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Volume 9 Issue 05May 2015Matthias Müller

Thomas Jüstel

GrapheneThe Future of Everything?

Research & Development

Latest Journals

Novel Patents

Idee: Prof. Dr. rer. nat.Thomas Jüstel Redaktion: Matthias Müller Kontakt: [email protected]

Research & Development ....................................................................................................................... 1

Plasmonic Nanodiscs Boost 2-D Material’s Light Emission ........................................................... 1

Graphene light bulbs: what's the secret sauce? ................................................................................ 2

Shuji Nakamura: GaN-on-GaN Will Become the Next Generation LED Technology ................... 5

New highs for the LED .................................................................................................................... 9

Ultraschnelle Photodetektoren mit Graphen .................................................................................. 11

Latest Journals ...................................................................................................................................... 12

Bright White-Emitting Phosphors Ba2Gd(BO3)2Cl:Dy3+/Dy3+-Tm3+ for Hg-Free Lamps and White LEDs Applications .............................................................................................................. 12

Preparation and luminescence properties of Sr7Zr(PO4)6:Dy3+ single-phase full-color phosphor . 12

Highly Bright Yellow-Green-Emitting CuInS2 Colloidal Quantum Dots with Core/Shell/Shell Architecture for White Light-Emitting Diodes .............................................................................. 13

CdSe Quantum dot-conducting polymer hybrid structure for Phosphor-free white light-emitting diodes.............................................................................................................................................. 13

Synthesis and Characterization of Novel Nitride Phosphors Ca5Si2N6:Eu2+/Ce3+ ......................... 14

Novel Patents ......................................................................................................................................... 15

Yellow-emitting phosphor and white light-emitting element having it ......................................... 15

Bluish green emitting phosphor for white light emitting diode and white led device using it ...... 15

White LED chip including a tunneling structure formed by metal oxide layers, metal nitride layers and/or metal oxynitride layers, and white LED packaging device ...................................... 16

New nitridoalumosilicate phosphor for solid state lighting ........................................................... 16

Solar simulator based on UV-LED/phosphors ............................................................................... 17

Wordsearch............................................................................................................................................ 18

Volume 9 Issue 05 May 2015

Research & Development

Plasmonic Nanodiscs Boost 2-D Material’s Light Emission

Silver nanodiscs on monolayer molybdenun disulfide. Courtesy of Northwestern University. Augmenting molybdenum disulfide with plasmonic nanodiscs transforms the 2-D material into a promising light emitter. Researchers at Northwestern and Arizona State universities have found that a periodic array of 130-nm silver discs on top of a sheet of MoS2 enhances the semiconductor’s light emission as much as 12 times. The use of nanostructures instead of a continuous film allows the material to retain its flexibility. “We have known that these plasmonic nanostructures have the ability to attract and trap light in a small volume,” said Northwestern postdoctoral researcher Serkan Butun. “Now we’ve shown that placing silver

nanodiscs over the material results in 12 times more light emission.” The effect stems “from the fact that plasmonic resonance couples to both excitation and emission fields and thus boosts the light-matter interaction at the nanoscale,” the researchers wrote in Nano Letters (doi: 10.1021/acs.nanolett.5b00407). Similar engineering of other 2-D materials could lead to a new breed of photodetectors, sensors and photovoltaic devices, they said. Monolayer MoS2 is strong, lightweight and flexible, making it a good candidate for applications such as flexible electronics. But on its own, the material has very little interaction with light, limiting its use in light-emitting and -absorbing applications. “The problem with these materials is that they are just one monolayer thick,” said Northwestern professor Dr. Koray Aydin. “So the amount of material that is available for light emission or light absorption is very limited. In order to use these materials for practical photonic and opto-electric applications, we needed to increase their interactions with light.”

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Graphene light bulbs: what's the secret sauce? Claims that a University of Manchester spin-out will be selling graphene-enabled efficient LED bulbs within months look optimistic at best.

The simple structure of graphene belies some remarkable physical properties, many of which look like they will prove to be valuable in optics and photonics products of the future. Exactly what function the two-dimensional monolayer material performs in the bulbs developed by Manchester's National Graphene Institute remains a mystery for now. This week’s announcement from the University of Manchester that a spin-out company would soon be manufacturing new and more efficient light bulbs incorporating graphene has generated plenty of media coverage – even attracting the attention of BBC News and the Financial Times. In part, that’s because although the two-dimensional form of carbon and its remarkable physical properties would seem to have much to offer the commercial world, there’s very little yet in the way of genuine graphene products. And that’s not at all surprising. Such fundamental scientific breakthroughs can take a long time to come to fruition outside of the laboratory. In the world of optics, we only

have to look at the example provided by lasers. Once a solution looking for a problem, they are now indispensable. Right now graphene seems to be at that awkward, in-between stage. Discovered just over a decade ago, by University of Manchester scientists, in technological terms it remains very young. But with the large sums of money being invested in graphene development - £61 million in Manchester’s National Graphene Institute (officially opened by UK Chancellor George Osborne in March) and a remarkable €1 billion via the European Commission’s decade-long flagship research project - there will inevitably be growing pressure to realize tangible economic benefits. Zero technical details Taken at face value, this week’s light bulb announcement seems to be exactly the kind of thing that everybody is hoping for: scientific endeavor turned into technological, economic and societal benefit in the form of cheaper, more efficient lighting that may help cut fuel bills and carbon dioxide emissions. Within months, we’re told, these new light bulbs will be on the shelves. On closer inspection, there is precious little to report. The University of Manchester is certainly keeping its cards close to its chest, giving precisely zero details about how its graphene-enabled LED bulbs perform in terms of standard industry metrics like lumen output, efficacy, white-light characteristics or color rendering properties. It won’t even say precisely what function the graphene in its bulbs actually performs. “Due to commercial confidentiality it is difficult to give any technical details at this stage,” claims Colin Bailey. No less a figure than the University of Manchester’s deputy

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vice-chancellor, he has provided the public face of the graphene light bulb development. Commercial confidentialities are of course very real, but it is also rare to witness such reticence to answer simple questions. Faced with a complete absence of technical information, media reports have run with vague suggestions that the graphene bulb will be 10 per cent more efficient than existing technology and cost less than $15 to buy. But such comparisons are meaningless without detailing exactly what the bulb is producing or the energy it consumes – a light bulb might look simple enough, but making an accurate and meaningful measurement of the light that it emits and how efficiently it does that most certainly isn’t. The cost of today’s LED bulbs also varies wildly, largely according to brightness and quality, but even high-quality examples from the likes of Cree (two years ago) and Philips are already priced well below $15. Graphene Lighting PLC What little we do know relates to the spin-out company that has been set up to commercialize the bulbs, Graphene Lighting – although Manchester is less than keen to tell us much about that either. Registered with Companies House in the UK, Graphene Lighting recently changed its legal status to become a public limited company (PLC), ahead of a purported plan to float on the Canadian stock market. Bailey says that the start-up currently has an acting CEO and CFO (though he would not say who they are) and is working with the Canadian financial group Industrial Alliance Securities. “The first capital investment has been secured and we will be looking to float the company on the Canadian Stock Market in the future,” he told optics.org. “We have interviewed for a

permanent CEO and are in the process of making an appointment.” Thanks to Companies House documents, we know that among the directors of Graphene Lighting PLC is Chung-Ping Lai. Taiwanese national Lai is also the CEO of Bluestone Global Technology (BGT), a manufacturer of large-area graphene material that signed a £5 million collaborative research partnership with the University of Manchester in September 2013. BGT Materials Ltd, of which Lai is also CEO, is based at Manchester’s Photon Science Institute. According to company documents signed by Lai, Bluestone Global Technology Ltd changed its name to Graphene Lighting Ltd in November 2014, before becoming a PLC in late January. As of December 2014, Lai was listed as the sole director and the company had assets of a single pound. A more recent filing from mid-February lists 140,000 ordinary shares with a nominal value of $210,000. Heat or light? Graphene Lighting recently appointed another director, in the form of Ching-Yu Lu. Lu’s name appears on a couple of recent papers published by Manchester’s graphene researchers, including one collaboration with Bluestone and a team in California detailing the thermal properties of graphene-copper-graphene films. In that Nano Letters paper, they showed that a single atomic plane of graphene deposited on either side of a thin film of copper by chemical vapor deposition increased the thermal conductivity of the copper by as much as 24 per cent – although that has been attributed to changes in copper morphology during graphene deposition, rather than to the graphene itself. “Enhancement of thermal properties of graphene-capped copper films is important for thermal management of advanced electronic

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chips and proposed applications of graphene,” the authors wrote in their abstract, while on the BGT Materials web site the company says that graphene’s high electrical conductivity and transparency suggests future use as an electrode material in LED and organic LED applications. Whether those ideas have anything to do with the light bulbs that Bailey says Graphene Lighting is aiming to ramp to volume

production within months remains to be seen – or not. If that does come to pass, the “graphene LED bulbs”, as Bailey describes them, could lay genuine claim to be the first mass-produced graphene product. But with so little known about these bulbs, not least how, where and when they will be manufactured, right now it appears that the University of Manchester is generating far more promotional heat than high-efficacy light.

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Shuji Nakamura: GaN-on-GaN Will Become the Next Generation LED Technology

Left to right: Epistar Chairman B.J. Lee and Shuji Nakamura, Nobel Laureate in Physics and UCSB professor. (LEDinside) The upcoming LED technology will be GaN-on-GaN LEDs, affirmed Nobel Laureate in Physics Shuji Nakamura and fellow colleague at University of California, Santa Barbara (UCSB) Professor Steven DenBaars at an exclusive forum hosted by Taiwanese leading chip LED manufacturer Epistar on Wednesday at the company headquarters in Hsinchu, Taiwan. (For those unfamiliar with Nakamura’s rock star status in the LED and lighting industry, the bottom section of this article gives an overview of the birth of blue LEDs.)

Nakamura and DenBaars: Forget about GaN-on-Si LEDs! LED technology has rapidly developed since the first GaN on sapphire LEDs hit the market in the 1990s. Manufacturers have been raising the energy efficiency of GaN LEDs over the years, raising it to about 300 lm/w last year. However, the efficiency of GaN on sapphire is nearing a peak, as improvements in energy efficiency have gradually slowed in recent years. Droop remains the major technology challenge for GaN on sapphire and to overcome this, manufacturers would have to push droop to 100 to drive the sapphire five to six times harder, said DenBaars. In addition, sapphire costs has led LED manufacturers to search for alternative solutions. Two different technology approaches have emerged, one being GaN-on-Si to drive down LED costs, and the other GaN-on-GaN developed by UCSB research team, which aims to deliver higher performing LEDs. Responding to the future of GaN-on-Si LEDs, DenBaars said without hesitation: “I think it is a waste of time.” Analysis by Phlips Lumileds and Strategy Limited have indicated there was no cost advantage for it over GaN on sapphire LEDs, he explained. This view was also shared by Nakamura, who urged the industry to focus on GaN-on-GaN technology. “GaN-on-GaN, only one girlfriend,” he said. He also challenged industry experts to aim for the “ultimate technology.” GaN-on-Si material first emerged in the semiconductor industry in 1970s, but only a few LED manufacturers including Toshiba and Samsung are investing heavily in this technology. Silicon wafers cost less than

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sapphire, but high lattice mismatch between GaN and silicon result in higher defect density rates in epitaxal layers. Moreover, the substrates often bend, or warp in semiconductor language. GaN-on-Si wafers bend in the growth process as it cools down at room temperature because of the high thermal expansion coefficient (TCE) mismatch between GaN and silicon.[1] In the near future, GaN-on-Si might not be the solution for LEDs, but DenBaars envisioned the technology might have a good chance in drivers. This could be achieved through vertical integration manufacturing, said DenBaars, who’s research is also in high power devices. Power devices are often grown on silicon, added Nakamura.

Left to right: Epistar Chairman B.J. Lee and Shuji Nakamura, Nobel Laureate in Physics and UCSB professor. (LEDinside) GaN-on-GaN LEDs the future of LED technology Nakamura and DenBaars urged for GaN on sapphire manufacturers hitting the efficiency

ceiling to invest in GaN-on-GaN research, upholding this as the ultimate LED technology and the next viable option was laser (which we will address in a separate article). The advantages of GaN-on-GaN LEDs include its substrate structure and efficiency level. GaN substrates facilitation rates is much lower than GaN on sapphire, and its current density is five times higher than sapphire, said Nakamura. According to info published by Soraa, the company Nakamura and DenBaars co-founded, the LEDs have an efficiency closer to laser, which translates to lower droop than conventional LEDs. Costs is the biggest stumbling block for the development of GaN-on-GaN LEDs. GaN substrates are very expensive, and can be four to five times higher than sapphire, said DenBaars. To overcome this, the UCSB research team has been testing ammono-thermal technology to grow GaN crystals, but costs remain high. Instead costly Hydride Vapour Phase Epitaxy (HVPE) crystal growth methods are used, said Nakamura. Yet, Nakamura remained optimistic that ammono-thermal GaN crystal growth methods would be the answer to driving down substrate costs in the future, it would be possible to grow 4-inch, 6-inch and 8-inch GaN wafers in the future, added Nakamura. The research team is also testing growing GaN on different crystal planes to create semi-polar LEDs to see if it can drive down costs, said DenBaars. GaN-on-GaN is good for directional lighting applications where high brightness and density is required, such as MR16 LED lamps, explained Debaars. In the meantime, before GaN-on-GaN fully takes off, manufacturers are unlikely to ditch good old sapphire substrates because of the cost advantages it has over both silicon and GaN substrates.

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LiFi and UV LED might be industry next killer app Asked about the next major application for LEDs, the two LED experts did not pin point UV LEDs. Sure, UV LEDs would remain promising in the medical sterilization and detection industry, where there could be big area for growth, said DenBaars. The sector was, however, attracting a lot of competition as more manufacturer aim to join, he observed. As for UV technology barriers, UVC efficiency is very low, and there needs to be a big breaktrhough to reach better efficiency, explained DenBaars. LEDs in communication applications could be the next big thing, such as LiFi. In U.S., there has been 20 new LiFi startups over the past year, said DenBaars. Modulation has not been fast enough, but if LiFi picks up it could be a killer application. LiFi signals, which rely on LED light transmission, are known to be more secure than traditional WiFi signals. The future trend for LED technology will be in GaN-on-GaN from DenBaars and Nakamura’s perspective, and niche markets such as LiFi and UV LED might be the answer for manufacturers searching for a new direction.

All attendees at Epistar's exclusive forum featuring Professors Shuji Nakamura and Steven DenBaars. (LEDinside) Birth of blue LED walkthrough Nakamura started researching on GaN material in 1988, when he was a Nichia

Chemical employee. Back in the day, it was difficult to create high quality GaN crystals, since most of the industry thought it was not worthwhile to build a surface for GaN crystals. Even though GaN was recognized as a blue light material in the industry, it was considered nearly impossible to build p-type layers on the material[2]. DenBaars, who was working as a technical staff at Hewlett-Packard's Opkoelectroncis Division at the time, recalls LED expert George Craford, who was the division leader then, told him to drop GaN LEDs. Most experts in the LED industry were betting on II-VI semiconductor material, such as zinc selenium (ZnSe) at the time, explained DenBaars. To overcome some of these technical difficulties, Nakamura built two MOCVD equipment in 1990 to meet the challenge of creating high quality GaN. Eventually, he developed a GaN LED technique that was much more cost effective from Akasaki and Amano. The method he developed in 1992 was growing a thin layer of GaN at low temperature first, and growing subsequent layers at higher temperatures. By heating the GaN material Nakamura was able to create a functional P-type. In contrast, Professors Isamu Akasaki and Hiroshi Amano of Nagoya University, Japan, developed their first high-quality gallium nitride crystal in 1986 by growing high quality GaN on top of a layer of aluminium nitride on the sapphire substrate. They created a p-type layer by the end of the 1980s, and presented the first functional blue LED at around the same time as Nakamura. The three Japanese scientists’ breakthrough in gallium nitride (GaN) material broke a 30 year LED technology impasse of making highly efficient blue LEDs. By overcoming the GaN technology barrier, their work in blue LEDs finally paved the way for the emergence of white lights, which is created by mixing red, blue and green LEDs. This significantly broadened the application of LEDs, and brought LEDs from backlight applications to general lighting market. (For more info please see here.)

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In 2000, Nakamura resigned as head of Nichia R&D to become a professor at the College of Engineering at UCSB. Together with fellow UCSB professors DenBaars and Jim Speck, the three later went on to co-found LED company Soraa in 2008. DenBaars is a veteran in the LED industry, having accumulated extensive experience in fabrication of visible LEDs at HP from 1998-1991. He later received a NSF Young Investigator award in 1994, and the IEEE Fellow award in 2005. Working on the same research team as Nakamura, DenBaars research interests are in wide-bandgap semiconductors (GaN based), and application in blue LEDs, lasers and high power devices.

Since inventing the blue LED in 1993, Japanese media have been anticipating the day he would become a Nobel Laureate, said Nakamura. They had been waiting on his doorsteps patiently for 20 years for the announcement.It was not until 2014 that Nakamura, Akasaki and Amano was jointly awarded a Nobel Prize in Physics for their invention of blue LEDs. For some reason, the Nobel Prize Committee made no mention about InGaN, noted Nakamura. “I was actually very depressed when they announced the prize because they made no mention of InGaN,” said Nakamura. InGaN was the key to making high efficiency LEDs, he added.

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New highs for the LED

Soraa claims that its LEDs set new benchmarks for generating and extracting light

A scanning electron microscope image of the triangular volumetric flip-chip device produced by Soraa. This LED has an extraction efficiency of 90 percent and a peak internal quantum efficiency of 95 percent. Soraa claims to have broken the record for LED wall-plug efficiency for high current densities and temperatures found within a lighting fixture. The latest device has the ‘triangular volumetric’ design of its predecessors, but with the notable refinement of a flip-chip architecture that features both contacts on the same side of the device. “We show that our improved design is superior across the line – extraction, epitaxy, electrical efficiency – and thus better demonstrates the extremely high potential of GaN-on-GaN technology,” remarks Soraa’s Christophe Hurni. The West-coast outfit uses HVPE-grown GaN substrates as a foundation for its LEDs. According to Hurni, this platform provides many advantages over sapphire, silicon and SiC, including: better material quality, thanks to low-dislocation-density substrates; and

better light extraction for high-power-density LEDs. The latest triangular, volumetric LEDs emit at around 415 nm, have 400 µm-long sides, and have n- and p-type contacts on the bottom of the structure. Wall plug efficiency peaks at 84 percent at 25 °C, and is 70 percent at 100 A cm-2 – and this level of performance is maintained at 85 °C. Delivering high performance at this elevated temperature is crucial, argues Hurni. “Real-world lighting systems heat up during operation, and even with good heat-sinking, a junction temperature of 85 °C or above is common.” The team have evaluated all the factors that influence the wall-plug efficiency – it is the product of the package efficiency, extraction efficiency and internal quantum efficiency. The packaged efficiency, which is the ratio of photons emitted by the chip to those escaping the test package, is 94 percent, according to ray-tracing software. The package has not been optimised for the die, but there is actually little benefit in doing so, according to Hurni: “In practice, package efficiency only matters for phosphor-converted white light.” Efforts at Soraa have shown that extraction efficiency – the ratio of photons escaping the device to those radiated by the active region – is limited by thin-film LED architectures. A combination of surface roughness and chip shaping is able to increase the extraction efficiency of light of all trajectories, with advanced modelling by the team indicating an improvement of 10 percent over thin-film device structures. Comparisons of values from the light extraction model and experimental results on a series of chips suggest that the latest device has an extraction efficiency of 90 percent.

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The third factor governing the wall-plug efficiency is the internal quantum efficiency, and this is influenced by defects, active region design, current-density-induced droop and thermal effects. Using a native substrate helps to reduce some of these loss mechanisms, because the epilayers have fewer defects and there is greater freedom in the design of the structure. Measurements indicate that the internal quantum efficiency peaks at 95 percent at 25 °C and 92 percent at 85 °C. Droop is very

low, with the internal quantum efficiency still 85 percent at 85 °C and a current density of 100 A cm-2, a value that is representative of realistic operating conditions. The team has applied the well-known ABC model to plots of internal quantum efficiency as a function of current density. These simulations, which include phase-space filling effects, confirm the view held by those at Soraa that Auger scattering is the most plausible cause of droop.

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Ultraschnelle Photodetektoren mit Graphen

Wissenschaftler des europäischen Forschungsprojektverbundes "Graphene Flagship" entwickeln einen Photodetektor, der einfallendes Licht in Femtosekunden in elektrische Signale umwandelt. Damit könnten ultraschnelle elektronische Schaltungen zur optischen Kommunikation und verschiedener anderer Anwendungen realisiert werden.

Schematische Darstellung einer ultraschnellen Photospannungserzeugung nach Absorption von IR-Licht zwischen zwei Graphenbereichen mit unterschiedlichen Ferminiveaus Die Umwandlung von Licht in Strom ist Grundlage für eine Reihe von Technologien, Solarzellen, Digitalkameras und Kommunikation mittels optischer Fasern. Dabei ist die Betriebsgeschwindigkeit wesentlich. Bei der Photodetektion wird durch den photothermoelektrischen Effekt Strom erzeugt, wenn das einfallende Licht auf die Grenzfläche zwischen Graphenschichten mit unterschiedlichen Dotierungen fällt. Bei dem Prozess kommt es zur Anregung und Elektron-Loch-Paarbildung, gefolgt von der Ladungsträgererwärmung. Die Elektronen kühlen dann ab bis zum thermischen Gleichgewicht mit dem Atomgitter. Dies erfolgt auf der Pikosekunden-Zeitskala, die Schaltraten sind hierbei auf ein paar hundert

Gigahertz begrenzt. Eine viel schnellere Umschaltung im Terhertzbereich (entspricht Femtosekunden Dauer) kann durch effiziente Ladungsträgererwärmung erzielt werden. Hierfür forschen Wissenschaftler seit einiger Zeit mit Graphen als einem vielversprechendes Material für ultraschnelle Breitbandphotodetektoren, deren Leistungsfähigkeit von der Schaltgeschwindigkeit abhängt. Physiker am Institut für Photonische Wissenschaften (ICFO) in Barcelona arbeiten mit Kollegen in den USA und Spanien an der Entwicklung effizienter Ladungsträgererwärmung. Die Forscher konnten durch die Messung der Laserpulsdauer von 50 Femtosekunden zeigen, dass sich Photostrom mittels Graphen auf dieser Zeitskala erzeugen lässt. Die Energie der einfallenden Photonen wird bei diesem Material effizient in Ladunsgträgererwärmung umgewandelt, mit konstanter spektraler Empfindlichkeit zwischen VIS- und IR-Wellenlängenbereich von 500 und 1500 nm. "Graphene Photodetektoren zeigen faszinierende Leistung und Eigenschaften, so dass eine breite Palette von Anwendungen möglich wird", so ICFO Pro. Frank Koppens. Im Rahmen des Graphen Flagship-Programmes sollen Anwendungen wie multispektrale Bildgebung bis hin zur ultraschnellen Kommunikation entwickelt werden. "Graphene Flagship" ist ein internationales Forschungs-Industrie-Konsortium, teilfinanziert durch die Europäischen Kommission. Ziel ist die Entwicklung von Graphen und verwandter zweidimensionaler Materialien.

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Latest Journals

Bright White-Emitting Phosphors Ba2Gd(BO3)2Cl:Dy3+/Dy3+-Tm3+ for Hg-Free Lamps and White LEDs Applications Spectroscopic properties of Ba2Gd(BO3)2Cl: Dy3+ and Ba2Gd(BO3)2Cl: Dy3+, Tm3+ under vacuum ultraviolet (VUV) and ultraviolet (UV) light excitations were investigated. Dy3+ single-doped Ba2Gd(BO3)2Cl showed broad absorption band in the VUV region, and bright warm white light with chromaticity coordinates (CIE) of (0.340, 0.381) upon VUV excitation at 172 nm, demonstrating this phosphor's applicability in mercury free lamps. Upon direct excitation Tm3+ from its 6F6 level to 1D2 level, the decrease of emission intensity and lifetime of Tm3+ 1D2–3F4 emission with increasing concentration of Dy3+ in Ba2Gd(BO3)2Cl: Dy3+, Tm3+ confirmed the occurrence of energy transfer from Tm3+ to Dy3+. In addition, Ba2Gd(BO3)2Cl: Dy3+, Tm3+ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm3+. When 1% Tm3+ and 5% Dy3+ were codoped in the Ba2Gd(BO3)2Cl, intensive white-emitting light with CIE of (0.352, 0.328) and correlated color temperature of 4589 K was achieved upon 358 nm excitation, revealing the potential application of Ba2Gd(BO3)2Cl: Dy3+, Tm3+ for white light-emitting diodes (LEDs). J. Am. Ceram. Soc. 98 (2015) 1195-1200. DOI: 10.1111/jace.13452

Preparation and luminescence properties of Sr7Zr(PO4)6:Dy3+ single-phase full-color phosphor Novel single-phase white-light-emitting Sr7Zr(PO4)6:Dy3+ phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reactions. The phases and luminescent properties of the obtained Sr7Zr(PO4)6:Dy3+ phosphors were characterized. The results show that the luminescence spectra excited by 350 nm consist of two characteristic blue and yellow bands, corresponding to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. When x > 0.02, the concentration quenching effect occurred, and the critical transfer distance (Rc) was ~19.247 Å. The energy transfer of the Dy3+ ions is the electric dipole–dipole interaction mechanism. The International Commission on Illumination chromaticity coordinates for Sr7−x Zr(PO4)6:xDy3+ phosphors were located in the white region. The developed phosphor has great potential as a single-component white-light-emitting phosphor for UV-LEDs. J. Mater. Sci.: Materials in Electronics. (2015) Pages Ahead of Print. DOI:10.1007/s10854-015-2967-6

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Highly Bright Yellow-Green-Emitting CuInS2 Colloidal Quantum Dots with Core/Shell/Shell Architecture for White Light-Emitting Diodes

In this study, we report bright yellow-green-emitting CuInS2 (CIS)-based quantum dots (QDs) and two-band white light-emitting diodes (LEDs) using them. To achieve high quantum efficiency (QE) of yellow-green-emitting CIS QDs, core/shell/shell strategy was introduced to high quality CIS cores (QE = 31.7%) synthesized by using metal–oleate precursors and 1-dodecanethiol. The CIS/ZnS/ZnS QDs showed a high QE of 80.0% and a peak wavelength of 559 nm under the excitation of 450 nm, which is well matched with dominant wavelength of blue LEDs. The formation of core/shell/shell structure was confirmed by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-optical emission spectroscopy analyses. Intense and broad yellow-green emission band of the CIS/ZnS/ZnS is beneficial for bright two-band white light. When the CIS/ZnS/ZnS was coated on the blue LEDs, the fabricated white LED showed bright natural white light (luminous efficacy (ηL) = 80.3 lm·W–1, color rendering index (Ra) = 73, correlated color temperature (Tc) = 6140 K). The QD–white LED package showed a high light conversion efficiency of 72.6%. In addition, the CIS/ZnS/ZnS-converted white LED showed relatively stable white light against the variation of forward bias currents of 20–150 mA [color coordinates (x, y) =

(0.3320−0.3207, 0.2997−0.2867), Ra = 70–72, Tc = 5497–6375 K]. ACS Appl. Mater. Interfaces 7 (2015) 6764–6771. DOI: 10.1021/acsami.5b00166 CdSe Quantum dot-conducting polymer hybrid structure for Phosphor-free white light-emitting diodes A phosphor-free near-white-light-emitting diode (LED) is demonstrated by using a conducting polymer, poly(3, 4-ethylenedioxythiophene):poly(styrenesulphonic acid) (PEDOT:PSS) and a CdSe quantum dot (QD) composite layer that was fabricated by using a simple and inexpensive solution-based process. The PEDOT:PSS is deposited using a spin-coating method and shows an optical transmittance between 70 to 80% in the visible wavelength spectral range. The PEDOT:PSS embedding the CdSe QD composite layer shows a strong yellow emission at 587 nm. The electrical properties of an InGaN-based LED with PEDOT:PSS embedding CdSe QDs shows a forward operating voltage of 5.8 V, which is larger by 1.9 V compared to the voltage without the CdSe QDs. The electroluminescence spectra of an LED with PEDOT:PSS embedding CdSe QDs shows dual peaks at 447 and 580 nm, which are emitted from an InGaN quantum well and the CdSe QD layers, respectively. This indicates that the PEDOT:PSS embedding the CdSe QD composite layer acts as a transparent conducting electrode and a wavelength converter for white LED applications. J. Korean Phys. Soc. 66 (2015) 785-789. DOI:10.3938/jkps.66.785

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Synthesis and Characterization of Novel Nitride Phosphors Ca5Si2N6:Eu2+/Ce3+ The novel nitride phosphor Ca5Si2N6: Eu2+/Ce3+ were successfully synthesized at 1450 °C via a solid-state reaction method under a nitrogen atmosphere. The photoluminescence of Ca5Si2N6: Eu2+/Ce3+ shows that the phosphors have the main emission peak at 609 and 470 nm, respectively. The phosphor Ca5Si2N6: Eu2+ can be excited in the range from 350 to 480 nm, which makes it the attractive candidate phosphors for the application in phosphor-converted light-

emitting diodes as red phosphors. The Ca5Si2N6:Ce3+ can be effectively excited by near ultraviolet. Moreover, the effect of doping concentration on the luminescence property is investigated. - See more at: http://www.asianjournalofchemistry.co.in/user/journal/viewarticle.aspx?ArticleID=27_3_28#sthash.mjeEGB4Z.dpuf Asian J. Chem. 27 (2015) 938-940. DOI: 10.14233/ajchem.2015.17668

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Novel Patents

Yellow-emitting phosphor and white light-emitting element having it The present invention provides a yellow-emitting phosphor comprising MyLn6+x/3-ySi11-zAlzO1-x+y+zN20+x-y-z:RE (0 ≤ x ≤ 1; 0 < y < 6 + x/3; 0 ≤ z ≤ 5; Ln = rare earth element contg. Y and Sc; M = alk. earth metal element; RE = activator contg. Ce). The title has the phosphor and a blue light-emitting diode (LED). The phosphor having good color rendering property is provided at a low cost. JP 2015063680

Bluish green emitting phosphor for white light emitting diode and white led device using it

The invention relates to bluish green emitting phosphor for white light emitting diode and white LED device using it. The bluish green emitting phosphor is shown with AaBbOcNdCe:REh (A is selected from Be, Mg, Ca, Sr, Ba and Ra; B is selected from Si, Ge and Sn; C is C or selected from Cl, F and Br; RE is selected from Eu, Ce, Sm, Er, Yb, Dy, Gd, Tm, Lu, Pr, Nd, Pm and Ho; 0 < a ≤ 15; 0 < b ≤ 15; 0 < c ≤ 15; 0 < d ≤ 20; 0 < e ≤ 10; 0 < h ≤ 10). The bluish green emitting phosphor has high efficiency, high temp. stability, little crystal defects, and good light emitting property. When coating blue phosphor and red phosphor on blue LED, through adding the bluish green emitting phosphor, white LED device can be manufd. KR 1510124

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White LED chip including a tunneling structure formed by metal oxide layers, metal nitride layers and/or metal oxynitride layers, and white LED packaging device White light-emitting diode (LED) chips are described which comprise a P-type layer; a tunneling structure disposed over the P-type layer and comprising a first barrier layer, an active layer and a second barrier layer, where the first barrier layer comprises a first material layer, the active layer comprises a second material layer, and the second barrier layer comprises a third material layer; an N-type layer disposed over the tunneling structure; an N-type electrode in contact with the N-type layer; and a P-type electrode in contact with the P-type layer, where an energy gap of the second material layer is lower than an energy gap of the first material layer and an energy gap of the third material layer, where each of the first material layer, the second material layer and the third material layer is a metal oxide layer, a metal nitride layer or a metal oxynitride layer. The inventive white LED and LED packages do not contain any phosphor, but are capable of emitting white light.

US 20150091019

New nitridoalumosilicate phosphor for solid state lighting The invention provides, amongst others for application in a lighting unit, a phosphor having the formula M1-x-y-zZzAaBbCcDdEeN6-

nOn:ESx,REy, with M = selected from the group consisting of divalent Ca, Sr, and Ba; Z = selected from the group consisting of monovalent Na, K, and Rb; B = selected from the group consisting of divalent Mg, Mn, Zn, and Cd; C = selected from the group consisting of trivalent B, Al and Ga; D = selected from the group consisting of tetravalent Si, Ge, Ti, and Hf; A = selected from the group consisting of monovalent Li, and Cu; E = selected for the group consisting of P, V, Nb, and Ta; ES = selected from the group consisting of divalent Eu, Sm and Yb; RE = selected from the group consisting of trivalent Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm; 0 ≤ x ≤ 0.2; 0 ≤ y ≤ 0.2; 0 < x+y ≤ 0.4; 0 ≤ z < 1; x + y + z < 1; 0 ≤ n ≤ 0.75; 0 ≤ a ≤ 2 (such as 0 ≤ b ≤ 0.5); 0 ≤ b ≤2;0 ≤ c ≤ 4;0 ≤ d ≤ 4; 0 ≤ e ≤ 4; a + b = 2; c + d + e = 4; and a + 2b + 3c +4d + e + y -z = 16-n.

WO 2015044106

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Solar simulator based on UV-LED/phosphors The invention relates to a solar simulator having the spectral distribution analogous to that of the solar radiation, comprising a UV-emitting LED having the intensity max. in 300-400 nm, and phosphor powders that are optically excited by the UV-emitting LED.

JP 2015060921

17


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