Newsletter - fh-muenster.de · Volume 10 Issue 02 February 2016 Research & Development Effects ofExpiring Phosphors and QD IP on the LED Applications ... patents published worldwide

NewsletterTailored Optical MaterialsNewsletterTailored Optical Materials

Volume 10 Issue 02February 2016Matthias Müller

Thomas Jüstel

Research & Development

Latest Journals

Novel Patents

Current Patent Situation

China Rules The World

Conception: Prof. Dr. rer. nat.Thomas Jüstel Edited by: Matthias Müller Contact: [email protected]

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

Effects of Expiring Phosphors and QD IP on the LED Applications Patent Landscape ................. 1

Latest Research Publications in the Journal of Solid State Lighting ............................................... 4

Incandescent Bulb Redesign Recycles Waste Radiation ................................................................. 6

Kupfer macht organische Leuchtdioden effizienter ......................................................................... 8

Making Light Work – Light Sources for Modern Lighting Requirements .................................... 10

Latest Journals ...................................................................................................................................... 14

A deep red phosphor Li2MgTiO4:Mn4+ exhibiting abnormal emission: Potential application as color converter for warm w-LEDs ................................................................................................. 14

Photoluminescence properties of Li2Mg2 (WO4)3:Eu3+ red phosphor with high color purity for white LEDs applications ................................................................................................................ 14

Green-to-red tunable luminescence of Eu3+-doped K3Y(VO4)2 phosphors ................................... 15

Energy transfer and tunable luminescence of Na2(Y,Eu)Mg2V3O12 phosphors for white LED applications ..................................................................................................................................... 15

Novel Patents ......................................................................................................................................... 16

Astral lamp capable of regulating color temperature and luminosity ............................................ 16

A high-brightness tungstate red phosphor powder and its preparation method ............................. 16

Led and phosphor spatial segregation technology ......................................................................... 17

A type of n-b double-doped sic substrate gan-based no phosphor powder efficient white led structure and its preparation method and application ..................................................................... 17

Volume 10 Issue 02 February 2016

Research & Development

Effects of Expiring Phosphors and QD IP on the LED Applications Patent Landscape The latest Yoel report on will especially concentrate on the question how IP forces will evolve, with fundamental patent expiring in the next years? The report provides a detailed picture of the patent landscape for LED downconverters, namely Phosphors & Quantum Dots (QD). It covers patents published worldwide up to September 2015. More than 7,510 patent families relevant to the scope of this report have been selected.

The original report contains a lot of interesting and iportant information and graphs like for instance the "Focus on China: Remote Phosphors" chart Key Features of the Report are: • IP trends including time evolution and countries of filing • What has happened since the last report (2013 edition) • Phosphor & QDs LED market data and forecasts • Ranking of main patent applicants • Joint developments and IP collaboration network of main patent applicants • Key patents and fundamental granted patents near expiration • Relative strength of main companies' IP portfolios

• Matrix showing patent applicants and patented technologies • Segmentation of patents by technology and phosphor compositions • Deep IP analysis of new trend compositions and QDs • Complete review and deep analysis of litigations and licensing landscape (50+ slides) • Analysis of IP publication of Chinese players • Excel database with all patents analyzed in the report (7510+ patent families), including technology segmentation Objectives of this patent landscape are to: • Understand the IP landscape for Phosphors & QDs • Identify key patents • Understand trends in Phosphors & QDs IP • Identify the major IP players in Phosphors & QDs and the relative strength of their patent portfolio • Identify new IP players in Phosphors & QDs • Identify IP collaboration networks between key players • Identify main patent litigations The last 2 years have seen some major changes on the LED market with important boom of lighting applications and the growth of Chinese LED industry. On the phosphor front, nitrides are the dominant red phosphors for high CRI lighting and wide color gamut displays. Suppliers have proliferated despite IP restrictions. But a new material, Mn4+ doped PFS (potassium fluorosilicate) developed by GE and already manufactured by Denka, Nichia, GE and others could challenge the dominance of nitrides in display applications thanks to its extremely narrow

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band. Quantum Dots (QDs) have also emerged as highly credible options for displays thanks to design flexibility (adjustable emission wavelength) and very narrow band emission. YAG is the best yellow phosphor for white LEDs. But its use is restricted by strong IP owned by Nichia. Silicates are the best substitute but still lag slightly in performance. With critical IP to start expiring from 2017 and prices significantly lower than any alternative, we expect YAG to become ubiquitous by the end of the decade and silicate to decrease significantly unless breakthrough in performance and cost are achieved. Phosphor IP is a major force in LEDs and contributed heavily in shaping its industry with more than 70 litigation cases involving around 50 companies. The LED industry keeps bracing for the expiration of many fundamental patents. This could help relative newcomers such as Chinese LED packaging companies expand their market overseas. In the meantime, Everlight has been accentuating its effort to invalidate most of Nichia's fundamental patents and Osram and Nichia have continued strictly enforcing their IP via multiple litigations while the BOSE consortium has expended its licensing program for Silicate phosphors to various Chinese LED packaging companies. More than 7,510 patented inventions related to Phosphors & QDs have been published worldwide up to September 2015. The first patents were published by Japanese companies (Mitsubishi, Toshiba, Nichia, NIMS, Panasonic…). But patenting activity really took off over the 2003-2007 period after development of first high brightness GaN-based blue LED from Nichia. A second wave of patent publications started in 2010, mainly originating from AOT, Samsung and Stanley Electric. The increase in patent publications focused on Phosphor Composition follows same trend although more slowly. Chinese LED phosphor players such as Sunfor Light have recently entered the LED Phosphors & QDs IP arena.

Overall, patent filings peaked in 2013, and have been slowing down since. Meanwhile, granted patents worldwide should increase after successful processing of the numerous pending patent applications. We expect patent filings to continue driven by innovation in nitride phosphors or new compositions such as Mn4+ activated phosphors or QDs that haven’t reached their technology maturity yet and for which adoption in commercial applications such as displays is just starting. Identify Key Players More than 200 patent applicants are involved in Phosphors and QDs for LED. Most of the major LED and Phosphors manufacturers are present in the list of the top patent applicants, including Nichia, Cree, Osram, Philips, Toyoda Gosei, Samsung, LG and Seoul Semiconductor. The report provides a ranking with all major LED and phosphor manufacturers present and analysis of the relative strength of the key patent holders derived from their portfolio size, patent citations networks, countries of patents filings, current legal status of patents. Many key players are being challenged as their fundamental patents are approaching their expiration dates. To keep fending off new entrants, leading LED makers will increasingly have to rely on more recent applications, including continuations of those fundamental patents belonging to the same families. Panasonic leads patents assignees for LED with wavelength converters and ranks 7th in patents citing specific phosphor compositions. While not usually perceived as a leading LED player, the company is very active in LED R&D, including in the development of new phosphor compositions. But its LED related portfolio extends beyond phosphor related inventions. This broad portfolio allows the company to operate relatively freely in the LED space. Similarly, Toshiba shows a strong IP related activity despite a relatively moderate revenue position within the LED industry. It remains to be seem how the

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company’s recent decision to exit the white LED business will impact its overall LED lighting strategy. Patented Technology and IP Strategy The 7,510+ patented inventions selected for this study have been manually categorized by technology segment. The existing Phosphor & QDs for LED applications IP include LEDs using phosphors or QDs, phosphors compositions, QDs and LEDs with remote configuration patents. A special focus is provided on phosphors compositions (in particular for nitrides and new compositions) , QDs, free-Cd QDs and Chinese players. Nichia and Osram lead in garnet compositions. Both had fundamental patents filed in 1996 regarding YAG, TAG and multiple other garnet phosphors. They are followed by Philips and Mitsubishi. Some other players are leading the Silicates/Orthosilicates segment. However, the strongest composition patents in this category of materials belongs to the BOSE consortium including Litec/Merck, LWB, Toyoda Gosei. The Nitride / Oxynitride sections are dominated by Japanese players. Others big companies also own some IP on nitride compositions. Beside, other assignees on the list mention the use of Nitrides with LEDs but, for the most, haven’t developed compositions themselves. Among the phosphor makers, six companies are the most active in developing other compositions. In China, the most active companies/universities researching phosphor compositions are mostly focusing on Nitrides but also on new

compositions such as Europium activated Molybdates, Vanadates, Chlorine Borates, Tungstates and Antimonates. IP Litigation Aanalysis and Key Patents IP will keep playing a considerable role in this industry restructuring. In our analysis, we have identified various key players: Nichia, Cree, Osram, Philips, Seoul Semiconductor, Mitsubishi, …. Thus, we provide a complete and deep understanding of IP litigation history including litigated patents families and most cited patent families in litigations. The analysis include litigation strategy and licensing agreement focused on Garnet, Silicates and Nitrides phosphors compositions. For each key players, litigations and licensing are examined with granted fundamental patents near expiration dates. We have identified key patents which could provide significant returns to their owners, in terms of market share, freedom of exploitation and additional revenue stream from royalties. Useful Patent Database (7,500+ patent families) Our report also includes an Excel database containing all of the analyzed patents (7,500+ patent families). This database allows for multi-criteria searches and includes patent publication number, hyperlinks to the original documents, priority date, title, abstract, patent assignees, technological segments and legal status for each member of the patent family.

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Latest Research Publications in the Journal of Solid State Lighting On December 24th and 29th, 2015, three new articles have been published in the SpringerOpen Journal of Solid State Lighting. The three articles are titled "Optical Role of Die Attach Adhesive for White LED Emitters: Light Output Enhancement without Chip-Level Reflectors", "The Importance of Intrinsically Photosensitive Retinal Ganglion Cells and Implications for Lighting Design", and "Towards Perceptual Accuracy in 3D Visualizations of Illuminated Indoor Environments".

Human photoreceptor spectral sensitivity functions (from "The Importance of Intrinsically Photosensitive Retinal Ganglion Cells and Implications for Lighting Design") Optical Role of Die Attach Adhesive for White LED Emitters: Light Output Enhancement without Chip-Level Reflectors A thin optical reflector is often introduced to the backside of the standard mesa type light emitting diode (LED) chip with the aim to enhance its light output. However, most of the reported light output enhancements because of backside reflector (BR) introduction might not be relevant. This is because the reported measurement is often from a naked LED chip instead of a packaged LED emitter, and those based on the packaged emitters employing conventional silver based die attach adhesive

(DAA). The actual role of BR, which is expected to be greatly influenced by the packaging materials and processes, is investigated for the monotonic blue color and white LED emitters using Monte-Carlo simulations. Contrary to prior reports, it is demonstrated for the first time that the role of BR can be diminished when the optically transparent DAA is used and other key packaging materials and processes are optimized, i.e., the light output for a packaged emitter with a BR-free chip can be as high as that of the packaged emitter using the same chip but with an added BR. About Authors & Authors' contributions: Gunwoo Kim (GK), Yu-Chou Shih (YCS), Jiun-Pyng You (JPY), and Frank G. Shi (FGS) GK proposed the topic, established simulation models and carried out simulations. YCS carried out experimental study and analyzed the results. JPY analyzed the simulation and experimental results and helped in their interpretation. FGS collaborated with the corresponding author in the construction of manuscript. All authors read and approved the final manuscript. The Importance of Intrinsically Photosensitive Retinal Ganglion Cells and Implications for Lighting Design The article is a summary of research results and gives a good overview on a topic with many still unanswered questions which is currently often discussed very controversially. The authors reviewed the role of melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) in light-dependent functions, including circadian rhythm that is important for health and visual perception.

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They finally discussed the implications for lighting design. About Authors & Authors' contributions: Dingcai Cao (DC), and Pablo A. Barrionuevo (PAB) DC conducted literature search, graphic preparation and data analysis and wrote the manuscript. PAB assisted in literature search, graphic preparation, data analysis and manuscript preparation. Both authors read and approved the final manuscript. Towards Perceptual Accuracy in 3D Visualizations of Illuminated Indoor Environments Through a series of experiments, the authors have measured the extent to which 3D visualizations of a variety of lighting conditions in an indoor environment can accurately convey primary perceptual attributes. The goal was to build and rigorously test perceptually accurate visual simulation tooling, which can be valuable in the design, development, and control of complex digital solid-state lighting systems. The experiments included assessments of lighting-related perceptual attributes in a real-world environment and a variety of virtual presentations. Iteratively improving choices in modeling, light simulation, tonemapping, and display led to a robust and honest visualization pipeline that provides a perceptual match of the real world for most

perceptual attributes and that is nearly equivalent in perceptual performance to photography. One persistently difficult attribute is scene brightness, as observers consistently overestimate the brightness of dimmed scenes in virtual presentations. In this paper the authors explain the experimental 3D visualization pipeline variables that were addressed, the perceptual attributes that were measured, and the statistical methods that were applied to evaluate the success. About Authors & Authors' contributions: Michael J. Murdoch (MM), Mariska G. M. Stokkermans (MS), and Marc Lambooij (ML) MM led the project that included this research, [co-] designed all experimental variations, and drafted much of this paper. MS co-designed and executed several experiments, performed the statistical analyses, and drafted the results section. ML co-designed and executed one experiment and assisted with analyses and paper draft. All authors edited and approved the final manuscript. Further Information and Downloads: More information about the article and authors "Optical Role of Die Attach Adhesive for White LED Emitters: Light Output Enhancement without Chip-Level Reflectors" is available at the SpringerOpen Journal of Solid State Lighting website.

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Incandescent Bulb Redesign Recycles Waste Radiation

A nanophotonic incandescent light bulb demonstrates the ability to tailor light radiated by a hot object. Courtesy of Ognjen Ilic. CAMBRIDGE, Mass., Jan. 11, 2016 — A redesigned incandescent light bulb recycles heat radiation to emit visible light with an efficiency comparable to that of some fluorescent and LED bulbs. The ubiquitous incandescent light bulb is a high-temperature thermal emitter, producing mostly invisible and, in the context of illumination, unwanted IR light. Now researchers from the Massachusetts Institute of Technology (MIT) have designed a bulb that mitigates wasted energy. The proof-of-concept incandescent bulbs are more energy efficient, and elements of their design could also improve the performance of other hot thermal emitters such as thermophotovoltaic devices, wherein external heat causes the material to glow, emitting light that is converted into an electric current by an absorbing photovoltaic element. "Light radiated from a hot object can be quite useful, whether that object is an incandescent

filament or the sun," said postdoctoral researcher Ognjen Ilic. Thermal emitters operating at moderate temperatures often feature nanopatterned surfaces that alter emission wavelengths, the researchers said. But at high temperatures — above 3000 K — nanostructures on the surface of the emitter deteriorate. "A 3000° filament is one of the hottest and the most challenging sources to work with," said Ilic. "It's also what makes it a crucial test of our approach." To address the challenge, the team surrounded the hot element with nanophotonic structures that spectrally filter the emitted light, allowing it to reflect or pass through according to wavelength. Because the filters were not in direct physical contact with the emitter, the nanostructures kept their integrity at high temperatures. "The key advance was to design a photonic structure that transmits visible light and reflects infrared light for a very wide range of angles," said Ilic. "Conventional photonic filters usually operate for a single incidence angle. The challenge for us was to extend the desired optical properties across all directions," a feat they achieved using numerical optimization techniques. The research also involved redesigning the incandescent filament from scratch using a planar filament with a large area, which allowed it to efficiently reabsorb light reflected by the filter. "In a regular light bulb, the filament is a long and curly piece of tungsten wire," said professor Peter Bermel, now at Purdue University. "Here, the filament is laser-

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machined out of a flat sheet of tungsten: it is completely planar." In addition to energy efficiency, the design achieves near-ideal color rendering. In fact, one reason incandescent bulbs have remained the dominant light source over the years, the researchers said, is because their warm light reproduces surrounding colors in a more appealing way than, for example, fluorescent lights.

Ongoing research will examine issues of thermal stability and lifetime. The materials involved, however, are abundant and inexpensive, said professor John Joannopoulos, and the filters are amenable to large-scale deposition. The study was published in Nature Nanotechnology (doi: 10.1038/nnano.2015.309).

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Kupfer macht organische Leuchtdioden effizienter Der Einsatz von Kupfer als Leuchtstoff ermöglicht kostengünstige und umweltverträgliche organische Leuchtdioden (OLEDs). Wissenschaftler haben nun das zugrundeliegende quantenmechanische Phänomen des Intersystem Crossing in einem Kupferkomplex gemessen.

Farbstoffe als Grundlage für organische Leuchtdioden werden dank dem Wissen über ihre Quantenmechanik maßgeschneidert OLEDs bestehen aus ultradünnen Schichten organischer Materialien, die als Emitter dienen, zwischen zwei Elektroden. Beim Anlegen einer Spannung werden Elektronen von der Kathode sowie Löcher (positive Ladungen) von der Anode in den Emitter injiziert. Dort treffen Elektronen und Löcher zu gebundenen Elektronen-Loch-Paaren zusammen. Bei diesen sogenannten Exzitonen handelt es sich um Quasiteilchen im angeregten Zustand. Sie zerfallen anschließend in ihren Ausgangszustand und geben dabei Energie frei. Allerdings können die Exzitonen zwei verschiedene Zustände annehmen: Singulett-Exzitonen zerfallen sofort wieder und senden Licht aus, während Triplett-Exzitonen ihre Energie als Wärme freigeben. In OLEDs treten gewöhnlich 25 Prozent Singuletts und 75 Prozent Tripletts auf. Um die Energieeffizienz einer OLED zu erhöhen,

müssen auch die Triplett-Exzitonen zur Lichterzeugung genutzt werden. Dies geschieht in herkömmlichen organischen Leuchtdioden durch die Beimischung von Schwermetallen wie Iridium oder Platin. Eine kostengünstigere und umweltverträglichere Möglichkeit besteht im Einsatz von Kupferkomplexen als Emittermaterialien. Dabei sorgt thermisch aktivierte verzögerte Fluoreszenz (TADF – Thermally Activated Delayed Fluorescence) für eine hohe Lichtausbeute und damit hohe Effizienz: Triplett-Exzitonen werden in Singulett-Exzitonen verwandelt, die wiederum Photonen aussenden. TADF beruht auf dem quantenmechanischen Phänomen des Intersystem Crossing (ISC), einem Übergang von einem elektronischen Anregungszustand in einen anderen mit veränderterer Multiplizität. Bei organischen Molekülen ist dabei die Spin-Bahn-Kopplung bestimmend, d. h. die Wechselwirkung des Bahndrehimpulses eines Elektrons in einem Atom mit dem Spin des Elektrons. So lassen sich alle Exzitonen, Tripletts wie Singuletts, zur Lichterzeugung nutzen. Kupfer als Leuchtstoff erreicht mit TADF eine Effizienz von 100 Prozent. Stefan Bräse und Larissa Bergmann vom Institut für Organische Chemie (IOC) des Karlsruher Instituts für Technologie (KIT) haben nun gemeinsam mit Forschern der Firma CYNORA und der Universität Saint Andrews (Großbritannien) erstmals die Geschwindigkeit des Intersystem Crossing in einem hoch lumineszierenden Kupfer(I)-Komplex in festem Zustand mit TADF gemessen. Als Zeitkonstante für das Intersystem Crossing von Singulett zu Triplett ermittelten die Wissenschaftler 27 Pikosekunden. Der umgekehrte Vorgang – Reverse Intersystem Crossing – von Triplet zu Singulett erfolgt langsamer und führt zu einer TADF, die durchschnittlich 11,5

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Mikrosekunden anhält. Diese Messungen führen zu einem besseren Verständnis der Mechanismen, die zu TADF führen, und erleichtern damit die gezielte Entwicklung von TADF-Materialien für energieeffiziente OLEDs. Originalveröffentlichung: [L. Bergmann, G. J. Hedley, T. Baumann, S. Bräse, I. D. W. Samuel, Direct observation of intersystem crossing in a thermally activated delayed fluorescence copper complex in the solid state, Science Advances (January 2016), DOI: 10.1126/sciadv.1500889]

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Making Light Work – Light Sources for Modern Lighting Requirements

Light emitting diodes (LEDs) have come a long way since the 1960s and 1970s when they were used as small indicators or made up into seven-segment displays in watches and early calculators. Today, the range of colors and the intensity has seen them find applications in everything from environmental lighting to automotive lamps. But with that maturity comes a range of different problems, not the least of which is controlling light output, especially in environmental applications. A lot of effort is put into making LEDs and LED light sources look good and achieving the right quality. If LEDs are used in offices or homes, they need to have low glare so they do not dazzle the occupants. This is normally done using some kind of enclosure and lens system, but that can have an adverse effect on the efficiency of the light, and given efficiency is one of the main selling points of this type of illumination that is obviously not desirable. LEDs also provide the ability to integrate the light into the fabric of a building. They can replace ceiling tiles or be embedded in pillars and posts; they can be fixed into concrete and wood and be made part of the structure of the space being illuminated. However, using conventional techniques, they still need some optical system to reduce the glare and direct the light. This adds to the thickness, making the aesthetic element more difficult. Typically, an optical element would be attached onto the LED itself. This would normally be some kind of plastic lens, and that has become the standard way of doing this. Also available are flexible circuits containing the LEDs and these can be cut to length and embedded into the building material, but again some sort of plastic lens is needed.

Figure 1: Flexible edge-lit LED solutions are allowed by using different approaches like this laser-cut acrylic light guide This makes it thicker and removes some of the flexibility, turning it almost back into a normal light fitting. It becomes clunky again. A more recent development that gets round some of these problems are light tiles that mount the LEDs into transparent plastics, which can have the necessary optical characteristics preinstalled, thus retaining the flexibility without a dramatic increase in thickness. Edge-Lit LED Technology One of the better-known LED technologies is edge-lit. This can be effective in delivering thin lighting panels with a Lambertian output beam distribution. This was the technology that brought LED televisions to the consumer market. Typically, this consists of a PMMA (polymethyl methacrylate) light-guide plate covering the extent of the LCD panel. LED light sources are placed along one, two or four edges of the PMMA light-guide plate. The light from the LEDs is coupled into the light-guide plate and guided by total internal reflection (TIR). Light extraction features disturb the TIR and allow light to escape. The pattern of the light extraction supports uniform distribution of the escaped light behind the LCD panel when configured with a rear reflector.

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In recent years, edge-lit LED technology has been used in lighting applications, for example 600 by 600mm Lambertian ceiling tiles. However, its main advantages of uniformity with a thin system thickness are best deployed for backlighting applications like in signage. A disadvantage of this technology is its power consumption. As the area of the backlight increases, the power consumption rises non-linearly due to the increased optical absorption and scattering losses within the light-guide polymer as the distance from the edge to the center grows. Because of the optical losses due to scattering, coupling and light-guiding, optical efficiency falls into the 40% to 60% range, in other words 60% to 40% of the light energy is lost. Coupling losses come from surface scattering and Fresnel reflection. Wave guiding losses are because of absorption in the PMMA. OLEDs Organic LEDs (OLEDs) use an organic compound to emit the light in response to an electric current. They can be used without a backlight, can display deep black levels and are thinner and lighter than an LCD, and with a higher contrast ratio. Though OLED is a technology mostly associated with display applications from televisions to mobile phones, there is a lot of research in making it a more suitable method of solid-sate lighting. Desk lights using OLEDs are on the market –though quite expensive – and many predict that luminaires using OLED panels will become commonly available. Already, there are companies offering OLED panels as samples for research purposes and for some more expensive installations. At the current development stage, technology does still have several drawbacks to being solved, though. Notably the limited lifetime and degradation over time is not constant across the colors, in that blue degrades more quickly, damaging the color balance.

Figure 2: Flexible OLEDs are a technology lighting manufacturers and lighting designers are hoping will mature There are also still serious efficiency problems, and therefore they have higher power consumption. Without a proper extra sealing, they can easily be damaged by water and moisture. However, ongoing research is addressing these issues. Light Tiles Light tiles are polymer films with the LED embedded inside. They are mechanically flexible and transparent, and form a light guide with the optics integrated onto the film surface. This allows functional, narrow asymmetric beam formation from the tile surface for lighting and a uniform spread of light across the surface for thin and optically efficient back lighting.

Figure 3: The integration of LEDs in a polymer film to manufacture “light-tiles” is another promising solution for flexible light sources

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Figure 4: High efficacy LEDs encapsulated in a thin light-guide which is mechanically flexible. Optics on a light-guide surface enables both narrow (>10°) asymmetric beam angle control for lighting and uniform illumination for backlighting A single light tile can contain a range of high efficacy LEDs with a high color rendering index and various correlated color temperatures. The LEDs are embedded in a 2D array within multi-layer polymer composite films, which act as a light guide structure to spread the light inside the tile using TIR. The transparent substrate mounts the LEDs mechanically and electrically, and they are encapsulated to form the two-layer light guide structure. The light is emitted parallel to the surface of the polymers and is trapped inside the composite layer by TIR. Refractive optical surface features can be on one or more surfaces of the light guide structure at the air interface. These disturb the TIR and allow the light to escape in a way that controls the illumination uniformity for backlighting applications and the beam angle distribution profile for lighting applications. For example, high quality prisms and a single LED orientation can create narrow emitted asymmetric beam angle distribution or a regular 2D pattern. Graded light extraction features can achieve uniform spatial distribution to a backlight graphic or screen. The tile can be transparent and the light output can be single or double sided. An added advantage of this method is that good thermal management is inherent because the LEDs are distributed across a large surface area. This means designs are possible where the LED junction temperature does not exceed 20 ̊C above ambient. Thus often no external heat sink or spreader is needed.

Figure 5: Design LED lighting technology features a 2-D LED array in a multi-layer structure. Encapsulation of LEDs maximizes optical coupling, which is reflected from the optical medium interface by total internal reflection (TIR). Surface features disrupt TIR and extract light. Control of pattern and form of surface features provides control of relative light extraction The resultant illumination panels are typically less than 1 mm thick including the flexible circuit, light guide and outer graphics. Because they are solid-state products, lifetime is typically longer than ten years. They require low voltage power supplies and are intrinsically safe. For lighting and backlighting modules, different shapes and sizes up to one meter square are possible. For curved form factors, a bend radius of more than 50 mm is achievable as is a luminous flux density up to 20,000 lumens per square meter. Beam angles range from narrow asymmetric to Lambertian. Comparing Technologies Light tiles have up to 90” optical efficiency, which can be up to two times more efficient than edge-lit LEDs, and they are more mechanically flexible and have an asymmetric beam angle down to just ten degrees. They score even better when compared with OLED in that their lifetime is around five times longer, they are up to four times more efficient and again, are more mechanically flexible. The alternative of mounting the LED on a PCB with secondary optics can be up to five times thicker and is less mechanically flexible. The narrow asymmetric beam angle in light tiles improves lighting control and they provide uniform illumination for backlighting. Light tiles are also modular and cut-able.

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Electroluminescent lamps can also provide thin uniform lighting but they need a higher power supply and have limited color range and light output. On power consumption, with light tiles this increases linearly with area as opposed to non-linearly with edge-lit technology. Direct-lit LED technology is also better than edge-lit for power saving and optical efficiency but not as good as with light tiles. For lifetime and thermal management, direct-lit and light tiles are similar, and both better than edge-lit. Design Challenges The challenge for the lighting designer is to achieve an acceptable level of brightness while still maintaining a uniformity of light. Uniformity can be key to the user experience as it creates an impression of higher quality. Bright spots need to be avoided and the light has to be directed to where it is needed. Sometimes this can involve sacrificing the LED efficiency gains, say when the light is emitted in an unwanted direction it is often absorbed rather than redirected to where it is more useful. Diffusers are also often used to reduce hot spots and create uniformity. The norm is for the diffuser to sit over the direct point source of LED light and damp down the differences between the hot spots and darker areas. This can lead to efficiency losses above 50 per cent of the emitted light. When this is added to other absorption losses, efficiency can be reduced by more than 70%. This is one area where the light tiles can really help as the light is injected into a light guide, which allows the gradual and controlled escape of the light throughout the length of the guide. There are no hot spots and no need for light absorbing diffusers. Printed dots on the light guide control the

location and uniformity of the escaping light. Uniformity can be above 70 per cent, a level beyond which the human eye cannot detect any variations. Rear reflectors can prevent the system absorbing light and redirect it to increase efficiency even more. Light-blocking features can be added to increase optical isolation and contrast. Printed light guides can also be easily modified if there are late changes to the design. Displays can be flexible or can be formed into curves. They can use any combination of red, green, blue and white light sources to create features such as color fading and secret-until-lit effects. Easily customized, the tiles can be made in different shapes, sizes and colors. They can also be integrated into furniture or architectural materials. The size, shape, lumen density and beam angle are all under the control of the designers, who thus have the freedom to put light of any color where and when they want. Future Developments Technologies like the described liones already extend the design options for luminaire and lighting designers. But future technologies will further improve the opportunities. For instance, the current research into light tiles is looking at integrating microLED and nanoLED technology to achieve a narrow device beam profile that will improve light coupling. This will lead to further cost reduction as well as improved performance. There is even the possibility to create uniform and diffuse sheets of light that would look like illuminated paper.

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Latest Journals

A deep red phosphor Li2MgTiO4:Mn4+ exhibiting abnormal emission: Potential application as color converter for warm w-LEDs

The exploration of new red phosphor based on rare-earth free ion activated oxide is of great practical value in the field of phosphors converted white light-emitting diode (w-LED) lightings. Here, we report on a novel Mn4+-doped Li2MgTiO4 phosphor prepared by a solid-state reaction route, matching with the blue chips and showing strong deep red emission with an abnormal broad band centered at ∼676 nm. The crystal structure of

Li2MgTiO4 is identified and investigated by Rietveld refinement. The crystal field strength (Dq) and the Racah parameters (B and C) are estimated to evaluate the nephelauxetic effect of Mn4+ suffered in Li2MgTiO4 host lattice. The calculated results well conform to show linear dependence of E(2Eg) on β1 parameter which may provide an indication of the Mn4+emission position on the basis of β1. The photoluminescence properties are investigated systematically with the aid of diffuse reflection spectra, steady and transient state fluorescence measurements at high, low and room temperature. Concentration quenching and thermal quenching are elucidated in detail. As proof of concept, the as-prepared Li2MgTiO4:Mn and commercial YAG:Ce phosphors are applied to the package of a blue LED chip to fabricate a warm w-LED. Chem. Eng. J. 288 (2016) 596-607. DOI: 10.1016/j.cej.2015.12.027

Photoluminescence properties of Li2Mg2 (WO4)3:Eu3+ red phosphor with high color purity for white LEDs applications A series of novel Eu3+ doped tungstate Li2Mg2 (WO4)3 red phosphors were successfully synthesized by a solid-state reaction method. The phase structure, photoluminescence properties and thermal stability of the phosphor were investigated in detail. The Li2Mg2 (WO4)3:Eu3+ phosphors show dominant emission peak at 620 nm (5D0→7F2 transition) upon the strongest excitation at 398 nm (7F0→5L6 transition). The optimal doping concentration of Eu3+ is determined to be 0.06 mol in order to obtain the maximum emission intensity. The dependence of the emission intensity on temperature denominates that Li2Mg2

(WO4)3:Eu3+ phosphor has a relatively good thermal quenching effect. The Commission Internationale del’Eclairage coordinates was measured as (0.678, 0.322) with high color purity, being close to the National Television Standard Committee system standard for red chromaticity (0.670, 0.330). The above studies indicate that Li2Mg2 (WO4)3:Eu3+ is a promising candidate as the red phosphor for near ultraviolet-based white LEDs application. J. Lumin. 172 (2016) 180-184. DOI: 10.1016/j.jlumin.2015.12.021

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Green-to-red tunable luminescence of Eu3+-doped K3Y(VO4)2 phosphors A series of K3Y(VO4)2:Eu3+ phosphors were synthesized by a high-temperature solid-state reaction method. The luminescence properties were characterized by means of photoluminescence excitation and emission spectra, CIE chromaticity, and concentration quenching. The excitation spectrum exhibits a broad band centered at about 324 nm in the region from 215 to 375 nm corresponding to an overlap of the charge transfer transitions of VO4 3− and O2− → Eu3+. The present phosphors exhibit green and red colors due to the host emissions of host and Eu3+ ions. The intensity ratio of 5D0 → 7F2 to 5D0 → 7F1 is highly dependent on the Eu3+ ions

concentration due to the structure change of host. Eu3+-doped K3Y(VO4)2 phosphors show tunable CIE color coordinates from green to red dependent on Eu3+ content and excitation wavelength. The ideal red and warm white lights have been obtained from the phosphors by appropriately adjusted excitation wavelength. The results indicate that K3Y(VO4)2:Eu3+ is potential phosphors for white light-emitting diodes applications and color display devices. J. Mater. Sci. 51 (2016) 903-910. DOI: 10.1007/s10853-015-9418-x

Energy transfer and tunable luminescence of Na2(Y,Eu)Mg2V3O12 phosphors for white LED applications

A series of solid-solution phosphors Na2(Y,Eu)Mg2V3O12 were prepared using solution combustion reaction. X-ray diffraction studies verified the formation of

single phase Na2(Y,Eu)Mg2V3O12 with garnet structure. Na2(Y,Eu)Mg2V3O12 phosphors show not only a broad emission band with a maximum at 510 nm due to the [VO4]3− group but also several sharp emission lines due to the Eu3+ ions. The energy transfer from [VO4]3− to Eu3+ was discussed on the base of the spectral analysis. The color-tunable emissions of the Na2(Y,Eu)Mg2V3O12 phosphor as a function of Y/Eu ratio are realized by continuously generating the varied hues from yellowish-green to reddish-orange. This indicates that the obtained phosphor may have potential applications in the field of UV-based white LEDs. Mater. Res.Bull. 169 196–203. DOI: 10.1016/j.materresbull.2015.09.026

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Novel Patents

Astral lamp capable of regulating color temperature and luminosity

[Machine Translation of Descriptors]. The invention relates to astral lamp capable of regulating color temperature and luminosity.

Light necessary for surgical environment can be obtained with LED as light source of medical astral lamp, and the light source color temperature can be regulated according to the surgical purpose. High-output white light LED is used, and three different phosphor fluorescent substances are coated on the LED surface. The LED luminosity is individually regulated based on the phosphor kinds, and the color temperature can be freely regulated. The LED light source is formed from one package, and when color is regulated, color is uniformly dispersed and mixed without aggregation. So the color temperature and luminosity can be regulated. KR 1581379

A high-brightness tungstate red phosphor powder and its preparation method

The present invention discloses a high-brightness tungstate red phosphor powder and its prepn. method. The high-brightness tungstate red phosphor powder has chem. formula of : CaGd2-x-yYyEux(WO4)4, x = 0.1, 0.2, 0.3, 0.4, 0.5, y = 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. The title prepn. method comprises the steps of : weighing CaCO3,

Gd2O3, Y2O3, Eu2O3 and WO3, mixing to obtain mixt. A, ball milled the mixt. A to obtain mixt. B, drying the mixt. B to obtain mixed powder C, fully grinding, and sieving with 200-300 mesh of sieve to obtain mixed powder D, calcining at 900-1100 C for 4-6 h, and cooling to room temp. to obtain the product. The usefulness of the present invention is that : the phosphor of the present invention solves the problems that the existing red fluorescent material for white LED has poor stability, poor color purity and low luminous efficiency; the prepn. process of the present invention by adjusting Y3+, Eu3+ ions doping amt. and process parameters, can prep. monodisperse spherical powder with high purity, uniform doping and controlled size, makes phosphor have high stability and high color purity, and can be effectively excited by near UV and blue light. KR 1581379

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Led and phosphor spatial segregation technology

[Machine Translation of Descriptors]. The present invention relates to a LED and phosphor spatial segregation technology, provides a LED and phosphor spatial isolation structure, used to solve a series of problems caused by the complex package structure of the traditional white LED. the present invention LED lighting structure consists of

LED, light-emitting mask, driver three parts. wherein the light-emitting mask is coated around LED, and separated from LED; light-emitting mask and LED is filled with vacuum or thermal protective gas; phosphor is coated surface on light-emitting mask or mixed with light-emitting mask; light-emitting mask shape may be an incandescent shape, fluorescent tube shape or street lamp glass maskshape; light-emitting mask may be made of glass, plastic, resin and other materials. it has a simple process, low cost, good luminous and thermal conduction effects, can be used directly for LED incandescent lamp, LED fluorescent lamp, LED street lamp and other places. CN 105221946

A type of n-b double-doped sic substrate gan-based no phosphor powder efficient white led structure and its preparation method and application

[Machine Translation of Descriptors]. The present invention relates to a N-B double-doped SiC substrate GaN-based no phosphor powder efficient white LED structure and its prepn. method and application, including successively B-N double-doped SiC substrate, GaN buffer layer, undoped GaN layer, N-

GaN layer, UV multi-quantum well layer, blu-ray multi-quantum well layer and P-GaN layer. The white LED structure is inverted structure, the yellow belt of B-N double-doped SiC substrate excited by UV light in UV multi-quantum well layer gives out light, and then combines with blue belt emitted by blu-ray multi-quantum well layer, B-N ouble-doped SiC substrate emits white light out, compared to the normal package LED chip architecture, light-emitting surface has no electrodes, it greatly increases the light-emitting area, improves the optical efficiency. The present invention does not use phosphor powder for secondary quantum conversion, improves equipment utilization, simplifies the process, improves LED energy conversion efficiency and lifetime, improves the quality of outgoing light, has luminous stability and product repeatability. CN 105226150

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Newsletter - fh-muenster.de · Volume 10 Issue 02 February 2016 Research & Development Effects ofExpiring Phosphors and QD IP on the LED Applications ... patents published worldwide