Newsletter€¦ · Newsletter Tailored Optical Materials Volume 10 Issue 06 Matthias Müller June 2016 Thomas Jüstel Research & Development Latest Journals Novel Patents Burn The

NewsletterTailored Optical Materials

Volume 10 Issue 06June 2016Matthias Müller

Thomas Jüstel

Research & Development

Latest Journals

Novel Patents

Burn The Pain

Green Light Eases Migraine

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

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

230 VAC Driven LED Modules with Strongly Reduced Flicker, by euroLighting ....................... 1

White Hybrid Light-Emitting Diodes: A Plausible Solution for Commercialization and Health Issues, by the University of Erlangen-Nuremberg (FAU) ............................................................. 7

A new spintronics material promises huge leaps in computer data storage ................................. 13

Light-Driven Nitrogen Fixation ................................................................................................. 15

Researchers unveil submicroscopic tunable, optical amplifier .................................................... 16

Green Light for Migraine Relief ................................................................................................ 18

Latest Journals ................................................................................................................................. 20

Rapid synthesis and luminescence properties of Sr3SiO5:Eu2+ .................................................... 20

Electronic Structure Descriptor for the Discovery of Narrow-Band Red-Emitting Phosphors ..... 20

Non-rare-earth BaMgAl10-2xO17:xMn4+,xMg2+: a narrow-band red phosphor for high-power warm w‑LED ...................................................................................................................................... 21

Effects of the surface area of phosphor powders on colour coordinate variance ......................... 22

Luminescent behaviour of Mn4+ ions in seven coordination environment of K3ZrF7 .................. 22

Novel Patents .................................................................................................................................... 23

Boronitride halide oxide phosphors and their preparation and use .............................................. 23

A simulated sunlight led light source and its preparation method ............................................... 23

White light source for approximating solar light and capable of reproducing the subtle fluctuations in solar light and white light system ........................................................................ 24

Barium fluorogermanate red light material for white light LED and its preparation method ....... 24

Volume 10 Issue 06 June 2016

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Research & Development

230 VAC Driven LED Modules with Strongly Reduced Flicker, by euroLighting One of the continuing trends in LED lighting is toward AC driven LED modules. Big progress has been made regarding dimmability and reduction of flicker. However, there are still differences in the various concepts that lead to very different results. Wolfgang Endrich, founder and managing director of euroLighting presents a recently improved new concept to significantly reduce flicker.

A more peak-shaped waveform of the light output

from another AC driven approach The US Ministry of Energy (DOE) has forecasted in their annual F&E plan regarding solid state lighting 2015 that by 2030 about 80% of all luminaires in the United States will be operating with LED. This would create a reduction of about 60% in the consumption of electricity. Even the losses by the LED driver could add up to 10% or more and the failure rate of the LED driver is up to 52% for Asian products. Therefore the US Ministry of Energy recommends the usage of AC-LED driver technology and called it the “coming next generation of light sources”. Designing a new LED luminaire poses great challenges today – including selecting the right LEDs and a suitable power supply unit.

The new AC technology has now substantially simplified this process: It allows direct control of the LEDs with 230 V AC and generates virtually flicker-free light with very good dimming properties. Having to develop a dedicated power supply unit can significantly delay a new project. It is much easier now to use the new AC technology with direct control through 230 V AC – with obvious advantages: In addition to considerable cost reductions, LEDs from different manufacturers can be used and combined in one circuit. It is now possible to use a much smaller power supply unit which can be integrated unobtrusively into any housing and can be included already on the PCB of the LED. Direct Control with 230 V Directly controlling an LED with 230 VAC may sound puzzling especially with regard to the so-called safety extra low voltage. Appropriate safety measures and insulation can quickly dispel these doubts. The newly designed IC, the IC EL01, allows LED driver circuits to be operated directly with 230 VAC while generating almost flicker-free light. The 230 V mains AC power is rectified and fed into an AC direct driver without smoothing. The driver pulses with 100 – 120 Hz and operates the LEDs with constant current and a voltage between 40 – 70 VDC. This produces the advantage that LEDs from different manufacturers specified for voltages between 2 and 70 V can be controlled directly. With an operating voltage of 70 V, numerous DC LEDs with different voltages (max. 70 V) can be directly operated in a group. So if an LED has an operating voltage of, for example, 2 V,


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Figure 1: AC driving mode with the new designed IC up to 35 LEDs of this type can be connected in series. The circuit and the required power input can easily be expanded through the use of further ICs. Different Dimming Concepts In Germany and in Asian countries, numerous products have already been equipped with AC technology for many years. It has proven successful, e.g. in retrofit lamps, GU10, ceiling spotlights, ceiling floodlights up to 120 W, area luminaires with 62 x 62 cm and LED tubes. The market also offers numerous ICs that can be used to implement AC direct circuits. They have one significant difference, though: These circuits can generally be dimmed, but in two ways. New concept using multiple new designed ICs The new IC and the circuit created with it, allows simultaneous dimming of the entire luminaire. That means all LEDs are dimmed evenly (Figures 2a-e). Figures 2 show that the EL01 LED modules can easily be dimmed without changing the

Figure 2 a-e: The EL01 LED modules dimmed to 5 W

(a), dimmed to 2 W (b), dimmed to 1 W (c), chips are

mounted all around the edge (d), leading to an even

thermal distribution (e). Many other AC concepts use a

sequential dimming concept with just one central IC

luminous flux modulation - Luminous flux modulation dimmed to 5 W (a), dimmed to 2 W (b), dimmed to 1 W (c), EL01 Chips are mounted all around the edge (d), leading to an even thermal distribution (e). Reference concept using one IC for sequential dimming The most common approach is to implement sequential dimming of individual assemblies. This involves supplying individual groups with full power and adding more groups if more brightness is required. This has certain disadvantages: Not all LEDs can be dimmed at the same time so that the thermal load varies and is not distributed evenly across the entire area. The circuit created with this system uses only one central IC. The dimming of a conventional AC driven LED module using the sequential dimming approach for example dimmed to 6 W results in a luminous flux modulation of approx. 9 ms with some LEDs being already less bright. Dimmed to 4 W, some LEDs are completely off. The placement of the IC and such a concept can also result also in an uneven heat dissipation, where hot spots can appear. The new concept uses several ICs which ensures an even thermal load. This makes a useful life of 50,000 h absolutely realistic. Furthermore, this IC features an NTC characteristic which reduces the full power from 85° C to prevent overheating. Long-term tests with these components of over 30,000 hours have shown many advantages: A greatly simplified circuit without electrolytic capacitors and inductivities or transformers. The useful life of the circuit corresponds to that of LEDs with > 50,000 hours, uniform dimmability of the circuit without additional circuitry components as well as flicker-free light at all power levels. About Flicker-Free AC Lighting Questions about flicker-free light, especially AC light, and how to measure and to specify


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it, may arise at this point. To be fair, it should be pointed out that fluorescent tubes operated with conventional or low loss magnetic ballasts also flicker at 100 Hz and the light output is reduced at lower ambient temperatures. Fluorescent lamps operated with an ECG, including energy saving lamps work at 40 – 50 kHz so that the lamps normally do not flicker visibly. In reality, however, things are a little bit different. While a higher switching frequency is used, the input capacitors are often too small for cost reasons. This causes the high frequency circuit in the lamp to be supplied with a strongly pulsating voltage. This pulsation creates a brightness modulation in the emitted light, which is why these lamps often have a rather high level of flicker at 100 Hz. As already mentioned, all conventional light sources - including incandescent, high intensity discharge (HID) and fluorescent – modulate luminous flux and intensity, whether perceptible or not. Many terms are used when referring to this time-variation, including flicker, flutter and shimmer. The flicker produced by electric light sources can be a function of how it converts AC electricity to light. It can also be the result of noise of transient events on AC distribution lines. Electrical flicker should not be confused with photometric flicker, which is the characteristic modulation of the light source caused by electrical input rather than disturbances. Light source characteristics that can affect photometric flicker vary by technology. For LEDs, flicker characteristics are primarily a function of the LED driver. Photometric flicker from magnetically-ballasted fluorescent, metal halide and high pressure sodium lamps has been a concern of the lighting community because of its potential human impact which range from distraction or mild annoyance to neurological problems. The effects of flicker are dependent

on the light modulation characteristics of the given source, the ambient light conditions, the sensitivity of the individuals using the space, and the tasks performed. Low-frequency flicker can induce seizures in people with photosensitive epilepsy, and the flicker in magnetically-ballasted fluorescent lamps used for office lighting has been linked to headaches, fatigue, blurred vision, eyestrain, and reduced visual task performance for certain populations. Flicker can also produce hazardous phantom array effects. Back to the AC circuits: 100% flicker-free light only comes from the sun: Even traditional filament light bulbs just offer and nearly flicker-free light. However, there are considerable differences between the chip solutions of the compared concepts. Flicker fusion threshold When evaluating temporal uniformity as a quality criterion for lighting, fast and slow changes have to be considered separately. Fast changes are the temporal fluctuation of luminous flux of the emitted light due to the pulsating fluctuations of the input, e.g. with AC operation. A crucial factor for whether this fluctuation is perceived as irritating is the flicker fusion threshold of the eye, which also depends on individual circumstances. If the frequency of the luminous flux modulation is above this fusion threshold we can no longer perceive it. This limit frequency, where periodically occurring stimuli are just starting to be perceived as a stimulus, is called flicker fusion threshold and is below 100 Hz for most individuals while a good part - I believe over 50% - of the people don’t even recognize flicker above 70 Hz. Therefore, the relevant flicker frequency for many applications is recognized to be approximately around these 70 Hz. It is also referred to as pulsation. Below this fusion threshold, however, the luminous flux modulation is perceived as an irritating flicker. Eyes are particularly sensitive to this in peripheral vision. Fast moving objects (e.g. lathes) can additionally


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Figure 3: Flux modulation in a PWM system create stroboscopic effects with the resulting phantom array effect. Relatively slow changes (in the domain of seconds to minutes) in illumination can have a rather positive influence on the human state of mind. The variability of lighting through artificial indoor lighting systems is only slowly gaining significance as a quality aspect. Monotonous constant lighting creates a tiring effect in the long term and has no positive influence on concentration and efficiency. There is DC and (DC + AC) light. The following formula applies for dimming LEDs with the usual pulse width modulation (PWM), which is typically a (DC + AC) light: W = (φmax - φmin ) / φmean_WLED = within ≤ 1 W < ∞ Disadvantage: This creates a considerable luminous flux modulation (Figure 3). Criteria for good flicker-free light Two criteria are important for good lighting: The clock frequency of the LEDs has to be well above the flicker fusion threshold. The direct AC control for concept 1 as described has a frequency of 100 Hz. Furthermore, the light intensity should be as uniform as possible. That means rectangular light intensities create a balanced light while wedge-shaped light peaks are perceived as irritating. (Figures 4 a + b).

Figure 4 a&b: Light fluctuations of different AC driven

LED modules. The new concept: trapezoidal light curve

(a), LED module using a conventional concept: wedge-

shaped light peaks (b) (luminous flux modulation is

measured with an ultrafast photodiode in normal

operation and dimmed) Figures 4 a & b demonstrate the light fluctuations of different AC driven LED modules. EL01 LED module from euroLighting: trapezoidal light curve (a), LED module from a different manufacturer: wedge-shaped light peaks (b); (luminous flux modulation is measured with an ultrafast photodiode. Normal operation and dimmed). Quantifying Flicker After all considerations about the theory we will explain in the following how to measure the flicker. A very interesting report was issued by the “US Department of Energy – Energy Efficiency & Renewable Energy”. The following explanations will refer to this report and the direct fact sheet [1].


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The following will refer on the basis of this “fact sheet”: The percentage of flicker at the modulation index and the flicker index. But the result will be the realization that there is not a good or a bad flicker. It really depends on the application whether it is indoor or outdoor usage and finally the human being. Low flicker sources should always be used for both ambient lighting and task lighting in offices, classrooms, laboratories, corridors, and industrial spaces. Minimizing flicker is especially important where susceptible populations spend considerable time such as hospitals, clinics, medical offices, classrooms, and daycare centers. In contrast, flicker may be less of a concern for parking lots, roadways, or other exterior lighting where light levels are lower and people spend less time. In the above mentioned report of the US Department of Energy show a very good example to explain what we are talking about now. How to Measure Flicker Three analysis methods are suitable and relevant for the calculation of photometrical flicker, which may not be mixed up with voltage or current flickering in electric circuits. These are the flicker index and percent flicker, and less common the modulation index. All three methods have in common that they are relative measures. The flicker index takes into account the waveform of the light output as well as its amplitude according to the handbook. The flicker index assumes values from 0 to 1.0, with 0 for steady light output. Higher values indicate an increased possibility of noticeable lamp flicker, as well as stroboscopic effect. Percent flicker and the flicker index are used to compare the new technology with a conventional AC module.

Figure 5: Periodic wave form characteristics used in the

calculation of flicker metrics (modified from IES

Lighting Handbook, 10th Edition) In figure 5 the yellow line shows the luminous ripple and the blue curve shows the current. The zero line is the red line and the violet line is the average light output. Figures 6 a & b show two trapezoid light output waveforms and the related flicker parameters as flicker index and flicker %. Flicker indices and flicker percentages of the examples from figures 6 a + b: Flicker Index for Figure 6 a Fi = Area 1 / (Area 1 + Area 2) = 9 / ( 9 + 19) = 0,32 Percentage of Flicker for Figure 6 a F% = (Max - Min) / (Max + Min) x 100% = (2,3 - 0,5) / (2,3 + 0,5) x 100% = 64,3 % Flicker Index for Figure 6 b Fi = Area 1 / (Area 1 + Area 2)= 1 / (1 + 3) = 0,25 Percentage of Flicker for Figure 6b F% = (Max - Min) / (Max + Min) x 100% = ( 2,4 - 0,3 ) / ( 2,4 + 0,3) x 100% = 77,8 % A comparison of the measurement diagrams in figures 6 a & b and figure 7 show the distinct different shapes of the light output waveforms (yellow lines). While the waveforms in the figures 6 a & b are trapezoid shaped, the waveform in figure 7 is peak-shaped. All measurements were made


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Figures 6 a&b: Two trapezoid light output waveforms

and the related flicker parameters as flicker index and

flicker % with AC driver ICs under the same conditions and may give an idea which light output curve better suites the requirements for the human eyes. It is the trapezoid shape with its bigger amount of light above the average light output line. This means that area 1 is larger. Therefore the flicker will be much less visible.

Figure 7: A more peak-shaped waveform of the light

output from another AC driven approach Final Remarks The report of the US Department of Energy comes to the conclusion that flicker is creating increasing attention from manufacturers, as well as the standards and specification community. Some manufacturers appear to be giving flicker increased design priority, as evidenced by the improved performance of new product generations. The IES and CIE are considering the development of measurement standards, and IEEE group is working on recommended practices for evaluating flicker risks. Collectively, these efforts may make it easier for designers and specifiers to minimize the risk of flicker-induced problems for their clients in the near future. References [1] SSL.energy.gov - the direct fact sheet feedback to: [email protected].


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White Hybrid Light-Emitting Diodes: A Plausible Solution for Commercialization and Health Issues, by the University of Erlangen-Nuremberg (FAU)

One of the challenges in terms of commercialization of white LEDs is the need for cheap, inorganic phosphors. In this context, hybrid LEDs have recently emerged as a new approach based on downconverting organic coatings. The authors, Pedro B. Coto from the Institute for Theoretical Physics, Marlene Pröschel and Uwe Sonnewald from the Department of Biology, and Lukas Niklaus, Michael D. Weber and Rubén D. Costa from the Department of Chemistry and Pharmacy at the University of Erlangen-Nuremberg (FAU), describe this technology and cover recent breakthroughs and their prospects.

Top - chemical structures of the compounds used for

developing matrices, Bottom - chemical structures of

down-converting compounds Nowadays, more than 20% of the total of domestic energy consumption is devoted to artificial lighting, but it is still dominated by incandescent light sources and compact fluorescent lamps. Generally speaking, although they have almost been fully developed, they are considered to be inefficient and environmentally unfriendly. Indeed, both the USA and the EU have stated that inorganic white light-emitting diodes (WLEDs) will drive the future of artificial lighting for both indoor and outdoor purposes [1]. This is based on their impressive theoretical efficiency limit of around 400

lm/W and the low-cost per lumen, which is falling a 10-fold every decade [2]. Indeed, recent market studies have estimated that over 14 billion Euros could be saved by replacing old illumination systems by WLEDs [1]. For instance, according to a McKinsey study, it is assumed that LEDs will account for 70% of the global lighting market in 2020, which corresponds to 101 billion Euros (Figure 1) [1a]. At the same time, due to economics of scale, production costs will fall to about 32% of 2014 values by 2020 [1]. These impressive expectations have been established for monochromatic LEDs, but not yet for WLEDs, due to the use of a top coating based on inorganic phosphors (IP) like Y3Al5O12; YAG:Ce3+ derivatives. About Concerns Regarding IP Coated LEDs The main drawbacks of IP-based coating methods are: • High production cost due to the need of a chemical vapor deposition method • Intrinsic high cost of the raw materials, since they are very rare • Lack of near-infrared and/or deep-red emitters, and • Lack of cost efficient protocols to recycle the IPs [1, 3] Thus, problems with the IP coatings will lead to a predicted increase of production costs of IPs by 5% until 2020. This is even more critical if we consider that today the IPs account for up to one fifth of the production costs of LEDs (Figure 1) [1, 3]. A switch to organic light-emitting diodes (OLEDs) for general illumination is still not possible, since OLEDs feature only half the efficiency and about a 50-times higher price compared to LEDs on a dollars per kilo-lumen-basis as


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Figure 1: Top: Predictions of the growth of LED

luminaire with respect to unit sales from 2012 to 2018

(Source: Smallwood, Strategies Unlimited, DOE SSL

Manufacturing R&D Workshop, San Diego, 2012)

Bottom: Cost distribution for high-and mid-power LED.

(Source: LEDCOM model 1b) well as still having issues with the lack of recycling protocols [4]. Thus, alternative IPs and/or approaches are sought by both the scientific and industrial communities, as this route does not meet the requirements of “Green Photonics” in terms of ecological sustainability, low energy consumption, and the use of low-cost and renewable materials [1, 3]. Besides the future market issues associated with the IPs, scientists and social institutions have started to evaluate the impact of WLEDs on human health [5]. Here, the question is: are LEDs as safe as old illumination systems? This addresses both visual and non-visual effects on human health caused by the strong brightness in concert with the light spectrum of WLEDs. The visual effects involve three major considerations, namely flickering, glare, and blue light hazard [5, 6]. Going from less to more dangerous concerns, it is expected that flickering will not be very important in the future, since most of the high quality LED sources feature rectifiers and filters that effectively reduce the light flickering to almost zero. However, this could be critical for people with a risk of suffering

epileptic seizures - e.g., a few seconds exposition at 3-70 Hz and susceptibility to migraines and eye fatigue - e.g., a few hours exposition at 100-200 Hz. Glare is the second most dangerous factor if we consider high power outdoor lighting systems that can cause temporary and reversible loss of vision, damage to the eye tissues, etc. Still there are no international standards to evaluate this effect for single point sources. Finally, the so-called blue-light hazard is associated with the use of a high blue component -e.g. InGaN -in combination with yellowish orange emitting IPs that typically provides a cold white light spectrum. As a matter of fact, exposition of high-intensity blue light leads to retinal damage, such as the death of photoreceptors - i.e. necrosis and/or apoptosis - at wavelengths between 440-490 nm, and damage of retinal pigment epithelium by means of an autophagy process [6a-c]. Although our body has repair mechanisms, the photochemical damage is considered to be accumulative upon interrupted exposition times. Up to date, ANSI/IESNA RP27, CIE S009, and IEC 62471 are international standards to determine the blue-harmful light in terms of brightness, distance, number of sources, and exposition times [5, 6]. Here, the scale ranges from • RG0 - i.e. no risk or unlimited exposition without hazard effect • to RG1 - i.e. low risk at times ranging from 100-10000 s • to RG2 - i.e. moderate risk at times of 0.25-100 s • and finally, to RG3 - i.e. high risk at times lower than 0.25 s Examples of RG2 LEDs involve indoor and outdoor lamps and luminaires with high brightness, such as automotive headlights, flash lights, frontal headlights, and some bright LED display panels. In general, many of the blue and cold white LEDs are considered RG1 or RG2, while white warm LEDs are all considered RG0. Importantly, these studies do not cover human cases like those dealing with the above-mentioned


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diseases, affecting children’s eyes that feature a lens that is more transparent to blue and UV radiation and a macula that does not contain enough protective yellow pigments, as well as old people, whose eyes have accumulated blue-sensitive lipofuscin derivatives with age. In addition, none of the above-mentioned studies consider the effects of lifelong cumulated exposures to blue light at both high- and low-dose exposure, as well as the effect of the UV irradiation or the lack of N-IR contribution compared to the sun light spectrum in, for instance, skin problems and/or vitamin D production. Finally, the non-visual effects involve a change in brain chemistry induced by light exposition [5, 6d&e]. Although it is well-known that a high blue contribution in the light spectrum produces a decrease of the melatonin levels, affecting the circadian rhythms, mood, alertness, appetite, sleep quality, etc., a clear relationship with the illuminance level, the exposure duration, the timing of the exposure, and the light spectrum is not well established yet. However, it is well-known that warm white light - i.e., light with a dominant yellow, orange, and/or red contributions - is less effective in reducing melatonin than cold white light. It is important to keep in mind that, since the sun light spectrum changes over the course of a day, the human vision has become significantly sensitive to the changes in the solar spectrum - i.e. human eyes feature photopic (day), mesopic (sunset) and scotopic (dim-light) visions. As an example, our eyes are more sensitive to the blue component of the white LEDs (especially cool white LEDs) during the night. White Hybrid LEDs as a Reasonable Alternative Taking the above described concerns about commercialization and health seriously, it is obvious to state that although WLEDs will rule the future market [1, 3], there are clear needs to seek after new down-converting approaches to provide warm white LEDs that

Figure 2: Representation of a commercial WLED (top)

and WHLED (bottom) with organic down-converting

packing coatings fulfill the green economic requirements [1, 3, 5]. In this context the potential of white hybrid light-emitting diodes (WHLEDs) sets in [7-10]. In detail, this technology aims to replacing IPs for organic down-converting materials. Here, the WHLED architecture consists of the same electronics and emitting chips as those developed for commercial UV- and blue-LEDs, but coating or replacing the packing system with a down-converting organic compound (Figure 2). The latter is excited by the chip and the overall light spectrum of the WHLED involves both the emission of the LED (UV or blue) and the emission of the packing. Down-converting organic compounds consist of several families like small-molecules, polymers, quantum dots, coordination complexes, and most recently fluorescent proteins (Figure 3). Among them, small-molecules, polymers, and fluorescent proteins are the most interesting materials due to lack of toxicity, low-cost production/recycling, and ease of chemical design to cover all the visible and NIR regions towards mimicking the sun light spectrum. The state-of-the-art WHLEDs designed and tested under laboratory conditions show very


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Figure 3: Top - chemical structures of the compounds

used for developing matrices based on (a) thermal/UV

curing polymers, (b) MOFs, (c) cellulose, and (d)

rubber-like materials. Bottom - chemical structures of

down-converting compounds, namely (e) small-

molecules, (f) polymers, (g) coordination complexes

and (h) fluorescent proteins promising results in terms of luminous efficiencies and color quality. For instance, WHLEDs have shown efficiency values of up to 60 lm/W with Commission International d’Eclairage (CIE) coordinates of 0.30 / 0.30, color rendering index (CRI) up to 90, and correlate color temperature (CCT) between 2500-6500 K. The only drawback is the moderate stability of around hundred hours under operation conditions. This is not totally related to the intrinsic photostability of the organic compounds, but also to their interaction with the components of the matrix chosen to encapsulate the organic compounds. Here, scientists have developed four different approaches [7-10]. In chronological order, several researchers have mixed fluorescent compounds like small-molecules, polymers, and quantum dots with matrices based on silicones and/or epoxies derivatives that require UV and/or thermal curing procedures to obtain a robust encapsulation [7a-d]. Here, only WHLEDs prepared with toxic quantum dots show interesting stabilities of at least several days [7b&d], while those with small-molecules and polymers feature only a few minutes or hours [7a&d]. As such, this approach has shown limitations in terms of degradation of the compounds upon preparation, phase separation issues, and lack of protocols to efficiently implement them into blue-LEDs. The most plausible approach is to previously encapsulate the organic compounds and then to implement them into

the down-converting coating [7d]. The second approach involves the use of metal organic frameworks (MOFs) that show a porous morphology that allows to adsorb several mixtures of down-converting materials to cover the whole visible spectrum (Figure 3) [8]. Recently, this idea has been carried out with the use of three different non-toxic small-molecules that provide WHLEDs with CRI over 90 [8b]. This approach is easily applicable to any commercial LED and it is versatile with respect to the type of down-converting materials, but the stability in terms of luminous efficiency and color quality as well as the development of MOFs based on cheap an environmentally friendly metals still remain a challenge. Recently, several groups have developed a down-converting system based on a cellulose matrix and a mixture of blue, green, and red quantum dots [9]. The preparation of the composite is quick and facile to reproduce, but its compatibility with other materials and the stability of the WHLED needs to be assessed to elucidate its prospect. Finally, we have recently developed a new encapsulation system that consists of mixing branched and linear polymers under vigorous stirring followed by the partial evaporation of the solvent under vacuum conditions [10]. This leads to a rubber-like material, in which any kind of down-converting material can be applied and easily recycled. Indeed, this matrix was developed to allow the use of fluorescent proteins as down-converting coating for WHLEDs. Hereafter, this new device will be referred to as Bio-WHLED. Fluorescent proteins are environmentally-friendly compounds and are easily produced by means of their expression in E. coli, which is a low-cost and up-scalable technique [11]. Despite these assets, the need of water-based buffer solutions and their low intrinsically stability under ambient conditions and high temperatures have hampered their use in the optoelectronic field. However, once they are embedded into the rubber-like matrix, the fluorescent proteins show stabilities of several months without affecting the features of the


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rubber-like encapsulation (Figure 4). Similar to the cellulose-based WHLEDs, different amounts and mixtures of the fluorescent proteins can be integrated into the rubber-like material, but we encountered that the best results are achieved by using a bottom-up energy transfer cascade coating (Figure 4). Here, the UV- and/or blue emission of the chip is absorbed by the protein coating that further emits light at a higher wavelength. More importantly, the ratio of down-conversion efficiency - i.e. the ratio between the maxima related to the down-converting coating and the chip - can be increased up to values of 400% by means of increasing the amount of proteins or the thickness of the coating (Figure 4). The excess of emission from the first coating can be used to excite a second coating that features emission at higher wavelengths. This procedure can be repeated as many times as required to cover up the whole visible spectrum (Figure 4). In addition, it can be extended to the NIR region, since the rubber-like encapsulation features transmittance values of around 95% and refractive index values superior to 1.8 and the cascade architecture circumvent energy loss issues due to undesired energy transfer process. In detail, the Bio-WHLEDs shown in figure 4 have been prepared by covering commercial UV- or blue- LED by a double- or triple-layer coatings - i.e. a blue LED (450 nm) and green (520 nm) / red (650 nm) or an UV LED (390 nm) and blue (480 nm) / green (520 nm) / red (650 nm) fluorescent proteins, respectively. These devices show a light spectrum that consists of the sum of the peaks of all the components of the LED - i.e. those from the chip and the down-converting packing, providing easy-to-tune light spectrum with, for instance, CIE coordinates of 0.32 / 0.33, CRI up to 80, and luminous efficiencies of 50 lm/W. More interestingly, the luminous efficiency and color quality stay constant over hundreds of hours with a loss of less than 10% of its initial values (Figure 4).

Figure 4: (a) Pictures of gels and rubber-like materials

based on fluorescent proteins. (b) Top, absorption

spectra over time suggest high stability under ambient

storage. Bottom, pictures of the rubbers upon UV

excitation. (c) The design of the first Bio-WHLEDs (top)

and its performance under continuous working

conditions (bottom) In view of the aforementioned, WHLEDs can be considered as an attractive approach in terms of replacing the expensive and rare IPs, resulting in a strong reduction of the total prize of the LED, and efficiently converting the blue emission of the chip to the more necessary low-energy component for developing warm white emitting LEDs that are not dangerous to human health. WHLEDs can easily use filters and attenuators to avoid the flickering and the glare issues. Though the only roadblock seems to be stability towards the commercial implementation of the technology. This is even more critical if we consider the development of high power LED arrays, in which high temperatures are reached. To this end, two major considerations need to be addressed in the near future. The packing system must feature: • An easy-to-fabricate protocol without using thermal/UV curing procedures • Low cost raw materials and recycling protocols • High transmittance, refractive index, and mechanical robustness The down-converting compounds must be: • Easy and cheap to produce


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• Nontoxic • Easy to tune in terms of high absorption extinction coefficients and fluorescent quantum yields • Thermo- and photo-stable under ambient conditions Conclusions Taking these considerations into account, the Bio-WHLEDs bear great potential for future breakthroughs. However, more efforts need to be devoted to circumvent the loss of color quality that is related to denaturation of the proteins and to enhance the thermal stability of both the matrix and the proteins. Currently, we are designing more thermo- and photo-stable fluorescent proteins and polymers to further enhance the performance of the Bio-WHLEDs featuring warm white emissions and even more relevant to mimic the sun light spectrum. References [1] a) McKinsey & Company, Lighting the way - Perspectives on the global lighting market / second edition, 2012; b) US Department of Energy, Life-Cycle Assessment of Energy and Environmental Impacts of LED Lighting Products, 2012; Top Sector HTSM - Innovation Contract, Lighting the future, 2013; US Department of Energy, Manufacturing Roadmap Solid-State Lighting Research and Development, 2014. [2] Haitz, R. et al. Phys. Status Solidi A, 2011, 17, 208. [3] Federation of National Manufacturers Association for Luminaires and Electrotechnical Components for Luminaires in the European Union & European Lamp Companies Federation (CELMA & ELC), The European Lighting Industry’s Considerations Regarding the need for an EU Green Paper On Solid State Lighting, 2011. [4] a) Dehen, W. CEO of OSRAM in ZVEI: AMPERE - Das Magazin der Elektroindustrie

(http://www.zvei.org/Publikationen/ZVEI-AMPERE-1-2014.pdf) 2014; b) Volz, D. et al. Green Chem., 2015, 17, 1988. [5] a) The Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR of the European Commission, Health Effects of Artificial Light, 2012. http://ec.europa.eu/health/ scientific_committees/opinions_layman/artificial-light/en/index. htm#1; b) Martinsons, C. et al. International Energy Agency 4E Solid State Lighting, Solid State Lighting Annex - Potential Health Issues of Solid State Lighting Final Report 2014. [6] a) Jaadane, I. et al. Free Radic Biol Med. 2015, 84, 373; b) Shang, Y. M. et al Environ Health Perspect. 2014, 122, 269; c) Marquioni-Ramella, M. D. et al. Photochem. Photobiol. Sci., 2015, 14, 1560; d) Bonmati-Carrion, M. A. et al. Int. J. Mol. Sci. 2014, 15, 23448; e) Madrid-Navarro, J. et al. Current Pharm. Design, 2015, 21, 3453. [7] a) Huyal, I. O. et al. J. Mater. Chem. 2008, 18, 3568; b) Jang, E.-P. et al. Nanotechnology 2013, 24, 045607; c) Yoo, H. et al. Nanoscale, 2015, 7, 12860; d) Findlay, N. J. et al. Adv. Mater. 2014, 26, 7290. [8] a) Sun, C.-Y. et al. Nat. Commun. 2013, 4, 2717; b) Tetsuka, H. et al. J. Mater. Chem. C 2015, 3, 3536; c) Cui, Y. et al. Adv. Funct. Mater. 2015, 25, 4796. [9] a) Zhou, D. et al. ACS Appl. Mater. Interfaces 2015, 7, 15830; b) Tetsuka, H. et al. J. Mater. Chem. C 2015, 3, 3536. [10] a) Weber, M. D. et al. Adv. Mater. 2015, 27, 5493; b) Weber, M. D. et al. Rubber-like Material for the Immobilization of Proteins and its Use in Lighting, Diagnosis and Biocatalysis EP-1674, 15173026.4 (pending) [11] a) Shcherbakova, D. M. et al. Current Opin. Chem. Biol. 2014, 20, 60; b) Chudakov, D. M. et al. Physiol. Rev. 2010, 90, 1103.


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A new spintronics material promises huge leaps in computer data storage

Figure 1: Schematic depiction of the spin ordering in

an antiferromagnet (left) and a ferromagnet (right). An international team of researchers have been using Diamond Light Source to examine what could be the future of computer storage, with results published in Science. The action centres on a new device made from a novel antiferromagnetic material, which holds the promise of ultra-high density data storage. It uses spintronics rather than electronics to store the data making it resistant to external magnetic fields, and external radiation, and it remains stable when the power is turned off. Furthermore, this all happens at room temperature in a material that is relatively easy to make. This is a combination of features that the data storage industry values very highly. Rotating pair of spins We have known about and studied antiferromagnetic materials for decades, but they were not thought to have any potential as magnetic storage media. The reason is down to the way their magnetism is aligned on the atomic level. Each atom in a magnetic material has a property called 'spin' which can be thought of as a tiny bar magnet, with a north and a south pole. In ferromagnetic

materials, the atomic spins are all lined up in the same direction, which is why they have a measurable magnetic field and act as large scale magnets. The regions in antiferromagnets are, by contrast, arranged head to toe as shown in Fig. 1. This means that the spins effectively cancel each other out and they have no external magnetic field. A normal data bit is stored by using a current to flip the orientation of the spins. This is not possible with antiferromagnetic materials but Dr Peter Wadley and his colleagues have tackled the problem a different way; a spintronic approach that rotates pairs of spins rather than flipping them end over end. Dr Wadley said: "If you turn them all together they turn easily, whereas individually they don't move. The physics is beautiful but complex yet the practice is relatively simple. We use an electric current to write, that is turn, a bit and then a smaller current to read it." Crucially, the current density required is in the same order as that used in commercial data storage devices. Watching them spin The evidence for this comes from an experimental single bit storage device that Dr Wadley and colleagues have been investigating at Diamond. It is a thin film of antiferromagnetic copper manganese arsenide (CuMnAs) grown by molecular epitaxy on a semiconductor base at the University of Nottingham. The team has shown that they can read and write to this device, but they needed more information on the behaviour of the affected regions. The lack of external magnetic field makes it very hard to see what is going on. "There is an electrical signal but it is very faint," said Dr Wadley. Instead the team used X-ray magnetic linear dichroism photoemission electron microscopy (XMLD-PEEM) available at Diamond.


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Figure 2: (a) Optical microscopy image of the device

used for PEEM imaging. (b) XMLD PEEM image of the

domain structure in the central region of the cross.

Vertically aligned spin domains appear black and

horizontally aligned domain appear white. The CuMnAs film was exposed to a beam of highly tuned monochromatic polarised X-rays. This displaced electrons from the material which were then detected by an electron microscope. The resulting images, essentially black and white photos, showed the magnetism on the surface of the material (Fig. 2). By comparing images before and after writing a bit of information, the researchers clearly showed that the spin orientation of the domains changed in response to the pulse of current, supporting the electrical readouts from the storage cell. Further experiments were conducted under magnetic fields up to 12T (enough to completely wipe a conventional magnetic storage device) and at temperatures between 150K and 304K, and in both cases the information remained intact.

Ticking the data storage boxes The new antiferromagnetic material has a range of properties that make it very attractive for use in data storage. It is not adversely affected by either temperature or strong magnetic fields, meaning it is a very robust method of storing information. The fact that it does not have any external magnetic field means that it cannot be measured by an external device. This makes it very secure as well as robust. On a smaller scale, the fact that individual regions do not have an external magnetic field means that they can be packed together far closer than current magnetic storage devices. In these the domains interfere with each other unless separated by a minimum distance. And finally, it has a very high theoretical switching speed, anything up to a 1,000 times faster than current magnetic media. Perhaps the most intriguing idea is that this CuMnAs film is just one of many possible antiferromagnets and is unlikely to be the best. It has been a very valuable experimental tool, but is the only one to be tested in this way to date. It is perfectly possible that material scientists will be able to produce other antiferromagnets with better properties, adding to the already vast potential of this research.


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Light-Driven Nitrogen Fixation

Coauthor and CU-Boulder assistant professor Gordana

Dukovic [Credit: CU-Boulder] A group of U.S. scientists report a new light-driven nitrogen-fixing process for converting dinitrogen (N2) into ammonia (NH3)—the main ingredient in fertilizer (Science, doi: 10.1126/science.aaf2091). The authors say their process, which makes use of nanomaterials and naturally occurring enzymes, could be the next revolution in fertilizer production, reducing agriculture’s dependence on fossil fuels. There are two common methods for converting the nitrogen in the atmosphere into a form that’s usable to plants and animals. In the first, bacteria in plant roots catalyze atmospheric nitrogen into ammonia with an enzyme called nitrogenase and a large amount of chemical energy from adenosine triphosphate (ATP) molecules. The second is an energy-intensive industrial process called the Haber-Bösch method, which revolutionized fertilizer production a century ago—but which consumes two percent of the world’s fossil fuel and releases “appreciable amounts” of carbon dioxide into the atmosphere. Light-harvesting nanocrystals The new light-driven process integrates nanoscience and biochemistry, eliminating the need for massive amounts of chemical energy from ATP or environmentally unfriendly fossil fuels. It uses cadmium sulfide nanocrystals to harvest energy from sunlight or artificial light. In the system, these nanorods—tuned to absorb photons at a 405-

nm wavelength—are combined with molybdenum-iron (MoFe) hydrogenase, the same enzyme used in natural bacterial nitrogen fixation. As sunlight strikes the nanocrystals, the absorbed photons kick out photoexcited electrons, which the nitrogenase uses for catalytic reduction of dinitrogen to ammonia. After the reaction, an organic chemical buffer, HEPES, serves as a “sacrificial electron donor” that resets the electrons in the nanorods, allowing them to catalyze the next round of the reaction. Approaching bacterial reaction rates Thus, under the new process, photon-absorbing nanorods, rather than bacterial ATP, provide the chemical energy and electron source driving ammonia production. During demonstrations, the team found that the system could produce some 315 ± 55 nanomoles of NH3 per milligram of MoFe protein. That’s 63 percent of the natural ATP-coupled reaction rate used by nitrogen-fixing bacteria under optimal conditions. And, the authors note, “the light-harvesting properties of nanomaterials are highly tunable,” a property that sets up the possibility of using such nanomaterials as a customizable electron source to drive other difficult catalytic transformations. The authors believe their light-driven process could also contribute to the development of cleaner fuel technologies, including fuel cells to store solar energy. The study was funded by the U.S. Department of Energy’s National Renewable Energy Laboratory and involved researchers from the University of Colorado Boulder (CU-Boulder), Utah State University and Montana State University.


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Researchers unveil submicroscopic tunable, optical amplifier

Rice University's new light-amplifying nanoparticle

consists of a 190-nanometer diameter sphere of

barium tin oxide surrounded by a 30-nanometer-thick

shell of gold. Credit: Alejandro Manjavacas /Rice

University

Rice University photonics researchers have unveiled a new nanoparticle amplifier that can generate infrared light and boost the output of one light by capturing and converting energy from a second light. The innovation, the latest from Rice's Laboratory for Nanophotonics (LANP), is described online in a paper in the American Chemical Society journal Nano Letters. The device functions much like a laser, but while lasers have a fixed output frequency, the output from Rice's nanoscale "optical parametric amplifier" (OPA) can be tuned over a range of frequencies that includes a portion of the infrared spectrum. "Tunable infrared OPA light sources today cost around a $100,000 and take up a good bit of space on a tabletop or lab bench," said study lead author Yu Zhang, a former Rice graduate student at LANP. "What we've demonstrated, in principle, is a single nanoparticle that serves the same function and is about 400 nanometers in diameter." By comparison, that's about 15 times smaller than a red blood cell, and Zhang said shrinking an infrared light source to such a small scale could open doors to new kinds of

chemical sensing and molecular imaging that aren't possible with today's state-of-the-art nanoscale infrared spectroscopy. Zhang, who earned his Ph.D. from Rice in 2014 and today works at Lam Research in Fremont, Calif., said parametric amplification has been used for decades in microelectronics. It involves two input signals, one weak and one strong, and two corresponding outputs. The outputs are also strong and weak, but the energy from the more powerful input—known as the "pump"—is used to amplify the weak incoming "signal" and make it the more powerful output. The low-power output—known as the "idler"—contains a residual fraction of the pump energy. "Optical parametric amplifiers operate with light rather than electricity," said LANP Director Naomi Halas, the lead scientist on the new study and the director of Rice's Smalley-Curl Institute. "In OPAs, a strong pump light dramatically amplifies a weak 'seed' signal and generates an idler light at the same time. In our case, the pump and signal frequencies are visible, and the idler is infrared." While the pump laser in Rice's device has a fixed wavelength, both the signal and idler frequencies are tunable. "People have previously demonstrated nanoscale infrared lasers, but we believe this is the first tunable nanoscale infrared light source," Halas said. The breakthrough is the latest for Halas' lab, the research arm of Rice's Smalley-Curl Institute that specializes in the study of light-activated nanoparticles. For example, some metallic nanoparticles convert light into plasmons, waves of electrons that flow like a fluid across a particle's surface. In dozens of studies over the past two decades, LANP


17

Rice University's new light-amplifying nanoparticle

consists of a 190-nanometer diameter sphere of

barium tin oxide surrounded by a 30-nanometer-thick

shell of gold. Credit: Alejandro Manjavacas /Rice

University

researchers have explored the basic physics of plasmonics and shown that plasmonic interactions can be harnessed for applications as diverse as medical diagnostics, cancer treatment, solar-energy collection and optical computing. One of LANP's specialties is the design of multifunctional plasmonic nanoparticles that interact with light in more than one way. Zhang said the nanoscale OPA project required LANP's team to create a single particle that could simultaneously resonate with three frequencies of light.

"There are intrinsic inefficiencies in the OPA process, but we were able to make up for these by designing a surface plasmon with triple resonances at the pump, signal and idler frequencies," Zhang said. "The strategy allowed us to demonstrate tunable emission over a range of infrared frequencies—an important potential step for further development of the technology." Zhang said former Rice physics postdoctoral researcher Alejandro Manjavacas—now at the University of New Mexico—performed the necessary calculations to design the triple resonant nanoparticle. Halas said the project also showcased the multidisciplinary strength of LANP. "In nanophotonics, applied and fundamental research go hand in hand because a deep understanding of the fundamental physics is what allows us to optimize particle design. That's why one of LANP's primary missions is to bring theoreticians and experimentalists together, and this project is a great example of how that pays off."


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Green Light for Migraine Relief

Exposure to a narrow band of green light may reduce light sensitivity and headache severity Light sensitivity, or photophobia, is a frequent symptom of migraine headaches, which affect nearly 15 percent of the world’s population. Harvard Medical School researchers at Beth Israel Deaconess Medical Center have found that exposing migraine sufferers to a narrow band of green light significantly reduces photophobia and can reduce headache severity. The study was published May 17 in Brain. “Although photophobia is not usually as incapacitating as headache pain itself, the inability to endure light can be disabling,” said Rami Burstein, the HMS John Hedley-Whyte Professor of Anaesthesia at Beth Israel Deaconess and lead author of the study. “More than 80 percent of migraine attacks are associated with and exacerbated by light sensitivity, leading many migraine sufferers to seek the comfort of darkness and isolate themselves from work, family and everyday activities,” said Burstein, who is vice chair of research in the Department of Anesthesia, Critical Care and Pain Medicine and academic director of the Comprehensive Headache Center at Beth Israel Deaconess. Five years ago, Burstein and colleagues made the surprising discovery that blue light hurts migraine patients who are blind. This finding prompted the idea that abnormal sensitivity to light during migraine could be alleviated by blocking blue light. Because that earlier study involved only blind patients who could not detect all colors of light, Burstein and his colleagues devised a way to study the effects of different colors of

light on headache in patients without visual impairment. In the current study, Burstein and colleagues found that of all light to which migraine sufferers are exposed, a narrow band of green light worsens migraine significantly less than all other colors of light and that at low intensities green light can even reduce headache pain. Of 69 participants, 41 completed the study. “These findings offer real hope to patients with migraines and a promising path forward for researchers and clinicians.”—Rami Burstein. The researchers asked patients experiencing acute migraine attacks to report any change in headache when exposed to different intensities of blue, green, amber and red light. At high intensity of light—as in a well-lit office—nearly 80 percent of patients reported intensification of headache with exposure to all colors but green. Unexpectedly, the researchers found that green light even reduced pain by about 20 percent. To understand exactly why green light causes less pain to patients with migraines, Burstein and colleagues designed experiments in which they measured the magnitude of the electrical signals generated by the retina (in the eye) and the cortex (in the brain) of these patients in response to each color of light. They found that blue and red lights generated the largest signals in both the retina and the cortex and that green light generated the smallest signals. Next, applying techniques recently developed by Rodrigo Noseda, HMS assistant professor of anaesthesia at Beth Israel Deaconess, they used animal models of migraine to study neurons in the thalamus, an area of the brain that transmits information about light from


19

the eye to the cortex. These neurons were found to be most responsive to blue light and least responsive to green light, explaining why the migraine brain responds favorably to green light. “These findings offer real hope to patients with migraines and a promising path forward for researchers and clinicians,” said Burstein. Burstein is now working to develop a more affordable light bulb that emits “pure” (narrow-band wavelength) green light at low intensity, as well as affordable sunglasses that block all but this narrow band of pure green light.

Currently, the cost of one such light bulb is prohibitively high, and the technology to block all but pure green light in sunglasses is available only in light microscopy, which is also very costly. This study was supported by National Institutes of Health grants R37 NS079678 and RO1 NS069847. Adapted from a Beth Israel Deaconess news release.


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Latest Journals

Rapid synthesis and luminescence properties of Sr3SiO5:Eu2+ Sr3SiO5:Eu2+ phosphors were synthesized rapidly through a microwave sintering method with the presence of activated carbon powder. The detailed compn. and morphol. were characterized by X-ray diffraction (XRD) and SEM (SEM). The influences of sintering time, fluxing agent (BaF2) content and rare earth ion doping concn. on its photoluminescence (PL) properties were also investigated. It was clear in PL spectra that a broad emission band peaking at 570nm was obtained in as-prepd. phosphors under a blue light excitation. Meanwhile, non-radiative transitions between Eu2+ ions in the Sr3SiO5 host had also been

demonstrated to be attributable to dipole-dipole interactions, and the crit. distance calcd. by the quenching concn. was estd. to be 10.56 Å. The samples were uniform in diam. and regular in morphol. In other words, the Sr3SiO5:Eu2+ phosphors possessed a potential application for white light emitting diodes (LEDs). Funct. Mater. Lett. 9 (2016) 1650028-1-

1650028-5.

DOI: 10.1142/S1793604716500284

Electronic Structure Descriptor for the Discovery of Narrow-Band Red-Emitting Phosphors

Narrow-band red-emitting phosphors are a critical component of phosphor-converted light-emitting diodes for highly efficient illumination-grade lighting. In this work, we report the discovery of a quantitative descriptor for narrow-band Eu2+-activated emission identified through a comparison of the electronic structures of known narrow-band and broad-band phosphors. We find that a narrow emission bandwidth is characterized by a large splitting of more than 0.1 eV between the two highest Eu2+ 4f7 bands. By

incorporating this descriptor in a high-throughput first-principles screening of 2259 nitride compounds, we identify five promising new nitride hosts for Eu2+-activated red-emitting phosphors that are predicted to exhibit good chemical stability, thermal quenching resistance, and quantum efficiency, as well as narrow-band emission. Our findings provide important insights into the emission characteristics of rare-earth activators in phosphor hosts and a general strategy to the discovery of phosphors with a desired emission peak and bandwidth. Chem. Mater. ??? (2016) ???-???.

Article ASAP

DOI: 10.1021/acs.chemmater.6b01496


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Non-rare-earth BaMgAl10-2xO17:xMn4+,xMg2+: a narrow-band red phosphor for high-power warm w‑LED

Owing to the low-price and admirable luminescent characteristics for warm white-LED (w-LED) application, non-rare-earth Mn4+-activated red phosphor has emerged as a potent competitor to the commercial Eu2+-doped nitrides in recent years. In this work, the novel red-emitting phosphor BaMgAl10-

2xO17: xMn4+, xMg2+ is successfully synthesized, which exhibits bright and narrow-band luminescence peaking at 660 nm with FWHM of merely ~30 nm, upon blue light excitation. XRD Rietveld refinement and HRTEM observation demonstrate the synthesized product a pure hexagonal BaMgAl10O17 (BMA) phase. The unique structural feature of BMA, i.e., the alternative arrangement of Mn4+-doped MgAl10O16/un-doped BaO layers in z direction, and that of Mn4+-doped [AlO6]/un-doped [AlO4] groups in x-y plane, is found favoring the efficient Mn4+ luminescence by reducing the non-radiative energy loss channels. Unlike the

previously reported hosts, BMA allows for the accommodation of Mg2+ into lattice without destabilizing the crystal structure. Remarkably, partition of Mg2+ in the host not only greatly enhances the Mn4+ luminescence by 1.84 times, but also retards the concentration quenching effect induced by the Mn4+ dipole-dipole interaction owing to the reduced number of Mn4+-Mn4+-O2- pairs (caused by the isovalent co-substitution of Mn4+-Mg2+ for Al3+-Al 3+ to maintain charge balance). Spectroscopic study demonstrates that the optimized BMA: 0.02Mn4+, 0.02Mg2+ luminescence exhibits a high color purity of 98.3%, a good color stability against heat, and an excellent resistance to thermal impact. When incorporating BMA: 0.02Mn4+, 0.02Mg2+ plus YAG: Ce3+ phosphors into an oxide glass matrix in various ratios, the phosphor-in-glass (PiG) color converters are obtained which inherit the spectral properties of the original powders. Thanks to the red supplement of Mn4+ activators, chromaticity parameters of w-LED fabricated by coupling PiG with blue chip are well tuned with CCT decreasing from 6608 K to 3622 K, and CRI increasing from 68.4 to 86.0, meeting the requirement for in-door lightings. Chem. Mater. (2016) ???-???.

Just Accepted Manuscript

DOI: 10.1021/acs.chemmater.6b01303


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Effects of the surface area of phosphor powders on colour coordinate variance In this study, the colour coordinate behaviours according to the surface area of phosphors were investigated to implement the colour coordinate of the desired zone in a random colour coordinate. For this purpose, the mixing ratio and dispensing amount of a green phosphor (Ce:YAG) and three red phosphors (CaAlSiN3:Eu2+) with different specific surface areas were adjusted, and the corresponding colour coordinate behaviour was examined. As a result, the colour coordinate behaviour was found to be considerably influenced by the mixing ratio of

red and green phosphors and the surface area of the phosphor powder particles. In conclusion, the colour coordinate of the desired zone can be more efficiently implemented by predicting the characteristics of different types of phosphors and their colour coordinate behaviours. The findings of this study are expected to greatly increase the yield of the light-emitting diode industry. Adv. Appl. Ceram. 115 (2016) 210-215.

DOI: 10.1080/17436753.2015.1117692

Luminescent behaviour of Mn4+ ions in seven coordination environment of K3ZrF7

A single-phased Mn4+ doped fluorozirconate red phosphor, K3ZrF7:Mn4+, has been successfully synthesized. Its structure, morphology, composition and optical properties were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometer, atomic absorption spectroscopy, diffuse reflectance spectra, photoluminescence spectra and the luminescence decay curve. It was found that

Mn4+ ion only coordinating with seven F- anions in K3ZrF7 crystal field can possessed intense red emission under blue light illumination. Mixing the obtained K3ZrF7:Mn4+ red phosphor with commercial Y3Al5O12:Ce3+ and coating the mixture on blue-GaN chip, obvious warm white light with low correlated color temperature (2970 K) and high color rendering index (Ra = 91.4 and R9 = 72) were achieved from the white light-emitting diode devices. Dalton Trans. ?? (2016) ??-??.

Accepted Manuscript

DOI: 10.1039/C6DT01693F


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Novel Patents

Boronitride halide oxide phosphors and their preparation and use

Compds. are claimed which are described by the general formula Aa(EA)b(Ln)cBeN2e+fOg(BNO)h(Hal)i (A = ≥1 of Li, Na, and K; EA = ≥1 of Mg, Sr, Ca, and Ba; Ln = ≥1 of Sc, Y, La, Gd, and Lu; Hal =

≥1 of F, Cl, Br, and I; 0 ≤ a ≤ 3; 0 ≤ b ≤ 5; 0 ≤ c ≤ 6; 1 ≤ e ≤ 4; 0 ≤ f ≤ 2; 0 ≤ g ≤ 6; 0 ≤ h ≤ 1; 0 ≤ i ≤ 1; a + 2b + 3c = 3e + 3f + 2g + 2h + i; 2 ≤ a + b + c ≤ 6; and 2 ≤ e + f + g + h + i ≤ 6, with the restriction that Ca2BN2F:Eu is excluded) and doped with ≥10 mol % Eu, Ce, Sm, and/or Pr. Methods for prepg. the compds. are described which entail forming a mixt. including a nitride of ≥1 of A, EA, and/or Ln, B nitride, and a Eu, Ce, Sm, and/or Pr source; and calcining the mixt. under non-oxidizing conditions. The use of the compds. as phosphors and light sources contg. the compds. (e.g., in phosphor-converted light-emitting diodes) are also described. WO 2016055140 A1

A simulated sunlight led light source and its preparation method

[Machine Translation of Descriptors]. The present invention discloses a simulated sunlight LED light source, the LED light source comprises a blue LED chip and LED phosphors, LED phosphor represented by the following components: blue-green powder

10-20 %with emission wavelength of 490-510nm, green powder 70-80% with mission wavelength of 520-540nm, orange powder1.5-5% with emission wavelength of 600-620nm, red powder 4-12.3% with emission wavelength of 630-660 nm. Correspondingly, the invention also provides a preparation process of simulated sunlight LED light source. According to the present invention, the spectrum of the LED light source is close to the sun spectrum, the light emitting uniformity is good, the color rendering is good, the color temperature is within the desired range of sunlight. CN 105552196 A


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White light source for approximating solar light and capable of reproducing the subtle fluctuations in solar light and white light system

The present invention relates to a white light source for approximating solar light and capable of reproducing the subtle fluctuations in solar light and white light system. The white light source is equipped with a light source unit which includes a light emitting diode, a light emitting diode chip, a phosphor

layer covering the light emitting diode chip, blue phosphor, a blue-green phosphor, a green, yellow and red phosphor mixed with a resin. The light emitted from the light source unit has a correlated color temp. corresponding to a chromaticity point located on a CIE chromaticity diagram and having a deviation of -0.005 to +0.005, inclusive, relative to a black body radiation locus. The emitted light satisfies the formula 0.2≤[(P(λ)×V(λ))/(P(λmax1)×V(λmax1))-(B (λ)×V(λ))/(B(λmax2)×V(λmax2))]≤+0.2. According to the present invention, it is possible to provide the white light source for approximating solar light and capable of reproducing the subtle fluctuations along with a white light system. WO 2016067609 A1

Barium fluorogermanate red light material for white light LED and its preparation method

The chem. compn. of the barium fluorogermanate red light material is BaO:4GeO2:xMn4+:yMgF2, wherein: 0.001%≤x≤1.0%; 1.0%≤y≤5.0%. The barium

fluorogermanate red light material is prepd. by solid phase synthesis method, and the method comprises the steps of proportioning barium carbonate, germanium oxide, manganese carbonate and magnesium fluoride, grinding for 10-30 min, pre-sintering at 300-500 °C in air for 3-5 h, cooling, grinding and sintering at 700-900 °C in air for 3-5 h. The barium fluorogermanate red light material can emit bright red light upon excitation by 300-500 nm light. The barium fluorogermanate red light material is used for manufg. white light LED.

CN 105462585 A

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Newsletter€¦ · Newsletter Tailored Optical Materials Volume 10 Issue 06 Matthias Müller June 2016 Thomas Jüstel Research & Development Latest Journals Novel Patents Burn The