Strong geometrical effects in submillimeter selective area growth and light extraction of GaN light emitting diodes on sapphire

DOE PAGES

Tanaka, Atsunori; Chen, Renjie; Jungjohann, Katherine L.; ...

2015-11-27

Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. Our detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates is reported here, and we utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO 2. We show that the mask opening diameter leads to as much as 4 times increasemore » in the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We also observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Lastly, such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.« less

Origin of the Electroluminescence from Annealed-ZnO/GaN Heterojunction Light-Emitting Diodes.

PubMed

Hsu, Kai-Chiang; Hsiao, Wei-Hua; Lee, Ching-Ting; Chen, Yan-Ting; Liu, Day-Shan

2015-11-16

This paper addressed the effect of post-annealed treatment on the electroluminescence (EL) of an n -ZnO/ p -GaN heterojunction light-emitting diode (LED). The bluish light emitted from the 450 °C-annealed LED became reddish as the LED annealed at a temperature of 800 °C under vacuum atmosphere. The origins of the light emission for these LEDs annealed at various temperatures were studied using measurements of electrical property, photoluminescence, and Auger electron spectroscopy (AES) depth profiles. A blue-violet emission located at 430 nm was associated with intrinsic transitions between the bandgap of n -ZnO and p -GaN, the green-yellow emission at 550 nm mainly originating from the deep-level transitions of native defects in the n -ZnO and p -GaN surfaces, and the red emission at 610 nm emerging from the Ga-O interlayer due to interdiffusion at the n -ZnO/ p -GaN interface. The above-mentioned emissions also supported the EL spectra of LEDs annealed at 700 °C under air, nitrogen, and oxygen atmospheres, respectively.

Top-emitting organic light-emitting diodes.

PubMed

Hofmann, Simone; Thomschke, Michael; Lüssem, Björn; Leo, Karl

2011-11-07

We review top-emitting organic light-emitting diodes (OLEDs), which are beneficial for lighting and display applications, where non-transparent substrates are used. The optical effects of the microcavity structure as well as the loss mechanisms are discussed. Outcoupling techniques and the work on white top-emitting OLEDs are summarized. We discuss the power dissipation spectra for a monochrome and a white top-emitting OLED and give quantitative reports on the loss channels. Furthermore, the development of inverted top-emitting OLEDs is described.

Metal organic vapour-phase epitaxy growth of GaN wires on Si (111) for light-emitting diode applications

PubMed Central

2013-01-01

GaN wires are grown on a Si (111) substrate by metal organic vapour-phase epitaxy on a thin deposited AlN blanket and through a thin SiNx layer formed spontaneously at the AlN/Si interface. N-doped wires are used as templates for the growth of core-shell InGaN/GaN multiple quantum wells coated by a p-doped shell. Standing single-wire heterostructures are connected using a metallic tip and a Si substrate backside contact, and the electroluminescence at room temperature and forward bias is demonstrated at 420 nm. This result points out the feasibility of lower cost nitride-based wires for light-emitting diode applications. PMID:23391377

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

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

Enhanced light extraction from a GaN-based green light-emitting diode with hemicylindrical linear grating structure.

PubMed

Jin, Yuanhao; Yang, Fenglei; Li, Qunqing; Zhu, Zhendong; Zhu, Jun; Fan, Shoushan

2012-07-02

Significant enhancement in the light output from GaN-based green light-emitting diodes (LEDs) was achieved with a hemicylindrical grating structure on the top layer of the diodes. The grating structure was first optimized by the finite-difference time-domain (FDTD) method, which showed that the profile of the grating structure was critical for light extraction efficiency. It was found that the transmission efficiency of the 530 nm light emitted from the inside of the GaN LED increased for incidence angles between 23.58° and 60°. Such a structure was fabricated by electron-beam lithography and an etching method. The light output power from the LED was increased approximately 4.7 times compared with that from a conventional LED. The structure optimization is the key to the great increase in transmission efficiency. Furthermore, the light emitted from the edge of the LED units could be collected and extracted by the grating structures in adjacent LED units, thus enhancing the performance of the whole LED chip.

Organic light emitting diode with light extracting electrode

DOEpatents

Bhandari, Abhinav; Buhay, Harry

2017-04-18

An organic light emitting diode (10) includes a substrate (20), a first electrode (12), an emissive active stack (14), and a second electrode (18). At least one of the first and second electrodes (12, 18) is a light extracting electrode (26) having a metallic layer (28). The metallic layer (28) includes light scattering features (29) on and/or in the metallic layer (28). The light extracting features (29) increase light extraction from the organic light emitting diode (10).

Ultraviolet light-absorbing and emitting diodes consisting of a p-type transparent-semiconducting NiO film deposited on an n-type GaN homoepitaxial layer

NASA Astrophysics Data System (ADS)

Nakai, Hiroshi; Sugiyama, Mutsumi; Chichibu, Shigefusa F.

2017-05-01

Gallium nitride (GaN) and related (Al,Ga,In)N alloys provide practical benefits in the production of light-emitting diodes (LEDs) and laser diodes operating in ultraviolet (UV) to green wavelength regions. However, obtaining low resistivity p-type AlN or AlGaN of large bandgap energies (Eg) is a critical issue in fabricating UV and deep UV-LEDs. NiO is a promising candidate for useful p-type transparent-semiconducting films because its Eg is 4.0 eV and it can be doped into p-type conductivity of sufficiently low resistivity. By using these technologies, heterogeneous junction diodes consisting of a p-type transparent-semiconducting polycrystalline NiO film on an n-type single crystalline GaN epilayer on a low threading-dislocation density, free-standing GaN substrate were fabricated. The NiO film was deposited by using the conventional RF-sputtering method, and the GaN homoepitaxial layer was grown by metalorganic vapor phase epitaxy. They exhibited a significant photovoltaic effect under UV light and also exhibited an electroluminescence peak at 3.26 eV under forward-biased conditions. From the conduction and valence band (EV) discontinuities, the NiO/GaN heterointerface is assigned to form a staggered-type (TYPE-II) band alignment with the EV of NiO higher by 2.0 eV than that of GaN. A rectifying property that is consistent with the proposed band diagram was observed in the current-voltage characteristics. These results indicate that polycrystalline NiO functions as a hole-extracting and injecting layer of UV optoelectronic devices.

Demonstrating the Light-Emitting Diode.

ERIC Educational Resources Information Center

Johnson, David A.

1995-01-01

Describes a simple inexpensive circuit which can be used to quickly demonstrate the basic function and versatility of the solid state diode. Can be used to demonstrate the light-emitting diode (LED) as a light emitter, temperature sensor, light detector with both a linear and logarithmic response, and charge storage device. (JRH)

Natural substrate lift-off technique for vertical light-emitting diodes

NASA Astrophysics Data System (ADS)

Lee, Chia-Yu; Lan, Yu-Pin; Tu, Po-Min; Hsu, Shih-Chieh; Lin, Chien-Chung; Kuo, Hao-Chung; Chi, Gou-Chung; Chang, Chun-Yen

2014-04-01

Hexagonal inverted pyramid (HIP) structures and the natural substrate lift-off (NSLO) technique were demonstrated on a GaN-based vertical light-emitting diode (VLED). The HIP structures were formed at the interface between GaN and the sapphire substrate by molten KOH wet etching. The threading dislocation density (TDD) estimated by transmission electron microscopy (TEM) was reduced to 1 × 108 cm-2. Raman spectroscopy indicated that the compressive strain from the bottom GaN/sapphire was effectively released through the HIP structure. With the adoption of the HIP structure and NSLO, the light output power and yield performance of leakage current could be further improved.

Amber light-emitting diode comprising a group III-nitride nanowire active region

DOEpatents

Wang, George T.; Li, Qiming; Wierer, Jr., Jonathan J.; Koleske, Daniel

2014-07-22

A temperature stable (color and efficiency) III-nitride based amber (585 nm) light-emitting diode is based on a novel hybrid nanowire-planar structure. The arrays of GaN nanowires enable radial InGaN/GaN quantum well LED structures with high indium content and high material quality. The high efficiency and temperature stable direct yellow and red phosphor-free emitters enable high efficiency white LEDs based on the RGYB color-mixing approach.

Hybrid tunnel junction contacts to III-nitride light-emitting diodes

NASA Astrophysics Data System (ADS)

Young, Erin C.; Yonkee, Benjamin P.; Wu, Feng; Oh, Sang Ho; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.

2016-02-01

In this work, we demonstrate highly doped GaN p-n tunnel junction (TJ) contacts on III-nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10-4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a (20\\bar{2}\\bar{1}) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

Suspended light-emitting diode featuring a bottom dielectric distributed Bragg reflector

NASA Astrophysics Data System (ADS)

Cai, Wei; Wang, Wei; Zhu, Bingcheng; Gao, Xumin; Zhu, Guixia; Yuan, Jialei; Wang, Yongjin

2018-01-01

Here, we propose, fabricate and characterize the light manipulation of a suspended-membrane InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED) with a dielectric distributed Bragg reflector (DBR) positioned at the bottom, implemented on a GaN-on-silicon platform. Silicon removal is conducted to obtain the suspended MQW-LED architecture, and back wafer thinning of the epitaxial film is performed to improve the device performance. A 6-pair SiO2/Ta2O5 DBR is deposited on the backside to manipulate the emitted light. The experimental results demonstrate that the bottom dielectric DBR exhibits high reflectivity and distinctly changes the light emission, which are consistent with the performed simulation results. This work represents a significant step towards the realization of inexpensive, electrically driven and simply fabricated GaN VCSELs for potential use in number of applications.

GaN light-emitting device based on ionic liquid electrolyte

NASA Astrophysics Data System (ADS)

Hirai, Tomoaki; Sakanoue, Tomo; Takenobu, Taishi

2018-06-01

Ionic liquids (ILs) are attractive materials for fabricating unique hybrid devices based on electronics and electrochemistry; thus, IL-gated transistors and organic light-emitting devices of light-emitting electrochemical cells (LECs) are investigated for future low-voltage and high-performance devices. In LECs, voltage application induces the formation of electrochemically doped p–n homojunctions owing to ion rearrangements in composites of semiconductors and electrolytes, and achieves electron–hole recombination for light emission at the homojunctions. In this work, we applied this concept of IL-induced electrochemical doping to the fabrication of GaN-based light-emitting devices. We found that voltage application to the layered IL/GaN structure accumulated electrons on the GaN surface owing to ion rearrangements and improved the conductivity of GaN. The ion rearrangement also enabled holes to be injected by the strong electric field of electric double layers on hole injection contacts. This simultaneous injection of holes and electrons into GaN mediated by ions achieves light emission at a low voltage of around 3.4 V. The light emission from the simple IL/GaN structure indicates the usefulness of an electrochemical technique in generating light emission with great ease of fabrication.

Recent developments in white light emitting diodes

NASA Astrophysics Data System (ADS)

Lohe, P. P.; Nandanwar, D. V.; Belsare, P. D.; Moharil, S. V.

2018-05-01

In the recent years solid state lighting based on LEDs has revolutionized lighting technology. LEDs have many advantages over the conventional lighting based on fluorescent and incandescent lamps such as mercury free, high conversion efficiency of electrical energy into light, long lifetime reliability and ability to use with many types of devices. LEDs have emerged as a new potentially revolutionary technology that could save up to half of energy used for lighting applications. White LEDs would be the most important light source in the future, so much so that this aspect had been highlighted by the Nobel committee during the award of 2014 Nobel Prize for Physics. Recent advancement in the fabrication of GaN chip capable of emitting in blue and near UV region paved way for fabrication of white LED lamps. Mainly there are two approaches used for preparing white emitting solid state lamp. In the first approach blue light (λ=450 nm) emitted from the InGaN LED chip is partially absorbed by the YAG:Ce3+ phosphor coated on it and re-emitted as yellow fluorescence. A white light can be generated by the combination of blue + yellow emission bands. These lamps are already available. But they are suffering from major drawback that their Colour Rendering Index (CRI) is low. In the second approach, white LEDs are made by coating near ultraviolet emitting (360 to 410nm) LED with a mixture of high efficiency red, green and blue emitting phosphors, analogous to the fluorescent lamp. This method yields lamps with better color rendition. Addition of a yellow emitting phosphor improves CRI further. However conversion efficiency is compromised to some extent. Further the cost of near UV emitting chip is very high compared to blue emitting chips. Thus cost and light output wise, near UV chips are much inferior to blue chips. Recently some rare earth activated oxynitrides, silicates, fluorides have emerged as an important family of luminescent materials for white LED application

Fabrication of full-color GaN-based light-emitting diodes on nearly lattice-matched flexible metal foils.

PubMed

Kim, Hyeryun; Ohta, Jitsuo; Ueno, Kohei; Kobayashi, Atsushi; Morita, Mari; Tokumoto, Yuki; Fujioka, Hiroshi

2017-05-18

GaN-based light-emitting diodes (LEDs) have been widely accepted as highly efficient solid-state light sources capable of replacing conventional incandescent and fluorescent lamps. However, their applications are limited to small devices because their fabrication process is expensive as it involves epitaxial growth of GaN by metal-organic chemical vapor deposition (MOCVD) on single crystalline sapphire wafers. If a low-cost epitaxial growth process such as sputtering on a metal foil can be used, it will be possible to fabricate large-area and flexible GaN-based light-emitting displays. Here we report preparation of GaN films on nearly lattice-matched flexible Hf foils using pulsed sputtering deposition (PSD) and demonstrate feasibility of fabricating full-color GaN-based LEDs. It was found that introduction of low-temperature (LT) grown layers suppressed the interfacial reaction between GaN and Hf, allowing the growth of high-quality GaN films on Hf foils. We fabricated blue, green, and red LEDs on Hf foils and confirmed their normal operation. The present results indicate that GaN films on Hf foils have potential applications in fabrication of future large-area flexible GaN-based optoelectronics.

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.

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

Low-threshold voltage ultraviolet light-emitting diodes based on (Al,Ga)N metal-insulator-semiconductor structures

NASA Astrophysics Data System (ADS)

Liang, Yu-Han; Towe, Elias

2017-12-01

Al-rich III-nitride-based deep-ultraviolet (UV) (275-320 nm) light-emitting diodes are plagued with a low emission efficiency and high turn-on voltages. We report Al-rich (Al,Ga)N metal-insulator-semiconductor UV light-emitting Schottky diodes with low turn-on voltages of <3 V, which are about half those of typical (Al,Ga)N p-i-n diodes. Our devices use a thin AlN film as the insulator and an n-type Al0.58Ga0.42N film as the semiconductor. To improve the efficiency, we inserted a GaN quantum-well structure between the AlN insulator and the n-type Al x Ga1- x N semiconductor. The benefits of the quantum-well structure include the potential to tune the emission wavelength and the capability to confine carriers for more efficient radiative recombination.

Super-Lattice Light Emitting Diodes (SLEDS) on GaAs

DTIC Science & Technology

2016-03-31

Super-Lattice Light Emitting Diodes (SLEDS) on GaAs Kassem Nabha1, Russel Ricker2, Rodney McGee1, Nick Waite1, John Prineas2, Sydney Provence2...infrared light emitting diodes (LEDs). Typically, the LED arrays are mated with CMOS read-in integrated circuit (RIIC) chips using flip-chip bonding. In...circuit (RIIC) chips using flip-chip bonding. This established technology is called Hybrid-super-lattice light emitting diodes (Hybrid- SLEDS). In

Perovskite Materials for Light-Emitting Diodes and Lasers.

PubMed

Veldhuis, Sjoerd A; Boix, Pablo P; Yantara, Natalia; Li, Mingjie; Sum, Tze Chien; Mathews, Nripan; Mhaisalkar, Subodh G

2016-08-01

Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An aluminium nitride light-emitting diode with a wavelength of 210 nanometres.

PubMed

Taniyasu, Yoshitaka; Kasu, Makoto; Makimoto, Toshiki

2006-05-18

Compact high-efficiency ultraviolet solid-state light sources--such as light-emitting diodes (LEDs) and laser diodes--are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond and III-V nitride semiconductors (GaN, AlGaN and AlN; refs 3-10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride (AlN), which has a very wide direct bandgap of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.

Silver free III-nitride flip chip light-emitting-diode with wall plug efficiency over 70% utilizing a GaN tunnel junction

NASA Astrophysics Data System (ADS)

Yonkee, B. P.; Young, E. C.; DenBaars, S. P.; Nakamura, S.; Speck, J. S.

2016-11-01

A molecular beam epitaxy regrowth technique was demonstrated on standard industrial patterned sapphire substrate light-emitting diode (LED) epitaxial wafers emitting at 455 nm to form a GaN tunnel junction. By using an HF pretreatment on the wafers before regrowth, a voltage of 3.08 V at 20 A/cm2 was achieved on small area devices. A high extraction package was developed for comparison with flip chip devices which utilize an LED floating in silicone over a BaSO4 coated header and produced a peak external quantum efficiency (EQE) of 78%. A high reflectivity mirror was designed using a seven-layer dielectric coating backed by aluminum which has a calculated angular averaged reflectivity over 98% between 400 and 500 nm. This was utilized to fabricate a flip chip LED which had a peak EQE and wall plug efficiency of 76% and 73%, respectively. This flip chip could increase light extraction over a traditional flip chip LED due to the increased reflectivity of the dielectric based mirror.

Laterally injected light-emitting diode and laser diode

DOEpatents

Miller, Mary A.; Crawford, Mary H.; Allerman, Andrew A.

2015-06-16

A p-type superlattice is used to laterally inject holes into an III-nitride multiple quantum well active layer, enabling efficient light extraction from the active area. Laterally-injected light-emitting diodes and laser diodes can enable brighter, more efficient devices that impact a wide range of wavelengths and applications. For UV wavelengths, applications include fluorescence-based biological sensing, epoxy curing, and water purification. For visible devices, applications include solid state lighting and projection systems.

High-quality vertical light emitting diodes fabrication by mechanical lift-off technique

NASA Astrophysics Data System (ADS)

Tu, Po-Min; Hsu, Shih-Chieh; Chang, Chun-Yen

2011-10-01

We report the fabrication of mechanical lift-off high quality thin GaN with Hexagonal Inversed Pyramid (HIP) structures for vertical light emitting diodes (V-LEDs). The HIP structures were formed at the GaN/sapphire substrate interface under high temperature during KOH wet etching process. The average threading dislocation density (TDD) was estimated by transmission electron microscopy (TEM) and found the reduction from 2×109 to 1×108 cm-2. Raman spectroscopy analysis revealed that the compressive stress of GaN epilayer was effectively relieved in the thin-GaN LED with HIP structures. Finally, the mechanical lift-off process is claimed to be successful by using the HIP structures as a sacrificial layer during wafer bonding process.

III-N light emitting diodes fabricated using RF nitrogen gas source MBE

NASA Astrophysics Data System (ADS)

Van Hove, J. M.; Carpenter, G.; Nelson, E.; Wowchak, A.; Chow, P. P.

1996-07-01

Homo- and heterojunction III-N light emitting diodes using RF atomic nitrogen plasma molecular beam epitaxy have been grown. GaN films deposited on sapphire using this growth technique exhibited an extremely sharp X-ray diffraction with a full width half maximum of 112 arc sec. p-type doping of the nitride films was done with elemental Mg and resulted in as-grown p-type material with resistivities as low as 2 Ω · cm. Both homo- and heterojunction LEDs showed clear rectification. Emission from the GaN homojunction deposited on n-type SiC was peaked at 410 nm while the AlGaNGaN(Zn)AlGaN double heterojunction LEDs emission was centered about 520 nm.

Enhanced characteristics of blue InGaN /GaN light-emitting diodes by using selective activation to modulate the lateral current spreading length

NASA Astrophysics Data System (ADS)

Lin, Ray-Ming; Lu, Yuan-Chieh; Chou, Yi-Lun; Chen, Guo-Hsing; Lin, Yung-Hsiang; Wu, Meng-Chyi

2008-06-01

We have studied the characteristics of blue InGaN /GaN multiquantum-well light-emitting diodes (LEDs) after reducing the length of the lateral current path through the transparent layer through formation of a peripheral high-resistance current-blocking region in the Mg-doped GaN layer. To study the mechanism of selective activation in the Mg-doped GaN layer, we deposited titanium (Ti), gold (Au), Ti /Au, silver, and copper individually onto the Mg-doped GaN layer and investigated their effects on the hole concentration in the p-GaN layer. The Mg-doped GaN layer capped with Ti effectively depressed the hole concentration in the p-GaN layer by over one order of magnitude relative to that of the as-grown layer. This may suggest that high resistive regions are formed by diffusion of Ti and depth of high resistive region from the p-GaN surface depends on the capped Ti film thickness. Selective activation of the Mg-doped GaN layer could be used to modulate the length of the lateral current path. Furthermore, the external quantum efficiency of the LEDs was improved significantly after reducing the lateral current spreading length. In our best result, the external quantum efficiency was 52.3% higher (at 100mA) than that of the as-grown blue LEDs.

Broadband light-emitting diode

DOEpatents

Fritz, Ian J.; Klem, John F.; Hafich, Michael J.

1998-01-01

A broadband light-emitting diode. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3-2 .mu.m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-division-multiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft.

Broadband light-emitting diode

DOEpatents

Fritz, I.J.; Klem, J.F.; Hafich, M.J.

1998-07-14

A broadband light-emitting diode is disclosed. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3--2 {micro}m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-divisionmultiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft. 10 figs.

Effect of interfacial composition on Ag-based Ohmic contact of GaN-based vertical light emitting diodes

NASA Astrophysics Data System (ADS)

Wu, Ning; Xiong, Zhihua; Qin, Zhenzhen

2018-02-01

By investigating the effect of a defective interface structure on Ag-based Ohmic contact of GaN-based vertical light-emitting diodes, we found a direct relationship between the interfacial composition and the Schottky barrier height of the Ag(111)/GaN(0001) interface. It was demonstrated that the Schottky barrier height of a defect-free Ag(111)/GaN(0001) interface was 2.221 eV, and it would be dramatically decreased to 0.375 eV with the introduction of one Ni atom and one Ga vacancy at the interface structure. It was found that the tunability of the Schottky barrier height can be attributed to charge accumulations around the interfacial defective regions and an unpinning of the Fermi level, which explains the experimental phenomenon of Ni-assisted annealing improving the p-type Ohmic contact characteristic. Lastly, we propose a new method of using Cu as an assisted metal to realize a novel Ag-based Ohmic contact. These results provide a guideline for the fabrication of high-quality Ag-based Ohmic contact of GaN-based vertical light-emitting diodes.

Enhanced efficiency of light emitting diodes with a nano-patterned gallium nitride surface realized by soft UV nanoimprint lithography

NASA Astrophysics Data System (ADS)

Zhou, Weimin; Min, Guoquan; Song, Zhitang; Zhang, Jing; Liu, Yanbo; Zhang, Jianping

2010-05-01

This paper reports a significant enhancement in the extraction efficiency of nano-patterned GaN light emitting diodes (LED) realized by soft UV nanoimprint lithography. The 2 inch soft stamp was fabricated using a replication stamp of anodic alumina oxide (AAO) membrane. The light output power was enhanced by 10.9% compared to that of the LED sample without a nano-patterned surface. Up to 41% enhancement in photoluminescence intensity was obtained from the nano-patterned GaN LED sample. The method is simple, cheap and suitable for mass production.

Selective-area nanoheteroepitaxy for light emitting diode (LED) applications

NASA Astrophysics Data System (ADS)

Wildeson, Isaac H.

generate built-in electric fields with magnitudes that are one-tenth those on the polar c-plane with the same (In,Ga)N composition. The lateral strain relaxation innate in the nanoheterostructures allows greater coherent InN incorporation in the nanopyramids as compared to thin-film heterostructures, as confirmed by electroluminescence and transmission electron microscopy. In addition to applications for light emitting diodes, selective area growth of GaN nanostructures is also important for biological and sensing applications. A process for fabricating porous GaN nanorods is presented that also relies on selective-area organometallic vapor phase epitaxy. The nanopore walls are primarily outlined by nonpolar planes, and the diameter of the nanopore can be controlled by the diameter of the opening in the dielectric template and the growth time. The lining of the nanopore walls is comprised of crystalline GaN, which makes these structures interesting for sensing, electrical and optical applications.

Evaluation of light-emitting diode beacon light fixtures.

DOT National Transportation Integrated Search

2009-12-01

Rotating beacons containing filament light sources have long been used on highway maintenance trucks : to indicate the presence of the truck to other drivers. Because of advances in light-emitting diode (LED) : technologies, flashing lights containin...

Light Converting Inorganic Phosphors for White Light-Emitting Diodes

PubMed Central

Chen, Lei; Lin, Chun-Che; Yeh, Chiao-Wen; Liu, Ru-Shi

2010-01-01

White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or near-ultraviolet (nUV) LEDs) and photoluminescence phosphors. These solid-state LED lamps, rather than organic light emitting diode (OLED) or polymer light-emitting diode (PLED), have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability and long operating lifetime. To meet with the further requirement of high color rendering index, warm light with low color temperature, high thermal stability and higher energy efficiency for WLEDs, new phosphors that can absorb excitation energy from blue or nUV LEDs and generate visible emissions efficiently are desired. The criteria of choosing the best phosphors, for blue (450−480 nm) and nUV (380−400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance of light between the emission from blue-nUV LEDs and the emissions from phosphors (such as yellow from Y3Al5O12:Ce3+) is important to obtain white light with proper color rendering index and color temperature. Here, we will review the status of phosphors for LEDs and prospect the future development.

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.

Efficient and bright organic light-emitting diodes on single-layer graphene electrodes

NASA Astrophysics Data System (ADS)

Li, Ning; Oida, Satoshi; Tulevski, George S.; Han, Shu-Jen; Hannon, James B.; Sadana, Devendra K.; Chen, Tze-Chiang

2013-08-01

Organic light-emitting diodes are emerging as leading technologies for both high quality display and lighting. However, the transparent conductive electrode used in the current organic light-emitting diode technologies increases the overall cost and has limited bendability for future flexible applications. Here we use single-layer graphene as an alternative flexible transparent conductor, yielding white organic light-emitting diodes with brightness and efficiency sufficient for general lighting. The performance improvement is attributed to the device structure, which allows direct hole injection from the single-layer graphene anode into the light-emitting layers, reducing carrier trapping induced efficiency roll-off. By employing a light out-coupling structure, phosphorescent green organic light-emitting diodes exhibit external quantum efficiency >60%, while phosphorescent white organic light-emitting diodes exhibit external quantum efficiency >45% at 10,000 cd m-2 with colour rendering index of 85. The power efficiency of white organic light-emitting diodes reaches 80 lm W-1 at 3,000 cd m-2, comparable to the most efficient lighting technologies.

A charge inverter for III-nitride light-emitting diodes

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

Zhang, Zi-Hui, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn; Zhang, Yonghui; Bi, Wengang, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn

In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO{sub 2} insulator layer on the p{sup +}-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p{sup +}-GaN and SiO{sub 2} insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constantmore » of the thin SiO{sub 2} layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p{sup +}-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm{sup 2} LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.« less

Perspective: Toward efficient GaN-based red light emitting diodes using europium doping

NASA Astrophysics Data System (ADS)

Mitchell, Brandon; Dierolf, Volkmar; Gregorkiewicz, Tom; Fujiwara, Yasufumi

2018-04-01

While InGaN/GaN blue and green light-emitting diodes (LEDs) are commercially available, the search for an efficient red LED based on GaN is ongoing. The realization of this LED is crucial for the monolithic integration of the three primary colors and the development of nitride-based full-color high-resolution displays. In this perspective, we will address the challenges of attaining red luminescence from GaN under current injection and the methods that have been developed to circumvent them. While several approaches will be mentioned, a large emphasis will be placed on the recent developments of doping GaN with Eu3+ to achieve an efficient red GaN-based LED. Finally, we will provide an outlook to the future of this material as a candidate for small scale displays such as mobile device screens or micro-LED displays.

Combinational light emitting diode-high frequency focused ultrasound treatment for HeLa cell.

PubMed

Choe, Se-Woon; Park, Kitae; Park, Chulwoo; Ryu, Jaemyung; Choi, Hojong

2017-12-01

Light sources such as laser and light emitting diode or ultrasound devices have been widely used for cancer therapy and regenerative medicines, since they are more cost-effective and less harmful than radiation therapy, chemotherapy or magnetic treatment. Compared to laser and low intensity ultrasound techniques, light emitting diode and high frequency focused ultrasound shows enhanced therapeutic effects, especially for small tumors. We propose combinational light emitting diode-high frequency focused ultrasound treatment for human cervical cancer HeLa cells. Individual red, green, and blue light emitting diode light only, high frequency focused ultrasound only, or light emitting diode light combined with high frequency focused ultrasound treatments were applied in order to characterize the responses of HeLa cells. Cell density exposed by blue light emitting diode light combined with high frequency focused ultrasound (2.19 ± 0.58%) was much lower than that of cells exposed by red and green light emitting diode lights (81.71 ± 9.92% and 61.81 ± 4.09%), blue light emitting diode light (11.19 ± 2.51%) or high frequency focused ultrasound only (9.72 ± 1.04%). We believe that the proposed combinational blue light emitting diode-high frequency focused ultrasound treatment could have therapeutic benefits to alleviate cancer cell proliferation.

Beyond conventional c-plane GaN-based light emitting diodes: A systematic exploration of LEDs on semi-polar orientations

NASA Astrophysics Data System (ADS)

Monavarian, Morteza

Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the "Green Gap", is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the "quantum confined Stark effect") and low indium incorporation efficiency that are the two main factors that contribute to the Green Gap phenomenon. One possible approach that holds promise for a new generation of green and yellow light emitting devices with higher efficiency is the deployment of nonpolar and semi-polar crystallographic orientations of GaN to eliminate or mitigate polarization fields. In theory, the use of other GaN planes for light emitters could also enhance the efficiency of indium incorporation compared to c-plane. In this thesis, I present a systematic exploration of the suitable GaN orientation for future lighting technologies. First, in order to lay the groundwork for further studies, it is important to discuss the analysis of processes limiting LED efficiency and some novel designs of active regions to overcome these limitations. Afterwards, the choice of nonpolar orientations as an alternative is discussed. For nonpolar orientation, the (1100)-oriented (mo-plane) structures on patterned Si (112) and freestanding m-GaN are studied. The semi-polar orientations having substantially reduced polarization field are found to be more promising for light-emitting diodes (LEDs) owing to high indium incorporation efficiency predicted by theoretical studies. Thus, the semi-polar orientations are given close attention as alternatives for future LED technology

High-luminosity blue and blue-green gallium nitride light-emitting diodes.

PubMed

Morkoç, H; Mohammad, S N

1995-01-06

Compact and efficient sources of blue light for full color display applications and lighting eluded and tantalized researchers for many years. Semiconductor light sources are attractive owing to their reliability and amenability to mass manufacture. However, large band gaps are required to achieve blue color. A class of compound semiconductors formed by metal nitrides, GaN and its allied compounds AIGaN and InGaN, exhibits properties well suited for not only blue and blue-green emitters, but also for ultraviolet emitters and detectors. What thwarted engineers and scientists from fabricating useful devices from these materials in the past was the poor quality of material and lack of p-type doping. Both of these obstacles have recently been overcome to the point where highluminosity blue and blue-green light-emitting diodes are now available in the marketplace.

InGaN based micro light emitting diodes featuring a buried GaN tunnel junction

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

Malinverni, M., E-mail: marco.malinverni@epfl.ch; Martin, D.; Grandjean, N.

GaN tunnel junctions (TJs) are grown by ammonia molecular beam epitaxy. High doping levels are achieved with a net acceptor concentration close to ∼10{sup 20 }cm{sup −3}, thanks to the low growth temperature. This allows for the realization of p-n junctions with ultrathin depletion width enabling efficient interband tunneling. n-p-n structures featuring such a TJ exhibit low leakage current densities, e.g., <5 × 10{sup −5} A cm{sup −2} at reverse bias of 10 V. Under forward bias, the voltage is 3.3 V and 4.8 V for current densities of 20 A cm{sup −2} and 2000 A cm{sup −2}, respectively. The specific series resistance of the whole device ismore » 3.7 × 10{sup −4} Ω cm{sup 2}. Then micro-light emitting diodes (μ-LEDs) featuring buried TJs are fabricated. Excellent current confinement is demonstrated together with homogeneous electrical injection, as seen on electroluminescence mapping. Finally, the I-V characteristics of μ-LEDs with various diameters point out the role of the access resistance at the current aperture edge.« less

Organic light emitting diode with surface modification layer

DOEpatents

Basil, John D.; Bhandari, Abhinav; Buhay, Harry; Arbab, Mehran; Marietti, Gary J.

2017-09-12

An organic light emitting diode (10) includes a substrate (12) having a first surface (14) and a second surface (16), a first electrode (32), and a second electrode (38). An emissive layer (36) is located between the first electrode (32) and the second electrode (38). The organic light emitting diode (10) further includes a surface modification layer (18). The surface modification layer (18) includes a non-planar surface (30, 52).

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

Wheat Under LED's (Light Emitting Diodes)

NASA Technical Reports Server (NTRS)

2004-01-01

Astroculture is a suite of technologies used to produce and maintain a closed controlled environment for plant growth. The two most recent missions supported growth of potato, dwarf wheat, and mustard plants, and provided scientists with the first opportunity to conduct true plant research in space. Light emitting diodes have particular usefulness for plant growth lighting because they emit a much smaller amount of radiant heat than do conventional lighting sources and because they have potential of directing a higher percentage of the emitted light onto plants surfaces. Furthermore, the high output LED's have emissions in the 600-700 nm waveband, which is of highest efficiency for photosynthesis by plants.

Highly efficient all-nitride phosphor-converted white light emitting diode

NASA Astrophysics Data System (ADS)

Mueller-Mach, Regina; Mueller, Gerd; Krames, Michael R.; Höppe, Henning A.; Stadler, Florian; Schnick, Wolfgang; Juestel, Thomas; Schmidt, Peter

2005-07-01

The development and demonstration of a highly efficient warm-white all-nitride phosphor-converted light emitting diode (pc-LED) is presented utilizing a GaN based quantum well blue LED and two novel nitrogen containing luminescent materials, both of which are doped with Eu2+. For color conversion of the primary blue the nitridosilicates M2Si5N8 (orange-red) and MSi2O2N2 (yellow-green), with M = alkaline earth, were employed, thus achieving a high luminous efficiency (25 lumen/W at 1 W input), excellent color quality (correlated color temperature CCT = 3200 K, general color rendering index Ra > 90) and the highest proven color stability of any pc-LED obtained so far. Thus, these novel all-nitride LEDs are superior to both incandescent and fluorescent lamps and may therefore become the next generation of general lighting sources.

An entangled-light-emitting diode.

PubMed

Salter, C L; Stevenson, R M; Farrer, I; Nicoll, C A; Ritchie, D A; Shields, A J

2010-06-03

An optical quantum computer, powerful enough to solve problems so far intractable using conventional digital logic, requires a large number of entangled photons. At present, entangled-light sources are optically driven with lasers, which are impractical for quantum computing owing to the bulk and complexity of the optics required for large-scale applications. Parametric down-conversion is the most widely used source of entangled light, and has been used to implement non-destructive quantum logic gates. However, these sources are Poissonian and probabilistically emit zero or multiple entangled photon pairs in most cycles, fundamentally limiting the success probability of quantum computational operations. These complications can be overcome by using an electrically driven on-demand source of entangled photon pairs, but so far such a source has not been produced. Here we report the realization of an electrically driven source of entangled photon pairs, consisting of a quantum dot embedded in a semiconductor light-emitting diode (LED) structure. We show that the device emits entangled photon pairs under d.c. and a.c. injection, the latter achieving an entanglement fidelity of up to 0.82. Entangled light with such high fidelity is sufficient for application in quantum relays, in core components of quantum computing such as teleportation, and in entanglement swapping. The a.c. operation of the entangled-light-emitting diode (ELED) indicates its potential function as an on-demand source without the need for a complicated laser driving system; consequently, the ELED is at present the best source on which to base future scalable quantum information applications.

High-Brightness Blue Light-Emitting Diodes Enabled by a Directly Grown Graphene Buffer Layer.

PubMed

Chen, Zhaolong; Zhang, Xiang; Dou, Zhipeng; Wei, Tongbo; Liu, Zhiqiang; Qi, Yue; Ci, Haina; Wang, Yunyu; Li, Yang; Chang, Hongliang; Yan, Jianchang; Yang, Shenyuan; Zhang, Yanfeng; Wang, Junxi; Gao, Peng; Li, Jinmin; Liu, Zhongfan

2018-06-08

Single-crystalline GaN-based light-emitting diodes (LEDs) with high efficiency and long lifetime are the most promising solid-state lighting source compared with conventional incandescent and fluorescent lamps. However, the lattice and thermal mismatch between GaN and sapphire substrate always induces high stress and high density of dislocations and thus degrades the performance of LEDs. Here, the growth of high-quality GaN with low stress and a low density of dislocations on graphene (Gr) buffered sapphire substrate is reported for high-brightness blue LEDs. Gr films are directly grown on sapphire substrate to avoid the tedious transfer process and GaN is grown by metal-organic chemical vapor deposition (MOCVD). The introduced Gr buffer layer greatly releases biaxial stress and reduces the density of dislocations in GaN film and In x Ga 1- x N/GaN multiple quantum well structures. The as-fabricated LED devices therefore deliver much higher light output power compared to that on a bare sapphire substrate, which even outperforms the mature process derived counterpart. The GaN growth on Gr buffered sapphire only requires one-step growth, which largely shortens the MOCVD growth time. This facile strategy may pave a new way for applications of Gr films and bring several disruptive technologies for epitaxial growth of GaN film and its applications in high-brightness LEDs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polarized edge emission from GaN-based light-emitting diodes sandwiched by dielectric/metal hybrid reflectors

NASA Astrophysics Data System (ADS)

Yan, L. J.; Sheu, J. K.; Huang, F. W.; Lee, M. L.

2010-12-01

Edge-emitting c-plane GaN/sapphire-based light-emitting diodes (LEDs) sandwiched by two dielectric/metal hybrid reflectors on both sapphire and GaN surfaces were studied to determine their light emission polarization. The hybrid reflectors comprised dielectric multiple thin films and a metal layer. The metal layers of Au or Ag used in this study were designed to enhance the polarization ratio from S-polarization (transverse electric wave, TE) to P-polarization (transverse magnetic wave, TM). The two sets of optimized dielectric multi thin films served as matching layers for wide-angle incident light on both sapphire and GaN surfaces. To determine which reflector scheme would achieve a higher polarization ratio, simulations of the reflectance at the hybrid reflectors on sapphire (or GaN) interface were performed before the fabrication of experimental LEDs. Compared with conventional c-plane InGaN/GaN/sapphire LEDs without dielectric/metal hybrid reflectors, the experimental LEDs exhibited higher polarization ratio (ITE-max/ITM-max) with r=2.174 (˜3.37 dB) at a wavelength of 460 nm. In contrast, the original polarized light (without dielectric/metal hybrid reflectors) was partially contributed (r=1.398) by C-HH or C-LH (C band to the heavy-hole sub-band or C band to the crystal-field split-off sub-band) transitions along the a-plane or m-plane direction.

Long Persistent Light Emitting Diode Indicators

ERIC Educational Resources Information Center

Jia, Dongdong; Ma, Yiwei; Hunter, D. N.

2007-01-01

An undergraduate laboratory was designed for undergraduate students to make long persistent light emitting diode (LED) indicators using phosphors. Blue LEDs, which emit at 465 nm, were characterized and used as an excitation source. Long persistent phosphors, SrAl[subscript 2]O[subscript 4]:Eu[superscript 2+],Dy[superscript 3+] (green) and…

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

Graphene as current spreading layer on AlGaInP light emitting diodes

NASA Astrophysics Data System (ADS)

Guo, Xia; Feng, Yajie; Liu, Qiaoli; Hu, Anqi; He, Xiaoying; Hu, Zonghai

2018-05-01

Due to high transmittance and high mobility, graphene is one of the promising candidates for a current spreading layer, which is crucial to light emitting diode (LED) performance. In this paper, improved AlGaInP LED performance was reported after graphene was applied on the GaP surface. Due to its lowered work function difference than with the GaN material, the electrical properties remain the same without additional voltage bias. The light output power is enhanced by about 40% under the current injection of 5 mA at room temperature, which was confirmed by the light emission profile analysis in this study. Such results indicate that raphene is a promising candidate as a current spreading layer under low current injection.

High extraction efficiency ultraviolet light-emitting diode

DOEpatents

Wierer, Jonathan; Montano, Ines; Allerman, Andrew A.

2015-11-24

Ultraviolet light-emitting diodes with tailored AlGaN quantum wells can achieve high extraction efficiency. For efficient bottom light extraction, parallel polarized light is preferred, because it propagates predominately perpendicular to the QW plane and into the typical and more efficient light escape cones. This is favored over perpendicular polarized light that propagates along the QW plane which requires multiple, lossy bounces before extraction. The thickness and carrier density of AlGaN QW layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. At Al>0.3, thinner QW layers (<2.5 nm are preferred) result in light preferentially polarized parallel to the QW plane. Also, active regions consisting of six or more QWs, to reduce carrier density, and with thin barriers, to efficiently inject carriers in all the QWs, are preferred.

Detection and modeling of leakage current in AlGaN-based deep ultraviolet light-emitting diodes

DOE PAGES

Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; ...

2015-03-01

Current-voltage (IV) characteristics of two AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) with differing densities of open-core threading dislocations (nanopipes) are analyzed. A three-diode circuit is simulated to emulate the IV characteristics of the DUV-LEDs, but is only able to accurately model the lower leakage current, lower nanopipe density DUV-LED. It was found that current leakage through the nanopipes in these structures is rectifying, despite nanopipes being previously established as inherently n-type. Using defect-sensitive etching, the nanopipes are revealed to terminate within the p-type GaN capping layer of the DUV-LEDs. The circuit model is modified to account for another p-nmore » junction between the n-type nanopipes and the p-type GaN, and an excellent fit to the IV characteristics of the leaky DUV-LED is achieved.« less

Reshaping Light-Emitting Diodes To Increase External Efficiency

NASA Technical Reports Server (NTRS)

Rogowski, Robert; Egalon, Claudio

1995-01-01

Light-emitting diodes (LEDs) reshaped, according to proposal, increasing amount of light emitted by decreasing fraction of light trapped via total internal reflection. Results in greater luminous output power for same electrical input power; greater external efficiency. Furthermore, light emitted by reshaped LEDs more nearly collimated (less diffuse). Concept potentially advantageous for conventional red-emitting LEDs. More advantageous for new "blue" LEDs, because luminous outputs and efficiencies of these devices very low. Another advantage, proposed conical shapes achieved relatively easily by chemical etching of semiconductor surfaces.

Direct grafting of long-lived luminescent indicator dyes to GaN light-emitting diodes for chemical microsensor development.

PubMed

López-Gejo, Juan; Navarro-Tobar, Álvaro; Arranz, Antonio; Palacio, Carlos; Muñoz, Elías; Orellana, Guillermo

2011-10-01

Two new methods for covalent functionalization of GaN based on plasma activation of its surface are presented. Both of them allow attachment of sulfonated luminescent ruthenium(II) indicator dyes to the p- and n-type semiconductor as well as to the surface of nonencapsulated chips of GaN light-emitting diodes (blue LEDs). X-ray photoelectron spectroscopy analysis of the functionalized semiconductor confirms the formation of covalent bonds between the GaN surface and the dye. Confocal fluorescence microscopy with single-photon-timing (SPT) detection has been used for characterization of the functionalized surfaces and LED chips. While the ruthenium complex attached to p-GaN under an oxygen-free atmosphere gives significantly long mean emission lifetimes for the indicator dye (ca. 2000 ns), the n-GaN-functionalized surfaces display surprisingly low values (600 ns), suggesting the occurrence of a quenching process. A photoinduced electron injection from the dye to the semiconductor conduction band, followed by a fast back electron transfer, is proposed to be responsible for the excited ruthenium dye deactivation. This process invalidates the use of the n-GaN/dye system for sensing applications. However, for p-GaN/dye materials, the luminescence decay accelerates in the presence of O(2). The moderate sensitivity is attributed to the fact that only a monolayer of indicator dye is anchored to the semiconductor surface but serves as a demonstrator device. Moreover, the luminescence decays of the functionalized LED chip measured with excitation of either an external (laser) source or the underlying LED emission (from p-GaN/InGaN quantum wells) yield the same mean luminescence lifetime. These results pave the way for using advanced LEDs to develop integrateable optochemical microsensors for gas analysis. © 2011 American Chemical Society

Room temperature current injection polariton light emitting diode with a hybrid microcavity.

PubMed

Lu, Tien-Chang; Chen, Jun-Rong; Lin, Shiang-Chi; Huang, Si-Wei; Wang, Shing-Chung; Yamamoto, Yoshihisa

2011-07-13

The strong light-matter interaction within a semiconductor high-Q microcavity has been used to produce half-matter/half-light quasiparticles, exciton-polaritons. The exciton-polaritons have very small effective mass and controllable energy-momentum dispersion relation. These unique properties of polaritons provide the possibility to investigate the fundamental physics including solid-state cavity quantum electrodynamics, and dynamical Bose-Einstein condensates (BECs). Thus far the polariton BEC has been demonstrated using optical excitation. However, from a practical viewpoint, the current injection polariton devices operating at room temperature would be most desirable. Here we report the first realization of a current injection microcavity GaN exciton-polariton light emitting diode (LED) operating under room temperature. The exciton-polariton emission from the LED at photon energy 3.02 eV under strong coupling condition is confirmed through temperature-dependent and angle-resolved electroluminescence spectra.

Evaluation of light-emitting diode beacon light fixtures : final report.

DOT National Transportation Integrated Search

2009-12-01

Rotating beacons containing filament light sources have long been used on highway maintenance trucks : to indicate the presence of the truck to other drivers. Because of advances in light-emitting diode (LED) : technologies, flashing lights containin...

Broadband mid-infrared superlattice light-emitting diodes

NASA Astrophysics Data System (ADS)

Ricker, R. J.; Provence, S. R.; Norton, D. T.; Boggess, T. F.; Prineas, J. P.

2017-05-01

InAs/GaSb type-II superlattice light-emitting diodes were fabricated to form a device that provides emission over the entire 3-5 μm mid-infrared transmission window. Variable bandgap emission regions were coupled together using tunnel junctions to emit at peak wavelengths of 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.4 μm, 4.7 μm, and 5.0 μm. Cascading the structure recycles the electrons in each emission region to emit several wavelengths simultaneously. At high current densities, the light-emitting diode spectra broadened into a continuous, broadband spectrum that covered the entire mid-infrared band. When cooled to 77 K, radiances of over 1 W/cm2 sr were achieved, demonstrating apparent temperatures above 1000 K over the 3-5 μm band. InAs/GaSb type-II superlattices are capable of emitting from 3 μm to 30 μm, and the device design can be expanded to include longer emission wavelengths.

Organic light-emitting diode materials

DOEpatents

Aspuru-Guzik, Alan; Gomez-Bombarelli, Rafael; Aguilera-Iparraguirre, Jorge; Baldo, Marc; Van Voorhis, Troy; Hirzel, Timothy D.; Bahlke, Matthias; McMahon, David; Wu, Tony Chang-Chi

2018-05-15

Described herein are molecules for use in organic light emitting diodes. Example molecules comprise at least one moiety A and at least one moiety D. Values and preferred values of the moieties A and D are described herein. The molecules comprise at least one atom selected from Si, Se, Ge, Sn, P, or As.

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.

Light Emitting Diode (LED)

NASA Technical Reports Server (NTRS)

1997-01-01

A special lighting technology was developed for space-based commercial plant growth research on NASA's Space Shuttle. Surgeons have used this technology to treat brain cancer on Earth, in two successful operations. The treatment technique called photodynamic therapy, requires the surgeon to use tiny pinhead-size Light Emitting Diodes (LEDs) (a source releasing long wavelengths of light) to activate light-sensitive, tumor-treating drugs. Laser light has been used for this type of surgery in the past, but the LED light illuminates through all nearby tissues, reaching parts of a tumor that shorter wavelengths of laser light carnot. The new probe is safer because the longer wavelengths of light are cooler than the shorter wavelengths of laser light, making the LED less likely to injure normal brain tissue near the tumor. It can also be used for hours at a time while still remaining cool to the touch. The LED probe consists of 144 tiny pinhead-size diodes, is 9-inches long, and about one-half-inch in diameter. The small balloon aids in even distribution of the light source. The LED light source is compact, about the size of a briefcase, and can be purchased for a fraction of the cost of a laser. The probe was developed for photodynamic cancer therapy by the Marshall Space Flight Center under a NASA Small Business Innovative Research program grant.

Improved light extraction efficiency of GaN-based flip-chip light-emitting diodes with an antireflective interface layer

NASA Astrophysics Data System (ADS)

Wu, Dongxue; Ma, Ping; Liu, Boting; Zhang, Shuo; Wang, Junxi; Li, Jinmin

2016-05-01

GaN-based flip-chip light-emitting diodes (FC-LEDs) grown on nanopatterned sapphire substrates (NPSS) are fabricated using self-assembled SiO2 nanospheres as masks during inductively coupled plasma etching. By controlling the pattern spacing, epitaxial GaN can be grown from the top or bottom of patterns to obtain two different GaN/substrate interfaces. The optoelectronic characteristics of FC-LED chips with different GaN/sapphire interfaces are studied. The FC-LED with an antireflective interface layer consisting of a NPSS with GaN in the pattern spacings demonstrates better optical properties than the FC-LED with an interface embedded with air voids. Our study indicates that the two types of FC-LEDs grown on NPSS show higher crystal quality and improved electrical and optical characteristics compared with those of FC-LEDs grown on conventional planar sapphire substrates.

Aluminum-nanodisc-induced collective lattice resonances: Controlling the light extraction in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Auer-Berger, Manuel; Tretnak, Veronika; Wenzl, Franz-Peter; Krenn, Joachim R.; List-Kratochvil, Emil J. W.

2017-10-01

We examine aluminum-nanodisc-induced collective lattice resonances as a means to enhance the efficiency of organic light emitting diodes. Thus, nanodisc arrays were embedded in the hole transporting layer of a solution-processed phosphorescent organic blue-light emitting diode. Through extinction spectroscopy, we confirm the emergence of array-induced collective lattice resonances within the organic light emitting diode. Through finite-difference time domain simulations, we show that the collective lattice resonances yield an enhancement of the electric field intensity within the emissive layer. The effectiveness for improving the light generation and light outcoupling is demonstrated by electro-optical characterization, realizing a gain in a current efficiency of 35%.

The Light-Emitting Diode as a Light Detector

ERIC Educational Resources Information Center

Baird, William H.; Hack, W. Nathan; Tran, Kiet; Vira, Zeeshan; Pickett, Matthew

2011-01-01

A light-emitting diode (LED) and operational amplifier can be used as an affordable method to provide a digital output indicating detection of an intense light source such as a laser beam or high-output LED. When coupled with a microcontroller, the combination can be used as a multiple photogate and timer for under $50. A similar circuit is used…

GaN-Based Light-Emitting Diodes Grown on Nanoscale Patterned Sapphire Substrates with Void-Embedded Cortex-Like Nanostructures

NASA Astrophysics Data System (ADS)

Lin, Yu-Sheng; Yeh, J. Andrew

2011-09-01

High-efficiency GaN-based light-emitting diodes (LEDs) with an emitting wavelength of 438 nm were demonstrated utilizing nanoscale patterned sapphire substrates with void-embedded cortex-like nanostructures (NPSS-VECN). Unlike the previous nanopatterned sapphire substrates, the presented substrate has a new morphology that can not only improve the crystalline quality of GaN epilayers but also generate a void-embedded nanostructural layer to enhance light extraction. Under a driving current of 20 mA, the external quantum efficiency of an LED with NPSS-VECN is enhanced by 2.4-fold compared with that of the conventional LED. Moreover, the output powers of two devices respectively are 33.1 and 13.9 mW.

Light-Emitting Diodes: A Hidden Treasure

ERIC Educational Resources Information Center

Planinšic, Gorazd; Etkina, Eugenia

2014-01-01

LEDs, or light-emitting diodes, are cheap, easy to purchase, and thus commonly used in physics instruction as indicators of electric current or as sources of light (Fig. 1). In our opinion LEDs represent a unique piece of equipment that can be used to collect experimental evidence, and construct and test new ideas in almost every unit of a general…

Method and apparatus for improving the performance of light emitting diodes

DOEpatents

Lowery, Christopher H.; McElfresh, David K.; Burchet, Steve; Adolf, Douglas B.; Martin, James

1996-01-01

A method for increasing the resistance of a light emitting diode and other semiconductor devices to extremes of temperature is disclosed. During the manufacture of the light emitting diode, a liquid coating is applied to the light emitting die after the die has been placed in its lead frame. After the liquid coating has been placed on the die and its lead frames, a thermosetting encapsulant material is placed over the coating. The operation that cures the thermosetting material leaves the coating liquid intact. As the die and the encapsulant expand and contract at different rates with respect to changes in temperature, and as in known light emitting diodes the encapsulating material adheres to the die and lead frames, this liquid coating reduces the stresses that these different rates of expansion and contraction normally cause by eliminating the adherence of the encapsulating material to the die and frame.

Design Considerations for a Water Treatment System Utilizing Ultra-Violet Light Emitting Diodes

DTIC Science & Technology

2014-03-27

DESIGN CONSIDERATIONS FOR A WATER TREATMENT SYSTEM UTILIZING ULTRA-VIOLET LIGHT EMITTING DIODES...the United States. ii AFIT-ENV-14-M-58 DESIGN CONSIDERATIONS FOR A WATER TREATMENT SYSTEM UTILIZING ULTRA-VIOLET LIGHT EMITTING DIODES...DISTRIBUTION UNLIMITED. iii AFIT-ENV-14-M-58 DESIGN CONSIDERATIONS FOR A WATER TREATMENT SYSTEM UTILIZING ULTRA-VIOLET LIGHT EMITTING

Optical design of tunnel lighting with white light-emitting diodes.

PubMed

Tsai, Ming-Shiou; Lee, Xuan-Hao; Lo, Yi-Chien; Sun, Ching-Cherng

2014-10-10

This paper presents a tunnel lighting design consisting of a cluster light-emitting diode and a free-form lens. Most of the energy emitted from the proposed luminaire is transmitted onto the surface of the road in front of drivers, and the probability that that energy is emitted directly into drivers' eyes is low. Compared with traditional fluorescent lamps, the proposed luminaire, of which the optical utilization factor, optical efficiency, and uniformity are, respectively, 44%, 92.5%, and 0.72, exhibits favorable performance in energy saving, glare reduction, and traffic safety.

Assessment of the performance of light-emitting diode roadway lighting technology.

DOT National Transportation Integrated Search

2015-10-01

This study, championed by the Virginia Department of Transportation (VDOT) Traffic Engineering : Division, involved a thorough investigation of light-emitting diode (LED) roadway lighting technology by : testing six types of roadway luminaires (inclu...

Efficiency enhancement of blue light emitting diodes by eliminating V-defects from InGaN/GaN multiple quantum well structures through GaN capping layer control

NASA Astrophysics Data System (ADS)

Tsai, Sheng-Chieh; Li, Ming-Jui; Fang, Hsin-Chiao; Tu, Chia-Hao; Liu, Chuan-Pu

2018-05-01

A facile method for fabricating blue light-emitting diodes (B-LEDs) with small embedded quantum dots (QDs) and enhanced light emission is demonstrated by tuning the temperature of the growing GaN capping layer to eliminate V-defects. As the growth temperature increases from 770 °C to 840 °C, not only does the density of the V-defects reduce from 4.12 ∗ 108 #/cm2 nm to zero on a smooth surface, but the QDs also get smaller. Therefore, the growth mechanism of smaller QDs assisted by elimination of V-defects is discussed. Photoluminescence and electroluminescence results show that smaller embedded QDs can improve recombination efficiency, and thus achieve higher peak intensity with smaller peak broadening. Accordingly, the external quantum efficiency of the B-LEDs with smaller QDs is enhanced, leading to a 6.8% increase in light output power in lamp-form package LEDs.

Mn2- x Y x (MoO4)3 Phosphor Excited by UV GaN-Based Light-Emitting Diode for White Emission

NASA Astrophysics Data System (ADS)

Chen, Lung-Chien; Tseng, Zong-Liang; Hsu, Ting-Chun; Yang, Shengyi; Chen, Yuan-Bin

2017-04-01

One option for low-cost white light-emitting diodes (LEDs) is the combination of a near-ultraviolet (UV) LED chip (382 nm) and a single phosphor. Such Mn2- x Y x (MoO4)3 single phosphors have been fabricated by a simple solid-state reaction route and their emission color tuned by controlling the Mn doping amount. The chromaticity coordinates of the white light emitted by the UV GaN LED with the MnY(MoO4)3 phosphor were x = 0.5204 and y = 0.4050 [correlated color temperature (CCT) = 7958 K].

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.

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.

White organic light-emitting diodes with ultra-thin mixed emitting layer

NASA Astrophysics Data System (ADS)

Jeon, T.; Forget, S.; Chenais, S.; Geffroy, B.; Tondelier, D.; Bonnassieux, Y.; Ishow, E.

2012-02-01

White light can be obtained from Organic Light Emitting Diodes by mixing three primary colors, (i.e. red, green and blue) or two complementary colors in the emissive layer. In order to improve the efficiency and stability of the devices, a host-guest system is generally used as an emitting layer. However, the color balance to obtain white light is difficult to control and optimize because the spectrum is very sensitive to doping concentration (especially when a small amount of material is used). We use here an ultra-thin mixed emitting layer (UML) deposited by thermal evaporation to fabricate white organic light emitting diodes (WOLEDs) without co-evaporation. The UML was inserted in the hole-transporting layer consisting of 4, 4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (α-NPB) instead of using a conventional doping process. The UML was formed from a single evaporation boat containing a mixture of two dipolar starbust triarylamine molecules (fvin and fcho) presenting very similar structures and thermal properties and emitting in complementary spectral regions (orange and blue respectively) and mixed according to their weight ratio. The composition of the UML specifically allows for fine tuning of the emission color despite its very thin thickness down to 1 nm. Competitive energy transfer processes from fcho and the host interface toward fvin are key parameters to control the relative intensity between red and blue emission. White light with very good CIE 1931 color coordinate (0.34, 0.34) was obtained by simply adjusting the UML film composition.

Vacuum Nanohole Array Embedded Phosphorescent Organic Light Emitting Diodes

PubMed Central

Jeon, Sohee; Lee, Jeong-Hwan; Jeong, Jun-Ho; Song, Young Seok; Moon, Chang-Ki; Kim, Jang-Joo; Youn, Jae Ryoun

2015-01-01

Light extraction from organic light-emitting diodes that utilize phosphorescent materials has an internal efficiency of 100% but is limited by an external quantum efficiency (EQE) of 30%. In this study, extremely high-efficiency organic light emitting diodes (OLEDs) with an EQE of greater than 50% and low roll-off were produced by inserting a vacuum nanohole array (VNHA) into phosphorescent OLEDs (PhOLEDs). The resultant extraction enhancement was quantified in terms of EQE by comparing experimentally measured results with those produced from optical modeling analysis, which assumes the near-perfect electric characteristics of the device. A comparison of the experimental data and optical modeling results indicated that the VNHA extracts the entire waveguide loss into the air. The EQE obtained in this study is the highest value obtained to date for bottom-emitting OLEDs. PMID:25732061

Poly (p-phenyleneneacetylene) light-emitting diodes

DOEpatents

Shinar, Joseph; Swanson, Leland S.; Lu, Feng; Ding, Yiwei; Barton, Thomas J.; Vardeny, Zeev V.

1994-10-04

Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes.

Poly (p-phenyleneacetylene) light-emitting diodes

DOEpatents

Shinar, J.; Swanson, L.S.; Lu, F.; Ding, Y.; Barton, T.J.; Vardeny, Z.V.

1994-10-04

Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes. 8 figs.

Light-Emitting Diodes: Learning New Physics

ERIC Educational Resources Information Center

Planinšic, Gorazd; Etkina, Eugenia

2015-01-01

This is the third paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide the readers with the description of experiments and pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper, published…

Light-Emitting Diodes: Solving Complex Problems

ERIC Educational Resources Information Center

Planinšic, Gorazd; Etkina, Eugenia

2015-01-01

This is the fourth paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide readers with the description of experiments and the pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper provided…

Multilayer white lighting polymer light-emitting diodes

NASA Astrophysics Data System (ADS)

Gong, Xiong; Wang, Shu; Heeger, Alan J.

2006-08-01

Organic and polymer light-emitting diodes (OLEDs/PLEDs) that emit white light are of interest and potential importance for use in active matrix displays (with color filters) and because they might eventually be used for solid-state lighting. In such applications, large-area devices and low-cost of manufacturing will be major issues. We demonstrated that high performance multilayer white emitting PLEDs can be fabricated by using a blend of luminescent semiconducting polymers and organometallic complexes as the emission layer, and water-soluble (or ethanol-soluble) polymers/small molecules (for example, PVK-SO 3Li) as the hole injection/transport layer (HIL/HTL) and water-soluble (or ethanol-soluble) polymers/small molecules (for example, t-Bu-PBD-SO 3Na) as the electron injection/transport layer (EIL/HTL). Each layer is spin-cast sequentially from solutions. Illumination quality light is obtained with stable Commission Internationale d'Eclairage coordinates, stable color temperatures, and stable high color rendering indices, all close to those of "pure" white. The multilayer white-emitting PLEDs exhibit luminous efficiency of 21 cd/A, power efficiency of 6 lm/W at a current density of 23 mA/cm2 with luminance of 5.5 x 10 4 cd/m2 at 16 V. By using water-soluble (ethanol-soluble) polymers/small molecules as HIL/HTL and polymers/small molecules as EIL/ETL, the interfacial mixing problem is solved (the emissive polymer layer is soluble in organic solvents, but not in water/ ethanol). As a result, this device architecture and process technology can potentially be used for printing large-area multiplayer light sources and for other applications in "plastic" electronics. More important, the promise of producing large areas of high quality white light with low-cost manufacturing technology makes the white multilayer white-emitting PLEDs attractive for the development of solid state light sources.

Flip-chip light emitting diode with resonant optical microcavity

DOEpatents

Gee, James M.; Bogart, Katherine H.A.; Fischer, Arthur J.

2005-11-29

A flip-chip light emitting diode with enhanced efficiency. The device structure employs a microcavity structure in a flip-chip configuration. The microcavity enhances the light emission in vertical modes, which are readily extracted from the device. Most of the rest of the light is emitted into waveguided lateral modes. Flip-chip configuration is advantageous for light emitting diodes (LEDs) grown on dielectric substrates (e.g., gallium nitride LEDs grown on sapphire substrates) in general due to better thermal dissipation and lower series resistance. Flip-chip configuration is advantageous for microcavity LEDs in particular because (a) one of the reflectors is a high-reflectivity metal ohmic contact that is already part of the flip-chip configuration, and (b) current conduction is only required through a single distributed Bragg reflector. Some of the waveguided lateral modes can also be extracted with angled sidewalls used for the interdigitated contacts in the flip-chip configuration.

An intraocular micro light-emitting diode device for endo-illumination during pars plana vitrectomy.

PubMed

Koelbl, Philipp S; Lingenfelder, Christian; Spraul, Christoph W; Kampmeier, Juergen; Koch, Frank Hj; Kim, Yong Keun; Hessling, Martin

2018-03-01

Development of a new, fiber-free, single-use endo-illuminator for pars plana vitrectomy as a replacement for fiber-based systems with external light sources. The hand-guided intraocularly placed white micro light-emitting diode is evaluated for its illumination properties and potential photochemical and thermal hazards. A micro light-emitting diode was used to develop a single-use intraocular illumination system. The light-source-on-tip device was implemented in a prototype with 23G trocar compatible outer diameter of 0.6 mm. The experimental testing was performed on porcine eyes. All calculations of possible photochemical and thermal hazards during the application of the intraocular micro light-emitting diode were calculated according to DIN EN ISO 15007-2: 2014. The endo-illuminator generated a homogeneous and bright illumination of the intraocular space. The color impression was physiologic and natural. Contrary to initial apprehension, the possible risk caused by inserting a light-emitting diode into the intraocular vitreous was much smaller when compared to conventional fiber-based illumination systems. The photochemical and thermal hazards allowed a continuous exposure time to the retina of at least 4.7 h. This first intraocular light source showed that a light-emitting diode can be introduced into the eye. The system can be built as single-use illumination system. This light-source-on-tip light-emitting diode-endo-illumination combines a chandelier wide-angle illumination with an adjustable endo-illuminator.

Improved output power of GaN-based light-emitting diodes grown on a nanopatterned sapphire substrate

NASA Astrophysics Data System (ADS)

Chan, Chia-Hua; Hou, Chia-Hung; Tseng, Shao-Ze; Chen, Tsing-Jen; Chien, Hung-Ta; Hsiao, Fu-Li; Lee, Chien-Chieh; Tsai, Yen-Ling; Chen, Chii-Chang

2009-07-01

This letter describes the improved output power of GaN-based light-emitting diodes (LEDs) formed on a nanopatterned sapphire substrate (NPSS) prepared through etching with a self-assembled monolayer of 750-nm-diameter SiO2 nanospheres used as the mask. The output power of NPSS LEDs was 76% greater than that of LEDs on a flat sapphire substrate. Three-dimensional finite-difference time-domain calculation predicted a 40% enhancement in light extraction efficiency of NPSS LEDs. In addition, the reduction of full widths at half maximum in the ω-scan rocking curves for the (0 0 2) and (1 0 2) planes of GaN on NPSS suggested improved crystal quality.

Broadband visible light source based on AllnGaN light emitting diodes

DOEpatents

Crawford, Mary H.; Nelson, Jeffrey S.

2003-12-16

A visible light source device is described based on a light emitting diode and a nanocluster-based film. The light emitting diode utilizes a semiconductor quantum well structure between n-type and p-type semiconductor materials on the top surface a substrate such as sapphire. The nanocluster-based film is deposited on the bottom surface of the substrate and can be derived from a solution of MoS.sub.2, MoSe.sub.2, WS.sub.2, and WSe.sub.2 particles of size greater than approximately 2 nm in diameter and less than approximately 15 nm in diameter, having an absorption wavelength greater than approximately 300 nm and less than approximately 650 nm.

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.

Carrier-injection studies in GaN-based light-emitting-diodes

NASA Astrophysics Data System (ADS)

Nguyen, Dinh Chuong; Vaufrey, David; Leroux, Mathieu

2015-09-01

Although p-type GaN has been achieved by Mg doping, the low hole-mobility still remains a difficulty for GaN-based light-emitting diodes (LEDs). Due to the lack of field-dependent-velocity model for holes, in GaN-based LED simulations, the hole mobility is usually supposed to remain constant. However, as the p-GaN-layer conductivity is lower than the n-GaN-layer conductivity, a strong electric-field exists in the p-side of an LED when the applied voltage exceeds the LED's built-in voltage. Under the influence of this field, the mobilities of electrons and holes are expected to decrease. Based on a field-dependent-velocity model that is usually used for narrow-bandgap materials, an LED structure is modelled with three arbitrarily chosen hole saturation-velocities. The results show that a hole saturation-velocity lower than 4x106 cm/s can negatively affect the LED's behaviors.

Ultraviolet laser ablation as technique for defect repair of GaN-based light-emitting diodes

NASA Astrophysics Data System (ADS)

Passow, Thorsten; Kunzer, Michael; Pfeuffer, Alexander; Binder, Michael; Wagner, Joachim

2018-03-01

Defect repair of GaN-based light-emitting diodes (LEDs) by ultraviolet laser micromachining is reported. Percussion and helical drilling in GaN by laser ablation were investigated using 248 nm nanosecond and 355 nm picosecond pulses. The influence of laser ablation including different laser parameters on electrical and optical properties of GaN-based LED chips was evaluated. The results for LEDs on sapphire with transparent conductive oxide p-type contact on top as well as for thin-film LEDs are reported. A reduction of leakage current by up to six orders in magnitude and homogeneous luminance distribution after proper laser defect treatment were achieved.

Effect of Dopant Activation on Device Characteristics of InGaN-based Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Lacroce, Nicholas; Liu, Guangyu; Tan, Chee-Keong; Arif, Ronald A.; Lee, Soo Min; Tansu, Nelson

2015-03-01

Achieving high uniformity in growths and device characteristics of InGaN-based light-emitting diodes (LEDs) is important for large scale manufacturing. Dopant activation and maintaining control of variables affecting dopant activation are critical steps in the InGaN-based light emitting diodes (LEDs) fabrication process. In the epitaxy of large scale production LEDs, in-situ post-growth annealing is used for activating the Mg acceptor dopant in the p-AlGaN and p-GaN of the LEDs. However, the annealing temperature varies with respect to position in the reactor chamber, leading to severe uniform dopant activation issue across the devices. Thus, it is important to understand how the temperature gradient and the resulting variance in Mg acceptor activation will alter the device properties. In this work, we examine the effect of varying p-type doping levels in the p-GaN layers and AlGaN electron blocking layer of the GaN LEDs on the optoelectronic properties including the band profile, carrier concentration, current density, output power and quantum efficiency. By understanding the variations and its effect, the identification of the most critical p-type doping layer strategies to address this variation will be clarified.

Investigating Bandgap Energies, Materials, and Design of Light-Emitting Diodes

ERIC Educational Resources Information Center

Wagner, Eugene P., II

2016-01-01

A student laboratory experiment to investigate the intrinsic and extrinsic bandgaps, dopant materials, and diode design in light-emitting diodes (LEDs) is presented. The LED intrinsic bandgap is determined by passing a small constant current through the diode and recording the junction voltage variation with temperature. A second visible…

Light emission mechanism of mixed host organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Song, Wook; Lee, Jun Yeob

2015-03-01

Light emission mechanism of organic light-emitting diodes with a mixed host emitting layer was studied using an exciplex type mixed host and an exciplex free mixed host. Monitoring of the current density and luminance of the two type mixed host devices revealed that the light emission process of the exciplex type mixed host was dominated by energy transfer, while the light emission of the exciplex free mixed host was controlled by charge trapping. Mixed host composition was also critical to the light emission mechanism, and the contribution of the energy transfer process was maximized at 50:50 mixed host composition. Therefore, it was possible to manage the light emission process of the mixed host devices by managing the mixed host composition.

High efficiency III-nitride light-emitting diodes

DOEpatents

Crawford, Mary; Koleske, Daniel; Cho, Jaehee; Zhu, Di; Noemaun, Ahmed; Schubert, Martin F; Schubert, E. Fred

2013-05-28

Tailored doping of barrier layers enables balancing of the radiative recombination among the multiple-quantum-wells in III-Nitride light-emitting diodes. This tailored doping enables more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop in high-power III-Nitride LEDs. Mitigation of the efficiency droop in III-Nitride LEDs may enable the pervasive market penetration of solid-state-lighting technologies in high-power lighting and illumination.

A flexible top-emitting organic light-emitting diode on steel foil

NASA Astrophysics Data System (ADS)

Xie, Zhiyuan; Hung, Liang-Sun; Zhu, Furong

2003-11-01

An efficient flexible top-emitting organic light-emitting diode (FTOLED) was developed on a thin steel foil. The FTOLED was constructed on the spin-on-glass (SOG)-coated steel substrate with an organic stack of NPB/Alq 3 sandwiched by a highly reflective Ag anode and a semitransparent Sm cathode. An ultrathin plasma-polymerized hydrocarbon film (CF X) was interposed between the Ag anode and the NPB layer to enhance hole-injection, and an additional Alq 3 layer was overlaid on the Sm cathode to increase light output. The FTOLED showed a peak efficiency of 4.4 cd/A higher than 3.7 cd/A of a convention NPB/Alq 3-based bottom-emitting OLED.

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

PubMed Central

Zhang, Liuqi; Yang, Xiaolei; Jiang, Qi; Wang, Pengyang; Yin, Zhigang; Zhang, Xingwang; Tan, Hairen; Yang, Yang (Michael); Wei, Mingyang; Sutherland, Brandon R.; Sargent, Edward H.; You, Jingbi

2017-01-01

Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m−2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date. PMID:28589960

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Liuqi; Yang, Xiaolei; Jiang, Qi; Wang, Pengyang; Yin, Zhigang; Zhang, Xingwang; Tan, Hairen; Yang, Yang (Michael); Wei, Mingyang; Sutherland, Brandon R.; Sargent, Edward H.; You, Jingbi

2017-06-01

Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m-2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

Polymer Light-Emitting Diode (PLED) Process Development

DTIC Science & Technology

2003-12-01

conclusions and recommendations for Phase II of the Flexible Display Program. 15. SUBJECT TERMS LIGHT EMITTING DIODES LIQUID CRYSTAL DISPLAY SYSTEMS...space for Phase I and II confined by backplane complexity and substrate form...12 Figure 6. Semi automated I-V curve measurement setup consisting of Keithley power supply, computer and

Indium-incorporation efficiency in semipolar (11-22) oriented InGaN-based light emitting diodes

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Metzner, Sebastian; Izyumskaya, Natalia; Okur, Serdal; Zhang, Fan; Can, Nuri; Das, Saikat; Avrutin, Vitaliy; Özgür, Ümit; Bertram, Frank; Christen, Jürgen; Morkoç, Hadis

2015-03-01

Reduced electric field in semipolar (1122) GaN/InGaN heterostructures makes this orientation attractive for high efficiency light emitting diodes. In this work, we investigated indium incorporation in semipolar (1122) GaN grown by metal-organic chemical vapor deposition on planar m-plane sapphire substrates. Indium content in the semipolar material was compared with that in polar c-plane samples grown under the same conditions simultaneously side by side on the same holder. The investigated samples incorporated dual GaN/InGaN/GaN double heterostructures with 3nm wide wells. In order to improve optical quality, both polar and semipolar templates were grown using an in-situ epitaxial lateral overgrowth (ELO) technique. Indium incorporation efficiency was derived from the comparison of PL spectra measured on the semipolar and polar structures at the highest excitation density, which allowed us to minimize the effect of quantum confined Stark effect on the emission wavelength. Our data suggests increased indium content in the semipolar material by up to 3.0%, from 15% In in c- GaN to 18% In in (1122) GaN.

Determining Planck's Constant Using a Light-emitting Diode.

ERIC Educational Resources Information Center

Sievers, Dennis; Wilson, Alan

1989-01-01

Describes a method for making a simple, inexpensive apparatus which can be used to determine Planck's constant. Provides illustrations of a circuit diagram using one or more light-emitting diodes and a BASIC computer program for simplifying calculations. (RT)

Nanoparticle embedded p-type electrodes for GaN-based flip-chip light emitting diodes.

PubMed

Kwak, Joon Seop; Song, J O; Seong, T Y; Kim, B I; Cho, J; Sone, C; Park, Y

2006-11-01

We have investigated high-quality ohmic contacts for flip-chip light emitting diodes using Zn-Ni nanoparticles/Ag schemes. The Zn-Ni nanoparticles/Ag contacts produce specific contact resistances of 10(-5)-10(-6) omegacm2 when annealed at temperatures of 330-530 degrees C for 1 min in air ambient, which are much better than those obtained from the Ag contacts. It is shown that blue InGaN/GaN multi-quantum well light emitting diodes fabricated with the annealed Zn-Ni nanoparticles/Ag contacts give much lower forward-bias voltages at 20 mA compared with those of the multi-quantum well light emitting diodes made with the as-deposited Ag contacts. It is further presented that the multi-quantum well light emitting diodes made with the Zn-Ni nanoparticles/Ag contacts show similar output power compared to those fabricated with the Ag contact layers.

Operation of AC Adapters Visualized Using Light-Emitting Diodes

ERIC Educational Resources Information Center

Regester, Jeffrey

2016-01-01

A bridge rectifier is a diamond-shaped configuration of diodes that serves to convert alternating current(AC) into direct current (DC). In our world of AC outlets and DC electronics, they are ubiquitous. Of course, most bridge rectifiers are built with regular diodes, not the light-emitting variety, because LEDs have a number of disadvantages. For…

Enhanced light extraction efficiency of GaN-based light-emittng diodes by nitrogen implanted current blocking layer

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

Kim, Yong Deok; Oh, Seung Kyu; Park, Min Joo

Highlights: • A nitrogen implanted current-blocking layer was successfully demonstrated. • Light-extraction efficiency and radiant intensity was increased by more than 20%. • Ion implantation was successfully implemented in GaN based light-emitting diodes. - Abstract: GaN-based light emitting diodes (LEDs) with a nitrogen implanted current-blocking layer (CBL) were successfully demonstrated for improving the light extraction efficiency (LEE) and radiant intensity. The LEE and radiant intensity of the LEDs with a shallow implanted CBL with nitrogen was greatly increased by more than 20% compared to that of a conventional LED without the CBL due to an increase in the effective currentmore » path, which reduces light absorption at the thick p-pad electrode. Meanwhile, deep implanted CBL with a nitrogen resulted in deterioration of the LEE and radiant intensity because of formation of crystal damage, followed by absorption of the light generated at the multi-quantum well(MQW). These results clearly suggest that ion implantation method, which is widely applied in the fabrication of Si based devices, can be successfully implemented in the fabrication of GaN based LEDs by optimization of implanted depth.« less

Organic light-emitting diodes from homoleptic square planar complexes

DOEpatents

Omary, Mohammad A

2013-11-12

Homoleptic square planar complexes [M(N.LAMBDA.N).sub.2], wherein two identical N.LAMBDA.N bidentate anionic ligands are coordinated to the M(II) metal center, including bidentate square planar complexes of triazolates, possess optical and electrical properties that make them useful for a wide variety of optical and electrical devices and applications. In particular, the complexes are useful for obtaining white or monochromatic organic light-emitting diodes ("OLEDs"). Improved white organic light emitting diode ("WOLED") designs have improved efficacy and/or color stability at high brightness in single- or two-emitter white or monochrome OLEDs that utilize homoleptic square planar complexes, including bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) ("Pt(ptp).sub.2").

Flexible White Light Emitting Diodes Based on Nitride Nanowires and Nanophosphors

PubMed Central

2016-01-01

We report the first demonstration of flexible white phosphor-converted light emitting diodes (LEDs) based on p–n junction core/shell nitride nanowires. GaN nanowires containing seven radial In0.2Ga0.8N/GaN quantum wells were grown by metal–organic chemical vapor deposition on a sapphire substrate by a catalyst-free approach. To fabricate the flexible LED, the nanowires are embedded into a phosphor-doped polymer matrix, peeled off from the growth substrate, and contacted using a flexible and transparent silver nanowire mesh. The electroluminescence of a flexible device presents a cool-white color with a spectral distribution covering a broad spectral range from 400 to 700 nm. Mechanical bending stress down to a curvature radius of 5 mm does not yield any degradation of the LED performance. The maximal measured external quantum efficiency of the white LED is 9.3%, and the wall plug efficiency is 2.4%. PMID:27331079

Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control.

PubMed

Sun, Liangfeng; Choi, Joshua J; Stachnik, David; Bartnik, Adam C; Hyun, Byung-Ryool; Malliaras, George G; Hanrath, Tobias; Wise, Frank W

2012-05-06

Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr(-1) m(-2)) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH(2) groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.

Structural, electrical and optical characterization of high brightness phosphor-free white light emitting diodes

NASA Astrophysics Data System (ADS)

Omiya, Hiromasa

Much interest currently exists in GaN and related materials for applications such as light-emitting devices operating in the amber to ultraviolet range. Solid-state lighting (SSL) using these materials is widely being investigated worldwide, especially due to their high-energy efficiency and its impact on environmental issues. A new approach for solid-state lighting uses phosphor-free white light emitting diodes (LEDs) that consist of blue, green, and red quantum wells (QW), all in a single device. This approach leads to improved color rendering, and directionality, compared to the conventional white LEDs that use yellow phosphor on blue or ultraviolet emitters. Improving the brightness of these phosphor-free white LEDs should enhance and accelerate the development of SSL technology. The main objective of the research reported in this dissertation is to provide a comprehensive understanding of the nature of the multiple quantum wells used in phosphor-free white LEDs. This dissertation starts with an introduction to lighting history, the fundamental concepts of nitride semiconductors, and the evolution of LED technology. Two important challenges in LED technology today are metal-semiconductor contacts and internal piezoelectric fields present in quantum well structures. Thus, the main portion of this dissertation consists of three parts dealing with metal-semiconductor interfaces, single quantum well structures, and multiple quantum well devices. Gold-nickel alloys are widely used as contacts to the p-region of LEDs. We have performed a detailed study for its evolution under standard annealing steps. The atomic arrangement of gold at its interface with GaN gives a clear explanation for the improved ohmic contact performance. We next focus on the nature of InGaN QWs. The dynamic response of the QWs was studied with electron holography and time-resolved cathodoluminescence. Establishing the correlation between energy band structure and the light emission spectra

234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes

NASA Astrophysics Data System (ADS)

Liu, Cheng; Ooi, Yu Kee; Islam, S. M.; Xing, Huili Grace; Jena, Debdeep; Zhang, Jing

2018-01-01

Deep ultraviolet (DUV) AlN-delta-GaN quantum well (QW) light-emitting diodes (LEDs) with emission wavelengths of 234 nm and 246 nm are proposed and demonstrated in this work. Our results reveal that the use of AlN-delta-GaN QW with ˜1-3 monolayer GaN delta-layer can achieve a large transverse electric (TE)-polarized spontaneous emission rate instead of transverse magnetic-polarized emission, contrary to what is observed in conventional AlGaN QW in the 230-250 nm wavelength regime. The switching of light polarization in the proposed AlN-delta-GaN QW active region is attributed to the rearrangement of the valence subbands near the Γ-point. The light radiation patterns obtained from angle-dependent electroluminescence measurements for the Molecular Beam Epitaxy (MBE)-grown 234 nm and 246 nm AlN-delta-GaN QW LEDs show that the photons are mainly emitted towards the surface rather than the edge, consistent with the simulated patterns achieved by the finite-difference time-domain modeling. The results demonstrate that the proposed AlN-delta-GaN QWs would potentially lead to high-efficiency TE-polarized surface-emitting DUV LEDs.

Phototoxic action of light emitting diode in the in vitro viability of Trichophyton rubrum.

PubMed

Amorim, José Cláudio Faria; Soares, Betania Maria; Alves, Orley Araújo; Ferreira, Marcus Vinícius Lucas; Sousa, Gerdal Roberto; Silveira, Lívio de Barros; Piancastelli, André Costa Cruz; Pinotti, Marcos

2012-01-01

Trichophyton rubrum is the most common agent of superficial mycosis of the skin and nails causing long lasting infections and high recurrence rates. Current treatment drawbacks involve topical medications not being able to reach the nail bed at therapeutic concentrations, systemic antifungal drugs failing to eradicate the fungus before the nails are renewed, severe side effects and selection of resistant fungal isolates. Photodynamic therapy (PDT) has been a promising alternative to conventional treatments. This study evaluated the in vitro effectiveness of toluidine blue O (TBO) irradiated by Light emitting diode (LED) in the reduction of T. rubrum viability. The fungal inoculums' was prepared and exposed to different TBO concentrations and energy densities of Light emitting diode for evaluate the T. rubrum sensibility to PDT and production effect fungicidal after photodynamic treatment. In addition, the profiles of the area and volume of the irradiated fungal suspensions were also investigated. A small reduction, in vitro, of fungal cells was observed after exposition to 100 µM toluidine blue O irradiated by 18 J/cm² Light emitting diode. Fungicidal effect occurred after 25 µM toluidine blue O irradiation by Light emitting diode with energy density of 72 J/cm². The analysis showed that the area and volume irradiated by the Light emitting diode were 52.2 mm² and 413.70 mm³, respectively. The results allowed to conclude that Photodynamic therapy using Light emitting diode under these experimental conditions is a possible alternative approach to inhibit in vitro T. rubrum and may be a promising new treatment for dermatophytosis caused by this fungus.

Progress in Piezo-Phototronic-Effect-Enhanced Light-Emitting Diodes and Pressure Imaging.

PubMed

Pan, Caofeng; Chen, Mengxiao; Yu, Ruomeng; Yang, Qing; Hu, Youfan; Zhang, Yan; Wang, Zhong Lin

2016-02-24

Wurtzite materials exhibit both semiconductor and piezoelectric properties under strains due to the non-central symmetric crystal structures. The three-way coupling of semiconductor properties, piezoelectric polarization and optical excitation in ZnO, GaN, CdS and other piezoelectric semiconductors leads to the emerging field of piezo-phototronics. This effect can efficiently manipulate the emission intensity of light-emitting diodes (LEDs) by utilizing the piezo-polarization charges created at the junction upon straining to modulate the energy band diagrams and the optoelectronic processes, such as generation, separation, recombination and/or transport of charge carriers. Starting from fundamental physics principles, recent progress in piezo-phototronic-effect-enhanced LEDs is reviewed; following their development from single-nanowire pressure-sensitive devices to high-resolution array matrices for pressure-distribution mapping applications. The piezo-phototronic effect provides a promising method to enhance the light emission of LEDs based on piezoelectric semiconductors through applying static strains, and may find perspective applications in various optoelectronic devices and integrated systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

A method used to overcome polarization effects in semi-polar structures of nitride light-emitting diodes emitting green radiation

NASA Astrophysics Data System (ADS)

Morawiec, Seweryn; Sarzała, Robert P.; Nakwaski, Włodzimierz

2013-11-01

Polarization effects are studied within nitride light-emitting diodes (LEDs) manufactured on standard polar and semipolar substrates. A new theoretical approach, somewhat different than standard ones, is proposed to this end. It is well known that when regular polar GaN substrates are used, strong piezoelectric and spontaneous polarizations create built-in electric fields leading to the quantum-confined Stark effects (QCSEs). These effects may be completely avoided in nonpolar crystallographic orientations, but then there are problems with manufacturing InGaN layers of relatively high Indium contents necessary for the green emission. Hence, a procedure leading to partly overcoming these polarization problems in semi-polar LEDs emitting green radiation is proposed. The (11 22) crystallographic substrate orientation (inclination angle of 58∘ to c plane) seems to be the most promising because it is characterized by low Miller-Bravais indices leading to high-quality and high Indium content smooth growth planes. Besides, it makes possible an increased Indium incorporation efficiency and it is efficient in suppressing QCSE. The In0.3Ga0.7N/GaN QW LED grown on the semipolar (11 22) substrate has been found as currently the optimal LED structure emitting green radiation.

High Intensity Organic Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Qi, Xiangfei

This thesis is dedicated to the fabrication, modeling, and characterization to achieve high efficiency organic light-emitting diodes (OLEDs) for illumination applications. Compared to conventional lighting sources, OLEDs enabled the direct conversion of electrical energy into light emission and have intrigued the world's lighting designers with the long-lasting, highly efficient illumination. We begin with a brief overview of organic technology, from basic organic semiconductor physics, to its application in optoelectronics, i.e. light-emitting diodes, photovoltaics, photodetectors and thin-film transistors. Due to the importance of phosphorescent materials, we will focus on the photophysics of metal complexes that is central to high efficiency OLED technology, followed by a transient study to examine the radiative decay dynamics in a series of phosphorescent platinum binuclear complexes. The major theme of this thesis is the design and optimization of a novel architecture where individual red, green and blue phosphorescent OLEDs are vertically stacked and electrically interconnected by the compound charge generation layers. We modeled carrier generation from the metal-oxide/doped organic interface based on a thermally assisted tunneling mechanism. The model provides insights to the optimization of a stacked OLED from both electrical and optical point of view. To realize the high intensity white lighting source, the efficient removal of heat is of a particular concern, especially in large-area devices. A fundamental transfer matrix analysis is introduced to predict the thermal properties in the devices. The analysis employs Laplace transforms to determine the response of the system to the combined effects of conduction, convection, and radiation. This perspective of constructing transmission matrices greatly facilitates the calculation of transient coupled heat transfer in a general multi-layer composite. It converts differential equations to algebraic forms, and

The fabrication of white light-emitting diodes using the n-ZnO/NiO/p-GaN heterojunction with enhanced luminescence.

PubMed

Abbasi, Mazhar Ali; Ibupoto, Zafar Hussain; Hussain, Mushtaque; Nur, Omer; Willander, Magnus

2013-07-13

Cheap and efficient white light-emitting diodes (LEDs) are of great interest due to the energy crisis all over the world. Herein, we have developed heterojunction LEDs based on the well-aligned ZnO nanorods and nanotubes on the p-type GaN with the insertion of the NiO buffer layer that showed enhancement in the light emission. Scanning electron microscopy have well demonstrated the arrays of the ZnO nanorods and the proper etching into the nanotubes. X-ray diffraction study describes the wurtzite crystal structure array of ZnO nanorods with the involvement of GaN at the (002) peak. The cathodoluminescence spectra represent strong and broad visible emission peaks compared to the UV emission and a weak peak at 425 nm which is originated from GaN. Electroluminescence study has shown highly improved luminescence response for the LEDs fabricated with NiO buffer layer compared to that without NiO layer. Introducing a sandwich-thin layer of NiO between the n-type ZnO and the p-type GaN will possibly block the injection of electrons from the ZnO to the GaN. Moreover, the presence of NiO buffer layer might create the confinement effect.

Deep ultraviolet light-emitting and laser diodes

NASA Astrophysics Data System (ADS)

Khan, Asif; Asif, Fatima; Muhtadi, Sakib

2016-02-01

Nearly all the air-water purification/polymer curing systems and bio-medical instruments require 250-300 nm wavelength ultraviolet light for which mercury lamps are primarily used. As a potential replacement for these hazardous mercury lamps, several global research teams are developing AlGaN based Deep Ultraviolet (DUV) light emitting diodes (LEDs) and DUV LED Lamps and Laser Diodes over Sapphire and AlN substrates. In this paper, we review the current research focus and the latest device results. In addition to the current results we also discuss a new quasipseudomorphic device design approach. This approach which is much easier to integrate in a commercial production setting was successfully used to demonstrate UVC devices on Sapphire substrates with performance levels equal to or better than the conventional relaxed device designs.

Naturally formed graded junction for organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Shao, Yan; Yang, Yang

2003-09-01

In this letter, we report naturally-formed graded junctions (NFGJ) for organic light-emitting diodes (OLEDs). These junctions are fabricated using single thermal evaporation boat loaded with uniformly mixed charge transport and light-emitting materials. Upon heating, materials sublimate sequentially according to their vaporizing temperatures forming the graded junction. Two kinds of graded structures, sharp and shallow graded junctions, can be formed based on the thermal properties of the selected materials. The NFGJ OLEDs have shown excellent performance in both brightness and lifetime compared with heterojunction devices.

Using light emitting diodes in traffic signals : final report.

DOT National Transportation Integrated Search

1998-07-01

In 1993, the Oregon Department of Transportation (ODOT) began testing red light emitting diodes (LED's) as a replacement to the incandescent lamps in vehicular and pedestrian signals. Field performance was found to be reliable and subsequently ODOT b...

Weak-microcavity organic light-emitting diodes with improved light out-coupling.

PubMed

Cho, Sang-Hwan; Song, Young-Woo; Lee, Joon-gu; Kim, Yoon-Chang; Lee, Jong Hyuk; Ha, Jaeheung; Oh, Jong-Suk; Lee, So Young; Lee, Sun Young; Hwang, Kyu Hwan; Zang, Dong-Sik; Lee, Yong-Hee

2008-08-18

We propose and demonstrate weak-microcavity organic light-emitting diode (OLED) displays with improved light-extraction and viewing-angle characteristics. A single pair of low- and high-index layers is inserted between indium tin oxide (ITO) and a glass substrate. The electroluminescent (EL) efficiencies of discrete red, green, and blue weak-microcavity OLEDs are enhanced by 56%, 107%, and 26%, respectively, with improved color purity. Moreover, full-color passive-matrix bottom-emitting OLED displays are fabricated by employing low-index layers of two thicknesses. As a display, the EL efficiency of white color was 27% higher than that of a conventional OLED display.

Micro and nano-structured green gallium indium nitride/gallium nitride light-emitting diodes

NASA Astrophysics Data System (ADS)

Stark, Christoph J. M.

Light-emitting diodes (LEDs) are commonly designed and studied based on bulk material properties. In this thesis different approaches based on patterns in the nano and micrometer length scale range are used to tackle low efficiency in the green spectral region, which is known as “green gap”. Since light generation and extraction are governed by microscopic processes, it is instructive to study LEDs with lateral mesa sizes scaled to the nanometer range. Besides the well-known case of the quantum size effect along the growth direction, a continuous lateral scaling could reveal the mechanisms behind the purported absence of a green gap in nanowire LEDs and the role of their extraction enhancement. Furthermore the possibility to modulate strain and piezoelectric polarization by post growth patterning is of practical interest, because the internal electric fields in conventional wurtzite GaN LEDs cause performance problems. A possible alternative is cubic phase GaN, which is free of built-in polarization fields. LEDs on cubic GaN could show the link between strong polarization fields and efficiency roll-off at high current densities, also known as droop. An additional problem for all nitride-based LEDs is efficient light extraction. For a planar GaN LED only roughly 8% of the generated light can be extracted. Novel lightextraction structures with extraction-favoring geometry can yield significant increase in light output power. To investigate the effect of scaling the mesa dimension, micro and nano-sized LED arrays of variable structure size were fabricated. The nano-LEDs were patterned by electron beam lithography and dry etching. They contained up to 100 parallel nano-stripe LEDs connected to one common contact area. The mesa width was varied over 1 μm, 200 nm, and 50 nm. These LEDs were characterized electrically and optically, and the peak emission wavelength was found to depend on the lateral structure size. An electroluminescence (EL) wavelength shift of 3 nm

All-solution processed transparent organic light emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Min; Höfle, Stefan; Czolk, Jens; Mertens, Adrian; Colsmann, Alexander

2015-11-01

In this work, we report on indium tin oxide-free, all-solution processed transparent organic light emitting diodes (OLEDs) with inverted device architecture. Conductive polymer layers are employed as both transparent cathodes and transparent anodes, with the top anodes having enhanced conductivities from a supporting stochastic silver nanowire mesh. Both electrodes exhibit transmittances of 80-90% in the visible spectral regime. Upon the incorporation of either yellow- or blue-light emitting fluorescent polymers, the OLEDs show low onset voltages, demonstrating excellent charge carrier injection from the polymer electrodes into the emission layers. Overall luminances and current efficiencies equal the performance of opaque reference OLEDs with indium tin oxide and aluminium electrodes, proving excellent charge carrier-to-light conversion within the device.

Inversion by metalorganic chemical vapor deposition from N- to Ga-polar gallium nitride and its application to multiple quantum well light-emitting diodes

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

Hosalli, A. M.; Van Den Broeck, D. M.; Bedair, S. M.

2013-12-02

We demonstrate a metalorganic chemical vapor deposition growth approach for inverting N-polar to Ga-polar GaN by using a thin inversion layer grown with high Mg flux. The introduction of this inversion layer allowed us to grow p-GaN films on N-polar GaN thin film. We have studied the dependence of hole concentration, surface morphology, and degree of polarity inversion for the inverted Ga-polar surface on the thickness of the inversion layer. We then use this approach to grow a light emitting diode structure which has the MQW active region grown on the advantageous N-polar surface and the p-layer grown on themore » inverted Ga-polar surface.« less

Monolithic integration of GaN-based light-emitting diodes and metal-oxide-semiconductor field-effect transistors.

PubMed

Lee, Ya-Ju; Yang, Zu-Po; Chen, Pin-Guang; Hsieh, Yung-An; Yao, Yung-Chi; Liao, Ming-Han; Lee, Min-Hung; Wang, Mei-Tan; Hwang, Jung-Min

2014-10-20

In this study, we report a novel monolithically integrated GaN-based light-emitting diode (LED) with metal-oxide-semiconductor field-effect transistor (MOSFET). Without additionally introducing complicated epitaxial structures for transistors, the MOSFET is directly fabricated on the exposed n-type GaN layer of the LED after dry etching, and serially connected to the LED through standard semiconductor-manufacturing technologies. Such monolithically integrated LED/MOSFET device is able to circumvent undesirable issues that might be faced by other kinds of integration schemes by growing a transistor on an LED or vice versa. For the performances of resulting device, our monolithically integrated LED/MOSFET device exhibits good characteristics in the modulation of gate voltage and good capability of driving injected current, which are essential for the important applications such as smart lighting, interconnection, and optical communication.

LIGHT-EMITTING DIODE TECHNOLOGY IMPROVES INSECT TRAPPING

PubMed Central

GILLEN, JONATHON I.; MUNSTERMANN, LEONARD E.

2008-01-01

In a climate of increased funding for vaccines, chemotherapy, and prevention of vector-borne diseases, fewer resources have been directed toward improving disease and vector surveillance. Recently developed light-emitting diode (LED) technology was applied to standard insect-vector traps to produce a more effective lighting system. This approach improved phlebotomine sand fly capture rates by 50%, and simultaneously reduced the energy consumption by 50–60%. The LEDs were incorporated into 2 lighting designs, 1) a LED combination bulb for current light traps and 2) a chip-based LED design for a modified Centers for Disease Control and Prevention light trap. Detailed descriptions of the 2 designs are presented. PMID:18666546

Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex.

PubMed

Tang, Huaijun; Meng, Guoyun; Chen, Zeyu; Wang, Kaimin; Zhou, Qiang; Wang, Zhengliang

2017-06-16

A novel orange cationic iridium(III) complex [(TPTA)₂Ir(dPPOA)]PF₆ (TPTA: 3,4,5-triphenyl-4 H -1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)₂Ir(dPPOA)]PF₆ has high thermal stability with a decomposition temperature ( T d ) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)₂Ir(dPPOA)]PF₆ was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y₃Al₅O 12 :Ce 3+ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I'Eclairage ) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency ( η L ) was 128.5 lm∙W -1 . Such a cold white LED became a neutral white LED when [(TPTA)₂Ir(dPPOA)]PF₆ was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and η L was 85.2 lm∙W -1 . It further became a warm white LED when [(TPTA)₂Ir(dPPOA)]PF₆ was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and η L was 46.1 lm∙W -1 . The results show that [(TPTA)₂Ir(dPPOA)]PF₆ is a promising phosphor candidate for fabricating warm white LEDs.

Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex

PubMed Central

Tang, Huaijun; Meng, Guoyun; Chen, Zeyu; Wang, Kaimin; Zhou, Qiang; Wang, Zhengliang

2017-01-01

A novel orange cationic iridium(III) complex [(TPTA)2Ir(dPPOA)]PF6 (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)2Ir(dPPOA)]PF6 has high thermal stability with a decomposition temperature (Td) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)2Ir(dPPOA)]PF6 was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I’Eclairage) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency (ηL) was 128.5 lm∙W−1. Such a cold white LED became a neutral white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and ηL was 85.2 lm∙W−1. It further became a warm white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and ηL was 46.1 lm∙W−1. The results show that [(TPTA)2Ir(dPPOA)]PF6 is a promising phosphor candidate for fabricating warm white LEDs. PMID:28773020

77 FR 75446 - Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-20

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-784] Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant the Joint Motion To Terminate the... sale within the United States after importation of certain light-emitting diodes and products...

Fabrication of poly(p-phenyleneacetylene) light-emitting diodes

DOEpatents

Shinar, J.; Swanson, L.S.; Lu, F.; Ding, Y.

1994-08-02

Acetylene-containing poly(p-phenyleneacetylene) (PPA)-based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes. 8 figs.

Fabrication of poly(p-phenyleneacetylene) light-emitting diodes

DOEpatents

Shinar, Joseph; Swanson, Leland S.; Lu, Feng; Ding, Yiwei

1994-08-02

Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as A1 or A1/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes.

Safety of light emitting diodes in toys.

PubMed

Higlett, M P; O'Hagan, J B; Khazova, M

2012-03-01

Light emitting diodes (LEDs) are increasingly being used in toys. An assessment methodology is described for determining the accessible emission limits for the optical radiation from the toys, which takes account of expected use and reasonably foreseeable misuse of toys. Where data are available, it may be possible to assess the toy from the data sheet alone. If this information is not available, a simple measurement protocol is proposed.

Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

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

Liu, Chao; Cai, Yuefei; Liu, Zhaojun

2015-05-04

We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrownmore » n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme.« less

A tunable lighting system integrated by inorganic and transparent organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Jing-jing; Zhang, Tao; Jin, Ya-fang; Liu, Shi-shen; Yuan, Shi-dong; Cui, Zhao; Zhang, Li; Wang, Wei-hui

2014-05-01

A tunable surface-emitting integrated lighting system is constructed using a combination of inorganic light-emitting diodes (LEDs) and transparent organic LEDs (OLEDs). An RB two-color LED is used to supply red and blue light emission, and a green organic LED is used to supply green light emission. Currents of the LED and OLED are tuned to produce a white color, showing different Commission Internationale d'Eclairage (CIE) chromaticity coordinates and correlated color temperatures with a wide adjustable range. Such an integration can compensate for the lack of the LED's luminance uniformity and the transparent OLED's luminance intensity.

Plasma treatment of p-GaN/n-ZnO nanorod light-emitting diodes

NASA Astrophysics Data System (ADS)

Leung, Yu Hang; Ng, Alan M. C.; Djurišic, Aleksandra B.; Chan, Wai Kin; Fong, Patrick W. K.; Lui, Hsien Fai; Surya, Charles

2014-03-01

Zinc oxide (ZnO) is a material of great interest for short-wavelength optoelectronic applications due to its wide band gap (3.37 eV) and high exciton binding energy (60 meV). Due to the difficulty in stable p-type doping of ZnO, other p-type materials such as gallium nitride (GaN) have been used to form heterojunctions with ZnO. p-GaN/n-ZnO heterojunction devices, in particular light-emitting diodes (LED) have been extensively studied. There was a huge variety of electronic properties and emission colors on the reported devices. It is due to the different energy alignment at the interface caused by different properties of the GaN layer and ZnO counterpart in the junction. Attempts have been made on modifying the heterojunction by various methods, such as introducing a dielectric interlayer and post-growth surface treatment, and changing the growth methods of ZnO. In this study, heterojunction LED devices with p-GaN and ZnO nanorods array are demonstrated. The ZnO nanorods were grown by a solution method. The ZnO nanorods were exposed to different kinds of plasma treatments (such as nitrogen and oxygen) after the growth. It was found that the treatment could cause significant change on the optical properties of the ZnO nanorods, as well as the electronic properties and light emissions of the resultant LED devices.

Light Emitting Diode Flashlights as Effective and Inexpensive Light Sources for Fluorescence Microscopy

PubMed Central

Robertson, J. Brian; Zhang, Yunfei; Johnson, Carl Hirschie

2009-01-01

Summary Light-emitting diodes (LEDs) are becoming more commonly used as light sources for fluorescence microscopy. We describe the adaptation of a commercially available LED flashlight for use as a source for fluorescence excitation. This light source is long-lived, inexpensive, and is effective for excitation in the range of 440–600 nm. PMID:19772530

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.

Improving light extraction of InGaN-based light emitting diodes with a roughened p-GaN surface using CsCl nano-islands.

PubMed

Wei, Tongbo; Kong, Qingfeng; Wang, Junxi; Li, Jing; Zeng, Yiping; Wang, Guohong; Li, Jinmin; Liao, Yuanxun; Yi, Futing

2011-01-17

InGaN-based light emitting diodes (LEDs) with a top nano-roughened p-GaN surface are fabricated using self-assembled CsCl nano-islands as etch masks. Following formation of hemispherical GaN nano-island arrays, electroluminescence (EL) spectra of roughened LEDs display an obvious redshift due to partial compression release in quantum wells through Inductively Coupled Plasma (ICP) etching. At a 350-mA current, the enhancement of light output power of LEDs subjected to ICP treatment with durations of 50, 150 and 250 sec compared with conventional LED have been determined to be 9.2, 70.6, and 42.3%, respectively. Additionally, the extraction enhancement factor can be further improved by increasing the size of CsCl nano-island. The economic and rapid method puts forward great potential for high performance lighting devices.

Genetic algorithms used for the optimization of light-emitting diodes and solar thermal collectors

NASA Astrophysics Data System (ADS)

Mayer, Alexandre; Bay, Annick; Gaouyat, Lucie; Nicolay, Delphine; Carletti, Timoteo; Deparis, Olivier

2014-09-01

We present a genetic algorithm (GA) we developed for the optimization of light-emitting diodes (LED) and solar thermal collectors. The surface of a LED can be covered by periodic structures whose geometrical and material parameters must be adjusted in order to maximize the extraction of light. The optimization of these parameters by the GA enabled us to get a light-extraction efficiency η of 11.0% from a GaN LED (for comparison, the flat material has a light-extraction efficiency η of only 3.7%). The solar thermal collector we considered consists of a waffle-shaped Al substrate with NiCrOx and SnO2 conformal coatings. We must in this case maximize the solar absorption α while minimizing the thermal emissivity ɛ in the infrared. A multi-objective genetic algorithm has to be implemented in this case in order to determine optimal geometrical parameters. The parameters we obtained using the multi-objective GA enable α~97.8% and ɛ~4.8%, which improves results achieved previously when considering a flat substrate. These two applications demonstrate the interest of genetic algorithms for addressing complex problems in physics.

High speed visible light communication using blue GaN laser diodes

NASA Astrophysics Data System (ADS)

Watson, S.; Viola, S.; Giuliano, G.; Najda, S. P.; Perlin, P.; Suski, T.; Marona, L.; Leszczyński, M.; Wisniewski, P.; Czernecki, R.; Targowski, G.; Watson, M. A.; White, H.; Rowe, D.; Laycock, L.; Kelly, A. E.

2016-10-01

GaN-based laser diodes have been developed over the last 20 years making them desirable for many security and defence applications, in particular, free space laser communications. Unlike their LED counterparts, laser diodes are not limited by their carrier lifetime which makes them attractive for high speed communication, whether in free space, through fiber or underwater. Gigabit data transmission can be achieved in free space by modulating the visible light from the laser with a pseudo-random bit sequence (PRBS), with recent results approaching 5 Gbit/s error free data transmission. By exploiting the low-loss in the blue part of the spectrum through water, data transmission experiments have also been conducted to show rates of 2.5 Gbit/s underwater. Different water types have been tested to monitor the effect of scattering and to see how this affects the overall transmission rate and distance. This is of great interest for communication with unmanned underwater vehicles (UUV) as the current method using acoustics is much slower and vulnerable to interception. These types of laser diodes can typically reach 50-100 mW of power which increases the length at which the data can be transmitted. This distance could be further improved by making use of high power laser arrays. Highly uniform GaN substrates with low defectivity allow individually addressable laser bars to be fabricated. This could ultimately increase optical power levels to 4 W for a 20-emitter array. Overall, the development of GaN laser diodes will play an important part in free space optical communications and will be vital in the advancement of security and defence applications.

Light Emitting Diodes (LEDs)

NASA Technical Reports Server (NTRS)

1997-01-01

A special lighting technology was developed for space-based commercial plant growth research on NASA's Space Shuttle. Surgeons have used this technology to treat brain cancer on Earth, in two successful operations. The treatment technique, called Photodynamic Therapy, requires the surgeon to use tiny, pinhead-size Light Emitting Diodes (LEDs) (a source that releases long wavelengths of light ) to activate light-sensitive, tumor-treating drugs. 'A young woman operated on in May 1999 has fully recovered with no complications and no evidence of the tumor coming back,' said Dr. Harry Whelan, a pediatric neurologist at the Medical Hospital of Wisconsin in Milwaukee. Laser light has been used for this type of surgery in the past, but the LED light illuminates through all nearby tissues, reaching parts of a tumor that shorter wavelengths of laser light carnot. The new probe is safer because the longer wavelengths of light are cooler than the shorter wavelengths of laser light, making the LED less likely to injure normal brain tissue near the tumor. It can be used for hours at a time while still remaining cool to the touch. The LED light source is compact, about the size of a briefcase, and can be purchased for a fraction of the cost of a laser. The LEDs, developed and managed by NASA's Marshall Space Flight Center, have been used on seven Space Shuttle flights inside the Microgravity Astroculture Facility. This technology has also been successfully used to further commercial research in crop growth.

Thermally evaporated hybrid perovskite for hetero-structured green light-emitting diodes

NASA Astrophysics Data System (ADS)

Mariano, Fabrizio; Listorti, Andrea; Rizzo, Aurora; Colella, Silvia; Gigli, Giuseppe; Mazzeo, Marco

2017-10-01

Thermal evaporation of green-light emitting perovskite (MaPbBr3) films is reported. Morphological studies show that a soft thermal treatment is needed to induce an outstanding crystal growth and film organization. Hetero-structured light-emitting diodes, embedding as-deposited and annealed MAPbBr3 films as active layers, are fabricated and their performances are compared, highlighting that the perovskite evolution is strongly dependent on the growing substrate, too.

GaN-based light-emitting diodes on various substrates: a critical review.

PubMed

Li, Guoqiang; Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Wang, Haiyan; Lin, Zhiting; Zhou, Shizhong

2016-05-01

GaN and related III-nitrides have attracted considerable attention as promising materials for application in optoelectronic devices, in particular, light-emitting diodes (LEDs). At present, sapphire is still the most popular commercial substrate for epitaxial growth of GaN-based LEDs. However, due to its relatively large lattice mismatch with GaN and low thermal conductivity, sapphire is not the most ideal substrate for GaN-based LEDs. Therefore, in order to obtain high-performance and high-power LEDs with relatively low cost, unconventional substrates, which are of low lattice mismatch with GaN, high thermal conductivity and low cost, have been tried as substitutes for sapphire. As a matter of fact, it is not easy to obtain high-quality III-nitride films on those substrates for various reasons. However, by developing a variety of techniques, distincts progress has been made during the past decade, with high-performance LEDs being successfully achieved on these unconventional substrates. This review focuses on state-of-the-art high-performance GaN-based LED materials and devices on unconventional substrates. The issues involved in the growth of GaN-based LED structures on each type of unconventional substrate are outlined, and the fundamental physics behind these issues is detailed. The corresponding solutions for III-nitride growth, defect control, and chip processing for each type of unconventional substrate are discussed in depth, together with a brief introduction to some newly developed techniques in order to realize LED structures on unconventional substrates. This is very useful for understanding the progress in this field of physics. In this review, we also speculate on the prospects for LEDs on unconventional substrates.

Three-Dimensional Hetero-Integration of Faceted GaN on Si Pillars for Efficient Light Energy Conversion Devices.

PubMed

Kim, Dong Rip; Lee, Chi Hwan; Cho, In Sun; Jang, Hanmin; Jeon, Min Soo; Zheng, Xiaolin

2017-07-25

An important pathway for cost-effective light energy conversion devices, such as solar cells and light emitting diodes, is to integrate III-V (e.g., GaN) materials on Si substrates. Such integration first necessitates growth of high crystalline III-V materials on Si, which has been the focus of many studies. However, the integration also requires that the final III-V/Si structure has a high light energy conversion efficiency. To accomplish these twin goals, we use single-crystalline microsized Si pillars as a seed layer to first grow faceted Si structures, which are then used for the heteroepitaxial growth of faceted GaN films. These faceted GaN films on Si have high crystallinity, and their threading dislocation density is similar to that of GaN grown on sapphire. In addition, the final faceted GaN/Si structure has great light absorption and extraction characteristics, leading to improved performance for GaN-on-Si light energy conversion devices.

Experimental effective intensity of steady and flashing light emitting diodes for aircraft anti-collision lighting.

DOT National Transportation Integrated Search

2013-08-01

Research was conducted to determine the effective intensity of flashing lights that incorporate light-emitting diodes (LEDs). LEDs require less power and have the ability to flash without the addition of moving parts. Compared with incandescent bulbs...

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

NASA Astrophysics Data System (ADS)

Kashiwagi, Y.; Koizumi, A.; Takemura, Y.; Furuta, S.; Yamamoto, M.; Saitoh, M.; Takahashi, M.; Ohno, T.; Fujiwara, Y.; Murahashi, K.; Ohtsuka, K.; Nakamoto, M.

2014-12-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

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.

Frequency-Downconversion Stability of PMMA Coatings in Hybrid White Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Caruso, Fulvio; Mosca, Mauro; Rinella, Salvatore; Macaluso, Roberto; Calì, Claudio; Saiano, Filippo; Feltin, Eric

2016-01-01

We report on the properties of a poly(methyl methacrylate)-based coating used as a host for an organic dye in hybrid white light-emitting diodes. The device is composed by a pump source, which is a standard inorganic GaN/InGaN blue light-emitting diode (LED) emitting at around 450 nm, and a spin-coated conversion layer making use of Lumogen® F Yellow 083. Under prolonged irradiation, the coating exhibits significant bleaching, thus degrading the color rendering performance of the LED. We present experimental results that confirm that the local temperature rise of the operating diode does not affect the conversion layer. It is also proven that, during the test, the photostability of the organic dye is compromised, resulting in a chromatic shift from Commission Internationale de l'Eclairage (CIE) ( x; y) coordinates (0.30;0.39) towards the color of the pump (0.15;0.04). Besides photodegradation of the dye, we address a phenomenon attributed to modification of the polymer matrix activated by the LED's blue light energy as confirmed by ultraviolet-visible and Fourier-transform infrared spectroscopic analyses. Three methods for improving the overall stability of the organic coating are presented.

Differential carrier lifetime and transport effects in electrically injected III-nitride light-emitting diodes

NASA Astrophysics Data System (ADS)

Rashidi, A.; Nami, M.; Monavarian, M.; Aragon, A.; DaVico, K.; Ayoub, F.; Mishkat-Ul-Masabih, S.; Rishinaramangalam, A.; Feezell, D.

2017-07-01

This work describes a small-signal microwave method for determining the differential carrier lifetime and transport effects in electrically injected InGaN/GaN light-emitting diodes (LEDs). By considering the carrier diffusion, capture, thermionic escape, and recombination, the rate equations are used to derive an equivalent small-signal electrical circuit for the LEDs, from which expressions for the input impedance and modulation response are obtained. The expressions are simultaneously fit to the experimental data for the input impedance and modulation response for nonpolar InGaN/GaN micro-LEDs on free-standing GaN substrates. The fittings are used to extract the transport related circuit parameters and differential carrier lifetimes. The dependence of the parameters on the device diameter and current density is reported. We also derive approximations for the modulation response under low and high injection levels and show that the transport of carriers affects the modulation response of the device, especially at low injection levels. The methods presented are relevant to the design of high-speed LEDs for visible-light communication.

Compact light-emitting diode lighting ring for video-assisted thoracic surgery.

PubMed

Lu, Ming-Kuan; Chang, Feng-Chen; Wang, Wen-Zhe; Hsieh, Chih-Cheng; Kao, Fu-Jen

2014-01-01

In this work, a foldable ring-shaped light-emitting diode (LED) lighting assembly, designed to attach to a rubber wound retractor, is realized and tested through porcine animal experiments. Enabled by the small size and the high efficiency of LED chips, the lighting assembly is compact, flexible, and disposable while providing direct and high brightness lighting for more uniform background illumination in video-assisted thoracic surgery (VATS). When compared with a conventional fiber bundle coupled light source that is usually used in laparoscopy and endoscopy, the much broader solid angle of illumination enabled by the LED assembly allows greatly improved background lighting and imaging quality in VATS.

New yellow Ba 0.93Eu 0.07Al 2O 4 phosphor for warm-white light-emitting diodes through single-emitting-center conversion

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

Li, Xufan; Budai, John D.; Liu, Feng

2013-01-01

Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature <4000 K) with good color rendition (i.e., color rendering index >80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors’ emission spectrum. Here, we report a new yellow Ba 0.93Eu 0.07Al 2O 4 phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature <4000 K and color rendering index >80more » were readily achieved when combining the Ba 0.93Eu 0.07Al 2O 4 phosphor with a blue light-emitting diode (440–470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index >80) can be achieved based on single-phosphor, single-emitting-center conversion.« less

Stacked Device of Polymer Light-Emitting Diode Driven by Metal-Base Organic Transistor

NASA Astrophysics Data System (ADS)

Yoneda, Kazuhiro; Nakayama, Ken-ichi; Yokoyama, Masaaki

2008-02-01

We fabricated a new light-emitting device that combined a polymer light-emitting diode (PLED) and a vertical-type metal-base organic transistor (MBOT) through a floating electrode. By employing a layered floating electrode of Mg:Ag/Au, the MBOT on the PLED was operated successfully and a current amplification factor of approximately 20 was observed. The PLED luminescence exceeding 100 cd/m2 can be modulated using the MBOT with a low base voltage (2.8 V) and VCC (8 V). The emission contrast (on/off ratio) was improved with insertion of an insulating layer under the base, and the cut-off frequency was estimated to be 8 kHz. This device is expected to be a promising driving system of organic light-emitting diode (OLED), realizing low voltage and high numerical aperture.

Light-emitting diode technology status and directions: Opportunities for horticultural lighting

DOE PAGES

Tsao, Jeffrey Y.; Pattison, P. Morgan; Krames, Michael R.

2016-01-01

Here, light-emitting diode (LED) technology has advanced rapidly over the last decade, primarily driven by display and general illumination applications ("solid-state lighting (SSL) for humans"). These advancements have made LED lighting technically and economically advantageous not only for these applications, but also, as an indirect benefit, for adjacent applications such as horticultural lighting ("SSL for plants"). Moreover, LED technology has much room for continued improvement. In the near-term, these improvements will continue to be driven by SSL for humans (with indirect benefit to SSL for plants), the most important of which can be anticipated.

Bactericidal effects of a high-power, red light-emitting diode on two periodontopathic bacteria in antimicrobial photodynamic therapy in vitro.

PubMed

Umeda, Makoto; Tsuno, Akiko; Okagami, Yoshihide; Tsuchiya, Fumito; Izumi, Yuichi; Ishikawa, Isao

2011-11-01

  Light-emitting diodes have been investigated as new light activators for photodynamic therapy. We investigated the bactericidal effects of high-power, red light-emitting diodes on two periodontopathic bacteria in vitro.   A light-emitting diode (intensity: 1100 mW/cm(2) , peak wavelength: 650 nm) was used to irradiate a bacterial solution for either 10 or 20 s. Bacterial solutions (Porphyromonas gingivalis or Aggregatibacter actinomycetemcomitans) at a concentration of 2.5 × 10(6) c.f.u./mL were mixed with an equal volume of either methylene blue or toluidine blue O (0-20 μg/mL) and added to titer plate wells. The plate wells were irradiated with red light-emitting diode light from a distance of 22 or 40 mm. The contents were diluted, and 50 μL was smeared onto blood agar plates. After 1 week of culturing, bacterial c.f.u. were counted.   The light-emitting diode energy density was estimated to be approximately 4 and 8 J/cm(2) after 10 and 20 s of irradiation, respectively. Red light-emitting diode irradiation for 10 s from a distance of 22 mm, combined with methylene blue at concentrations >10 μg/mL, completely killed Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans.   High-power, red light-emitting diode irradiation with a low concentration of dye showed effective bactericidal effects against two periodontopathic bacteria. © 2011 Blackwell Publishing Asia Pty Ltd.

InGaN/GaN light-emitting diode having direct hole injection plugs and its high-current operation.

PubMed

Kim, Sungjoon; Cho, Seongjae; Jeong, Jaedeok; Kim, Sungjun; Hwang, Sungmin; Kim, Garam; Yoon, Sukho; Park, Byung-Gook

2017-03-20

The light-emitting diode (LED) with an improved hole injection and straightforward process integration is proposed. p-type GaN direct hole injection plugs (DHIPs) are formed on locally etched multiple-quantum wells (MQWs) by epitaxial lateral overgrowth (ELO) method. We confirm that the optical output power is increased up to 23.2% at an operating current density of 100 A/cm². Furthermore, in order to identify the origin of improvement in optical performance, the transient light decay time and light intensity distribution characteristics were analyzed on the DHIP LED devices. Through the calculation of the electroluminescence (EL) decay time, internal quantum efficiency (IQE) is extracted along with the recombination parameters, which reveals that the DHIPs have a significant effect on enhancement of radiative recombination and reduction of efficiency droop. Furthermore, the mapping PL reveals that the DHIP LED also has a potential to improve the light extraction efficiency by hexagonal pyramid shaped DHIPs.

Tuning the emission of ZnO nanorods based light emitting diodes using Ag doping

NASA Astrophysics Data System (ADS)

Echresh, Ahmad; Chey, Chan Oeurn; Shoushtari, Morteza Zargar; Nur, Omer; Willander, Magnus

2014-11-01

We have fabricated, characterized, and compared ZnO nanorods/p-GaN and n-Zn0.94Ag0.06O nanorods/p-GaN light emitting diodes (LEDs). Current-voltage measurement showed an obvious rectifying behaviour of both LEDs. A reduction of the optical band gap of the Zn0.94Ag0.06O nanorods compared to pure ZnO nanorods was observed. This reduction leads to decrease the valence band offset at n-Zn0.94Ag0.06O nanorods/p-GaN interface compared to n-ZnO nanorods/p-GaN heterojunction. Consequently, this reduction leads to increase the hole injection from the GaN to the ZnO. From electroluminescence measurement, white light was observed for the n-Zn0.94Ag0.06O nanorods/p-GaN heterojunction LEDs under forward bias, while for the reverse bias, blue light was observed. While for the n-ZnO nanorods/p-GaN blue light dominated the emission in both forward and reverse biases. Further, the LEDs exhibited a high sensitivity in responding to UV illumination. The results presented here indicate that doping ZnO nanorods might pave the way to tune the light emission from n-ZnO/p-GaN LEDs.

Synthesis and characterization of organic/inorganic heterostructure films for hybrid light emitting diode

NASA Astrophysics Data System (ADS)

Toyama, Toshihiko; Ichihara, Tokuyuki; Yamaguchi, Daisuke; Okamoto, Hiroaki

2007-10-01

Thin-film light emitting devices based on organic materials have been gathering attentions for applying a flat-panel display and a solid-state lighting. Alternatively, inorganic technologies such as Si-based thin-film technology have been growing almost independently. It is then expected that combining the Si-based thin-film technology with the organic light emitting diode (OLED) technology will develop innovative devices. Here, we report syntheses of the hybrid light emitting diode (LED) with a heterostructure consisting of p-type SiC x and tris-(8-hydroxyquinoline) aluminum films and characterization for the hybrid LEDs. We present the energy diagram of the heterostructure, and describe that the use of high dark conductivities of the p-type SiC x as well as inserting wide-gap intrinsic a-SiC x at the p-type SiC x/Alq interface are effective for improving device performance.

Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Deng, Lingling; Zhou, Hongwei; Chen, Shufen; Shi, Hongying; Liu, Bin; Wang, Lianhui; Huang, Wei

2015-02-01

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the use of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.

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.

Atom Probe Tomography Analysis of Gallium-Nitride-Based Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Prosa, Ty J.; Olson, David; Giddings, A. Devin; Clifton, Peter H.; Larson, David J.; Lefebvre, Williams

2014-03-01

Thin-film light-emitting diodes (LEDs) composed of GaN/InxGa1-xN/GaN quantum well (QW) structures are integrated into modern optoelectronic devices because of the tunable InGaN band-gap enabling emission of the full visible spectrum. Atom probe tomography (APT) offers unique capabilities for 3D device characterization including compositional mapping of nano-volumes (>106 nm3) , high detection efficiency (>50%), and good sensitivity. In this study, APT is used to understand the distribution of dopants as well as Al and In alloying agents in a GaN device. Measurements using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) have also been made to improve the accuracy of the APT analysis by correlating the information content of these complimentary techniques. APT analysis reveals various QW and other optoelectronic structures including a Mg p-GaN layer, an Al-rich electron blocking layer, an In-rich multi-QW region, and an In-based super-lattice structure. The multi-QW composition shows good quantitative agreement with layer thickness and spacing extracted from a high resolution TEM image intensity analysis.

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

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

Kashiwagi, Y., E-mail: kasiwagi@omtri.or.jp; Yamamoto, M.; Saitoh, M.

2014-12-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

Effect of threading defects on InGaN /GaN multiple quantum well light emitting diodes

NASA Astrophysics Data System (ADS)

Ferdous, M. S.; Wang, X.; Fairchild, M. N.; Hersee, S. D.

2007-12-01

Photoelectrochemical etching was used to measure the threading defect (TD) density in InGaN multiple quantum well light-emitting diodes (LEDs) fabricated from commercial quality epitaxial wafers. The TD density was measured in the LED active region and then correlated with the previously measured characteristics of these LEDs. It was found that the reverse leakage current increased exponentially with TD density. The temperature dependence of this dislocation-related leakage current was consistent with a hopping mechanism at low reverse-bias voltage and Poole-Frenkel emission at higher reverse-bias voltage. The peak intensity and spectral width of the LED electroluminescence were found to be only weakly dependent on TD density for the measured TD range of 1×107-2×108cm-2.

Investigation of organic light emitting diodes for interferometric purposes

NASA Astrophysics Data System (ADS)

Pakula, Anna; Zimak, Marzena; Sałbut, Leszek

2011-05-01

Recently the new type of light source has been introduced to the market. Organic light emitting diode (OLED) is not only interesting because of the low applying voltage, wide light emitting areas and emission efficiency. It gives the possibility to create a light source of a various shape, various color and in the near future very likely even the one that will change shape and spectrum in time in controlled way. Those opportunities have not been in our reach until now. In the paper authors try to give an answer to the question if the new light source -OLED - is suitable for interferometric purposes. Tests cover the short and long term spectrum stability, spectrum changes due to the emission area selection. In the paper the results of two OLEDs (red and white) are shown together with the result of an attempt to use them in an interferometric setup.

Nanobeam Photonic Crystal Cavity Light-Emitting Diodes

DTIC Science & Technology

2011-01-01

Nanobeam photonic crystal cavity light-emitting diodes Gary Shambat,1,a) Bryan Ellis,1 Jan Petykiewicz,1 Marie A. Mayer,2 Tomas Sarmiento ,1 James...J. H. Ryou, P. B. Deotare, R. Dupuis, and M. Loncar, Appl. Phys. Lett. 97, 051104 (2010). 5Y. Gong, B. Ellis, G. Shambat, T. Sarmiento , J. S. Harris...F. Karouta, S. He, and R. W. van der Heijden, Appl. Phys. Lett. 97, 151105 (2010). 9B. Ellis, M. A. Mayer, G. Shambat, T. Sarmiento , J. Harris, E. E

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

NASA Astrophysics Data System (ADS)

Anthopoulos, Thomas D.; Markham, Jonathan P. J.; Namdas, Ebinazar B.; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2003-06-01

High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation fac-tris(2-phenylpyridine) iridium cored dendrimer when blended with 4,4'-bis(N-carbazolyl)biphenyl and electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m2. These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.

Wireless Power Transmission to Organic Light Emitting Diode Lighting Panel with Magnetically Coupled Resonator

NASA Astrophysics Data System (ADS)

Kim, Yong-Hae; Han, Jun-Han; Kang, Seung-Youl; Cheon, Sanghoon; Lee, Myung-Lae; Ahn, Seong-Deok; Zyung, Taehyoung; Lee, Jeong-Ik; Moon, Jaehyun; Chu, Hye Yong

2012-09-01

We are successful to lit the organic light emitting diode (OLED) lighting panel through the magnetically coupled wireless power transmission technology. For the wireless power transmission, we used the operation frequency 932 kHz, specially designed double spiral type transmitter, small and thin receiver on the four layered printed circuit board, and schottky diodes for the full bridge rectifier. Our white OLED is a hybrid type, in which phosphorescent and fluorescent organics are used together to generate stable white color. The total efficiency of power transmission is around 72%.

Light emitting diodes (LED): applications in forest and native plant nurseries

Treesearch

Thomas D. Landis; Jeremiah R. Pinto; R. Kasten Dumroese

2013-01-01

It was quotes like this that made us want to learn more about light emitting diodes (LED). Other than knowing that LEDs were the latest innovation in artificial lighting, we knew that we had a lot to learn. So we started by reviewing some of the basics. The following review is a brief synopsis of how light affects plants and some discussion about LED lighting. If you...

Light-extraction enhancement for light-emitting diodes: a firefly-inspired structure refined by the genetic algorithm

NASA Astrophysics Data System (ADS)

Bay, Annick; Mayer, Alexandre

2014-09-01

The efficiency of light-emitting diodes (LED) has increased significantly over the past few years, but the overall efficiency is still limited by total internal reflections due to the high dielectric-constant contrast between the incident and emergent media. The bioluminescent organ of fireflies gave incentive for light-extraction enhance-ment studies. A specific factory-roof shaped structure was shown, by means of light-propagation simulations and measurements, to enhance light extraction significantly. In order to achieve a similar effect for light-emitting diodes, the structure needs to be adapted to the specific set-up of LEDs. In this context simulations were carried out to determine the best geometrical parameters. In the present work, the search for a geometry that maximizes the extraction of light has been conducted by using a genetic algorithm. The idealized structure considered previously was generalized to a broader variety of shapes. The genetic algorithm makes it possible to search simultaneously over a wider range of parameters. It is also significantly less time-consuming than the previous approach that was based on a systematic scan on parameters. The results of the genetic algorithm show that (1) the calculations can be performed in a smaller amount of time and (2) the light extraction can be enhanced even more significantly by using optimal parameters determined by the genetic algorithm for the generalized structure. The combination of the genetic algorithm with the Rigorous Coupled Waves Analysis method constitutes a strong simulation tool, which provides us with adapted designs for enhancing light extraction from light-emitting diodes.

Development of 1300 nm GaAs-Based Microcavity Light-Emitting Diodes

DTIC Science & Technology

2001-06-01

vertical - cavity surface emitting lasers ( VCSEL ) and micro- cavity light- emitting diodes (MC-LED) for short-to-medium... epitaxial growth run [1 ]. Self-organized In(Ga)As quantum dot (QD) heterostructures grown by molecular beam epitaxy ( MBE ) are promising candidates as...successfully grown by molecular beam epitaxy on GaAs substrates without the need to rely on any in-situ calibration technique. Fabricated

Characteristics of blue organic light emitting diodes with different thick emitting layers

NASA Astrophysics Data System (ADS)

Li, Chong; Tsuboi, Taiju; Huang, Wei

2014-08-01

We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.

High-Fluence Light-Emitting Diode-Generated Red Light Modulates the Transforming Growth Factor-Beta Pathway in Human Skin Fibroblasts.

PubMed

Mamalis, Andrew; Jagdeo, Jared

2018-05-24

Skin fibrosis is a significant medical problem with limited available treatment modalities. The key cellular characteristics include increased fibroblast proliferation, collagen production, and transforming growth factor-beta (TGF-B)/SMAD pathway signaling. The authors have previously shown that high-fluence light-emitting diode red light (HF-LED-RL) decreases cellular proliferation and collagen production. Herein, the authors investigate the ability of HF-LED-RL to modulate the TGF-B/SMAD pathway. Normal human dermal fibroblasts were cultured and irradiated with a commercially available hand-held LED array. After irradiation, cell lysates were collected and levels of pSMAD2, TGF-Beta 1, and TGF-Beta I receptor were measured using Western blot. High-fluence light-emitting diode red light decreased TGF-Beta 1 ligand (TGF-B1) levels after irradiation. 320 J/cm HF-LED-RL resulted in 59% TGF-B1 and 640 J/cm HF-LED-RL resulted in 54% TGF-B1, relative to controls. 640 J/cm HF-LED-RL resulted in 62% pSMAD2 0 hours after irradiation, 65% pSMAD2 2 hours after irradiation, and 95% 4 hours after irradiation, compared with matched controls. High-fluence light-emitting diode red light resulted in no significant difference in transforming growth factor-beta receptor I levels compared with matched controls. Skin fibrosis is a significant medical problem with limited available treatment modalities. Light-emitting diode-generated red light is a safe, economic, and noninvasive modality that has a body of in vitro evidence supporting the reduction of key cellular characteristics associated with skin fibrosis.

Hybrid daylight/light-emitting diode illumination system for indoor lighting.

PubMed

Ge, Aiming; Qiu, Peng; Cai, Jinlin; Wang, Wei; Wang, Junwei

2014-03-20

A hybrid illumination method using both daylight and light-emitting diodes (LEDs) for indoor lighting is presented in this study. The daylight can be introduced into the indoor space by a panel-integration system. The daylight part and LEDs are combined within a specific luminaire that can provide uniform illumination. The LEDs can be turned on and dimmed through closed-loop control when the daylight illuminance is inadequate. We simulated the illumination and calculated the indoor lighting efficiency of our hybrid daylight and LED lighting system, and compared this with that of LED and fluorescent lighting systems. Simulation results show that the efficiency of the hybrid daylight/LED illumination method is better than that of LED and traditional lighting systems, under the same lighting conditions and lighting time; the method has hybrid lighting average energy savings of T5 66.28%, and that of the LEDs is 41.62%.

Hydrothermal growth and luminescent properties of nonpolar a-plane (11 2 - 0) ZnCdO films for light-emitting diodes

NASA Astrophysics Data System (ADS)

Baik, Kwang Hyeon; Kim, Jimin; Jang, Soohwan

2018-03-01

Nonpolar a-plane ZnCdO films have been obtained on a-plane GaN using a simple low-cost hydrothermal growth method at the low temperature of 80 °C. The morphological, structural, optical, and electrical properties of a-plane ZnCdO films with various Cd contents have been investigated and compared. The photoluminescence peak of the a-plane Zn0.957Cd 0.043O film, was observed to be centered at 429 nm at 25 °C. We demonstrated a heterostructure light-emitting diode (LED) using nonpolar n-type Zn0.957Cd0.043O/p-type GaN films. The rectifying behavior of the current-voltage characteristics was observed with a turn-on voltage of 5 V. The electroluminescence of the LED showed emission peaks including 430 nm, which indicates the near-band-edge emission of a-plane Zn0.957Cd0.043O at 25 °C.

Clinical comparison between the bleaching efficacy of light-emitting diode and diode laser with sodium perborate.

PubMed

Koçak, Sibel; Koçak, Mustafa Murat; Sağlam, Baran Can

2014-04-01

The aim of this clinical study was to test the efficacy of a light-emitting diode (LED) light and a diode laser, when bleaching with sodium perborate. Thirty volunteers were selected to participate in the study. The patients were randomly divided into two groups. The initial colour of each tooth to be bleached was quantified with a spectrophotometer. In group A, sodium perborate and distilled water were mixed and placed into the pulp chamber, and the LED light was source applied. In group B, the same mixture was used, and the 810 nm diode laser was applied. The final colour of each tooth was quantified with the same spectrophotometer. Initial and final spectrophotometer values were recorded. Mann-Whitney U-test and Wicoxon tests were used to test differences between both groups. Both devices successfully whitened the teeth. No statistical difference was found between the efficacy of the LED light and the diode laser. © 2013 The Authors. Australian Endodontic Journal © 2013 Australian Society of Endodontology.

Manufacturing polymer light emitting diode with high luminance efficiency by solution process

NASA Astrophysics Data System (ADS)

Kim, Miyoung; Jo, SongJin; Yang, Ho Chang; Yoon, Dang Mo; Kwon, Jae-Taek; Lee, Seung-Hyun; Choi, Ju Hwan; Lee, Bum-Joo; Shin, Jin-Koog

2012-06-01

While investigating polymer light emitting diodes (polymer-LEDs) fabricated by solution process, surface roughness influences electro-optical (E-O) characteristics. We expect that E-O characteristics such as luminance and power efficiency related to surface roughness and layer thickness of emitting layer with poly-9-Vinylcarbazole. In this study, we fabricated polymer organic light emitting diodes by solution process which guarantees easy, eco-friendly and low cost manufacturing for flexible display applications. In order to obtain high luminescence efficiency, E-O characteristics of these devices by varying parameters for printing process have been investigated. Therefore, we optimized process condition for polymer-LEDs by adjusting annealing temperatures of emission, thickness of emission layer showing efficiency (10.8 cd/A) at 10 mA/cm2. We also checked wavelength dependent electroluminescence spectrum in order to find the correlation between the variation of efficiency and the thickness of the layer.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN.

PubMed

Soh, C B; Liu, W; Yong, A M; Chua, S J; Chow, S Y; Tripathy, S; Tan, R J N

2010-08-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO(2) film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, η(extraction,) was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN

NASA Astrophysics Data System (ADS)

Soh, C. B.; Liu, W.; Yong, A. M.; Chua, S. J.; Chow, S. Y.; Tripathy, S.; Tan, R. J. N.

2010-11-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO2 film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, ηextraction, was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

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

Deng, Lingling; Zhou, Hongwei; Chen, Shufen, E-mail: iamsfchen@njupt.edu.cn

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the usemore » of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.« less

Stacking multiple connecting functional materials in tandem organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Tao; Wang, Deng-Ke; Jiang, Nan; Lu, Zheng-Hong

2017-02-01

Tandem device is an important architecture in fabricating high performance organic light-emitting diodes and organic photovoltaic cells. The key element in making a high performance tandem device is the connecting materials stack, which plays an important role in electric field distribution, charge generation and charge injection. For a tandem organic light-emitting diode (OLED) with a simple Liq/Al/MoO3 stack, we discovered that there is a significant current lateral spreading causing light emission over an extremely large area outside the OLED pixel when the Al thickness exceeds 2 nm. This spread light emission, caused by an inductive electric field over one of the device unit, limits one’s ability to fabricate high performance tandem devices. To resolve this issue, a new connecting materials stack with a C60 fullerene buffer layer is reported. This new structure permits optimization of the Al metal layer in the connecting stack and thus enables us to fabricate an efficient tandem OLED having a high 155.6 cd/A current efficiency and a low roll-off (or droop) in current efficiency.

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.

Enhanced performance of photonic crystal GaN light-emitting diodes with graphene transparent electrodes

NASA Astrophysics Data System (ADS)

Ge, Hai-Liang; Xu, Chen; Xu, Kun; Xun, Meng; Wang, Jun; Liu, Jie

2015-03-01

The two-dimensional (2D) triangle lattice air hole photonic crystal (PC) GaN-based light-emitting diodes (LED) with double-layer graphene transparent electrodes (DGTE) have been produced. The current spreading effect of the double-layer graphene (GR) on the surface of the PC structure of the LED has been researched. Specially, we found that the part of the graphene suspending over the air hole of the PC structure was of much higher conductivity, which reduced the average sheet resistance of the graphene transparent conducting electrode and improved the current spreading of the PC LED. Therefore, the work voltage of the DGTE-PC LED was obviously decreased, and the output power was greatly enhanced. The COMSOL software was used to simulate the current density distribution of the samples. The results show that the etching of PC structure results in the degradation of the current spreading and that the graphene transparent conducting electrode can offer an uniform current spreading in the DGTE-PC LED. PACS: 85.60.Jb; 68.65.Pq; 42.70.Qs

Light extraction from organic light-emitting diodes for lighting applications by sand-blasting substrates.

PubMed

Chen, Shuming; Kwok, Hoi Sing

2010-01-04

Light extraction from organic light-emitting diodes (OLEDs) by scattering the light is one of the effective methods for large-area lighting applications. In this paper, we present a very simple and cost-effective method to rough the substrates and hence to scatter the light. By simply sand-blasting the edges and back-side surface of the glass substrates, a 20% improvement of forward efficiency has been demonstrated. Moreover, due to scattering effect, a constant color over all viewing angles and uniform light pattern with Lambertian distribution has been obtained. This simple and cost-effective method may be suitable for mass production of large-area OLEDs for lighting applications.

Colonic Marking With Near-Infrared, Light-Emitting, Diode-Activated Indocyanine Green for Laparoscopic Colorectal Surgery.

PubMed

Nagata, Jun; Fukunaga, Yosuke; Akiyoshi, Takashi; Konishi, Tsuyoshi; Fujimoto, Yoshiya; Nagayama, Satoshi; Yamamoto, Noriko; Ueno, Masashi

2016-02-01

Accurate identification of the location of colorectal lesions is crucial during laparoscopic surgery. Endoscopic marking has been used as an effective preoperative marker for tumor identification. We investigated the feasibility and safety of an imaging method using near-infrared, light-emitting, diode-activated indocyanine green fluorescence in colorectal laparoscopic surgery. This was a single-institution, prospective study. This study was conducted in a tertiary referral hospital. We enrolled 24 patients who underwent laparoscopic surgery. Indocyanine green and India ink were injected into the same patients undergoing preoperative colonoscopy for colon cancer. During subsequent laparoscopic resection of colorectal tumors, the colon was first observed with white light. Then, indocyanine green was activated with a light-emitting diode at 760 nm as the light source. Near-infrared-induced fluorescence showed tumor location clearly and accurately in all 24 of the patients. All of the patients who underwent laparoscopic surgery after marking had positive indocyanine green staining at the time of surgery. Perioperative complications attributed to dye use were not observed. This study is limited by the cost of indocyanine green detection, the timing of the colonoscopy and tattooing in relation to the operation and identification with indocyanine green, and the small size of the series. These data suggest that our novel method for colonic marking with fluorescence imaging of near-infrared, light-emitting, diode-activated indocyanine green is feasible and safe. This method is useful, has no adverse effects, and can be used for perioperative identification of tumor location. Near-infrared, light-emitting, diode-activated indocyanine green has potential use as a colonic marking agent.

A single blue nanorod light emitting diode.

PubMed

Hou, Y; Bai, J; Smith, R; Wang, T

2016-05-20

We report a light emitting diode (LED) consisting of a single InGaN/GaN nanorod fabricated by a cost-effective top-down approach from a standard LED wafer. The device demonstrates high performance with a reduced quantum confined Stark effect compared with a standard planar counterpart fabricated from the same wafer, confirmed by optical and electrical characterization. Current density as high as 5414 A cm(-2) is achieved without significant damage to the device due to the high internal quantum efficiency. The efficiency droop is mainly ascribed to Auger recombination, which was studied by an ABC model. Our work provides a potential method for fabricating compact light sources for advanced photonic integrated circuits without involving expensive or time-consuming fabrication facilities.

Contrast-enhancement in organic light-emitting diodes.

PubMed

Wu, Zhaoxin; Wang, Liduo; Qiu, Yong

2005-03-07

A high-contrast organic light-emitting diode (OLED) structure is presented. Because of poor contrast of conventional OLED resulting from high reflective metal cathode, the hybrid cathode structure was developed for low reflectivity. It consists the semitransparent cathode layers, passivation layers and a thick light-absorbing film. By optical reflectivity measurement and OLED electrical characterization tests for both OLED with the hybrid cathode and conventional OLED, it was found that the spectrum reflectance of OLED with hybrid cathode is among 8%-12%, about eight times lower than the conventional one when the two types of devices have similar turn-on voltages and current-voltage characteristics. The hybrid cathode for the high-contrast OLED is easily fabricated and its optical reflectance is slightly dependent on wavelength.

Optimization of freeform lightpipes for light-emitting-diode projectors.

PubMed

Fournier, Florian; Rolland, Jannick

2008-03-01

Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

Optimization of freeform lightpipes for light-emitting-diode projectors

NASA Astrophysics Data System (ADS)

Fournier, Florian; Rolland, Jannick

2008-03-01

Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

Organic light-emitting diodes with direct contact-printed red, green, blue, and white light-emitting layers

NASA Astrophysics Data System (ADS)

Chen, Sun-Zen; Peng, Shiang-Hau; Ting, Tzu-Yu; Wu, Po-Shien; Lin, Chun-Hao; Chang, Chin-Yeh; Shyue, Jing-Jong; Jou, Jwo-Huei

2012-10-01

We demonstrate the feasibility of using direct contact-printing in the fabrication of monochromatic and polychromatic organic light-emitting diodes (OLEDs). Bright devices with red, green, blue, and white contact-printed light-emitting layers with a respective maximum luminance of 29 000, 29 000, 4000, and 18 000 cd/m2 were obtained with sound film integrity by blending a polymeric host into a molecular host. For the red OLED as example, the maximum luminance was decreased from 29 000 to 5000 cd/m2 as only the polymeric host was used, or decreased to 7000 cd/m2 as only the molecular host was used. The markedly improved device performance achieved in the devices with blended hosts may be attributed to the employed polymeric host that contributed a good film-forming character, and the molecular host that contributed a good electroluminescence character.

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.

Effect of 3C-SiC intermediate layer in GaN—based light emitting diodes grown on Si(111) substrate

NASA Astrophysics Data System (ADS)

Zhu, Youhua; Wang, Meiyu; Li, Yi; Tan, Shuxin; Deng, Honghai; Guo, Xinglong; Yin, Haihong; Egawa, Takashi

2017-03-01

GaN-based light emitting diodes (LEDs) have been grown by metalorganic chemical vapor deposition on Si(111) substrate with and without 3C-SiC intermediate layer (IL). Structural property has been characterized by means of atomic force microscope, X-ray diffraction, and transmission electron microscope measurements. It has been revealed that a significant improvement in crystalline quality of GaN and superlattice epitaxial layers can be achieved by using 3C-SiC as IL. Regarding of electrical and optical characteristics, it is clearly observed that the LEDs with its IL have a smaller leakage current and higher light output power comparing with the LEDs without IL. The better performance of LEDs using 3C-SiC IL can be contributed to both of the improvements in epitaxial layers quality and light extraction efficiency. As a consequence, in terms of optical property, a double enhancement of the light output power and external quantum efficiency has been realized.

Improved heat dissipation in gallium nitride light-emitting diodes with embedded graphene oxide pattern.

PubMed

Han, Nam; Cuong, Tran Viet; Han, Min; Ryu, Beo Deul; Chandramohan, S; Park, Jong Bae; Kang, Ji Hye; Park, Young-Jae; Ko, Kang Bok; Kim, Hee Yun; Kim, Hyun Kyu; Ryu, Jae Hyoung; Katharria, Y S; Choi, Chel-Jong; Hong, Chang-Hee

2013-01-01

The future of solid-state lighting relies on how the performance parameters will be improved further for developing high-brightness light-emitting diodes. Eventually, heat removal is becoming a crucial issue because the requirement of high brightness necessitates high-operating current densities that would trigger more joule heating. Here we demonstrate that the embedded graphene oxide in a gallium nitride light-emitting diode alleviates the self-heating issues by virtue of its heat-spreading ability and reducing the thermal boundary resistance. The fabrication process involves the generation of scalable graphene oxide microscale patterns on a sapphire substrate, followed by its thermal reduction and epitaxial lateral overgrowth of gallium nitride in a metal-organic chemical vapour deposition system under one-step process. The device with embedded graphene oxide outperforms its conventional counterpart by emitting bright light with relatively low-junction temperature and thermal resistance. This facile strategy may enable integration of large-scale graphene into practical devices for effective heat removal.

Multicolor white light-emitting diodes for illumination applications

NASA Astrophysics Data System (ADS)

Chi, Solomon W. S.; Chen, Tzer-Perng; Tu, Chuan-Cheng; Chang, Chih-Sung; Tsai, Tzong-Liang; Hsieh, Mario C. C.

2004-01-01

Semiconductor light emitting diode (LED) has become a promising device for general-purpose illumination applications. LED has the features of excellent durability, long operation life, low power consumption, no mercury containing and potentially high efficiency. Several white LED technologies appear capable of meeting the technical requirements of illumination. In this paper we present a new multi-color white (MCW) LED as a high luminous efficacy, high color rendering index and low cost white illuminator. The device consists of two LED chips, one is AlInGaN LED for emitting shorter visible spectra, another is AlInGaP LED for emitting longer visible spectra. At least one chip in the MCW-LED has two or more transition energy levels used for emitting two or more colored lights. The multiple colored lights generated from the MCW-LED can be mixed into a full-spectral white light. Besides, there is no phosphors conversion layer used in the MCW-LED structure. Therefore, its color rendering property and illumination efficiency are excellent. The Correlated Color Temperature (CCT) of the MCW-LED may range from 2,500 K to over 10,000 K. The theoretical General Color Rendering Index (Ra) could be as high as 94, which is close to the incandescent and halogen sources, while the Ra of binary complementary white (BCW) LED is about 30 ~ 45. Moreover, compared to the expensive ternary RGB (Red AlInGaP + Green AlInGaN + Blue AlInGaN) white LED sources, the MCW-LED uses only one AlInGaN chip in combination with one cheap AlInGaP chip, to form a low cost, high luminous performance white light source. The MCW-LED is an ideal light source for general-purpose illumination applications.

Non-Toxic Gold Nanoclusters for Solution-Processed White Light-Emitting Diodes.

PubMed

Chao, Yu-Chiang; Cheng, Kai-Ping; Lin, Ching-Yi; Chang, Yu-Li; Ko, Yi-Yun; Hou, Tzu-Yin; Huang, Cheng-Yi; Chang, Walter H; Lin, Cheng-An J

2018-06-11

Solution-processed optoelectronic devices are attractive because of the potential low-cost fabrication and the compatibility with flexible substrate. However, the utilization of toxic elements such as lead and cadmium in current optoelectronic devices on the basis of colloidal quantum dots raises environmental concerns. Here we demonstrate that white-light-emitting diodes can be achieved by utilizing non-toxic and environment-friendly gold nanoclusters. Yellow-light-emitting gold nanoclusters were synthesized and capped with trioctylphosphine. These gold nanoclusters were then blended with the blue-light-emitting organic host materials to form the emissive layer. A current efficiency of 0.13 cd/A was achieved. The Commission Internationale de l'Eclairage chromaticity coordinates of (0.27, 0.33) were obtained from our experimental analysis, which is quite close to the ideal pure white emission coordinates (0.33, 0.33). Potential applications include innovative lighting devices and monitor backlight.

Air-void embedded GaN-based light-emitting diodes grown on laser drilling patterned sapphire substrates

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

Liu, Hao; Li, Yufeng; Wang, Shuai

Air-void structure was introduced in GaN-based blue light-emitting diodes (LED) with one-step growth on periodic laser drilling patterned sapphire substrate, which free of any photolithography or wet/dry etching process. The influence of filling factors (FF) of air-void on crystal quality and optical performance were investigate. Transmission electron microscopy images and micro-Raman spectroscopy indicated that the dislocation was bended and the partially compressed strain was released. When FF was 55.43%, compared with the LED structure grown on flat sapphire substrate, the incorporation of air-void was observed to reduce the compressed stress of ∼20% and the luminance intensity has improved by 128%.more » Together with the simulated reflection intensity enhancement by finite difference time-domain (FDTD) method, we attribute the enhanced optical performance to the combined contribution of strong back-side light reflection of air-void and better GaN epitaxial quality. This approach provides a simple replacement to the conventional air-void embedded LED process.« less

Stacking multiple connecting functional materials in tandem organic light-emitting diodes

PubMed Central

Zhang, Tao; Wang, Deng-Ke; Jiang, Nan; Lu, Zheng-Hong

2017-01-01

Tandem device is an important architecture in fabricating high performance organic light-emitting diodes and organic photovoltaic cells. The key element in making a high performance tandem device is the connecting materials stack, which plays an important role in electric field distribution, charge generation and charge injection. For a tandem organic light-emitting diode (OLED) with a simple Liq/Al/MoO3 stack, we discovered that there is a significant current lateral spreading causing light emission over an extremely large area outside the OLED pixel when the Al thickness exceeds 2 nm. This spread light emission, caused by an inductive electric field over one of the device unit, limits one’s ability to fabricate high performance tandem devices. To resolve this issue, a new connecting materials stack with a C60 fullerene buffer layer is reported. This new structure permits optimization of the Al metal layer in the connecting stack and thus enables us to fabricate an efficient tandem OLED having a high 155.6 cd/A current efficiency and a low roll-off (or droop) in current efficiency. PMID:28225028

Printable candlelight-style organic light-emitting diode

NASA Astrophysics Data System (ADS)

Jou, J. H.; Singh, M.; Song, W. C.; Liu, S. H.

2017-06-01

Candles or oil lamps are currently the most friendly lighting source to human eyes, physiology, ecosystems, artifacts, environment, and night skies due to their blue light-less emission. Candle light also exhibits high light-quality that provides visual comfort. However, they are relatively low in power efficacy (0.3 lm/W), making them energy-wasting, besides having problems like scorching hot, burning, catching fire, flickering, carbon blacking, oxygen consuming, and release of green house gas etc. In contrast, candlelight organic light-emitting diode (OLED) can be made blue-hazard free and energy-efficient. The remaining challenges are to maximize its light-quality and enable printing feasibility, the latter of which would pave a way to cost-effective manufacturing. We hence demonstrate herein the design and fabrication of a candlelight OLED via wet-process. From retina protection perspective, its emission is 13, 12 and 8 times better than those of the blue-enriched white CFL, LED and OLED. If used at night, it is 9, 6 and 4 times better from melatonin generation perspective.

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.

Aggregation in organic light emitting diodes

NASA Astrophysics Data System (ADS)

Meyer, Abigail

Organic light emitting diode (OLED) technology has great potential for becoming a solid state lighting source. However, there are inefficiencies in OLED devices that need to be understood. Since these inefficiencies occur on a nanometer scale there is a need for structural data on this length scale in three dimensions which has been unattainable until now. Local Electron Atom Probe (LEAP), a specific implementation of Atom Probe Tomography (APT), is used in this work to acquire morphology data in three dimensions on a nanometer scale with much better chemical resolution than is previously seen. Before analyzing LEAP data, simulations were used to investigate how detector efficiency, sample size and cluster size affect data analysis which is done using radial distribution functions (RDFs). Data is reconstructed using the LEAP software which provides mass and position data. Two samples were then analyzed, 3% DCM2 in C60 and 2% DCM2 in Alq3. Analysis of both samples indicated little to no clustering was present in this system.

Rosin-enabled ultraclean and damage-free transfer of graphene for large-area flexible organic light-emitting diodes

PubMed Central

Zhang, Zhikun; Du, Jinhong; Zhang, Dingdong; Sun, Hengda; Yin, Lichang; Ma, Laipeng; Chen, Jiangshan; Ma, Dongge; Cheng, Hui-Ming; Ren, Wencai

2017-01-01

The large polymer particle residue generated during the transfer process of graphene grown by chemical vapour deposition is a critical issue that limits its use in large-area thin-film devices such as organic light-emitting diodes. The available lighting areas of the graphene-based organic light-emitting diodes reported so far are usually <1 cm2. Here we report a transfer method using rosin as a support layer, whose weak interaction with graphene, good solubility and sufficient strength enable ultraclean and damage-free transfer. The transferred graphene has a low surface roughness with an occasional maximum residue height of about 15 nm and a uniform sheet resistance of 560 Ω per square with about 1% deviation over a large area. Such clean, damage-free graphene has produced the four-inch monolithic flexible graphene-based organic light-emitting diode with a high brightness of about 10,000 cd m−2 that can already satisfy the requirements for lighting sources and displays. PMID:28233778

Non-Ideal Properties of Gallium Nitride Based Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Shan, Qifeng

The spectacular development of gallium nitride (GaN) based light-emitting diodes (LEDs) in recent years foreshadows a new era for lighting. There are still several non-ideal properties of GaN based LEDs that hinder their widespread applications. This dissertation studies these non-ideal properties including the large reverse leakage current, large subthreshold forward leakage current, an undesired parasitic cyan luminescence and high-concentration deep levels in GaInN blue LEDs. This dissertation also studies the thermal properties of GaInN LEDs. Chapter 1 gives a brief introduction of non-ideal properties of GaN based LEDs. The leakage current of GaN based LEDs, defects in epitaxially grown GaN devices, and doping problems of p-type GaN materials are discussed. The transient junction temperature measurement technique for GaN based LEDs is introduced. The leakage current of an LED includes the subthreshold forward leakage current and the reverse leakage current. The leakage current of GaN based LEDs affects the reliability, electrostatic discharge resilience, and sub-threshold power consumption. In Chapter 2, the reverse leakage current of a GaInN LED is analyzed by temperaturedependent current-voltage measurements. At low temperature, the reverse leakage current is attributed to the variable-range-hopping conduction. At high temperature, the reverse leakage current is attributed to a thermally-assisted multi-step tunneling. The thermal activation energies (95 meV ~ 162 meV), extracted from the Arrhenius plot for the reverse current in the high-temperature range, indicate a thermally activated tunneling process. Additional room-temperature capacitance-voltage (C-V) measurements are performed to obtain information on the depletion width and doping concentration of the LED. The average internal electric field is estimated by the C-V measurements. The strong internal electric field enhances the thermal emission of electrons in the

Electrical contact of wurtzite GaN mircrodisks on p-type GaN template

NASA Astrophysics Data System (ADS)

Tsai, Cheng-Da; Lo, Ikai; Wang, Ying-Chieh; Hsu, Yu-Chi; Shih, Cheng-Hung; Pang, Wen-Yuan; You, Shuo-Ting; Hu, Chia-Hsuan; Chou, Mitch M. C.; Yang, Chen-Chi; Lin, Yu-Chiao

2015-03-01

We developed a back processing to fabricate a secure electrical contact of wurtzite GaN microdisk on a transparent p-type GaN template with the orientation, [10-10]disk // [10-10]template. GaN microdisks were grown on LiAlO2 substrate by using plasma-assisted molecular beam epitaxy. In the further study, we analyzed the TEM specimen of a sample with annealed GaN microdisk/p-typed GaN template by selection area diffraction (SAD) to confirm the alignment of the microdisks with the template at the interface. From the I-V measurements performed on the samples, we obtained a threshold voltage of ~ 5.9 V for the current passing through the GaN microdisks with a resistance of ~ 45 K Ω. The electrical contact can be applied to the nanometer-scaled GaN light-emitting diode.

Benzoporphyrin derivative and light-emitting diode for use in photodynamic therapy: Applications of space light-emitting diode technology

NASA Astrophysics Data System (ADS)

Whelan, Harry T.; Houle, John M.; Bajic, Dawn M.; Schmidt, Meic H.; Reichert, Kenneth W.; Meyer, Glenn A.

1998-01-01

Photodynamic therapy (PDT) is a cancer treatment modality that recently has been applied as adjuvant therapy for brain tumors. PDT consists of intravenously injecting a photosensitizer, which preferentially accumulates in tumor cells, into a patient and then activating the photosensitizer with a light source. This results in free radical generation followed by cell death. The development of more effective light sources for PDT of brain tumors has been facilitated by applications of space light-emitting diode array technology; thus permitting deeper tumor penetration of light and use of better photosensitizers. Currently, the most commonly used photosensitizer for brain tumor PDT is Photofrin®. Photofrin® is a heterogeneous mixture of compounds derived from hematoporphyrin. Photofrin® is activated with a 630 nm laser light and does destroy tumor cells in animal models and humans. However, treatment failure does occur using this method. Most investigators attribute this failure to the limited penetration of brain tissue by a 630 nm laser light and to the fact that Photofrin® has only a minor absorption peak at 630 nm, meaning that only a small fraction of the chemical is activated. Benzoporphyrin Derivative Monoacid Ring A (BPD) is a new, second generation photosensitizer that can potentially improve PDT for brain tumors. BPD has a major absorption peak at 690 nm, which gives it two distinct advantages over Photofrin®. First, longer wavelengths of light penetrate brain tissue more easily so that larger tumors could be treated, and second, the major absorption peak means that a larger fraction of the drug is activated upon exposure to light. In the first part of this project we have studied the tumoricidal effects of BPD in vitro using 2A9 canine glioma and U373 human glioblastoma cell cultures. Using light emitting diodes (LED) with a peak emission of 688 nm as a light source, cell kill of up to 86 percent was measured in these cell lines by tumor DNA synthesis

Ultraviolet Light Emitting Diode Use in Advanced Oxidation Processes

DTIC Science & Technology

2014-03-27

or medium pressure mercury lamps , but UV light emitting diodes ( LEDs ) have the capacity to be used for water disinfection also. Traditional mercury...based upon the phosphors that are selected and used to coat the inside of the glass tube from which these lamps are produced. A UV LED is...Research has demonstrated the ability to use UV LEDs in place of mercury lamps to achieve the same 7 disinfection capacity, and limited research has

Optical Experiments Using Mini-Torches with Red, Green and Blue Light Emitting Diodes

ERIC Educational Resources Information Center

Kamata, Masahiro; Matsunaga, Ai

2007-01-01

We have developed two kinds of optical experiments: color mixture and fluorescence, using mini-torches with light emitting diodes (LEDs) that emit three primary colors. Since the tools used in the experiments are simple and inexpensive, students can easily retry and develop the experiments by themselves. As well as giving an introduction to basic…

Comparative study of (0001) and (11\\bar{2}2) InGaN based light emitting diodes

NASA Astrophysics Data System (ADS)

Pristovsek, Markus; Humphreys, Colin J.; Bauer, Sebastian; Knab, Manuel; Thonke, Klaus; Kozlowski, Grzegorz; O'Mahony, Donagh; Maaskant, Pleun; Corbett, Brian

2016-05-01

We have systematically investigated the doping of (11\\bar{2}2) with Si and Mg by metal-organic vapour phase epitaxy for light emitting diodes (LEDs). By Si doping of GaN we reached electron concentrations close to 1020 cm-3, but the topography degrades above mid 1019 cm-3. By Mg doping we reached hole concentrations close to 5 × 1017 cm-3, using Mg partial pressures about 3× higher than those for (0001). Exceeding the maximum Mg partial pressure led to a quick degradation of the sample. Low resistivities as well as high hole concentrations required a growth temperature of 900 °C or higher. At optimised conditions the electrical properties as well as the photoluminescence of (11\\bar{2}2) p-GaN were similar to (0001) p-GaN. The best ohmic p-contacts were achieved by NiAg metallisation. A single quantum well LED emitting at 465 nm was realised on (0001) and (11\\bar{2}2). Droop (sub-linear increase of the light output power) occurred at much higher current densities on (11\\bar{2}2). However, the light output of the (0001) LED was higher than that of (11\\bar{2}2) until deep in the droop regime. Our LEDs as well as those in the literature indicate a reduction in efficiency from (0001) over semi-polar to non-polar orientations. We propose that reduced fields open a loss channel for carriers.

Safety Evaluation of Converting Traffic Signals From Incandescent to Light-emitting Diodes : Summary Report

DOT National Transportation Integrated Search

2013-08-01

Across the Nation, many agencies have been replacing conventional incandescent light bulbs in traffic signals with light-emitting diodes (LED) (see figure 1 and figure 2). LEDs are primarily installed to reduce energy consumption and decrease mainten...

Electroluminescence property of organic light emitting diode (OLED)

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

Özdemir, Orhan; Kavak, Pelin; Saatci, A. Evrim

2013-12-16

Transport properties of electrons and holes were investigated not only in a anthracene-containing poly(p-phenylene-ethynylene)- alt - poly(p-phenylene-vinylene) (PPE-PPV) polymer (AnE-PVstat) light emitting diodes (OLED) but also in an ITO/Ag/polymer/Ag electron and ITO/PEDOT:PSS/polymer/Au hole only devices. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer.

Light intensity and quality from sole-source light-emitting diodes impact growth, morphology, and nutrient content of Brassica microgreens

USDA-ARS?s Scientific Manuscript database

Multi-layer vertical production systems using sole-source (SS) lighting can be used for microgreen production; however, traditional SS lighting can consume large amounts of electrical energy. Light-emitting diodes (LEDs) offer many advantages over conventional light sources including: high photoelec...

High-performance light-emitting diodes based on carbene-metal-amides

NASA Astrophysics Data System (ADS)

Di, Dawei; Romanov, Alexander S.; Yang, Le; Richter, Johannes M.; Rivett, Jasmine P. H.; Jones, Saul; Thomas, Tudor H.; Abdi Jalebi, Mojtaba; Friend, Richard H.; Linnolahti, Mikko; Bochmann, Manfred; Credgington, Dan

2017-04-01

Organic light-emitting diodes (OLEDs) promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed OLEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 nanoseconds at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, so that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of the donor and acceptor moieties about the bridge. Unlike other systems with low exchange energy, substantial oscillator strength is sustained at the singlet-triplet degeneracy point.

Stolephorus sp Behavior in Different LED (Light Emitting Diode) Color and Light Intensities

NASA Astrophysics Data System (ADS)

Fitri Aristi, D. P.; Ramadanita, I. A.; Hapsari, T. D.; Susanto, A.

2018-02-01

This research aims to observe anchovy (Stolephorus sp) behavior under different LED light intensities that affect eye physiology (cell cone structure). The materials used were Stolephorus sp taken from the waters off Jepara and 13 and 10 watt light emitting diode (LED). The research method was an experiment conducted from March through August 2015 in the waters off Jepara. Data analysis of visual histology and fish respond was carried out at the fishing gear material laboratory, anatomy and cultivate. Cone cell structure (mosaic cone) of Stolephorus sp forms a connected regular square pattern with every single cone surrounded by four double cones, which indicate that anchovies are sensitive to light. The 13 watt LED (628 lux) has faster response than the 10 watt LED (531 lux) as it has wider and higher emitting intensity, which also attracts fish to gather quicker.

Extraction of surface plasmons in organic light-emitting diodes via high-index coupling.

PubMed

Scholz, Bert J; Frischeisen, Jörg; Jaeger, Arndt; Setz, Daniel S; Reusch, Thilo C G; Brütting, Wolfgang

2012-03-12

The efficiency of organic light-emitting diodes (OLEDs) is still limited by poor light outcoupling. In particular, the excitation of surface plasmon polaritons (SPPs) at metal-organic interfaces represents a major loss channel. By combining optical simulations and experiments on simplified luminescent thin-film structures we elaborate the conditions for the extraction of SPPs via coupling to high-index media. As a proof-of-concept, we demonstrate the possibility to extract light from wave-guided modes and surface plasmons in a top-emitting white OLED by a high-index prism.

n-ZnO/p-GaN heterojunction light-emitting diodes featuring a buried polarization-induced tunneling junction

NASA Astrophysics Data System (ADS)

Li, Ling; Zhang, Yuantao; Yan, Long; Jiang, Junyan; Han, Xu; Deng, Gaoqiang; Chi, Chen; Song, Junfeng

2016-12-01

n-ZnO/p-GaN heterojunction light-emitting diodes with a p-GaN/Al0.1Ga0.9N/n+-GaN polarization-induced tunneling junction (PITJ) were fabricated by metal-organic chemical vapor deposition. An intense and sharp ultraviolet emission centered at ˜396 nm was observed under forward bias. Compared with the n-ZnO/p-GaN reference diode without PITJ, the light intensity of the proposed diode is increased by ˜1.4-folds due to the improved current spreading. More importantly, the studied diode operates continuously for eight hours with the decay of only ˜3.5% under 20 mA, suggesting a remarkable operating stability. The results demonstrate the feasibility of using PITJ as hole injection layer for high-performance ZnO-based light-emitting devices.

Measurement of the water content in oil and oil products using IR light-emitting diode-photodiode optrons

NASA Astrophysics Data System (ADS)

Bogdanovich, M. V.; Kabanau, D. M.; Lebiadok, Y. V.; Shpak, P. V.; Ryabtsev, A. G.; Ryabtsev, G. I.; Shchemelev, M. A.; Andreev, I. A.; Kunitsyna, E. V.; Ivanov, E. V.; Yakovlev, Yu. P.

2017-02-01

The feasibility of using light-emitting devices, the radiation spectrum of which has maxima at wavelengths of 1.7, 1.9, and 2.2 μm for determining the water concentration in oil and oil products (gasoline, kerosene, diesel fuel) has been demonstrated. It has been found that the measurement error can be lowered if (i) the temperature of the light-emitting diode is maintained accurate to 0.5-1.0°C, (ii) by using a cell through which a permanently stirred analyte is pumped, and (iii) by selecting the repetition rate of radiation pulses from the light-emitting diodes according to the averaging time. A meter of water content in oil and oil products has been developed that is built around IR light-emitting device-photodiode optrons. This device provides water content on-line monitoring accurate to 1.5%.

Demonstration Assessment of Light-Emitting Diode (LED) Post-Top Lighting at Central Park in New York City

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

Myer, Michael; Goettel, Russell T.; Kinzey, Bruce R.

2012-09-30

A review of five post-top light-emitting diode (LED) pedestrian luminaires installed in New York City's Central Park for possible replacement to the existing metal halide post-top luminaire. This report reviews the energy savings potential and lighting delivered by the LED post-top luminaires.

Tandem Organic Light-Emitting Diodes.

PubMed

Fung, Man-Keung; Li, Yan-Qing; Liao, Liang-Sheng

2016-12-01

A tandem organic light-emitting diode (OLED) is an organic optoelectronic device that has two or more electroluminescence (EL) units connected electrically in series with unique intermediate connectors within the device. Researchers have studied this new OLED architecture with growing interest and have found that the current efficiency of a tandem OLED containing N EL units (N > 1) should be N times that of a conventional OLED containing only a single EL unit. Therefore, this new architecture is potentially useful for constructing high-efficiency, high-luminance, and long-lifetime OLED displays and organic solid-state lighting sources. In a tandem OLED, the intermediate connector plays a crucial role in determining the effectiveness of the stacked EL units. The interfaces in the connector control the inner charge generation and charge injection into the adjacent EL units. Meanwhile, the transparency and the thickness of the connector affect the light output of the device. Therefore, the intermediate connector should be made to meet both the electrical and optical requirements for achieving optimal performance. Here, recent advances in the research of the tandem OLEDs is discussed, with the main focus on material selection and interface studies in the intermediate connectors, as well as the optical design of the tandem OLEDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Solution-processed multilayer polymer light-emitting diode without intermixing

NASA Astrophysics Data System (ADS)

Kasparek, C.; Blom, P. W. M.

2017-01-01

The intermixing of two emissive layers in a four-layer solution-processed polymeric light-emitting diode with a hole injection, two emissive layers, and one hole-blocking layer is investigated. The relative emission of both emissive layers is measured and compared to a calculated recombination profile across the device using drift-diffusion simulations. A good agreement between the measured and calculated relative emission was found, supporting that there is no intermixing in the two emissive materials.

Electronic Two-Transition-Induced Enhancement of Emission Efficiency in Polymer Light-Emitting Diodes

PubMed Central

Chen, Ren-Ai; Wang, Cong; Li, Sheng; George, Thomas F.

2013-01-01

With the development of experimental techniques, effective injection and transportation of electrons is proven as a way to obtain polymer light-emitting diodes (PLEDs) with high quantum efficiency. This paper reveals a valid mechanism for the enhancement of quantum efficiency in PLEDs. When an external electric field is applied, the interaction between a negative polaron and triplet exciton leads to an electronic two-transition process, which induces the exciton to emit light and thus improve the emission efficiency of PLEDs. PMID:28809346

ZnCuInS/ZnSe/ZnS quantum dot-based downconversion light-emitting diodes and their thermal effect

DOE PAGES

Liu, Wenyan; Zhang, Yu; Wang, Dan; ...

2015-08-13

The quantum dot-based light-emitting diodes (QD-LEDs) were fabricated using blue GaN chips and red-, yellow-, and green-emitting ZnCuInS/ZnSe/ZnS QDs. The power efficiencies were measured as 14.0 lm/W for red, 47.1 lm/W for yellow, and 62.4 lm/W for green LEDs at 2.6 V. The temperature effect of ZnCuInS/ZnSe/ZnS QDs on these LEDs was investigated using CIE chromaticity coordinates, spectral wavelength, full width at half-maximum (FWHM) and power efficiencies (PE). The thermal quenching induced by the increased surface temperature of the device was confirmed to be one of the important factors to decrease power efficiencies while the CIE chromaticity coordinates changed littlemore » due to the low emission temperature coefficients of 0.022, 0.050 and 0.068 nm/°C for red-, yellow- and green-emitting ZnCuInS/ZnSe/ZnS QDs. Lastly this indicates that ZnCuInS/ZnSe/ZnS QDs are more suitable for down-conversion LEDs compared to CdSe QDs.« less

Lighting theory and luminous characteristics of white light-emitting diodes

NASA Astrophysics Data System (ADS)

Uchida, Yuji; Taguchi, Tsunemasa

2005-12-01

A near-ultraviolet (UV)-based white light-emitting diode (LED) lighting system linked with a semiconductor InGaN LED and compound phosphors for general lighting applications is proposed. We have developed for the first time a novel type of high-color rendering index (Ra) white LED light source, which is composed of near-UV LED and multiphosphor materials showing orange (O), yellow (Y), green (G), and blue (B) emissions. The white LED shows the superior characteristics of luminous efficacy and high Ra to be about 40 lm/W and 93, respectively. Luminous and chromaticity characteristics, and their spectral distribution of the present white LED can be evaluated using the multipoint LED light source theory. It is revealed that the OYGB white LED can provide better irradiance properties than that of conventional white LEDs. Near-UV white LED technologies, in conjunction with phosphor blends, can offer superior color uniformity, high Ra, and excellent light quality. Consequently we are carrying out a "white LEDs for medical applications" program in the second phase of this national project from 2004 to 2009.

Direct Observation of the Biaxial Stress Effect on Efficiency Droop in GaN-based Light-emitting Diode under Electrical Injection.

PubMed

Zheng, Jinjian; Li, Shuiqing; Chou, Chilun; Lin, Wei; Xun, Feilin; Guo, Fei; Zheng, Tongchang; Li, Shuping; Kang, Junyong

2015-12-04

Light-emitting diode (LED) efficiency has attracted considerable interest because of the extended use of solid-state lighting. Owing to lack of direct measurement, identification of the reasons for efficiency droop has been restricted. A direct measurement technique is developed in this work for characterization of biaxial stress in GaN-based blue LEDs under electrical injection. The Raman shift of the GaN E2 mode evidently decreases by 4.4 cm(-1) as the driving current on GaN-based LEDs increases to 700 mA. Biaxial compressive stress is released initially and biaxial tensile stress builds up as the current increases with respect to the value of stress-free GaN. First-principles calculations reveal that electron accumulation is responsible for the stress variation in InxGa1-xN/GaN quantum wells, and then reduces the transition probability among quantum levels. This behavior is consistent with the measured current-dependent external quantum efficiency. The rule of biaxial stress-dependent efficiency is further validated by controlling the biaxial stress of GaN-based LEDs with different sapphire substrate thicknesses. This work provides a method for direct observation of the biaxial stress effect on efficiency droop in LEDs under electrical injection.

Direct Observation of the Biaxial Stress Effect on Efficiency Droop in GaN-based Light-emitting Diode under Electrical Injection

PubMed Central

Zheng, Jinjian; Li, Shuiqing; Chou, Chilun; Lin, Wei; Xun, Feilin; Guo, Fei; Zheng, Tongchang; Li, Shuping; Kang, Junyong

2015-01-01

Light-emitting diode (LED) efficiency has attracted considerable interest because of the extended use of solid-state lighting. Owing to lack of direct measurement, identification of the reasons for efficiency droop has been restricted. A direct measurement technique is developed in this work for characterization of biaxial stress in GaN-based blue LEDs under electrical injection. The Raman shift of the GaN E2 mode evidently decreases by 4.4 cm−1 as the driving current on GaN-based LEDs increases to 700 mA. Biaxial compressive stress is released initially and biaxial tensile stress builds up as the current increases with respect to the value of stress-free GaN. First-principles calculations reveal that electron accumulation is responsible for the stress variation in InxGa1−xN/GaN quantum wells, and then reduces the transition probability among quantum levels. This behavior is consistent with the measured current-dependent external quantum efficiency. The rule of biaxial stress-dependent efficiency is further validated by controlling the biaxial stress of GaN-based LEDs with different sapphire substrate thicknesses. This work provides a method for direct observation of the biaxial stress effect on efficiency droop in LEDs under electrical injection. PMID:26634816

Properties of excited states in organic light emitting diodes and lasers

NASA Astrophysics Data System (ADS)

Giebink, Noel C.

The field of organic semiconductors has grown rapidly over the past decade with the development of light emitting diodes, solar cells, and lasers that promise a new generation of low-cost, flexible optoelectronic devices. In each case, the behavior of molecular excited states, or excitons, is of fundamental importance. The present study explores the nature and interactions of such excited states in the attempt to develop an electrically pumped organic semiconductor laser, and to improve the performance and operational stability of organic light emitting diodes. We begin by investigating intrinsic loss processes in optically pumped organic semiconductor lasers and demonstrate that exciton annihilation implies a fundamental limit that will prevent lasing by electrical injection in currently known materials. Searching for an alternative approach to reach threshold leads us to study metastable geminate charge pairs, where we find that optically generated excitons can be accumulated over time in an external electric field via these intermediate states. Upon field turn-off, the excitons are immediately restored, leading to a sudden burst of excitation density over 30 times higher than that generated by the pump alone. Unfortunately, we identify limitations that have thus far prevented reaching laser threshold with this technique. In a parallel push toward high power density, we investigate the origins of quantum efficiency roll-off in organic light emitting diodes (OLEDs) and find that it is dominated by loss of charge balance in the majority of fluorescent and phosphorescent devices. The second major theme of this work involves understanding the intrinsic modes of OLED operational degradation. Based on extensive modeling and supported directly by experimental evidence, we identify exciton-charge carrier annihilation reactions as a principle degradation pathway. Exploiting the diffusion of triplet excitons, we show that fluorescence and phosphorescence can be combined to

Manipulating Refractive Index in Organic Light-Emitting Diodes.

PubMed

Salehi, Amin; Chen, Ying; Fu, Xiangyu; Peng, Cheng; So, Franky

2018-03-21

In a conventional organic light-emitting diode (OLED), only a fraction of light can escape to the glass substrate and air. Most radiation is lost to two major channels: waveguide modes and surface plasmon polaritons. It is known that reducing the refractive indices of the constituent layers in an OLED can enhance light extraction. Among all of the layers, the refractive index of the electron transport layer (ETL) has the largest impact on light extraction because it is the layer adjacent to the metallic cathode. Oblique angle deposition (OAD) provides a way to manipulate the refractive index of a thin film by creating an ordered columnar void structure. In this work, using OAD, the refractive index of tris(8-hydroxyquinoline)aluminum (Alq3) can be tuned from 1.75 to 1.45. With this low-index ETL deposited by OAD, the resulting phosphorescent OLED shows nearly 30% increase in light extraction efficiency.

Light-modulating pressure sensor with integrated flexible organic light-emitting diode.

PubMed

Cheneler, D; Vervaeke, M; Thienpont, H

2014-05-01

Organic light-emitting diodes (OLEDs) are used almost exclusively for display purposes. Even when implemented as a sensing component, it is rarely in a manner that exploits the possible compliance of the OLED. Here it is shown that OLEDs can be integrated into compliant mechanical micro-devices making a new range of applications possible. A light-modulating pressure sensor is considered, whereby the OLED is integrated with a silicon membrane. It is shown that such devices have potential and advantages over current measurement techniques. An analytical model has been developed that calculates the response of the device. Ray tracing numerical simulations verify the theory and show that the design can be optimized to maximize the resolution of the sensor.

Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes.

PubMed

Liu, Xiao-Ke; Chen, Zhan; Zheng, Cai-Jun; Liu, Chuan-Lin; Lee, Chun-Sing; Li, Fan; Ou, Xue-Mei; Zhang, Xiao-Hong

2015-04-08

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrical and Optical Enhancement in Internally Nanopatterned Organic Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Fina, Michael Dane

Organic light-emitting diodes (OLEDs) have made tremendous technological progress in the past two decades and have emerged as a top competitor for next generation light-emitting displays and lighting. State-of-the-art OLEDs have been reported in literature to approach, and even surpass, white fluorescent tube efficiency. However, despite rapid technological progress, efficiency metrics must be improved to compete with traditional inorganic light-emitting diode (LED) technology. Organic materials possess specialized traits that permit manipulations to the light-emitting cavity. Overall, as demonstrated within, these modifications can be used to improve electrical and optical device efficiencies. This work is focused at analyzing the effects that nanopatterned geometric modifications to the organic active layers play on device efficiency. In general, OLED efficiency is complicated by the complex, coupled processes which contribute to spontaneous dipole emission. A composite of three sub-systems (electrical, exciton and optical) ultimately dictate the OLED device efficiency. OLED electrical operation is believed to take place via a low-mobility-modified Schottky injection process. In the injection-limited regime, geometric effects are expected to modify the local electric field leading to device current enhancement. It is shown that the patterning effect can be used to enhance charge carrier parity, thereby enhancing overall recombination. Current density and luminance characteristics are shown to be improved by OLED nanopatterning from both the model developed within and experimental techniques. Next, the optical enhancement effects produced by the nanopatterned array are considered. Finite-difference time-domain (FDTD) simulations are used to determine positional, spectral optical enhancement for the nanopatterned device. The results show beneficial effects to the device performance. The optical enhancements are related to the reduction in internal radiative

Synthesis and luminescent properties of Tb3Al5O12:Ce3+ phosphors for warm white light emitting diodes

NASA Astrophysics Data System (ADS)

Meng, Qinghuan; Liu, Ying; Fu, Yujie; Zu, Yuangang; Zhou, Zhenbao

2018-01-01

A series of Tb3Al5O12:Ce3+ phosphors were successfully synthesized by a precipitation method. The pure Tb3Al5O12 phase was obtained in the synthesized Tb3Al5O12:Ce3+ phosphors after heat treatments at 500 °C in air for 3 h. The excitation spectra of Tb3Al5O12:Ce3+ phosphors include excitation bands corresponding to Tb3+ and Ce3+ ions. Under the excitation at 455 nm, Tb3Al5O12:Ce3+ phosphors show emission band at around 553 nm. The critical doping concentration of Ce3+ in Tb3Al5O12 is 6mol%, which shows the highest emission intensity. White light-emitting diodes were fabricated by combining InGaN-based blue light-emitting diodes with Tb3Al5O12:Ce3+ and Y3Al5O12:Ce3+ phosphors. The Tb3Al5O12:Ce3+ based white light-emitting diode shows a lower color temperature than that of Y3Al5O12:Ce3+ based white light-emitting diode. The experimental results clearly indicate that the prepared Tb3Al5O12:Ce3+ has potential applications in white light emitting diodes.

Recent advances in light outcoupling from white organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Gather, Malte C.; Reineke, Sebastian

2015-01-01

Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ˜100% yield. However, the extraction of photons remains rather inefficient (typically <30%). Here, we provide an introduction to the underlying physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal-metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.

Evaluation of inorganic and organic light-emitting diode displays for signage application

NASA Astrophysics Data System (ADS)

Sharma, Pratibha; Kwok, Harry

2006-08-01

High-brightness, inorganic light-emitting diodes (LEDs) have been successfully utilized for edge-lighting of large displays for signage. Further interest in solid-state lighting technology has been fueled with the emergence of small molecule and polymer-based organic light-emitting diodes (OLEDs). In this paper, edgelit inorganic LED-based displays and state-of-the-art OLED-based displays are evaluated on the basis of electrical and photometric measurements. The reference size for a signage system is assumed to be 600 mm x 600mm based on the industrial usage. With the availability of high power light-emitting diodes, it is possible to develop edgelit signage systems of the standard size. These displays possess an efficacy of 18 lm/W. Although, these displays are environmentally friendly and efficient, they suffer from some inherent limitations. Homogeneity of displays, which is a prime requirement for illuminated signs, is not accomplished. A standard deviation of 3.12 lux is observed between the illuminance values on the surface of the display. In order to distribute light effectively, reflective gratings are employed. Reflective gratings aid in reducing the problem but fail to eliminate it. In addition, the overall cost of signage is increased by 50% with the use of these additional components. This problem can be overcome by the use of a distributed source of light. Hence, the organic-LEDs are considered as a possible contender. In this paper, we experimentally determine the feasibility of using OLEDs for signage applications and compare their performance with inorganic LEDs. Passive matrix, small-molecule based, commercially available OLEDs is used. Design techniques for implementation of displays using organic LEDs are also discussed. It is determined that tiled displays based on organic LEDs possess better uniformity than the inorganic LED-based displays. However, the currently available OLEDs have lower light-conversion efficiency and higher costs than the

Enhanced optical power of GaN-based light-emitting diode with compound photonic crystals by multiple-exposure nanosphere-lens lithography

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

Zhang, Yonghui; Wei, Tongbo, E-mail: tbwei@semi.ac.cn; Xiong, Zhuo

2014-07-07

The light-emitting diodes (LEDs) with single, twin, triple, and quadruple photonic crystals (PCs) on p-GaN are fabricated by multiple-exposure nanosphere-lens lithography (MENLL) process utilizing the focusing behavior of polystyrene spheres. Such a technique is easy and economical for use in fabricating compound nano-patterns. The optimized tilted angle is decided to be 26.6° through mathematic calculation to try to avoid the overlay of patterns. The results of scanning electron microscopy and simulations reveal that the pattern produced by MENLL is a combination of multiple ovals. Compared to planar-LED, the light output power of LEDs with single, twin, triple, and quadruple PCsmore » is increased by 14.78%, 36.03%, 53.68%, and 44.85% under a drive current 350 mA, respectively. Furthermore, all PC-structures result in no degradation of the electrical properties. The stimulated results indicate that the highest light extraction efficiency of LED with the clover-shape triple PC is due to the largest scattering effect on propagation of light from GaN into air.« less

The Use of Light-Emitting Diodes (LEDs) as Green and Red/Far-Red Light Sources in Plant Physiology.

ERIC Educational Resources Information Center

Jackson, David L.; And Others

1985-01-01

The use of green, red, and far-red light-emitting diodes (LEDs) as light sources for plant physiological studies is outlined and evaluated. Indicates that LED lamps have the advantage over conventional light sources in that they are lightweight, low-cost, portable, easily constructed, and do not require color filters. (Author/DH)

Solution epitaxy of gallium-doped ZnO on p-GaN for heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Le, H. Q.; Lim, S. K.; Goh, G. K. L.; Chua, S. J.; Ang, N. S. S.; Liu, W.

2010-09-01

We report white light emission from a Ga-doped ZnO/p-GaN heterojunction light-emitting diode which was fabricated by growing gallium-doped ZnO film on the p-GaN in water at 90°C. As determined from Ga-doped ZnO films grown on (111) oriented MgAl2O4 spinel single crystal substrates, thermal treatment at 600°C in nitrogen ambient leads to a carrier concentration of 3.1×1020 cm-3 (and carrier mobility of 28 cm2/Vs) which is two orders of magnitude higher than that of the undoped films. Electroluminescence emissions at wavelengths of 393 nm (3.155 eV) and 529.5 nm (2.4 eV) were observed under forward bias in the heterojunction diode and white light could be visibly observed. The high concentration of electrons supplied from the Ga-doped ZnO films helped to enhance the carrier recombination and increase the light-emitting efficiency of the heterojunction diode.

Hybrid GaN LED with capillary-bonded II-VI MQW color-converting membrane for visible light communications

NASA Astrophysics Data System (ADS)

Santos, Joao M. M.; Jones, Brynmor E.; Schlosser, Peter J.; Watson, Scott; Herrnsdorf, Johannes; Guilhabert, Benoit; McKendry, Jonathan J. D.; De Jesus, Joel; Garcia, Thor A.; Tamargo, Maria C.; Kelly, Anthony E.; Hastie, Jennifer E.; Laurand, Nicolas; Dawson, Martin D.

2015-03-01

The rapid emergence of gallium-nitride (GaN) light-emitting diodes (LEDs) for solid-state lighting has created a timely opportunity for optical communications using visible light. One important challenge to address this opportunity is to extend the wavelength coverage of GaN LEDs without compromising their modulation properties. Here, a hybrid source for emission at 540 nm consisting of a 450 nm GaN micro-sized LED (micro-LED) with a micron-thick ZnCdSe/ZnCdMgSe multi-quantum-well color-converting membrane is reported. The membrane is liquid-capillary-bonded directly onto the sapphire window of the micro-LED for full hybridization. At an injection current of 100 mA, the color-converted power was found to be 37 μW. At this same current, the -3 dB optical modulation bandwidth of the bare GaN and hybrid micro-LEDs were 79 and 51 MHz, respectively. The intrinsic bandwidth of the color-converting membrane was found to be power-density independent over the range of the micro-LED operation at 145 MHz, which corresponds to a mean carrier lifetime of 1.9 ns.

Phosphorescent Organic Light Emitting Diodes Implementing Platinum Complexes

NASA Astrophysics Data System (ADS)

Ecton, Jeremy Exton

Organic light emitting diodes (OLEDs) are a promising approach for display and solid state lighting applications. However, further work is needed in establishing the availability of efficient and stable materials for OLEDs with high external quantum efficiency's (EQE) and high operational lifetimes. Recently, significant improvements in the internal quantum efficiency or ratio of generated photons to injected electrons have been achieved with the advent of phosphorescent complexes with the ability to harvest both singlet and triplet excitons. Since then, a variety of phosphorescent complexes containing heavy metal centers including Os, Ni, Ir, Pd, and Pt have been developed. Thus far, the majority of the work in the field has focused on iridium based complexes. Platinum based complexes, however, have received considerably less attention despite demonstrating efficiency's equal to or better than their iridium analogs. In this study, a series of OLEDs implementing newly developed platinum based complexes were demonstrated with efficiency's or operational lifetimes equal to or better than their iridium analogs for select cases. In addition to demonstrating excellent device performance in OLEDs, platinum based complexes exhibit unique photophysical properties including the ability to form excimer emission capable of generating broad white light emission from a single emitter and the ability to form narrow band emission from a rigid, tetradentate molecular structure for select cases. These unique photophysical properties were exploited and their optical and electrical properties in a device setting were elucidated. Utilizing the unique properties of a tridentate Pt complex, Pt-16, a highly efficient white device employing a single emissive layer exhibited a peak EQE of over 20% and high color quality with a CRI of 80 and color coordinates CIE(x=0.33, y=0.33). Furthermore, by employing a rigid, tetradentate platinum complex, PtN1N, with a narrow band emission into a

Effect of 670-nm Light-Emitting Diode Light On Neuronal Cultures

NASA Technical Reports Server (NTRS)

Wong-Riley, Margaret T. T.; Whelan, Harry T.

2002-01-01

Light close to and within the near infrared range has documented benefits for promoting wound healing in human and animal studies. Our preliminary results using light-emitting diodes (LEDs) in this range have also demonstrated two-to five-fold increases in growth-phase-specific DNA synthesis in normal fibroblasts, muscle cells, osteoblasts, and mucosal epithelial cells in tissue cultures. However, the mechanisms of action of such light on cells are poorly understood. We hypothesized that the therapeutic effects of such light result from the stimulation of cellular events associated with increases in cytochrome oxidase activity. As a first step in testing our hypothesis, we subjected primary neuronal cultures to impulse blockade by tetrodotoxin (TTX), a voltage-dependent sodium channel blocker, and applied LED light at 670 nm to determine if it could partially or fully reverse the reduction of cytochrome oxidase activity by TTX. The wavelength and parameters were previously tested to be beneficial for wound healing.

Manipulating Ion Migration for Highly Stable Light-Emitting Diodes with Single-Crystalline Organometal Halide Perovskite Microplatelets.

PubMed

Chen, Mingming; Shan, Xin; Geske, Thomas; Li, Junqiang; Yu, Zhibin

2017-06-27

Ion migration has been commonly observed as a detrimental phenomenon in organometal halide perovskite semiconductors, causing the measurement hysteresis in solar cells and ultrashort operation lifetimes in light-emitting diodes. In this work, ion migration is utilized for the formation of a p-i-n junction at ambient temperature in single-crystalline organometal halide perovskites. The junction is subsequently stabilized by quenching the ionic movement at a low temperature. Such a strategy of manipulating the ion migration has led to efficient single-crystalline light-emitting diodes that emit 2.3 eV photons starting at 1.8 V and sustain a continuous operation for 54 h at ∼5000 cd m -2 without degradation of brightness. In addition, a whispering-gallery-mode cavity and exciton-exciton interaction in the perovskite microplatelets have both been observed that can be potentially useful for achieving electrically driven laser diodes based on single-crystalline organometal halide perovskite semiconductors.

Dr. Harry Whelan With the Light Emitting Diode Probe

NASA Technical Reports Server (NTRS)

1999-01-01

The red light from the Light Emitting Diode (LED) probe shines through the fingers of Dr. Harry Whelan, a pediatric neurologist at the Children's Hospital of Wisconsin in Milwaukee. Dr. Whelan uses the long waves of light from the LED surgical probe to activate special drugs that kill brain tumors. Laser light previously has been used for this type of surgery, but the LED light illuminates through all nearby tissues, reaching parts of tumors that shorter wavelengths of laser light carnot. The new probe is safer because the longer wavelengths of light are cooler than the shorter wavelengths of laser light, making the LED less likely to injure normal brain tissue near the tumor. Also, it can be used for hours at a time while still remaining cool to the touch. The probe was developed for photodynamic cancer therapy under a NASA Small Business Innovative Research Program grant. The program is part of NASA's Technology Transfer Department at the Marshall Space Flight Center.

A Simple, Small-Scale Lego Colorimeter with a Light-Emitting Diode (LED) Used as Detector

ERIC Educational Resources Information Center

Asheim, Jonas; Kvittingen, Eivind V.; Kvittingen, Lise; Verley, Richard

2014-01-01

This article describes how to construct a simple, inexpensive, and robust colorimeter from a few Lego bricks, in which one light-emitting diode (LED) is used as a light source and a second LED as a light detector. The colorimeter is suited to various grades and curricula.

Mesoscopic Perovskite Light-Emitting Diodes.

PubMed

Palma, Alessandro Lorenzo; Cinà, Lucio; Busby, Yan; Marsella, Andrea; Agresti, Antonio; Pescetelli, Sara; Pireaux, Jean-Jacques; Di Carlo, Aldo

2016-10-03

Solution-processed hybrid bromide perovskite light-emitting-diodes (PLEDs) represent an attractive alternative technology that would allow overcoming the well-known severe efficiency drop in the green spectrum related to conventional LEDs technologies. In this work, we report on the development and characterization of PLEDs fabricated using, for the first time, a mesostructured layout. Stability of PLEDs is a critical issue; remarkably, mesostructured PLEDs devices tested in ambient conditions and without encapsulation showed a lifetime well-above what previously reported with a planar heterojunction layout. Moreover, mesostructured PLEDs measured under full operative conditions showed a remarkably narrow emission spectrum, even lower than what is typically obtained by nitride- or phosphide-based green LEDs. A dynamic analysis has shown fast rise and fall times, demonstrating the suitability of PLEDs for display applications. Combined electrical and advanced structural analyses (Raman, XPS depth profiling, and ToF-SIMS 3D analysis) have been performed to elucidate the degradation mechanism, the results of which are mainly related to the degradation of the hole-transporting material (HTM) and to the perovskite-HTM interface.

Ultrastrong light-matter coupling in electrically doped microcavity organic light emitting diodes

NASA Astrophysics Data System (ADS)

Mazzeo, M.; Genco, A.; Gambino, S.; Ballarini, D.; Mangione, F.; Di Stefano, O.; Patanè, S.; Savasta, S.; Sanvitto, D.; Gigli, G.

2014-06-01

The coupling of the electromagnetic field with an electronic transition gives rise, for strong enough light-matter interactions, to hybrid states called exciton-polaritons. When the energy exchanged between light and matter becomes a significant fraction of the material transition energy an extreme optical regime called ultrastrong coupling (USC) is achieved. We report a microcavity embedded p-i-n monolithic organic light emitting diode working in USC, employing a thin film of squaraine dye as active layer. A normalized coupling ratio of 30% has been achieved at room temperature. These USC devices exhibit a dispersion-less angle-resolved electroluminescence that can be exploited for the realization of innovative optoelectronic devices. Our results may open the way towards electrically pumped polariton lasers.

Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

PubMed

Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

2014-06-11

Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

Light-extraction efficiency and forward voltage in GaN-based light-emitting diodes with different patterns of V-shaped pits

NASA Astrophysics Data System (ADS)

Wang, Min-Shuai; Huang, Xiao-Jing

2013-08-01

We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaN-based light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaN-based light-emitting diodes (LEDs) with surface V-pits in different densities and regions were grown by metal—organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.

Alleviation of efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with trapezoidal quantum barriers

NASA Astrophysics Data System (ADS)

Kim, Sang-Jo; Lee, Kwang Jae; Park, Seong-Ju

2018-06-01

We numerically investigated the effects of trapezoidal quantum barriers (QBs) on efficiency droop in InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs). Simulations showed that the electrostatic field in QWs of LEDs with trapezoidal barriers is reduced because of the reduced sheet charge density at the QW-QB interface caused by the thin GaN layer in trapezoidal QBs. Additionally, the InGaN grading region in trapezoidal QBs suppresses hot carrier transport and this enhances efficient carrier injection into the QWs. The electroluminescence intensity of an LED with trapezoidal QBs is increased by 10.2% and 6.7% at 245 A cm‑2 when compared with the intensities of LEDs with square-type GaN barriers and multilayer barriers, respectively. The internal quantum efficiency (IQE) droop of an LED with trapezoidal QBs is 16% at 300 A cm‑2, while LEDs with square-type GaN barriers and multilayer barriers have IQE droop of 31% and 24%, respectively. This IQE droop alleviation in LEDs with trapezoidal QBs is attributed to the reduced energy band bending, efficient hole injection, and more uniform hole distribution in the MQWs that results from reduction of the piezoelectric field by the trapezoidal QBs. These results indicate that the trapezoidal QB in MQWs is promising for enhanced efficiency in high-power GaN-based LEDs.

Solution-Grown ZnO Films toward Transparent and Smart Dual-Color Light-Emitting Diode.

PubMed

Huang, Xiaohu; Zhang, Li; Wang, Shijie; Chi, Dongzhi; Chua, Soo Jin

2016-06-22

An individual light-emitting diode (LED) capable of emitting different colors of light under different bias conditions not only allows for compact device integration but also extends the functionality of the LED beyond traditional illumination and display. Herein, we report a color-switchable LED based on solution-grown n-type ZnO on p-GaN/n-GaN heterojunction. The LED emits red light with a peak centered at ∼692 nm and a full width at half-maximum of ∼90 nm under forward bias, while it emits green light under reverse bias. These two lighting colors can be switched repeatedly by reversing the bias polarity. The bias-polarity-switched dual-color LED enables independent control over the lighting color and brightness of each emission with two-terminal operation. The results offer a promising strategy toward transparent, miniaturized, and smart LEDs, which hold great potential in optoelectronics and optical communication.

Quantum key distribution with an entangled light emitting diode

NASA Astrophysics Data System (ADS)

Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Farrer, I.; Ritchie, D. A.; Shields, A. J.

2015-12-01

Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurements also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.

Light-emitting diodes for analytical chemistry.

PubMed

Macka, Mirek; Piasecki, Tomasz; Dasgupta, Purnendu K

2014-01-01

Light-emitting diodes (LEDs) are playing increasingly important roles in analytical chemistry, from the final analysis stage to photoreactors for analyte conversion to actual fabrication of and incorporation in microdevices for analytical use. The extremely fast turn-on/off rates of LEDs have made possible simple approaches to fluorescence lifetime measurement. Although they are increasingly being used as detectors, their wavelength selectivity as detectors has rarely been exploited. From their first proposed use for absorbance measurement in 1970, LEDs have been used in analytical chemistry in too many ways to make a comprehensive review possible. Hence, we critically review here the more recent literature on their use in optical detection and measurement systems. Cloudy as our crystal ball may be, we express our views on the future applications of LEDs in analytical chemistry: The horizon will certainly become wider as LEDs in the deep UV with sufficient intensity become available.

Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices.

PubMed

O'Toole, Martina; Diamond, Dermot

2008-04-07

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements.

Fabrication and characterization of a germanium nanowire light emitting diode

NASA Astrophysics Data System (ADS)

Greil, Johannes; Bertagnolli, Emmerich; Salem, Bassem; Baron, Thierry; Gentile, Pascal; Lugstein, Alois

2017-12-01

In this letter, we demonstrate the feasibility of a germanium nanowire light emitting diode as a reasonable approach for downscaling of CMOS compatible light sources. We show room-temperature direct bandgap electroluminescence from axial p-n junction nanowire devices. The electron population in the Γ valley, necessary for direct bandgap emission, is achieved by high injection current densities. Carrier temperature is consistently found to be higher than the lattice temperature, indicating inhibited carrier cooling in small diameter wires. Strong polarization of the emission parallel to the nanowire axis is observed and attributed to dielectric contrast phenomena.

Optical Properties of Hybrid Inorganic/Organic Thin Film Encapsulation Layers for Flexible Top-Emission Organic Light-Emitting Diodes.

PubMed

An, Jae Seok; Jang, Ha Jun; Park, Cheol Young; Youn, Hongseok; Lee, Jong Ho; Heo, Gi-Seok; Choi, Bum Ho; Lee, Choong Hun

2015-10-01

Inorganic/organic hybrid thin film encapsulation layers consist of a thin Al2O3 layer together with polymer material. We have investigated optical properties of thin film encapsulation layers for top-emission flexible organic light-emitting diodes. The transmittance of hybrid thin film encapsulation layers and the electroluminescent spectrum of organic light-emitting diodes that were passivated by hybrid organic/inorganic thin film encapsulation layers were also examined as a function of the thickness of inorganic Al203 and monomer layers. The number of interference peaks, their intensity, and their positions in the visible range can be controlled by varying the thickness of inorganic Al2O3 layer. On the other hand, changing the thickness of monomer layer had a negligible effect on the optical properties. We also verified that there is a trade-off between transparency in the visible range and the permeation of water vapor in hybrid thin film encapsulation layers. As the number of dyads decreased, optical transparency improved while the water vapor permeation barrier was degraded. Our study suggests that, in top-emission organic light-emitting diodes, the thickness of each thin film encapsulation layer, in particular that of the inorganic layer, and the number of dyads should be controlled for highly efficient top-emission flexible organic light-emitting diodes.

A promising red-emitting phosphor for white-light-emitting diodes prepared by a modified solid-state reaction

NASA Astrophysics Data System (ADS)

Ren, Fuqiang; Chen, Donghua

2010-02-01

Using urea, boric acid and polyethylene glycol (PEG) as auxiliary reagents, the novel red-emitting phosphors Ca 19Zn 2 (PO 4) 14:Eu 3+ have been successfully synthesized by a modified solid-state reaction. Thermogravimetric (TG) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectra were used to characterize the resulting phosphors. The dependence of the photoluminescence properties of Ca 19Zn 2 (PO 4) 14:Eu 3+ phosphors upon urea, boric acid and PEG concentration and the quadric-sintered temperature were investigated. Luminescent measurements showed that the phosphors can be efficiently excited by ultraviolet (UV) to visible region, emitting a red light with a peak wavelength of 616 nm. The material has potential application as a fluorescent material for ultraviolet light-emitting diodes (UV-LEDs).

Flexible bottom-emitting white organic light-emitting diodes with semitransparent Ni/Ag/Ni anode.

PubMed

Koo, Ja-Ryong; Lee, Seok Jae; Lee, Ho Won; Lee, Dong Hyung; Yang, Hyung Jin; Kim, Woo Young; Kim, Young Kwan

2013-05-06

We fabricated a flexible bottom-emitting white organic light-emitting diode (BEWOLED) with a structure of PET/Ni/Ag/Ni (3/6/3 nm)/ NPB (50 nm)/mCP (10 nm)/7% FIrpic:mCP (10 nm)/3% Ir(pq)(2) acac:TPBi (5 nm)/7% FIrpic:TPBi (5 nm)/TPBi (10 nm)/Liq (2 nm)/ Al (100 nm). To improve the performance of the BEWOLED, a multilayered metal stack anode of Ni/Ag/Ni treated with oxygen plasma for 60 sec was introduced into the OLED devices. The Ni/Ag/Ni anode effectively enhanced the probability of hole-electron recombination due to an efficient hole injection into and charge balance in an emitting layer. By comparing with a reference WOLED using ITO on glass, it is verified that the flexible BEWOLED showed a similar or better electroluminescence (EL) performance.

A white organic light emitting diode based on anthracene-triphenylamine derivatives

NASA Astrophysics Data System (ADS)

Jiang, Quan; Qu, Jianjun; Yu, Junsheng; Tao, Silu; Gan, Yuanyuan; Jiang, Yadong

2010-10-01

White organic lighting-diode (WOLED) can be used as flat light sources, backlights for liquid crystal displays and full color displays. Recently, a research mainstream of white OLED is to develop the novel materials and optimize the structure of devices. In this work a WOLED with a structure of ITO/NPB/PAA/Alq3: x% rubrene/Alq3/Mg: Ag, was fabricated. The device has two light-emitting layers. NPB is used as a hole transport layer, PAA as a blue emitting layer, Alq3: rubrene host-guest system as a yellow emitting layer, and Alq3 close to the cathode as an electron transport layer. In the experiment, the doping concentration of rubrene was optimized. WOLED 1 with 4% rubrene achieved a maximum luminous efficiency of 1.80 lm/W, a maximum luminance of 3926 cd/m2 and CIE coordinates of (0.374, 0.341) .WOLED 2 with 2% rubrene achieved a maximum luminous efficiency of 0.65 lm/W, a maximum luminance of 7495cd/m2 and CIE coordinates of (0.365,0.365).

Fabrication of white light-emitting diodes based on UV light-emitting diodes with conjugated polymers-(CdSe/ZnS) quantum dots as hybrid phosphors.

PubMed

Jung, Hyunchul; Chung, Wonkeun; Lee, Chang Hun; Kim, Sung Hyun

2012-07-01

White light-emitting diodes (LEDs) were fabricated using GaN-based 380-nm UV LEDs precoated with the composite of blue-emitting polymer (poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(2-methoxy-5-{2-ethylhexyloxy)-1 ,4-phenylene)]), yellow green-emitting polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)]), and 605-nm red-emitting quantum dots (QDs). CdSe cores were obtained by solvothermal route using CdO, Se precursors and ZnS shells were synthesized by using diethylzinc, and hexamethyldisilathiane precursors. The optical properties of CdSe/ZnS QDs were characterized by UV-visible and photoluminescence (PL) spectra. The structural data and composition of the QDs were transmission electron microscopy (TEM), and EDX technique. The quantum yield and size of the QDs were 58.7% and about 6.7 nm, respectively. Three-band white light was generated by hybridizing blue (430 nm), green (535 nm), and red (605 nm) emission. The color-rendering index (CRI) of the device was extremely improved by introducing the QDs. The CIE-1931 chromaticity coordinate, color temperature, and CRI of a white LED at 20 mA were (0.379, 0.368), 3969 K, and 90, respectively.

Accuracy Improvement for Light-Emitting-Diode-Based Colorimeter by Iterative Algorithm

NASA Astrophysics Data System (ADS)

Yang, Pao-Keng

2011-09-01

We present a simple algorithm, combining an interpolating method with an iterative calculation, to enhance the resolution of spectral reflectance by removing the spectral broadening effect due to the finite bandwidth of the light-emitting diode (LED) from it. The proposed algorithm can be used to improve the accuracy of a reflective colorimeter using multicolor LEDs as probing light sources and is also applicable to the case when the probing LEDs have different bandwidths in different spectral ranges, to which the powerful deconvolution method cannot be applied.

Ultraviolet light-emitting diodes in water disinfection.

PubMed

Vilhunen, Sari; Särkkä, Heikki; Sillanpää, Mika

2009-06-01

The novel system of ultraviolet light-emitting diodes (UV LEDs) was studied in water disinfection. Conventional UV lamps, like mercury vapor lamp, consume much energy and are considered to be problem waste after use. UV LEDs are energy efficient and free of toxicants. This study showed the suitability of LEDs in disinfection and provided information of the effect of two emitted wavelengths and different test mediums to Escherichia coli destruction. Common laboratory strain of E. coli (K12) was used and the effects of two emitted wavelengths (269 and 276 nm) were investigated with two photolytic batch reactors both including ten LEDs. The effects of test medium were examined with ultrapure water, nutrient and water, and nutrient and water with humic acids. Efficiency of reactors was almost the same even though the one emitting higher wavelength had doubled optical power compared to the other. Therefore, the effect of wavelength was evident and the radiation emitted at 269 nm was more powerful. Also, the impact of background was studied and noticed to have only slight deteriorating effect. In the 5-min experiment, the bacterial reduction of three to four log colony-forming units (CFU) per cubic centimeter was achieved, in all cases. When turbidity of the test medium was greater, part of the UV radiation was spent on the absorption and reactions with extra substances on liquid. Humic acids can also coat the bacteria reducing the sensitivity of the cells to UV light. The lower wavelength was distinctly more efficient when the optical power is considered, even though the difference of wavelengths was small. The reason presumably is the greater absorption of DNA causing more efficient bacterial breakage. UV LEDs were efficient in E. coli destruction, even if LEDs were considered to have rather low optical power. The effect of wavelengths was noticeable but the test medium did not have much impact. This study found UV LEDs to be an optimal method for bacterial

Optimization of light quality from color mixing light-emitting diode systems for general lighting

NASA Astrophysics Data System (ADS)

Thorseth, Anders

2012-03-01

Given the problem of metamerisms inherent in color mixing in light-emitting diode (LED) systems with more than three distinct colors, a method for optimizing the spectral output of multicolor LED system with regards to standardized light quality parameters has been developed. The composite spectral power distribution from the LEDs are simulated using spectral radiometric measurements of single commercially available LEDs for varying input power, to account for the efficiency droop and other non-linear effects in electrical power vs. light output. The method uses electrical input powers as input parameters in a randomized steepest decent optimization. The resulting spectral power distributions are evaluated with regard to the light quality using the standard characteristics: CIE color rendering index, correlated color temperature and chromaticity distance. The results indicate Pareto optimal boundaries for each system, mapping the capabilities of the simulated lighting systems with regard to the light quality characteristics.

High-quality GaN epitaxially grown on Si substrate with serpentine channels

NASA Astrophysics Data System (ADS)

Wei, Tiantian; Zong, Hua; Jiang, Shengxiang; Yang, Yue; Liao, Hui; Xie, Yahong; Wang, Wenjie; Li, Junze; Tang, Jun; Hu, Xiaodong

2018-06-01

A novel serpentine-channeled mask was introduced to Si substrate for low-dislocation GaN epitaxial growth and the fully coalesced GaN film on the masked Si substrate was achieved for the first time. Compared with the epitaxial lateral overgrowth (ELOG) growth method, this innovative mask only requires one-step epitaxial growth of GaN which has only one high-dislocation region per mask opening. This new growth method can effectively reduce dislocation density, thus improving the quality of GaN significantly. High-quality GaN with low dislocation density ∼2.4 × 107 cm-2 was obtained, which accounted for about eighty percent of the GaN film in area. This innovative technique is promising for the growth of high-quality GaN templates and the subsequent fabrication of high-performance GaN-based devices like transistors, laser diodes (LDs), and light-emitting diodes (LEDs) on Si substrate.

Low Level Light Therapy with Light-Emitting Diodes for the Aging Face.

PubMed

Calderhead, R Glen; Vasily, David B

2016-07-01

Low level light therapy (LLLT) with light-emitting diodes (LEDs) is emerging from the mists of black magic as a solid medico-scientific modality, with a substantial buildup of corroborative bodies of evidence for its efficacy and elucidation of the modes of action. Reports are appearing from many different specialties; however, of particular interest to plastic surgeons treating the aging face is the proven action of LED-LLLT on skin cells in both the epidermis and dermis and enhanced blood flow. Thus, LED-LLLT is a safe and effective stand-alone therapy for patients who are prepared to wait until the final effect is perceived. Copyright © 2016 Elsevier Inc. All rights reserved.

Effect of arylamine hole-transport units on the performance of blue polyspirobifulorene light-emitting diodes

NASA Astrophysics Data System (ADS)

Abbaszadeh, Davood; Nicolai, Herman T.; Crǎciun, N. Irina; Blom, Paul W. M.

2014-11-01

The operation of blue light-emitting diodes based on polyspirobifluorene with a varying number of N ,N ,N',N' tetraaryldiamino biphenyl (TAD) hole-transport units (HTUs) is investigated. Assuming that the electron transport is not affected by the incorporation of TAD units, model calculations predict that a concentration of 5% HTU leads to an optimal efficiency for this blue-emitting polymer. However, experimentally an optimum performance is achieved for 10% TAD HTUs. Analysis of the transport and recombination shows that polymer light-emitting diodes with 5%, 7.5%, and 12.5% TAD units follow the predicted behavior. The enhanced performance of the polymer with 10% TAD originates from a decrease in the number of electron traps, which is typically a factor of three lower than the universal value found in many polymers. This reduced number of traps leads to a reduction of nonradiative recombination and exciton quenching at the cathode.

Light-emitting diode street lights reduce last-ditch evasive manoeuvres by moths to bat echolocation calls

PubMed Central

Wakefield, Andrew; Stone, Emma L.; Jones, Gareth; Harris, Stephen

2015-01-01

The light-emitting diode (LED) street light market is expanding globally, and it is important to understand how LED lights affect wildlife populations. We compared evasive flight responses of moths to bat echolocation calls experimentally under LED-lit and -unlit conditions. Significantly, fewer moths performed ‘powerdive’ flight manoeuvres in response to bat calls (feeding buzz sequences from Nyctalus spp.) under an LED street light than in the dark. LED street lights reduce the anti-predator behaviour of moths, shifting the balance in favour of their predators, aerial hawking bats. PMID:26361558

Monolithically Integrated Metal/Semiconductor Tunnel Junction Nanowire Light-Emitting Diodes.

PubMed

Sadaf, S M; Ra, Y H; Szkopek, T; Mi, Z

2016-02-10

We have demonstrated for the first time an n(++)-GaN/Al/p(++)-GaN backward diode, wherein an epitaxial Al layer serves as the tunnel junction. The resulting p-contact free InGaN/GaN nanowire light-emitting diodes (LEDs) exhibited a low turn-on voltage (∼2.9 V), reduced resistance, and enhanced power, compared to nanowire LEDs without the use of Al tunnel junction or with the incorporation of an n(++)-GaN/p(++)-GaN tunnel junction. This unique Al tunnel junction overcomes some of the critical issues related to conventional GaN-based tunnel junction designs, including stress relaxation, wide depletion region, and light absorption, and holds tremendous promise for realizing low-resistivity, high-brightness III-nitride nanowire LEDs in the visible and deep ultraviolet spectral range. Moreover, the demonstration of monolithic integration of metal and semiconductor nanowire heterojunctions provides a seamless platform for realizing a broad range of multifunctional nanoscale electronic and photonic devices.

Doping concentration effect on performance of single QW double-heterostructure InGaN/AlGaN light emitting diode

NASA Astrophysics Data System (ADS)

Halim, N. Syafira Abdul; Wahid, M. Halim A.; Hambali, N. Azura M. Ahmad; Rashid, Shanise; Shahimin, Mukhzeer M.

2017-11-01

Light emitting diode (LED) employed a numerous applications such as displaying information, communication, sensing, illumination and lighting. In this paper, InGaN/AlGaN based on one quantum well (1QW) light emitting diode (LED) is modeled and studied numerically by using COMSOL Multiphysics 5.1 version. We have selected In0.06Ga0.94N as the active layer with thickness 50nm sandwiched between 0.15μm thick layers of p and n-type Al0.15Ga0.85N of cladding layers. We investigated an effect of doping concentration on InGaN/AlGaN double heterostructure of light-emitting diode (LED). Thus, energy levels, carrier concentration, electron concentration and forward voltage (IV) are extracted from the simulation results. As the doping concentration is increasing, the performance of threshold voltage, Vth on one quantum well (1QW) is also increases from 2.8V to 3.1V.

Efficient Light Extraction from Organic Light-Emitting Diodes Using Plasmonic Scattering Layers

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

Rothberg, Lewis

2012-11-30

Our project addressed the DOE MYPP 2020 goal to improve light extraction from organic light-emitting diodes (OLEDs) to 75% (Core task 6.3). As noted in the 2010 MYPP, “the greatest opportunity for improvement is in the extraction of light from [OLED] panels”. There are many approaches to avoiding waveguiding limitations intrinsic to the planar OLED structure including use of textured substrates, microcavity designs and incorporating scattering layers into the device structure. We have chosen to pursue scattering layers since it addresses the largest source of loss which is waveguiding in the OLED itself. Scattering layers also have the potential tomore » be relatively robust to color, polarization and angular distributions. We note that this can be combined with textured or microlens decorated substrates to achieve additional enhancement.« less

Engineering future light emitting diodes and photovoltaics with inexpensive materials: Integrating ZnO and Si into GaN-based devices

NASA Astrophysics Data System (ADS)

Bayram, C.; Shiu, K. T.; Zhu, Y.; Cheng, C. W.; Sadana, D. K.; Teherani, F. H.; Rogers, D. J.; Sandana, V. E.; Bove, P.; Zhang, Y.; Gautier, S.; Cho, C.-Y.; Cicek, E.; Vashaei, Z.; McClintock, R.; Razeghi, M.

2013-03-01

Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our

Best practices : bus signage for persons with visual impairments : light-emitting diode (LED) signs

DOT National Transportation Integrated Search

2004-01-01

This best-practices report provides key information regarding the use of Light-Emitting Diode (LED) sign technologies to present destination and route information on transit vehicles. It will assist managers and engineers in the acquisition and use o...

Highly-efficient GaN-based light-emitting diode wafers on La0.3Sr1.7AlTaO6 substrates

PubMed Central

Wang, Wenliang; Yang, Weijia; Gao, Fangliang; Lin, Yunhao; Li, Guoqiang

2015-01-01

Highly-efficient GaN-based light-emitting diode (LED) wafers have been grown on La0.3Sr1.7AlTaO6 (LSAT) substrates by radio-frequency molecular beam epitaxy (RF-MBE) with optimized growth conditions. The structural properties, surface morphologies, and optoelectronic properties of as-prepared GaN-based LED wafers on LSAT substrates have been characterized in detail. The characterizations have revealed that the full-width at half-maximums (FWHMs) for X-ray rocking curves of GaN(0002) and GaN(10-12) are 190.1 and 210.2 arcsec, respectively, indicating that high crystalline quality GaN films have been obtained. The scanning electron microscopy and atomic force microscopy measurements have shown the very smooth p-GaN surface with the surface root-mean-square (RMS) roughness of 1.3 nm. The measurements of low-temperature and room-temperature photoluminescence help to calculate the internal quantum efficiency of 79.0%. The as-grown GaN-based LED wafers have been made into LED chips with the size of 300 × 300 μm2 by the standard process. The forward voltage, the light output power and the external quantum efficiency for LED chips are 19.6 W, 2.78 V, and 40.2%, respectively, at a current of 20 mA. These results reveal the high optoelectronic properties of GaN-based LEDs on LSAT substrates. This work brings up a broad future application of GaN-based devices. PMID:25799042

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

Quantum key distribution with an entangled light emitting diode

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

Dzurnak, B.; Stevenson, R. M.; Nilsson, J.

Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurementsmore » also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.« less

Colored lenses suppress blue light-emitting diode light-induced damage in photoreceptor-derived cells.

PubMed

Hiromoto, Kaho; Kuse, Yoshiki; Tsuruma, Kazuhiro; Tadokoro, Nobuyuki; Kaneko, Nobuyuki; Shimazawa, Masamitsu; Hara, Hideaki

2016-03-01

Blue light-emitting diodes (LEDs) in liquid crystal displays emit high levels of blue light, exposure to which is harmful to the retina. Here, we investigated the protective effects of colored lenses in blue LED light-induced damage to 661W photoreceptor-derived cells. We used eight kinds of colored lenses and one lens that reflects blue light. Moreover, we evaluated the relationship between the protective effects of the lens and the transmittance of lens at 464 nm. Lenses of six colors, except for the SY, PN, and reflective coating lenses, strongly decreased the reduction in cell damage induced by blue LED light exposure. The deep yellow lens showed the most protective effect from all the lenses, but the reflective coating lens and pink lens did not show any effects on photoreceptor-derived cell damage. Moreover, these results were correlated with the lens transmittance of blue LED light (464 nm). These results suggest that lenses of various colors, especially deep yellow lenses, may protect retinal photoreceptor cells from blue LED light in proportion to the transmittance for the wavelength of blue LED and the suppression of reactive oxygen species production and cell damage.

Embeded photonic crystal at the interface of p-GaN and Ag reflector to improve light extraction of GaN-based flip-chip light-emitting diode

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

Zhen, Aigong; Ma, Ping, E-mail: maping@semi.ac.cn; Zhang, Yonghui

2014-12-22

In this experiment, a flip-chip light-emitting diode with photonic crystal was fabricated at the interface of p-GaN and Ag reflector via nanospheres lithography technique. In this structure, photonic crystal could couple with the guide-light efficiently by reason of the little distance between photonic crystal and active region. The light output power of light emitting diode with embedded photonic crystal was 1.42 times larger than that of planar flip-chip light-emitting diode. Moreover, the embedded photonic crystal structure makes the far-field divergence angle decreased by 18° without spectra shift. The three-dimensional finite difference time domain simulation results show that photonic crystal couldmore » improve the light extraction, and enhance the light absorption caused by Ag reflector simultaneously, because of the roughed surface. The depth of photonic crystal is the key parameter affecting the light extraction and absorption. Light extraction efficiency increases with the depth photonic crystal structure rapidly, and reaches the maximum at the depth 80 nm, beyond which light extraction decrease drastically.« less

Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices

PubMed Central

O'Toole, Martina; Diamond, Dermot

2008-01-01

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements. PMID:27879829

Topical methyl-aminolevulinate photodynamic therapy using red light-emitting diode light for treatment of multiple actinic keratoses: A randomized, double-blind, placebo-controlled study.

PubMed

Pariser, David; Loss, Robert; Jarratt, Michael; Abramovits, William; Spencer, James; Geronemus, Roy; Bailin, Philip; Bruce, Suzanne

2008-10-01

The use of light-emitting diode light offers practical advantages in photodynamic therapy (PDT) with topical methyl-aminolevulinate (MAL) for management of actinic keratoses (AK). We sought to evaluate the efficacy of MAL PDT using red light-emitting diode light. We conducted a multicenter, double-blind, randomized study. A total of 49 patients with 363 AK lesions had 16.8% MAL cream applied under occlusion for 3 hours, and 47 patients with 360 AK lesions had vehicle cream similarly applied. The lesions were then illuminated (630 nm, light dose 37 J/cm2) with repeated treatment 1 week later. Complete lesion and patient (all lesions showing complete response) response rates were evaluated 3 months after last treatment. MAL PDT was superior (P<.0001) to vehicle PDT with respect to lesion complete response (86.2% vs 52.2%, odds ratio 6.9 [95% confidence interval 4.7-10.3]) and patient complete response (59.2% vs 14.9%, odds ratio 13.2 [95% confidence interval 4.1-43.1]). The study population may not be representative of all patients with AK. MAL PDT using red light-emitting diode light is an appropriate treatment alternative for multiple AK lesions.

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

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

Flexible inorganic light emitting diodes based on semiconductor nanowires

PubMed Central

Guan, Nan; Dai, Xing; Babichev, Andrey V.; Julien, François H.

2017-01-01

The fabrication technologies and the performance of flexible nanowire light emitting diodes (LEDs) are reviewed. We first introduce the existing approaches for flexible LED fabrication, which are dominated by organic technologies, and we briefly discuss the increasing research effort on flexible inorganic LEDs achieved by micro-structuring and transfer of conventional thin films. Then, flexible nanowire-based LEDs are presented and two main fabrication technologies are discussed: direct growth on a flexible substrate and nanowire membrane formation and transfer. The performance of blue, green, white and bi-color flexible LEDs fabricated following the transfer approach is discussed in more detail. PMID:29568439

Recycled Thermal Energy from High Power Light Emitting Diode Light Source.

PubMed

Ji, Jae-Hoon; Jo, GaeHun; Ha, Jae-Geun; Koo, Sang-Mo; Kamiko, Masao; Hong, JunHee; Koh, Jung-Hyuk

2018-09-01

In this research, the recycled electrical energy from wasted thermal energy in high power Light Emitting Diode (LED) system will be investigated. The luminous efficiency of lights has been improved in recent years by employing the high power LED system, therefore energy efficiency was improved compared with that of typical lighting sources. To increase energy efficiency of high power LED system further, wasted thermal energy should be re-considered. Therefore, wasted thermal energy was collected and re-used them as electrical energy. The increased electrical efficiency of high power LED devices was accomplished by considering the recycled heat energy, which is wasted thermal energy from the LED. In this work, increased electrical efficiency will be considered and investigated by employing the high power LED system, which has high thermal loss during the operating time. For this research, well designed thermoelement with heat radiation system was employed to enhance the collecting thermal energy from the LED system, and then convert it as recycled electrical energy.

Hole trap formation in polymer light-emitting diodes under current stress

NASA Astrophysics Data System (ADS)

Niu, Quan; Rohloff, Roland; Wetzelaer, Gert-Jan A. H.; Blom, Paul W. M.; Crǎciun, N. Irina

2018-06-01

Polymer light-emitting diodes (PLEDs) are attractive for use in large-area displays and lighting panels, but their limited stability under current stress impedes commercialization. In spite of large efforts over the last two decades a fundamental understanding of the degradation mechanisms has not been accomplished. Here we demonstrate that the voltage drift of a PLED driven at constant current is caused by the formation of hole traps, which leads to additional non-radiative recombination between free electrons and trapped holes. The observed trap formation rate is consistent with exciton-free hole interactions as the main mechanism behind PLED degradation, enabling us to unify the degradation behaviour of various poly(p-phenylene) derivatives. The knowledge that hole trap formation is the cause of PLED degradation means that we can suppress the negative effect of hole traps on voltage and efficiency by blending the light-emitting polymer with a large-bandgap semiconductor. Owing to trap-dilution these blended PLEDs show unprecedented stability.

A lamp light-emitting diode-induced fluorescence detector for capillary electrophoresis.

PubMed

Xu, Jing; Xiong, Yan; Chen, Shiheng; Guan, Yafeng

2008-07-15

A light-emitting diode-induced fluorescence detector (LED-FD) for capillary electrophoresis was constructed and evaluated. A lamp LED with an enhanced emission spectrum and a band pass filter was used as the excitation light source. Refractive index matching fluid (RIMF) was used in the detection cell to reduce scattering light and the noise level. The limit of detection (LOD) for fluorescein was 1.5 nM (SNR=3). The system exhibited linear responses in the range of 1 x 10(-8) to 5 x 10(-6)M (R=0.999). Application of the lamp LED-FD for the analysis of FITC-labeled ephedra herb extract by capillary electrophoresis was demonstrated.

Ultra High p-doping Material Research for GaN Based Light Emitters

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

Vladimir Dmitriev

2007-06-30

The main goal of the Project is to investigate doping mechanisms in p-type GaN and AlGaN and controllably fabricate ultra high doped p-GaN materials and epitaxial structures. Highly doped p-type GaN-based materials with low electrical resistivity and abrupt doping profiles are of great importance for efficient light emitters for solid state lighting (SSL) applications. Cost-effective hydride vapor phase epitaxial (HVPE) technology was proposed to investigate and develop p-GaN materials for SSL. High p-type doping is required to improve (i) carrier injection efficiency in light emitting p-n junctions that will result in increasing of light emitting efficiency, (ii) current spreading inmore » light emitting structures that will improve external quantum efficiency, and (iii) parameters of Ohmic contacts to reduce operating voltage and tolerate higher forward currents needed for the high output power operation of light emitters. Highly doped p-type GaN layers and AlGaN/GaN heterostructures with low electrical resistivity will lead to novel device and contact metallization designs for high-power high efficiency GaN-based light emitters. Overall, highly doped p-GaN is a key element to develop light emitting devices for the DOE SSL program. The project was focused on material research for highly doped p-type GaN materials and device structures for applications in high performance light emitters for general illumination P-GaN and p-AlGaN layers and multi-layer structures were grown by HVPE and investigated in terms of surface morphology and structure, doping concentrations and profiles, optical, electrical, and structural properties. Tasks of the project were successfully accomplished. Highly doped GaN materials with p-type conductivity were fabricated. As-grown GaN layers had concentration N{sub a}-N{sub d} as high as 3 x 10{sup 19} cm{sup -3}. Mechanisms of doping were investigated and results of material studies were reported at several International conferences

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.

Applications of Light Emitting Diodes in Health Care.

PubMed

Dong, Jianfei; Xiong, Daxi

2017-11-01

Light emitting diodes (LEDs) have become the main light sources for general lighting, due to their high lumen efficiency and long life time. Moreover, their high bandwidth and the availability of diverse wavelength contents ranging from ultraviolet to infrared empower them with great controllability in tuning brightness, pulse durations and spectra. These parameters are the essential ingredients of the applications in medical imaging and therapies. Despite the fast advances in both LED technologies and their applications, few reviews have been seen to link the controllable emission properties of LEDs to these applications. The objective of this paper is to bridge this gap by reviewing the main control techniques of LEDs that enable creating enhanced lighting patterns for imaging and generating effective photon doses for photobiomodulation. This paper also provides the basic mechanisms behind the effective LED therapies in treating cutaneous and neurological diseases. The emerging field of optogenetics is also discussed with a focus on the application of LEDs. The multidisciplinary topics reviewed in this paper can help the researchers in LEDs, imaging, light therapy and optogenetics better understand the basic principles in each other's field; and hence to stimulate the application of LEDs in health care.

Hand-Drawn Resistors and a Simple Tester Using a Light-Emitting Diode

ERIC Educational Resources Information Center

Kamata, Masahiro; Abe, Mayumi

2012-01-01

A thick line drawn on a sheet of paper with a 6B pencil is electrically conductive and its resistance can be roughly estimated using a simple tester made of a light-emitting diode (LED) and a lithium coin-type cell. Using this hand-drawn resistor and the LED tester, we developed teaching materials that help students to understand how electrical…

GaN-based photon-recycling green light-emitting diodes with vertical-conduction structure.

PubMed

Sheu, Jinn-Kong; Chen, Fu-Bang; Yen, Wei-Yu; Wang, Yen-Chin; Liu, Chun-Nan; Yeh, Yu-Hsiang; Lee, Ming-Lun

2015-04-06

A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stacked on a green unipolar InGaN/GaN MQW was epitaxially grown at the same sapphire substrate. Photon recycling green light-emitting diodes(LEDs) with vertical-conduction feature on silicon substrates were then fabricated by wafer bonding and laser lift-off techniques. The green InGaN/GaN QWs were pumped with n-UV light to reemit low-energy photons when the LEDs were electrically driven with a forward current. Efficiency droop is potentially insignificant compared with the direct green LEDs due to the increase of effective volume of active layer in the optically pumped green LEDs, i.e., light emitting no longer limited in the QWs nearest to the p-type region to cause severe Auger recombination and carrier overflow losses.

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.

Investigation of Light-Emitting Diode (LED) Point Light Source Color Visibility against Complex Multicolored Backgrounds

DTIC Science & Technology

2017-11-01

sent from light-emitting diodes (LEDs) of 5 colors ( green , red, white, amber, and blue). Experiment 1 involved controlled laboratory measurements of...A-4 Red LED calibration curves and quadratic curve fits with R2 values . 37 Fig. A-5 Green LED calibration curves and quadratic curve fits with R2...36 Table A-4 Red LED calibration measurements ................................................... 36 Table A-5 Green LED

Arbitrary helicity control of circularly polarized light from lateral-type spin-polarized light-emitting diodes at room temperature

NASA Astrophysics Data System (ADS)

Nishizawa, Nozomi; Aoyama, Masaki; Roca, Ronel C.; Nishibayashi, Kazuhiro; Munekata, Hiro

2018-05-01

We demonstrate arbitrary helicity control of circularly polarized light (CPL) emitted at room temperature from the cleaved side facet of a lateral-type spin-polarized light-emitting diode (spin-LED) with two ferromagnetic electrodes in an antiparallel magnetization configuration. Driving alternate currents through the two electrodes results in polarization switching of CPL with frequencies up to 100 kHz. Furthermore, tuning the current density ratio in the two electrodes enables manipulation of the degree of circular polarization. These results demonstrate arbitrary electrical control of polarization with high speed, which is required for the practical use of lateral-type spin-LEDs as monolithic CPL light sources.

Fish scale terrace GaInN/GaN light-emitting diodes with enhanced light extraction

NASA Astrophysics Data System (ADS)

Stark, Christoph J. M.; Detchprohm, Theeradetch; Zhao, Liang; Paskova, Tanya; Preble, Edward A.; Wetzel, Christian

2012-12-01

Non-planar GaInN/GaN light-emitting diodes were epitaxially grown to exhibit steps for enhanced light emission. By means of a large off-cut of the epitaxial growth plane from the c-plane (0.06° to 2.24°), surface morphologies of steps and inclined terraces that resemble fish scale patterns could controllably be achieved. These patterns penetrate the active region without deteriorating the electrical device performance. We find conditions leading to a large increase in light-output power over the virtually on-axis device and over planar sapphire references. The process is found suitable to enhance light extraction even without post-growth processing.

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

White emission from non-planar InGaN/GaN MQW LEDs grown on GaN template with truncated hexagonal pyramids.

PubMed

Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Lai, Wei-Chih; Sheu, Jinn-Kong

2015-04-06

Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering.

PubMed

Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Murali, Banavoth; Sarmah, Smritakshi P; Yuan, Mingjian; Sinatra, Lutfan; Alyami, Noktan M; Liu, Jiakai; Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Comin, Riccardo; Hedhili, Mohamed N; Mohammed, Omar F; Lu, Zheng Hong; Kim, Dong Ha; Sargent, Edward H; Bakr, Osman M

2016-10-01

A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX 3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A new light emitting diode-light emitting diode portable carbon dioxide gas sensor based on an interchangeable membrane system for industrial applications.

PubMed

de Vargas-Sansalvador, I M Pérez; Fay, C; Phelan, T; Fernández-Ramos, M D; Capitán-Vallvey, L F; Diamond, D; Benito-Lopez, F

2011-08-12

A new system for CO(2) measurement (0-100%) based on a paired emitter-detector diode arrangement as a colorimetric detection system is described. Two different configurations were tested: configuration 1 (an opposite side configuration) where a secondary inner-filter effect accounts for CO(2) sensitivity. This configuration involves the absorption of the phosphorescence emitted from a CO(2)-insensitive luminophore by an acid-base indicator and configuration 2 wherein the membrane containing the luminophore is removed, simplifying the sensing membrane that now only contains the acid-base indicator. In addition, two different instrumental configurations have been studied, using a paired emitter-detector diode system, consisting of two LEDs wherein one is used as the light source (emitter) and the other is used in reverse bias mode as the light detector. The first configuration uses a green LED as emitter and a red LED as detector, whereas in the second case two identical red LEDs are used as emitter and detector. The system was characterised in terms of sensitivity, dynamic response, reproducibility, stability and temperature influence. We found that configuration 2 presented a better CO(2) response in terms of sensitivity. Copyright © 2011 Elsevier B.V. All rights reserved.

The use of ionic salt dyes as amorphous, thermally stable emitting layers in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Chondroudis, Konstantinos; Mitzi, David B.

2000-01-01

The conversion of two neutral dye molecules (D) to ionic salts (H2N-D-NH2ṡ2HX) and their utilization as emitting layers in organic light-emitting diodes (OLEDs) is described. The dye salts, AEQTṡ2HCl and APTṡ2HCl, can be deposited as amorphous films using conventional evaporation techniques. X-ray diffraction and scanning electron microscopy analysis, coupled with thermal annealing studies, demonstrate the resistance of the films to crystallization. This stability is attributed to strong ionic forces between the relatively rigid molecules. OLEDs incorporating such salts for emitting layers exhibit better thermal stability compared with devices made from the corresponding neutral dyes (H2N-D-NH2). These results suggest that ionic salts may more generally enable the formation of thermally stable, amorphous emitting, and charge transporting layers.

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.

Heterojunction light emitting diodes fabricated with different n-layer oxide structures on p-GaN layers by magnetron sputtering

NASA Astrophysics Data System (ADS)

Kong, Bo Hyun; Han, Won Suk; Kim, Young Yi; Cho, Hyung Koun; Kim, Jae Hyun

2010-06-01

We grew heterojunction light emitting diode (LED) structures with various n-type semiconducting layers by magnetron sputtering on p-type GaN at high temperature. Because the undoped ZnO used as an active layer was grown under oxygen rich atmosphere, all LED devices showed the EL characteristics corresponding to orange-red wavelength due to high density of oxygen interstitial, which was coincident with the deep level photoluminescence emission of undoped ZnO. The use of the Ga doped layers as a top layer provided the sufficient electron carriers to active region and resulted in the intense EL emission. The LED sample with small quantity of Mg incorporated in MgZnO as an n-type top layer showed more intense emission than the LED with ZnO, in spite of the deteriorated electrical and structural properties of the MgZnO film. This might be due to the improvement of output extraction efficiency induced by rough surface.

Laser-induced periodic structures for light extraction efficiency enhancement of GaN-based light emitting diodes.

PubMed

Chen, Jiun-Ting; Lai, Wei-Chih; Kao, Yu-Jui; Yang, Ya-Yu; Sheu, Jinn-Kong

2012-02-27

The laser-induced periodic surface structure technique was used to form simultaneously dual-scale rough structures (DSRS) with spiral-shaped nanoscale structure inside semi-spherical microscale holes on p-GaN surface to improve the light-extraction efficiency of light-emitting diodes (LEDs). The light output power of DSRS-LEDs was 30% higher than that of conventional LEDs at an injection current of 20 mA. The enhancement in the light output power could be attributed to the increase in the probability of photons to escape from the increased surface area of textured p-GaN surface.

High-Efficiency All-Solution-Processed Light-Emitting Diodes Based on Anisotropic Colloidal Heterostructures with Polar Polymer Injecting Layers.

PubMed

Castelli, Andrea; Meinardi, Francesco; Pasini, Mariacecilia; Galeotti, Francesco; Pinchetti, Valerio; Lorenzon, Monica; Manna, Liberato; Moreels, Iwan; Giovanella, Umberto; Brovelli, Sergio

2015-08-12

Colloidal quantum dots (QDs) are emerging as true candidates for light-emitting diodes with ultrasaturated colors. Here, we combine CdSe/CdS dot-in-rod heterostructures and polar/polyelectrolytic conjugated polymers to demonstrate the first example of fully solution-based quantum dot light-emitting diodes (QD-LEDs) incorporating all-organic injection/transport layers with high brightness, very limited roll-off and external quantum efficiency as high as 6.1%, which is 20 times higher than the record QD-LEDs with all-solution-processed organic interlayers and exceeds by over 200% QD-LEDs embedding vacuum-deposited organic molecules.

Room temperature polariton light emitting diode with integrated tunnel junction.

PubMed

Brodbeck, S; Jahn, J-P; Rahimi-Iman, A; Fischer, J; Amthor, M; Reitzenstein, S; Kamp, M; Schneider, C; Höfling, S

2013-12-16

We present a diode incorporating a large number (12) of GaAs quantum wells that emits light from exciton-polariton states at room temperature. A reversely biased tunnel junction is placed in the cavity region to improve current injection into the device. Electroluminescence studies reveal two polariton branches which are spectrally separated by a Rabi splitting of 6.5 meV. We observe an anticrossing of the two branches when the temperature is lowered below room temperature as well as a Stark shift of both branches in a bias dependent photoluminescence measurement.

Effect of Stepwise Doping on Lifetime and Efficiency of Blue and White Phosphorescent Organic Light Emitting Diodes.

PubMed

Lee, Song Eun; Lee, Ho Won; Lee, Seok Jae; Koo, Ja-ryong; Lee, Dong Hyung; Yang, Hyung Jin; Kim, Hye Jeong; Yoon, Seung Soo; Kim, Young Kwan

2015-02-01

We investigated a light emission mechanism of blue phosphorescent organic light emitting diodes (PHOLEDs), using a stepwise doping profile of 2, 8, and 14 wt.% within the emitting layer (EML). We fabricated several blue PHOLEDs with phosphorescent blue emitter iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2]picolinate doped in N,N'-dicarbazolyl-3,5-benzene as a p-type host material. A blue PHOLED with the highest doping concentration as part of the EML close to an electron transporting layer showed a maximum luminous efficiency of 20.74 cd/A, and a maximum external quantum efficiency of 10.52%. This can be explained by effective electron injection through a highly doped EML side. Additionally, a white OLED based on the doping profile was fabricated with two thin red EMLs within a blue EML maintaining a thickness of 30 nm for the entire EML. Keywords: Blue Phosphorescent Organic Light Emitting Diodes, Stepwise Doping Structure, Charge Trapping Effect.

Light-emitting diode-based multiwavelength diffuse optical tomography system guided by ultrasound

PubMed Central

Yuan, Guangqian; Alqasemi, Umar; Chen, Aaron; Yang, Yi; Zhu, Quing

2014-01-01

Abstract. Laser diodes are widely used in diffuse optical tomography (DOT) systems but are typically expensive and fragile, while light-emitting diodes (LEDs) are cheaper and are also available in the near-infrared (NIR) range with adequate output power for imaging deeply seated targets. In this study, we introduce a new low-cost DOT system using LEDs of four wavelengths in the NIR spectrum as light sources. The LEDs were modulated at 20 kHz to avoid ambient light. The LEDs were distributed on a hand-held probe and a printed circuit board was mounted at the back of the probe to separately provide switching and driving current to each LED. Ten optical fibers were used to couple the reflected light to 10 parallel photomultiplier tube detectors. A commercial ultrasound system provided simultaneous images of target location and size to guide the image reconstruction. A frequency-domain (FD) laser-diode-based system with ultrasound guidance was also used to compare the results obtained from those of the LED-based system. Results of absorbers embedded in intralipid and inhomogeneous tissue phantoms have demonstrated that the LED-based system provides a comparable quantification accuracy of targets to the FD system and has the potential to image deep targets such as breast lesions. PMID:25473884

Usability of light-emitting diodes in precision approach path indicator systems by individuals with marginal color vision.

DOT National Transportation Integrated Search

2014-05-01

To save energy, the FAA is planning to convert from incandescent lights to light-emitting diodes (LEDs) in : precision approach path indicator (PAPI) systems. Preliminary work on the usability of LEDs by color vision-waivered pilots (Bullough, Skinne...

Very low color-temperature organic light-emitting diodes for lighting at night

NASA Astrophysics Data System (ADS)

Jou, Jwo-Huei; Tang, Ming-Chun; Chen, Pin-Chu; Chen, Szu-Hao; Shen, Shih-Ming; Chen, Chien-Chih; Wang, Ching-Chiun; Chen, Chien-Tien

2011-12-01

Light sources with low color temperature (CT) are essential for their markedly less suppression effect on the secretion of melatonin, and high power efficiency is crucial for energy-saving. To provide visual comfort, the light source should also have a reasonably high color rendering index (CRI). In this report, we demonstrate the design and fabrication of low CT and high efficiency organic light-emitting diodes. The best resultant device exhibits a CT of 1,880 K, much lower than that of incandescent bulbs (2,000-2,500 K) and even as low as that of candles, (1,800-2,000 K), a beyond theoretical limit external quantum efficiency 22.7 %, and 36.0 lm/W at 100 cd/m 2. The high efficiency of the proposed device may be attributed to its interlayer, which helps effectively distribute the entering carriers into the available recombination zones.

NASA sponsored Light Emitting Diode (LED) development helps in cancer treatment

NASA Technical Reports Server (NTRS)

1997-01-01

What started out as an attempt to develop a light which would allow for the growth of plants in space led to a remarkable discovery: The Light Emitting Diode (LED). This device through extensive study and experimentation has developed into a tool used by surgeons in the fight against brain cancer in children. Pictured is a mock-up of brain surgery being performed. By encapsulating the end of the LED with a balloon, light is diffused over a larger area of the brain allowing the surgeon a better view. This is one of many programs that begin as research for the space program, and through extensive study end up benefitting all of mankind.

Trap-assisted and Langevin-type recombination in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Wetzelaer, G. A. H.; Kuik, M.; Nicolai, H. T.; Blom, P. W. M.

2011-04-01

Trapping of charges is known to play an important role in the charge transport of organic semiconductors, but the role of traps in the recombination process has not been addressed. Here we show that the ideality factor of the current of organic light-emitting diodes (OLEDs) in the diffusion-dominated regime has a temperature-independent value of 2, which reveals that nonradiative trap-assisted recombination dominates the current. In contrast, the ideality factor of the light output approaches unity, demonstrating that luminance is governed by recombination of the bimolecular Langevin type. This apparent contradiction can be resolved by measuring the current and luminance ideality factor for a white-emitting polymer, where both free and trapped charge carriers recombine radiatively. With increasing bias voltage, Langevin recombination becomes dominant over trap-assisted recombination due to its stronger dependence on carrier density, leading to an enhancement in OLED efficiency.

Color stable white phosphorescent organic light emitting diodes with red emissive electron transport layer

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

Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin

2015-06-28

We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m{sup 2}. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq){submore » 3} as phosphorescent red dopant in electron transport layer.« less

Improving the Stability of Metal Halide Perovskite Materials and Light-Emitting Diodes.

PubMed

Cho, Himchan; Kim, Young-Hoon; Wolf, Christoph; Lee, Hyeon-Dong; Lee, Tae-Woo

2018-01-25

Metal halide perovskites (MHPs) have numerous advantages as light emitters such as high photoluminescence quantum efficiency with a direct bandgap, very narrow emission linewidth, high charge-carrier mobility, low energetic disorder, solution processability, simple color tuning, and low material cost. Based on these advantages, MHPs have recently shown unprecedented radical progress (maximum current efficiency from 0.3 to 42.9 cd A -1 ) in the field of light-emitting diodes. However, perovskite light-emitting diodes (PeLEDs) suffer from intrinsic instability of MHP materials and instability arising from the operation of the PeLEDs. Recently, many researchers have devoted efforts to overcome these instabilities. Here, the origins of the instability in PeLEDs are reviewed by categorizing it into two types: instability of (i) the MHP materials and (ii) the constituent layers and interfaces in PeLED devices. Then, the strategies to improve the stability of MHP materials and PeLEDs are critically reviewed, such as A-site cation engineering, Ruddlesden-Popper phase, suppression of ion migration with additives and blocking layers, fabrication of uniform bulk polycrystalline MHP layers, and fabrication of stable MHP nanoparticles. Based on this review of recent advances, future research directions and an outlook of PeLEDs for display applications are suggested. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Instense red phosphors for UV light emitting diode devices.

PubMed

Cao, Fa-Bin; Tian, Yan-Wen; Chen, Yong-Jie; Xiao, Lin-Jiu; Liu, Yun-Yi

2010-03-01

Ca(x)Sr1-x-1.5y-0.5zMoO4:yEu3+ zNa+ red phosphors were prepared by solid-state reaction using Na+ as charge supply for LEDs (light emitting diodes). The content of charge compensator, Ca2+ concentration, synthesis temperature, reaction time, and Eu3+ concentration were the keys to improving the properties of luminescence and crystal structure of red phosphors. The photoluminescence spectra shows the red phosphors are effectively excited at 616 nm by 311 nm, 395 nm, and 465 nm light. The wavelengths of 395 and 465 nm nicely match the widely applied emission wavelengths of ultraviolet or blue LED chips. Its chromaticity coordinates (CIE) are calculated to be x = 0.65, y = 0.32. Bright red light can be observed by the naked eye from the LED-based Ca0.60Sr0.25MoO4:0.08Eu3+ 0.06Na+.

Nano-honeycomb structured transparent electrode for enhanced light extraction from organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Shi, Xiao-Bo; Qian, Min; Wang, Zhao-Kui; Liao, Liang-Sheng

2015-06-01

A universal nano-sphere lithography method has been developed to fabricate nano-structured transparent electrode, such as indium tin oxide (ITO), for light extraction from organic light-emitting diodes (OLEDs). Perforated SiO2 film made from a monolayer colloidal crystal of polystyrene spheres and tetraethyl orthosilicate sol-gel is used as a template. Ordered nano-honeycomb pits on the ITO electrode surface are obtained by chemical etching. The proposed method can be utilized to form large-area nano-structured ITO electrode. More than two folds' enhancement in both current efficiency and power efficiency has been achieved in a red phosphorescent OLED which was fabricated on the nano-structured ITO substrate.

Light Emitting Diodes for Fiber Optic Communications.

DTIC Science & Technology

1981-03-31

asC.3~~ in.(c)- above and do- (1) pcait by volu.3 of dicst.iLle =zto.- Pazo 10 .61Edd, tcxcopt colvonts used cha-l bo: * ( a ) Methyl. alcohbl I7or 04...AD £101 480 LASER DIODE LABS INC NEW BRUNSWICK NJ / 1 / L I GT EMITTING DIODES FOR FIBER OPTIC COWMICATIONS.Cul AR, at A GENNARO DAARO-76-C-813 NA 1...PRArrcmA. P . 1"UNISPE-D TO DDC CONTAINE A II&~-’llryBE v., R OF :AO , MflG DO 9W CORADCOM U S ARMY COMMUNICATIONS RESEARCH 9 DEVELOPMENT COMMAND

Dual-Color Emission in Hybrid III-Nitride/ZnO Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Namkoong, Gon; Trybus, Elaissa; Cheung, Maurice C.; Doolittle, W. Alan; Cartwright, Alexander N.; Ferguson, Ian; Seong, Tae-Yeon; Nause, Jeff

2010-02-01

We report dual-color production of the blue and green regions using hybrid nitride/ZnO light emitting diode (LED) structures grown on ZnO substrates. The blue emission is ascribed to the near-band edge transition in InGaN while green emission is related to Zn-related defect levels formed by the unintentional interdiffusion of Zn into the InGaN active layer from the ZnO substrates.

Inkjet Printing of Organic Light-Emitting Diodes Based on Alcohol-Soluble Polyfluorenes

NASA Astrophysics Data System (ADS)

Odod, A. V.; Gadirov, R. M.; Solodova, T. A.; Kurtsevich, A. E.; Il'gach, D. M.; Yakimanskii, A. V.; Burtman, V.; Kopylova, T. N.

2018-04-01

Ink compositions for inkjet printing based on poly(9.9-dioctylfluorene) and its alcohol-soluble analog are created. Current-voltage, brightness-voltage, and spectral characteristics are compared for one- and twolayer polymer structures of organic light-emitting diodes. It is shown that the efficiency of the alcohol-soluble polyfluorene analog is higher compared to poly(9.9-dioctylfluorene), and the possibility of viscosity optimization is higher compared to aromatic chlorinated solvents.

Detection of Single Molecules Illuminated by a Light-Emitting Diode

PubMed Central

Gerhardt, Ilja; Mai, Lijian; Lamas-Linares, Antía; Kurtsiefer, Christian

2011-01-01

Optical detection and spectroscopy of single molecules has become an indispensable tool in biological imaging and sensing. Its success is based on fluorescence of organic dye molecules under carefully engineered laser illumination. In this paper we demonstrate optical detection of single molecules on a wide-field microscope with an illumination based on a commercially available, green light-emitting diode. The results are directly compared with laser illumination in the same experimental configuration. The setup and the limiting factors, such as light transfer to the sample, spectral filtering and the resulting signal-to-noise ratio are discussed. A theoretical and an experimental approach to estimate these parameters are presented. The results can be adapted to other single emitter and illumination schemes. PMID:22346610

Electrophoretic deposition of fluorescent Cu and Au sheets for light-emitting diodes

NASA Astrophysics Data System (ADS)

Liu, Jiale; Wu, Zhennan; Li, Tingting; Zhou, Ding; Zhang, Kai; Sheng, Yu; Cui, Jianli; Zhang, Hao; Yang, Bai

2015-12-01

Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to building blocks with 2D features. However, the studies are mainly focused on simplex building blocks. The utilization of multiplex building blocks is rarely reported. In this work, we demonstrate a controlled EPD of Cu and Au sheets, which are 2D assemblies of luminescent Cu and Au nanoclusters. Systematic investigations reveal that both the deposition efficiency and the thickness are determined by the lateral size of the sheets. For Cu sheets with a large lateral size, a high ζ-potential and strong face-to-face van der Waals interactions facilitate the deposition with high efficiency. However, for Au sheets, the small lateral size and ζ-potential limit the formation of a thick film. To solve this problem, the deposition dynamics are controlled by increasing the concentration of the Au sheets and adding acetone. This understanding permits the fabrication of a binary EPD film by the stepwise deposition of Cu and Au sheets, thus producing a luminescent film with both Cu green emission and Au red emission. A white light-emitting diode prototype with color coordinates (x, y) = (0.31, 0.36) is fabricated by employing the EPD film as a color conversion layer on a 365 nm GaN clip and further tuning the amount of deposited Cu and Au sheets.Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to

Light-Emitting Diode (LED) Traps Improve the Light-Trapping of Anopheline Mosquitoes.

PubMed

Costa-Neta, B M; da Silva, A A; Brito, J M; Moraes, J L P; Rebêlo, J M M; Silva, F S

2017-11-07

Numerous advantages over the standard incandescent lamp favor the use of light-emitting diodes (LEDs) as an alternative and inexpensive light source for sampling medically important insects in surveillance studies. Previously published studies examined the response of mosquitoes to different wavelengths, but data on anopheline mosquito LED attraction are limited. Center for Disease Control and Prevention-type light traps were modified by replacing the standard incandescent lamp with 5-mm LEDs, one emitting at 520 nm (green) and the other at 470 nm (blue). To test the influence of moon luminosity on LED catches, the experiments were conducted during the four lunar phases during each month of the study period. A total of 1,845 specimens representing eight anopheline species were collected. Anopheles (Nyssorhynchus) evansae (35.2%) was the most frequently collected, followed by An. (Nys.) triannulatus (21.9%), An. (Nys.) goeldii (12.9%), and An. (Nys.) argyritarsis (11.5%). The green LED was the most attractive light source, accounting for 43.3% of the individuals collected, followed by the blue (31.8%) and control (24.9%) lights. The LED traps were significantly more attractive than the control, independent of the lunar phase. Light trapping of anopheline mosquitoes was more efficient when the standard incandescent lamp was replaced with LEDs, regardless of the moon phase. The efficiency of LEDs improves light trapping results, and it is suggested that the use of LEDs as an attractant for anopheline mosquitoes should be taken into consideration when sampling anopheline mosquitoes. © The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Near-field photometry for organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Li, Rui; Harikumar, Krishnan; Isphording, Alexandar; Venkataramanan, Venkat

2013-03-01

Organic Light Emitting Diode (OLED) technology is rapidly maturing to be ready for next generation of light source for general lighting. The current standard test methods for solid state lighting have evolved for semiconductor sources, with point-like emission characteristics. However, OLED devices are extended surface emitters, where spatial uniformity and angular variation of brightness and colour are important. This necessitates advanced test methods to obtain meaningful data for fundamental understanding, lighting product development and deployment. In this work, a near field imaging goniophotometer was used to characterize lighting-class white OLED devices, where luminance and colour information of the pixels on the light sources were measured at a near field distance for various angles. Analysis was performed to obtain angle dependent luminous intensity, CIE chromaticity coordinates and correlated colour temperature (CCT) in the far field. Furthermore, a complete ray set with chromaticity information was generated, so that illuminance at any distance and angle from the light source can be determined. The generated ray set is needed for optical modeling and design of OLED luminaires. Our results show that luminance non-uniformity could potentially affect the luminaire aesthetics and CCT can vary with angle by more than 2000K. This leads to the same source being perceived as warm or cool depending on the viewing angle. As OLEDs are becoming commercially available, this could be a major challenge for lighting designers. Near field measurement can provide detailed specifications and quantitative comparison between OLED products for performance improvement.

Impact of Plasma Electron Flux on Plasma Damage-Free Sputtering of Ultrathin Tin-Doped Indium Oxide Contact Layer on p-GaN for InGaN/GaN Light-Emitting Diodes.

PubMed

Son, Kwang Jeong; Kim, Tae Kyoung; Cha, Yu-Jung; Oh, Seung Kyu; You, Shin-Jae; Ryou, Jae-Hyun; Kwak, Joon Seop

2018-02-01

The origin of plasma-induced damage on a p -type wide-bandgap layer during the sputtering of tin-doped indium oxide (ITO) contact layers by using radiofrequency-superimposed direct current (DC) sputtering and its effects on the forward voltage and light output power (LOP) of light-emitting diodes (LEDs) with sputtered ITO transparent conductive electrodes (TCE) is systematically studied. Changing the DC power voltage from negative to positive bias reduces the forward voltages and enhances the LOP of the LEDs. The positive DC power drastically decreases the electron flux in the plasma obtained by plasma diagnostics using a cutoff probe and a Langmuir probe, suggesting that the repulsion of plasma electrons from the p -GaN surface can reduce plasma-induced damage to the p -GaN. Furthermore, electron-beam irradiation on p -GaN prior to ITO deposition significantly increases the forward voltages, showing that the plasma electrons play an important role in plasma-induced damage to the p -GaN. The plasma electrons can increase the effective barrier height at the ITO/deep-level defect (DLD) band of p -GaN by compensating DLDs, resulting in the deterioration of the forward voltage and LOP. Finally, the plasma damage-free sputtered-ITO TCE enhances the LOP of the LEDs by 20% with a low forward voltage of 2.9 V at 20 mA compared to LEDs with conventional e-beam-evaporated ITO TCE.

Modeling of light-emitting diode wavefronts for the optimization of transmission holograms.

PubMed

Karthaus, Daniela; Giehl, Markus; Sandfuchs, Oliver; Sinzinger, Stefan

2017-06-20

The objective of applying transmission holograms in automotive headlamp systems requires the adaptation of holograms to divergent and polychromatic light sources like light-emitting diodes (LEDs). In this paper, four different options to describe the scalar light waves emitted by a typical automotive LED are regarded. This includes a new approach to determine the LED's wavefront from interferometric measurements. Computer-generated holograms are designed considering the different LED approximations and recorded into a photopolymer. The holograms are reconstructed with the LED and the resulting images are analyzed to evaluate the quality of the wave descriptions. In this paper, we show that our presented new approach leads to better results in comparison to other wave descriptions. The enhancement is evaluated by the correlation between reconstructed and ideal images. In contrast to the next best approximation, a spherical wave, the correlation coefficient increased by 0.18% at 532 nm, 1.69% at 590 nm, and 0.75% at 620 nm.

An Exciplex Host for Deep-Blue Phosphorescent Organic Light-Emitting Diodes.

PubMed

Lim, Hyoungcheol; Shin, Hyun; Kim, Kwon-Hyeon; Yoo, Seung-Jun; Huh, Jin-Suk; Kim, Jang-Joo

2017-11-01

The use of exciplex hosts is attractive for high-performance phosphorescent organic light-emitting diodes (PhOLEDs) and thermally activated delayed fluorescence OLEDs, which have high external quantum efficiency, low driving voltage, and low efficiency roll-off. However, exciplex hosts for deep-blue OLEDs have not yet been reported because of the difficulties in identifying suitable molecules. Here, we report a deep-blue-emitting exciplex system with an exciplex energy of 3.0 eV. It is composed of a carbazole-based hole-transporting material (mCP) and a phosphine-oxide-based electron-transporting material (BM-A10). The blue PhOLEDs exhibited maximum external quantum efficiency of 24% with CIE coordinates of (0.15, 0.21) and longer lifetime than the single host devices.

ZnO PN Junctions for Highly-Efficient, Low-Cost Light Emitting Diodes

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

David P. Norton; Stephen Pearton; Fan Ren

2007-09-30

By 2015, the US Department of Energy has set as a goal the development of advanced solid state lighting technologies that are more energy efficient, longer lasting, and more cost-effective than current technology. One approach that is most attractive is to utilize light-emitting diode technologies. Although III-V compound semiconductors have been the primary focus in pursuing this objective, ZnO-based materials present some distinct advantages that could yield success in meeting this objective. As with the nitrides, ZnO is a direct bandgap semiconductor whose gap energy (3.2 eV) can be tuned from 3.0 to 4 eV with substitution of Mg formore » higher bandgap, Cd for lower bandgap. ZnO has an exciton binding energy of 60 meV, which is larger than that for the nitrides, indicating that it should be a superior light emitting semiconductor. Furthermore, ZnO thin films can be deposited at temperatures on the order of 400-600 C, which is significantly lower than that for the nitrides and should lead to lower manufacturing costs. It has also been demonstrated that functional ZnO electronic devices can be fabricated on inexpensive substrates, such as glass. Therefore, for the large-area photonic application of solid state lighting, ZnO holds unique potential. A significant impediment to exploiting ZnO in light-emitting applications has been the absence of effective p-type carrier doping. However, the recent realization of acceptor-doped ZnO material overcomes this impediment, opening the door to ZnO light emitting diode development In this project, the synthesis and properties of ZnO-based pn junctions for light emitting diodes was investigated. The focus was on three issues most pertinent to realizing a ZnO-based solid state lighting technology, namely (1) achieving high p-type carrier concentrations in epitaxial and polycrystalline films, (2) realizing band edge emission from pn homojunctions, and (3) investigating pn heterojunction constructs that should yield efficient

Organic light-emitting diodes with a spacer enhanced exciplex emission

NASA Astrophysics Data System (ADS)

Yan, Fei; Chen, Rui; Sun, Handong; Wei Sun, Xiao

2014-04-01

By introducing a spacer molecule into the blended exciplex emissive layer, the performance of the bulk heterojunction exciplex organic light-emitting diodes (OLEDs) was improved dramatically; the maximum luminous efficiency was enhanced by about 22% from 7.9 cd/A to 9.7 cd/A, and the luminous efficiency drop was reduced by 28% at 400 mA/cm2. Besides the suppressed annihilation of exciton, the time-resolved photoluminescence measurements indicated that the spacer enhanced the delayed fluorescence through increasing the backward intersystem crossing rate from the triplet to singlet exciplex state. This method is useful for developing high performance exciplex OLEDs.

General method to evaluate substrate surface modification techniques for light extraction enhancement of organic light emitting diodes

NASA Astrophysics Data System (ADS)

Krummacher, B. C.; Mathai, M. K.; Choong, V.; Choulis, S. A.; So, F.; Winnacker, A.

2006-09-01

The external light output of organic light emitting diodes (OLEDs) can be increased by modifying the light emitting surface. The apparent light extraction enhancement is given by the ratio between the efficiency of the unmodified device and the efficiency of the modified device. This apparent light extraction enhancement is dependent on the OLED architecture itself and is not the correct value to judge the effectiveness of a technique to enhance light outcoupling due to substrate surface modification. We propose a general method to evaluate substrate surface modification techniques for light extraction enhancement of OLEDs independent from the device architecture. This method is experimentally demonstrated using green electrophosphorescent OLEDs with different device architectures. The substrate surface of these OLEDs was modified by applying a prismatic film to increase light outcoupling from the device stack. It was demonstrated that the conventionally measured apparent light extraction enhancement by means of the prismatic film does not reflect the actual performance of the light outcoupling technique. Rather, by comparing the light extracted out of the prismatic film to that generated in the OLED layers and coupled into the substrate (before the substrate/air interface), a more accurate evaluation of light outcoupling enhancement can be achieved. Furthermore we show that substrate surface modification can change the output spectrum of a broad band emitting OLED.

Recent advances in conjugated polymers for light emitting devices.

PubMed

Alsalhi, Mohamad Saleh; Alam, Javed; Dass, Lawrence Arockiasamy; Raja, Mohan

2011-01-01

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review.

Recent Advances in Conjugated Polymers for Light Emitting Devices

PubMed Central

AlSalhi, Mohamad Saleh; Alam, Javed; Dass, Lawrence Arockiasamy; Raja, Mohan

2011-01-01

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review. PMID:21673938

Low driving voltage blue, green, yellow, red and white organic light-emitting diodes with a simply double light-emitting structure.

PubMed

Zhang, Zhensong; Yue, Shouzhen; Wu, Yukun; Yan, Pingrui; Wu, Qingyang; Qu, Dalong; Liu, Shiyong; Zhao, Yi

2014-01-27

Low driving voltage blue, green, yellow, red and white phosphorescent organic light-emitting diodes (OLEDs) with a common simply double emitting layer (D-EML) structure are investigated. Our OLEDs without any out-coupling schemes as well as n-doping strategies show low driving voltage, e.g. < 2.4 V for onset and < 3 V for 1000 cd/m2, and high efficiency of 32.5 lm/W (13.3%), 58.8 lm/W (14.3%), 55.1 lm/W (14.6%), 24.9 lm/W (13.7%) and 45.1 lm/W (13.5%) for blue, green, yellow, red and white OLED, respectively. This work demonstrates that the low driving voltages and high efficiencies can be simultaneously realized with a common simply D-EML structure.

Light-emitting diodes based on colloidal silicon quantum dots

NASA Astrophysics Data System (ADS)

Zhao, Shuangyi; Liu, Xiangkai; Pi, Xiaodong; Yang, Deren

2018-06-01

Colloidal silicon quantum dots (Si QDs) hold great promise for the development of printed Si electronics. Given their novel electronic and optical properties, colloidal Si QDs have been intensively investigated for optoelectronic applications. Among all kinds of optoelectronic devices based on colloidal Si QDs, QD light-emitting diodes (LEDs) play an important role. It is encouraging that the performance of LEDs based on colloidal Si QDs has been significantly increasing in the past decade. In this review, we discuss the effects of the QD size, QD surface and device structure on the performance of colloidal Si-QD LEDs. The outlook on the further optimization of the device performance is presented at the end.

Long-lifetime thin-film encapsulated organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Wong, F. L.; Fung, M. K.; Tao, S. L.; Lai, S. L.; Tsang, W. M.; Kong, K. H.; Choy, W. M.; Lee, C. S.; Lee, S. T.

2008-07-01

Multiple fluorocarbon (CFx) and silicon nitride (Si3N4) bilayers were applied as encapsulation cap on glass-based organic light-emitting diodes (OLEDs). When CFx/Si3N4 bilayers were deposited onto the OLED structure, the devices showed performance worse than one without any encapsulation. The adverse effects were attributed to the damage caused by reaction species during the thin-film deposition processes. To solve this problem, a CuPc interlayer was found to provide effective protection to the OLED structure. With a structure of CuPc/(CFx/Si3N4)×5, the encapsulated device showed an operation lifetime over 8000 h (higher than 80% of that achieved with a conventional metal encapsulation).

High efficiency white organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Gang; Dong, Weili; Gao, Hongyan; Tian, Xiaocui; Zhao, Lina; Jiang, Wenlong; Zhang, Xiyan

2015-06-01

The light emitting diodes with the structure of ITO/ m-MTDATA(20 nm)/NPB(10 nm)/CBP BCzVBi ( x, nm, 10%)/CBP(3 nm)/CBP: Ir(ppy)3: DCJTB(10 nm, 8 and 1%)/Bphen(30 nm)/Cs2CO3: Ag2O (2 nm, 20%)/Al (100 nm) employing phosphorescence sensitization and fluorescence doping, were manufactured. The performance of the devices was studied by adjusting the thickness of fluorescence dopant layer ( x = 15, 20, 25, and 30). The best performance was achieved when its thickness was 25 nm. The device has the maximum luminance of 20260 cd/m2 at applied voltage of 14 V and the maximum current efficiency of 11.70 cd/A at 7 V. The device displays a continuous change of color from yellow to white. The CIE coordinates change from (0.49, 0.48) to (0.32, 0.39) when the driving voltage is varied from 5 to 15 V.

Highly Efficient Spectrally Stable Red Perovskite Light-Emitting Diodes.

PubMed

Tian, Yu; Zhou, Chenkun; Worku, Michael; Wang, Xi; Ling, Yichuan; Gao, Hanwei; Zhou, Yan; Miao, Yu; Guan, Jingjiao; Ma, Biwu

2018-05-01

Perovskite light-emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi-2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light-emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi-2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m -2 and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

High-performance organic light-emitting diodes comprising ultrastable glass layers

PubMed Central

Rodríguez-Viejo, Javier

2018-01-01

Organic light-emitting diodes (OLEDs) are one of the key solid-state light sources for various applications including small and large displays, automotive lighting, solid-state lighting, and signage. For any given commercial application, OLEDs need to perform at their best, which is judged by their device efficiency and operational stability. We present OLEDs that comprise functional layers fabricated as ultrastable glasses, which represent the thermodynamically most favorable and, thus, stable molecular conformation achievable nowadays in disordered solids. For both external quantum efficiencies and LT70 lifetimes, OLEDs with four different phosphorescent emitters show >15% enhancements over their respective reference devices. The only difference to the latter is the growth condition used for ultrastable glass layers that is optimal at about 85% of the materials’ glass transition temperature. These improvements are achieved through neither material refinements nor device architecture optimization, suggesting a general applicability of this concept to maximize the OLED performance, no matter which specific materials are used. PMID:29806029

Electronic Characteristics of Rare Earth Doped GaN Schottky Diodes

DTIC Science & Technology

2013-03-21

REPORT TYPE Master’s Thesis 3. DATES COVERED (From – To) 04 Sep 2011 - Mar 2013 4. TITLE AND SUBTITLE ELECTRONIC CHARACTERISTICS OF RARE EARTH ...ELECTRONIC CHARACTERISTICS OF RARE EARTH DOPED GaN SCHOTTKY DIODES THESIS Aaron B. Blanning...United States. AFIT-ENP-13-M-03 Electronic Characteristics of Rare Earth Doped GaN Schottky Diodes THESIS Presented to the Faculty

III-nitride nanowire LEDs and diode lasers: monolithic light sources on (001) Si emitting in the 600-1300nm range

NASA Astrophysics Data System (ADS)

Bhattacharya, P.; Hazari, A.; Jahangir, S.

2018-02-01

GaN-based nanowire heterostructure arrays epitaxially grown on (001)Si substrates have unique properties and present the potential to realize useful devices. The active light-emitting region in the nanowire heterostructures are usually InGaN disks, whose composition can be varied to tune the emission wavelength. We have demonstrated light emitting diodes and edgeemitting diode lasers with power outputs 10mW with emission in the 600-1300nm wavelength range. These light sources are therefore useful for a variety of applications, including silicon photonics. Molecular beam epitaxial growth of the nanowire heterostructure arrays on (001)Si substrates and the characteristics of 1.3μm nanowire array edge emitting lasers, guided wave photodiodes and a monolithic photonic integrated circuit designed for 1.3μm operation are described.

Novel Strategy for Photopatterning Emissive Polymer Brushes for Organic Light Emitting Diode Applications

PubMed Central

2017-01-01

A light-mediated methodology to grow patterned, emissive polymer brushes with micron feature resolution is reported and applied to organic light emitting diode (OLED) displays. Light is used for both initiator functionalization of indium tin oxide and subsequent atom transfer radical polymerization of methacrylate-based fluorescent and phosphorescent iridium monomers. The iridium centers play key roles in photocatalyzing and mediating polymer growth while also emitting light in the final OLED structure. The scope of the presented procedure enables the synthesis of a library of polymers with emissive colors spanning the visible spectrum where the dopant incorporation, position of brush growth, and brush thickness are readily controlled. The chain-ends of the polymer brushes remain intact, affording subsequent chain extension and formation of well-defined diblock architectures. This high level of structure and function control allows for the facile preparation of random ternary copolymers and red–green–blue arrays to yield white emission. PMID:28691078

Novel Strategy for Photopatterning Emissive Polymer Brushes for Organic Light Emitting Diode Applications.

PubMed

Page, Zachariah A; Narupai, Benjaporn; Pester, Christian W; Bou Zerdan, Raghida; Sokolov, Anatoliy; Laitar, David S; Mukhopadhyay, Sukrit; Sprague, Scott; McGrath, Alaina J; Kramer, John W; Trefonas, Peter; Hawker, Craig J

2017-06-28

A light-mediated methodology to grow patterned, emissive polymer brushes with micron feature resolution is reported and applied to organic light emitting diode (OLED) displays. Light is used for both initiator functionalization of indium tin oxide and subsequent atom transfer radical polymerization of methacrylate-based fluorescent and phosphorescent iridium monomers. The iridium centers play key roles in photocatalyzing and mediating polymer growth while also emitting light in the final OLED structure. The scope of the presented procedure enables the synthesis of a library of polymers with emissive colors spanning the visible spectrum where the dopant incorporation, position of brush growth, and brush thickness are readily controlled. The chain-ends of the polymer brushes remain intact, affording subsequent chain extension and formation of well-defined diblock architectures. This high level of structure and function control allows for the facile preparation of random ternary copolymers and red-green-blue arrays to yield white emission.

Application of highly ordered carbon nanotubes templates to field-emission organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Li, Chi-Shing; Su, Shui-Hsiang; Chi, Hsiang-Yu; Yokoyama, Meiso

2009-01-01

An anodic aluminum oxide (AAO) template was formed by a two-step anodization process. Carbon nanotubes (CNTs) were successfully synthesized along with AAO pores and the diameters of CNTs equaled those of AAO pores. The lengths of CNTs during a chemical vapor deposition synthesized process on the AAO template were effectively controlled. These AAO-CNTs exhibit excellent field emission with a low turn-on field (0.7 V/μm) and a low threshold field (1.4 V/μm). The field enhancement factor, calculated from the non-saturated region of the Fowler-Nordheim (F-N) plot, is about 8237. A novel field-emission organic light-emitting diode (FEOLED) combining AAO-CNTs cathodes as electron source with organic electroluminescent (EL) light-emitting layers coated on indium-tin-oxide (ITO) is produced. The uniform and dense luminescence image is obtained in the FEOLEDs. Organic EL light-emitting materials have lower working voltage than inorganic phosphor-coated fluorescent screens.

White light emitting diode based on InGaN chip with core/shell quantum dots

NASA Astrophysics Data System (ADS)

Shen, Changyu; Hong, Yan; Ma, Jiandong; Ming, Jiangzhou

2009-08-01

Quantum dots have many applications in optoelectronic device such as LEDs for its many superior properties resulting from the three-dimensional confinement effect of its carrier. In this paper, single chip white light-emitting diodes (WLEDs) were fabricated by combining blue InGaN chip with luminescent colloidal quantum dots (QDs). Two kinds of QDs of core/shell CdSe /ZnS and core/shell/shell CdSe /ZnS /CdS nanocrystals were synthesized by thermal deposition using cadmium oxide and selenium as precursors in a hot lauric acid and hexadecylamine trioctylphosphine oxide hybrid. This two kinds of QDs exhibited high photoluminescence efficiency with a quantum yield more than 41%, and size-tunable emission wavelengths from 500 to 620 nm. The QDs LED mainly consists of flip luminescent InGaN chip, glass ceramic protective coating, glisten cup, QDs using as the photoluminescence material, pyroceram, gold line, electric layer, dielectric layer, silicon gel and bottom layer for welding. The WLEDs had the CIE coordinates of (0.319, 0.32). The InGaN chip white-light-emitting diodes with quantum dots as the emitting layer are potentially useful in illumination and display applications.

Efficient Light Extraction of Organic Light-Emitting Diodes on a Fully Solution-Processed Flexible Substrate

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

Tong, Kwing; Liu, Xiaofeng; Zhao, Fangchao

A flexible, nanocomposite substrate for maximizing light outcoupling efficiencies of organic light-emitting diodes (OLEDs) is introduced. In depth investigation is performed on designing the integrated strategy based on considerations of surface conductivity, microcavity tuning, and internal light scattering. The resulting nanocomposite substrate consists of silver nanowires as the electrode and a high-index polymer layer and a light-scattering layer for light extraction. It is able to outcouple both the waveguide and the substrate modes, two modes accounting for significant losses in OLED device efficiency. With enhanced light outcoupling, white OLEDs subsequently fabricated on the nanocomposite substrates demonstrate performance metrics of 107more » lm W -1 power efficiency and 49% external quantum efficiency at 1000 cd m -2. Thus, the nanocomposite substrate is fabricated by solution processes at low temperatures for potentially low manufacturing cost.« less

Efficient Light Extraction of Organic Light-Emitting Diodes on a Fully Solution-Processed Flexible Substrate

DOE PAGES

Tong, Kwing; Liu, Xiaofeng; Zhao, Fangchao; ...

2017-07-18

A flexible, nanocomposite substrate for maximizing light outcoupling efficiencies of organic light-emitting diodes (OLEDs) is introduced. In depth investigation is performed on designing the integrated strategy based on considerations of surface conductivity, microcavity tuning, and internal light scattering. The resulting nanocomposite substrate consists of silver nanowires as the electrode and a high-index polymer layer and a light-scattering layer for light extraction. It is able to outcouple both the waveguide and the substrate modes, two modes accounting for significant losses in OLED device efficiency. With enhanced light outcoupling, white OLEDs subsequently fabricated on the nanocomposite substrates demonstrate performance metrics of 107more » lm W -1 power efficiency and 49% external quantum efficiency at 1000 cd m -2. Thus, the nanocomposite substrate is fabricated by solution processes at low temperatures for potentially low manufacturing cost.« less

Warm-White-Light-Emitting Diode Based on a Dye-Loaded Metal-Organic Framework for Fast White-Light Communication.

PubMed

Wang, Zhiye; Wang, Zi; Lin, Bangjiang; Hu, XueFu; Wei, YunFeng; Zhang, Cankun; An, Bing; Wang, Cheng; Lin, Wenbin

2017-10-11

A dye@metal-organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y 3 Al 5 O 12 :Ce 3+ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs.

Tunnel junction enhanced nanowire ultraviolet light emitting diodes

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

Sarwar, A. T. M. Golam; May, Brelon J.; Deitz, Julia I.

Polarization engineered interband tunnel junctions (TJs) are integrated in nanowire ultraviolet (UV) light emitting diodes (LEDs). A ∼6 V reduction in turn-on voltage is achieved by the integration of tunnel junction at the base of polarization doped nanowire UV LEDs. Moreover, efficient hole injection into the nanowire LEDs leads to suppressed efficiency droop in TJ integrated nanowire LEDs. The combination of both reduced bias voltage and increased hole injection increases the wall plug efficiency in these devices. More than 100 μW of UV emission at ∼310 nm is measured with external quantum efficiency in the range of 4–6 m%. The realization of tunnel junctionmore » within the nanowire LEDs opens a pathway towards the monolithic integration of cascaded multi-junction nanowire LEDs on silicon.« less

p-Type modulation doped InGaN/GaN dot-in-a-wire white-light-emitting diodes monolithically grown on Si(111).

PubMed

Nguyen, H P T; Zhang, S; Cui, K; Han, X; Fathololoumi, S; Couillard, M; Botton, G A; Mi, Z

2011-05-11

Full-color, catalyst-free InGaN/GaN dot-in-a-wire light-emitting diodes (LEDs) were monolithically grown on Si(111) by molecular beam epitaxy, with the emission characteristics controlled by the dot properties in a single epitaxial growth step. With the use of p-type modulation doping in the dot-in-a-wire heterostructures, we have demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm(2). The remarkable performance is attributed to the superior three-dimensional carrier confinement provided by the electronically coupled dot-in-a-wire heterostructures, the nearly defect- and strain-free GaN nanowires, and the significantly enhanced hole transport due to the p-type modulation doping.

A Strategy for Architecture Design of Crystalline Perovskite Light-Emitting Diodes with High Performance.

PubMed

Shi, Yifei; Wu, Wen; Dong, Hua; Li, Guangru; Xi, Kai; Divitini, Giorgio; Ran, Chenxin; Yuan, Fang; Zhang, Min; Jiao, Bo; Hou, Xun; Wu, Zhaoxin

2018-06-01

All present designs of perovskite light-emitting diodes (PeLEDs) stem from polymer light-emitting diodes (PLEDs) or perovskite solar cells. The optimal structure of PeLEDs can be predicted to differ from PLEDs due to the different fluorescence dynamics and crystallization between perovskite and polymer. Herein, a new design strategy and conception is introduced, "insulator-perovskite-insulator" (IPI) architecture tailored to PeLEDs. As examples of FAPbBr 3 and MAPbBr 3 , it is experimentally shown that the IPI structure effectively induces charge carriers into perovskite crystals, blocks leakage currents via pinholes in the perovskite film, and avoids exciton quenching simultaneously. Consequently, as for FAPbBr 3 , a 30-fold enhancement in the current efficiency of IPI-structured PeLEDs compared to a control device with poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) as hole-injection layer is achieved-from 0.64 to 20.3 cd A -1 -while the external quantum efficiency is increased from 0.174% to 5.53%. As the example of CsPbBr 3 , compared with the control device, both current efficiency and lifetime of IPI-structured PeLEDs are improved from 1.42 and 4 h to 9.86 cd A -1 and 96 h. This IPI architecture represents a novel strategy for the design of light-emitting didoes based on various perovskites with high efficiencies and stabilities. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Response of conifer species from three latitudinal populations to light spectra generated by light-emitting diodes and high-pressure sodium lamps

Treesearch

Kent G. Apostol; Kas Dumroese; Jeremy Pinto; Anthony S. Davis

2015-01-01

Light-emitting diode (LED) technology shows promise for supplementing photosynthetically active radiation (PAR) in forest nurseries because of the potential reduction in energy consumption and an ability to supply discrete wavelengths to optimize seedling growth. Our objective was to examine the effects of light spectra supplied by LED and traditional high-pressure...

Comment on "Enhancement of flip-chip white light-emitting diodes with a one-dimensional photonic crystal".

PubMed

Liu, Zong-Yuan; Liu, Sheng; Wang, Kai; Luo, Xiao-Bing

2010-06-01

We show that research presented in Opt. Lett.34, 301 (2009)OPLEDP0146-959210.1364/OL.34.000301 applied questionable phosphor definitions and a questionable simulation procedure for light-emitting diodes. Our simulation indicates that a one-dimensional photonic crystal is beneficial for color control but cannot improve the light extraction as asserted in that Letter.

Response of adult mosquitoes to light emitting diodes placed in resting boxes and in the field.

USDA-ARS?s Scientific Manuscript database

Resting boxes are passive devices used to attract and capture mosquitoes seeking shelter. Increasing the attractiveness of these devices could improve their effectiveness. Light emitting diodes (LEDs) can be attractive to mosquitoes when used together with other trapping devices. Therefore restin...

High brightness nonpolar a-plane (11-20) GaN light-emitting diodes

NASA Astrophysics Data System (ADS)

Jung, Sukkoo; Chang, Younghak; Bang, Kyu-Hyun; Kim, Hyung-Gu; Choi, Yoon-Ho; Hwang, Sung-Min; Baik, Kwang Hyeon

2012-02-01

We report on high brightness nonpolar a-plane InGaN/GaN LEDs using patterned lateral overgrowth (PLOG) epitaxy. High crystal-quality and smooth surfaces for a-plane GaN (a-GaN) films were achieved using PLOG with an array of hexagonal SiO2 patterns. The XRC FWHMs of as-grown PLOG a-GaN films were found to be 414 and 317 arcsec (450 and 455 arcsec for planar a-GaN films) along the c-axis and m-axis directions, respectively. Plan-view CL clearly reveals the periodic hexagonal patterns with higher band edge emission intensity, implying that the luminescence properties of a-GaN films lying above the SiO2 mask are improved. The light output powers of a-InGaN/GaN PLOG LEDs were measured to be 7.5 mW and 20 mW at drive currents of 20 mA and 100 mA, respectively. A negligible blue-shift was observed in the peak emission wavelength with increasing drive current up to 100 mA, indicating that there are no strong internal fields in nonpolar a-InGaN/GaN LEDs. We believe that nonpolar a-plane InGaN/GaN LEDs hold promise for efficient nitride emitters if the growth conditions are further optimized.

Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

NASA Astrophysics Data System (ADS)

Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob

2015-07-01

We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq)2(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq)2(acac). The lifetime of device (t95: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

Study of voltage decrease in organic light emitting diodes during the initial stage of lifetime

NASA Astrophysics Data System (ADS)

Cusumano, P.

2016-02-01

We report the results of lifetime DC testing at constant current of not-encapsulated organic light emitting diodes (OLEDs) based on Tris (8 idroxyquinoline) aluminum (Alq3) as emitting material. In particular, a voltage decrease during the initial stage of the lifetime test is observed. The cause of this behavior is also discussed, mainly linked to initial Joule self-heating of the device, rising its temperature above room temperature until thermal equilibrium is reached at steady state.

Noise reduction in digital lensless holographic microscopy by engineering the light from a light-emitting diode.

PubMed

Garcia-Sucerquia, Jorge

2013-01-01

By engineering the light from a light-emitting diode (LED) the noises present in digital lensless holographic microscopy (DLHM) are reduced. The partially coherent light from an LED is tailored to produce a spherical wavefront with limited coherence time and the spatial coherence needed by DLHM to work. DLHM with this engineered light source is used to image biological samples that cover areas of the order of mm(2). The ratio between the diameter of the area that is almost coherently illuminated to the diameter of the illumination area is utilized as parameter to quantify the performance of the DLHM with the engineered LED light source. Experimental results show that while the noises can be reduced effectively the spatial resolution can be kept in the micrometer range.

Sodium bromide additive improved film morphology and performance in perovskite light-emitting diodes

NASA Astrophysics Data System (ADS)

Li, Jinghai; Cai, Feilong; Yang, Liyan; Ye, Fanghao; Zhang, Jinghui; Gurney, Robert S.; Liu, Dan; Wang, Tao

2017-07-01

Organometal halide perovskite is a promising material to fabricate light-emitting diodes (LEDs) via solution processing due to its exceptional optoelectronic properties. However, incomplete precursor conversion and various defect states in the perovskite light-emitting layer lead to low luminance and external quantum efficiency of perovskite LEDs. We show here the addition of an optimum amount of sodium bromide in the methylammonium lead bromide (MAPbBr3) precursor during a one-step perovskite solution casting process can effectively improve the film coverage, enhance the crystallinity, and passivate ionic defects on the surface of MAPbBr3 crystal grains, resulting in LEDs with a reduced turn-on voltage from 2.8 to 2.3 V and an enhanced maximum luminance from 1059 to 6942 Cd/m2 when comparing with the pristine perovskite-based device.

Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p-n diodes and InGaN LEDs

NASA Astrophysics Data System (ADS)

Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

2017-12-01

Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal-organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p-n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm-3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10-3-3.4 × 10-3 Ω·cm2, and the turn-on voltages of the diodes.

Damage of photoreceptor-derived cells in culture induced by light emitting diode-derived blue light

PubMed Central

Kuse, Yoshiki; Ogawa, Kenjiro; Tsuruma, Kazuhiro; Shimazawa, Masamitsu; Hara, Hideaki

2014-01-01

Our eyes are increasingly exposed to light from the emitting diode (LED) light of video display terminals (VDT) which contain much blue light. VDTs are equipped with televisions, personal computers, and smart phones. The present study aims to clarify the mechanism underlying blue LED light-induced photoreceptor cell damage. Murine cone photoreceptor-derived cells (661 W) were exposed to blue, white, or green LED light (0.38 mW/cm2). In the present study, blue LED light increased reactive oxygen species (ROS) production, altered the protein expression level, induced the aggregation of short-wavelength opsins (S-opsin), resulting in severe cell damage. While, blue LED light damaged the primary retinal cells and the damage was photoreceptor specific. N-Acetylcysteine (NAC), an antioxidant, protected against the cellular damage induced by blue LED light. Overall, the LED light induced cell damage was wavelength-, but not energy-dependent and may cause more severe retinal photoreceptor cell damage than the other LED light. PMID:24909301

Substrate-Free InGaN/GaN Nanowire Light-Emitting Diodes.

PubMed

Neplokh, Vladimir; Messanvi, Agnes; Zhang, Hezhi; Julien, Francois H; Babichev, Andrey; Eymery, Joel; Durand, Christophe; Tchernycheva, Maria

2015-12-01

We report on the demonstration of substrate-free nanowire/polydimethylsiloxane (PDMS) membrane light-emitting diodes (LEDs). Metal-organic vapour-phase epitaxy (MOVPE)-grown InGaN/GaN core-shell nanowires were encapsulated into PDMS layer. After metal deposition to p-GaN, a thick PDMS cap layer was spin-coated and the membrane was manually peeled from the sapphire substrate, flipped upside down onto a steel holder, and transparent indium tin oxide (ITO) contact to n-GaN was deposited. The fabricated LEDs demonstrate rectifying diode characteristics. For the electroluminescence (EL) measurements, the samples were manually bonded using silver paint. The EL spectra measured at different applied voltages demonstrate a blue shift with the current increase. This shift is explained by the current injection into the InGaN areas of the active region with different average indium content.

Combination of carbon dot and polymer dot phosphors for white light-emitting diodes.

PubMed

Sun, Chun; Zhang, Yu; Sun, Kai; Reckmeier, Claas; Zhang, Tieqiang; Zhang, XiaoYu; Zhao, Jun; Wu, Changfeng; Yu, William W; Rogach, Andrey L

2015-07-28

We realized white light-emitting diodes with high color rendering index (85-96) and widely variable color temperatures (2805-7786 K) by combining three phosphors based on carbon dots and polymer dots, whose solid-state photoluminescence self-quenching was efficiently suppressed within a polyvinyl pyrrolidone matrix. All three phosphors exhibited dominant absorption in the UV spectral region, which ensured the weak reabsorption and no energy transfer crosstalk. The WLEDs showed excellent color stability against the increasing current because of the similar response of the tricolor phosphors to the UV light variation.

White polymeric light-emitting diodes with high color rendering index

NASA Astrophysics Data System (ADS)

Niu, Xiaodi; Ma, Liang; Yao, Bing; Ding, Junqiao; Tu, Guoli; Xie, Zhiyuan; Wang, Lixiang

2006-11-01

The efficient white polymeric light-emitting diodes based on a white emissive polymer doped with a red phosphorescent dopant were fabricated by spin-coating method. The emission spectrum of the device is broadened to cover the full visible region by doping the red phosphorescent dye and thereby realizes white emission with high color-rendering index (CRI). By controlling the contents of the doped electron-transporting 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and the red phosphorescent dopant, a luminous efficiency as high as 5.3cd/A and a power efficiency of 3lm/W were obtained with a CRI of 92.

Use of GaN as a Scintillating Ionizing Radiation Detector

NASA Astrophysics Data System (ADS)

Wensman, Johnathan; Guardala, Noel; Mathur, Veerendra; Alasagas, Leslie; Vanhoy, Jeffrey; Statham, John; Marron, Daniel; Millett, Marshall; Marsh, Jarrod; Currie, John; Price, Jack

2017-09-01

Gallium nitride (GaN) is a III/V direct bandgap semiconductor which has been used in light emitting diodes (LEDs) since the 1990s. Currently, due to a potential for increased efficiency, GaN is being investigated as a replacement for silicon in power electronics finding potential uses ranging from data centers to electric vehicles. In addition to LEDs and power electronics though, doped GaN can be used as a gamma insensitive fast neutron detector due to the direct band-gap, light propagation properties, and response to ionizing radiations. Investigation of GaN as a semiconductor scintillator for use in a radiation detection system involves mapping the response function of the detector crystal over a range of photon and neutron energies, and measurements of light generation in the GaN crystal due to proton, alpha, and nitrogen projectiles. In this presentation we discuss the measurements made to date, and plausible interpretations of the response functions. This work funded in part by the Naval Surface Warfare Center, Carderock Division In-house Laboratory Independent Research program.

Strain tunable light emitting diodes with germanium P-I-N heterojunctions

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

Lagally, Max G; Sanchez Perez, Jose Roberto

Tunable p-i-n diodes comprising Ge heterojunction structures are provided. Also provided are methods for making and using the tunable p-i-n diodes. Tunability is provided by adjusting the tensile strain in the p-i-n heterojunction structure, which enables the diodes to emit radiation over a range of wavelengths.

A lighting assembly based on red and blue light-emitting diodes as a lighting source for space agriculture

NASA Astrophysics Data System (ADS)

Avercheva, Olga; Berkovich, Yuliy A.; Smolyanina, Svetlana; Bassarskaya, Elizaveta; Zhigalova, Tatiana; Ptushenko, Vasiliy; Erokhin, Alexei

Light-emitting diodes (LEDs) are a promising lighting source for space agriculture due to their high efficiency, longevity, safety, and other factors. Assemblies based on red and blue LEDs have been recommended in literature, although not all plants show sufficient productivity in such lighting conditions. Adding of green LEDs proposed in some works was aimed at psychological support for the crew, and not at the improvement of plant growth. We studied the growth and the state of the photosynthetic apparatus in Chinese cabbage (Brassica chinensis L.) plants grown under red (650 nm) and blue (470 nm) light-emitting diodes (LEDs). Plants grown under a high-pressure sodium lamp (HPS lamp) were used as a control. The plants were illuminated with two photosynthetic photon flux levels: nearly 400 µE and about 100 µE. Plants grown under LEDs with 400 µE level, as compared to control plants, showed lower fresh weight, edible biomass, growth rate, and sugar content. The difference in fresh weight and edible biomass was even more pronounced in plants grown with 100 µE level; the data indicate that the adaptability of the test plants to insufficient lighting decreased. Under LEDs, we observed the decreasing of root growth and the absence of transition to the flowering stage, which points to a change in the hormonal balance in plants grown in such lighting conditions. We also found differences in the functioning of the photosynthetic apparatus and its reaction to a low lighting level. We have concluded that a lighting assembly with red and blue LEDs only is insufficient for the plant growth and productivity, and can bring about alterations in their adaptive and regulatory mechanisms. Further studies are needed to optimize the lighting spectrum for space agriculture, taking into account the photosynthetic, phototropic and regulatory roles of light. Using white LEDs or adding far-red and green LEDs might be a promising approach.

Highly efficient exciplex organic light-emitting diodes using thermally activated delayed fluorescent emitters as donor and acceptor materials.

PubMed

Jeon, Sang Kyu; Yook, Kyoung Soo; Lee, Jun Yeob

2016-06-03

Highly efficient exciplex type organic light-emitting diodes were developed using thermally activated delayed fluorescent emitters as donors and acceptors of an exciplex. Blue emitting bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) was a donor and 9,9'-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (DDCzTrz) and 9,9',9″-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,2,3-triyl)tris(9H-carbazole) (TCzTrz) were acceptor materials. The exciplexes of DMAC-DPS:TCzTrz and DMAC-DPS:DDCzTrz resulted in high photoluminescence quantum yield and high quantum efficiency in the green exciplex organic light-emitting diodes. High quantum efficiencies of 13.4% and 15.3% were obtained in the DMAC-DPS:DDCzTrz and DMAC-DPS:TCzTrz exciplex devices.

Highly efficient exciplex organic light-emitting diodes using thermally activated delayed fluorescent emitters as donor and acceptor materials

NASA Astrophysics Data System (ADS)

Jeon, Sang Kyu; Yook, Kyoung Soo; Lee, Jun Yeob

2016-06-01

Highly efficient exciplex type organic light-emitting diodes were developed using thermally activated delayed fluorescent emitters as donors and acceptors of an exciplex. Blue emitting bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) was a donor and 9,9‧-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (DDCzTrz) and 9,9‧,9″-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,2,3-triyl)tris(9H-carbazole) (TCzTrz) were acceptor materials. The exciplexes of DMAC-DPS:TCzTrz and DMAC-DPS:DDCzTrz resulted in high photoluminescence quantum yield and high quantum efficiency in the green exciplex organic light-emitting diodes. High quantum efficiencies of 13.4% and 15.3% were obtained in the DMAC-DPS:DDCzTrz and DMAC-DPS:TCzTrz exciplex devices.

The Photoluminescent Properties of New Cationic Iridium(III) Complexes Using Different Anions and Their Applications in White Light-Emitting Diodes.

PubMed

Yang, Hui; Meng, Guoyun; Zhou, Yayun; Tang, Huaijun; Zhao, Jishou; Wang, Zhengliang

2015-09-14

Three cationic iridium(III) complexes [Ir(ppy)₂(phen)][PF₆] (C1), [Ir(ppy)₂(phen)]₂SiF₆ (C2) and [Ir(ppy)₂(phen)]₂TiF₆ (C3) (ppy: 2-phenylpyridine, phen: 1, 10-phenanthroline) using different anions were synthesized and characterized by ¹H Nuclear magnetic resonance (¹HNMR), mass spectra (MS), Fourier transform infrared (FTIR) spectra and element analysis (EA). After the ultraviolet visible (UV-vis) absorption spectra, photoluminescent (PL) properties and thermal properties of the complexes were investigated, complex C1 and C3 with good optical properties and high thermal stability were used in white light-emitting diodes (WLEDs) as luminescence conversion materials by incorporation with 460 nm-emitting blue GaN chips. The integrative performances of the WLEDs fabricated with complex C1 and C3 are better than those fabricated with the widely used yellow phosphor Y₃Al₅O 12 :Ce 3+ (YAG). The color rendering indexes of the WLEDs with C1 and C3 are 82.0 and 82.6, the color temperatures of them are 5912 K and 3717 K, and the maximum power efficiencies of them are 10.61 Lm·W -1 and 11.41 Lm·W -1 , respectively.

Ultrafast Hot Carrier Dynamics in GaN and Its Impact on the Efficiency Droop.

PubMed

Jhalani, Vatsal A; Zhou, Jin-Jian; Bernardi, Marco

2017-08-09

GaN is a key material for lighting technology. Yet, the carrier transport and ultrafast dynamics that are central in GaN light-emitting devices are not completely understood. We present first-principles calculations of carrier dynamics in GaN, focusing on electron-phonon (e-ph) scattering and the cooling and nanoscale dynamics of hot carriers. We find that e-ph scattering is significantly faster for holes compared to electrons and that for hot carriers with an initial 0.5-1 eV excess energy, holes take a significantly shorter time (∼0.1 ps) to relax to the band edge compared to electrons, which take ∼1 ps. The asymmetry in the hot carrier dynamics is shown to originate from the valence band degeneracy, the heavier effective mass of holes compared to electrons, and the details of the coupling to different phonon modes in the valence and conduction bands. We show that the slow cooling of hot electrons and their long ballistic mean free paths (over 3 nm at room temperature) are a possible cause of efficiency droop in GaN light-emitting diodes. Taken together, our work sheds light on the ultrafast dynamics of hot carriers in GaN and the nanoscale origin of efficiency droop.

Caenorhabditis elegans as a model to study the impact of exposure to light emitting diode (LED) domestic lighting.

PubMed

Abdel-Rahman, Fawzia; Okeremgbo, Bethel; Alhamadah, Fatimah; Jamadar, Sakha; Anthony, Kevin; Saleh, Mahmoud A

2017-04-16

This study aimed to investigate the biological impact of exposure on domestic light emitting diodes (LED) lighting using the free-living nematode Caenorhabditis elegans as a model. Nematodes were separately exposed to white LED light covering the range of 380-750 nm, blue light at 450 nm and black light at 380-420 nm for one life cycle (egg to adult) with dark exposure as the control. Each light range induced stress to the nematode C. elegans such as reducing the number of the hatched eggs and/or delayed the maturation of the hatched eggs to the adult stage. In addition, it lowered or prevented the ability of adults to lay eggs and impaired the locomotion in the exposed worms. The observed type of biological stress was also associated with the production of reactive oxygen species (ROS) as compared to nematodes grown in the dark. It is concluded that the blue light component of white LED light may cause health problems, and further investigation is required to test commercial brands of white LEDs that emit different amounts of blue light.

Enhanced Phycocyanin Production from Spirulina platensis using Light Emitting Diode

NASA Astrophysics Data System (ADS)

Bachchhav, Manisha Bhanudas; Kulkarni, Mohan Vinayak; Ingale, Arun G.

2017-06-01

This work investigates the performance of different cultivation conditions using Light Emitting Diode (LED) as a light source for the production of phycocyanin from Spirulina platensis. With LEDs under autotrophic conditions, red LED produced maximum amount of biomass (8.95 g/l). As compared to autotrophic cultivation with fluorescent lamp (control), cultivations using LEDs under autotrophic and mixotrophic mode significantly enhanced the phycocyanin content. For autotrophic conditions (with LED) phycocyanin content was in the range of 103-242 mg/g of dry biomass, whereas for mixotrophic conditions (0.1% glucose and LED) it was in the range of 254-380 mg/g of dry biomass. Spirulina cultivated with yellow LED under mixotrophic conditions had 5.4-fold more phycocyanin (380 mg/g of dry biomass) than control (70 mg/g of dry biomass). The present study demonstrates that the LEDs under mixotrophic conditions gave sixfold (2497 mg/l) higher yields of phycocyanin as compared to autotrophic condition under white light (415 mg/l).

Direct Growth of III-Nitride Nanowire-Based Yellow Light-Emitting Diode on Amorphous Quartz Using Thin Ti Interlayer

NASA Astrophysics Data System (ADS)

Prabaswara, Aditya; Min, Jung-Wook; Zhao, Chao; Janjua, Bilal; Zhang, Daliang; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S.

2018-02-01

Consumer electronics have increasingly relied on ultra-thin glass screen due to its transparency, scalability, and cost. In particular, display technology relies on integrating light-emitting diodes with display panel as a source for backlighting. In this study, we undertook the challenge of integrating light emitters onto amorphous quartz by demonstrating the direct growth and fabrication of a III-nitride nanowire-based light-emitting diode. The proof-of-concept device exhibits a low turn-on voltage of 2.6 V, on an amorphous quartz substrate. We achieved 40% transparency across the visible wavelength while maintaining electrical conductivity by employing a TiN/Ti interlayer on quartz as a translucent conducting layer. The nanowire-on-quartz LED emits a broad linewidth spectrum of light centered at true yellow color ( 590 nm), an important wavelength bridging the green-gap in solid-state lighting technology, with significantly less strain and dislocations compared to conventional planar quantum well nitride structures. Our endeavor highlighted the feasibility of fabricating III-nitride optoelectronic device on a scalable amorphous substrate through facile growth and fabrication steps. For practical demonstration, we demonstrated tunable correlated color temperature white light, leveraging on the broadly tunable nanowire spectral characteristics across red-amber-yellow color regime.

Direct Growth of III-Nitride Nanowire-Based Yellow Light-Emitting Diode on Amorphous Quartz Using Thin Ti Interlayer.

PubMed

Prabaswara, Aditya; Min, Jung-Wook; Zhao, Chao; Janjua, Bilal; Zhang, Daliang; Albadri, Abdulrahman M; Alyamani, Ahmed Y; Ng, Tien Khee; Ooi, Boon S

2018-02-06

Consumer electronics have increasingly relied on ultra-thin glass screen due to its transparency, scalability, and cost. In particular, display technology relies on integrating light-emitting diodes with display panel as a source for backlighting. In this study, we undertook the challenge of integrating light emitters onto amorphous quartz by demonstrating the direct growth and fabrication of a III-nitride nanowire-based light-emitting diode. The proof-of-concept device exhibits a low turn-on voltage of 2.6 V, on an amorphous quartz substrate. We achieved ~ 40% transparency across the visible wavelength while maintaining electrical conductivity by employing a TiN/Ti interlayer on quartz as a translucent conducting layer. The nanowire-on-quartz LED emits a broad linewidth spectrum of light centered at true yellow color (~ 590 nm), an important wavelength bridging the green-gap in solid-state lighting technology, with significantly less strain and dislocations compared to conventional planar quantum well nitride structures. Our endeavor highlighted the feasibility of fabricating III-nitride optoelectronic device on a scalable amorphous substrate through facile growth and fabrication steps. For practical demonstration, we demonstrated tunable correlated color temperature white light, leveraging on the broadly tunable nanowire spectral characteristics across red-amber-yellow color regime.

Phosphorescence white organic light-emitting diodes with single emitting layer based on isoquinolinefluorene-carbazole containing host.

PubMed

Koo, Ja Ryong; Lee, Seok Jae; Hyung, Gun Woo; Kim, Bo Young; Shin, Hyun Su; Lee, Kum Hee; Yoon, Seung Soo; Kim, Woo Young; Kim, Young Kwan

2013-03-01

We have demonstrated a stable phosphorescent white organic light-emitting diodes (WOLEDs) using an orange emitter, Bis(5-benzoyl-2-(4-fluorophenyl)pyridinato-C,N) iridium(III)acetylacetonate [(Bz4Fppy)2Ir(III)acac] doped into a newly synthesized blue host material, 2-(carbazol-9-yl)-7-(isoquinolin-1-yl)-9,9-diethylfluorene (CzFliq). When 1 wt.% (Bz4Fppy)2Ir(III)acac was doped into emitting layer, it was realized an improved EL performance and a pure white color in the OLED. The optimum WOLED showed maximum values as a luminous efficiency of 10.14 cd/A, a power efficiency of 10.24 Im/W, a peak external quantum efficiency 4.07%, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39) at 8 V.

Light emitting diodes as a plant lighting source

NASA Technical Reports Server (NTRS)

Bula, R. J.; Tennessen, D. J.; Morrow, R. C.; Tibbitts, T. W.

1994-01-01

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 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). 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. A number of LED characteristics are of considerable importance in selecting a light source for plant lighting in a controlled environment facility. Of particular importance is the characteristic that light is generated by an LED at a rate far greater than the corresponding thermal radiation predicted by the bulk temperature of the device as defined by Plank's radiation law. This is in sharp contrast to other light sources, such as an incandescent or high intensity discharge lamp. A plant lighting system for controlled environments must provide plants with an adequate flux of photosynthetically active radiation, plus providing photons in the spectral regions that are involved in the photomorphogenic and phototropic responses that result in normal plant growth and development. Use of light sources that emit photons over a broad spectral range generally meet these two lighting requirements. Since the LED's emit over specific spectral regions, they must be carefully selected so that the levels of photsynthetically active and photomorphogenic and phototropic radiation meet these plant requirements.

Multiple night-time light-emitting diode lighting strategies impact grassland invertebrate assemblages.

PubMed

Davies, Thomas W; Bennie, Jonathan; Cruse, Dave; Blumgart, Dan; Inger, Richard; Gaston, Kevin J

2017-07-01

White light-emitting diodes (LEDs) are rapidly replacing conventional outdoor lighting technologies around the world. Despite rising concerns over their impact on the environment and human health, the flexibility of LEDs has been advocated as a means of mitigating the ecological impacts of globally widespread outdoor night-time lighting through spectral manipulation, dimming and switching lights off during periods of low demand. We conducted a three-year field experiment in which each of these lighting strategies was simulated in a previously artificial light naïve grassland ecosystem. White LEDs both increased the total abundance and changed the assemblage composition of adult spiders and beetles. Dimming LEDs by 50% or manipulating their spectra to reduce ecologically damaging wavelengths partially reduced the number of commoner species affected from seven to four. A combination of dimming by 50% and switching lights off between midnight and 04:00 am showed the most promise for reducing the ecological costs of LEDs, but the abundances of two otherwise common species were still affected. The environmental consequences of using alternative lighting technologies are increasingly well established. These results suggest that while management strategies using LEDs can be an effective means of reducing the number of taxa affected, averting the ecological impacts of night-time lighting may ultimately require avoiding its use altogether. © 2017 John Wiley & Sons Ltd.

Strategies to Achieve High-Performance White Organic Light-Emitting Diodes

PubMed Central

Zhang, Lirong; Li, Xiang-Long; Luo, Dongxiang; Xiao, Peng; Xiao, Wenping; Song, Yuhong; Ang, Qinshu; Liu, Baiquan

2017-01-01

As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs) have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin characteristics, and flexibility. In this invited review, the main parameters which are used to characterize the performance of WOLEDs are introduced. Subsequently, the state-of-the-art strategies to achieve high-performance WOLEDs in recent years are summarized. Specifically, the manipulation of charges and excitons distribution in the four types of WOLEDs (fluorescent WOLEDs, phosphorescent WOLEDs, thermally activated delayed fluorescent WOLEDs, and fluorescent/phosphorescent hybrid WOLEDs) are comprehensively highlighted. Moreover, doping-free WOLEDs are described. Finally, issues and ways to further enhance the performance of WOLEDs are briefly clarified. PMID:29194426

High-efficiency orange and tandem white organic light-emitting diodes using phosphorescent dyes with horizontally oriented emitting dipoles.

PubMed

Lee, Sunghun; Shin, Hyun; Kim, Jang-Joo

2014-09-03

Tandem white organic light-emitting diodes (WOLEDs) using horizontally oriented phosphorescent dyes in an exciplex-forming co-host are presented, along with an orange OLED. A high external quantum efficiency of 32% is achieved for the orange OLED at 1000 cd m(-2) and the tandem WOLEDs exhibit a high maximum EQE of 54.3% (PE of 63 lm W(-1)). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Organic Light-Emitting Diode-on-Silicon Pixel Circuit Using the Source Follower Structure with Active Load for Microdisplays

NASA Astrophysics Data System (ADS)

Kwak, Bong-Choon; Lim, Han-Sin; Kwon, Oh-Kyong

2011-03-01

In this paper, we propose a pixel circuit immune to the electrical characteristic variation of organic light-emitting diodes (OLEDs) for organic light-emitting diode-on-silicon (OLEDoS) microdisplays with a 0.4 inch video graphics array (VGA) resolution and a 6-bit gray scale. The proposed pixel circuit is implemented using five p-channel metal oxide semiconductor field-effect transistors (MOSFETs) and one storage capacitor. The proposed pixel circuit has a source follower with a diode-connected transistor as an active load for improving the immunity against the electrical characteristic variation of OLEDs. The deviation in the measured emission current ranges from -0.165 to 0.212 least significant bit (LSB) among 11 samples while the anode voltage of OLED is 0 V. Also, the deviation in the measured emission current ranges from -0.262 to 0.272 LSB in pixel samples, while the anode voltage of OLED varies from 0 to 2.5 V owing to the electrical characteristic variation of OLEDs.

Light-emitting diodes (LED) for domestic lighting: any risks for the eye?

PubMed

Behar-Cohen, F; Martinsons, C; Viénot, F; Zissis, G; Barlier-Salsi, A; Cesarini, J P; Enouf, O; Garcia, M; Picaud, S; Attia, D

2011-07-01

Light-emitting diodes (LEDs) are taking an increasing place in the market of domestic lighting because they produce light with low energy consumption. In the EU, by 2016, no traditional incandescent light sources will be available and LEDs may become the major domestic light sources. Due to specific spectral and energetic characteristics of white LEDs as compared to other domestic light sources, some concerns have been raised regarding their safety for human health and particularly potential harmful risks for the eye. To conduct a health risk assessment on systems using LEDs, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), a public body reporting to the French Ministers for ecology, for health and for employment, has organized a task group. This group consisted physicists, lighting and metrology specialists, retinal biologist and ophthalmologist who have worked together for a year. Part of this work has comprised the evaluation of group risks of different white LEDs commercialized on the French market, according to the standards and found that some of these lights belonged to the group risk 1 or 2. This paper gives a comprehensive analysis of the potential risks of white LEDs, taking into account pre-clinical knowledge as well as epidemiologic studies and reports the French Agency's recommendations to avoid potential retinal hazards. Copyright © 2011. Published by Elsevier Ltd.

Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

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

Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob, E-mail: sy96.lee@samsung.com

2015-07-27

We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq){sub 2}(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq){sub 2}(acac). The lifetime of device (t{sub 95}: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

GaN based nanorods for solid state lighting

NASA Astrophysics Data System (ADS)

Li, Shunfeng; Waag, Andreas

2012-04-01

In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

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.

RGB-Stack Light Emitting Diode Modules with Transparent Glass Circuit Board and Oil Encapsulation

PubMed Central

Li, Ying-Chang; Chang, Yuan-Hsiao; Singh, Preetpal; Chang, Liann-Be; Yeh, Der-Hwa; Chao, Ting-Yu; Jian, Si-Yun; Li, Yu-Chi; Lai, Chao-Sung; Ying, Shang-Ping

2018-01-01

The light emitting diode (LED) is widely used in modern solid-state lighting applications, and its output efficiency is closely related to the submounts’ material properties. Most submounts used today, such as low-power printed circuit boards (PCBs) or high-power metal core printed circuit boards (MCPCBs), are not transparent and seriously decrease the output light extraction. To meet the requirements of high light output and better color mixing, a three-dimensional (3-D) stacked flip-chip (FC) LED module is proposed and demonstrated. To realize light penetration and mixing, the mentioned 3-D vertically stacking RGB LEDs use transparent glass as FC package submounts called glass circuit boards (GCB). Light emitted from each GCB stacked LEDs passes through each other and thus exhibits good output efficiency and homogeneous light-mixing characteristics. In this work, the parasitic problem of heat accumulation, which caused by the poor thermal conductivity of GCB and leads to a serious decrease in output efficiency, is solved by a proposed transparent cooling oil encapsulation (OCP) method. PMID:29494534

RGB-Stack Light Emitting Diode Modules with Transparent Glass Circuit Board and Oil Encapsulation.

PubMed

Li, Ying-Chang; Chang, Yuan-Hsiao; Singh, Preetpal; Chang, Liann-Be; Yeh, Der-Hwa; Chao, Ting-Yu; Jian, Si-Yun; Li, Yu-Chi; Tan, Cher Ming; Lai, Chao-Sung; Chow, Lee; Ying, Shang-Ping

2018-03-01

The light emitting diode (LED) is widely used in modern solid-state lighting applications, and its output efficiency is closely related to the submounts' material properties. Most submounts used today, such as low-power printed circuit boards (PCBs) or high-power metal core printed circuit boards (MCPCBs), are not transparent and seriously decrease the output light extraction. To meet the requirements of high light output and better color mixing, a three-dimensional (3-D) stacked flip-chip (FC) LED module is proposed and demonstrated. To realize light penetration and mixing, the mentioned 3-D vertically stacking RGB LEDs use transparent glass as FC package submounts called glass circuit boards (GCB). Light emitted from each GCB stacked LEDs passes through each other and thus exhibits good output efficiency and homogeneous light-mixing characteristics. In this work, the parasitic problem of heat accumulation, which caused by the poor thermal conductivity of GCB and leads to a serious decrease in output efficiency, is solved by a proposed transparent cooling oil encapsulation (OCP) method.

Collimating lens for light-emitting-diode light source based on non-imaging optics.

PubMed

Wang, Guangzhen; Wang, Lili; Li, Fuli; Zhang, Gongjian

2012-04-10

A collimating lens for a light-emitting-diode (LED) light source is an essential device widely used in lighting engineering. Lens surfaces are calculated by geometrical optics and nonimaging optics. This design progress does not rely on any software optimization and any complex iterative process. This method can be used for any type of light source not only Lambertian. The theoretical model is based on point source. But the practical LED source has a certain size. So in the simulation, an LED chip whose size is 1 mm*1 mm is used to verify the feasibility of the model. The mean results show that the lenses have a very compact structure and good collimating performance. Efficiency is defined as the ratio of the flux in the illuminated plane to the flux from LED source without considering the lens material transmission. Just investigating the loss in the designed lens surfaces, the two types of lenses have high efficiencies of more than 90% and 99%, respectively. Most lighting area (possessing 80% flux) radii are no more than 5 m when the illuminated plane is 200 m away from the light source.

White polymer light-emitting diodes based on star-shaped polymers with an orange dendritic phosphorescent core.

PubMed

Zhu, Minrong; Li, Yanhu; Cao, Xiaosong; Jiang, Bei; Wu, Hongbin; Qin, Jingui; Cao, Yong; Yang, Chuluo

2014-12-01

A series of new star-shaped polymers with a triphenylamine-based iridium(III) dendritic complex as the orange-emitting core and poly(9,9-dihexylfluorene) (PFH) chains as the blue-emitting arms is developed towards white polymer light-emitting diodes (WPLEDs). By fine-tuning the content of the orange phosphor, partial energy transfer and charge trapping from the blue backbone to the orange core is realized to achieve white light emission. Single-layer WPLEDs with the configuration of ITO (indium-tin oxide)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer/CsF/Al exhibit a maximum current efficiency of 1.69 cd A(-1) and CIE coordinates of (0.35, 0.33), which is very close to the pure white-light point of (0.33, 0.33). To the best of our knowledge, this is the first report on star-shaped white-emitting single polymers that simultaneously consist of fluorescent and phosphorescent species. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fully porous GaN p-n junction diodes fabricated by chemical vapor deposition.

PubMed

Bilousov, Oleksandr V; Carvajal, Joan J; Geaney, Hugh; Zubialevich, Vitaly Z; Parbrook, Peter J; Martínez, Oscar; Jiménez, Juan; Díaz, Francesc; Aguiló, Magdalena; O'Dwyer, Colm

2014-10-22

Porous GaN based LEDs produced by corrosion etching techniques demonstrated enhanced light extraction efficiency in the past. However, these fabrication techniques require further postgrown processing steps, which increases the price of the final system. Also, the penetration depth of these etching techniques is limited, and affects not only the semiconductor but also the other elements constituting the LED when applied to the final device. In this paper, we present the fabrication of fully porous GaN p-n junctions directly during growth, using a sequential chemical vapor deposition (CVD) process to produce the different layers that form the p-n junction. We characterized their diode behavior from room temperature to 673 K and demonstrated their ability as current rectifiers, thus proving the potential of these fully porous p-n junctions for diode and LEDs applications. The electrical and luminescence characterization confirm that high electronic quality porous structures can be obtained by this method, and we believe this investigation can be extended to other III-N materials for the development of white light LEDs, or to reduce reflection losses and narrowing the output light cone for improved LED external quantum efficiencies.