Solution-Processable Carbazole-Based Conjugated Dendritic Hosts for Power-Efficient Blue-Electrophosphorescent Devices

A novel class of hosts suitable for solution processing has been developed based on a conjugated dendritic scaffold. By increasing the dendron generation, the highest occupied molecular orbital (HOMO) energy level can be tuned to facilitate hole injection, while the triplet energy remains at a high level, sufficient to host high-energy-triplet emitters. A power-efficient blue-electrophosphorescent device based on H2 (see figure) is presented.

MOCVD growth of cubic GaN: Materials and devices

Many impressive progresses have been made recently on the growth of cubic-phase GaN by MBE and MOCVD. In this paper, some of our recent progress will be reviewed, including the growth of high quality cubic InGaN films, InGaN/GaN heterostructure blue and green LEDs. Cubic-phase GaN films were grown on GaAs (100) substrates by MOCVD. Growth conditions were optimized to obtain pure cubic phase GaN films up to a thickness of 4 mum. An anomalous compressive strain was found in the as-grown GaN films in spite of a smaller lattice constant for GaN compared with that of GaAs substrates. The photoluminescence FWHM of high quality InGaN epilayers was less than 100 meV The InGaN/GaN heterostructure blue LED has intense electroluminescence with a FWHM of 20 nm.

Synthesis and Application of Thiadiazoloquinoxaline-Containing Chromophores as Dopants for Efficient Near-Infrared Organic Light-Emitting Diodes

series of a donor-acceptor-donor type of near-infrared (NIR) fluorescent chromophores based on [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) as an electron acceptor and triphenylamine as an electron donor are synthesized and characterized. By introducing pendent phenyl groups or changing the pi-conjugation length in the TQ core, we tuned tile energy levels of these chromophores, resulting in the NIR emission in a range from 784 to 868 nm. High thermal stability and glass transition temperatures allow these chromophores to be used as dopant emitters, which can be processed by vapor deposition for the fabrication of organic light-emitting diodes (OLEDs) having the multilayered structure of ITO/MoO3/NPB/Alq(3):dopant emitter/BCP/Alq(3)/LiF/Al. The electroluminescence spectra of the devices based on these new chromophores cover a range from 748 to 870 nm. With 2 wt % of dopant 1, the LED device shows an exclusive NIR emission at 752 nm with the external quantum efficiency (EQE) as high as 1.12% over a wide range of current density (e.g., around 200 mA cm(-2)).

High-efficiency GaN-based blue LEDs grown on nano-patterned sapphire substrates for solid-state lighting - art. no. 684103

Nano-patterning sapphire substrates technique has been developed for nitrides light-emitting diodes (LEDs) growths. It is expected that the strain induced by the lattice misfits between the GaN epilayers and the sapphire substrates can be effectively accommodated via the nano-trenches. The GaN epilayers grown on the nano-patterned sapphire substrates by a low-pressure metal organic chemical vapor deposition (MOCVD) are characterized by means of scanning electron microscopy (SEM), high-resolution x-ray diffraction (HRXRD) and photoluminescence (PL) techniques. In comparison with the planar sapphire substrate, about 46% increment in device performance is measured for the InGaN/GaN blue LEDs grown on the nano-patterned sapphire substrates.

Color filter-less technology of LED back light for LCD-TV - art. no. 68410G

Back Light Unit (BLU) and Color Filter are the two key components for the perfect color display of Liquid Crystal Display (LCD) device. LCD can not light actively itself, so a form of illumination, Back Light Unit is needed for its display. The color filter which consists of RGB primary colors, is used to generate three basic colors for LCD display. Traditional CCFL back light source has several disadvantages, while LED back light technology makes LCD obtain quite higher display quality than the CCFL back light. LCD device based on LED back light owns promoted efficiency of display. Moreover it can generate color gamut above 100% of the NTSC specification. Especially, we put forward an idea of Color Filter-Less technology that we design a film which is patterned of red and green emitting phosphors, then make it be excited by a blue light LED panel we fabricate, for its special emitting mechanism, this film can emit RGB basic color, therefore replace the color filter of LCD device. This frame typically benefits for lighting uniformity and provide pretty high light utilization ratio. Also simplifies back light structure thus cut down the expenses.

High-brightness GaN-based blue LEDs grown on a wet-patterned sapphire substrate - art. no. 68410T

Patterning sapphire substrate can relax the stress in the nitride epilayer, reduce the threading dislocation density, and significantly improve device performance. In this article, a wet-etching method for sapphire substrate is developed. The effect of substrate surface topographies on the quality of the GaN epilayers and corresponding device performance are investigated. The GaN epilayers grown on the wet-patterned sapphire substrates by MOCVD are characterized by means of scanning electrical microscopy (SEM), atomic force microscopy (AFM), high-resolution x-ray diffraction (HRXRD), and photoluminescence (PL) techniques. In comparison with the planar sapphire substrate, about a 22% increase in device performance with light output power of 13.31 mW@20mA is measured for the InGaN/GaN blue LEDs grown on the wet-patterned sapphire substrate.

Material Growth and Device Fabrication of GaN-Based Blue-Violet Laser Diodes

Studies on first GaN-based blue-violet laser diodes(LDs) in China mainland are reported.High quality GaN materials as well as GaN-based quantum wells laser structures are grown by metal-organic chemical vapor deposition method.The X-ray double-crystal diffraction rocking curve measurements show the full-width half maximum of 180" and 185" for (0002) symmetric reflection and (10(-1)2) skew reflection,respectively.A room temperature mobility of 850cm2/(V·s) is obtained for a 3μm thick GaN film.Gain guided and ridge geometry waveguide laser diodes are fabricated with cleaved facet mirrors at room temperature under pulse current injection.The lasing wavelength is 405.9nm.A threshold current density of 5kA/cm2 and an output light power over 100mW are obtained for ridge geometry waveguide laser diodes.

Synthesis and characterization of new carbazole/fluorene-based derivatives for blue-light-emitting devices

2,7-Bis(9-ethylcarbazol-3-yl)-9,9-di(2-ethylhexyl)fluorene and a segmented copolymer composed of the same chromophores alternated with hexamethylene fragments were synthesized. The obtained materials possess good solubility in common organic solvents, high thermal stability with 1% weight loss temperature of 350-370 degrees C, and suitable glass transition temperatures. Both derivatives show blue fluorescence in dilute solutions as well as in solid state, demonstrating that excimers are not formed in the thin films. The fluorescence spectra of the materials do not show any peaks in the long-wavelength region even after annealing at 200 degrees C in air. An organic LED with the configuration of ITO/copolymer/Al generates blue electroluminescence with the maximum peak at 416 nm, rather low turn-on voltage (4.0 V), and brightness of about 400 cd/m(2). The heterostructure device based on model derivative emitted stable blue light with low operation voltage (100 cd/m(2) at similar to 11 V) and demonstrated luminescence efficiency of 0.8 cd/A.

Spin injection in the multiple quantum-well LED structure with the Fe/AlO (x) injector

A spin-injection/-detection device has been fabricated based on the multiple quantum well light emitting diode (LED) structure. It is found that only a broad electroluminescence (EL) peak of a full width at half maximum of 8.6 nm appears at the wavelength of 801 nm in EL spectra with a circular luminescence polarization degree of 18%, despite PL spectra always show three well resolved peaks. The kinetic energy gained by injected electrons and holes in their drift along opposite directions broadens the EL peak, and makes three EL peaks converge together. The same process also destroys the injected spin polarization of electrons mainly dominated by the Bir-Aronov-Pikus spin relaxing mechanism.

High-power quantum-dot superluminescent LED with broadband drive current insensitive emission spectra using a tapered active region

High-power and broadband quantum-dot (QD) superluminescent light-emitting diodes are realized by using a combination of self-assembled QDs with a high density, large inhomogeneous broadening, a tapered angled pump region, and etched V groove structure. This broad-area device exhibits greater than 70-nm 3-dB bandwidth and drive current insensitive emission spectra with 100-mW output power under continuous-wave operation. For pulsed operation, greater than 200-mW output power is obtained.

Ultraviolet-blue electroluminescence from Gd3Ga5O12 : Ag

UV-blue light was obtained from a thin-film electroluminescence device using Gd3Ga5O12:Ag as a light-emitting layer, which was deposited by using electron-beam evaporation. The crystal composition and structure of Gd3Ga5O12:Ag were studied by x-ray powder diffraction, The Gd3Ga5O12:Ag has a photoluminescence emission which peaked at around 397 and 467 nm, which were attributed to the oxide vacancies and Ag+, respectively. The brightness of 32 cd/m(2) was obtained when an alternating voltage of 130 V at 1 kHz was applied. (C) 2000 American Institute of Physics. [S0003-6951(00)05031-2].

Research on color matching of LED backlight for large-color-gamut LCD application - art. no. 68410Y

Comparing with the conventional CCFL (Cold Cathode Fluorescent Lamp) backlight, three-basic-color LEDs backlight has some advantages such as good color reproduction, long life and lead free etc. Theoretically, the color gamut is determined by x, y coordinates of the three basic colors in CIE chromaticity diagram, and the x, y coordinates of each basic color can derived from the relative spectrum distribution (RSD) of the LED. In this paper, the red, green and blue LEDs' RSD models are established to calculate and analyze the color gamut of a backlight. By simulating those models, the relationships that the color gamut of a LED backlight varies with each color are analyzed, and the optimum combination of three colors is obtained within the given wavelengths ranges. Moreover, the combinations of three colors for the gamut of 115% NTSC and 110% NTSC are plotted in pictures, respectively.

GaN m-i-n LED grown by MOVPE

Undoped and Zinc-doped GaN films have been grown using TMGa, DEZn and Ammonia by MOVPE. The GaN blue-green LEDs of m-i-n structure have been fabricated. They can be operated at forward bias less than 5 volts. The EL peak wavelengths was from 455 nm to 504 nm.

Light-emitting-diode-induced fluorescence detector for capillary electrophoresis using optical fiber with spherical end

A simple fluorescence detector for capillary electrophoresis (CE) using a blue light-emitting-diode (LED) as excitation source is constructed and evaluated. An optical fiber was used to collect the fluorescence, and a flat end of the fiber was modified to spherical end, resulting in 50% increase of efficiency over the flat end. A simple device for optical alignment of the fibers and capillary column was designed. The concentration and mass detection limits for fluorescein were 1.8 x 10(-7) Mol l(-1) and 4.3 femol, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.

White Electroluminescence from a Star-Like Polymer with an Orange Emissive Core and Four Blue Emissive Arms

A star-like white light-emitting polymer with an orange emissive core and four blue emissive arms is designed and synthesized. White electroluminescence is observed with simultaneous orange emission from the core and blue emission from the arms. A single-layer device based on this polymer emits white light with CIE coordinates of (0.35, 0.39) and a luminous efficiency of 7.06 cd A(-1).