Efficient distributed control of light-emitting diode array lighting systems

We consider illumination rendering with distributed control of a lighting system with an array of light-emitting diodes (LEDs). As low-cost microprocessors become standard components in LED drivers, distributing the computation of the control signals to individual LED drivers becomes attractive. Common distributed control algorithms require each individual controller to exchange information with all the others and process it. This incurs too large a communication and processing overhead for a low-cost local controller. In this Letter, we propose a distributed control algorithm for achieving global illumination rendering, wherein a controller only needs to communicate within a selected neighborhood. We present design criteria for defining the communication neighborhood and study its impact on rendering performance.     

Invention,development, and status of the blue light-emitting diode,the enabler of solid-state lighting

The realization of the first high-brightness blue-light-emitting diodes (LEDs) in 1993 sparked a more than twenty-year period of intensive research to improve their efficiency. Solutions to critical challenges related to material quality, light extraction, and internal quantum efficiency have now enabled highly efficient blue LEDs that are used to generate white light in solid-state lighting systems that surpass the efficiency of conventional incandescent lighting by 15–20×. Here we discuss the initial invention of blue LEDs, historical developments that led to their current state-of-the-art performance, and potential future directions for blue LEDs and solid-state lighting.     

可调色红光有机电致发光器件

介绍了具有可调节发光光谱的高效红光有机发光二极管(OLED)器件,利用具有高三重态能量的9.9-螺二芴二苯基氧化磷(SPPO1)作为发光层的主体材料及空穴阻挡层,二(1-苯基异喹啉)(乙酰丙酮)合铱(III) (Ir(piq)2(acac))作为客体发光材料,在发光层内SPPO1的能量分别由福斯特和迪克斯特传递到Ir(piq)2(acac)的单重态和三重态从而发出红色磷光,通过调节磷光客体材料的比例得到最优器件结构,从而得到具有较好发光效率和发光亮度并可调节色纯的有机发光二极管器件。     

Non-doped-type white organic light-emitting diodes for lighting purpose

We demonstrate a non-doped white organic light-emitting diode (WOLED) in which the blue-, green- and red-emissions are generated from 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl, tris(8-hydroxyquinoline)aluminum (Alq) and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyl-julolidyl 9-enyl)-4H-pyran (DCJTB), which is used as an ultrathin layer. The DCJTB ultrathin layer plays the chromaticity tuning role in optimizing the white spectral band by modulating the location of the DCJTB ultrathin layer in the green emissive Alq layer. The optimized WOLED gives the Commission Internationale de l’Eclairage-1931 xy coordinates of (0.319, 0.335), a color rendering index of 91.2 at 10 V, a maximum brightness of 21010 cd/m² at 12 V and a maximum current efficiency of 5.17 cd/A at 6.6 V. The electroluminescence mechanism of the white device is also discussed.     

Phosphor-converted light-emitting diode based on ZnO-based heterojunction

A phosphor-converted light-emitting diode (LED) was realized by coating BaMg₂Al₁₆O₂₇:Eu²⁺·Mn²⁺ and (SrCaPO₄)·B₂O₃:Eu²⁺·Na⁺ phosphors onto an n-ZnO/i-MgO/p-GaN heterojunction diode. Two emission bands at around 450 and 520 nm were observed in the phosphor-converted LED under the injection of continuous current. By analyzing the optical properties of the heterojunction diode and phosphors, it is concluded that the emission at 450 nm comes from (SrCaPO₄)·B₂O₃:Eu²⁺·Na⁺ phosphor, while the one at 520 nm comes from BaMg₂Al₁₆O₂₇:Eu²⁺·Mn²⁺ phosphor under the excitation of the light emitted from the n-ZnO/i-MgO/p-GaN heterojunction diode. The results reported in this paper may provide a route to ZnO-based phosphor-converted LEDs for future lighting or displaying purpose.     

The Monte-Carlo model of a light-emitting diode

The first complete Monte-Carlo model of a surface light-emitting diode is presented in this paper. In the model all important phenomena (including the two-dimensional diffusion of minority carriers before their recombination in the active region and the re-emission of radiation) are taken into account. The influence of various construction parameters on the external quantum efficiency of the homojunction GaAs diode is examined.     

Flexible Ag electrode for quantum dot light-emitting diode

In this paper, we have fabricated quantum dot light-emitting diode (QD-LED) based on silver (Ag) electrode. The QD-LED with Ag electrode is demonstrated with decreased leakage current, improved luminous efficiency, low turn-on voltages, and saturated emission exhibiting the Commission Internationale de l’Enclairage coordinates of (0.59, 0.40). Meanwhile, compared to the QD-LED with indium tin oxide-coated polyethylene terephthalate electrode, the electroluminescence intensity was enhanced twice for QD-LED based on Ag electrode, and turn-on voltage was reduced to 4.7 V, which was attributed to the higher conductivity and better transmission of Ag electrode.     

A light-emitting diode fabricated from horse-heart cytochrome c

We have fabricated a light-emitting diode from horse-heart cytochrome c and measured the electro-luminescence (EL) spectra. The spectra exhibit broad peaks around 530 and 690 nm, and a weak shoulder around 410 nm. The EL spectra are completely different from the photo-luminescence spectra previously reported. The appearance of the 690 nm emission band suggests the charge-transfer between the iron and the axial methionine ligand plays a crucial role in the electrical conduction in the cytochrome c film.     

Aluminum nitride substrates for ultraviolet light-emitting diode structures

Currently, wafers of aluminum nitride cut from bulk aluminum nitride crystals (AlN) grown by sublimation are considered promising substrates for obtaining light-emitting diode structures based on nitrides of the third group. In this study, the structural characteristics and electrical properties of AlN, as a prospective substrate material for light-emitting diode heterostructures based on AlGaN/GaN, were investigated. The substrate working surface ((0001) plane, Al-polar) was specifically prepared for epitaxial growth using chemical-mechanical polishing. The surface roughness (“epi-ready”), as estimated by atomic force microscopy, did not exceed 0.3 nm.     

Study on electroluminescence from porous silicon light-emitting diode

Porous silicon (PS) light-emitting diode (LED) with an ITO/PS/p-Si/Al structure was fabricated by anodic oxidation method. Photoluminescence (PL) of the PS LED was measured with a peak at 593 nm, and electroluminescence (EL) was measured with a peak at 556 nm under the conditions of 7.5-V forward bias and 210-mA current intensity. The spectral width of EL was measured to be about 160 nm.     

Lensless digital holographic microscope with light-emitting diode illumination

We demonstrate the operation of a digital in-line microscope with LED illumination. We show with a practical example that, for typical setups, the limited temporal coherence and the spatial incoherence of the source do not affect the resolving power of the system. On the contrary, important advantages are obtained in terms of signal-to-noise ratio and alignment simplification.     

Indistinguishable entangled photons generated by a light-emitting diode

A linear optical quantum computer relies on interference between photonic qubits for logic, and entanglement for near-deterministic operation. Here we measure the interference and entanglement properties of photons emitted by a quantum dot embedded within a light-emitting diode. We show that pairs of simultaneously generated photons are entangled, and indistinguishable from subsequently generated photons. We measure entanglement fidelity of 0.87 and two-photon-interference visibility of 0.60 ± 0.05. The visibility, limited by detector jitter, could be improved by optical cavity designs.     

Improving organic light-emitting diode performance with patterned structures

The influence nano- and micro- structures on light extraction and carrier injection characteristics in organic light-emitting diodes (OLEDs) is examined. The results demonstrate device enhancement from two distinctive patterning scales: embedded microstructure arrays for improved light extraction and imprinted nanostructures for carrier injection enhancement. Further, based on these results, a two-level imprinting stamp is designed which simultaneously produces a micron-sized pattern for facilitating light extraction and a nanometer-sized pattern to improve carrier injection. Additionally, this scalable patterning technology circumvents imprinting misalignment while preserving its compatibility with rollto- roll technology.     

Analytical model of light-emitting diode with patterned contact

In this paper we develop an analytical model for the light-emitting diode (LED) with the metal p-contact patterned as an array of thin strips. The model is based on conformal mapping approach and accounts for the overlapped fringing electric fields created by the adjacent strips. We derive analytical expressions for the electric potential, current injected into the LED active region and power of light extracted via the openings in the pattern. Spatial distribution of electric potential and LED radiation pattern are calculated. Further investigations are necessary to elucidate the contribution of the side walls of the strips on the LED output performance.     

Cascaded deep ultraviolet light-emitting diode via tunnel junction

The Al Ga N-based deep ultraviolet(DUV) light-emitting diode(LED) is an alternative DUV light source to replace traditional mercury-based lamps. However, the state-of-the-art DUV LEDs currently exhibit poor wall-plug efficiency and low light output power, which seriously hinder their commercialization. In this work, we design and report a tunnel-junctioncascaded(TJC) DUV LED, which enables multiple radiative recombinations within the active regions. Therefore, the light output power of the TJC-DUV LEDs is more than doubled compared to the conventional DUV LED. Correspondingly, the wall-plug efficiency of the TJC-DUV LED is also significantly boosted by 25% at 60 m A.     

Spatially correlated light emission from a resonant-cavity light-emitting diode

We present the angular-resolved intensity noise characteristics of a resonant-cavity light-emitting diode under quiet pumping conditions. Measurements by a sensitivity-enhanced lock-in amplifier detection scheme yielded a spatial anticorrelation between the intensity noise of the central and peripheral parts of the emitted far field. Proposals for possible explanations of this anticorrelation from a semiconductor emitter point of view and its consequences for applications in quantum optical imaging are discussed.     

Improved contrast polymer light-emitting diode with optical interference layers

An improved contrast polymer light diode based on the destructive optical interference layers deposited between the glass substrate and ITO anode is fabricated. It is unnecessary to be considered that the additional optical interference structure will impede carrier injection from the electrode to the carrier-transporting layer. Due to the quarter-wavelength thickness of medial ITO layer, the reflected light from first Cr layer is inverted 180° out of phase with the reflected light from second Cr layer, resulting in the destructive interference. It is evident that the contrast ratio of the device with the optical interference structure is about three times higher than that of the conventional device.     

Microlens array diffuser for a light-emitting diode backlight system

Microlens array (MLA) diffusers for light-emitting diode (LED) backlight systems have been developed. A high fill-factor photoresist mold for the MLA was fabricated using three-dimensional diffuser lithography, and the patterns were transferred to a nickel master mold for UV-curable polymer replication. The fabricated microlens had various paraboloidal profiles, and its aspect ratio was controlled from 1.0 to 2.1. The MLA diffuser showed a batwing radiation pattern with a radiation angle of 150 degrees. The fabricated MLA diffuser may greatly enhance the color-mixing characteristics of LED backlight systems and help reduce the number of LEDs required.     

The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

The scalability of the tunnel-regenerated multi-active-region （TRMAR） structure has been investigated for the application in light-emitting diodes （LEDs）. The use of the TRMAR structure was proved theoretically to have unique advantages over conventional slngle-active-layer structures in virtually every aspect, such as high quantum efficiency, high power and low leakage. Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.