamirzaev, V. T., E-mail: tim@isp.nsc.ru; Gaisler, V. A.; Shamirzaev, T. S.

The spectrum of ultraviolet (UV) InGaN/GaN light-emitting diodes and its dependence on the current flowing through the structure are studied. The intensity of the UV contribution to the integrated diode luminescence increases steadily with increasing density of current flowing through the structure, despite a drop in the emission quantum efficiency. The electroluminescence excitation conditions that allow the fraction of UV emission to be increased to 97% are established. It is shown that the nonuniform generation of extended defects, which penetrate the active region of the light-emitting diodes as the structures degrade upon local current overheating, reduces the integrated emission intensitymore » but does not affect the relative intensity of diode emission in the UV (370 nm) and visible (550 nm) spectral ranges.« less

Two-dimensional CdS nanosheet-based TFT and LED nanodevices.

PubMed

Ye, Yu; Yu, Bin; Gao, Zhiwei; Meng, Hu; Zhang, Hui; Dai, Lun; Qin, Guogang

2012-05-17

Semiconductor nanosheets have several unique applications in electronic and optoelectronic nanodevices. We have successfully synthesized single-crystalline n-type CdS nanosheets via a chemical vapor deposition (CVD) method in a Cd-enriched ambient. The as-synthesized nanosheets are typically 40-100 nm thick, 10-300 µm wide, and up to several millimeters long. Using the nanosheets, we fabricated for the first time (to our knowledge), nano thin-film transistors (nano-TFTs) based on individual CdS nanosheets. A typical unit of such nanosheet TFTs has a high on-off ratio (∼1.7 ×10(9)) and peak transconductance (∼14.1µS), which to our knowledge are the best values reported so far for semiconductor nano-TFTs. In addition, we fabricated n-CdS nanosheet/p(+)-Si heterojunction light emitting diodes (LEDs) with a top electrode structure. This structure, where the n-type electrode is directly above the junction, has the advantage of a large active region and injection current favorable for high-efficiency electroluminescence (EL) and lasing. Room-temperature spectra of the LEDs consist of only an intense CdS band-edge emission peak (∼507.7 nm) with a full width at half-maximum of about 14 nm.

Magnetoelectroluminescence of organic heterostructures: Analytical theory and spectrally resolved measurements

NASA Astrophysics Data System (ADS)

Liu, Feilong; Kelley, Megan R.; Crooker, Scott A.; Nie, Wanyi; Mohite, Aditya D.; Ruden, P. Paul; Smith, Darryl L.

2014-12-01

The effect of a magnetic field on the electroluminescence of organic light emitting devices originates from the hyperfine interaction between the electron/hole polarons and the hydrogen nuclei of the host molecules. In this paper, we present an analytical theory of magnetoelectroluminescence for organic semiconductors. To be specific, we focus on bilayer heterostructure devices. In the case we are considering, light generation at the interface of the donor and acceptor layers results from the formation and recombination of exciplexes. The spin physics is described by a stochastic Liouville equation for the electron/hole spin density matrix. By finding the steady-state analytical solution using Bloch-Wangsness-Redfield theory, we explore how the singlet/triplet exciplex ratio is affected by the hyperfine interaction strength and by the external magnetic field. To validate the theory, spectrally resolved electroluminescence experiments on BPhen/m-MTDATA devices are analyzed. With increasing emission wavelength, the width of the magnetic field modulation curve of the electroluminescence increases while its depth decreases. These observations are consistent with the model.

Thin film electroluminescent cells on the basis of Ce-doped CaGa2S4 and SrGa2S4 prepared by flash evaporation method

NASA Astrophysics Data System (ADS)

Gambarov, E.; Bayramov, A.; Kato, A.; Iida, S.

2006-09-01

Ce-doped CaGa2S4 and SrGa2S4 thin film electroluminescent (TFEL) devices were prepared for the first time on the basis of films deposited by flash evaporation method. Significant crystallization, stoichiometry improvement of the films and increase of photoluminescence intensity were found after annealing in H2S and O2 gas stream. EL spectra of the cells exhibited the characteristic double-band emission similar to that seen for Ce3+ activated CaGa2S4 and SrGa2S4 films under photon excitation. Applied voltage and frequency dependences of the electroluminescence were studied. Low voltage operation as low as 20 V was observed for these cells. Luminance of about 4 cd/m2 at 100 V operating voltage with 2.5 kHz frequency was achieved for the TFEL cell with films annealed in O2 gas stream.

Carbon-electroluminescence: An organic approach to lighting

NASA Astrophysics Data System (ADS)

Kumari, Sonali; Chaudhary, Tarun; Chandran, Vivek; Lokeshwari, M.; Shastry, K.

2018-05-01

Over the recent years, quantum dots have garnered massive following and peaked in interest among the scientific community due to their versatility, exotic properties, ease of preparation and low cost. As the demand for faster, reliable and energy efficient electronic devices intensifies, extra emphasis is laid on the development of smart materials capable of satiating this need. Electroluminescent organic quantum dots have emerged as one of the prime contenders in addressing the ecological, economic and technological constraints. Application of such luminescent nanoparticles as fluorescent light converters in LEDs is touted as one of the reliable and easiest avenues in realizing and developing newer energy efficient technologies for the next millennia. One promising candidate is zig-zag graphene quantum dots, which exhibits high electro-luminescence due to a phenomenon known as quantum confinement (where size of the nano-particle is of the same order or less than that of Bohr exciton radius). In this paper, we aim to provide a review of past and present research in the synthesis and development of luminescence using organic quantum dots.

Progress and Prospects in Stretchable Electroluminescent Devices

NASA Astrophysics Data System (ADS)

Wang, Jiangxin; Lee, Pooi See

2017-03-01

Stretchable electroluminescent (EL) devices are a new form of mechanically deformable electronics that are gaining increasing interests and believed to be one of the essential technologies for next generation lighting and display applications. Apart from the simple bending capability in flexible EL devices, the stretchable EL devices are required to withstand larger mechanical deformations and accommodate stretching strain beyond 10%. The excellent mechanical conformability in these devices enables their applications in rigorous mechanical conditions such as flexing, twisting, stretching, and folding.The stretchable EL devices can be conformably wrapped onto arbitrary curvilinear surface and respond seamlessly to the external or internal forces, leading to unprecedented applications that cannot be addressed with conventional technologies. For example, they are in demand for wide applications in biomedical-related devices or sensors and soft interactive display systems, including activating devices for photosensitive drug, imaging apparatus for internal tissues, electronic skins, interactive input and output devices, robotics, and volumetric displays. With increasingly stringent demand on the mechanical requirements, the fabrication of stretchable EL device is encountering many challenges that are difficult to resolve. In this review, recent progresses in the stretchable EL devices are covered with a focus on the approaches that are adopted to tackle materials and process challenges in stretchable EL devices and delineate the strategies in stretchable electronics. We first introduce the emission mechanisms that have been successfully demonstrated on stretchable EL devices. Limitations and advantages of the different mechanisms for stretchable EL devices are also discussed. Representative reports are reviewed based on different structural and material strategies. Unprecedented applications that have been enabled by the stretchable EL devices are reviewed. Finally, we summarize with our perspectives on the approaches for the stretchable EL devices and our proposals on the future development in these devices.

Synthesis of Ferrite Nickel Nano-particles and Its Role as a p-Dopant in the Improvement of Hole Injection of an Organic Light-Emitting Diode

NASA Astrophysics Data System (ADS)

Noori, Maryam; Jafari, Mohammad Reza; Hosseini, Sayed Mohsen; Shahedi, Zahra

2017-07-01

We fabricated an organometallic complex based on zinc ions using zinc complex as a fluorescent in organic light-emitting diodes (OLEDs). Also, the nano-particles of ferrite nickel were produced in a simple aqueous system prepared by mixing Ni (NO3)2, Fe (NO3)3 and deionized water solutions. The synthesized zinc bis (8-hydroxyquinoline) (Znq2) complex and NiFe2O4 nano-particles were characterized by using x-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) as well as photoluminescence spectroscopy analysis. Their energy level was also determined by some cyclic voltammetry (CV) measurements. The maximum green photoluminescence was observed at 565 nm. The nano-particles of ferrite nickel were utilized in preparation of OLEDs by blending of the magnetic nano-particles with PEDOT:PSS and Zn-complex solutions. The electrical and optical performance of prepared OLEDs with/without doped nano-particle was studied. The samples were configured into two structures: (1) Indium Tin Oxide (ITO)/ poly(3,4-ethylenedi-oxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Znq2/(2-4-biphenylyl)-5-phenyl-oxadiazole (PBD)/aluminum (Al) and (2) ITO/PEDOT:PSS:NiFe2O4(NPs)/Znq2/PBD/Al. Obtained results showed that the current density and electroluminescence efficiency were increased and the turn-on voltage decreased (about 3 V) by using nano-particles into a PEDOT:PSS layer (Hole transport layer). Also, the electroluminescence efficiency was decreased by incorporating magnetic nano-particles into a Zn-complex layer (emissive layer). It was found that utilizing NiFe2O4 nano-particles caused an increase of hole-injection layer conductivity effectively and a decrease of the turn-on voltage.

Intense deep-blue electroluminescence from ITO/Y₂O₃/Ag structure.

PubMed

Yin, Xue; Wang, Shenwei; Li, Ling; Mu, Guangyao; Tang, Ying; Duan, Wubiao; Yi, Lixin

2015-07-13

ITO/Y₂O₃/Ag devices were fabricated using Y₂O₃ films as insulator. Four intense and sharp lines with half-peak width of 4 nm were observed for the 293.78 nm InI, 316.10 nm InI, 444.82 nm InII and 403.07 nm InIII transitions. Luminescence mechanism was illustrated by cross-section of the devices based on the analysis of surface morphology. Under the action of strong electric field, the loss of K-shell electrons led to the occurrence of characteristic radiation of indium ions. In addition, the device with turn-on voltage of 10V demonstrates typical I-V diode characteristics. Moreover, Y₂O₃/In₂O₃ multiple films as the insulation layer instead of single Y₂O₃ films was found to improve the device performance with excellent CIE (x, y) coordinates (0.16, 0.03).

Transport properties of doped AlP for the development of conductive AlP/GaP distributed Bragg reflectors and their integration into light-emitting diodes

NASA Astrophysics Data System (ADS)

Hestroffer, Karine; Sperlich, Dennis; Dadgostar, Shabnam; Golz, Christian; Krumland, Jannis; Masselink, William Ted; Hatami, Fariba

2018-05-01

The transport properties of n- and p-doped AlP layers grown by gas-source molecular beam epitaxy are investigated. n- and p-types of conductivities are achieved using Si and Be with peak room-temperature mobilities of 59.6 cm2/Vs and 65.0 cm2/Vs for electrons and holes, respectively. Si-doping results are then used for the design of n-doped AlP/GaP distributed Bragg reflectors (DBRs) with an ohmic resistance of about 7.5 ± 0.1 Ω. The DBRs are integrated as bottom mirrors in GaP-based light-emitting diodes (LEDs) containing InGaP/GaP quantum dots. The functionality of the LED structure and the influence of the DBRs on the InGaP/GaP electroluminescence spectra are demonstrated.

Substituent Effects In a Series of 1,7-C60(RF)2 Compounds (RF = CF3, C2F5, n-C3F7, i-C3F7, n-C4F9, s-C4F9, n-C8F17): Electron Affinities, Reduction Potentials, and E(LUMO) Values Are Not Always Correlated

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuvychko, Igor V.; Whitaker, James B.; Larson, Bryon W.

Substituent effects are of paramount importance in virtually all fields of fundamental and applied chemistry. Classical and modern examples can be found in organic chemistry (Hammett parameters and Charton steric parameters), inorganic chemistry (trans effect and trans influence), organometallic chemistry (phosphine cone angles), physical chemistry (linear free energy relationships and DFT), biochemistry (protein tertiary structure), medicinal chemistry (SAR maps and BioMAP analysis), polymer chemistry (nonlinear optical and permeation properties and glass transition temperatures), and materials chemistry (stability and luminescent properties of electroluminescent devices and light-to-power conversion efficiencies of fullerene-derivative-based OPV devices).

A colour-tunable, weavable fibre-shaped polymer light-emitting electrochemical cell

NASA Astrophysics Data System (ADS)

Zhang, Zhitao; Guo, Kunping; Li, Yiming; Li, Xueyi; Guan, Guozhen; Li, Houpu; Luo, Yongfeng; Zhao, Fangyuan; Zhang, Qi; Wei, Bin; Pei, Qibing; Peng, Huisheng

2015-04-01

The emergence of wearable electronics and optoelectronics requires the development of devices that are not only highly flexible but can also be woven into textiles to offer a truly integrated solution. Here, we report a colour-tunable, weavable fibre-shaped polymer light-emitting electrochemical cell (PLEC). The fibre-shaped PLEC is fabricated using all-solution-based processes that can be scaled up for practical applications. The design has a coaxial structure comprising a modified metal wire cathode and a conducting aligned carbon nanotube sheet anode, with an electroluminescent polymer layer sandwiched between them. The fibre shape offers unique and promising advantages. For example, the luminance is independent of viewing angle, the fibre-shaped PLEC can provide a variety of different and tunable colours, it is lightweight, flexible and wearable, and it can potentially be woven into light-emitting clothes for the creation of smart fabrics.

Growth and characterization of vertical cavity structures on InP with GaAsSb/AlAsSb Bragg mirrors for 1.55 μm emission

NASA Astrophysics Data System (ADS)

Genty, Frédéric; Almuneau, Guilhem; Chusseau, Laurent; Wilk, Arnaud; Gaillard, Serge; Boissier, Guilhem; Grech, Pierre; Jacquet, Joel

1999-05-01

With the aim of fabricating vertical cavity semiconductor lasers (VCSEL), the molecular beam epitaxy growth of GaAsSb using two different element-V precursor sets has been first evaluated. Alloy compositions as well as ease of achieving lattice-matching are compared with both (As 2-Sb 4) or (As 2-Sb 2). Change in the growth mode process that depends on the precursor couple is presumed to influence strongly As and Sb incorporation rates thereby causing difficulties in reaching lattice-matching with Sb 4. The above study has allowed the fabrication of a fully doped 3 λ/2 monolithic Sb-based VCSEL on InP. The main devices performing at 77 K are a 200 nm wide stopband centered at 1.5 μm and a clear cavity resonance at 1.53 μm from which electroluminescence has been observed.

Triphenylvinyl anthracene based emitter for non-doped blue light emitting devices with unusual emission behavior

NASA Astrophysics Data System (ADS)

Islam, Amjad; Zhang, Dongdong; Usman, Khurram; Siddique, Ahmad Hassan; Wattoo, Abdul Ghafar; Khalid, Hamad; Ouyang, Xinhua; Duan, Lian; Ge, Ziyi

2018-05-01

A novel blue luminogen based on triphenylvinyl anthracene was synthesized. The photophysical, thermal and aggregation induced emission as well as electroluminescent properties were investigated. The luminogen demonstrated typical aggregation caused quenching (ACQ) effect. A non-doped organic light emitting device was fabricated and realized a current efficiency of 3.25 cd/A, an external quantum efficiency of 1.41%, power efficiency of 2.11 m/W and a maximum luminance of 11761.8 cd/m2 were achieved.

Integrated fuses for OLED lighting device

DOEpatents

Pschenitzka, Florian [San Jose, CA

2007-07-10

An embodiment of the present invention pertains to an electroluminescent lighting device for area illumination. The lighting device is fault tolerant due, in part, to the patterning of one or both of the electrodes into strips, and each of one or more of these strips has a fuse formed on it. The fuses are integrated on the substrate. By using the integrated fuses, the number of external contacts that are used is minimized. The fuse material is deposited using one of the deposition techniques that is used to deposit the thin layers of the electroluminescent lighting device.

Electroluminescence of a polythiophene molecular wire suspended between a metallic surface and the tip of a scanning tunneling microscope.

PubMed

Reecht, Gaël; Scheurer, Fabrice; Speisser, Virginie; Dappe, Yannick J; Mathevet, Fabrice; Schull, Guillaume

2014-01-31

The electroluminescence of a polythiophene wire suspended between a metallic surface and the tip of a scanning tunneling microscope is reported. Under positive sample voltage, the spectral and voltage dependencies of the emitted light are consistent with the fluorescence of the wire junction mediated by localized plasmons. This emission is strongly attenuated for the opposite polarity. Both emission mechanism and polarity dependence are similar to what occurs in organic light emitting diodes (OLED) but at the level of a single molecular wire.

Colloidal quantum dot active layers for light emitting diodes

NASA Astrophysics Data System (ADS)

Pagan, Jennifer G.; Stokes, Edward B.; Patel, Kinnari; Burkhart, Casey C.; Ahrens, Michael T.; Barletta, Philip T.; O'Steen, Mark

2006-07-01

In this paper the preliminary results of incorporating a novel active layer into a GaN light emitting diode (LED) are discussed. Integration of colloidal CdSe quantum dots into a GaN LED active layer is demonstrated. Properties of p-type Mg doped overgrowth GaN are examined via circular transmission line method (CTLM). Effects on surface roughness due to the active layer incorporation are examined using atomic force microscopy (AFM). Electroluminescence of LED test structures is reported, and an ideality factor of n = 1.6 is demonstrated.

Ultrahigh-efficiency solution-processed simplified small-molecule organic light-emitting diodes using universal host materials

PubMed Central

Han, Tae-Hee; Choi, Mi-Ri; Jeon, Chan-Woo; Kim, Yun-Hi; Kwon, Soon-Ki; Lee, Tae-Woo

2016-01-01

Although solution processing of small-molecule organic light-emitting diodes (OLEDs) has been considered as a promising alternative to standard vacuum deposition requiring high material and processing cost, the devices have suffered from low luminous efficiency and difficulty of multilayer solution processing. Therefore, high efficiency should be achieved in simple-structured small-molecule OLEDs fabricated using a solution process. We report very efficient solution-processed simple-structured small-molecule OLEDs that use novel universal electron-transporting host materials based on tetraphenylsilane with pyridine moieties. These materials have wide band gaps, high triplet energy levels, and good solution processabilities; they provide balanced charge transport in a mixed-host emitting layer. Orange-red (~97.5 cd/A, ~35.5% photons per electron), green (~101.5 cd/A, ~29.0% photons per electron), and white (~74.2 cd/A, ~28.5% photons per electron) phosphorescent OLEDs exhibited the highest recorded electroluminescent efficiencies of solution-processed OLEDs reported to date. We also demonstrate a solution-processed flexible solid-state lighting device as a potential application of our devices. PMID:27819053

Fabrication of an Organic Light-Emitting Diode from New Host π Electron Rich Zinc Complex

NASA Astrophysics Data System (ADS)

Jafari, Mohammad Reza; Janghouri, Mohammad; Shahedi, Zahra

2017-01-01

A new π electron rich zinc complex was used as a fluorescent material in organic light-emitting diodes (OLEDs). Devices with a structure of indium tin oxide/poly (3,4-ethylenedi-oxythiophene):poly(styrenesulfonate) (PEDOT: PSS) (50 nm)/polyvinylcarbazole (60 nm)/Zn: %2 porphyrin derivatives (45 nm)/Al (150 nm) were fabricated. Porphyrin derivatives accounting for 2 wt.% in the π electron rich zinc complex were used as a host. The electroluminescence (EL) spectra of porphyrin derivatives indicated a red shift, as π electron rich zinc complex EL spectra. The device (4) has also a luminance of 3420 cd/m2 and maximum efficiency of 1.58 cd/A at 15 V, which are the highest values among four devices. The result of Commission International del'Eclairage (CIE) (X, Y) coordinate and EL spectrum of device (3) indicated that it is more red shifted compared to other devices. Results of this work indicate that π electron rich zinc complex is a promising host material for high efficiency red OLEDs and has a simple structure compared to Alq3-based devices.

All metalorganic chemical vapor phase epitaxy of p/n-GaN tunnel junction for blue light emitting diode applications

NASA Astrophysics Data System (ADS)

Neugebauer, S.; Hoffmann, M. P.; Witte, H.; Bläsing, J.; Dadgar, A.; Strittmatter, A.; Niermann, T.; Narodovitch, M.; Lehmann, M.

2017-03-01

We report on III-Nitride blue light emitting diodes (LEDs) comprising a GaN-based tunnel junction (TJ) all realized by metalorganic vapor phase epitaxy in a single growth process. The TJ grown atop the LED structures consists of a Mg-doped GaN layer and subsequently grown highly Ge-doped GaN. Long thermal annealing of 60 min at 800 °C is important to reduce the series resistance of the LEDs due to blockage of acceptor-passivating hydrogen diffusion through the n-type doped top layer. Secondary ion mass spectroscopy measurements reveal Mg-incorporation into the topmost GaN:Ge layer, implying a non-abrupt p-n tunnel junction and increased depletion width. Still, significantly improved lateral current spreading as compared to conventional semi-transparent Ni/Au p-contact metallization and consequently a more homogeneous electroluminescence distribution across 1 × 1 mm2 LED structures is achieved. Direct estimation of the depletion width is obtained from electron holography experiments, which allows for a discussion of the possible tunneling mechanism.

Emission Characteristics of InGaN/GaN Core-Shell Nanorods Embedded in a 3D Light-Emitting Diode.

PubMed

Jung, Byung Oh; Bae, Si-Young; Lee, Seunga; Kim, Sang Yun; Lee, Jeong Yong; Honda, Yoshio; Amano, Hiroshi

2016-12-01

We report the selective-area growth of a gallium nitride (GaN)-nanorod-based InGaN/GaN multiple-quantum-well (MQW) core-shell structure embedded in a three-dimensional (3D) light-emitting diode (LED) grown by metalorganic chemical vapor deposition (MOCVD) and its optical analysis. High-resolution transmission electron microscopy (HR-TEM) observation revealed the high quality of the GaN nanorods and the position dependence of the structural properties of the InGaN/GaN MQWs on multiple facets. The excitation and temperature dependences of photoluminescence (PL) revealed the m-plane emission behaviors of the InGaN/GaN core-shell nanorods. The electroluminescence (EL) of the InGaN/GaN core-shell-nanorod-embedded 3D LED changed color from green to blue with increasing injection current. This phenomenon was mainly due to the energy gradient and deep localization of the indium in the selectively grown InGaN/GaN core-shell MQWs on the 3D architecture.

RF sputter deposition of SrS:Eu and ZnS:Mn thin film electroluminescent phosphors

NASA Astrophysics Data System (ADS)

Droes, Steven Roy

1998-09-01

The radio-frequency (rf) sputter deposition of thin film electroluminescent (TFEL) materials was studied. Thin films of strontium sulfide doped with europium (SrS:Eu) and zinc sulfide doped with manganese (ZnS:Mn) were RF sputter deposited at different conditions. Photoluminescent and electroluminescent behaviors of these films were examined. Photoluminescent active, crystalline films of SrS:Eu were deposited at temperatures from 300o C to 650o C. The best temperature was 400o C, where a PL efficiency of 35% was achieved. Films were deposited at two power levels (90 and 120 watts) and five H2S concentrations (0.6%, 1.3%, 2.4%, 4.0% and 5.3%). The H2S concentration affected the crystallinity of the films and the PL performance. Lower H2S concentrations resulted in films with smaller crystallite sizes and poorer PL performance. Increased H2S concentrations increased the PL intensity and the overall spectra resembled that of an efficient SrS:Eu powder. Although there was a correlation between crystallinity and PL performance other factors such as europium concentration, distribution, and local environment also influence PL performance. Analytical results suggested that, although a film may be crystalline and have the correct europium concentration, unless the europium is in the correct localized environment, optimum PL response will not be achieved. Increased H2S concentrations produced films with europium located in optimum locations. Contrary to vacuum or chemical vapor deposited films, the sputter deposited films showed no trailing edge emission during electroluminescence. A suggested reason for this lack of a trailing edge emission in these films is that the sputter deposition process produces phosphor- insulator interfaces without shallow trap states. A statistical design of experiments approach was implemented for the sputter deposition of ZnS:Mn. The effects of four factors (substrate temperature, chamber pressure, power to the target, and H2S concentration) on three responses (deposition rate, stoichiometry, and PL performance) were studied. A 1/2 fractional factorial showed that each of the factors had a significant influence on at least one response. A large experimental error with subsequent Box-Behnken experiments, however, indicated that some uncontrolled factor was influencing the quality of the films. The large experimental error prevented the development of reliable experimental models based on the Box-Behnken results.

The effect of the thicknesses of the various layers on the colour emitted by an organic electroluminescent device

NASA Astrophysics Data System (ADS)

Jolinat, P.; Clergereaux, R.; Farenc, J.; Destruel, P.

1998-05-01

Organic electroluminescent diodes based on thin organic layers are one of the most promising next-generation systems for the backlighting of the liquid crystal screens. Among other methods to obtain white light, three-layer luminescent devices with each layer emitting one of the three fundamental colours have been studied here. Red, green and blue light were produced by 0022-3727/31/10/018/img1 doped with Nile red, 0022-3727/31/10/018/img1 and TPD layers respectively. A fourth thin film of TAZ has been inserted between TPD and 0022-3727/31/10/018/img1 to control injection of electrons into the TPD. The effect of the layers' thicknesses on the spectral emission of the device has been examined. Results show that the thicknesses of TAZ and doped 0022-3727/31/10/018/img1 layers have to be controlled to within a precision of better than 5 Å. The discussion turns on the possibility of applying this technology to screen backlighting.

Investigations on electroluminescent tapes and foils in relation to their applications in automotive

NASA Astrophysics Data System (ADS)

Plotog, Ioan

2015-02-01

The electroluminescent (EL) tapes or foils having barrier films for an additional level of protection against the toughest environments conditions, offer a large area of applications. The EL lights, due to their characteristics, began to be used not only in the entertainment industry, but also for automotive and aerospace applications. In the paper, the investigations regarding EL foils technical performances in relation to their applications as light sources in automotive ambient light were presented. The experiments were designed based on the results of EL foils electrical properties previous investigations done in laboratory conditions, taking into account the range of automotive ambient temperatures for sinusoidal alternative supply voltage. The measurements for different temperatures were done by keeping the EL foils into electronic controlled oven that ensures the dark enclosure offering conditions to use a lux-meter in order to measure and maintain under control light emission intensity. The experiments results define the EL foils characteristics as load in automotive ambient temperatures condition, assuring so the data for optimal design of a dedicated inverter.

Sharp green electroluminescence from 1H-pyrazolo[3,4-b]quinoline-based light-emitting diodes

NASA Astrophysics Data System (ADS)

Tao, Y. T.; Balasubramaniam, E.; Danel, A.; Jarosz, B.; Tomasik, P.

2000-09-01

A multilayer organic light-emitting diode was fabricated using a fluorescent compound {6-N,N-diethylamino-1-methyl-3-phenyl-1H-pyrazolo[3,4-b]quinoline} (PAQ-NEt2) doped into the hole-transporting layer of NPB {4,4'-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl}, with the TPBI {2,2',2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole]} as an electrontransporting material. At 16% PAQ-NEt2 doping concentration, the device gave a sharp, bright, and efficient green electroluminescence (EL) peaked at around 530 nm. The full width at half maximum of the EL is 60 nm, which is 60% of the green emission from typical NPB/AlQ [where AlQ=tris(8-hydroxyquinoline) aluminum] device. For the same concentration, a maximum luminance of 37 000 cd/m2 was obtained at 10.0 V and the maximum power, luminescence, and external quantum efficiencies were obtained 4.2 lm/W, 6.0 cd/A, and 1.6%, respectively, at 5.0 V.

Visible electroluminescence from a ZnO nanowires/p-GaN heterojunction light emitting diode.

PubMed

Baratto, C; Kumar, R; Comini, E; Faglia, G; Sberveglieri, G

2015-07-27

In the current paper we apply catalyst assisted vapour phase growth technique to grow ZnO nanowires (ZnO nws) on p-GaN thin film obtaining EL emission in reverse bias regime. ZnO based LED represents a promising alternative to III-nitride LEDs, as in free devices: the potential is in near-UV emission and visible emission. For ZnO, the use of nanowires ensures good crystallinity of the ZnO, and improved light extraction from the interface when the nanowires are vertically aligned. We prepared ZnO nanowires in a tubular furnace on GaN templates and characterized the p-n ZnO nws/GaN heterojunction for LED applications. SEM microscopy was used to study the growth of nanowires and device preparation. Photoluminescence (PL) and Electroluminescence (EL) spectroscopies were used to characterize the heterojunction, showing that good quality of PL emission is observed from nanowires and visible emission from the junction can be obtained from the region near ZnO contact, starting from onset bias of 6V.

Bright Electroluminescence from Single Graphene Nanoribbon Junctions

NASA Astrophysics Data System (ADS)

Chong, Michael C.; Afshar-Imani, Nasima; Scheurer, Fabrice; Cardoso, Claudia; Ferretti, Andrea; Prezzi, Deborah; Schull, Guillaume

2018-01-01

Thanks to their highly tunable band gaps, graphene nanoribbons (GNRs) with atomically precise edges are emerging as mechanically and chemically robust candidates for nanoscale light emitting devices of modulable emission color. While their optical properties have been addressed theoretically in depth, only few experimental studies exist, limited to ensemble measurements and without any attempt to integrate them in an electronic-like circuit. Here we report on the electroluminescence of individual GNRs suspended between the tip of a scanning tunneling microscope (STM) and a Au(111) substrate, constituting thus a realistic opto-electronic circuit. Emission spectra of such GNR junctions reveal a bright and narrow band emission of red light, whose energy can be tuned with the bias voltage applied to the junction, but always lying below the gap of infinite GNRs. Comparison with {\\it ab initio} calculations indicate that the emission involves electronic states localized at the GNR termini. Our results shed light on unpredicted optical transitions in GNRs and provide a promising route for the realization of bright, robust and controllable graphene-based light emitting devices.

Structural and optical properties of semi-polar (11-22) InGaN/GaN green light-emitting diode structure

NASA Astrophysics Data System (ADS)

Zhao, Guijuan; Wang, Lianshan; Li, Huijie; Meng, Yulin; Li, Fangzheng; Yang, Shaoyan; Wang, Zhanguo

2018-01-01

Semi-polar (11-22) InGaN multiple quantum well (MQW) green light-emitting diode (LED) structures have been realized by metal-organic chemical vapor deposition on an m-plane sapphire substrate. By introducing double GaN buffer layers, we improve the crystal quality of semi-polar (11-22) GaN significantly. The vertical alignment of the diffraction peaks in the (11-22) X-ray reciprocal space mapping indicates the fully strained MQW on the GaN layer. The photoluminescence spectra of the LED structure show stronger emission intensity along the [1-100] InGaN/GaN direction. The electroluminescence emission of the LED structure is very broad with peaks around 550 nm and 510 nm at the 100 mA current injection for samples A and B, respectively, and exhibits a significant blue-shift with increasing drive current.

Electroluminescent Yb2O3:Er and Yb2Si2O7:Er nanolaminate films fabricated by atomic layer deposition on silicon

NASA Astrophysics Data System (ADS)

Ouyang, Zhongtao; Yang, Yang; Sun, Jiaming

2018-06-01

Atomic layer doped Yb2O3:Er and Yb2Si2O7:Er nanolaminate films are fabricated on silicon by atomic layer deposition, and ∼1530 nm electroluminescence (EL) is obtained from the metal-oxide-semiconductor light-emitting devices (MOSLEDs) based on these films. The Yb2O3 films transfer to Yb2Si2O7 phase after annealing above 1000 °C. Intense photoluminescence from Yb2Si2O7 film confirms high efficiency and energy transfer under optical excitation, but the limited electron conduction restricts the EL performance. EL from the Yb2O3:Er MOSLED outperforms, presenting an external quantum efficiency up to 8.5% and the power efficiency of 1 × 10-3. The EL is derived to result from the impact excitation of Er3+ ions by hot electrons, which stem from Fowler-Nordheim tunneling mechanism under sufficient bias voltage. The critical distance for the cross relaxation of doped Er3+ ions in nanolaminate Yb2O3 matrix is experimentally determined to be ∼3 nm. Such devices manifest the technological potential of Er-doped Yb-oxides for applications in silicon-based optoelectronics.

Efficient Carrier-to-Exciton Conversion in Field Emission Tunnel Diodes Based on MIS-Type van der Waals Heterostack.

PubMed

Wang, Shunfeng; Wang, Junyong; Zhao, Weijie; Giustiniano, Francesco; Chu, Leiqiang; Verzhbitskiy, Ivan; Zhou Yong, Justin; Eda, Goki

2017-08-09

We report on efficient carrier-to-exciton conversion and planar electroluminescence from tunnel diodes based on a metal-insulator-semiconductor (MIS) van der Waals heterostack consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS 2 ). These devices exhibit excitonic electroluminescence with extremely low threshold current density of a few pA·μm -2 , which is several orders of magnitude lower compared to the previously reported values for the best planar EL devices. Using a reference dye, we estimate the EL quantum efficiency to be ∼1% at low current density limit, which is of the same order of magnitude as photoluminescence quantum yield at the equivalent excitation rate. Our observations reveal that the efficiency of our devices is not limited by carrier-to-exciton conversion efficiency but by the inherent exciton-to-photon yield of the material. The device characteristics indicate that the light emission is triggered by injection of hot minority carriers (holes) to n-doped WS 2 by Fowler-Nordheim tunneling and that hBN serves as an efficient hole-transport and electron-blocking layer. Our findings offer insight into the intelligent design of van der Waals heterostructures and avenues for realizing efficient excitonic devices.

Method for producing high energy electroluminescent devices

DOEpatents

Meyerson, Bernard S.; Scott, Bruce A.; Wolford, Jr., Donald J.

1992-09-29

A method is described for fabricating electroluminescent devices exhibiting visible electroluminescence at room temperature, where the devices include at least one doped layer of amorphous hydrogenated silicon (a-Si:H). The a-Si:H layer is deposited on a substrate by homogeneous chemical vapor deposition (H-CVD) in which the substrate is held at a temperature lower than about 200.degree. C. and the a-Si:H layer is doped in-situ during deposition, the amount of hydrogen incorporated in the deposited layer being 12-50 atomic percent. The bandgap of the a-Si:H layer is between 1.6 and 2.6 eV, and in preferrable embodiments is between 2.0 and 2.6 eV. The conductivity of the a-Si:H layer is chosen in accordance with device requirements, and can be 10.sup.16 -10.sup.19 carriers/cm.sup.2. The bandgap of the a-Si:H layer depends at least in part on the temperature of the substrate on which the layer is deposited, and can be "tuned" by changing the substrate temperature.

Magnetoelectroluminescence of organic heterostructures: Analytical theory and spectrally resolved measurements

DOE PAGES

Liu, Feilong; Kelley, Megan R.; Crooker, Scott A.; ...

2014-12-22

The effect of a magnetic field on the electroluminescence of organic light emitting devices originates from the hyperfine interaction between the electron/hole polarons and the hydrogen nuclei of the host molecules. In this paper, we present an analytical theory of magnetoelectroluminescence for organic semiconductors. To be specific, we focus on bilayer heterostructure devices. In the case we are considering, light generation at the interface of the donor and acceptor layers results from the formation and recombination of exciplexes. The spin physics is described by a stochastic Liouville equation for the electron/hole spin density matrix. By finding the steady-state analytical solutionmore » using Bloch-Wangsness-Redfield theory, we explore how the singlet/triplet exciplex ratio is affected by the hyperfine interaction strength and by the external magnetic field. In order to validate the theory, spectrally resolved electroluminescence experiments on BPhen/m-MTDATA devices are analyzed. With increasing emission wavelength, the width of the magnetic field modulation curve of the electroluminescence increases while its depth decreases. Furthermore, these observations are consistent with the model.« less

Observation and discussion of avalanche electroluminescence in GaN p-n diodes offering a breakdown electric field of 3 MV cm‑1

NASA Astrophysics Data System (ADS)

Mandal, S.; Kanathila, M. B.; Pynn, C. D.; Li, W.; Gao, J.; Margalith, T.; Laurent, M. A.; Chowdhury, S.

2018-06-01

We report on the first observation of avalanche electroluminescence resulting from band-to-band recombination (BTBR) of electron hole pairs at the breakdown limit of Gallium Nitride p-n diodes grown homo-epitaxially on single crystalline GaN substrates. The diodes demonstrated a near ideal breakdown electric field of 3 MV cm‑1 with electroluminescence (EL) demonstrating sharp peaks of emission energies near and at the band gap of GaN. The high critical electric field, near the material limit of GaN, was achieved by generating a smooth curved mesa edge with low plasma damage, using etch engineering without any use of field termination. The superior material quality was critical for such a near-ideal performance. An electric field of 3 MV cm‑1 recorded at the breakdown resulted in impact ionization, confirmed by a positive temperature dependence of the breakdown voltage. The spectral data provided evidence of BTBR of electron hole pairs that were generated by avalanche carrier multiplication in the depletion region.

Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO{sub 2} films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Chen; Gao, Zhifei; Wang, Canxing

2015-09-28

We report on multicolor and near-infrared electroluminescence (EL) from the devices using rare-earth doped TiO{sub 2} (TiO{sub 2}:RE) films as light-emitting layers, which are ascribed to the impact excitation of RE{sup 3+} ions, with the EL onset voltages below 10 V. The devices are in the structure of ITO/TiO{sub 2}:RE/SiO{sub 2}/Si, in which the SiO{sub 2} layer is ∼10 nm thick and RE includes Eu, Er, Tm, Nd, and so on. With sufficiently high positive voltage applied on the ITO electrode, the conduction electrons in Si can tunnel into the conduction band of SiO{sub 2} layer via the trap-assisted tunneling mechanism, gainingmore » the potential energy ∼4 eV higher than the conduction band edge of TiO{sub 2}. Therefore, as the electrons in the SiO{sub 2} layer drift into the TiO{sub 2}:RE layer, they become hot electrons. Such hot electrons impact-excite the RE{sup 3+} ions incorporated into the TiO{sub 2} host, leading to the characteristic emissions.« less

Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Kyu Kim, Jung; Bae, Sukang; Yi, Yeonjin; Jin Park, Myung; Jin Kim, Sang; Myoung, Nosoung; Lee, Chang-Lyoul; Hee Hong, Byung; Hyeok Park, Jong

2015-06-01

Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions.

Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes.

PubMed

Kyu Kim, Jung; Bae, Sukang; Yi, Yeonjin; Jin Park, Myung; Jin Kim, Sang; Myoung, NoSoung; Lee, Chang-Lyoul; Hee Hong, Byung; Hyeok Park, Jong

2015-06-11

Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions.

Effect of n-type doping level on direct band gap electroluminescence intensity for asymmetric metal/Ge/metal diodes

NASA Astrophysics Data System (ADS)

Maekura, T.; Tanaka, K.; Motoyama, C.; Yoneda, R.; Yamamoto, K.; Nakashima, H.; Wang, D.

2017-10-01

The direct band gap electroluminescence (EL) intensity was investigated for asymmetric metal/Ge/metal diodes fabricated on n-type Ge with doping levels in the range of 4.0 × 1013-3.1 × 1018 cm-3. Up to a doping level of 1016 cm-3 order, commercially available (100) n-Ge substrates were used. To obtain a doping level higher than 1017 cm-3 order, which is commercially unavailable, n+-Ge/p-Ge structures were fabricated by Sb doping on p-type (100) Ge substrates with an in-diffusion at 600 °C followed by a push-diffusion at 700 °C-850 °C. The EL intensity was increased with increasing doping level up to 1.0 × 1018 cm-3. After that, it was decreased with a further increase in n-type doping level. This EL intensity decrease is explained by the decreased number of holes in the active region. One reason is the difficulty in hole injection through the PtGe/n-Ge contact due to the occurring of tunneling electron current. Another reason is the loss of holes caused by both the small thickness of n+-Ge layer and the existence of n+p junction.

Synthesis, characterization of dihydrolipoic acid capped gold nanoparticles, and functionalization by the electroluminescent luminol.

PubMed

Roux, Stéphane; Garcia, Bruno; Bridot, Jean-Luc; Salomé, Murielle; Marquette, Christophe; Lemelle, Laurence; Gillet, Phillipe; Blum, Loïc; Perriat, Pascal; Tillement, Olivier

2005-03-15

The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH > or = 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged.

Microscale localization and isolation of light emitting imperfections in monocrystalline silicon solar cells

NASA Astrophysics Data System (ADS)

Gajdoš, Adam; Škvarenina, Lubomír.; Škarvada, Pavel; Macků, Robert

2017-12-01

An imperfections or defects may appear in fabricated monocrystalline solar cells. These microstructural imperfections could have impact on the parameters of whole solar cell. The research is divided into two parts, firstly, the detection and localization defects by using several techniques including current-voltage measurement, scanning probe microscopy (SPM), scanning electron microscope (SEM) and electroluminescence. Secondly, the defects isolation by a focused ion beam (FIB) milling and impact of a milling process on solar cells. The defect detection is realized by I-V measurement under reverse biased sample. For purpose of localization, advantage of the fact that defects or imperfections in silicon solar cells emit the visible and near infrared electroluminescence under reverse biased voltage is taken, and CCD camera measurement for macroscopic localization of these spots is applied. After rough macroscopic localization, microscopic localization by scanning probe microscopy combined with a photomultiplier (shadow mapping) is performed. Defect isolation is performed by a SEM equipped with the FIB instrument. FIB uses a beam of gallium ions which modifies crystal structure of a material and may affect parameters of solar cell. As a result, it is interesting that current in reverse biased sample with isolated defect is smaller approximately by 2 orders than current before isolation process.

White Polymer Light-Emitting Diodes Based on Exciplex Electroluminescence from Polymer Blends and a Single Polymer.

PubMed

Liang, Junfei; Zhao, Sen; Jiang, Xiao-Fang; Guo, Ting; Yip, Hin-Lap; Ying, Lei; Huang, Fei; Yang, Wei; Cao, Yong

2016-03-09

In this Article, we designed and synthesized a series of polyfluorene derivatives, which consist of the electron-rich 4,4'-(9-alkyl-carbazole-3,6-diyl)bis(N,N-diphenylaniline) (TPA-Cz) in the side chain and the electron-deficient dibenzothiophene-5,5-dioxide (SO) unit in the main chain. The resulting copolymer PF-T25 that did not comprise the SO unit exhibited blue light-emission with the Commission Internationale de L'Eclairage coordinates of (0.16, 0.10). However, by physically blending PF-T25 with a blue light-emitting SO-based oligomer, a novel low-energy emission correlated to exciplex emerged due to the appropriate energy level alignment of TPA-Cz and the SO-based oligomers, which showed extended exciton lifetime as confirmed by time-resolved photoluminescent spectroscopy. The low-energy emission was also identified in copolymers consisting of SO unit in the main chain, which can effectively compensate for the high-energy emission to produce binary white light-emission. Polymer light-emitting diodes based on the exciplex-type single greenish-white polymer exhibit the peak luminous efficiency of 2.34 cd A(-1) and the maximum brightness of 12 410 cd m(-2), with Commission Internationale de L'Eclairage color coordinates (0.27, 0.39). The device based on such polymer showed much better electroluminescent stability than those based on blending films. These observations indicated that developing a single polymer with the generated exciplex emission can be a novel and effective molecular design strategy toward highly stable and efficient white polymer light-emitting diodes.

Voltage color tunable OLED with (Sm,Eu)-β-diketonate complex blend

NASA Astrophysics Data System (ADS)

Reyes, R.; Cremona, M.; Teotonio, E. E. S.; Brito, H. F.; Malta, O. L.

2004-09-01

Light emission from organic electroluminescent diodes (OLEDs) in which mixed samarium and europium β-diketonate complexes, [Sm 0.7Eu 0.3(TTA) 3(TPPO) 2], was used as the emitting layer is described. The electroluminescence spectra exhibit narrow peaks arising from 4f-intraconfigurational transitions of the Sm 3+ and Eu 3+ ions and a broad emission band attributed to the electrophosphorescence of the TTA ligand. The intensity ratio of the peaks determined by the bias voltage applied to the OLED, together with the ligand electrophosphorescence, allows to obtain a voltage-tunable color light source.

Thermo-optical properties of 1H[3,4-b] quinoline films used in electroluminescent devices

NASA Astrophysics Data System (ADS)

Jaglarz, Janusz; Kępińska, Mirosława; Sanetra, Jerzy

2014-06-01

Electroluminescence cells with H[3,4-b] quinoline layers are promising devices for a blue light emitting EL diode. This work measured the optical reflectance as a function of temperature in copolymers PAQ layers deposited on Si crystalline substrate. Using the extended Cauchy dispersion model of the film refractive index we determined the thermo-optical coefficients for quinoline layers in the temperature range of 76-333 K from combined ellipsometric and spectrofotometric studies. The obtained values of thermo-optical coefficients of thin PAQ film, were negative and ranged in 5-10 × 10-4 [1/K].

Electroluminescent Properties in Organic Light-Emitting Diode Doped with Two Guest Dyes

NASA Astrophysics Data System (ADS)

Mori, Tatsuo; Kim, Hyeong-Gweon; Mizutani, Teruyoshi; Lee, Duck-Chool

2001-09-01

An organic light-emitting diode (OLED) with a squarylium dye-doped aluminium quinoline (Alq3) emission layer prepared by vapor deposition method has a pure red emission. However, since its luminance and electroluminescence (EL) efficiency is poor, the authors attended to improve the EL efficiency by doping a photosensitizer dye (a styryl dye, DCM) in an emission layer. The EL efficiency and luminance of DCM- and Sq-doped OLEDs are 2-3 times higher than those of only Sq-doped OLEDs. It was found that the excited energy is transferred from Alq3 to Sq through DCM.

A route to improved extraction efficiency of light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhu, H.; Shan, C. X.; Wang, L. K.; Yang, Y.; Zhang, J. Y.; Yao, B.; Shen, D. Z.; Fan, X. W.

2010-01-01

The electroluminescence from an n-MgZnO/i-ZnO/MgO/p-GaN asymmetric double heterojunction has been demonstrated. With the injection of electrons from n-MgZnO and holes from p-GaN, an intense ultraviolet emission coming from the ZnO active layer was observed. It is revealed that the emission intensity of the diode recorded from the MgZnO side is significantly larger than that from the MgO side because of the asymmetric waveguide structure formed by the lower refractive index of MgO than that of MgZnO. The asymmetric waveguide structure reported in this letter may promise a simple and effective route to light-emitting diodes with improved light-extraction efficiency.

Discrimination between spin-dependent charge transport and spin-dependent recombination in π-conjugated polymers by correlated current and electroluminescence-detected magnetic resonance

NASA Astrophysics Data System (ADS)

Kavand, Marzieh; Baird, Douglas; van Schooten, Kipp; Malissa, Hans; Lupton, John M.; Boehme, Christoph

2016-08-01

Spin-dependent processes play a crucial role in organic electronic devices. Spin coherence can give rise to spin mixing due to a number of processes such as hyperfine coupling, and leads to a range of magnetic field effects. However, it is not straightforward to differentiate between pure single-carrier spin-dependent transport processes which control the current and therefore the electroluminescence, and spin-dependent electron-hole recombination which determines the electroluminescence yield and in turn modulates the current. We therefore investigate the correlation between the dynamics of spin-dependent electric current and spin-dependent electroluminescence in two derivatives of the conjugated polymer poly(phenylene-vinylene) using simultaneously measured pulsed electrically detected (pEDMR) and optically detected (pODMR) magnetic resonance spectroscopy. This experimental approach requires careful analysis of the transient response functions under optical and electrical detection. At room temperature and under bipolar charge-carrier injection conditions, a correlation of the pEDMR and the pODMR signals is observed, consistent with the hypothesis that the recombination currents involve spin-dependent electronic transitions. This observation is inconsistent with the hypothesis that these signals are caused by spin-dependent charge-carrier transport. These results therefore provide no evidence that supports earlier claims that spin-dependent transport plays a role for room-temperature magnetoresistance effects. At low temperatures, however, the correlation between pEDMR and pODMR is weakened, demonstrating that more than one spin-dependent process influences the optoelectronic materials' properties. This conclusion is consistent with prior studies of half-field resonances that were attributed to spin-dependent triplet exciton recombination, which becomes significant at low temperatures when the triplet lifetime increases.

Preparation and single molecule structure of electroactive polysilane end-grafted on a crystalline silicon surface

NASA Astrophysics Data System (ADS)

Furukawa, Kazuaki; Ebata, Keisuke

2000-12-01

Electrically active polysilanes of poly(methylphenylsilane) (PMPS) and poly[bis(p-n-butylphenyl)silane] (PBPS), which are, respectively, known as a good hole transporting material and a near-ultraviolet electroluminescent material, are end-grafted directly on a crystalline silicon surface. The single polysilane molecules are clearly distinguished one from the other on the surface by means of atomic force microscopy observations. End-grafted single molecules of PMPS are observed as dots while end-grafted PBPS appear as worms extending for more than 100 nm on the crystalline silicon surface.

Monolithically Integrated Mid-Infrared Quantum Cascade Laser and Detector

PubMed Central

Schwarz, Benedikt; Reininger, Peter; Detz, Hermann; Zederbauer, Tobias; Andrews, Aaron Maxwell; Schrenk, Werner; Strasser, Gottfried

2013-01-01

We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we can measure the light intensity of the laser on the same chip without the need of external lenses or detectors. Based on a bound-to-continuum design, the bi-functional active region has an inherent broad electro-luminescence spectrum of 200 cm−1, which indicate sits use for single mode laser arrays. We have measured a peak signal of 191.5 mV at theon-chip detector, without any amplification. The room-temperature pulsed emission with an averaged power consumption of 4 mW and the high-speed detection makes these devices ideal for low-power sensors. The combination of the on-chip detection functionality, the broad emission spectrum and the low average power consumption indicates the potential of our bi-functional quantum cascade structures to build a mid-infrared lab-on-a-chip based on quantum cascade laser technology. PMID:23389348

High Color-Purity Green, Orange, and Red Light-Emitting Didoes Based on Chemically Functionalized Graphene Quantum Dots

NASA Astrophysics Data System (ADS)

Kwon, Woosung; Kim, Young-Hoon; Kim, Ji-Hee; Lee, Taehyung; Do, Sungan; Park, Yoonsang; Jeong, Mun Seok; Lee, Tae-Woo; Rhee, Shi-Woo

2016-04-01

Chemically derived graphene quantum dots (GQDs) to date have showed very broad emission linewidth due to many kinds of chemical bondings with different energy levels, which significantly degrades the color purity and color tunability. Here, we show that use of aniline derivatives to chemically functionalize GQDs generates new extrinsic energy levels that lead to photoluminescence of very narrow linewidths. We use transient absorption and time-resolved photoluminescence spectroscopies to study the electronic structures and related electronic transitions of our GQDs, which reveals that their underlying carrier dynamics is strongly related to the chemical properties of aniline derivatives. Using these functionalized GQDs as lumophores, we fabricate light-emitting didoes (LEDs) that exhibit green, orange, and red electroluminescence that has high color purity. The maximum current efficiency of 3.47 cd A-1 and external quantum efficiency of 1.28% are recorded with our LEDs; these are the highest values ever reported for LEDs based on carbon-nanoparticle phosphors. This functionalization of GQDs with aniline derivatives represents a new method to fabricate LEDs that produce natural color.

White light-emitting organic electroluminescent devices

DOEpatents

Shiang, Joseph John; Duggal, Anil Raj; Parthasarathy, Gautam

2006-06-20

A light-emitting device comprises a light-emitting member, which comprises two electrodes, at least two organic electroluminescent ("EL") materials disposed between the electrodes, a charge blocking material disposed between the electrodes, and at least one photoluminescent ("PL") material. The light-emitting member emits electromagnetic ("EM") radiation having a first spectrum in response to a voltage applied across the two electrodes. The PL material absorbs a portion of the EM radiation emitted by the light-emitting member and emits EM radiation having second spectrum different than the first spectrum. Each of the organic EL materials emits EM radiation having a wavelength range selected from the group consisting of blue and red wavelength ranges.

Optically pumped lasing and electroluminescence of formamidinium perovskite semiconductors prepared by the cast-capping method

NASA Astrophysics Data System (ADS)

Sasaki, Fumio; Nguyen, Van-Cao; Yanagi, Hisao

2018-03-01

Optically pumped lasing and electroluminescence (EL) have been observed in solution-processed perovskite semiconducting materials of formamidinium lead bromide, CH(NH2)2PbBr3. Microcavities with flat surfaces and sharp edges have been easily obtained by the simple solution process called the “cast-capping method”. The crystals show clear multimode lasing of Fabry-Pérot cavities. The mode intervals are well explained by the optical constants with large dispersions of the materials. We have also fabricated EL devices and obtained clear EL in a single layer of the materials, but the EL intensity has been quenched rapidly.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geng, R.; Mayhew, N. T.; Nguyen, T. D., E-mail: ngtho@uga.edu

We report studies of magneto-conductance (MC) and magneto-electroluminescence (MEL) in polymer light-emitting electrochemical planar devices using “super-yellow” poly-(phenylene vinylene). We observed consistent negative MC while MEL becomes positive when electroluminescence quantum efficiency (ELQE) increases. At an optimal ELQE, the MC has a much narrower width than the MEL, indicating that the MC and MEL do not share a common origin. However, MC reverses and has the same width as MEL when exposed to a threshold laser power. We show that the e-h pair model can explain the positive MEL and MC while the negative MC can be explained by themore » bipolaron model.« less

Dispenser printed electroluminescent lamps on textiles for smart fabric applications

NASA Astrophysics Data System (ADS)

de Vos, Marc; Torah, Russel; Tudor, John

2016-04-01

Flexible electroluminescent (EL) lamps are fabricated onto woven textiles using a novel dispenser printing process. Dispenser printing utilizes pressurized air to deposit ink onto a substrate through a syringe and nozzle. This work demonstrates the first use of this technology to fabricate EL lamps. The luminance of the dispenser printed EL lamps is compared to screen-printed EL lamps, both printed on textile, and also commercial EL lamps on polyurethane film. The dispenser printed lamps are shown to have a 1.5 times higher luminance than the best performing commercially available lamp, and have a comparable performance to the screen-printed lamps.

Extremely low amplified spontaneous emission threshold and blue electroluminescence from a spin-coated octafluorene neat film

NASA Astrophysics Data System (ADS)

Kim, D.-H.; Sandanayaka, A. S. D.; Zhao, L.; Pitrat, D.; Mulatier, J. C.; Matsushima, T.; Andraud, C.; Ribierre, J. C.; Adachi, C.

2017-01-01

We report on the photophysical, amplified spontaneous emission (ASE), and electroluminescence properties of a blue-emitting octafluorene derivative in spin-coated films. The neat film shows an extremely low ASE threshold of 90 nJ/cm2, which is related to its high photoluminescence quantum yield of 87% and its large radiative decay rate of 1.7 × 109 s-1. Low-threshold organic distributed feedback semiconductor lasers and fluorescent organic light-emitting diodes with a maximum external quantum efficiency as high as 4.4% are then demonstrated, providing evidence that this octafluorene derivative is a promising candidate for organic laser applications.

Red electroluminescence and photoluminescence properties of new porphyrin compounds

NASA Astrophysics Data System (ADS)

Zhang, X. H.; Xie, Z. Y.; Wu, F. P.; Zhou, L. L.; Wong, O. Y.; Lee, C. S.; Kwong, H. L.; Lee, S. T.; Wu, S. K.

2003-12-01

Three new porphyrin compounds with saturated red emission were synthesized and their photoluminescence and electroluminescence were studied. The emission of the new dopants peaked at about 635-655 nm and the half-width of the emission peaks was very narrow (below 30 nm). Of the three porphyrin compounds, the one (TBDPP) with the smallest conjugation system had the highest fluorescent quantum yield of 21% in solution. Organic light-emitting diodes using TBDPP as a dopant showed saturated red emission (CIE coordinates of x=0.69, y=0.29) with a luminance of 150 cd/m 2 at a driving voltage of 22 V.

Transient electroluminescence on pristine and degraded phosphorescent blue OLEDs

NASA Astrophysics Data System (ADS)

Niu, Quan; Blom, Paul W. M.; May, Falk; Heimel, Paul; Zhang, Minlu; Eickhoff, Christian; Heinemeyer, Ute; Lennartz, Christian; Crǎciun, N. Irina

2017-11-01

In state-of-the-art blue phosphorescent organic light-emitting diode (PHOLED) device architectures, electrons and holes are injected into the emissive layer, where they are carried by the emitting and hole transporting units, respectively. Using transient electroluminescence measurements, we disentangle the contribution of the electrons and holes on the transport and efficiency of both pristine and degraded PHOLEDs. By varying the concentration of hole transporting units, we show that for pristine PHOLEDs, the transport is electron dominated. Furthermore, degradation of the PHOLEDs upon electrical aging is not related to the hole transport but is governed by a decrease in the electron transport due to the formation of electron traps.

The nature of trapping sites and recombination centres in PVK and PVK-PBD electroluminescent matrices seen by spectrally resolved thermoluminescence

NASA Astrophysics Data System (ADS)

Glowacki, Ireneusz; Szamel, Zbigniew

2010-07-01

Two electroluminescent polymer matrices poly(N-vinylcarbazole) (PVK) and PVK with 40 wt% of 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) were studied using spectrally resolved thermoluminescence (SRTL) in the temperature range 15-325 K. The comparison of the SRTL results with the electroluminescence (EL) spectra has allowed identification of the localized (trapping) sites and the radiative recombination centres present in the investigated matrices. In the neat PVK films deep traps with a depth about 200 meV, related to triplet excimers dominate, while in the PVK-PBD (40 wt%) blend films the traps that are related to triplet exciplexes formed by the carbazole groups and the PBD molecules dominate. Depth of the traps in the PVK-PBD blend is somewhat lower than that in the neat PVK. An analysis of the EL spectra shows that in the PVK and in the PVK-PBD blend the dominant radiative centres are singlet excimers and singlet exciplexes, respectively. However, in the neat PVK some contributions of the triplet monomer and the triplet excimer states in the EL were also detected.

Electroluminescence dependence on the organic thickness in ZnO nano rods/Alq3 heterostructure devices.

PubMed

Kan, Pengzhi; Wang, Yongsheng; Zhao, Suling; Xu, Zheng; Wang, Dawei

2011-04-01

ZnO nanorods are synthesised by a hydrothermal method on ITO glass. Their crystallization and morphology are detected by XRD and SEM, respectively. The results show that the ZnO nanorod array has grown primarily along a direction aligned perpendicular to the ITO substrate. The average height and diameter of the nanorods is about 130 nm and 30 nm, respectively. Then ZnO nano rods/Alq3 heterostructure LEDs are prepared by thermal evaporation of Alq3 molecules. The thicknesses of the Alq3 layers are 130 nm, 150 nm, 170 nm and 190 nm, respectively. The electroluminescence of the devices is detected under different DC bias voltages. The exciton emission of Alq3 is detected in all devices. When the thickness of Alq3 is 130 nm, the UV electroluminescence of ZnO is around 382 nm, and defect emissions around 670 nm and 740 nm are detected. Defect emissions of ZnO nanorods are prominent. When the thickness of Alq3 increases to over 170 nm, it is difficult to observe defect emissions from the ZnO nano rods. In such devices, the exciton emission of Alq3 is more prominent than other emissions under different bias voltage.

Electrochemical synthesis of MoS2 quantum dots embedded nanostructured porous silicon with enhanced electroluminescence property

NASA Astrophysics Data System (ADS)

Shrivastava, Megha; Kumari, Reeta; Parra, Mohammad Ramzan; Pandey, Padmini; Siddiqui, Hafsa; Haque, Fozia Z.

2017-11-01

In this report we present the successful enhancement in electroluminescence (EL) in nanostructured n-type porous silicon (PS) with an idea of embedding luminophorous Molybdenum disulfide (MoS2) quantum dots (QD's). Electrochemical anodization technique was used for the formation of PS surface and MoS2 QD's were prepared using the electrochemical route. Spin coating technique was employed for the proper incorporation of MoS2 QD's within the PS nanostructures. The crystallographic analysis was performed using X-ray diffraction (XRD), Raman and Fourier transform infrared (FT-IR) spectroscopy techniques. However, surface morphology was determined using Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The optical measurements were performed on photoluminescence (PL) spectrophotometer; additionally for electroluminescence (EL) study special arrangement of instrumental setup was made at laboratory level which provides novelty to this work. A diode prototype was made comprising Ag/MoS2:PS/Silicon/Ag for EL study. The MoS2:PS shows a remarkable concentration dependent enhancement in PL as well as in EL intensities, which paves a way to better utilize this strategy in optoelectronic device applications.

[The role of BCP in electroluminescence of multilayer organic light-emitting devices].

PubMed

Deng, Zhao-Ru; Yang, Sheng-Yi; Lou, Zhi-Dong; Meng, Ling-Chuan

2009-03-01

As a hole-blocking layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is usually used in blue and white light electroluminescent devices. The ability of blocking holes of BCP layer depends on its thickness, and basically holes can tunnel through thin BCP layer. In order to know the role of BCP layer in electroluminescence (EL) of multilayer organic light-emitting diodes (OLEDs), in the present paper, the authors designed a multilayer OLED ITO/NPB/BCP/Alq3 : DCJTB/Alq3/Al and investigated the influence of thickness of BCP on the EL spectra of multilayer OLEDs at different applied voltages. The experimental data show that thin BCP layer can block holes partially and tune the energy transfer between different emissive layers, and in this way, it is easy to obtain white emission, but its EL spectra will change with the applied voltages. The EL spectra of multilayer device will remain relatively stable when BCP layer is thick enough, and the holes can hardly tunnel through when the thickness of BCP layer is more than 15 nm. Furthermore, the stability of EL spectra of the multilayer OLED at different applied voltages was discussed.

Optical and electrical properties of composites based on functional components of an electroluminescent layer

NASA Astrophysics Data System (ADS)

Avanesyan, V. T.; Rakina, A. V.; Sychov, M. M.; Vasina, E. S.

2016-07-01

Optical and electrical properties of cyanoethyl ether of polyvinyl alcohol with filling of barium titanate BaTiO3 modified by shungite carbon nanoparticles are studied. It is found that the modification affects the diffuse reflectance spectra and dispersion characteristics of the impedance components due to a change in the nature of interfacial interactions in the system. The values of the forbidden band width for various modifier and filler concentrations are determined.

Magnetic field enhanced electroluminescence in organic light emitting diodes based on electron donor-acceptor exciplex blends

NASA Astrophysics Data System (ADS)

Baniya, Sangita; Basel, Tek; Sun, Dali; McLaughlin, Ryan; Vardeny, Zeev Valy

2016-03-01

A useful process for light harvesting from injected electron-hole pairs in organic light emitting diodes (OLED) is the transfer from triplet excitons (T) to singlet excitons (S) via reverse intersystem crossing (RISC). This process adds a delayed electro-luminescence (EL) emission component that is known as thermally activated delayed fluorescence (TADF). We have studied electron donor (D)/acceptor(A) blends that form an exciplex manifold in which the energy difference, ΔEST between the lowest singlet (S1) and triplet (T1) levels is relatively small (<100 meV), and thus allows RISC at ambient temperature. We found that the EL emission in OLED based on the exciplex blend is enhanced up to 40% by applying a relatively weak magnetic field of 50 mT at ambient. Moreover the MEL response is activated with activation energy similar that of the EL emission. This suggests that the large magneto-EL originates from an additional spin-mixing channel between singlet and triplet states of the generated exciplexes, which is due to TADF. We will report on the MEL dependencies on the temperature, bias voltage, and D-A materials for optimum OLED performance. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

Near-infrared roll-off-free electroluminescence from highly stable diketopyrrolopyrrole light emitting diodes

PubMed Central

Sassi, Mauro; Buccheri, Nunzio; Rooney, Myles; Botta, Chiara; Bruni, Francesco; Giovanella, Umberto; Brovelli, Sergio; Beverina, Luca

2016-01-01

Organic light emitting diodes (OLEDs) operating in the near-infrared spectral region are gaining growing relevance for emerging photonic technologies, such as lab-on-chip platforms for medical diagnostics, flexible self-medicated pads for photodynamic therapy, night vision and plastic-based telecommunications. The achievement of efficient near-infrared electroluminescence from solution-processed OLEDs is, however, an open challenge due to the low photoluminescence efficiency of most narrow-energy-gap organic emitters. Diketopyrrolopyrrole-boron complexes are promising candidates to overcome this limitation as they feature extremely high photoluminescence quantum yield in the near-infrared region and high chemical stability. Here, by incorporating suitably functionalized diketopyrrolopyrrole derivatives emitting at ~760 nm in an active matrix of poly(9,9-dioctylfluorene-alt-benzothiadiazole) and without using complex light out-coupling or encapsulation strategies, we obtain all-solution-processed NIR-OLEDs with external quantum efficiency as high as 0.5%. Importantly, our test-bed devices show no efficiency roll-off even for high current densities and high operational stability, retaining over 50% of the initial radiant emittance for over 50 hours of continuous operation at 10 mA/cm2, which emphasizes the great applicative potential of the proposed strategy. PMID:27677240

Secondary scintillation yield of xenon with sub-percent levels of CO 2 additive for rare-event detection

DOE PAGES

Henriques, C. A. O.; Freitas, E. D. C.; Azevedo, C. D. R.; ...

2017-09-12

Xe–CO 2 mixtures are important alternatives to pure xenon in Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification with applications in the important field of rare event detection such as directional dark matter, double electron capture and double beta decay detection. The addition of CO 2 to pure xenon at the level of 0.05–0.1% can reduce significantly the scale of electron diffusion from 10 mm / √m to 2.5mm / √m, with high impact on the discrimination efficiency of the events through pattern recognition of the topology of primary ionization trails. We have measured the electroluminescence (EL)more » yield of Xe–CO 2 mixtures, with sub-percent CO 2 concentrations. We demonstrate that the EL production is still high in these mixtures, 70% and 35% relative to that produced in pure xenon, for CO 2 concentrations around 0.05% and 0.1%, respectively. In conclusion, the contribution of the statistical fluctuations in EL production to the energy resolution increases with increasing CO 2 concentration, being smaller than the contribution of the Fano factor for concentrations below 0.1% CO 2.« less

Secondary scintillation yield of xenon with sub-percent levels of CO2 additive for rare-event detection

NASA Astrophysics Data System (ADS)

Henriques, C. A. O.; Freitas, E. D. C.; Azevedo, C. D. R.; González-Díaz, D.; Mano, R. D. P.; Jorge, M. R.; Fernandes, L. M. P.; Monteiro, C. M. B.; Gómez-Cadenas, J. J.; Álvarez, V.; Benlloch-Rodríguez, J. M.; Borges, F. I. G. M.; Botas, A.; Cárcel, S.; Carríon, J. V.; Cebrían, S.; Conde, C. A. N.; Díaz, J.; Diesburg, M.; Esteve, R.; Felkai, R.; Ferrario, P.; Ferreira, A. L.; Goldschmidt, A.; Gutiérrez, R. M.; Hauptman, J.; Hernandez, A. I.; Hernando Morata, J. A.; Herrero, V.; Jones, B. J. P.; Labarga, L.; Laing, A.; Lebrun, P.; Liubarsky, I.; López-March, N.; Losada, M.; Martín-Albo, J.; Martínez-Lema, G.; Martínez, A.; McDonald, A. D.; Monrabal, F.; Mora, F. J.; Moutinho, L. M.; Muñoz Vidal, J.; Musti, M.; Nebot-Guinot, M.; Novella, P.; Nygren, D. R.; Palmeiro, B.; Para, A.; Pérez, J.; Querol, M.; Renner, J.; Ripoll, L.; Rodríguez, J.; Rogers, L.; Santos, F. P.; dos Santos, J. M. F.; Simón, A.; Sofka, C.; Sorel, M.; Stiegler, T.; Toledo, J. F.; Torrent, J.; Tsamalaidze, Z.; Veloso, J. F. C. A.; Webb, R.; White, J. T.; Yahlali, N.; NEXT Collaboration

2017-10-01

Xe-CO2 mixtures are important alternatives to pure xenon in Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification with applications in the important field of rare event detection such as directional dark matter, double electron capture and double beta decay detection. The addition of CO2 to pure xenon at the level of 0.05-0.1% can reduce significantly the scale of electron diffusion from 10 mm /√{m} to 2.5 mm /√{m}, with high impact on the discrimination efficiency of the events through pattern recognition of the topology of primary ionization trails. We have measured the electroluminescence (EL) yield of Xe-CO2 mixtures, with sub-percent CO2 concentrations. We demonstrate that the EL production is still high in these mixtures, 70% and 35% relative to that produced in pure xenon, for CO2 concentrations around 0.05% and 0.1%, respectively. The contribution of the statistical fluctuations in EL production to the energy resolution increases with increasing CO2 concentration, being smaller than the contribution of the Fano factor for concentrations below 0.1% CO2.

Electroluminescent refrigeration by ultra-efficient GaAs light-emitting diodes

NASA Astrophysics Data System (ADS)

Patrick Xiao, T.; Chen, Kaifeng; Santhanam, Parthiban; Fan, Shanhui; Yablonovitch, Eli

2018-05-01

Electroluminescence—the conversion of electrons to photons in a light-emitting diode (LED)—can be used as a mechanism for refrigeration, provided that the LED has an exceptionally high quantum efficiency. We investigate the practical limits of present optoelectronic technology for cooling applications by optimizing a GaAs/GaInP double heterostructure LED. We develop a model of the design based on the physics of detailed balance and the methods of statistical ray optics, and predict an external luminescence efficiency of ηext = 97.7% at 263 K. To enhance the cooling coefficient of performance, we pair the refrigerated LED with a photovoltaic cell, which partially recovers the emitted optical energy as electricity. For applications near room temperature and moderate power densities (1.0-10 mW/cm2), we project that an electroluminescent refrigerator can operate with up to 1.7× the coefficient of performance of thermoelectric coolers with ZT = 1, using the material quality in existing GaAs devices. We also predict superior cooling efficiency for cryogenic applications relative to both thermoelectric and laser cooling. Large improvements to these results are possible with optoelectronic devices that asymptotically approach unity luminescence efficiency.

Secondary scintillation yield of xenon with sub-percent levels of CO 2 additive for rare-event detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henriques, C. A. O.; Freitas, E. D. C.; Azevedo, C. D. R.

Xe–CO 2 mixtures are important alternatives to pure xenon in Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification with applications in the important field of rare event detection such as directional dark matter, double electron capture and double beta decay detection. The addition of CO 2 to pure xenon at the level of 0.05–0.1% can reduce significantly the scale of electron diffusion from 10 mm / √m to 2.5mm / √m, with high impact on the discrimination efficiency of the events through pattern recognition of the topology of primary ionization trails. We have measured the electroluminescence (EL)more » yield of Xe–CO 2 mixtures, with sub-percent CO 2 concentrations. We demonstrate that the EL production is still high in these mixtures, 70% and 35% relative to that produced in pure xenon, for CO 2 concentrations around 0.05% and 0.1%, respectively. In conclusion, the contribution of the statistical fluctuations in EL production to the energy resolution increases with increasing CO 2 concentration, being smaller than the contribution of the Fano factor for concentrations below 0.1% CO 2.« less

Efficient luminescent solar cells based on tailored mixed-cation perovskites

PubMed Central

Bi, Dongqin; Tress, Wolfgang; Dar, M. Ibrahim; Gao, Peng; Luo, Jingshan; Renevier, Clémentine; Schenk, Kurt; Abate, Antonio; Giordano, Fabrizio; Correa Baena, Juan-Pablo; Decoppet, Jean-David; Zakeeruddin, Shaik Mohammed; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Hagfeldt, Anders

2016-01-01

We report on a new metal halide perovskite photovoltaic cell that exhibits both very high solar-to-electric power-conversion efficiency and intense electroluminescence. We produce the perovskite films in a single step from a solution containing a mixture of FAI, PbI2, MABr, and PbBr2 (where FA stands for formamidinium cations and MA stands for methylammonium cations). Using mesoporous TiO2 and Spiro-OMeTAD as electron- and hole-specific contacts, respectively, we fabricate perovskite solar cells that achieve a maximum power-conversion efficiency of 20.8% for a PbI2/FAI molar ratio of 1.05 in the precursor solution. Rietveld analysis of x-ray diffraction data reveals that the excess PbI2 content incorporated into such a film is about 3 weight percent. Time-resolved photoluminescence decay measurements show that the small excess of PbI2 suppresses nonradiative charge carrier recombination. This in turn augments the external electroluminescence quantum efficiency to values of about 0.5%, a record for perovskite photovoltaics approaching that of the best silicon solar cells. Correspondingly, the open-circuit photovoltage reaches 1.18 V under AM 1.5 sunlight. PMID:26767196

Extremely flexible, transparent, and strain-sensitive electroluminescent device based on ZnS:Cu-polyvinyl butyral composite and silver nanowires

NASA Astrophysics Data System (ADS)

Jun, Sungwoo; Kim, Youngmin; Ju, Byeong-Kwon; Kim, Jong-Woong

2018-01-01

A multifunctional alternate current electroluminescent device (ACEL) was achieved by compositing ZnS:Cu particles in polyvinyl butyral (PVB) with two layers of percolated silver nanowire (AgNW) electrodes. The strong hydrogen bonding interactions and entanglement of PVB chains considerably strengthened the PVB, and thus, the cured mixture of ZnS:Cu particles and freestanding PVB required no additional support. The device was fabricated by embedding AgNWs on both sides of the ZnS:Cu-PVB composite film using an inverted layer process and intense-pulsed-light treatment. The strong affinity of PVB to the polyvinyl pyrrolidone (PVP) layer, which capped the AgNWs, mechanically stabilized the device to such an extent that it could resist 10,000 bending cycles under a curvature radius of 500 μm. Using AgNW networks in both the top and bottom electrodes made a double-sided light-emitting device that could be applied to wearable lightings or flexible digital signage. The capacitance formed in the device sensitively varied with the applied bending and unfolding, thus demonstrating that the device can also be used as a deformation sensor.

Piezo-phototronic effect on electroluminescence properties of p-type GaN thin films.

PubMed

Hu, Youfan; Zhang, Yan; Lin, Long; Ding, Yong; Zhu, Guang; Wang, Zhong Lin

2012-07-11

We present that the electroluminescence (EL) properties of Mg-doped p-type GaN thin films can be tuned by the piezo-phototronic effect via adjusting the minority carrier injection efficiency at the metal-semiconductor (M-S) interface by strain induced polarization charges. The device is a metal-semiconductor-metal structure of indium tin oxide (ITO)-GaN-ITO. Under different straining conditions, the changing trend of the transport properties of GaN films can be divided into two types, corresponding to the different c-axis orientations of the films. An extreme value was observed for the integral EL intensity under certain applied strain due to the adjusted minority carrier injection efficiency by piezoelectric charges introduced at the M-S interface. The external quantum efficiency of the blue EL at 430 nm was changed by 5.84% under different straining conditions, which is 1 order of magnitude larger than the change of the green peak at 540 nm. The results indicate that the piezo-phototronic effect has a larger impact on the shallow acceptor states related EL process than on the one related to the deep acceptor states in p-type GaN films. This study has great significance on the practical applications of GaN in optoelectronic devices under a working environment where mechanical deformation is unavoidable such as for flexible/printable light emitting diodes.

Defect-induced infrared electroluminescence from radial GaInP/AlGaInP quantum well nanowire array light- emitting diodes

NASA Astrophysics Data System (ADS)

Hussain, Laiq; Karimi, Mohammad; Berg, Alexander; Jain, Vishal; Borgström, Magnus T.; Gustafsson, Anders; Samuelson, Lars; Pettersson, Håkan

2017-12-01

Radial GaInP/AlGaInP nanowire array light-emitting diodes (LEDs) are promising candidates for novel high-efficiency solid state lighting due to their potentially large strain-free active emission volumes compared to planar LEDs. Moreover, by proper tuning of the diameter of the nanowires, the fraction of emitted light extracted can be significantly enhanced compared to that of planar LEDs. Reports so far on radial growth of nanowire LED structures, however, still point to significant challenges related to obtaining defect-free radial heterostructures. In this work, we present evidence of optically active growth-induced defects in a fairly broad energy range in vertically processed radial GaInP/AlGaInP quantum well nanowire array LEDs using a variety of complementary experimental techniques. In particular, we demonstrate strong infrared electroluminescence in a spectral range centred around 1 eV (1.2 μm) in addition to the expected red light emission from the quantum well. Spatially resolved cathodoluminescence studies reveal a patchy red light emission with clear spectral features along the NWs, most likely induced by variations in QW thickness, composition and barriers. Dark areas are attributed to infrared emission generated by competing defect-assisted radiative transitions, or to trapping mechanisms involving non-radiative recombination processes. Possible origins of the defects are discussed.

Synthesis and photoluminescence properties of novel Schiff base type polymer-rare earth complexes containing furfural-based bidentate Schiff base ligands

NASA Astrophysics Data System (ADS)

Gao, Baojiao; Zhang, Dandan; Li, Yanbin

2018-03-01

Luminescent polymer-rare earth complexes are an important class of photoluminescence and electroluminescence materials. Via molecular design, two furfural-based bidentate Schiff base ligands, furfural-aniline (FA) type ligand and furfural-cyclohexylamine (FC) type ligand, were bonded on the side chains of polysulfone (PSF), respectively, forming two functionalized macromolecules, PSF-FA and PSF-FC. And then through respective coordination reactions of the two functionalized macromolecules with Eu(Ⅲ) ion and Tb(Ⅲ) ion, novel luminescent binary and ternary (with 1,10-phenanthroline as the second ligand) polymer-rare earth complexes were synthesized. For these complexes, on basis of the characterization of their chemical structures, they photoluminescence properties were main researched, and the relationship between their luminescent properties and structures was explored. The experimental results show that the complexes coming from PSF-FA and Eu(Ⅲ) ion including binary and ternary complexes emit strong red luminescence, indicating that the bonded bidentate Schiff base ligand FA can sensitize the fluorescence emission of Eu(III) ion. While the complexes coming from PSF-FC and Tb(Ⅲ) ion produce green luminescence, displaying that the bonded bidentate Schiff base ligand FC can sensitize the fluorescence emission of Tb(Ⅲ) ion. The fluorescence emission intensities of the ternary complexes were stronger than that of binary complexes, reflecting the important effect of the second ligand. The fluorescence emission of the solid film of complexes is much stronger than that of the solutions of complexes. Besides, by comparison, it is found that the furfural (as a heteroaromatic compound)-based Schiff base type polymer-rare earth complexes have stronger fluorescence emission and higher energy transfer efficiency than salicylaldehyde (as a common aromatic compound)-based Schiff base type polymer-rare earth complexes.

Exciton dynamics of C60-based single-photon emitters explored by Hanbury Brown-Twiss scanning tunnelling microscopy.

PubMed

Merino, P; Große, C; Rosławska, A; Kuhnke, K; Kern, K

2015-09-29

Exciton creation and annihilation by charges are crucial processes for technologies relying on charge-exciton-photon conversion. Improvement of organic light sources or dye-sensitized solar cells requires methods to address exciton dynamics at the molecular scale. Near-field techniques have been instrumental for this purpose; however, characterizing exciton recombination with molecular resolution remained a challenge. Here, we study exciton dynamics by using scanning tunnelling microscopy to inject current with sub-molecular precision and Hanbury Brown-Twiss interferometry to measure photon correlations in the far-field electroluminescence. Controlled injection allows us to generate excitons in solid C60 and let them interact with charges during their lifetime. We demonstrate electrically driven single-photon emission from localized structural defects and determine exciton lifetimes in the picosecond range. Monitoring lifetime shortening and luminescence saturation for increasing carrier injection rates provides access to charge-exciton annihilation dynamics. Our approach introduces a unique way to study single quasi-particle dynamics on the ultimate molecular scale.

Comparison of CIGS solar cells made with different structures and fabrication techniques

DOE PAGES

Mansfield, Lorelle M.; Garris, Rebekah L.; Counts, Kahl D.; ...

2016-11-03

Cu(In, Ga)Se2 (CIGS)-based solar cells from six fabricators were characterized and compared. The devices had differing substrates, absorber deposition processes, buffer materials, and contact materials. The effective bandgaps of devices varied from 1.05 to 1.22 eV, with the lowest optical bandgaps occurring in those with metal-precursor absorber processes. Devices with Zn(O, S) or thin CdS buffers had quantum efficiencies above 90% down to 400 nm. Most voltages were 250-300 mV below the Shockley-Queisser limit for their bandgap. Electroluminescence intensity tracked well with the respective voltage deficits. Fill factor (FF) was as high as 95% of the maximum for each device'smore » respective current and voltage, with higher FF corresponding to lower diode quality factors (~1.3). An in-depth analysis of FF losses determined that diode quality reflected in the quality factor, voltage-dependent photocurrent, and, to a lesser extent, the parasitic resistances are the limiting factors. As a result, different absorber processes and device structures led to a range of electrical and physical characteristics, yet this investigation showed that multiple fabrication pathways could lead to high-quality and high-efficiency solar cells.« less

White-emissive tandem-type hybrid organic/polymer diodes with (0.33, 0.33) chromaticity coordinates.

PubMed

Guo, Tzung-Fang; Wen, Ten-Chin; Huang, Yi-Shun; Lin, Ming-Wei; Tsou, Chuan-Cheng; Chung, Chia-Tin

2009-11-09

This study reports fabrication of white-emissive, tandem-type, hybrid organic/polymer light-emitting diodes (O/PLED). The tandem devices are made by stacking a blue-emissive OLED on a yellow-emissive phenyl-substituted poly(para-phenylene vinylene) copolymer-based PLED and applying an organic oxide/Al/molybdenum oxide (MoO(3)) complex structure as a connecting structure or charge-generation layer (CGL). The organic oxide/Al/MoO(3) CGL functions as an effective junction interface for the transport and injection of opposite charge carriers through the stacked configuration. The electroluminescence (EL) spectra of the tandem-type devices can be tuned by varying the intensity of the emission in each emissive component to yield the visible-range spectra from 400 to 750 nm, with Commission Internationale de l'Eclairage chromaticity coordinates of (0.33, 0.33) and a high color rendering capacity as used for illumination. The EL spectra also exhibit good color stability under various bias conditions. The tandem-type device of emission with chromaticity coordinates, (0.30, 0.31), has maximum brightness and luminous efficiency over 25,000 cd/m(2) and approximately 4.2 cd/A, respectively.

A Solution Processed Flexible Nanocomposite Electrode with Efficient Light Extraction for Organic Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Li, Lu; Liang, Jiajie; Chou, Shu-Yu; Zhu, Xiaodan; Niu, Xiaofan; Zhibinyu; Pei, Qibing

2014-03-01

Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m2 with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost.

A solution processed flexible nanocomposite electrode with efficient light extraction for organic light emitting diodes.

PubMed

Li, Lu; Liang, Jiajie; Chou, Shu-Yu; Zhu, Xiaodan; Niu, Xiaofan; ZhibinYu; Pei, Qibing

2014-03-17

Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m(2) with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost.

A Solution Processed Flexible Nanocomposite Electrode with Efficient Light Extraction for Organic Light Emitting Diodes

PubMed Central

Li, Lu; Liang, Jiajie; Chou, Shu-Yu; Zhu, Xiaodan; Niu, Xiaofan; ZhibinYu; Pei, Qibing

2014-01-01

Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m2 with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost. PMID:24632742

Study of 3D-growth conditions for selective area MOVPE of high aspect ratio GaN fins with non-polar vertical sidewalls

NASA Astrophysics Data System (ADS)

Hartmann, Jana; Steib, Frederik; Zhou, Hao; Ledig, Johannes; Nicolai, Lars; Fündling, Sönke; Schimpke, Tilman; Avramescu, Adrian; Varghese, Tansen; Trampert, Achim; Straßburg, Martin; Lugauer, Hans-Jürgen; Wehmann, Hergo-Heinrich; Waag, Andreas

2017-10-01

GaN fins are 3D architectures elongated in one direction parallel to the substrate surface. They have the geometry of walls with a large height to width ratio as well as small footprints. When appropriate symmetry directions of the GaN buffer are used, the sidewalls are formed by non-polar {1 1 -2 0} planes, making the fins particularly suitable for many device applications like LEDs, FETs, lasers, sensors or waveguides. The influence of growth parameters like temperature, pressure, V/III ratio and total precursor flow on the fin structures is analyzed. Based on these results, a 2-temperature-step-growth was developed, leading to fins with smooth side and top facets, fast vertical growth rates and good homogeneity along their length as well as over different mask patterns. For the core-shell growth of fin LED heterostructures, the 2-temperature-step-growth shows much smoother sidewalls and less crystal defects in the InGaN QW and p-GaN shell compared to structures with cores grown in just one step. Electroluminescence spectra of the 2-temperature-step-grown fin LED are demonstrated.

Comparison of CIGS solar cells made with different structures and fabrication techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mansfield, Lorelle M.; Garris, Rebekah L.; Counts, Kahl D.

Cu(In, Ga)Se2 (CIGS)-based solar cells from six fabricators were characterized and compared. The devices had differing substrates, absorber deposition processes, buffer materials, and contact materials. The effective bandgaps of devices varied from 1.05 to 1.22 eV, with the lowest optical bandgaps occurring in those with metal-precursor absorber processes. Devices with Zn(O, S) or thin CdS buffers had quantum efficiencies above 90% down to 400 nm. Most voltages were 250-300 mV below the Shockley-Queisser limit for their bandgap. Electroluminescence intensity tracked well with the respective voltage deficits. Fill factor (FF) was as high as 95% of the maximum for each device'smore » respective current and voltage, with higher FF corresponding to lower diode quality factors (~1.3). An in-depth analysis of FF losses determined that diode quality reflected in the quality factor, voltage-dependent photocurrent, and, to a lesser extent, the parasitic resistances are the limiting factors. As a result, different absorber processes and device structures led to a range of electrical and physical characteristics, yet this investigation showed that multiple fabrication pathways could lead to high-quality and high-efficiency solar cells.« less

High-efficiency red electroluminescent device based on multishelled InP quantum dots.

PubMed

Jo, Jung-Ho; Kim, Jong-Hoon; Lee, Ki-Heon; Han, Chang-Yeol; Jang, Eun-Pyo; Do, Young Rag; Yang, Heesun

2016-09-01

We report on the synthesis of highly fluorescent red-emitting InP quantum dots (QDs) and their application to the fabrication of a high-efficiency QD-light-emitting diode (QLED). The core/shell heterostructure of the QDs is elaborately tailored toward a multishelled structure with a composition-gradient ZnSeS intermediate shell and an outer ZnS shell. Using the resulting InP/ZnSeS/ZnS QDs as an emitting layer, all-solution-processible red InP QLEDs are fabricated with a hybrid multilayered device structure having an organic hole transport layer (HTL) and an inorganic ZnO nanoparticle electron transport layer. Two HTLs of poly(9-vinlycarbazole) or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4^'-(N-(4-sec-butylphenyl))diphenyl-amine), whose hole mobilities are different by at least three orders of magnitude, are individually applied for QLED fabrication and such HTL-dependent device performances are compared. Our best red device displays exceptional figures of merit such as a maximum luminance of 2849  cd/m², a current efficiency of 4.2  cd/A, and an external quantum efficiency of 2.5%.

Multi-spectral investigation of bulk and facet failures in high-power single emitters at 980 nm

NASA Astrophysics Data System (ADS)

Yanson, Dan; Levy, Moshe; Shamay, Moshe; Cohen, Shalom; Shkedy, Lior; Berk, Yuri; Tessler, Renana; Klumel, Genadi; Rappaport, Noam; Karni, Yoram

2013-03-01

Reliable single emitters delivering >10W in the 9xx nm spectral range, are common building blocks for fiber laser pumps. As facet passivation techniques can suppress or delay catastrophic optical mirror damage (COMD) extending emitter reliability into hundreds of thousands of hours, other, less dominant, failure modes such as intra-chip catastrophic optical bulk damage (COBD) become apparent. Based on our failure statistics in high current operation, only ~52% of all failures can be attributed to COMD. Imaging through a window opened in the metallization on the substrate (n) side of a p-side down mounted emitter provides valuable insight into both COMD and COBD failure mechanisms. We developed a laser ablation process to define a window on the n-side of an InGaAs/AlGaAs 980nm single emitter that is overlaid on the pumped 90μm stripe on the p-side. The ablation process is compatible with the chip wire-bonding, enabling the device to be operated at high currents with high injection uniformity. We analyzed both COMD and COBD failed emitters in the electroluminescence and mid-IR domains supported by FIB/SEM observation. The ablated devices revealed branching dark line patterns, with a line origin either at the facet center (COMD case) or near the stripe edge away from the facet (COBD case). In both cases, the branching direction is always toward the rear facet (against the photon density gradient), with SEM images revealing a disordered active layer structure. Absorption levels between 0.22eV - 0.55eV were observed in disordered regions by FT-IR spectroscopy. Temperature mapping of a single emitter in the MWIR domain was performed using an InSb detector. We also report an electroluminescence study of a single emitter just before and after failure.

Origin of a counterintuitive yellow light-emitting electrochemical cell based on a blue-emitting heteroleptic copper(i) complex.

PubMed

Weber, Michael D; Garino, Claudio; Volpi, Giorgio; Casamassa, Enrico; Milanesio, Marco; Barolo, Claudia; Costa, Rubén D

2016-06-07

This work provides the synthesis, structural characterization, electrochemical and photophysical features, as well as the application in light-emitting electrochemical cells (LECs) of a novel heteroleptic copper(i) complex - [Cu(impy)(POP)][PF6], where impy is 3-(2-methoxyphenyl)-1-(pyridine-2-yl)imidazo[1,5-a]pyridine and POP is bis{2-(diphenylphosphanyl)phenyl}ether. This compound shows blue photoluminescence (PL, λ = 450 nm) in solution and solid-state and excellent redox stability. Despite these excellent features, the electroluminescence (EL) response is located at ∼550 nm. Although the EL spectrum of LECs is typically red-shifted compared to the PL of the electroluminescent material, a shift of ca. 100 nm represents the largest one reported in LECs. To date, the large shift phenomena have been attributed to (i) a change in the nature of the lowest emitting state due to a concentration effect of the films, (ii) a reversible substitution of the ligands due to the weak coordination to the Cu(i), and (iii) a change in the distribution of the excited states due to polarization effects. After having discarded these along with others like the irreversible degradation of the emitter during device fabrication and/or under operation conditions, driving conditions, active layer composition, and changes in the excited states under different external electrical stimuli, we attribute the origin of this unexpected shift to a lack of a thermally activated delayed fluorescence (TADF) process due to the solely ligand-centered character of the excited states. As such, the lack of a charge transfer character in the excited states leads to a blue-fluorescence and yellow-phosphorescence photo- and electro-responses, respectively. This corroborates recent studies focused on the design of TADF for heteroleptic copper(i) complexes. Overall, this work is a clear insight into the design of new copper(i) complexes towards the preparation of blue LECs, which are still unexplored.

Cryogenic gaseous photomultipliers and liquid hole- multipliers: advances in THGEM-based sensors for future noble-liquid TPCs

NASA Astrophysics Data System (ADS)

Arazi, L.; Coimbra, A. E. C.; Erdal, E.; Israelashvili, I.; Rappaport, M. L.; Shchemelinin, S.; Vartsky, D.; dos Santos, J. M. F.; A, Breskin

2015-11-01

Dual-phase noble-liquid TPCs are presently the most sensitive instruments for direct dark matter detection. Scaling up existing ton-scale designs to the multi-ton regime may prove to be technologically challenging. This includes both large-area coverage with affordable high-QE UV-photon detectors, and maintaining high precision in measuring the charge and light signals of rare events with keV-scale energy depositions. We present our recent advances in two complementary approaches to these problems: large-area cryogenic gaseous photomultipliers (GPM) for UV-photon detection, and liquid-hole multipliers (LHM) that provide electroluminescence light in response to ionization electrons and primary scintillation photons, using perforated electrodes immersed within the noble liquid. Results from a 10 cm diameter GPM coupled to a dual-phase liquid- xenon TPC demonstrate the feasibility of recording - for the first time - both primary (“S1”) and secondary (“S2”) scintillation signals, over a very broad dynamic range. The detector, comprising a triple-THGEM structure with CsI on the first element, has been operating stably at 180 K with gains larger than 105; it provided high single-photon detection efficiency - in the presence of massive alpha-particle induced S2 signals; S1 scintillation signals were recorded with time resolutions of 1.2 ns (RMS). Results with the LHM operated in liquid xenon yielded large photon gains, with a pulse-height resolution of 11% (RMS) for alpha-particle induced S2 signals. The detector response was stable over several months. The response of the S2 signals to rapid changes in pressure lead to the conclusion that the underlying mechanism for S2 light is electroluminescence in xenon bubbles trapped below the immersed THGEM electrode. Both studies have the potential of paving the way towards new designs of dual- and single-phase noble-liquid TPCs that could simplify the conception of future multi-ton detectors of dark matter and other rare events.

Light-emitting device with organic electroluminescent material and photoluminescent materials

DOEpatents

McNulty, Thomas Francis; Duggal, Anil Raj; Turner, Larry Gene; Shiang, Joseph John

2005-06-07

A light-emitting device comprises a light-emitting member, which comprises two electrodes and an organic electroluminescent material disposed between the electrodes, and at least one organic photoluminescent ("PL") material. The light-emitting member emits light having a first spectrum in response to a voltage applied across the two electrodes. The organic PL material absorbs a portion of the light emitted by the light-emitting member and emits light having second spectrum different than the first spectrum. The light-emitting device can include an inorganic PL material that absorbs another portion of the light emitted from the light-emitting member and emits light having a third spectrum different than both the first and the second spectra.

InP electroluminescence as a tool to directly monitor carrier leakage in InGaAsP/InP buried heterostructure lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, M.B.; Brody, E.; Sowell, B.

1987-12-15

Direct measurements of homojunction and heterojunction carrier leakage currents in InGaAsP/InP buried heterostructure lasers have been made by monitoring the electroluminescence (EL) at 0.96 ..mu..m in the InP confinement layers. These EL measurements show directly, for the first time, a correlation between homojunction leakage currents and the sublinearity in the 1.3-..mu..m light output-current characteristic. The observed decrease in the 0.96-..mu..m intensity with increasing p-dopant concentration is a direct confirmation that heterojunction leakage is reduced when the doping level in the p-InP confinement layer is increased.

Localized Surface Plasmon-Enhanced Electroluminescence in OLEDs by Self-Assembly Ag Nanoparticle Film

NASA Astrophysics Data System (ADS)

He, Xiaoxiao; Wang, Wenjun; Li, Shuhong; Wang, Qingru; Zheng, Wanquan; Shi, Qiang; Liu, Yunlong

2015-12-01

We fabricated Ag nanoparticle (NP) film in organic light emission diodes (OLEDs), and a 23 times increase in electroluminescence (EL) at 518 nm was probed by time-resolved EL measurement. The luminance and relative external quantum efficiency (REQE) were increased by 5.4 and 3.7 times, respectively. There comes a new energy transport way that localized surface plasmons (LSPs) would absorb energy that corresponds to the electron-hole pair before recombination, promoting the formation of electron-hole pair and exciting local surface plasmon resonance (LSPR). The extended lifetime of Alq3 indicates the existence of strong interaction between LSPR and exciton, which decreases the nonradiative decay rate of OLEDs.

Mechanically flexible organic electroluminescent device with directional light emission

DOEpatents

Duggal, Anil Raj; Shiang, Joseph John; Schaepkens, Marc

2005-05-10

A mechanically flexible and environmentally stable organic electroluminescent ("EL") device with directional light emission comprises an organic EL member disposed on a flexible substrate, a surface of which is coated with a multilayer barrier coating which includes at least one sublayer of a substantially transparent organic polymer and at least one sublayer of a substantially transparent inorganic material. The device includes a reflective metal layer disposed on the organic EL member opposite to the substrate. The reflective metal layer provides an increased external quantum efficiency of the device. The reflective metal layer and the multilayer barrier coating form a seal around the organic EL member to reduce the degradation of the device due to environmental elements.

Magneto-electroluminescence effects in the single-layer organic light-emitting devices with macrocyclic aromatic hydrocarbons

NASA Astrophysics Data System (ADS)

Pham, S.-T.; Ikemoto, K.; Suzuki, K. Z.; Izumi, T.; Taka, H.; Kita, H.; Sato, S.; Isobe, H.; Mizukami, S.

2018-02-01

Magneto-electroluminescence (MEL) effects are observed in single-layer organic light-emitting devices (OLEDs) comprising only macrocyclic aromatic hydrocarbons (MAHs). The fluorescence devices were prepared using synthesized MAHs, namely, [n]cyclo-meta-phenylene ([n]CMP, n = 5, 6). The MEL ratio of the resulting OLED is 1%-2% in the spectral wavelength range of 400-500 nm, whereas it becomes negative (-1.5% to -2%) in the range from 650 to 700 nm. The possible physical origins of the sign change in the MEL are discussed. This wavelength-dependent sign change in the MEL ratio could be a unique function for future single-layer OLEDs capable of magnetic-field-induced color changes.

Hydrogen effects on the electroluminescence of n-ZnO nanorod/p-GaN film heterojunction light-emitting diodes.

PubMed

Fang, Fang; Zhao, Dongxu; Li, Binghui; Zhang, Zhenzhong; Shen, Dezhen

2010-07-07

Through a facile low-temperature solution process, vertically n-type ZnO nanorod arrays were grown on a GaN film to form a n-ZnO nanorod/p-GaN film heterojunction. A study of the electroluminescence (EL) characteristics of the heterojunction in air and in air with 2000 ppm hydrogen revealed the sensitivity of such a device to the surrounding atmosphere. The additional hydrogen shallow donors increased the effective electron concentration in ZnO nanorods and the EL recombination zone changed from the ZnO nanorods to the GaN film, which can be identified visually from the color change.

Spectral features and voltage effects in high-field electroluminescence of AlN filamentary nanocrystals

NASA Astrophysics Data System (ADS)

Weinstein, I. A.; Vokhmintsev, A. S.; Chaikin, D. V.; Afonin, Yu. D.

2016-11-01

The high-field electroluminescence (EL) spectra for Al-rich AlN nanowhiskers varying applied voltage were studied. The observed 2.70 eV emission, which can be considered as superposition of two Gaussian bands in 2.75 and 2.53 eV, was analyzed. It was shown that Fowler-Nordheim effect took place in EL mechanism with participation of capturing levels of ON- and VN-centers when AlN nanowhiskers were exposed to an external field of 2.5 ÷ 10 V/μm. Obtained results and made conclusions are in a good agreement with independent electron field emission measurements for different one-dimensional AlN nanostructures.

Wearable Triboelectric Generator for Powering the Portable Electronic Devices.

PubMed

Cui, Nuanyang; Liu, Jinmei; Gu, Long; Bai, Suo; Chen, Xiaobo; Qin, Yong

2015-08-26

A cloth-base wearable triboelectric nanogenerator made of nylon and Dacron fabric was fabricated for harvesting body motion energy. Through the friction between forearm and human body, the generator can turn the mechanical energy of an arm swing into electric energy and power an electroluminescent tubelike lamp easily. The maximum output current and voltage of the generator reach up to 0.2 mA and 2 kV. Furthermore, this generator can be easily folded, kneaded, and cleaned like a common garment.

A Field Visibility Comparison between Electroluminescent Sources and Standard U.S. Coast Guard Incandescent Aids-to-Navigation Sources.

DTIC Science & Technology

1982-10-01

this is critical. All buoy and many shore based systems employ back-up systems . In the case of buoys, 4 -when a lamp fails to emit, a new lamp is...88 LIST OF TABLES 1. Incandescent Source Table of Information -------------------- 38 2. Background Information on Subjects...functional aids-to-navigation system . The principal component of this system is the lighted aid which exists in many forms, from the wind and wave

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jr., Jie Jerry; Sista, Srinivas Prasad; Shi, Xiaolei

Optoelectronic devices with enhanced internal outcoupling include a substrate, an anode, a cathode, an electroluminescent layer, and an electron transporting layer comprising inorganic nanoparticles dispersed in an organic matrix.

Tip-enhanced near-field optical microscopy

PubMed Central

Mauser, Nina; Hartschuh, Achim

2013-01-01

Tip-enhanced near-field optical microscopy (TENOM) is a scanning probe technique capable of providing a broad range of spectroscopic information on single objects and structured surfaces at nanometer spatial resolution and with highest detection sensitivity. In this review, we first illustrate the physical principle of TENOM that utilizes the antenna function of a sharp probe to efficiently couple light to excitations on nanometer length scales. We then discuss the antenna-induced enhancement of different optical sample responses including Raman scattering, fluorescence, generation of photocurrent and electroluminescence. Different experimental realizations are presented and several recent examples that demonstrate the capabilities of the technique are reviewed. PMID:24100541

Determining the Origin of Half-bandgap-voltage Electroluminescence in Bifunctional Rubrene/C60 Devices

PubMed Central

Chen, Qiusong; Jia, Weiyao; Chen, Lixiang; Yuan, De; Zou, Yue; Xiong, Zuhong

2016-01-01

Lowering the driving voltage of organic light-emitting diodes (OLEDs) is an important approach to reduce their energy consumption. We have fabricated a series of bifunctional devices (OLEDs and photovoltaics) using rubrene and fullerene (C60) as the active layer, in which the electroluminescence threshold voltage(~1.1 V) was half the value of the bandgap of rubrene. Magneto-electroluminescence (MEL) response of planner heterojunction diodes exhibited a small increase in response to a low magnetic field strength (<20 mT); however, a very large decay was observed at a high magnetic field strength (>20 mT). When a hole-transport layer with a low mobility was included in these devices, the MEL response reversed in shape, and simultaneously, the EL threshold voltage became larger than the bandgap voltage. When bulk heterojunction device was examined, the amplitude of MEL curves presented an anomalous voltage-dependence. Following an analysis of the MEL responses of these devices, we proposed that the EL of half-bandgap-voltage device originated from bimolecular triplet-triplet annihilation in the rubrene film, rather than from singlet excitons that formed via an interface auger recombination. This work provides critical insight into the mechanisms of OLED emission and will help advance the applications of bifunctional devices. PMID:27142285

Vapochromic LED

DOEpatents

Kunugi, Yoshihito; Mann, Kent R.; Miller, Larry L.; Exstrom, Christopher L.

2003-06-17

A sandwich device was prepared by electrodeposition of an insoluble layer of oligomerized tris(4-(2-thienyl)phenyl)amine onto conducting indium-tin oxide coated glass, spin coating the stacked platinum compound, tetrakis(p-decylphenylisocyano)platinum tetranitroplatinate, from toluene onto the oligomer layer, and then coating the platinum complex with aluminum by vapor deposition. This device showed rectification of current and gave electroluminescence. The electroluminescence spectrum (.lambda..sub.max =545 nm) corresponded to the photoluminescence spectrum of the platinum complex. Exposure of the device to acetone vapor caused the electroemission to shift to 575 nm. Exposure to toluene vapor caused a return to the original spectrum. These results demonstrate a new type of sensor that reports the arrival of organic vapors with an electroluminescent signal. The sensor comprises (a) a first electrode; (b) a hole transport layer formed on the first electrode; (c) a sensing/emitting layer formed on the hole transport layer, the sensing/emitting layer comprising a material that changes color upon exposure to the analyte vapors; (d) an electron conductor layer formed on the sensing layer; and (e) a second electrode formed on the electron conductor layer. The hole transport layer emits light at a shorter wavelength than the sensing/emitting layer and at least the first electrode comprises an optically transparent material.

Vapochromic LED

DOEpatents

Kunugi, Yoshihito; Mann, Kent R.; Miller, Larry L.; Exstrom, Christopher L.

2002-01-15

A sandwich device was prepared by electrodeposition of an insoluble layer of oligomerized tris(4-(2-thienyl)phenyl)amine onto conducting indium-tin oxide coated glass, spin coating the stacked platinum compound, tetrakis(p-decylphenylisocyano)platinum tetranitroplatinate, from toluene onto the oligomer layer, and then coating the platinum complex with aluminum by vapor deposition. This device showed rectification of current and gave electroluminescence. The electroluminescence spectrum (.mu..sub.max =545 nm) corresponded to the photoluminescence spectrum of the platinum complex. Exposure of the device to acetone vapor caused the electroemission to shift to 575 nm. Exposure to toluene vapor caused a return to the original spectrum. These results demonstrate a new type of sensor that reports the arrival of organic vapors with an electroluminescent signal. The sensor comprises (a) a first electrode; (b) a hole transport layer formed on the first electrode; (c) a sensing/emitting layer formed on the hole transport layer, the sensing/emitting layer comprising a material that changes color upon exposure to the analyte vapors; (d) an electron conductor layer formed on the sensing layer; and (e) a second electrode formed on the electron conductor layer. The hole transport layer emits light at a shorter wavelength than the sensing/emitting layer and at least the first electrode comprises an optically transparent material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jian; Turner, Eric

Iridium compounds and their uses are disclosed herein. For example, carbazole containing iridium compounds are disclosed. The compounds are useful in many devices, including, but not limited to, electroluminescent devices.

Electrical and Optical Characterization of Nanowire based Semiconductor Devices

NASA Astrophysics Data System (ADS)

Ayvazian, Talin

This research project is focused on a new strategy for the creation of nanowire based semiconductor devices. The main goal is to understand and optimize the electrical and optical properties of two types of nanoscale devices; in first type lithographically patterned nanowire electrodeposition (LPNE) method has been utilized to fabricate nanowire field effect transistors (NWFET) and second type involved the development of light emitting semiconductor nanowire arrays (NWLED). Field effect transistors (NWFETs) have been prepared from arrays of polycrystalline cadmium selenide (pc-CdSe) nanowires using a back gate configuration. pc-CdSe nanowires were fabricated using the lithographically patterned nanowire electrode- position (LPNE) process on SiO2 /Si substrates. After electrodeposition, pc-CdSe nanowires were thermally annealed at 300 °C x 4 h either with or without exposure to CdCl 2 in methanol a grain growth promoter. The influence of CdCl2 treatment was to increase the mean grain diameter as determined by X-ray diffraction pattern and to convert the crystal structure from cubic to wurtzite. Transfer characteristics showed an increase of the field effect mobility (mu eff) by an order of magnitude and increase of the Ion/I off ratio by a factor of 3-4. Light emitting devices (NW-LED) based on lithographically patterned pc-CdSe nanowire arrays have been investigated. Electroluminescence (EL) spectra of CdSe nanowires under various biases exhibited broad emission spectra centered at 750 nm close to the band gap of CdSe (1.7eV). To enhance the intensity of the emitted light and the external quantum efficiency (EQE), the distance between the contacts were reduced from 5 mum to less than 1 mum which increased the efficiency by an order of magnitude. Also, increasing the annealing temperature of nanowires from 300 °C x4 h to 450 This research project is focused on a new strategy for the creation of nanowire based semiconductor devices. The main goal is to understand and optimize the electrical and optical properties of two types of nanoscale devices; in first type lithographically patterned nanowire electrodeposition (LPNE) method has been utilized to fabricate nanowire field effect transistors (NWFET) and second type involved the development of light emitting semiconductor nanowire arrays (NWLED). Field effect transistors (NWFETs) have been prepared from arrays of polycrystalline cadmium selenide (pc-CdSe) nanowires using a back gate configuration. pc-CdSe nanowires were fabricated using the lithographically patterned nanowire electrode- position (LPNE) process on SiO2 /Si substrates. After electrodeposition, pc-CdSe nanowires were thermally annealed at 300 °C x 4 h either with or without exposure to CdCl2 in methanol- a grain growth promoter. The influence of CdCl2 treatment was to increase the mean grain diameter as determined by X-ray diffraction pattern and to convert the crystal structure from cubic to wurtzite. Transfer characteristics showed an increase of the field effect mobility (mueff<) by an order of magnitude and increase of the Ion/Ioff ratio by a factor of 3-4. Light emitting devices (NW-LED) based on lithographically patterned pc-CdSe nanowire arrays have been investigated. Electroluminescence (EL) spectra of CdSe nanowires under various biases exhibited broad emission spectra centered at 750 nm close to the band gap of CdSe (1.7eV). To enhance the intensity of the emitted light and the external quantum efficiency (EQE), the distance between the contacts were reduced from 5 mum to less than 1 mum which increased the efficiency by an order of magnitude. Also, increasing the annealing temperature of nanowires from 300 °C x4 h to 450 °C x 1h enhanced grain growth confirmed by structural characterization including X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman Spectroscopy. Correspondingly the light emission intensity and EQE improved due to this grain growth. Kelvin probe force microscopy (KPFM) was utilized to understand mechanism of light emission in CdSe nanowires. Arrays of CdTe nanowires were electrodeposited using LPNE process where the elec- trodeposition of pc-CdTe was carried out at two temperatures: 20 °C (cold) and 55 °C (hot). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) re- sults revealed higher crystallinity, larger grain size and presence of Te for nanowires prepared at 55°C compared to nanowires deposited at 20°C. Nanowires prepared at 55°C showed higher electrical conductivity and enhanced electroluminescence proper- ties, including higher light emission intensity and improved External Quantum Efficiency (EQE). Electrical conduction mechanism also investigated for CdTe nanowires. Thermionic emission over schottky barrier height was identified as the dominant charge transport mechanism in pc-CdTe nanowires.°C x 1h enhanced grain growth confirmed by structural characterization including X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman Spectroscopy. Correspondingly the light emission intensity and EQE improved due to this grain growth. Kelvin probe force microscopy (KPFM) was utilized to understand mechanism of light emission in CdSe nanowires. Arrays of CdTe nanowires were electrodeposited using LPNE process where the electrodeposition of pc-CdTe was carried out at two temperatures: 20 °C (cold) and 55 °C (hot). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) re- sults revealed higher crystallinity, larger grain size and presence of Te for nanowires prepared at 55°C compared to nanowires deposited at 20°C. Nanowires prepared at 55°C showed higher electrical conductivity and enhanced electroluminescence properties, including higher light emission intensity and improved External Quantum Efficiency (EQE). Electrical conduction mechanism also investigated for CdTe nanowires. Thermionic emission over schottky barrier height was identified as the dominant charge transport mechanism in pc-CdTe nanowires.

Contactless Electroluminescence Imaging for Cell and Module Characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, Steve

2015-06-14

Module performance can be characterized by imaging using baseline and periodic images to track defects and degradation. Both thermal images, which can be acquired during sunny operating conditions, and photoluminescence images, which could be acquired at night, can be collected without electrical connection. Electroluminescence (EL) images, which are useful to detect many types of defects such as cracks, interconnect and solder faults, and resistances, have typically required electrical connection to drive current in the cells and modules. Here, a contactless EL imaging technique is proposed, which provides an EL image without the need for electrical connection to drive current throughmore » the module. Such EL imaging has the capability to be collected at night without disruption to daytime power generation.« less

Electroluminescence in CdSe/PVA nanocomposites

NASA Astrophysics Data System (ADS)

Kumari, Sarita; Ramrakhiani, M.; Khare, P. K.

2018-05-01

The synthesis of II-VI nanocrystal into the polymer matrix to form nanocomposites with adjustable nanocrystal is of great interest size is a big challenge to the scientific community. In present work semiconducting CdSe/PVA thin film were synthesized by single step solution method with different concentration of CdSe. The as-prepared products were characterized by UV-Visible absorption spectra and FESEM. Absorption spectra of CdSe/PVA nanocomposites indicated that the position of absorption edge shifts to smaller wavelength by increasing the concentration of CdSe. For Electroluminescence a turn on voltage is required for light emission and brightness increases with voltage. Turn on voltage is found to decrease as CdSe concentration is increased. The voltage-current curve represents ohmic nature for all EL cells.

Features of high-temperature electroluminescence in an LED n-GaSb/n-InGaAsSb/p-AlGaAsSb heterostructure with high potential barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Danilov, L. V., E-mail: danleon84@mail.ru; Petukhov, A. A.; Mikhailova, M. P.

2016-06-15

The electroluminescent properties of a light-emitting diode n-GaSb/n-InGaAsSb/p-AlGaAsSb heterostructure with high potential barriers are studied in the temperature range of 290–470 K. An atypical temperature increase in the power of the long-wavelength luminescence band with an energy of 0.3 eV is experimentally observed. As the temperature increases to 470 K, the optical radiation power increases by a factor of 1.5–2. To explain the extraordinary temperature dependence of the radiation power, the recombination and carrier transport processes are theoretically analyzed in the heterostructure under study.

Electrical and Luminescent Properties of Color-Changeable Organic Electroluminescent Diode Using Squarylium Dyes

NASA Astrophysics Data System (ADS)

Mori, Tatsuo; Miyachi, Kiyokazu; Kichimi, Tomoaki; Mizutani, Teruyoshi

1994-12-01

The organic electoluminescent diode (LED) with squarylium (Sq) dye-doped Alq3 changes color upon application of voltage (current). The luminescent color from the organic LED changes from red (electroluminescence (EL) of Sq dye) at low voltage to light green (EL of Alq3) at high voltage. We studied the EL efficiency and EL spectrum of organic Sq-doped Alq3 LED with various doping positions in the emission layer. Consequentially, it was clarified that Sq doping near TPD considerably reduced the EL efficiency. The EL mechanism of the organic LED was concluded to be associated with the energy transfer from the excited Alq3 to the guest dye and hole trapping of the guest dye in Alq3.

Controlled electroluminescence of n-ZnMgO/p-GaN light-emitting diodes

NASA Astrophysics Data System (ADS)

Goh, E. S. M.; Yang, H. Y.; Han, Z. J.; Chen, T. P.; Ostrikov, K.

2012-12-01

Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.

Strong enhancement of emission efficiency in GaN light-emitting diodes by plasmon-coupled light amplification of graphene

NASA Astrophysics Data System (ADS)

Kim, Jong Min; Kim, Sung; Hwang, Sung Won; Kim, Chang Oh; Shin, Dong Hee; Kim, Ju Hwan; Jang, Chan Wook; Kang, Soo Seok; Hwang, Euyheon; Choi, Suk-Ho; El-Gohary, Sherif H.; Byun, Kyung Min

2018-02-01

Recently, we have demonstrated that excitation of plasmon-polaritons in a mechanically-derived graphene sheet on the top of a ZnO semiconductor considerably enhances its light emission efficiency. If this scheme is also applied to device structures, it is then expected that the energy efficiency of light-emitting diodes (LEDs) increases substantially and the commercial potential will be enormous. Here, we report that the plasmon-induced light coupling amplifies emitted light by ˜1.6 times in doped large-area chemical-vapor-deposition-grown graphene, which is useful for practical applications. This coupling behavior also appears in GaN-based LEDs. With AuCl3-doped graphene on Ga-doped ZnO films that is used as transparent conducting electrodes for the LEDs, the average electroluminescence intensity is 1.2-1.7 times enhanced depending on the injection current. The chemical doping of graphene may produce the inhomogeneity in charge densities (i.e., electron/hole puddles) or roughness, which can play a role as grating couplers, resulting in such strong plasmon-enhanced light amplification. Based on theoretical calculations, the plasmon-coupled behavior is rigorously explained and a method of controlling its resonance condition is proposed.

High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate.

PubMed

Muhammed, Mufasila M; Alwadai, Norah; Lopatin, Sergei; Kuramata, Akito; Roqan, Iman S

2017-10-04

We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga 2 O 3 ) substrate, obtained using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multiquantum well (MQW) grown on the masked β-Ga 2 O 3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ∼86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

2-(2-Hydroxyphenyl)benzimidazole-based four-coordinate boron-containing materials with highly efficient deep-blue photoluminescence and electroluminescence.

PubMed

Zhang, Zhenyu; Zhang, Houyu; Jiao, Chuanjun; Ye, Kaiqi; Zhang, Hongyu; Zhang, Jingying; Wang, Yue

2015-03-16

Two novel four-coordinate boron-containing emitters 1 and 2 with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of 1 or 2 exhibited high electron and hole mobility in the same order of magnitude 10(-4), as determined by time-of-flight. The fabricated electroluminescent devices that employed 1 or 2 as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.15, Y = 0.09) and (X = 0.16, Y = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes.

Surface electroluminescence phenomena correlated with trapping parameters of insulating polymers

NASA Astrophysics Data System (ADS)

Zhang, Guan-Jun; Yang, Kai; Dong, Ming; Zhao, Wen-Bin; Yan, Zhang

2007-12-01

Electroluminescence (EL) phenomena are closely linked to the space charge and degradation in insulating polymers, and dominated by the luminescence and trap centers. EL emission has been promising in defining the onset of electrical aging and in the investigation of dissipation mechanisms. Generally, polymeric degradation reveals the increment of the density of luminescence and trap centers, so a fundamental study is proposed to correlate the EL emission of insulating polymers and their trapping parameters. A sensitive photon counting system is constructed to detect the weak EL. The time- and phase-resolved EL characteristics from different polymers (LDPE, PP and PTFE) are investigated with a planar electrode configuration under stepped ac voltage in vacuum. In succession, each sample is charged with exposing to multi-needle corona discharge, and then its surface potential decay is continuously recorded at a constant temperature. Based on the isothermal relaxation current theory, the energy level and density of both electron and hole trap distribution in the surface layer of each polymer is obtained. It is preliminarily concluded that EL phenomena are strongly affected by the trap properties, and for different polymers, its EL intensity is in direct contrast to its surface trap density, and this can be qualitatively explained by the trapping and detrapping sequence of charge carriers in trap centers with different energy level.

Strong electroluminescence from SiO{sub 2}-Tb{sub 2}O{sub 3}-Al{sub 2}O{sub 3} mixed layers fabricated by atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rebohle, L., E-mail: l.rebohle@hzdr.de; Braun, M.; Wutzler, R.

2014-06-23

We report on the bright green electroluminescence (EL) with power efficiencies up to 0.15% of SiO{sub 2}-Tb{sub 2}O{sub 3}-mixed layers fabricated by atomic layer deposition and partly co-doped with Al{sub 2}O{sub 3}. The electrical, EL, and breakdown behavior is investigated as a function of the Tb and the Al concentration. Special attention has been paid to the beneficial role of Al{sub 2}O{sub 3} co-doping which improves important device parameters. In detail, it increases the maximum EL power efficiency and EL decay time, it nearly doubles the fraction of excitable Tb{sup 3+} ions, it shifts the region of high EL powermore » efficiencies to higher injection currents, and it reduces the EL quenching over the device lifetime by an approximate factor of two. It is assumed that the presence of Al{sub 2}O{sub 3} interferes the formation of Tb clusters and related defects. Therefore, the system SiO{sub 2}-Tb{sub 2}O{sub 3}-Al{sub 2}O{sub 3} represents a promising alternative for integrated, Si-based light emitters.« less

Exciplex: An Intermolecular Charge-Transfer Approach for TADF.

PubMed

Sarma, Monima; Wong, Ken-Tsung

2018-04-03

Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. In addition to pure TADF emitters achieved by the subtle manipulations of intramolecular charge transfer processes with sophisticated molecular structures, a new class of efficient TADF-based OLEDs with emitting layer formed by blending electron donor and acceptor molecules that involve intermolecular charge transfer have also been fabricated. In contrast to pure TADF materials, the exciplex-based systems can realize small ΔEST (0-0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, exciplex-based OLEDs have the prospective to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency. Therefore, the challenging issue of achieving small ΔEST in organic systems could be solved. In this article, we summarize and discuss the latest and most significant developments regarding these rapidly evolving functional materials, wherein the majority of the reported exciplex forming systems are categorized into two sub-groups, viz. (a) exciplex as TADF emitters and (b) those as hosts for fluorescent, phosphorescent and TADF dopants according to their structural features and applications. The working mechanisms of the direct electroluminescence from the donor/acceptor interface and the exciplex-forming systems as co-host for the realization of high efficiency OLEDs are reviewed and discussed. This article delivers a summary of the current progresses and achievements of exciplex-based researches and points out the future challenges to trigger more research endeavors to this growing field.

[Synthesis and spectral characteristics of novel di-schiff base derivatives incorporting oxadiazole ring].

PubMed

Chen, Tong-bin; Zhang, Xiong-lu; Fan, Xiao-lin; Li, Xun

2008-12-01

4-nitrobenzoic acid and hydraxine sulfate were cyclized with H3PO4/P2O5 to afford 2,5-bis(4-nitrophenyl)-1, 3,4-oxadiazole(1), then(1)was reduced to 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole using Zn/CaCl2 as reduction reagent, and at last, a series of novel di-schiff base derivatives containing oxadiazole ring were obtained by the reaction of 2,5-bis(4-aminophenyl)-1, 3,4-oxadiazole with aromatic aldehydes (yield: 65%-81%). The structures of these compounds were confirmed by 1H NMR, FTIR and MS. Their UV-Vis spectra as well as fluorescence spectra were studied and the electrochemical properties were tested with cyclic voltammetry. The UV-Vis spectroscopy results show that the characteristic absorption peaks of 1, 3, 4-oxadiazole unit and di-schiff base unit disappeared. The maximum absorption wavelength was detected at 345-357 nm because conjugation effect made the two energy bands partially hybrid and form a new energy band structure. Fluorescence spectroscopy results show that they emit strong blue and purple fluorescence, and the emission maximum wavelengths of di-schiff base are from 390 to 407 nm. Electrochemical properties results show that they have higher affinity energy (2.36-3.04 eV) and ionic potential (5.35-6.06 eV), which indicated that they have better electron-transporting properties than PBD except 3 a and 3 h. The results give a reference to further application to organic electroluminescent devices of the target compound.

GaAs/AlGaAs core multishell nanowire-based light-emitting diodes on Si.

PubMed

Tomioka, Katsuhiro; Motohisa, Junichi; Hara, Shinjiroh; Hiruma, Kenji; Fukui, Takashi

2010-05-12

We report on integration of GaAs nanowire-based light-emitting-diodes (NW-LEDs) on Si substrate by selective-area metalorganic vapor phase epitaxy. The vertically aligned GaAs/AlGaAs core-multishell nanowires with radial p-n junction and NW-LED array were directly fabricated on Si. The threshold current for electroluminescence (EL) was 0.5 mA (current density was approximately 0.4 A/cm(2)), and the EL intensity superlinearly increased with increasing current injections indicating superluminescence behavior. The technology described in this letter could help open new possibilities for monolithic- and on-chip integration of III-V NWs on Si.

Enhanced Optical and Electrical Properties of Polymer-Assisted All-Inorganic Perovskites for Light-Emitting Diodes.

PubMed

Ling, Yichuan; Tian, Yu; Wang, Xi; Wang, Jamie C; Knox, Javon M; Perez-Orive, Fernando; Du, Yijun; Tan, Lei; Hanson, Kenneth; Ma, Biwu; Gao, Hanwei

2016-10-01

Highly bright light-emitting diodes based on solution-processed all-inorganic perovskite thin film are demonstrated. The cesium lead bromide (CsPbBr 3 ) created using a new poly(ethylene oxide)-additive spin-coating method exhibits photoluminescence quantum yield up to 60% and excellent uniformity of electrical current distribution. Using the smooth CsPbBr 3 films as emitting layers, green perovskite-based light-emitting diodes (PeLEDs) exhibit electroluminescent brightness and efficiency above 53 000 cd m -2 and 4%: a new benchmark of device performance for all-inorganic PeLEDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of material matching on the stress-induced power degradation for light-redirecting-ribbon-based silicon photovoltaic modules

NASA Astrophysics Data System (ADS)

Gou, X. F.; Zhuang, H.; Zhu, J.; Li, X. Y.

2018-01-01

Light redirecting ribbons (LRR) have recently been adopted in crystalline silicon modules in PV industry. The introduction of this LRR may bring additional stress at the boundary of the busbar/wafer contact, which may probably lead to higher power loss after aging. The thermal cycle and electroluminescence (EL) test are employed in this work to investigate this stress-induced power degradation for LRR-based crystalline silicon modules. The obtained results demonstrate that with increase in the thickness of the EVA encapsulant or the decrease in the thickness of the LRR, the power degradation induced by stress can be effectively diminished.

Dominant transverse-electric polarized emission from 298 nm MBE-grown AlN-delta-GaN quantum well ultraviolet light-emitting diodes

NASA Astrophysics Data System (ADS)

Liu, Cheng; Ooi, Yu Kee; Islam, S. M.; Xing, Huili Grace; Jena, Debdeep; Zhang, Jing

2017-02-01

III-nitride based ultraviolet (UV) light emitting diodes (LEDs) are of considerable interest in replacing gas lasers and mercury lamps for numerous applications. Specifically, AlGaN quantum well (QW) based LEDs have been developed extensively but the external quantum efficiencies of which remain less than 10% for wavelengths <300 nm due to high dislocation density, difficult p-type doping and most importantly, the physics and band structure from the three degeneration valence subbands. One solution to address this issue at deep UV wavelengths is by the use of the AlGaN-delta-GaN QW where the insertion of the delta-GaN layer can ensure the dominant conduction band (C) - heavyhole (HH) transition, leading to large transverse-electric (TE) optical output. Here, we proposed and investigated the physics and polarization-dependent optical characterizations of AlN-delta- GaN QW UV LED at 300 nm. The LED structure is grown by Molecular Beam Epitaxy (MBE) where the delta-GaN layer is 3-4 monolayer (QW-like) sandwiched by 2.5-nm AlN sub-QW layers. The physics analysis shows that the use of AlN-delta-GaN QW ensures a larger separation between the top HH subband and lower-energy bands, and strongly localizes the electron and HH wave functions toward the QW center and hence resulting in 30-time enhancement in TEpolarized spontaneous emission rate, compared to that of a conventional Al0.35Ga0.65N QW. The polarization-dependent electroluminescence measurements confirm our theoretical analysis; a dominant TE-polarized emission was obtained at 298 nm with a minimum transverse-magnetic (TM) polarized emission, indicating the feasibility of high-efficiency TEpolarized UV emitters based on our proposed QW structure.

Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology

PubMed Central

Li, Ying-Chang; Chang, Liann-Be; Chen, Hou-Jen; Yen, Chia-Yi; Pan, Ke-Wei; Huang, Bohr-Ran; Kuo, Wen-Yu; Chow, Lee; Zhou, Dan; Popko, Ewa

2017-01-01

Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot and reported LED’s color rendering index (CRI) are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL) and electroluminescence (EL) spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI) of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications. PMID:28772792

Room Temperature Electroluminescence from Tensile-Strained Si0.13Ge0.87/Ge Multiple Quantum Wells on a Ge Virtual Substrate

PubMed Central

Lin, Guangyang; Chen, Ningli; Zhang, Lu; Huang, Zhiwei; Huang, Wei; Wang, Jianyuan; Xu, Jianfang; Chen, Songyan; Li, Cheng

2016-01-01

Direct band electroluminescence (EL) from tensile-strained Si0.13Ge0.87/Ge multiple quantum wells (MQWs) on a Ge virtual substrate (VS) at room temperature is reported herein. Due to the competitive result of quantum confinement Stark effect and bandgap narrowing induced by tensile strain in Ge wells, electroluminescence from Γ1-HH1 transition in 12-nm Ge wells was observed at around 1550 nm. As injection current density increases, additional emission shoulders from Γ2-HH2 transition in Ge wells and Ge VS appeared at around 1300–1400 nm and 1600–1700 nm, respectively. The peak energy of EL shifted to the lower energy side superquadratically with an increase of injection current density as a result of the Joule heating effect. During the elevation of environmental temperature, EL intensity increased due to a reduction of energy between L and Γ valleys of Ge. Empirical fitting of the relationship between the integrated intensity of EL (L) and injection current density (J) with L~Jm shows that the m factor increased with injection current density, suggesting higher light emitting efficiency of the diode at larger injection current densities, which can be attributed to larger carrier occupations in the Γ valley and the heavy hole (HH) valance band at higher temperatures. PMID:28773923

Room Temperature Electroluminescence from Tensile-Strained Si0.13Ge0.87/Ge Multiple Quantum Wells on a Ge Virtual Substrate.

PubMed

Lin, Guangyang; Chen, Ningli; Zhang, Lu; Huang, Zhiwei; Huang, Wei; Wang, Jianyuan; Xu, Jianfang; Chen, Songyan; Li, Cheng

2016-09-27

Direct band electroluminescence (EL) from tensile-strained Si 0.13 Ge 0.87 /Ge multiple quantum wells (MQWs) on a Ge virtual substrate (VS) at room temperature is reported herein. Due to the competitive result of quantum confinement Stark effect and bandgap narrowing induced by tensile strain in Ge wells, electroluminescence from Γ1-HH1 transition in 12-nm Ge wells was observed at around 1550 nm. As injection current density increases, additional emission shoulders from Γ2-HH2 transition in Ge wells and Ge VS appeared at around 1300-1400 nm and 1600-1700 nm, respectively. The peak energy of EL shifted to the lower energy side superquadratically with an increase of injection current density as a result of the Joule heating effect. During the elevation of environmental temperature, EL intensity increased due to a reduction of energy between L and Γ valleys of Ge. Empirical fitting of the relationship between the integrated intensity of EL ( L ) and injection current density ( J ) with L ~ J m shows that the m factor increased with injection current density, suggesting higher light emitting efficiency of the diode at larger injection current densities, which can be attributed to larger carrier occupations in the Γ valley and the heavy hole (HH) valance band at higher temperatures.

Influence of electromechanical coupling on optical properties of InGaN quantum-dot based light-emitting diodes.

PubMed

Barettin, Daniele; Maur, Matthias Auf der; Carlo, Aldo di; Pecchia, Alessandro; Tsatsulnikov, Andrei F; Sakharov, Alexei V; Lundin, Wsevolod V; Nikolaev, Andrei E; Usov, Sergey O; Cherkashin, Nikolay; Hÿtch, Martin J; Karpov, Sergey Yu

2017-01-06

The impact of electromechanical coupling on optical properties of light-emitting diodes (LEDs) with InGaN/GaN quantum-dot (QD) active regions is studied by numerical simulations. The structure, i.e. the shape and the average In content of the QDs, has been directly derived from experimental data on out-of-plane strain distribution obtained from the geometric-phase analysis of a high-resolution transmission electron microscopy image of an LED structure grown by metalorganic vapor-phase epitaxy. Using continuum [Formula: see text] calculations, we have studied first the lateral and full electromechanical coupling between the QDs in the active region and its impact on the emission spectrum of a single QD located in the center of the region. Our simulations demonstrate the spectrum to be weakly affected by the coupling despite the strong common strain field induced in the QD active region. Then we analyzed the effect of vertical coupling between vertically stacked QDs as a function of the interdot distance. We have found that QCSE gives rise to a blue-shift of the overall emission spectrum when the interdot distance becomes small enough. Finally, we compared the theoretical spectrum obtained from simulation of the entire active region with an experimental electroluminescence (EL) spectrum. While the theoretical peak emission wavelength of the selected central QD corresponded well to that of the EL spectrum, the width of the latter one was determined by the scatter in the structures of various QDs located in the active region. Good agreement between the simulations and experiment achieved as a whole validates our model based on realistic structure of the QD active region and demonstrates advantages of the applied approach.

Enhanced Output Power of Near-Ultraviolet Light-Emitting Diodes by p-GaN Micro-Rods

NASA Astrophysics Data System (ADS)

Wang, Dong-Sheng; Zhang, Ke-Xiong; Liang, Hong-Wei; Song, Shi-Wei; Yang, De-Chao; Shen, Ren-Sheng; Liu, Yang; Xia, Xiao-Chuan; Luo, Ying-Min; Du, Guo-Tong

2014-02-01

Near-ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) are grown by low-pressure metal-organic chemical vapor deposition. The scanning electronic microscope image shows that the p-GaN micro-rods are formed above the interface of p-AlGaN/p-GaN due to the rapid growth rate of p-GaN in the vertical direction. The p-GaN micro-rods greatly increase the escape probability of photons inside the LED structure. Electroluminescence intensities of the 372 nm UV LED lamps with p-GaN micro rods are 88% higher than those of the flat surface LED samples.

Investigation of germanium quantum-well light sources.

PubMed

Fei, Edward T; Chen, Xiaochi; Zang, Kai; Huo, Yijie; Shambat, Gary; Miller, Gerald; Liu, Xi; Dutt, Raj; Kamins, Theodore I; Vuckovic, Jelena; Harris, James S

2015-08-24

In this paper, we report a broad investigation of the optical properties of germanium (Ge) quantum-well devices. Our simulations show a significant increase of carrier density in the Ge quantum wells. Photoluminescence (PL) measurements show the enhanced direct-bandgap radiative recombination rates due to the carrier density increase in the Ge quantum wells. Electroluminescence (EL) measurements show the temperature-dependent properties of our Ge quantum-well devices, which are in good agreement with our theoretical models. We also demonstrate the PL measurements of Ge quantum-well microdisks using tapered-fiber collection method and quantify the optical loss of the Ge quantum-well structure from the measured PL spectra for the first time.

Electroluminescence in SrTiO3:Cr single-crystal nonvolatile memory cells

NASA Astrophysics Data System (ADS)

Alvarado, S. F.; La Mattina, F.; Bednorz, J. G.

2007-10-01

Materials chemistry has emerged as one of the most consistent fabrication tools for the rational delivery of high purity functional nanomaterials, engineered from molecular to microscopic scale at low cost and large scale. An overview of the major achievements and latest advances of a recently developed growth concept and low temperature aqueous synthesis method, for the fabrication of purpose-built large bandgap metal oxide semiconductor materials and oriented nano-arrays is presented. Important insight of direct relevance for semiconductor technology, optoelectronics, photovoltaics and photocatalysis for solar hydrogen generation, are revealed by in-depth investigations of the electronic structure of metal oxide nanostructures with new morphology and architecture, carried out at synchrotron radiation facilities.

Spectrally resolved hyperfine interactions between polaron and nuclear spins in organic light emitting diodes: Magneto-electroluminescence studies

NASA Astrophysics Data System (ADS)

Crooker, S. A.; Liu, F.; Kelley, M. R.; Martinez, N. J. D.; Nie, W.; Mohite, A.; Nayyar, I. H.; Tretiak, S.; Smith, D. L.; Ruden, P. P.

2014-10-01

We use spectrally resolved magneto-electroluminescence (EL) measurements to study the energy dependence of hyperfine interactions between polaron and nuclear spins in organic light-emitting diodes. Using layered devices that generate bright exciplex emission, we show that the increase in EL emission intensity I due to small applied magnetic fields of order 100 mT is markedly larger at the high-energy blue end of the EL spectrum (ΔI/I ˜ 11%) than at the low-energy red end (˜4%). Concurrently, the widths of the magneto-EL curves increase monotonically from blue to red, revealing an increasing hyperfine coupling between polarons and nuclei and directly providing insight into the energy-dependent spatial extent and localization of polarons.

Tunable electroluminescent color for 2, 5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds

NASA Astrophysics Data System (ADS)

Cheng, Gang; Zhang, Yingfang; Zhao, Yi; Liu, Shiyong; Xie, Zengqi; Xia, Hong; Hanif, Muddasir; Ma, Yuguang

2005-07-01

Exciplex emission is observed in electroluminescent (EL) spectrum of an organic light-emitting device (OLED), where 2, 5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds (trans-DPDSB), (8-hydroxyquinoline) aluminum, and N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) are used as light-emitting, electron-transporting, and hole-transporting layers, respectively. This emission can be dramatically weakened by inserting a hole-injecting layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) between the hole-transporting layer and the anode. Consequently, EL color of this OLED is tuned from white to blue. This phenomenon may result from the improvement of hole injection, which shifts the major recombination zone from the NPB/trans-DPDSB interface to the trans-DPDSB layer.

Enhanced out-coupling efficiency of organic light-emitting diodes using an nanostructure imprinted by an alumina nanohole array

NASA Astrophysics Data System (ADS)

Endo, Kuniaki; Adachi, Chihaya

2014-03-01

We demonstrate organic light-emitting diodes (OLEDs) with enhanced out-coupling efficiency containing nanostructures imprinted by an alumina nanohole array template that can be applied to large-emitting-area and flexible devices using a roll-to-roll process. The nanostructures are imprinted on a glass substrate by an ultraviolet nanoimprint process using an alumina nanohole array mold and then an OLED is fabricated on the nanostructures. The enhancement of out-coupling efficiency is proportional to the root-mean-square roughness of the nanostructures, and a maximum improvement of external electroluminescence quantum efficiency of 17% is achieved. The electroluminescence spectra of the OLEDs indicate that this improvement is caused by enhancement of the out-coupling of surface plasmon polaritons.

Simultaneous enhancement of photo- and electroluminescence in white organic light-emitting devices by localized surface plasmons of silver nanoclusters

NASA Astrophysics Data System (ADS)

Yu, Jingting; Zhu, Wenqing; Shi, Guanjie; Zhai, Guangsheng; Qian, Bingjie; Li, Jun

2017-02-01

White organic light-emitting devices (WOLEDs) with enhanced current efficiency and negligible color shifting equipped with an internal color conversion layer (CCL) were fabricated. They were attained by embedding a single layer of silver nanoclusters (SNCs) between the CCL and light-emitting layer (EML). The simultaneous enhancement of the photoluminescence (PL) of the CCL and electroluminescence (EL) of the EML were realized by controlling the thickness and size of the SNCs to match the localized surface plasmon resonance spectrum with the PL spectrum of the CCL and the EL spectrum of the EML. The WOLED with optimal SNCs demonstrated a 25.81% enhancement in current efficiency at 60 mA cm-2 and good color stability over the entire range of current density.

Theoretical and material studies of thin-film electroluminescent devices

NASA Technical Reports Server (NTRS)

Summers, C. J.

1989-01-01

Thin-film electroluminescent (TFEL) devices are studied for a possible means of achieving a high resolution, light weight, compact video display panel for computer terminals or television screens. The performance of TFEL devices depends upon the probability of an electron impact exciting a luminescent center which in turn depends upon the density of centers present in the semiconductor layer, the possibility of an electron achieving the impact excitation threshold energy, and the collision cross section itself. Efficiency of such a device is presently very poor. It can best be improved by increasing the number of hot electrons capable of impact exciting a center. Hot electron distributions and a method for increasing the efficiency and brightness of TFEL devices (with the additional advantage of low voltage direct current operation) are investigated.

Zn2GeO4 nanowires as efficient electron injection material for electroluminescent devices.

PubMed

Wang, Jiangxin; Yan, Chaoyi; Magdassi, Shlomo; Lee, Pooi See

2013-08-14

Pure phase Zn2GeO4 nanowires (NWs) were grown by the chemical vapor transport method on p-GaN: Mg/Al2O3 substrate. The as-grown Zn2GeO4 NWs exhibited n-type characteristic due to native defects and formed a p-n heterojunction with the p-GaN substrate. The unique energy level of Zn2GeO4 NWs promotes electron injection into GaN active region while suppressing hole injection into Zn2GeO4 NWs. The device exhibited an emission centered at 426 nm and a low turn-on voltage around 4 V. Zn2GeO4 NWs are first reported in this paper as promising electron transport and injection material for electroluminescent devices.

Superior characteristics of microscale light emitting diodes through tightly lateral oxide-confined scheme

NASA Astrophysics Data System (ADS)

Huang, Shen-Che; Li, Heng; Zhang, Zhe-Han; Chen, Hsiang; Wang, Shing-Chung; Lu, Tien-Chang

2017-01-01

We report on the design of the geometry and chip size-controlled structures of microscale light-emitting diodes (micro-LEDs) with a shallow-etched oxide-refilled current aperture and their performance. The proposed structure, which combines an indium-tin-oxide layer and an oxide-confined aperture, exhibited not only uniform current distribution but also remarkably tight current confinement. An extremely high injection level of more than 90 kA/cm2 was achieved in the micro-LED with a 5-μm aperture. Current spreading and the droop mechanism in the investigated devices were characterized through electroluminescence measurements, optical microscopy, and beam-view imaging. Furthermore, we utilized the β-model and S-model to elucidate current crowding and the efficiency droop phenomenon in the investigated micro-LEDs. The luminescence results evidenced the highly favorable performance of the fabricated micro-LEDs, which is a result of their more uniform current spreading and lower junction temperature relative to conventional LEDs. Moreover, the maximum endured current density could be further increased by reducing the aperture size of the micro-LEDs. The proposed design, which is expected to be beneficial for the development of high-performance array-based micro-LEDs, is practicable through current state-of-the-art processing techniques.

Pneumotachometer counts respiration rate of human subject

NASA Technical Reports Server (NTRS)

Graham, O.

1964-01-01

To monitor breaths per minute, two rate-to-analog converters are alternately used to read and count the respiratory rate from an impedance pneumograph sequentially displayed numerically on electroluminescent matrices.

Hyperfine spin interactions between polarons and nuclei in organic light emitting diodes: Magneto-EL measurements

NASA Astrophysics Data System (ADS)

Crooker, S. A.; Kelley, M. R.; Martinez, N.; Nie, W.; Mohite, A. D.; Smith, D. L.; Tretiak, S.; Ruden, P. P.

2014-03-01

Considerable attention in recent years has focused on the effects of applied magnetic fields on the conductance, photocurrent, electroluminescence (EL), and photoluminescence of nominally nonmagnetic organic semiconductor materials and devices. These magnetic field effects have proven useful in revealing the underlying physical mechanisms and relevant spin interactions that influence the electrical and optical properties in these organic systems (e.g., hyperfine coupling, exchange interactions, and spin-orbit coupling). Here we study the field-dependent properties of organic light-emitting diode (OLEDs) based on MTDATA/LiF/Bphen layered structures, in which exciplex recombination at the interface dominates the EL spectra. Small applied magnetic fields (~10 mT) are found to boost the net EL yield by up to 10%, due to a suppression of the mixing between singlet and triplet polaron pairs which, in turn, arises from hyperfine spin coupling of the polarons to the underlying nuclei of the host molecules. We discuss the dependence of these field-induced effects on the LiF barrier thickness, device bias, and on the orientation of the applied magnetic field, as well as the mechanisms responsible.

Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi

2015-08-15

Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originatedmore » from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.« less

Synthesis and electroluminescence property of new hexaphenylbenzene derivatives including amine group for blue emitters

PubMed Central

2013-01-01

Three new blue-emitting compounds of 5P-VA, 5P-VTPA, and 5P-DVTPA for organic light-emitting diode (OLED) based on hexaphenylbenzene moiety were demonstrated. Physical properties by the change of the substitution groups of the synthesized materials were systematically examined. Photoluminescence spectrum of the synthesized materials showed maximum emitting wavelengths of about 400 to 447 nm in solution state and 451 to 461 nm in film state, indicating deep blue emission color. OLED devices were fabricated by the synthesized compounds using vacuum deposit process as an emitting layer. The device structure was ITO/2-TNATA 60 nm/ NPB 15 nm/ EML 35 nm/ TPBi 20 nm/ LiF 1 nm/ Al 200 nm. External quantum efficiencies and CIE values of 5P-VA, 5P-VTPA, and 5P-DVTPA were 1.89%, 3.59%, 3.34%, and (0.154, 0.196), (0.150, 0.076), (0.148, 0.120), respectively. 5P-VTPA and 5P-DVTPA exhibited superior highly blue quality and thermal property such as high Td of 448°C and 449°C. PMID:24134333

P-doping-free III-nitride high electron mobility light-emitting diodes and transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Baikui; Tang, Xi; Chen, Kevin J., E-mail: eekjchen@ust.hk

2014-07-21

We report that a simple metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet emission at 3.4 eV at a small forward bias larger than ∼2 V at room temperature. Based on the surface states distribution of AlGaN, a mature impact-ionization-induced Fermi-level de-pinning model is proposed to explain the underlying mechanism of the electroluminescence (EL) process. By experimenting with different Schottky metals, Ni/Au and Pt/Au, we demonstrated that this EL phenomenon is a “universal” property of metal-AlGaN/GaN Schottky diodes. Since this light-emitting Schottky diode shares the same active structure and fabrication processes as the AlGaN/GaN high electron mobility transistors, straight-forward andmore » seamless integration of photonic and electronic functional devices has been demonstrated on doping-free III-nitride heterostructures. Using a semitransparent Schottky drain electrode, an AlGaN/GaN high electron mobility light-emitting transistor is demonstrated.« less

Fully Transparent Quantum Dot Light-Emitting Diode with a Laminated Top Graphene Anode.

PubMed

Yao, Li; Fang, Xin; Gu, Wei; Zhai, Wenhao; Wan, Yi; Xie, Xixi; Xu, Wanjin; Pi, Xiaodong; Ran, Guangzhao; Qin, Guogang

2017-07-19

A new method to employ graphene as top electrode was introduced, and based on that, fully transparent quantum dot light-emitting diodes (T-QLEDs) were successfully fabricated through a lamination process. We adopted the widely used wet transfer method to transfer bilayer graphene (BG) on polydimethylsiloxane/polyethylene terephthalate (PDMS/PET) substrate. The sheet resistance of graphene reduced to ∼540 Ω/□ through transferring BG for 3 times on the PDMS/PET. The T-QLED has an inverted device structure of glass/indium tin oxide (ITO)/ZnO nanoparticles/(CdSSe/ZnS quantum dots (QDs))/1,1-bis[(di-4-tolylamino)phenyl] cyclohexane (TAPC)/MoO 3 /graphene/PDMS/PET. The graphene anode on PDMS/PET substrate can be directly laminated on the MoO 3 /TAPC/(CdSSe/ZnS QDs)/ZnO nanoparticles/ITO/glass, which relied on the van der Waals interaction between the graphene/PDMS and the MoO 3 . The transmittance of the T-QLED is 79.4% at its main electroluminescence peak wavelength of 622 nm.

Wafer-scale controlled exfoliation of metal organic vapor phase epitaxy grown InGaN/GaN multi quantum well structures using low-tack two-dimensional layered h-BN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayari, Taha; Li, Xin; Voss, Paul L.

Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure tomore » be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.« less

Scanning Electron Microscopy | Materials Science | NREL

Science.gov Websites

platform. The electron microprobe JEOL 8900L is the preference when quantitative composition of specimens , electroluminescence, lateral transport measurements, NFCL JEOL JXA-8900L Electron probe microanalysis Quantitative

Light-emitting nanolattices with enhanced brightness

NASA Astrophysics Data System (ADS)

Ng, Ryan C.; Mandal, Rajib; Anthony, Rebecca J.; Greer, Julia R.

2017-02-01

Three-dimensional (3D) photonic crystals have potential in solid state lighting applications due to their advantages over conventional planar thin film devices. Periodicity in a photonic crystal structure enables engineering of the density of states to improve spontaneous light emission according to Fermi's golden rule. Unlike planar thin films, which suffer significantly from total internal reflection, a 3D architectured structure is distributed in space with many non-flat interfaces, which facilitates a substantial enhancement in light extraction. We demonstrate the fabrication of 3D nano-architectures with octahedron geometry that utilize luminescing silicon nanocrystals as active media with an aluminum cathode and indium tin oxide anode towards the realization of a 3D light emitting device. The developed fabrication procedure allows charge to pass through the nanolattice between two contacts for electroluminescence. These initial fabrication efforts suggest that 3D nano-architected devices are realizable and can reach greater efficiencies than planar devices.

Fabrication of a white electroluminescent device based on bilayered yellow and blue quantum dots.

PubMed

Kim, Jong-Hoon; Lee, Ki-Heon; Kang, Hee-Don; Park, Byoungnam; Hwang, Jun Yeon; Jang, Ho Seong; Do, Young Rag; Yang, Heesun

2015-03-12

Until now most work on colloidal quantum dot-light-emitting diodes (QLEDs) has been focused on the improvement of the electroluminescent (EL) performance of monochromatic devices, and multi-colored white QLEDs comprising more than one type of QD emitter have been rarely investigated. To demonstrate a white EL as a result of color mixing between blue and yellow, herein a unique combination of two dissimilar QDs of blue- CdZnS/ZnS plus a yellow-emitting Cu-In-S (CIS)/ZnS is used for the formation of the emitting layer (EML) of a multilayered QLED. First, the QLED consisting of a single EML randomly mixed with two QDs is fabricated, however, its EL is dominated by blue emission with the contribution of yellow emission substantially weaker. Thus, another EML configuration is devised in the form of a QD bilayer with two stacking sequences of CdZnS/ZnS//CIS/ZnS QD and vice versa. The QLED with the former stacking sequence shows an overwhelming contribution of blue EL, similar to the mixed QD EML-based device. Upon applying the oppositely stacked QD bilayer of CIS/ZnS//CdZnS/ZnS, however, a bicolored white EL can be successfully achieved by means of the effective extension of the radiative excitonic recombination zone throughout both QD EML regions. Such QD EML configuration-dependent EL results, which are discussed primarily using the proposed device energy level diagram, strongly suggest that the positional design of individual QD emitters is a critical factor for the realization of multicolored, white emissive devices.

Effect of the fabrication conditions of SiGe LEDs on their luminescence and electrical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalyadin, A. E.; Sobolev, N. A., E-mail: nick@sobolev.ioffe.rssi.ru; Strel’chuk, A. M.

2016-02-15

SiGe-based n{sup +}–p–p{sup +} light-emitting diodes (LEDs) with heavily doped layers fabricated by the diffusion (of boron and phosphorus) and CVD (chemical-vapor deposition of polycrystalline silicon layers doped with boron and phosphorus) techniques are studied. The electroluminescence spectra of both kinds of LEDs are identical, but the emission intensity of CVD diodes is ∼20 times lower. The reverse and forward currents in the CVD diodes are substantially higher than those in diffusion-grown diodes. The poorer luminescence and electrical properties of the CVD diodes are due to the formation of defects at the interface between the emitter and base layers.

Screen printed, transparent, and flexible electrodes based on graphene nanoplatelet pastes

NASA Astrophysics Data System (ADS)

Wróblewski, Grzegorz; Janczak, Daniel

Transparent, flexible and conducting graphene films were produced by screen printing method using printing pastes based on graphene nanoplatelets in polymer matrix. The transparency of received layers and the mechanical resistivity in several bending cycles were measured. Subsequently percolation threshold was investigated. Graphene layers were printed on diverse substrates (glass, Al2O3, PET) and afterwards for samples printed on glass different firing atmospheres (N2, H2, air) were studied. Best firing results (resistance decrease) were obtained for treatment in 250 °C in atmosphere of air. Finally investigation results were used to produce a transparent and elastic electrode for an electroluminescent display, showing the application potential of our graphene nanocomposite pastes.

Light emitting ceramic device

DOEpatents

Valentine, Paul; Edwards, Doreen D.; Walker, Jr., William John; Slack, Lyle H.; Brown, Wayne Douglas; Osborne, Cathy; Norton, Michael; Begley, Richard

2010-05-18

A light-emitting ceramic based panel, hereafter termed "electroceramescent" panel, is herein claimed. The electroceramescent panel is formed on a substrate providing mechanical support as well as serving as the base electrode for the device. One or more semiconductive ceramic layers directly overlay the substrate, and electrical conductivity and ionic diffusion are controlled. Light emitting regions overlay the semiconductive ceramic layers, and said regions consist sequentially of a layer of a ceramic insulation layer and an electroluminescent layer, comprised of doped phosphors or the equivalent. One or more conductive top electrode layers having optically transmissive areas overlay the light emitting regions, and a multi-layered top barrier cover comprising one or more optically transmissive non-combustible insulation layers overlay said top electrode regions.

White Light-Emitting Diodes Based on AgInS2/ZnS Quantum Dots with Improved Bandwidth in Visible Light Communication

PubMed Central

Ruan, Cheng; Zhang, Yu; Lu, Min; Ji, Changyin; Sun, Chun; Chen, Xiongbin; Chen, Hongda; Colvin, Vicki L.; Yu, William W.

2016-01-01

Quantum dot white light-emitting diodes (QD-WLEDs) were fabricated from green- and red-emitting AgInS2/ZnS core/shell QDs coated on GaN LEDs. Their electroluminescence (EL) spectra were measured at different currents, ranging from 50 mA to 400 mA, and showed good color stability. The modulation bandwidth of previously prepared QD-WLEDs was confirmed to be much wider than that of YAG:Ce phosphor-based WLEDs. These results indicate that the AgInS2/ZnS core/shell QDs are good color-converting materials for WLEDs and they are capable in visible light communication (VLC). PMID:28344270

Virtually pure near-infrared electroluminescence from exciplexes at polyfluorene/hexaazatrinaphthylene interfaces

NASA Astrophysics Data System (ADS)

Tregnago, G.; Fléchon, C.; Choudhary, S.; Gozalvez, C.; Mateo-Alonso, A.; Cacialli, F.

2014-10-01

Electronic processes at the heterojunction between chemically different organic semiconductors are of special significance for devices such as light-emitting diodes (LEDs) and photovoltaic diodes. Here, we report the formation of an exciplex state at the heterojunction of an electron-transporting material, a functionalized hexaazatrinaphthylene, and a hole-transporting material, poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)diphenylamine) (TFB). The energetics of the exciplex state leads to a spectral shift of ˜1 eV between the exciton and the exciplex peak energies (at 2.58 eV and 1.58 eV, respectively). LEDs incorporating such bulk heterojunctions display complete quenching of the exciton luminescence, and a nearly pure near-infrared electroluminescence arising from the exciplex (at ˜1.52 eV) with >98% of the emission at wavelengths above 700 nm at any operational voltage.

Strong electroluminescence from direct band and defects in Ge n+/p shallow junctions at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Guangyang; Li, Cheng, E-mail: lich@xmu.edu.cn; Chen, Chaowen

2016-05-09

Strong room temperature electroluminescence with two emission peaks at around 0.786 eV and 0.747 eV from Ge n+/p shallow junctions was reported. The peak at around 0.786 eV comes from direct band luminescence (DBL) in n + Ge regions, while the peak fixing at 0.747 eV is resulted from defects induced by ion implantation. Heavy n-type doping in Ge renders realization of strong defect-related luminescence (DRL) feasible. The peak intensity ratio of DRL/DBL decreases with increase of injection current since more electrons are filled in Γ valley. Above all, the Ge n+/p shallow junction is fully compatible with the source and drain in Gemore » metal-oxide-semiconductor field effect transistors.« less

Automatic Detection and Evaluation of Solar Cell Micro-Cracks in Electroluminescence Images Using Matched Filters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spataru, Sergiu; Hacke, Peter; Sera, Dezso

A method for detecting micro-cracks in solar cells using two dimensional matched filters was developed, derived from the electroluminescence intensity profile of typical micro-cracks. We describe the image processing steps to obtain a binary map with the location of the micro-cracks. Finally, we show how to automatically estimate the total length of each micro-crack from these maps, and propose a method to identify severe types of micro-cracks, such as parallel, dendritic, and cracks with multiple orientations. With an optimized threshold parameter, the technique detects over 90 % of cracks larger than 3 cm in length. The method shows great potentialmore » for quantifying micro-crack damage after manufacturing or module transportation for the determination of a module quality criterion for cell cracking in photovoltaic modules.« less

Highly stretchable electroluminescent skin for optical signaling and tactile sensing.

PubMed

Larson, C; Peele, B; Li, S; Robinson, S; Totaro, M; Beccai, L; Mazzolai, B; Shepherd, R

2016-03-04

Cephalopods such as octopuses have a combination of a stretchable skin and color-tuning organs to control both posture and color for visual communication and disguise. We present an electroluminescent material that is capable of large uniaxial stretching and surface area changes while actively emitting light. Layers of transparent hydrogel electrodes sandwich a ZnS phosphor-doped dielectric elastomer layer, creating thin rubber sheets that change illuminance and capacitance under deformation. Arrays of individually controllable pixels in thin rubber sheets were fabricated using replica molding and were subjected to stretching, folding, and rolling to demonstrate their use as stretchable displays. These sheets were then integrated into the skin of a soft robot, providing it with dynamic coloration and sensory feedback from external and internal stimuli. Copyright © 2016, American Association for the Advancement of Science.

Effects of Be acceptors on the spin polarization of carriers in p-i-n resonant tunneling diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Awan, I. T.; Galvão Gobato, Y.; Galeti, H. V. A.

In this paper, we have investigated the effect of Be acceptors on the electroluminescence and the spin polarization in GaAs/AlAs p-i-n resonant tunneling diodes. The quantum well emission comprise two main lines separated by ∼20 meV attributed to excitonic and Be-related transitions, which intensities show remarkably abrupt variations at critical voltages, particularly at the electron resonant peak where it shows a high-frequency bistability. The circular-polarization degree of the quantum-well electroluminescence also shows strong and abrupt variations at the critical bias voltages and it attains relatively large values (of ∼−75% at 15 T). These effects may be explored to design novel devices formore » spintronic applications such as a high-frequency spin-oscillators.« less

Violet-blue LEDs based on p-GaN/n-ZnO nanorods and their stability.

PubMed

Jha, Shrawan; Qian, Jin-Cheng; Kutsay, Oleksandr; Kovac, Jaroslav; Luan, Chun-Yan; Zapien, Juan Antonio; Zhang, Wenjun; Lee, Shuit-Tong; Bello, Igor

2011-06-17

In this paper, we report a fabrication, characterization and stability study of p-GaN/n-ZnO nanorod heterojunction light-emitting devices (LEDs). The LEDs were assembled from arrays of n-ZnO vertical nanorods epitaxially grown on p-GaN. LEDs showed bright electroluminescence in blue (440 nm), although weaker violet (372 nm) and green-yellow (550 nm) spectral components were also observed. The device characteristics are generally stable and reproducible. The LEDs have a low turn-on voltage (∼5 V). The electroluminescence (EL) is intense enough to be noticed by the naked eye, at an injection current as low as ∼ 40 µA (2.1 × 10(-2) A cm(-2) at 7 V bias). Analysis of the materials, electrical and EL investigations point to the role of a high quality of p-n nano-heterojunction which facilitates a large rectification ratio (320) and a stable reverse current of 2.8 µA (1.4 × 10(-3) A cm(-2) at 5 V). Stability of EL characteristics was investigated in detail. EL intensity showed systematic degradation over a short duration when the LED was bias-stressed at 30 V. At smaller bias (<20 V) LEDs tend to show a stable and repeatable EL characteristic. Thus a simple low temperature solution growth method was successfully exploited to realize nanorod/film heterojunction LED devices with predictable characteristics.

Light emitting diodes as a plant lighting source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bula, R.J.; Tennessen, D.J.; Morrow, R.C.

1994-12-31

Electroluminescence in solid materials is defined as the generation of light by the passage of an electric current through a body of solid material under an applied electric field. A specific type of electroluminescence, first noted by Lossew in 1923, involves the generation of photons when electrons are passed through a p-n junction of certain solid materials (junction of a n-type semiconductor, an electron donor, and a p-type semiconductor, an electron acceptor). Development efforts to translate these observations into visible light emitting devices, however, was not undertaken until the 1950s. The term, light emitting diode (LEDs), was first used inmore » a report by Wolfe, et al., in 1955. The development of this light emitting semiconductor technology dates back less than 30 years. During this period of time, the LED has evolved from a rare and expensive light generating device to one of the most widely used electronic components. The most popular applications of the LED are as indicators or as optoelectronic switches. However, several recent advances in LED technology have made possible the utilization of LEDs for applications that require a high photon flux, such as for plant lighting in controlled environments. The new generation of LEDs based on a gallium aluminum arsenide (GaAlAS) semiconductor material fabricated as a double heterostructure on a transparent substrate has opened up many new applications for these LEDs.« less

High-temperature luminescence in an n-GaSb/n-InGaAsSb/p-AlGaAsSb light-emitting heterostructure with a high potential barrier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petukhov, A. A., E-mail: andrey-rus29@rambler.ru; Zhurtanov, B. E.; Kalinina, K. V.

2013-09-15

The electroluminescent properties of an n-GaSb/n-InGaAsSb/p-AlGaAsSb heterostructure with a high potential barrier in the conduction band (large conduction-band offset) at the n-GaSb/n-InGaAsSb type-II heterointerface ({Delta}E{sub c} = 0.79 eV) are studied. Two bands with peaks at 0.28 and 0.64 eV at 300 K, associated with radiative recombination in n-InGaAsSb and n-GaSb, respectively, are observed in the electroluminescence (EL) spectrum. In the entire temperature range under study, T = 290-480 K, additional electron-hole pairs are formed in the n-InGaAsSb active region by impact ionization with hot electrons heated as a result of the conduction-band offset. These pairs contribute to radiative recombination,more » which leads to a nonlinear increase in the EL intensity and output optical power with increasing pump current. A superlinear increase in the emission power of the long-wavelength band is observed upon heating in the temperature range T = 290-345 K, and a linear increase is observed at T > 345 K. This work for the first time reports an increase in the emission power of a light-emitting diode structure with increasing temperature. It is shown that this rise is caused by a decrease in the threshold energy of the impact ionization due to narrowing of the band gap of the active region.« less

Resonant-cavity light-emitting diodes for optical interconnects

NASA Astrophysics Data System (ADS)

Jin, Xu

This dissertation addresses the issues related to external quantum efficiencies and light coupling efficiency of novel 1.3 mum Resonant-cavity light-emitting diodes (RCLEDs) on GaAs substrates. External quantum efficiency (QE) is defined as the number of extracted photons per injected electrons, i.e., the product of injection efficiency, internal QE, and light extraction efficiency. This study focuses on the latter two terms. Internal QE mainly depends on the properties of the active region quantum wells (QWs) used in the RCLEDs, such as composition, thickness, and strain compensation. GaAsSb/GaAs QW edge-emitting (EE) lasers are characterized experimentally to extract key parameters, such as internal QE and internal loss. With optimized QWs and a novel self-aligned EE lasers process, room temperature continuous wave (CW) operation of GaAsSb EE lasers has been demonstrated for the first time. The highest operational temperature for the EE lasers is 48°C at a wavelength as long as 1260 nm. This result is the best ever reported by a university group. In conventional LEDs, very little light generated by the active region, succeeds in escaping from the semiconductor material due to the small critical angle of total internal reflection. With the use of a resonant cavity, the light extraction efficiency of RCLEDs is significantly improved. Front and back reflectivities, detuning (offset) between resonant-cavity peak and electroluminescence, and electroluminescence linewidth have been identified as key factors influencing light extraction efficiency. Numerical simulations indicate that the fraction of luminescence transmitted through the top mirror of an optimized RCLED is around 9%, which is more than double that of conventional LEDs. This number will be larger when multiple reflections and photon recycling are considered; which are not included in the current model since they are structure dependent. The best GaAsSb/GaAs QW RCLEDs demonstrated in this work have shown narrow spectral linewidths of 7-10 nm, extracted light output power in the range of 200-300 muW, and modulation speed up to 300 MHz. This is the first demonstration of 1.3 muRCLEDs on GaAs substrates with performance comparable to InP based surface-emitting LEDs.

Materials for optoelectronic devices

DOEpatents

Shiang, Joseph John; Smigelski, Jr., Paul Michael

2015-01-27

Energy efficient optoelectronic devices include an electroluminescent layer containing a polymer made up of structural units of formula I and II; ##STR00001## wherein R.sup.1 and R.sup.2 are independently C.sub.22-44 hydrocarbyl, C.sub.22-44 hydrocarbyl containing one or more S, N, O, P, or Si atoms, oxaalkylaryl, or a combination thereof; R.sup.3 and R.sup.4 are independently H, C.sub.1-44 hydrocarbyl or C.sub.1-44 hydrocarbyl containing one or more S, N, O, P, or Si atoms, or R.sup.3 and R.sup.4, taken together, form a C.sub.2-10 monocyclic or bicyclic ring containing up to three S, N, O, P, or Si heteroatoms; and X is S, Se, or a combination thereof.

Electrically driven plasmon-exciton coupled random lasing in ZnO metal-semiconductor-metal devices

NASA Astrophysics Data System (ADS)

Suja, Mohammad; Debnath, Bishwajit; Bashar, Sunayna B.; Su, Longxing; Lake, Roger; Liu, Jianlin

2018-05-01

Electrically driven plasmon-exciton coupled random lasing is demonstrated by incorporating Ag nanoparticles on Cu-doped ZnO metal-semiconductor-metal (MSM) devices. Both photoluminescence and electroluminescence studies show that emission efficiencies have been enhanced significantly due to coupling between ZnO excitons and Ag surface plasmons. With the incorporation of Ag nanoparticles on ZnO MSM structures, internal quantum efficiency up to 6 times is demonstrated. Threshold current for lasing is decreased by as much as 30% while the output power is increased up to 350% at an injection current of 40 mA. A numerical simulation study reveals that hole carriers are generated in the ZnO MSM devices from impact ionization processes for subsequent plasmon-exciton coupled lasing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Dong, E-mail: wang.dong.539@m.kyushu-u.ac.jp; Maekura, Takayuki; Kamezawa, Sho

We demonstrated direct band gap (DBG) electroluminescence (EL) at room temperature from n-type bulk germanium (Ge) using a fin type asymmetric lateral metal/Ge/metal structure with TiN/Ge and HfGe/Ge contacts, which was fabricated using a low temperature (<400 °C) process. Small electron and hole barrier heights were obtained for TiN/Ge and HfGe/Ge contacts, respectively. DBG EL spectrum peaked at 1.55 μm was clearly observed even at a small current density of 2.2 μA/μm. Superlinear increase in EL intensity was also observed with increasing current density, due to superlinear increase in population of elections in direct conduction band. The efficiency of hole injection was alsomore » clarified.« less

High-speed GaN/GaInN nanowire array light-emitting diode on silicon(111).

PubMed

Koester, Robert; Sager, Daniel; Quitsch, Wolf-Alexander; Pfingsten, Oliver; Poloczek, Artur; Blumenthal, Sarah; Keller, Gregor; Prost, Werner; Bacher, Gerd; Tegude, Franz-Josef

2015-04-08

The high speed on-off performance of GaN-based light-emitting diodes (LEDs) grown in c-plane direction is limited by long carrier lifetimes caused by spontaneous and piezoelectric polarization. This work demonstrates that this limitation can be overcome by m-planar core-shell InGaN/GaN nanowire LEDs grown on Si(111). Time-resolved electroluminescence studies exhibit 90-10% rise- and fall-times of about 220 ps under GHz electrical excitation. The data underline the potential of these devices for optical data communication in polymer fibers and free space.

Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED

NASA Astrophysics Data System (ADS)

Titkov, Ilya E.; Yadav, Amit; Zerova, Vera L.; Zulonas, Modestas; Tsatsulnikov, Andrey F.; Lundin, Wsevolod V.; Sakharov, Alexey V.; Rafailov, Edik U.

2014-03-01

Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance.

Fabrication and Measurement of Electroluminescence and Electrical Properties of Organic Light-Emitting Diodes Containing Mott Insulator Nanocrystals.

PubMed

Nozoe, Soichiro; Kinoshita, Nobuaki; Matsuda, Masaki

2016-04-01

By using the short-time electrocrystallization technique, phthalocyanine (Pc)-based Mott insulator Co(Pc)(CN)2 . 2CHCl3 nanocrystals were fabricated and applied to organic light-emiting diodes (OLEDs). The fabricated device having the configuration ITO/Co(Pc)(CN)2 . 2CHCl3/Alq3/Al, in which ITO is indium-tin oxide and Alq3 is tris(8-hydroxyquinolinato)aluminum, showed clear emission from Alq3, suggesting the Mott insulator Co(Pc)(CN)2 . 2CHCl3 can work as useful hole-injection and transport material in OLEDs.

Quantum-dot light-emitting diodes utilizing CdSe /ZnS nanocrystals embedded in TiO2 thin film

NASA Astrophysics Data System (ADS)

Kang, Seung-Hee; Kumar, Ch. Kiran; Lee, Zonghoon; Kim, Kyung-Hyun; Huh, Chul; Kim, Eui-Tae

2008-11-01

Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe /ZnS nanocrystals in TiO2 thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO2/QDs /p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO2/QDs /Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.

Si based GeSn light emitter: mid-infrared devices in Si photonics

NASA Astrophysics Data System (ADS)

Yu, S. Q.; Ghetmiri, S. A.; Du, W.; Margetis, J.; Zhou, Y.; Mosleh, A.; Al-Kabi, S.; Nazzal, A.; Sun, G.; Soref, R. A.; Tolle, J.; Li, B.; Naseem, H. A.

2015-02-01

Ge1-xSnx/Ge thin films and Ge/Ge1-xSnx/Ge n-i-p double heterostructure (DHS) have been grown using commercially available reduced pressure chemical vapor deposition (RPCVD) reactor. The Sn compositional material and optical characteristics have been investigated. A direct bandgap GeSn material has been identified with Sn composition of 10%. The GeSn DHS samples were fabricated into LED devices. Room temperature electroluminescence spectra were studied. A maximum emission power of 28mW was obtained with 10% Sn LED under the injection current density of 800 A/cm2.

Experimental observation of polarized electroluminescence from edge-emission organic light emitting devices

NASA Astrophysics Data System (ADS)

Ran, G. Z.; Jiang, D. F.; Kan, Q.; Chen, H. D.

2010-12-01

We have observed a strongly polarized edge-emission from an organic light emitting device (OLED) with a silicon anode and a stacked Sm/Au (or Ag) cathode. For the OLED with a Sm/Au cathode, the transverse magnetic (TM) mode is stronger than the transverse electric (TE) mode by a factor of 2, while the polarization ratio of TM:TE is close to 300 for that with a Sm/Ag cathode. The polarization results from the scattering of surface plasmon polaritons at the device boundary. Such a silicon-based OLED is potentially an electrically excited SPP source in plasmonics.

Tunnel based spin injection devices for semiconductor spintronics

NASA Astrophysics Data System (ADS)

Jiang, Xin

This dissertation summarizes the work on spin-dependent electron transport and spin injection in tunnel based spintronic devices. In particular, it focuses on a novel three terminal hot electron device combining ferromagnetic metals and semiconductors---the magnetic tunnel transistor (MTT). The MTT has extremely high magnetic field sensitivity and is a useful tool to explore spin-dependent electron transport in metals, semiconductors, and at their interfaces over a wide energy range. In Chap. 1, the basic concept and fabrication of the MTT are discussed. Two types of MTTs, with ferromagnetic single and spin-valve base layers, respectively, are introduced and compared. In the following chapters, the transport properties of the MTT are discussed in detail, including the spin-dependent hot electron attenuation lengths in CoFe and NiFe thin films on GaAs (Chap. 2), the bias voltage dependence of the magneto-current (Chap. 3), the giant magneto-current effect in MTTs with a spin-valve base (Chap. 4), and the influence of non-magnetic seed layers on magneto-electronic properties of MTTs with a Si collector (Chap. 5). Chap. 6 concentrates on electrical injection of spin-polarized electrons into semiconductors, which is an essential ingredient in semiconductor spintronics. Two types of spin injectors are discussed: an MTT injector and a CoFe/MgO tunnel injector. The spin polarization of the injected electron current is detected optically by measuring the circular polarization of electroluminescence from a quantum well light emitting diode. Using an MTT injector a spin polarization of ˜10% is found for injection electron energy of ˜2 eV at 1.4K. This moderate spin polarization is most likely limited by significant electron spin relaxation at high energy. Much higher spin injection efficiency is obtained by using a CoFe/MgO tunnel injector with spin polarization values of ˜50% at 100K. The temperature and bias dependence of the electroluminescence polarization provides insight into spin relaxation mechanisms within the semiconductor heterostructure.

Non-Doped Sky-Blue OLEDs Based on Simple Structured AIE Emitters with High Efficiencies at Low Driven Voltages.

PubMed

Islam, Amjad; Zhang, Dongdong; Peng, Ruixiang; Yang, Rongjuan; Hong, Ling; Song, Wei; Wei, Qiang; Duan, Lian; Ge, Ziyi

2017-09-05

Blue organic light-emitting diodes (OLEDs) are necessary for flat-panel display technologies and lighting applications. To make more energy-saving, low-cost and long-lasting OLEDs, efficient materials as well as simple structured devices are in high demand. However, a very limited number of blue OLEDs achieving high stability and color purity have been reported. Herein, three new sky-blue emitters, 1,4,5-triphenyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole (TPEI), 1-(4-methoxyphenyl)-4,5-diphenyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole (TPEMeOPhI) and 1-phenyl-2,4,5-tris(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole (3TPEI), with a combination of imidazole and tetraphenylethene groups, have been developed. High photoluminescence quantum yields are obtained for these materials. All derivatives have demonstrated aggregation-induced emission (AIE) behavior, excellent thermal stability with high decomposition and glass transition temperatures. Non-doped sky-blue OLEDs with simple structure have been fabricated employing these materials as emitters and realized high efficiencies of 2.41 % (4.92 cd A -1 , 2.70 lm W -1 ), 2.16 (4.33 cd A -1 , 2.59 lm W -1 ) and 3.13 % (6.97 cd A -1 , 4.74 lm W -1 ) for TPEI, TPEMeOPhI and 3TPEI, with small efficiency roll-off. These are among excellent results for molecules constructed from the combination of imidazole and TPE reported so far. The high performance of a 3TPEI-based device shows the promising potential of the combination of imidazole and AIEgen for synthesizing efficient electroluminescent materials for OLED devices. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

White organic light-emitting diodes based on doped and ultrathin Rubrene layer

NASA Astrophysics Data System (ADS)

Li, Yi; Jiang, Yadong; Wen, Wen; Yu, Junsheng

2010-10-01

Based on a yellow fluorescent dye of 5, 6, 11, 12-tetraphenylnaphthacene (Rubrene), WOLEDs were fabricated, with doping structure and ultrathin layer structure utilized in the devices. By doping Rubrene into blue-emitting N,N'-bis-(1- naphthyl)-N,N'-biphenyl-1,1'-biphenyl-4,4'-diamine (NPB), the device with a structure of indium-tin-oxide (ITO)/NPB (40 nm)/NPB:Rubrene (0.25 wt%, 7 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (30 nm)/Mg:Ag exhibited a warm white light with Commissions Internationale De L'Eclairage (CIE) coordinates of (0.38, 0.41) at 12 V. The electroluminescent spectrum of the OLED consisted of blue and yellow fluorescent emissions, the intensity of blue emission increased gradually relative to the orange emission with increasing voltage. This is mainly due to the recombination zone shifted towards the anode side as the transmission rate of electrons grows faster than that of holes under higher bias voltage. A maximum luminance of 7300 cd/m2 and a maximum power efficiency of 0.57 lm/W were achieved. Comparatively, by utilizing ultrathin dopant layer, the device with a structure of ITO/NPB (40 nm)/Rubrene (0.3 nm)/NPB (7 nm)/BCP (30 nm)/Mg:Ag achieved a low turn-on voltage of 3 V and a more stable white light. The peaks of EL spectra located at 430 and 560 nm corresponding to the CIE coordinates of (0.32, 0.32) under bias voltage ranging from 5 to 15 V. A maximum luminance of 5630 cd/m2 and a maximum power efficiency of 0.6 lm/W were achieved. The balanced spectra were attributed to the stable confining of charge carriers and exciton by the thin emitting layers. Hence, with simple device structure and fabricating process, the device with ultrathin layer achieved low turn-on voltage, stable white light emitting and higher power efficiency.

Low cost solution-based materials processing methods for large area OLEDs and OFETs

NASA Astrophysics Data System (ADS)

Jeong, Jonghwa

In Part 1, we demonstrate the fabrication of organic light-emitting devices (OLEDs) with precisely patterned pixels by the spin-casting of Alq3 and rubrene thin films with dimensions as small as 10 mum. The solution-based patterning technique produces pixels via the segregation of organic molecules into microfabricated channels or wells. Segregation is controlled by a combination of weak adsorbing characteristics of aliphatic terminated self-assembled monolayers (SAMs) and by centrifugal force, which directs the organic solution into the channel or well. This novel patterning technique may resolve the limitations of pixel resolution in the method of thermal evaporation using shadow masks, and is applicable to the fabrication of large area displays. Furthermore, the patterning technique has the potential to produce pixel sizes down to the limitation of photolithography and micromachining techniques, thereby enabling the fabrication of high-resolution microdisplays. The patterned OLEDs, based upon a confined structure with low refractive index of SiO2, exhibited higher current density than an unpatterned OLED, which results in higher electroluminescence intensity and eventually more efficient device operation at low applied voltages. We discuss the patterning method and device fabrication, and characterize the morphological, optical, and electrical properties of the organic pixels. In part 2, we demonstrate a new growth technique for organic single crystals based on solvent vapor assisted recrystallization. We show that, by controlling the polarity of the solvent vapor and the exposure time in a closed system, we obtain rubrene in orthorhombic to monoclinic crystal structures. This novel technique for growing single crystals can induce phase shifting and alteration of crystal structure and lattice parameters. The organic molecules showed structural change from orthorhombic to monoclinic, which also provided additional optical transition of hypsochromic shift from that of the orthorhombic form. An intermediate form of the crystal exhibits an optical transition to the lowest vibrational energy level that is otherwise disallowed in the single-crystal orthorhombic form. The monoclinic form exhibits entirely new optical transitions and showed a possible structural rearrangement for increasing charge carrier mobility, making it promising for organic devices. These phenomena can be explained and proved by the chemical structure and molecular packing of the monoclinic form, transformed from orthorhombic crystalline structure.

Use of electroluminescence technology for highway signage.

DOT National Transportation Integrated Search

2001-09-30

Laboratory work will be combined with reviews of highway signage protocols, requirements and : potential applications that will lead to prototype design requirements for a typical highway sign that : should have the potential to improve safety for th...

Abnormal temperature dependent behaviors of intersystem crossing and triplet-triplet annihilation in organic planar heterojunction devices

NASA Astrophysics Data System (ADS)

Xiang, Jie; Chen, Yingbing; Yuan, De; Jia, Weiyao; Zhang, Qiaoming; Xiong, Zuhong

2016-09-01

Anomalous temperature dependent magneto-electroluminescence was observed at low and high magnetic field strength from organic planar heterojunction devices incorporated common phosphorescent host materials of N,N'-dicarbazolyl-3,5-benzene (mCP) or 4,4'-N,N'-dicarbazole-biphenyl (CBP) as an emissive layer. We found that intersystem crossing became stronger with decreasing temperature and that triplet-triplet annihilation (TTA) occurred at room temperature but ceased at low temperature. Analyses of the electroluminescence spectra of these devices and their temperature dependences indicated that the population of exciplex states increased at low temperature, which caused the abnormal behavior of intersystem crossing. Additionally, long lifetime of the excitons within mCP or CBP layer may allow TTA to occur at room temperature, while the reduced population of excitons at low temperature may account for the disappearance of TTA even though the excitons had increased lifetime.

Onset of the Efficiency Droop in GaInN Quantum Well Light-Emitting Diodes under Photoluminescence and Electroluminescence Excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Guan-Bo; Schubert, E. Fred; Cho, Jaehee

2015-08-19

The efficiency of Ga0.87In0.13N/GaN single and multiple quantum well (QW) light-emitting diodes is investigated under photoluminescence (PL) and electroluminescence (EL) excitation. By measuring the laser spot area (knife-edge method) and the absorbance of the GaInN QW (transmittance/reflectance measurements), the PL excitation density can be converted to an equivalent EL excitation density. The EL efficiency droop-onset occurs at an excitation density of 2.08 × 1026 cm–3 s–1 (J = 10 A/cm2), whereas no PL efficiency droop is found for excitation densities as high as 3.11 × 1027 cm–3 s–1 (J = 149 A/cm2). Considering Shockley–Read–Hall, radiative, and Auger recombination and includingmore » carrier leakage shows that the EL efficiency droop is consistent with a reduction of injection efficiency.« less

Green electroluminescence from Tb{sub 4}O{sub 7} films on silicon: Impact excitation of Tb{sup 3+} ions by hot carriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Chen; Jiang, Miaomiao; Zhou, Junwei

2016-02-01

We report on green electroluminescence (EL) due to the intra-4f transitions of the trivalent terbium (Tb{sup 3+}) ions inherent in a Tb{sub 4}O{sub 7} film that is sandwiched between the ITO film and heavily phosphorous- or boron-doped silicon (n{sup +}-Si or p{sup +}-Si) substrate, thus forming the so-called metal-oxide-semiconductor (MOS) device. The onset voltage of such EL is below 10 V. From the current-voltage characteristic and voltage-dependent EL spectra of the aforementioned MOS device, it is derived that the Tb-related green EL results from the impact excitation of Tb{sup 3+} ions by the hot electrons (holes), which stem from the electric-fieldmore » acceleration of the electrons (holes) injected from the n{sup +}-Si (p{sup +}-Si) substrate via the trap-assisted tunneling mechanism.« less

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices

PubMed Central

Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

2016-01-01

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers. PMID:27181337

A multilayered approach of Si/SiO to promote carrier transport in electroluminescence of Si nanocrystals

PubMed Central

2012-01-01

The electroluminescence (EL) and photoluminescence of Si nanocrystals (Si-nc) from multilayered samples of Si/SiO are investigated. Si-nc are formed within Si and SiO layers after furnace annealing. It is found that the presence of Si interlayers creates extra carrier paths for EL emission. A comparative study is further performed on a multilayered Si/SiO sample and a single-layered one with Si and SiO homogeneously mixed. Both samples have the same ratio of Si to O and the same contents of Si and O. The multilayered sample is found to have higher EL intensity, less turn-on voltage, lower resistance, and higher current efficiency than the single-layered one. The results indicate that Si interlayers in Si/SiO may act as carrier channels, which promote carrier transport and enhance the EL emission of Si-nc. PMID:22448989

Temperature tuning from direct to inverted bistable electroluminescence in resonant tunneling diodes

NASA Astrophysics Data System (ADS)

Hartmann, F.; Pfenning, A.; Rebello Sousa Dias, M.; Langer, F.; Höfling, S.; Kamp, M.; Worschech, L.; Castelano, L. K.; Marques, G. E.; Lopez-Richard, V.

2017-10-01

We study the electroluminescence (EL) emission of purely n-doped resonant tunneling diodes in a wide temperature range. The paper demonstrates that the EL originates from impact ionization and radiative recombination in the extended collector region of the tunneling device. Bistable current-voltage response and EL are detected and their respective high and low states are tuned under varying temperature. The bistability of the EL intensity can be switched from direct to inverted with respect to the tunneling current and the optical on/off ratio can be enhanced with increasing temperature. One order of magnitude amplification of the optical on/off ratio can be attained compared to the electrical one. Our observation can be explained by an interplay of moderate peak-to-valley current ratios, large resonance voltages, and electron energy loss mechanisms, and thus, could be applied as an alternative route towards optoelectronic applications of tunneling devices.

GaN for LED applications

NASA Technical Reports Server (NTRS)

Pankove, J. I.

1973-01-01

In order to improve the synthesis of GaN the effect of various growth and doping parameters has been studied. Although Be, Li, Mg, and Dy can be used to overcompensate native donors, the most interesting acceptor element is Zn. The emission spectrum and the luminescence efficiency depend on the growth temperature (below 800 C), on the partial pressure of the doping impurity, and on the duration of growth. Blue-green electroluminescence with a power efficiency of 0.1 percent and a brightness of 850 fL (at 0.6 mA and 22.5 V) was obtained. Some diodes allow the color of the emitted light to change by reversing the polarity of the bias. Continuous operation of a diode over a period of 5 months showed no evidence of degradation. The luminescence properties of ion-implanted GaN were studied. Delay effects were found in the electroluminescence of diodes, although, with a dc bias, a 70-MHz modulation was possible.

Inorganic Halide Perovskites for Efficient Light-Emitting Diodes.

PubMed

Yantara, Natalia; Bhaumik, Saikat; Yan, Fei; Sabba, Dharani; Dewi, Herlina A; Mathews, Nripan; Boix, Pablo P; Demir, Hilmi Volkan; Mhaisalkar, Subodh

2015-11-05

Lead-halide perovskites have transcended photovoltaics. Perovskite light-emitting diodes (PeLEDs) emerge as a new field to leverage on these fascinating semiconductors. Here, we report the first use of completely inorganic CsPbBr3 thin films for enhanced light emission through controlled modulation of the trap density by varying the CsBr-PbBr2 precursor concentration. Although pure CsPbBr3 films can be deposited from equimolar CsBr-PbBr2 and CsBr-rich solutions, strikingly narrow emission line (17 nm), accompanied by elongated radiative lifetimes (3.9 ns) and increased photoluminescence quantum yield (16%), was achieved with the latter. This is translated into the enhanced performance of the resulting PeLED devices, with lower turn-on voltage (3 V), narrow electroluminescence spectra (18 nm) and higher electroluminescence intensity (407 Cd/m(2)) achieved from the CsBr-rich solutions.

Electroluminescence of ZnO nanocrystal in sputtered ZnO-SiO2 nanocomposite light-emitting devices.

PubMed

Chen, Jiun-Ting; Lai, Wei-Chih; Chen, Chi-Heng; Yang, Ya-Yu; Sheu, Jinn-Kong; Lai, Li-Wen

2011-06-06

We have demonstrated the electroluminescence (EL) of Ga:ZnO/i-ZnO-SiO2 nanocomposite/p-GaN n-i-p heterostructure light-emitting devices (LEDs). ZnO nano-clusters with sizes distributing from 2 to 7nm were found inside the co-sputtered i-ZnO-SiO2 nanocomposite layer under the observation of high-resolution transparent electron microscope. A clear UV EL at 376 nm from i-ZnO-SiO2 nanocomposite in these p-i-n heterostructure LEDs was observed under the forward current of 9 mA. The EL emission peak at 376 and 427nm of the Ga:ZnO/i-ZnO-SiO2 nanocomposite/p-GaN n-i-p heterostructure LEDs were attributed to the radiative recombination from the ZnO clusters and the Mg acceptor levels in the p-GaN layer, respectively.

Improvement of UV electroluminescence of n-ZnO/p-GaN heterojunction LED by ZnS interlayer.

PubMed

Zhang, Lichun; Li, Qingshan; Shang, Liang; Wang, Feifei; Qu, Chong; Zhao, Fengzhou

2013-07-15

n-ZnO/p-GaN heterojunction light emitting diodes with different interfacial layers were fabricated by pulsed laser deposition. The electroluminescence (EL) spectra of the n-ZnO/p-GaN diodes display a broad blue-violet emission centered at 430 nm, whereas the n-ZnO/ZnS/p-GaN and n-ZnO/AlN/p-GaN devices exhibit ultraviolet (UV) emission. Compared with the AlN interlayer, which is blocking both electron and hole at hetero-interface, the utilization of ZnS as intermediate layer can lower the barrier height for holes and keep an effective blocking for electron. Thus, an improved UV EL intensity and a low turn-on voltage (~5V) were obtained. The results were studied by peak-deconvolution with Gaussian functions and were discussed using the band diagram of heterojunctions.

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices.

PubMed

Lu, Junfeng; Shi, Zengliang; Wang, Yueyue; Lin, Yi; Zhu, Qiuxiang; Tian, Zhengshan; Dai, Jun; Wang, Shufeng; Xu, Chunxiang

2016-05-16

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers.

Mid-infrared electroluminescence from InAs type-I quantum wells grown on InAsP/InP metamorphic buffers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Daehwan, E-mail: daehwan.jung@yale.edu; Larry Lee, Minjoo; Yu, Lan

We report room-temperature (RT) electroluminescence (EL) from InAs/InAs{sub x}P{sub 1−x} quantum well (QW) light-emitting diodes (LEDs) over a wide wavelength range of 2.50–2.94 μm. We demonstrate the ability to accurately design strained InAs QW emission wavelengths while maintaining low threading dislocation density, coherent QW interfaces, and high EL intensity. Investigation of the optical properties of the LEDs grown on different InAs{sub x}P{sub 1−x} metamorphic buffers showed higher EL intensity and lower thermal quenching for QWs with higher barriers and stronger carrier confinement. Strong RT EL intensity from LEDs with narrow full-width at half-maximum shows future potential for InAs QW mid-infrared lasermore » diodes on InAsP/InP.« less

Electrical investigations of hybrid OLED microcavity structures with novel encapsulation methods

NASA Astrophysics Data System (ADS)

Meister, Stefan; Brückner, Robert; Fröb, Hartmut; Leo, Karl

2016-04-01

An electrical driven organic solid state laser is a very challenging goal which is so far well beyond reach. As a step towards realization, we monolithically implemented an Organic Light Emitting Diode (OLED) into a dielectric, high quality microcavity (MC) consisting of two Distributed Bragg Reectors (DBR). In order to account for an optimal optical operation, the OLED structure has to be adapted. Furthermore, we aim to excite the device not only electrically but optically as well. Different OLED structures with an emission layer consisting of Alq3:DCM (2 wt%) were investigated. The External Quantum Efficiencies (EQE) of this hybrid structures are in the range of 1-2 %, as expected for this material combination. Including metal layers into a MC is complicated and has a huge impact on the device performance. Using Transfer-Matrix-Algorithm (TMA) simulations, the best positions for the metal electrodes are determined. First, the electroluminescence (EL) of the adjusted OLED structure on top of a DBR is measured under nitrogen atmosphere. The modes showed quality factors of Q = 60. After the deposition of the top DBR, the EL is measured again and the quality factors increased up to Q = 600. Considering the two 25-nm-thick-silver contacts a Q-factor of 600 is very high. The realization of a suitable encapsulation method is important. Two approaches were successfully tested. The first method is based on the substitution of a DBR layer with a layer produced via Atomic Layer Deposition (ALD). The second method uses a 0.15-mm-thick cover glass glued on top of the DBR with a 0.23-μm-thick single-component glue layer. Due to the working encapsulation, it is possible to investigate the sample under ambient conditions.

Discernment of Possible Organic Magnetic Field Effect Mechanisms Using Polymer Light-Emitting Electrochemical Cells

NASA Astrophysics Data System (ADS)

Geng, R.; Subedi, R. C.; Liang, S.; Nguyen, T. D.

2014-07-01

We report studies of magnetic field effect (MFE) in polymer light-emitting electrochemical cells (PLEC) using the "super-yellow" poly-(phenylene vynilene) (SY-PPV) polymer in vertical and planar device configurations. The purpose is to discern the existing MFE mechanisms in organic light emitting diodes (OLEDs) where the current and electroluminescence are strongly modulated by a small applied magnetic field. In particular, we investigate the mutual relationship between magneto-conductance (MC) and magneto-electroluminescence (MEL) by studying the role of polaron density dissociated from polaron pairs (PP) on these magnetic responses. In general, the dissociated polaron density is determined by the PP dissociation rate and the PP density. For the planar PLEC, which possesses a small dissociation rate, we observe small and negative MC at all applied voltages regardless of the emission intensity, while MEL becomes positive when electroluminescence quantum efficiency increases. The MC has a much narrower width than the MEL, indicating that the MC and MEL do not share a common origin. However, MC reverses and has the same width as MEL when the device is exposed to a threshold laser power. For the vertical PLEC, characterized by a large dissociation rate, MC and MEL are positive and have the same width. We discuss the results using the existing MFE mechanism in OLEDs. We show that the PP model can explain the positive MEL and MC, while the negative MC can be explained by the bipolaron model. Finally, we present a possibility to complete an all-organic PLEC magnetic sensor by using an inkjet printer.

InGaN Light-Emitting Diodes with an Embedded Nanoporous GaN Distributed Bragg Reflectors.

PubMed

Shiu, Guo-Yi; Chen, Kuei-Ting; Fan, Feng-Hsu; Huang, Kun-Pin; Hsu, Wei-Ju; Dai, Jing-Jie; Lai, Chun-Feng; Lin, Chia-Feng

2016-07-01

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n(+)-GaN) in the 12-period n(+)-GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.3 nm with a 57 nm linewidth and a 97.1% peak reflectivity. The effective cavity length (6.0λ), the effective penetration depth (278 nm) in the nanoporous DBR structure, and InGaN active layer matching to Fabry-Pérot mode order 12 were observed in the far-field photoluminescence radiative spectra. High electroluminescence emission intensity and line-width narrowing effect were measured in the DBR-LED compared with the non-treated LED structure. Non-linear emission intensity and line-width reducing effect, from 11.8 nm to 0.73 nm, were observed by increasing the laser excited power. Resonant cavity effect was observed in the InGaN LED with bottom nanoporous-DBR and top GaN/air interface.

InGaN Light-Emitting Diodes with an Embedded Nanoporous GaN Distributed Bragg Reflectors

PubMed Central

Shiu, Guo-Yi; Chen, Kuei-Ting; Fan, Feng-Hsu; Huang, Kun-Pin; Hsu, Wei-Ju; Dai, Jing-Jie; Lai, Chun-Feng; Lin, Chia-Feng

2016-01-01

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n+-GaN) in the 12-period n+-GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.3 nm with a 57 nm linewidth and a 97.1% peak reflectivity. The effective cavity length (6.0λ), the effective penetration depth (278 nm) in the nanoporous DBR structure, and InGaN active layer matching to Fabry-Pérot mode order 12 were observed in the far-field photoluminescence radiative spectra. High electroluminescence emission intensity and line-width narrowing effect were measured in the DBR-LED compared with the non-treated LED structure. Non-linear emission intensity and line-width reducing effect, from 11.8 nm to 0.73 nm, were observed by increasing the laser excited power. Resonant cavity effect was observed in the InGaN LED with bottom nanoporous-DBR and top GaN/air interface. PMID:27363290

Fabrication of a nano-cone array on a p-GaN surface for enhanced light extraction efficiency from GaN-based tunable wavelength LEDs.

PubMed

Soh, C B; Wang, B; Chua, S J; Lin, Vivian K X; Tan, Rayson J N; Tripathy, S

2008-10-08

We report on the fabrication of a nano-cone structured p-GaN surface for enhanced light extraction from tunable wavelength light emitting diodes (LEDs). Prior to p-contact metallization, self-assembled colloidal particles are deposited and used as a mask for plasma etching to create nano-cone structures on the p-GaN layer of LEDs. A well-defined periodic nano-cone array, with an average cone diameter of 300 nm and height of 150 nm, is generated on the p-GaN surface. The photoluminescence emission intensity recorded from the regions with the nano-cone array is increased by two times as compared to LEDs without surface patterning. The light output power from the LEDs with surface nano-cones shows significantly higher electroluminescence intensity at an injection current of 70 mA. This is due to the internal multiple scattering of light from the nano-cone sidewalls. Furthermore, we have shown that with an incorporation of InGaN nanostructures in the quantum well, the wavelength of these surface-patterned LEDs can be tuned from 517 to 488 nm with an increase in the injection current. This methodology may serve as a practical approach to increase the light extraction efficiency from wavelength tunable LEDs.

A room-temperature-operated Si LED with β-FeSi2 nanocrystals in the active layer: μW emission power at 1.5 μm

NASA Astrophysics Data System (ADS)

Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Balagan, S. A.; Dotsenko, S. A.; Galkin, K. N.; Galkin, N. G.; Shamirzaev, T. S.; Gutakovskii, A. K.; Latyshev, A. V.; Iinuma, M.; Terai, Y.

2017-03-01

This article describes the development of an Si-based light-emitting diode with β-FeSi2 nanocrystals embedded in the active layer. Favorable epitaxial conditions allow us to obtain a direct band gap type-I band alignment Si/β-FeSi2 nanocrystals/Si heterostructure with optical transition at a wavelength range of 1500-1550 nm at room temperature. Transmission electron microscopy data reveal strained, defect-free β-FeSi2 nanocrystals of diameter 6 and 25 nm embedded in the Si matrix. Intense electroluminescence was observed at a pumping current density as low as 0.7 A/cm2. The device reached an optical emission power of up to 25 μW at 9 A/cm2 with an external quantum efficiency of 0.009%. Watt-Ampere characteristic linearity suggests that the optical power margin of the light-emitting diode has not been exhausted. Band structure calculations explain the luminescence as being mainly due to radiative recombination in the large β-FeSi2 nanocrystals resulting from the realization of an indirect-to-direct band gap electronic configuration transformation arising from a favorable deformation of nanocrystals. The direct band gap structure and the measured short decay time of the luminescence of several tens of ns give rise to a fast operation speed for the device. Thus a method for developing a silicon-based photonic integrated circuit, combining complementary metal-oxide-semiconductor technology functionality and near-infrared light emission, is reported here.

Symmetry-breaking charge transfer in a zinc chlorodipyrrin acceptor for high open circuit voltage organic photovoltaics.

PubMed

Bartynski, Andrew N; Gruber, Mark; Das, Saptaparna; Rangan, Sylvie; Mollinger, Sonya; Trinh, Cong; Bradforth, Stephen E; Vandewal, Koen; Salleo, Alberto; Bartynski, Robert A; Bruetting, Wolfgang; Thompson, Mark E

2015-04-29

Low open-circuit voltages significantly limit the power conversion efficiency of organic photovoltaic devices. Typical strategies to enhance the open-circuit voltage involve tuning the HOMO and LUMO positions of the donor (D) and acceptor (A), respectively, to increase the interfacial energy gap or to tailor the donor or acceptor structure at the D/A interface. Here, we present an alternative approach to improve the open-circuit voltage through the use of a zinc chlorodipyrrin, ZCl [bis(dodecachloro-5-mesityldipyrrinato)zinc], as an acceptor, which undergoes symmetry-breaking charge transfer (CT) at the donor/acceptor interface. DBP/ZCl cells exhibit open-circuit voltages of 1.33 V compared to 0.88 V for analogous tetraphenyldibenzoperyflanthrene (DBP)/C60-based devices. Charge transfer state energies measured by Fourier-transform photocurrent spectroscopy and electroluminescence show that C60 forms a CT state of 1.45 ± 0.05 eV in a DBP/C60-based organic photovoltaic device, while ZCl as acceptor gives a CT state energy of 1.70 ± 0.05 eV in the corresponding device structure. In the ZCl device this results in an energetic loss between E(CT) and qV(OC) of 0.37 eV, substantially less than the 0.6 eV typically observed for organic systems and equal to the recombination losses seen in high-efficiency Si and GaAs devices. The substantial increase in open-circuit voltage and reduction in recombination losses for devices utilizing ZCl demonstrate the great promise of symmetry-breaking charge transfer in organic photovoltaic devices.

Aromatically C6- and C9-Substituted Phenanthro[9,10-d]imidazole Blue Fluorophores: Structure-Property Relationship and Electroluminescent Application.

PubMed

Chen, Wen-Cheng; Yuan, Yi; Xiong, Yuan; Rogach, Andrey L; Tong, Qing-Xiao; Lee, Chun-Sing

2017-08-09

In this study, a series of aromatically substituted phenanthro[9,10-d]imidazole (PI) fluorophores at C6 and C9 (no. 6 and 9 carbon atoms) have been synthesized and systematically characterized by theoretical, thermal, photophysical, electrochemical, and electroluminescent (EL) studies. C6 and C9 modifications have positive influences on the thermal properties of the new materials. Theoretical calculations suggest that the C6 and the C9 positions of PI are electronically different. Theoretical and experimental evidences of intramolecular charge transfer (ICT) between two identical moieties attaching to the C6 and the C9 positions are observed. Photophysical properties of the fluorophores are greatly influenced by size and conjugation extent of the substituents as well as linking steric hindrance. It is found that the C6 and C9 positions afford moderate conjugated extension compared to the C2 modification. Moreover, ICT characteristics of the new fluorophores increase as the size of the substituted aromatic group, and are partially influenced by steric hindrance, with the anthracene and the pyrene derivatives having the strongest ICT excited properties. EL performances of the fluorophores were evaluated as host emitters or dopants in organic light-emitting devices (OLEDs). Most of the devices showed significantly improved efficiencies compared to the OLED using the nonmodified emitter. Among all the devices, a 5 wt % TPI-Py doped device exhibited excellent performances with an external quantum efficiency >5% at 1000 cd/m 2 and a deep-blue color index of (0.155, 0.065), which are comparable to the most advanced deep-blue devices. Our study can give useful information for designing C6/C9-modificated PI fluorophores and provide an efficient approach for constructing high-performance deep-blue OLEDs.

Electroluminescence color tuning between green and red from metal-oxide-semiconductor devices fabricated by spin-coating of rare-earth (terbium + europium) organic compounds on silicon

NASA Astrophysics Data System (ADS)

Matsuda, Toshihiro; Hattori, Fumihiro; Iwata, Hideyuki; Ohzone, Takashi

2018-04-01

Color tunable electroluminescence (EL) from metal-oxide-semiconductor devices with the rare-earth elements Tb and Eu is reported. Organic compound liquid sources of (Tb + Ba) and Eu with various Eu/Tb ratios from 0.001 to 0.4 were spin-coated on an n+-Si substrate and annealed to form an oxide insulator layer. The EL spectra had only peaks corresponding to the intrashell Tb3+/Eu3+ transitions in the spectral range from green to red, and the intensity ratio of the peaks was appropriately tuned using the appropriate Eu/Tb ratios in liquid sources. Consequently, the EL emission colors linearly changed from yellowish green to yellowish orange and eventually to reddish orange on the CIE chromaticity diagram. The gate current +I G current also affected the EL colors for the medium-Eu/Tb-ratio device. The structure of the surface insulator films analyzed by cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS) has four layers, namely, (Tb4O7 + Eu2O3), [Tb4O7 + Eu2O3 + (Tb/Eu/Ba)SiO x ], (Tb/Eu/Ba)SiO x , and SiO x -rich oxide. The EL mechanism proposed is that electrons injected from the Si substrate into the SiO x -rich oxide and Tb/Eu/Ba-silicate layers become hot electrons accelerated in a high electric field, and then these hot electrons excite Tb3+ and Eu3+ ions in the Tb4O7/Eu2O3 layers resulting in EL emission from Tb3+ and Eu3+ intrashell transitions.

Physics Notes.

ERIC Educational Resources Information Center

School Science Review, 1979

1979-01-01

Included is information regarding: fabrication of light emitting diodes, their operation as semiconductors, and an experiment demonstrating electroluminescence; experimenting with Random Access Memory (RAM) circuits; demonstrating Coriolis effect; measuring the diameter of an electron beam, E.H.T. meters; launching a trolley by catapult; a "random…

InGaN pn-junctions grown by PA-MBE: Material characterization and fabrication of nanocolumn electroluminescent devices

NASA Astrophysics Data System (ADS)

Gherasoiu, I.; Yu, K. M.; Reichertz, L.; Walukiewicz, W.

2015-09-01

PN junctions are basic building blocks of many electronic devices and their performance depends on the structural properties of the component layers and on the type and the amount of the doping impurities incorporated. Magnesium is the common p-type dopant for nitride semiconductors while silicon and more recently germanium are the n-dopants of choice. In this paper, therefore we analyze the quantitative limits for Mg and Ge incorporation on GaN and InGaN with high In content. We also discuss the challenges posed by the growth and characterization of InGaN pn-junctions and we discuss the properties of large area, long wavelength nanocolumn LEDs grown on silicon (1 1 1) by PA-MBE.

Effects of interfacial stability between electron transporting layer and cathode on the degradation process of organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Chu, Ta-Ya; Lee, Yong-Han; Song, Ok-Keun

2007-11-01

The authors have demonstrated that the increase of electron injection barrier height between tris(8-hydroxyquinoline)aluminum (Alq3) and LiF /Al cathode is one of the most critical parameters to determine the reliability of organic light-emitting diode with the typical structure of indium tin oxide/N ,N'-bis(naphthalen-1-yl)-N ,N'-bis(phenyl) benzidine/Alq3/LiF /Al. The electrical properties of several devices (hole only, electron only, and integrated double-layered devices) have been measured in the function of operating time to analyze the bulk and interface property changes. Bulk properties of trap energy and mobility in an organic layer have been estimated by using trap-charge-limited currents and transient electroluminescence measurements.

Progress in Emission Efficiency of Organic Light-Emitting Diodes: Basic Understanding and Its Technical Application

NASA Astrophysics Data System (ADS)

Tsutsui, Tetsuo; Takada, Noriyuki

2013-11-01

The technical history of when and how the basic understanding of the emission efficiency of organic light-emitting diodes (OLEDs) was established over the last 50 years is described. At first, our understanding of emission efficiency in single-crystal and thin-film electroluminescence (EL) devices in the early stages before the Eastman-Kodak breakthrough, that is, the introduction of the concept of multilayer structures, is examined. Then our contemplation travels from the Eastman-Kodak breakthrough towards the presently widely accepted concept of emission efficiency. The essential issues concerning the emission efficiency of OLEDs are summarized to help readers to obtain a common understanding of OLED efficiency problems, and detailed discussions on the primary factors that determine emission efficiency are given. Finally, some comments on remaining issues are presented.

Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Cho, Himchan; Jeong, Su-Hun; Park, Min-Ho; Kim, Young-Hoon; Wolf, Christoph; Lee, Chang-Lyoul; Heo, Jin Hyuck; Sadhanala, Aditya; Myoung, NoSoung; Yoo, Seunghyup; Im, Sang Hyuk; Friend, Richard H.; Lee, Tae-Woo

2015-12-01

Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.

Organic Light Emitting Diodes with Opal Photonic Crystal Layer and Carbon Nanotube Anode

NASA Astrophysics Data System (ADS)

Ovalle Robles, Raquel; Del Rocio Nava, Maria; Williams, Christopher; Zhang, Mei; Fang, Shaoli; Lee, Sergey; Baughman, Ray; Zakhidov, Anvar

2007-03-01

We report electroluminescence intensity and spectral changes in light emission from organic light emitting diode (OLEDs) structures, which have thin transparent films of opal photonic crystal (PC). The anode in such PC-OLED is laminated on opal layer from free standing optically transparent multiwall carbon nanotubes (T-CNT) sheets made by dry spinning from CVD grown forests. Silica and polystyrene opal films were grown on glass substrates by vertical sedimentation in colloids in thermal baths and the particle size of opal spheres ranges from 300 nm to 450 nm. The use of T-CNTs, (coated by PEDOT-PSS to avoid shorting) as hole injector, allows to eliminate the use of vacuum deposition of metals and permits to achieve tunneling hole injection regime from CNT tips into Alq^3 emission layer

Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Liping; Chen, Jiangshan; Ma, Dongge, E-mail: mdg1014@ciac.ac.cn

2015-11-07

We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency,more » and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m{sup 2} luminance. The critical current density is as high as 210 mA/cm{sup 2}. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.« less

Emission of blue light from hydrogenated amorphous silicon carbide

NASA Astrophysics Data System (ADS)

Nevin, W. A.; Yamagishi, H.; Yamaguchi, M.; Tawada, Y.

1994-04-01

THE development of new electroluminescent materials is of current technological interest for use in flat-screen full-colour displays1. For such applications, amorphous inorganic semiconductors appear particularly promising, in view of the ease with which uniform films with good mechanical and electronic properties can be deposited over large areas2. Luminescence has been reported1 in the red-green part of the spectrum from amorphous silicon carbide prepared from gas-phase mixtures of silane and a carbon-containing species (usually methane or ethylene). But it is not possible to achieve blue luminescence by this approach. Here we show that the use of an aromatic species-xylene-as the source of carbon during deposition results in a form of amorphous silicon carbide that exhibits strong blue luminescence. The underlying structure of this material seems to be an unusual combination of an inorganic silicon carbide lattice with a substantial 'organic' π-conjugated carbon system, the latter dominating the emission properties. Moreover, the material can be readily doped with an electron acceptor in a manner similar to organic semiconductors3, and might therefore find applications as a conductivity- or colour-based chemical sensor.

Electrically and Optically Readable Light Emitting Memories

PubMed Central

Chang, Che-Wei; Tan, Wei-Chun; Lu, Meng-Lin; Pan, Tai-Chun; Yang, Ying-Jay; Chen, Yang-Fang

2014-01-01

Electrochemical metallization memories based on redox-induced resistance switching have been considered as the next-generation electronic storage devices. However, the electronic signals suffer from the interconnect delay and the limited reading speed, which are the major obstacles for memory performance. To solve this problem, here we demonstrate the first attempt of light-emitting memory (LEM) that uses SiO2 as the resistive switching material in tandem with graphene-insulator-semiconductor (GIS) light-emitting diode (LED). By utilizing the excellent properties of graphene, such as high conductivity, high robustness and high transparency, our proposed LEM enables data communication via electronic and optical signals simultaneously. Both the bistable light-emission state and the resistance switching properties can be attributed to the conducting filament mechanism. Moreover, on the analysis of current-voltage characteristics, we further confirm that the electroluminescence signal originates from the carrier tunneling, which is quite different from the standard p-n junction model. We stress here that the newly developed LEM device possesses a simple structure with mature fabrication processes, which integrates advantages of all composed materials and can be extended to many other material systems. It should be able to attract academic interest as well as stimulate industrial application. PMID:24894723

Effect of Annealing Time of YAG:Ce3+ Phosphor on White Light Chromaticity Values

NASA Astrophysics Data System (ADS)

Abd, Husnen R.; Hassan, Z.; Ahmed, Naser M.; Almessiere, Munirah Abdullah; Omar, A. F.; Alsultany, Forat H.; Sabah, Fayroz A.; Osman, Ummu Shuhada

2018-02-01

Yttrium and aluminium nitrate phosphors doped with cerium nitrate and mixed with urea (fuel) are prepared by using microwave-induced combustion synthesis according to the formula Y(3-0.06)Al5O12:0.06Ce3+ (YAG:Ce3+) to produce white light emitting diodes by conversion from blue indium gallium nitride-light emitting diode chips. The sintering time with fixed temperature (1050°C) for phosphor powder was optimized and found to be 5 h. The crystallinity, structure, chemical composition, luminescent properties with varying currents densities and chromaticity were characterized by x-ray diffraction, field emission-scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, photoluminescence emission, electroluminescence and standard CIE 1931 chromaticity diagram, respectively. The energy levels of Ce3+ in YAG were discussed based on its absorption and excitation spectra. The results show that the obtained YAG:Ce3+ phosphor sintered for 5 h has good crystallinity with pure phase, low agglomerate with spherical shaped particles and strong yellow emission, offering cool-white LED with tuneable correlated color temperature and a good color rendering index compared to those prepared by sintering for 2 h and as-prepared phosphor powders.

Design and characterization of free-running InGaAsP single-photon detector with active-quenching technique

NASA Astrophysics Data System (ADS)

Liu, Junliang; Zhang, Tingfa; Li, Yongfu; Ding, Lei; Tao, Junchao; Wang, Ying; Wang, Qingpu; Fang, Jiaxiong

2017-07-01

A free-running single-photon detector for 1.06 μm wavelength based on an InGaAsP/InP single-photon avalanche diode is presented. The detector incorporates an ultra-fast active-quenching technique to greatly lessen the afterpulsing effects. An improved method for avalanche characterization using electroluminescence is proposed, and the performance of the detector is evaluated. The number of avalanche carriers is as low as 1.68 ×106 , resulting in a low total afterpulse probability of 4% at 233 K, 10% detection efficiency, and 1 μs hold-off time.

Triplet exciton diffusion in fac-tris(2-phenylpyridine) iridium(III)-cored electroluminescent dendrimers

NASA Astrophysics Data System (ADS)

Namdas, Ebinazar B.; Ruseckas, Arvydas; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2005-02-01

We have studied triplet-triplet annihilation in neat films of electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3]-cored dendrimers containing phenylene- and carbazole-based dendrons with 2-ethylhexyloxy surface groups using time-resolved photoluminescence. From measured annihilation rates, the limiting current densities above which annihilation would dominate in dendrimer light-emitting devices are found to be >1A/cm2. The triplet exciton diffusion length varies in the range of 2-10 nm depending on the dendron size. The distance dependence of the nearest-neighbor hopping rate shows that energy transfer is dominated by the exchange mechanism.

Visual feedback in stuttering therapy

NASA Astrophysics Data System (ADS)

Smolka, Elzbieta

1997-02-01

The aim of this paper is to present the results concerning the influence of visual echo and reverberation on the speech process of stutterers. Visual stimuli along with the influence of acoustic and visual-acoustic stimuli have been compared. Following this the methods of implementing visual feedback with the aid of electroluminescent diodes directed by speech signals have been presented. The concept of a computerized visual echo based on the acoustic recognition of Polish syllabic vowels has been also presented. All the research nd trials carried out at our center, aside from cognitive aims, generally aim at the development of new speech correctors to be utilized in stuttering therapy.

Effect of horizontal molecular orientation on triplet-exciton diffusion in amorphous organic films

NASA Astrophysics Data System (ADS)

Sawabe, T.; Takasu, I.; Yonehara, T.; Ono, T.; Yoshida, J.; Enomoto, S.; Amemiya, I.; Adachi, C.

2012-09-01

Triplet harvesting is a candidate technology for highly efficient and long-life white OLEDs, where green or red phosphorescent emitters are activated by the triplet-excitons diffused from blue fluorescent emitters. We examined two oxadiazole-based electron transport materials with different horizontal molecular orientation as a triplet-exciton diffusion layer (TDL) in triplet-harvesting OLEDs. The device characteristics and the transient electroluminescent analyses of the red phosphorescent emitter showed that the triplet-exciton diffusion was more effective in the highly oriented TDL. The results are ascribed to the strong orbital overlap between the oriented molecules, which provides rapid electron exchange (Dexter energy transfer) in the TDL.

Realizing Rec. 2020 color gamut with quantum dot displays.

PubMed

Zhu, Ruidong; Luo, Zhenyue; Chen, Haiwei; Dong, Yajie; Wu, Shin-Tson

2015-09-07

We analyze how to realize Rec. 2020 wide color gamut with quantum dots. For photoluminescence, our simulation indicates that we are able to achieve over 97% of the Rec. 2020 standard with quantum dots by optimizing the emission spectra and redesigning the color filters. For electroluminescence, by optimizing the emission spectra of quantum dots is adequate to render over 97% of the Rec. 2020 standard. We also analyze the efficiency and angular performance of these devices, and then compare results with LCDs using green and red phosphors-based LED backlight. Our results indicate that quantum dot display is an outstanding candidate for achieving wide color gamut and high optical efficiency.

Ag/SiO2 nanoparticle-based plasmonic enhancement of light output in nanohole-patterned InGaN/GaN blue light-emitting diodes

NASA Astrophysics Data System (ADS)

Yun, Jin-Hyeon; Kim, Kyu Cheol; Yu, Yeon Tae; Yang, Jin Kyu; Polyakov, Alexander Y.; Lee, In-Hwan

2017-10-01

Improved performance of blue InGaN/GaN light-emitting diodes (LEDs) is realized as a result of fabricating nanohole patterns in the p-GaN contact layer and embedding the nanoholes with Ag/SiO2 nanoparticles to generate localized surface plasmons (LSPs). Good matching between LSP resonance energy and LED emission energy together with the close proximity between nanoparticles and the active region results in strong coupling between them. Consequently, the photoluminescence and electroluminescence intensities increased to 1.75 and 1.10, respectively, compared with nanohole patterned reference LEDs.

Disorder induced spin coherence in polyfluorene thin film semiconductors

NASA Astrophysics Data System (ADS)

Miller, Richard G.; van Schooten, Kipp; Malissa, Hans; Waters, David P.; Lupton, John M.; Boehme, Christoph

2014-03-01

Charge carrier spins in polymeric organic semiconductors significantly influence magneto-optoelectronic properties of these materials. In particular, spin relaxation times influence magnetoresistance and electroluminescence. We have studied the role of structural and electronic disorder in polaron spin-relaxation times. As a model polymer, we used polyfluorene, which can exist in two distinct morphologies: an amorphous (glassy) and an ordered (beta) phase. The phases can be controlled in thin films by preparation parameters and verified by photoluminescence spectroscopy. We conducted pulsed electrically detected magnetic resonance (pEDMR) measurements to determine spin-dephasing times by transient current measurements under bipolar charge carrier injection conditions and a forward bias. The measurements showed that, contrary to intuition, spin-dephasing times increase with material disorder. We attribute this behavior to a reduction in hyperfine field strength for carriers in the glassy phase due to increased structural disorder in the hydrogenated side chains, leading to longer spin coherence times. We acknowledge support by the Department of Energy, Office of Basic Energy Sciences under Award #DE-SC0000909.

Evidence and mechanism of efficient thermally activated delayed fluorescence promoted by delocalized excited states

PubMed Central

Hosokai, Takuya; Matsuzaki, Hiroyuki; Nakanotani, Hajime; Tokumaru, Katsumi; Tsutsui, Tetsuo; Furube, Akihiro; Nasu, Keirou; Nomura, Hiroko; Yahiro, Masayuki; Adachi, Chihaya

2017-01-01

The design of organic compounds with nearly no gap between the first excited singlet (S1) and triplet (T1) states has been demonstrated to result in an efficient spin-flip transition from the T1 to S1 state, that is, reverse intersystem crossing (RISC), and facilitate light emission as thermally activated delayed fluorescence (TADF). However, many TADF molecules have shown that a relatively appreciable energy difference between the S1 and T1 states (~0.2 eV) could also result in a high RISC rate. We revealed from a comprehensive study of optical properties of TADF molecules that the formation of delocalized states is the key to efficient RISC and identified a chemical template for these materials. In addition, simple structural confinement further enhances RISC by suppressing structural relaxation in the triplet states. Our findings aid in designing advanced organic molecules with a high rate of RISC and, thus, achieving the maximum theoretical electroluminescence efficiency in organic light-emitting diodes. PMID:28508081

Boron Arsenide and Boron Phosphide for High Temperature and Luminescent Devices. [semiconductor devices - crystal growth/crystal structure

NASA Technical Reports Server (NTRS)

Chu, T. L.

1975-01-01

The crystal growth of boron arsenide and boron phosphide in the form of bulk crystals and epitaxial layers on suitable substrates is discussed. The physical, chemical, and electrical properties of the crystals and epitaxial layers are examined. Bulk crystals of boron arsenide were prepared by the chemical transport technique, and their carrier concentration and Hall mobility were measured. The growth of boron arsenide crystals from high temperature solutions was attempted without success. Bulk crystals of boron phosphide were also prepared by chemical transport and solution growth techniques. Techniques required for the fabrication of boron phosphide devices such as junction shaping, diffusion, and contact formation were investigated. Alloying techniques were developed for the formation of low-resistance ohmic contacts to boron phosphide. Four types of boron phosphide devices were fabricated: (1) metal-insulator-boron phosphide structures, (2) Schottky barriers; (3) boron phosphide-silicon carbide heterojunctions; and (4) p-n homojunctions. Easily visible red electroluminescence was observed from both epitaxial and solution grown p-n junctions.

Multilevel organization in hybrid thin films for optoelectronic applications.

PubMed

Vohra, Varun; Bolognesi, Alberto; Calzaferri, Gion; Botta, Chiara

2009-10-20

In this work we report two simple approaches to prepare hybrid thin films displaying a high concentration of zeolite crystals that could be used as active layers in optoelectronic devices. In the first approach, in order to organize nanodimensional zeolite crystals of 40 nm diameter in an electroactive environment, we chemically modify their external surface and play on the hydrophilic/hydrophobic forces. We obtain inorganic nanocrystals that self-organize in honeycomb electroluminescent polymer structures obtained by breath figure formation. The different functionalizations of the zeolite surface result in different organizations inside the cavities of the polymeric structure. The second approach involving soft-litography techniques allows one to arrange single dye-loaded zeolite L crystals of 800 nm of length by mechanical loading into the nanocavities of a conjugated polymer. Both techniques result in the formation of thin hybrid films displaying three levels of organization: organization of the dye molecules inside the zeolite nanochannels, organization of the zeolite crystals inside the polymer cavities, and micro- or nanostructuration of the polymer.

Effects of Various Parameters on Structural and Optical Properties of CBD-Grown ZnS Thin Films: A Review

NASA Astrophysics Data System (ADS)

Sinha, Tarkeshwar; Lilhare, Devjyoti; Khare, Ayush

2018-02-01

Zinc sulfide (ZnS) thin films deposited by chemical bath deposition (CBD) technique have proved their capability in a wide area of applications including electroluminescent and display devices, solar cells, sensors, and field emitters. These semiconducting thin films have attracted a much attention from the scientific community for industrial and research purposes. In this article, we provide a comprehensive review on the effect of various parameters on various properties of CBD-grown ZnS films. In the first part, we discuss the historical background of ZnS, its basic properties, and the advantages of the CBD technique. Detailed discussions on the film growth, structural and optical properties of ZnS thin films affected by various parameters, such as bath temperature and concentration, deposition time, stirring speed, complexing agents, pH value, humidity in the environment, and annealing conditions, are also presented. In later sections, brief information about the recent studies and findings is also added to explore the scope of research work in this field.

Electronic structure of the polymer-cathode interface of an organic electroluminescent device investigated using operando hard x-ray photoelectron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ikeuchi, J.; Hamamatsu, H.; Miyamoto, T.

2015-08-28

The electronic structure of a polymer-cathode interface of an operating organic light-emitting diode (OLED) was directly investigated using hard X-ray photoelectron spectroscopy (HAXPES). The potential distribution profile of the light-emitting copolymer layer as a function of the depth under the Al/Ba cathode layer in the OLED depended on the bias voltage. We found that band bending occurred in the copolymer of 9,9-dioctylfluorene (50%) and N-(4-(2-butyl)-phenyl)diphenylamine (F8-PFB) layer near the cathode at 0 V bias, while a linear potential distribution formed in the F8-PFB when a bias voltage was applied to the OLED. Direct observation of the built-in potential and that bandmore » bending formed in the F8-PFB layer in the operating OLED suggested that charges moved in the F8-PFB layer before electron injection from the cathode.« less

Size-controlled InGaN/GaN nanorod LEDs with an ITO/graphene transparent layer

NASA Astrophysics Data System (ADS)

Shim, Jae-Phil; Seong, Won-Seok; Min, Jung-Hong; Kong, Duk-Jo; Seo, Dong-Ju; Kim, Hyung-jun; Lee, Dong-Seon

2016-11-01

We introduce ITO on graphene as a current-spreading layer for separated InGaN/GaN nanorod LEDs for the purpose of passivation-free and high light-extraction efficiency. Transferred graphene on InGaN/GaN nanorods effectively blocks the diffusion of ITO atoms to nanorods, facilitating the production of transparent ITO/graphene contact on parallel-nanorod LEDs, without filling the air gaps, like a bridge structure. The ITO/graphene layer sufficiently spreads current in a lateral direction, resulting in uniform and reliable light emission observed from the whole area of the top surface. Using KOH treatment, we reduce series resistance and reverse leakage current in nanorod LEDs by recovering the plasma-damaged region. We also control the size of the nanorods by varying the KOH treatment time and observe strain relaxation via blueshift in electroluminescence. As a result, bridge-structured LEDs with 8 min of KOH treatment show 15 times higher light-emitting efficiency than with 2 min of KOH treatment.

GdN nanoisland-based GaN tunnel junctions.

PubMed

Krishnamoorthy, Sriram; Kent, Thomas F; Yang, Jing; Park, Pil Sung; Myers, Roberto C; Rajan, Siddharth

2013-06-12

Tunnel junctions could have a great impact on gallium nitride and aluminum nitride-based devices such as light-emitting diodes and lasers by overcoming critical challenges related to hole injection and p-contacts. This paper demonstrates the use of GdN nanoislands to enhance interband tunneling and hole injection into GaN p-n junctions by several orders of magnitude, resulting in low tunnel junction specific resistivity (1.3 × 10(-3) Ω-cm(2)) compared to the previous results in wide band gap semiconductors. Tunnel injection of holes was confirmed by low-temperature operation of GaN p-n junction with a tunneling contact layer, and strong electroluminescence down to 20 K. The low tunnel junction resistance combined with low optical absorption loss in GdN is very promising for incorporation in GaN-based light emitters.

COUGAR: a liquid nitrogen cooled InGaAs camera for astronomy and electro-luminescence

NASA Astrophysics Data System (ADS)

Van Bogget, Urbain; Vervenne, Vincent; Vinella, Rosa Maria; van der Zanden, Koen; Merken, Patrick; Vermeiren, Jan

2014-06-01

A SWIR FPA was designed and manufactured with 640*512 pixels, 20 μm pitch and InGaAs detectors for electroluminescence characterization and astronomical applications in the [0.9 - 1.55 μm] range. The FPA is mounted in a liquid nitrogen dewar and is operated by a low noise frontend electronics. One of the biggest problem in designing sensors and cameras for electro-luminescence measurements is the autoillumination of the detectors by the readout circuit. Besides of proper shielding of the detectors, the ROIC shall be optimized for minimal electrical activity during the integration time of the very-weak signals coming from the circuit under test. For this reason a SFD (or Source Follower per Detector) architecture (like in the Hawaii sensor) was selected, resulting in a background limited performance of the detector. The pixel has a (somewhat arbitrary) full well capacity of 400 000 e- and a sensitivity of 2.17 μV/e-. The dark signal is app. 1 e-/pixel/sec and with the appropriate Fowler sampling the dark noise lowers below 5 e-rms. The power consumption of the circuit is limited 2 mW, allowing more than 24 hours of operation on less than 1 l of liquid nitrogen. The FPA is equipped with 4 outputs (optional readout on one single channel) and is capable of achieving 3 frames per second. Due to the non-destructive readout it is possible to determine in a dynamic way the optimal integration time for each observation. The Cougar camera is equipped with ultra-low noise power supply and bias lines; the electronics contain also a 24 bit AD converter to fully exploit the sensitivity of the FPA and the camera.

Modulating dual-wavelength multiple quantum wells in white light emitting diodes to suppress efficiency droop and improve color rendering index

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Yukun; Wang, Shuai; Zheng, Min

2015-10-14

In this paper, gallium nitride (GaN) based white light-emitting diodes (WLEDs) with modulated quantities of blue (In{sub 0.15}Ga{sub 0.85}N) quantum wells (QWs) and cyan QWs (In{sub 0.18}Ga{sub 0.82}N) in multiple QW (MQW) structures have been investigated numerically and experimentally. It is demonstrated that the optical performance of LEDs is sensitive to the quantities of cyan QWs in dual-wavelength MQW structures. Compared to the LEDs with respective 0, 4, and 8 cyan QWs (12 QWs in total), the optical performance of the sample with 6 cyan QWs is the best. The deterioration of the optical performance in the sample with lessmore » (4 pairs) cyan QWs or more (8 pairs) cyan QWs than 6 cyan QWs may be ascribed to weakened reservoir effect or more defects induced. Compared to conventional blue LEDs (12 blue QWs), the sample with 6 cyan QWs could effectively suppress the efficiency droop (the experimental droop ratio decreases from 50.3% to 39.5% at 80 A/cm{sup 2}) and significantly improve the color rendering index (CRI, increases from 66.4 to 77.0) simultaneously. We attribute the droop suppression to the strengthened reservoir effect and carrier confinement of deeper QWs (higher indium composition) incorporated in the dual-wavelength MQW structures, which lead to the better hole spreading and enhanced radiative recombination. Meanwhile, the remarkable experimental CRI improvement may result from the wider full-width at half-maximum of electroluminescence spectra and higher cyan intensity in WLED chips with dual-wavelength MQW structures.« less

Conductive polymer-based material

DOEpatents

McDonald, William F [Utica, OH; Koren, Amy B [Lansing, MI; Dourado, Sunil K [Ann Arbor, MI; Dulebohn, Joel I [Lansing, MI; Hanchar, Robert J [Charlotte, MI

2007-04-17

Disclosed are polymer-based coatings and materials comprising (i) a polymeric composition including a polymer having side chains along a backbone forming the polymer, at least two of the side chains being substituted with a heteroatom selected from oxygen, nitrogen, sulfur, and phosphorus and combinations thereof; and (ii) a plurality of metal species distributed within the polymer. At least a portion of the heteroatoms may form part of a chelation complex with some or all of the metal species. In many embodiments, the metal species are present in a sufficient concentration to provide a conductive material, e.g., as a conductive coating on a substrate. The conductive materials may be useful as the thin film conducting or semi-conducting layers in organic electronic devices such as organic electroluminescent devices and organic thin film transistors.

ZnS-Based ZnSTe:N/n-ZnS Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Ichino, Kunio; Kojima, Takahiro; Obata, Shunsuke; Kuroyanagi, Takuma; Nakazawa, Shoichi; Kashiyama, Shota

2013-11-01

ZnS1-xTex:N/n-ZnS diodes have been fabricated in an attempt to convert ZnS into p-type by Te incorporation and the resulting upward shift of the valence band maximum. The diodes exhibit clear rectification in the current-voltage characteristic and a peak of the electron-beam-induced current at the ZnS1-xTex:N/n-ZnS interface. Furthermore, a ZnS0.85Te0.15:N/n-ZnS diode exhibits blue-green electroluminescence due to self-activated emission in n-ZnS at 290 K under a forward current. These results suggest p-type conduction in ZnS1-xTex:N, and thus the LED operation of a ZnS-based pn-junction.

Light emitting ceramic device and method for fabricating the same

DOEpatents

Valentine, Paul; Edwards, Doreen D.; Walker Jr., William John; Slack, Lyle H.; Brown, Wayne Douglas; Osborne, Cathy; Norton, Michael; Begley, Richard

2004-11-30

A light-emitting ceramic based panel, hereafter termed "electroceramescent" panel, and alternative methods of fabrication for the same are claimed. The electroceramescent panel is formed on a substrate providing mechanical support as well as serving as the base electrode for the device. One or more semiconductive ceramic layers directly overlay the substrate, and electrical conductivity and ionic diffusion are controlled. Light emitting regions overlay the semiconductive ceramic layers, and said regions consist sequentially of a layer of a ceramic insulation layer and an electroluminescent layer, comprised of doped phosphors or the equivalent. One or more conductive top electrode layers having optically transmissive areas overlay the light emitting regions, and a multi-layered top barrier cover comprising one or more optically transmissive non-combustible insulation layers overlay said top electrode regions.

DNA as an Optical Material

DTIC Science & Technology

2011-07-01

the electron blocking function of the DNA layer; electroluminescence occurs in either the AlQ3 (green) or NPB layer (blue) layers. Source: J. A...been observed for sev- eral fluorescent materials with different HOMO/LUMO levels, including AlQ3 (green emission) and NPB (blue emission). OLEDs

Visible light electroluminescent diodes of indium-gallium phosphide

NASA Technical Reports Server (NTRS)

Clough, R.; Richman, D.; Tietjen, J.

1970-01-01

Vapor deposition and acceptor impurity diffusion techniques are used to prepare indium-gallium phosphide junctions. Certain problems in preparation are overcome by altering gas flow conditions and by increasing the concentration of phosphine in the gas. A general formula is given for the alloy's composition.

Co-deposition methods for the fabrication of organic optoelectronic devices

DOEpatents

Thompson, Mark E.; Liu, Zhiwei; Wu, Chao

2016-09-06

A method for fabricating an OLED by preparing phosphorescent metal complexes in situ is provided. In particular, the method simultaneously synthesizes and deposits copper (I) complexes in an organic light emitting device. Devices comprising such complexes may provide improved photoluminescent and electroluminescent properties.

Auger-generated hot carrier current in photo-excited forward biased single quantum well blue light emitting diodes

NASA Astrophysics Data System (ADS)

Espenlaub, Andrew C.; Alhassan, Abdullah I.; Nakamura, Shuji; Weisbuch, Claude; Speck, James S.

2018-04-01

We report on measurements of the photo-modulated current-voltage and electroluminescence characteristics of forward biased single quantum well, blue InGaN/GaN light emitting diodes with and without electron blocking layers. Low intensity resonant optical excitation of the quantum well was observed to induce an additional forward current at constant forward diode bias, in contrast to the usual sense of the photocurrent in photodiodes and solar cells, as well as an increased electroluminescence intensity. The presence of an electron blocking layer only slightly decreased the magnitude of the photo-induced current at constant forward bias. Photo-modulation at constant forward diode current resulted in a reduced diode bias under optical excitation. We argue that this decrease in diode bias at constant current and the increase in forward diode current at constant applied bias can only be due to additional hot carriers being ejected from the quantum well as a result of an increased Auger recombination rate within the quantum well.

TOPICAL REVIEW: Electrical transport modelling in organic electroluminescent devices

NASA Astrophysics Data System (ADS)

Walker, A. B.; Kambili, A.; Martin, S. J.

2002-10-01

Organic electroluminescent devices (OEDs) emit light when an electric current is applied to a thin film section. They arise from two main technology branches - small molecules and light emitting polymers. Apart from the insight offered into the fundamentals of their physics, which is relevant to topics such as electrical transport in biological systems and molecular computers, understanding how the mobilities in these systems vary with morphology and composition enables the design of improved materials for technological requirements, e.g. fast switching speeds for active matrix displays and polymer field effect transistors. In this review, we have focussed on the models of transport in OEDs that address the unusual nature of this transport and underpin device design. The review concludes with the following point: as new materials for use in OEDs continue to appear, modelling is essential for the prediction of their transport properties, which in turn leads to the establishment of fundamental trends in the behaviour of devices employing them.

Blue and green electroluminescence from CdSe nanocrystal quantum-dot-quantum-wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Y. F.; Cao, X. A., E-mail: xacao@mail.wvu.edu

2014-11-17

CdS/CdSe/ZnS quantum dot quantum well (QDQW) nanocrystals were synthesized using the successive ion layer adsorption and reaction technique, and their optical properties were tuned by bandgap and strain engineering. 3-monolayer (ML) CdSe QWs emitted blue photoluminescence at 467 nm with a spectral full-width-at-half-maximum of ∼30 nm. With a 3 ML ZnS cladding layer, which also acts as a passivating and strain-compensating layer, the QDQWs acquired a ∼35% quantum yield of the QW emission. Blue and green electroluminescence (EL) was obtained from QDQW light-emitting devices with 3–4.5 ML CdSe QWs. It was found that as the peak blueshifted, the overall EL was increasinglymore » dominated by defect state emission due to poor hole injection into the QDQWs. The weak EL was also attributed to strong field-induced charge separation resulting from the unique QDQW geometry, weakening the oscillator strength of optical transitions.« less

Effect of solution combusted TiO2 nanopowder within commercial BaTiO3 dielectric layer on the photoelectric properties for AC powder electroluminescence devices.

PubMed

Park, Sung; Choi, Gil Rak; Kim, Youn Cheol; Lee, Jae Chun; Lee, Ju Hyeon

2013-05-01

A unique synthesis method was developed, which is called solution combustion method (SCM). TiO2 nanopowder was synthesized by this method. This SCM TiO2 nanopowder (-35 nm) was added to the dielectric layer of AC powder electroluminescence (EL) device. The dielectric layer was made of commercial BaTiO3 powder (-1.2 microm) and binding polymer. 0, 5, 10 and 15 wt% of SCM TiO2 nanopowder was added to the dielectric layer during fabrication of AC powder EL device respectively. Dielectric constant of these four kinds of dielectric layers was measured. The brightness and current density of AC powder EL device were also measured. When 10 wt% of SCM TiO2 nanopowder was added, dielectric constant and brightness were increased by 30% and 101% respectively. Furthermore, the current density was decreased by 71%. This means that the brightness was double and the power consumption was one third.

Measurement of Relaxation Time of Excess Carriers in Si and CIGS Solar Cells by Modulated Electroluminescence Technique

DOE PAGES

Khatavkar, Sanchit; Muniappan, Kulasekaran; Kannan, Chinna V.; ...

2017-11-10

Excess carrier lifetime plays a crucial role in determining the efficiency of solar cells. In this paper, we use the frequency dependence of inphase and quadrature components of modulated electroluminescence (MEL) to measure the relaxation time (decay) of excess carriers. The advantage of the MEL technique is that the relaxation time is obtained directly from the angular frequency at which the quadrature component peaks. It does not need knowledge of the material parameters like mobility, etc., and can be used for any finished solar cells which have detectable light emission. The experiment is easy to perform with standard electrical equipment.more » For silicon solar cells, the relaxation time is dominated by recombination and hence, the relaxation time is indeed the excess carrier lifetime. In contrast, for the CIGS solar cells investigated here, the relaxation time is dominated by trapping and emission from shallow minority carrier traps.« less

STM-electroluminescence from clustered C3N4 nanodomains synthesized via green chemistry process.

PubMed

Andrade, E P; Costa, B B A; Chaves, C R; de Paula, A M; Cury, L A; Malachias, A; Safar, G A M

2018-01-01

A Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and synchrotron X-ray diffraction study on clustered C 3 N 4 nanoparticles (nanoflakes) is conducted on green-chemistry synthesized samples obtained from chitosan through high power sonication. Morphological aspects and the electronic characteristics are investigated. The observed bandgap of the nanoflakes reveals the presence of different phases in the material. Combining STM morphology, STS spectra and X-ray diffraction (XRD) results one finds that the most abundant phase is graphitic C 3 N 4 . A high density of defects is inferred from the XRD measurements. Additionally, STM-electroluminescence (STMEL) is detected in C 3 N 4 nanoflakes deposited on a gold substrate. The tunneling current creates photons that are three times more energetic than the tunneling electrons of the STM sample. We ponder about the two most probable models to explain the observed photon emission energy: either a nonlinear optical phenomenon or a localized state emission. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of interface voids on electroluminescence colors for ZnO microdisk/p-GaN heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Mo, Ran; Choi, Ji Eun; Kim, Hyeong Jin; Jeong, Junseok; Kim, Jong Chan; Kim, Yong-Jin; Jeong, Hu Young; Hong, Young Joon

2017-10-01

This study investigates the influence of voids on the electroluminescence (EL) emission color of ZnO microdisk/p-GaN heterojunction light-emitting diodes (LEDs). For this study, position-controlled microdisk arrays were fabricated on patterned p-GaN via wet chemical epitaxy of ZnO, and specifically, the use of trisodium citrate dihydrate (TCD) yielded high-density voids at the bottom of the microdisk. Greenish yellow or whitish blue EL was emitted from the microdisk LEDs formed with or without TCD, respectively, at reverse-bias voltages. Such different EL colors were found to be responsible for the relative EL intensity ratio between indigo and yellow emission peaks, which were originated from radiative recombination at p-GaN and ZnO, respectively. The relative EL intensity between dichromatic emissions is discussed in terms of (i) junction edge effect provoked by interfacial voids and (ii) electron tunneling probability depending on the depletion layer geometry.

Operating organic light-emitting diodes imaged by super-resolution spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, John T.; Granick, Steve

Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semi-conducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packedmore » chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. As a result, this points the way towards real-time analysis of materials design principles in devices as they actually operate.« less

Measurement of Relaxation Time of Excess Carriers in Si and CIGS Solar Cells by Modulated Electroluminescence Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khatavkar, Sanchit; Muniappan, Kulasekaran; Kannan, Chinna V.

Excess carrier lifetime plays a crucial role in determining the efficiency of solar cells. In this paper, we use the frequency dependence of inphase and quadrature components of modulated electroluminescence (MEL) to measure the relaxation time (decay) of excess carriers. The advantage of the MEL technique is that the relaxation time is obtained directly from the angular frequency at which the quadrature component peaks. It does not need knowledge of the material parameters like mobility, etc., and can be used for any finished solar cells which have detectable light emission. The experiment is easy to perform with standard electrical equipment.more » For silicon solar cells, the relaxation time is dominated by recombination and hence, the relaxation time is indeed the excess carrier lifetime. In contrast, for the CIGS solar cells investigated here, the relaxation time is dominated by trapping and emission from shallow minority carrier traps.« less

Correlation between the Open-Circuit Voltage and Charge Transfer State Energy in Organic Photovoltaic Cells.

PubMed

Zou, Yunlong; Holmes, Russell J

2015-08-26

In order to further improve the performance of organic photovoltaic cells (OPVs), it is essential to better understand the factors that limit the open-circuit voltage (VOC). Previous work has sought to correlate the value of VOC in donor-acceptor (D-A) OPVs to the interface energy level offset (EDA). In this work, measurements of electroluminescence are used to extract the charge transfer (CT) state energy for multiple small molecule D-A pairings. The CT state as measured from electroluminescence is found to show better correlation to the maximum VOC than EDA. The difference between EDA and the CT state energy is attributed to the Coulombic binding energy of the CT state. This correlation is demonstrated explicitly by inserting an insulating spacer layer between the donor and acceptor materials, reducing the binding energy of the CT state and increasing the measured VOC. These results demonstrate a direct correlation between maximum VOC and CT state energy.

Silver nanoparticles with 4,4‧-dicyanamidobiphenyl ligand: Synthesis, photoluminescent and electroluminescent properties and DFT calculations

NASA Astrophysics Data System (ADS)

Chiniforoshan, Hossein; Khalesi, Sara Bahmanpour; Tabrizi, Leila; Hajipour, Abdol R.; Chermahini, Alireza Najafi; Karimzadeh, Morteza

2015-02-01

In this research, a new complex of 4,4‧-dicyanamidobiphenyl (bpH2) ligand, Ag(bpH) has been synthesized and characterized by FT-IR, UV-Vis spectroscopies, and elemental analysis. The morphology and size of complex were determined by the scanning electron microscopy (SEM) image. The diameter of the complex was about 61 nm and the nanoparticles were spherical. TGA result indicated that this complex was thermally stable. Also, photoluminescent and electroluminescent properties of Ag(bpH) were reported. The blue-green light emission was observed by fabricating double-layer devices using Ag(bpH) as electron-transport and NPB as hole-transport material. In addition, this complex was optimized by B3LYP/LANL2DZ method. The calculated FT-IR and UV-Vis data are in better agreement with the experimental results. In addition to DFT calculations, natural bond orbital (NBO) was also performed at the same level of theory.

Electroluminescence of hot electrons in AlGaN/GaN high-electron-mobility transistors under radio frequency operation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brazzini, Tommaso, E-mail: tommaso.brazzini@bristol.ac.uk; Sun, Huarui; Uren, Michael J.

2015-05-25

Hot electrons in AlGaN/GaN high electron mobility transistors are studied during radio frequency (RF) and DC operation by means of electroluminescence (EL) microscopy and spectroscopy. The measured EL intensity is decreased under RF operation compared to DC at the same average current, indicating a lower hot electron density. This is explained by averaging the DC EL intensity over the measured load line used in RF measurements, giving reasonable agreement. In addition, the hot electron temperature is lower by up to 15% under RF compared to DC, again at least partially explainable by the weighted averaging along the specific load line.more » However, peak electron temperature under RF occurs at high V{sub DS} and low I{sub DS} where EL is insignificant suggesting that any wear-out differences between RF and DC stress of the devices will depend on the balance between hot-carrier and field driven degradation mechanisms.« less

Operating organic light-emitting diodes imaged by super-resolution spectroscopy

DOE PAGES

King, John T.; Granick, Steve

2016-06-21

Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semi-conducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packedmore » chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. As a result, this points the way towards real-time analysis of materials design principles in devices as they actually operate.« less

29 CFR 1910.34 - Coverage and definitions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 29 Labor 5 2014-07-01 2014-07-01 false Coverage and definitions. 1910.34 Section 1910.34 Labor... OCCUPATIONAL SAFETY AND HEALTH STANDARDS Exit Routes and Emergency Planning § 1910.34 Coverage and definitions... plans. (c) Definitions. Electroluminescent means a light-emitting capacitor. Alternating current excites...