Blue Light: A Fascinating Journey (Nobel Lecture)

Akasaki, Isamu

doi:10.1002/anie.201502664

Cited by 32 publications

(17 citation statements)

References 62 publications

(157 reference statements)

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“…1 H NMR was recorded with a Varian Gemin-400 or -300 spectrometer. Specific details of the new compounds' synthetic routes are summarized in ESI.…”

Section: Synthetic Proceduresmentioning

confidence: 99%

“…7b) of 4.16 cd A -1 and 5.15%, while the corresponding efficiencies for the 25BTPIPy-based device were 6.22 cd A -1 and 4.72% respectively. Theoretically, the EQE of a device can describe as, EQE = γ η out ϕ PL η r (1) where γ is recombination efficiency of hole and electron carriers, η out is the light out-coupling efficiency and η r is the ratio of radiative exciton. This EL emission with peak at 440 nm showed no observable change from 3 to 8 V (Fig 7c).…”

Section: Electroluminescent Propertiesmentioning

confidence: 99%

“…1 Among emitters of all colors, blue emitter has the widest energy gap, 2 especially deep-blue emitters often possess energy gaps > 3 eV. 1 Among emitters of all colors, blue emitter has the widest energy gap, 2 especially deep-blue emitters often possess energy gaps > 3 eV.…”

Section: Introductionmentioning

confidence: 99%

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A pyridine based meta-linking deep-blue emitter with high conjugation extent and electroluminescence efficiencies

et al. 2016

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We designed and synthesized a bipolar deep-blue emitter 2,6-bis(4-(1-(4-(tert-butyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)pyridine (26BTPIPy) based on a meta-linking D-π-A-π-D stucture. Comparing to its para-linking analogue (25BTPIPy), the meta-linking in 26BTPIPy effectively shortens molecular conjugated length and restricts intramolecular charge transfer. Interestingly, unlike most other meta-linking emitters, a high fluorescent yield can be maintained in 26BTPIPy. This may be attributed to a relatively planar structure at the benzenepyridine-benzene joint in 26BTPIPy leading to considerable overlapping of its frontier molecular orbitals. These suitable combination in properties endow 26BTPIPy with efficient deep-blue emission and good bipolar carrier tranporting characteristics. An organic lightemitting device using 26BTPIPy as emitter shows a low turn-on voltage (2.8 V), deep-blue emission with color index of (0.15, 0.09) and high current and external quantum efficiencies (4.16 cd A -1 and 5.15%). Besides, a bilayer device using 26BTPIPy as both emitting and electron-transporting material also gives high performance with current efficiency of 4.22 cd A -1 and color purity of (0.15, 0.11).

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“…1 H NMR was recorded with a Varian Gemin-400 or -300 spectrometer. Specific details of the new compounds' synthetic routes are summarized in ESI.…”

Section: Synthetic Proceduresmentioning

confidence: 99%

Section: Electroluminescent Propertiesmentioning

confidence: 99%

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A pyridine based meta-linking deep-blue emitter with high conjugation extent and electroluminescence efficiencies

et al. 2016

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“…In 1986, pioneering work of the low-temperature buffer layer technology enabled breakthroughs in the growth of high-quality semiconductor crystals, which led to the realization of p-type conductivity in for example, GaN, and consequently the invention of the world's first GaN p-n junction blue/ultraviolet LED [16]. As a result of the improvements of growth technologies for the fabrication of high-quality single crystals, ZnO gained renewed interest and the number of published paper increased more significantly than in the past, as shown in Figure 1.…”

Section: Nanoscience and Nanotechnologymentioning

confidence: 99%

Evaluation of zinc oxide nano-microtetrapods for biomolecule sensing applications

Zhao

Karlsson³

et al. 2015

SPIE Proceedings

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Zinc oxide (ZnO) is a well-known II-VI semiconductor material that has gained renewed interest in the past decade due to the developments of growth technologies and the availability of high-quality ZnO bulk single crystals. Owing to a wide direct band gap (3.37 eV), large exciton binding energy (60 meV), and high electron mobility (440 cm 2 V -1 s -1 ),ZnO has been used for applications including actuators, optoelectronics, and sensors. ZnO nanoparticles can be synthesized in a broad variety of morphologies, such as nanotetrapods, nanotubes, and nanowires. Among these nanostructures, the tetrapods have attracted significant attention due to their unique morphology consisting of four legs connected together in a tetrahedral symmetry. Recently, it has been reported that nano-microstructuredZnO tetrapods (ZnO-Ts) can be synthesized by flame transport synthesis (FTS) in a rapid and up-scalable approach. Compared to conventional ZnO nanoparticles, the nanomicrostructured ZnO-Ts can reduce cellular uptake, while still exhibiting specific nanomaterial properties due to the nanoscale tips. Moreover, the anisotropic ZnO-Ts have the advantages of multiple electron transfer paths, chemical stability, and biocompatibility, which make the ZnO-Ts promising candidates for biomolecule sensing applications.This work herein reports a systematical study on the structural, optical and electrochemical properties of the ZnO-Ts, which were synthesized by FTS using precursor Zn microparticles. The morphology of the ZnO-Ts was confirmed by scanning electron microscopy (SEM) as joint structures of four single crystalline legs, of which the diameter of each leg is 0.7-2.2 μm in average from the tip to the stem. The ZnO-Ts were dispersed in glucose solutions to study the photoluminescence as well as photocatalytic activity in a mimicked biological environment. The photoluminescence (PL) intensity in the ultraviolet (UV) region decreased with linear dependence on the glucose concentration up to 4 mM.The ZnO-Ts were also attached with glucose oxidase (GOx) and over coated with Nafion ® to form the active media for electrochemical glucose sensing. The active layers were confirmed by Fourier transform infrared spectroscopy (FT-IR). Furthermore, the current response of the active layers to glucose was studied by cyclic voltammetry (CV) in various glucose concentration conditions. Stable current response to glucose was detected with linear dependence on the glucose concentration up to 12 mM, which confirms the potential of ZnO-Ts for biomolecule sensing applications.

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“…Gallium nitride‐based light‐emitting diodes (LEDs) have revolutionized lighting systems and rapidly superseded traditional lighting technologies such as fluorescent and incandescent lamps due to their unique benefits such as low energy consumption, high power‐conversion efficiency, and a long lifetime . Although GaN LEDs exhibit excellent internal quantum efficiency due to the continuous improvements in the GaN epitaxial layer quality, the light trapping due to the total internal reflection (TIR) still limits the light extraction efficiency (LEE) of GaN.…”

Section: Introductionmentioning

confidence: 99%

3D Hierarchical Indium Tin Oxide Nanotrees for Enhancement of Light Extraction in GaN‐Based Light‐Emitting Diodes

Park

Kim

Kang

et al. 2016

Advanced Optical Materials

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the GaN epitaxial layer quality, [8] the light trapping due to the total internal reflection (TIR) still limits the light extraction efficiency (LEE) of GaN. This is caused by the abrupt change in the refractive indices across the interface between GaN (n = 2.5) and the sapphire substrate (n = 1.8) or air (n = 1).Many approaches have been suggested for mitigating the TIR effect such as, surface texturing, [9][10][11][12][13] antireflection (AR) coatings, [14][15][16] and photonic crystal structures. [17,18] The top-down surface texturing techniques using dry or photoelectrochemical etching have demonstrated nearly twofold enhancement in the light output power (LOP). [19] However, these etching techniques have innate limitations for use in lateral LEDs because the top p-GaN layer is so thin (typically less than 200 nm) that the etching process for p-GaN must be exactly controlled to avoid degradation of the GaN LEDs. Therefore, bottom-up approaches such as AR coatings with graded refractive index [20] or photonic crystal structures [21] are typically utilized in the lateral LEDs.ZnO nanostructures are one of the most intensively investigated materials that are integrated on the surface of the LEDs for reducing the TIR without compromising the electrical properties. Various morphologies of ZnO nanostructures such as, nanorods (NR), nanowires, and hierarchical 3D nanostructures, typically grown by a hydrothermal technique, were suggested for enhancing the LEE of GaN LEDs. [22][23][24][25] Although the effective refractive index (n air = 1 < n < n ZnO_bulk = 2.0) of Recently, 3D nanostructures have attracted much interest because of their interesting electrical/optical properties such as wave guiding modes, light scattering, antireflection effects, etc. In this work, a facile yet efficient method for the fabrication of hierarchical 3D indium tin oxide (ITO) nanotrees (NTs) and their integration in GaN-based blue-light-emitting diodes (LEDs) for efficient light-extraction are reported. The ITO NTs are fabricated by the obliqueangle (≈85°) deposition method at 240 °C using electron-beam evaporation. The ITO NTs grow via a self-catalytic vapor-liquid-solid mechanism with the branches having an epitaxial relationship with the trunks. The ITO NTs successively deposited on an ITO thin film as a p-contact layer are annealed at 600 °C for 1 min under ambient air in order to form a transparent ohmic contact. The indium gallium nitrde/gallium nitride (InGaN/GaN) LED with ITO NTs presents a 29.5% enhancement in the light output power at an injection current of 20 mA, compared to the reference LED with an ITO thin film p-contact. This enhancement is ascribed to the effective light extraction of the ITO NTs due to to the gradually decreasing profile of the refractive index from 2.08 (ITO thin film), 1.15 (dense ITO NTs), 1.06 (porous ITO NTs) to 1.0 (air). These results are in good agreement with the optical simulation by the COMSOL wave optics module.Figure 7. Light beam profile images of a) the reference and b) ITO-NT-integrate...

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Blue Light: A Fascinating Journey (Nobel Lecture)

Cited by 32 publications

References 62 publications

A pyridine based meta-linking deep-blue emitter with high conjugation extent and electroluminescence efficiencies

A pyridine based meta-linking deep-blue emitter with high conjugation extent and electroluminescence efficiencies

Evaluation of zinc oxide nano-microtetrapods for biomolecule sensing applications

3D Hierarchical Indium Tin Oxide Nanotrees for Enhancement of Light Extraction in GaN‐Based Light‐Emitting Diodes

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