Cyan Light-emitting Diodes Research Articles

Structural characterization, electronic and photophysical properties of phosphane-based copper(I) complexes and their application to cyan LEDs

Two dinuclear Cu(I) complexes, [Cu2(dppe)(dppbz)2I2](1) and [Cu2(dppb)(dppbz)2I2] (2) (dppe = 1, 2-bis(diphenylphosphino)ethane, dppb = 1,4-bis(diphenylphosphino)butane, dppbz = 1,2-bis (diphe nylphosphino)benzene), have been prepared and characterized by IR, TG, XRD, elemental analysis and X-ray crystal structure analysis. Structural analysis indicates that diphosphane ligands connect two Cu atoms to form the S-shape configurations in complexes 1 and 2. DFT calculations demonstrate that the HOMO → LUMO energy gap and Mülliken atomic charges for 1 and 2 are affected by increasing the alkyl chain length of diphosphane ligands, but the composition of HOMOs and LUMOs are hardly changed at the different alkyl chain length of diphosphane ligands. The solid-state luminescent properties of complexes 1 and 2 are observed at 77 K and 298 K, showing that the maximum emission lifetime and quantum yields respectively approach to 6 μs and 26 % at 298 K. Moreover, dinuclear Cu(I) complexes are used to fabricate the cyan light-emitting diodes with the maximum EQE of ca. 20 %.

Strain-Negligible Eu2+ Doping Enabled Color-Tunable Harsh Condition-Resistant Perovskite Nanocrystals for Superior Light-Emitting Diodes.

Cesium lead halide (CsPbX3, X = Br, Cl, I) perovskite nanocrystals (NCs) possess tunable band gaps across the entire visible spectral range and are promising for various optoelectronic device applications. However, poor performance in adverse conditions limits their further development in practical optoelectronics. Herein, highly stable perovskite NCs are developed by doping europium(II) (Eu2+) into the B-site of CsPbBr3 with negligible lattice distortion/strain. Eu2+-doped CsPbBr3 NCs exhibit tunable green-to-cyan emissions, high photoluminescence quantum yield, and good resistance to harsh conditions, including ultraviolet irradiation, erosion of moisture, and corrosion of polar solvent molecules. In particular, the thermal stability of CsPbBr3 NCs after Eu2+ doping is greatly enhanced under continuous heating in air, while exhibiting the emissions of Eu2+. Furthermore, a Eu2+-doped CsPbBr3 NC-based cyan light-emitting diode is fabricated, which exhibits narrow exciton emission driven under different current densities. This work would open the avenue to develop the rational lanthanide ion doping strategy for further advancing perovskite nanomaterials toward practical applications.

Graphene-Nanorod Enhanced Quasi-Van Der Waals Epitaxy for High Indium Composition Nitride Films.

The nitride films with high indium (In) composition play a crucial role in the fabrication of In-rich InGaN-basedoptoelectronic devices. However, a major limitation is In incorporation requiring a low temperature during growth at the expense of nitride dissociation. Here, to overcome this limitation, a strain-modulated growth method, namely the graphene (Gr)-nanorod (NR) enhanced quasi-van der Waals epitaxy, is proposed to increase the In composition in InGaN alloy. The lattice transparency of Gr enables constraint of in-plane orientation of nitride film and epitaxial relationships at the heterointerface. The Gr interlayer together with NRs buffer layer substantially reduces the stress of the GaN film by 74.4%, from 0.9 to 0.23GPa, and thus increases the In incorporation by 30.7%. The first principles calculations confirm that the release of strain accounts for the dramatic improvement. The photoluminescence peak of multiple quantum wells shifts from 461 to 497nm and the functionally small-sized cyan light-emitting diodes of 7×9mil2 are demonstrated. These findings provide an efficient approach for the growth of In-rich InGaN film and extend the applications of nitrides in advanced optoelectronic, photovoltaic, and thermoelectric devices.

Double-Stranded DNA Matrix for Photosensitization Switching

Photosensitization, originated from the activation of triplet states, is the basis of many photodynamic applications, but often competes with a series of nonradiative processes. Herein, we communic...

Spectral sensitivity and photoresponse in the rock bream Oplegnathus fasciatus and their relationships with the absorption maximum of the photoreceptor.

The spectral characteristics of visual pigments are a major determinant in eliciting a response to light. To study the absorption maximum of the photoreceptors and their sensitivity to light in fish, rod outer segments (ROS) and cone cells were purified from the rock bream Oplegnathus fasciatus adapted to the dark. Ultraviolet/visible spectroscopic analyses of the ROS in the dark and its difference spectra indicated an absorption maximum of the visual pigment at ~ 500nm, and each eye of 1-year-old rock bream contained at least 1.2nmol of rhodopsin-like visual pigments. Microspectrophotometric analysis of the cone cell outer segments led to identification of three visual pigments with individual absorption maxima at 425, 520, and 585nm. Monochromatic light-emitting diode (LED) modules with different wavelengths (violet 405nm, blue 465nm, cyan 505nm, green 530nm, amber 590nm, and red 655nm) were constructed to examine the spectral sensitivity and photoresponse in association with the absorption maximum of the photoreceptor. Analysis of chromophore decay upon illumination with each LED at low (27μmol/m2/s) and high (343μmol/m2/s) intensities showed the highest sensitivity of the photoreceptor upon illumination with the 505-nm cyan LED, followed by LEDs with wavelengths of 530nm > 465nm > 405nm > 590nm > 655nm. Photoresponse analysis of the fish using a video tracking system, in the dark and upon illumination, also showed faster movement of fish with illumination with the cyan LED followed by in the order of green ≈ blue > violet > amber > red. These results indicated that a light with a wavelength closer to the absorption maximum of rhodopsin was more effective in eliciting a response to the light.

GaN-Based Cyan Light-Emitting Diode with up to 1-GHz Bandwidth for High-Speed Transmission Over SI-POF

We demonstrate the performance of a novel cyan light-emitting diode (LED) on a patterned sapphire substrate for use as a light source for plastic optical fiber (POF) communications with the central wavelength at 500 nm. By significantly reducing the number of active InxGa1-xN/GaN multiple quantum wells and the thickness of the barrier layers down to 5 nm, such a device with an active diameter of 47 μm demonstrates a record high 3-dB electrical-to-optical bandwidth, as high as 1 and 0.7 GHz, among all the reported high-speed visible LEDs under room temperature and 110 °C operation, respectively. TO-Can packaging with a lens is used to enhance the POF coupling efficiency. Very-high data rates of 5.5 and 5.8 Gbit/s are achieved over step index POF under nonreturn-to-zero and 4-pulse amplitude modulation, respectively. When the POF transmission distance reaches 50 m, there is degradation in the maximum data rate for both modulation schemes to 1.3 Gbit/s due to the dispersion and attenuation of the POF.

III-Nitride Based Cyan Light-Emitting Diodes with GHz Bandwidth for High-Speed Visible Light Communication

A large reduction (from 17 to 5 nm) is made in the thickness of the barrier layers in the multiple-quantum-well region of III-nitride-based cyan light-emitting diodes (LEDs) grown on patterned sapphire substrates. This is shown to lead to a simultaneous improvement in the modulation speed, differential quantum efficiency, and maximum output power of the LEDs under both room temperature and 110 °C operation. With our novel device structure, we achieve a moderate output power (1.7 mW) with a record high 3-dB electrical-to-optical (E-O) bandwidth (1 GHz). The over twofold enhancement in the E-O bandwidth (~1 versus ~0.5 GHz) compared with that previously reported visible LEDs can be attributed to the more uniform distribution of injected carriers within the MQW region and the aggressive downscaling of the thickness of the total active layer, which leads to a shortening of the spontaneous recombination time.

Condenser-free contrast methods for transmitted-light microscopy.

Phase contrast microscopy allows the study of highly transparent yet detail-rich specimens by producing intensity contrast from phase objects within the sample. Presented here is a generalized phase contrast illumination schema in which condenser optics are entirely abrogated, yielding a condenser-free yet highly effective method of obtaining phase contrast in transmitted-light microscopy. A ring of light emitting diodes (LEDs) is positioned within the light-path such that observation of the objective back focal plane places the illuminating ring in appropriate conjunction with the phase ring. It is demonstrated that true Zernike phase contrast is obtained, whose geometry can be flexibly manipulated to provide an arbitrary working distance between illuminator and sample. Condenser-free phase contrast is demonstrated across a range of magnifications (4–100×), numerical apertures (0.13–1.65NA) and conventional phase positions. Also demonstrated is condenser-free darkfield microscopy as well as combinatorial contrast including Rheinberg illumination and simultaneous, colour-contrasted, brightfield, darkfield and Zernike phase contrast. By providing enhanced and arbitrary working space above the preparation, a range of concurrent imaging and electrophysiological techniques will be technically facilitated. Condenser-free phase contrast is demonstrated in conjunction with scanning ion conductance microscopy (SICM), using a notched ring to admit the scanned probe. The compact, versatile LED illumination schema will further lend itself to novel next-generation transmitted-light microscopy designs. The condenser-free illumination method, using rings of independent or radially-scanned emitters, may be exploited in future in other electromagnetic wavebands, including X-rays or the infrared.

Thermal management of edge-lit wide color gamut backlight for LCD using red laser diodes and cyan LEDs

The color gamut is one of the critical parameters that dictate the image quality of displays. The liquid crystal displays using white color light-emitting diodes (LEDs) as the backlight, though having been widely employed recently, are not very satisfactory in terms of their color gamut because of the broad spectrum inherent to white LEDs. This prompted the authors to develop improved liquid crystal displays using an edge-lit wide color gamut backlight that used red laser diodes and cyan LEDs. Generating laser beams with high color purity, the laser diodes are light sources with a significant effect on expanding the color gamut. However, laser diodes, red ones in particular, have unfavorable thermal characteristics. To cope with this shortcoming, the authors clearly defined the restrictive criteria for laying out two kinds of light source on the edge-lit backlight and made a prototype 55-type laser backlight for performance evaluation.

GaN-Based Miniaturized Cyan Light-Emitting Diodes on a Patterned Sapphire Substrate With Improved Fiber Coupling for Very High-Speed Plastic Optical Fiber Communication

We demonstrate the performance of a novel cyan light-emitting diode (LED) on a patterned sapphire (PS) substrate as a light source for plastic optical fiber (POF) communications with the central wavelength at 500 nm. To further enhance the external quantum efficiency (EQE) and output power of this miniaturized high-speed LED, a LED with a PS substrate is adopted. Furthermore, by greatly reducing the number of active <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\hbox{In}_{\rm x}\hbox{Ga}_{1 - {\rm x}}\hbox{N/GaN}$</tex></formula> multiple quantum wells (MQWs) to four and minimizing the device active area, we can achieve a record-high electrical-to-optical (E–O) bandwidth (as high as 400 MHz) among all the reported high-speed visible LEDs under a very small dc bias current (40 mA). The fiber coupling efficiency has been improved in 4 dB using lens with a 500- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu \hbox{m}$</tex></formula> diameter mounted on the LED chip. Thus, the maximum fiber-coupled power was <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-$</tex></formula> 2.67 dBm at the bias current of 40 mA. The 1.07-Gb/s data transmissions over a 50-m SI-POF fiber have been successfully demonstrated using this device at the bias current of 40 mA.

Non-emissive plastic colour filters for fluorescence detection

We report the fabrication of non-emissive short- and long-pass filters on plastic for high sensitivity fluorescence detection. The filters were prepared by overnight immersion of titania-coated polyethylene terephthalate (PET) in an appropriate dye solution - xylene cyanol for short-pass filtering and fluorescein disodium salt for long-pass filtering - followed by repeated washing to remove excess dye. The interface between the titania and the dye molecule induces efficient quenching of photo-generated excitons in the dye molecule, reducing auto-fluorescence to negligible values and so overcoming the principal weakness of conventional colour filters. Using the filters in conjunction with a 505 nm cyan light-emitting diode and a Si photodiode, dose-response measurements were made for T8661 Transfluosphere beads in the concentration range 1 × 10(9) to 1 × 10(5) beads μL(-1), yielding a limit of detection of 3 × 10(4) beads μL(-1). The LED/short-pass filter/T8661/long-pass filter/Si-photodiode combination reported here offers an attractive solution for sensitive, low cost fluorescence detection that is readily applicable to a wide range of bead-based immunodiagnostic assays.

Optimal Illuminance of Seven Major Lighting Colours in LED: Focus on Occupant Comfort and Communication in an Indoor Environment

This study aims to evaluate the optimal illuminance for each lighting colour of light-emitting diode (LED) light sources among the seven major lighting colours (red, green, blue, cyan, magenta, yellow and white); the focus was on the optimal combination of these colours for enhancement of occupant comfort and communication indoors. The evaluation of optimal illuminance for LED lighting colours found that the occupants felt the cyan LED light source was similar to a white light source, and that the relative brightness of the green lighting colour was higher than that for other colours. The evaluation of the permissible range of illuminance for LED lighting colours found that occupants believed the red lighting colours to be relatively darker; again, the relative brightness of green lighting was considered to be higher. An experiment with subjects for LED lighting colours (consisting of 19 patterns of 7 colours in the living room of a house) found that the optimal illuminance for occupants’ comfort was 32[lx]–119[lx], and for occupants’ communication was 107[lx]–584[lx]. These results satisfied the illuminance criteria of Korean Standards as the optimal illuminance for occupants’ comfort and communication in the living room.

A compact LED-based module for DNA capillary electrophoresis

A setup consisting of a bifurcated optical fiber made from high-transmission fused-silica cores with relatively high numerical apertures (NA=0.22), high-power cyan light-emitting diodes (LEDs) and Peltier cooling elements controlled by a proportional–integrative–derivative (PID) module is introduced to replace bulky, power- consuming lasers conventionally used in laser induced fluorescence (LIF) microchip capillary electrophoresis (μCE). The output fiber beam size, divergence, power distribution and power stability over time are documented. A modified epifluorescence microscope arrangement is used in conjunction with a compact fixed spectrometer aligned with a cooled charge-coupled device (CCD) camera for added sensitivity. Fluorescent dyes such as fluorescein, 6-carboxyfluorescein (6-FAM) and rhodamine B can be detected in cyclic olefin copolymer (COC) and glass microchannels at submicromolar levels. A single-stranded DNA oligonucleotide (10-mer) labeled with 6-FAM is also detected with reasonable signal-to-noise ratio when electrophoretically migrated at 100 V/cm. The compact LED excitation system presented herein will allow using capillary electrophoresis for DNA detection in compact mobile devices.

Structural and Electroluminescence Characteristics of Nonpolar Light-Emitting Diodes Fabricated on Lateral Epitaxially Overgrown a-Plane GaN

We report on the structural and electroluminescence characteristics of blue and cyan a-plane InGaN/GaN light-emitting diodes (LEDs). Cross-sectional transmission emission microscopy revealed the generation of occasional “asymmetric V-defects” in the active region. The blue and cyan LEDs exhibited rectifying behavior with forward voltages of 2.4 and 3.5 V at 20 mA, respectively and series resistances of 7 and 8 Ω, respectively. On-wafer dc output powers as high as 1.8 and 1.0 mW were measured at a drive current of 300 mA for the blue and the cyan LEDs, respectively. Electroluminescence measurement revealed an initial blue shift in the emission wavelength with the increase in the drive current. We speculate that the emission wavelength shift is due to the band-filling effect as a result of localization in the inclined non-{1120} oriented facets, which are polar in nature.