Newsletter - fh-muenster.de...of the UV LED market worldwide will grow from US$166 million in 2016 to US$555 million in 2021 at compound annual growth rate (CAGR) of 27%. “As the

NewsletterTailored Optical Materials

David Böhnisch

Reseach &

Development

Latest

Journals

Novel

Patents

Thomas Jüstel

January 2017Volume 11 Issue 01

LED Droop: The Role of the Phosphor

Conception: Prof. Dr. rer. nat.Thomas Jüstel

Edited by: David Böhnisch

Contact: [email protected]

Research & Development ....................................................................................................................... 3

Nichia’s Developments for Micro-LED and Other Lighting Technologies in 2017 ....................... 3

CRI should never be used in efficacy regulations but a new lumen definition should .................... 6

LED droop: The role of the phosphor ............................................................................................ 10

GE Lighting Signs KSF Red Phosphor License Agreement with Suijing Optoelectronics ........... 14

Lumileds Unveils First Compact UVA Emitter LUXEON UV U1 ............................................... 15

Latest Journals ...................................................................................................................................... 16

Luminescence properties of novel Ba2MgWO6:Eu3+ and g-C3N4/Ba2MgWO6:Eu3+ phosphors ... 16

Crystal structure, tunable luminescence and energy transfer properties of Na3La(PO4)2:Tb3+, Eu3+ phosphors........................................................................................................................................ 16

White Light Emitting MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) Phosphors for WLEDs ....................... 17

Synthesis, luminescence properties and electronic structure of Tb3+-doped Y4−xSiAlO8N:xTb3+ – a novel green phosphor with high thermal stability for white LEDs ................................................ 17

Photoluminescence study of a broad yellow-emitting phosphor K2ZrSi2O7:Bi3+ .......................... 18

Broadband Yellowish-Green Emitting Ba4Gd3Na3(PO4)6F2:Eu2+ Phosphor: Structure Refinement, Energy Transfer, and Thermal Stability ......................................................................................... 18

Novel Patents ......................................................................................................................................... 19

Radioactive contamination inspection device ................................................................................ 19

Light emitting device and manufacturing method thereof ............................................................. 19

Light emitting element for display device using exciplex and fluorescent substance to achieve high emission efficiency ................................................................................................................. 20

Wavelength conversion device, light source system and projection system .................................. 20

Backlight device and liquid crystal display device provided with same ........................................ 21

Volume 11 Issue 01 January 2017

3

Research & Development

Nichia’s Developments for Micro-LED and Other Lighting

Technologies in 2017 The slowdown in LED backlight market

including smartphone displays continued to

trend on into 2016 that even top player in the

industry Nichia is looking beyond this

particular market sector in its 2017 roadmap.

Left to right: Hinori Takagi, General

Manager, Intellecutal Property Department, Legal

and Intellectual Property Dept., Legal & Intellectual

property Division Administration Unit, Nichia, Chun

Chia Tai, Chairman and President of Nichia s Shanghai and Taiwan offices,Takashi Sakamoto,

Principal Technical Officer, Optoelectronics Products

The BU, Nichia.

Offset by oversupply and cutthroat price wars in 2015, LED backlight market competition remains intense and the market decreased steadily, by the start of 2016 growing number of LED manufacturers started to look into other niche lighting market applications, such as automotive lighting, UV LED, IR LED, and others.

Top Japanese LED manufacturer Nichia announced at a press conference to celebrate its 60th anniversary in Taipei, Taiwan on Tuesday that in 2017 it upheld a positive outlook for intelligent automotive headlight applications, human-centric smart lighting, micro-LEDs, lasers, and UV LED technologies.

Micro-LEDs trends to move from large

displays to smaller device

Previously, most industry experts such as CEA-LETI and Epistar noted smaller displays, such as wearables and smartphones would be the entry point for micro-LEDs, where it possessed considerable technology advantages over OLED and LCD, such as lower energy consumption, self-illuminating properties, brighter and more efficient illumination output.

Takashi Sakamoto, Principal Technical Officer of Optoelectronics Products at Nichia’s perspective on micro-LEDs surprisingly contradicted with mainstream opinion, instead of moving from smaller devices to larger screen applications, he pointed micro-LEDs would make its way in larger displays before moving to smaller ones.

He outlined the order of micro-LED applications would be: large TV displays, outdoor displays, indoor displays, monitors, smartphones, VR devices and lastly smart watches.

Asked why his micro-LED development order was reversed from most manufacturers, Sakamoto responded it depended on the market value and micro-LED technology. The wearable market value is small compared to the display and backlight market, which still has a considerably larger market share than the niche wearable market.

Technology wise it might be easier to make micro-LEDs for large displays before making smaller displays as well because of the size requirements for different applications, the tinnier the display the more miniature the


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micro-LED chip has to be, said Chun Chia Tai, Chairman and President of Nichia’s Shanghai and Taiwan offices.

“There are many different definitions on the market for micro-LEDs with sizes ranging from 3 to 4 micrometer, 50 micrometer, to even 200 micrometer,” said Tai. “Displays might use 30 micrometer to 40 micrometer sized micro-LEDs, while smartphone screens might require 3 micrometer.”

Tai said the company’s ultimate aim was to mass produce 3-micrometer sized micro-LEDs, and that the technology itself was not an issue.

Nichia’s micro-LEDs uses RGB LEDs, and develops most solutions in-house, but might not develop mass transfer solutions for the chips, said Sakamoto.

“It will take more than three years for micro-LED technology to fully mature, in the meantime you might see end products or applications with rudimentary micro-LED technology emerge on the market by 2017,” he added.

Nichia still working on UV-C LED

The Japanese manufacturer is rather successful in the UV-A LED market sector, where some of its products can be found in air purifiers, but is still developing 280 nanometer wavelength UV-C LEDs with longer lifetimes for water sanitization applications.

The company is working to improve the UV-C LED reliability and durability, but did not announce the product launch schedule.

UV LED products are projected to become increasingly widespread in home appliances, including air conditioners air purifiers and others.

Based on LEDinside estimates the total value of the UV LED market worldwide will grow

from US$166 million in 2016 to US$555 million in 2021 at compound annual growth rate (CAGR) of 27%.

“As the technology continues to improve, the global market value of UV-C LEDs for the sterilization/purification application is forecast to grow at a high CAGR of 56% from US$28 million in 2016 to US$ 257 million in 2021,” said Joanne Wu, Assistant Manager, Research Department, LEDinside.

Smaller countries might not need laser

headlights in cars

Speaking about laser headlight developments, Sakamoto noted the market remains relatively small with low market penetration rates. Even though German automotive makers, such as Audi and Benz, have embraced the advanced lighting technology, Japanese car makers especially those focused on the domestic market might require this feature at all.

“Laser headlights typically have a beam distance of 600 meters and above,” explained Sakamoto. “This might be necessary in Germany, but there is little demand to make a headlight with this illumination range in Japan, other than in certain areas in Hokkaido.”

Despite certain market limitations for laser headlights, Sakamoto projected the market would continue to grow with demands peaking at around 2018.

Nichia is also setting aside more resources to develop adaptive headlights, and is working with driver and power solution providers, such as Texas Instruments (TI) to develop smart headlights.

“There has been growing demand from clients to make smart headlights,” said Sakamoto.

The company is mass producing 4-chip LED packaged headlights, and for Daylight Running Lights (DRL) the leading Japanese LED maker is producing 3 millimeter LED


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packages. The company will not be making automotive LED modules that might put it in a competing position with clients.

The company’s automotive lighting revenue is projected to reach 55 billion Japanese Yen (US $) by 2016.

Sakamoto projected its automotive lighting business revenue will double in the future, while its laser lighting business would triple or quadruple.

Laser technology have a small revenue share in the company earnings, but Sakamoto estimated revenue would grow exponentially from the current 5% revenue share in 2017, to at least 17% by 2020.

Lighting in the future needs to provide

added value

Manufacturers overt emphasis on LED lumen output has become a bygone among top manufacturers, where human centric lighting, and luminaries with high color quality performance will become increasingly important, said Sakamoto.

Development of human centric lighting capable of color switching, or having Ra above 95, warm color temperature 2000-2200K LED, will become more common.

“Lighting quality often is sacrificed when LEDs are driven up to higher lumen output,” said Sakamoto. “We are working on making LEDs with better color performance, and might target the commercial lighting sector in the near future.”

Nichia’s Shanghai office is developing LED grow lights and conducting research on the most suitable LED lighting spectrum for plants.

For a manufacturer devoted to R&D to keep its technological competitive edge, Nichia will be investing about 40 billion Japanese Yen in total in 2017 to continue advancements numerous lighting technologies.


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CRI should never be used in efficacy regulations but a new lumen definition

should We believe that it is both important and appropriate for governments to be concerned with limiting wasted electric energy. Light sources that can provide the many benefits expected from lighting at a lower electric power should be formally encouraged or regulated by governments. But some policies that modify or patch efficacy guidelines with a color rendering index (CRI) requirement intended to ensure quality of light are fundamentally flawed. This article will explain how a revised look at the definition of the lumen could yield simple regulatory metrics that ensure efficient and quality light.

One of the important benefits provided by lighting is color quality. Several national governments (Australia, Canada, and the United States)1 and at least one state government (California through the California Energy Commission, or CEC 2016 policy)2 formally recognize the importance of color quality by including minimum requirements of the color rendering properties of light sources.

Unintended consequences

The idea behind such policies is that tighter restrictions on light source luminous efficacy (photopic lumens per watt) should not penalize color quality. The metric of choice by government regulators for characterizing the benefit of color quality has been the general CRI developed in the early 1960s. Briefly, CRI is a calculation procedure comparing the chromaticities of eight standard color chips illuminated by a reference source with their chromaticities when illuminated by a practical light source. The greater the chromaticity shift, the lower the CRI. The lower score applies even if people prefer the color quality rendered by the practical light source more than that provided by the reference source!

FIG. 1. Results from research performed by

Narendran and Deng show a negative correlation

between CRI and subjects' general preference and

skin tone preference under different light sources.

Fig. 1 shows results from a study of color rendering by Narendran and Deng3 that clearly demonstrate the inability of CRI to characterize the color preferences rendered by different light sources. These results strongly suggest that a minimum requirement for CRI will not guarantee peoples' satisfaction of the color quality of illumination provided by a light source.

In more recent work, Fig. 2 shows results from an experiment where subjects were asked to a) rate different LED light sources in terms of how appealing they render the colors of plastic blocks (columns 1 and 3) and b) their willingness to purchase those plastic blocks based on how they looked under those light sources (columns 2 and 4). Their responses were plotted as a function of CRI (columns 1 and 2) and of gamut area index, GAI (columns 3 and 4), a measure of color saturation or color vividness provided by a light source. GAI is a metric that the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute developed in 2010 as a complement to CRI.

Why CRI fails as a patch

Both Fig. 1 and 2 clearly show that higher values of CRI do not necessarily mean better color quality. Logically then, CRI should never be used by government regulators as a


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patch to luminous efficacy requirements to ensure that light sources will provide the expected benefit of color quality.

The fundamental problem is not, however, replacing one color quality patch with another one (e.g., GAI). Rather, the solution is to revise the current definition of luminous efficacy that is based upon photopic lumens per watt. The photopic luminous efficiency function, V( ), sets the wavelength range and the weighting of those wavelengths in the numerator of the luminous efficacy calculation (i.e., lumens). V( ) was developed in 1924 to represent "the spectral sensitivity of human vision".4 It is now known that V( ) is based on just two of the five photoreceptors in the human retina, the long-wavelength (L) sensitive and the middle-wavelength (M) sensitive cones. The other three retinal photoreceptors provide humans with sensitivity to shorter wavelengths, so V( ) is an inadequate and incorrect representation of human spectral sensitivity.

Color perception

The spectral bias of V( ) is particularly important for color quality, because it heavily discounts the significance of the short-wavelength (S) sensitive cone required for trichromatic color vision. (For background on color science, see the four-part series published by LEDs Magazine on the topic.) Rather than continue adding compensatory color quality patches to photopic luminous efficacy requirements, the definition of the luminous efficiency function underlying the lumen should change to be inclusive of all photoreceptors in the human retina.

FIG. 2. Research revealed subjective ratings of

overall appeal of color of plastic blocks and

willingness to purchase those plastic blocks based

on how they look under eight different LED light

sources, as a function of CRI (columns 1 and 2,

negative correlation) and GAI (columns 3 and 4,

positive correlation) for the LED sources evaluated.

Observers rated each of the eight LED light sources

sequentially, in random order at an illuminance of

420 lx inside a white diffuse viewing booth. One of

the three tile sets was predominantly blue (55%,

top row), one was predominantly red (55%, middle

row), and the third one had equal proportions of

red and blue blocks (35% each, bottom row). The

relatively small number of green and white blocks

was constant in all three tiles.

Fig. 3 shows the action spectra of the five photoreceptors in the human retina, taking into account pre-retinal filtering, along with the photopic luminous efficiency function, V( ), currently used to define the lumen, and the universal luminous efficiency function, U( ), proposed as a replacement. As Fig. 3 clearly shows, U( ) better represents the spectral sensitivity of human vision than V( ). Since luminous efficacy defined in terms of U( ) would no longer be inherently biased against the S-cone, government regulators would no longer need compensatory color quality patches to modify or complement their luminous efficacy requirements.


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FIG. 3. The graph shows the action spectra of the

five photoreceptors in the human retina, taking into

account pre-retinal filtering, along with the photopic luminous efficiency function, V λ , currently used to define the lumen, and the universal luminous efficiency function, U λ , proposed as a replacement.

Photopic and universal luminous efficacy

The table compares the photopic and the universal luminous efficacies of a selection of commercial light sources based on research in Reference 5. Notice that the two white LED light sources with the highest GAI, which is well correlated with color preference (Fig. 2), also have the highest universal luminous efficacy. This example helps demonstrate the fallacy of the myth that there is an inherent tradeoff between color quality and luminous efficacy. Notice too that these two sources do not have the highest CRI.

Consider high-pressure sodium (HPS), a source with high photopic luminous efficacy but poor color quality, as a hypothetical benchmark source for regulating minimum luminous efficacy. Except for HPS, all of the sources in the table would fail luminous efficacy requirements if the minimum photopic luminous efficacy was set at 107 lm/W.

In contrast, all of the sources in the table would pass if a minimum universal luminous efficacy was set at 138 lm/W. The table

shows that if HPS were taken as the benchmark source for luminous efficacy regulations, white light sources designed, fabricated, and sold to provide many lighting benefits, including good color rendering, would no longer need a regulatory patch to ensure they remain on the market.

Suggested regulatory actions

In sum, governments want to make sure that increasingly restrictive luminous efficacy requirements do not have collateral negative effects on the expected benefits provided by LED lighting. Among the many quality criteria added to luminous efficacy regulations (e.g., start time, lamp life, flicker), minimum color quality standards are commonly employed.1 CRI has traditionally been the color quality metric of choice among regulators.

Many research results, including those shown here, demonstrate that CRI should never be used as a color quality patch for luminous efficacy regulations. CRI is simply not predictive of user preference or willingness to purchase a light source. More fundamentally, V( ) is a biased representation of the spectral sensitivity of human vision, specifically discounting the role of S-cones required for good color vision.

Because U( ) is a more accurate representation of the spectral sensitivity of human vision, utilizing it for defining the lumen in luminous efficacy requirements elegantly and simply obviates regulatory patches for color quality. The myth that there is a necessary tradeoff between luminous efficacy and color rendering disappears once the spectral sensitivity of human vision is accurately represented by the universal lumen. This does not mean that minimum color quality criteria couldn't be included in government regulations, only that they need not be introduced to offset the spectral bias of V( ).


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A comparison of photopic and universal

luminous efficacies for a selection of

commercial light sources.

A more complete discussion of the universal luminous efficiency function, U( ), and more detailed, quantitative analyses of the electric energy wasted by using V( ) in luminous efficacy regulations have recently been published.5-8

REFERENCES

1. International Energy Agency (IEA), "Light's Labour's Lost: Policies for Energy-efficient Lighting in Support of the G8 Plan of Action," Paris: IEA, 2006.

2. California Energy Commission (CEC), "Proposed Revised Express Terms, 15-Day Language for Small Diameter Directional Lamp, Portable Luminaires, and General Service Light Emitting Diode Lamps," 2015 Appliance Efficiency Rulemaking Docket Number 15-AAER-6 (CEC-400-2015-044-15DAY-REV), January 2016.

3. N. Narendran and L. Deng, "Color rendering properties of LED light sources," Solid State Lighting II: Proc. SPIE, 4776, 61-67, 2002.

4. Commission Internationale de l'Éclairage, Commission Internationale de l'Éclairage Proc., Cambridge: Cambridge University Press, 1924.

5. M.S. Rea and A. Bierman, "A new rationale for setting light source luminous efficacy requirements," Lighting Res. and

Technol., first published on Sep. 10, 2016, doi:10.1177/1477153516668230.

6. M.S. Rea, Value Metrics for Better

Lighting, SPIE Press: Washington, USA, 2013.

7. M.S. Rea, "The lumen seen in a new light: Making distinctions between light, lighting and neuroscience," Lighting Res. and

Technol., May 2015, 47, 259-280, first published on Mar. 31, 2014, doi:10.1177/1477153514527599.

8. M.S. Rea, "Shedding light on light and lighting," 28th Session of the CIE, Manchester, UK, June 28-July 4, 2015, Vienna: Commission Internationale de l'Éclairage.


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LED droop: The role of the phosphor

Phosphors contribute to droop, but their

energy-sapping impact can be minimised

through LED design, or by casting them in a

ceramic form.

During the last decade, there has been a widespread, on-going debate over the origin of droop. Attempts to uncover the cause of droop have focused on the blue-emitting chip, which overlooks one of the key processes in the solid-state light bulb. As white light is produced by mixing the blue emission from the chip with that generated by an optically pumped phosphor, it is crucial to consider whether the phosphor is also prone to droop.

Figure 1. Efficiency droop is more severe in white

LEDs than it is in blue-emitting chips.

One way to illustrate that droop in white LEDs can be appreciably higher than that produced by the blue pump LED alone is to compare the normalized external quantum efficiency of a warm-white, 1 mm2 thin-film-flip-chip LED and its constituent blue pump LED at a range of drive currents (see Figure 1). Pulsed driving conditions distinguish between the impact of drive current density and thermal effects, and reveal that droop is significantly more severe in a white LED than a blue-emitting chip. These measurements have led our team at Lumileds to scrutinise Europium-doped red

nitride phosphors, which are commonly used in state-of-the-art LEDs to provide emission at longer wavelengths. This investigation involved measurements of quantum conversion efficiency for the LED phosphor at different temperatures and different intensities of blue light irradiance. To distinguish between the influence of temperature and irradiance, we employed pulsed excitation. Laser pulses were long enough to account for phosphor luminescence rise and fall times, and heating was avoided with a 1 kHz duty cycle. Our study has not been limited to the europium-doped nitride red phosphors, and includes the commonly used cerium-doped aluminium garnets. Both phosphors suffer from droop, but this is more pronounced in the europium-doped nitride reds – here phosphor photo-quenching is severe enough to contribute between 20 percent and 25 percent of the droop in warm-white LEDs. Compounding matters, the phosphor-related droop produces a shift in spectral output towards higher colour-correlated temperatures. As cerium-doped aluminium garnet is less prone to droop than europium-doped nitride red phosphors, at first glance it would appear that the solution is to use this in white-emitting LEDs. But such an approach is not practical, because the spectral output of this phosphor is not suitable for realising a high colour-rendering index. A better way forward is to understand the limitations of europium-doped nitride red phosphors and devise approaches to minimising the droop associated with them.


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Figure 2: The droop in efficiency is accompanied by

the shift in white LED spectra, which gives insights

into the process of photo-quenching in phosphors.

To gain greater insight into the underlying physics of europium-doped nitride reds, and the impact of photo quenching on LED performance, we prepared (Ba,Sr)2Si5N8: Eu2+ powders with varying europium concentration. Our quantum efficiency measurements revealed that the rate of quenching in (Ba,Sr)2Si5N8:Eu2+ increases with temperature and europium concentration (see Figure 4). These findings can guide phosphor material and LED architecture design, and lead to a better understanding of the physics of the quenching mechanism. We have fitted the experimental rate of phosphor quenching in our samples with a model for radiative and non-radiative recombination processes. This gives a close fit when using a term that is close to the quadratic of the concentration of excited Europium activators. This model replicates results for different concentrations and thicknesses, so long as the non-linear, non-radiative coefficient is kept constant.

Figure 3: The drop in quantum efficiency with

excitation varies with the phosphors used in state of

the art LEDs.

These insights suggest that of the two most probable candidates for the non-radiative processes − Foerster/Dexter cross relaxation and excited state absorption – it is the latter that is the likely culprit in phosphor quenching. As excited state absorption is excitation dependent, it is similar to the very familiar non-linear process of droop in InGaN quantum wells. This intrinsic loss mechanism for the phosphor cannot be eliminated, but it is possible to minimise its impact via engineering at the material and device level.

Figure 4: Photo-quenching in Eu2+ red nitrides

shows strong dependence on temperature and

activator concentration.

Our experiments point to an approach for reducing phosphor droop − cutting the activator concentration. The downside is that to realise a desired colour point, there must be a longer optical path for pump light through the phosphor. In practice, this means thicker or heavier-loaded converting layers, which lead to excessive scattering and heating and ultimately lower LED efficiency.


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One way to mitigate these unwanted consequences is to turn to ceramic phosphor materials. Their attributes include excellent thermal properties and greatly reduced optical scattering, which allows for thicker converting layers without efficiency penalties. This is a solution that we have adopted in a number of products that feature our Lumiramic phosphor technology (see Figure 5).

Figure 5: Lumiramic phosphor technology is well

suited for high power high temperature

applications. Here are some examples of Lumileds

automotive LED products which leverage the

Lumiramic technology.

LED devices can also be designed to minimise the quenching and its increase with temperature (the effect revealed in our measurements (see Figure 4)). The key is to reduce blue light irradiance and to draw the heat out of the phosphor layer as effectively as possible, while maintaining a low overall temperature. An illustration of this mitigation of photo-thermal quenching through LED design is provided by a comparison of two die-on-ceramic LED packages – one is a thin-film flip-chip, and the other a flip-chip architecture. With the thin-film flip-chip design − and any thin-film LED architecture for that matter − blue light is extracted through one side of the die. So, due to this, phosphor particles are positioned near the emitting surface of the die, in a thin layer of silicone.

In contrast, with a flip-chip architecture, the phosphor-filled converting layer can be placed on all five sides of the transparent sapphire substrate. This means that the blue light emitted by the active region of the pump LED can be distributed over a larger area than it would be with a thin-film design. What’s more, with a flip-chip, the heat of down-conversion is conducted through a larger contact area. The superiority of the flip-chip architecture over the thin-film flip-chip design is proven in our measurements of normalized optical power output (see Figure 6). As expected, the reduction in the intensity of the pump light on the phosphor, as well as better phosphor heat-sinking in the flip-chip LED, enables this type of design to be less afflicted by droop than its thin-film flip-chip cousin. For both designs, droop is more prevalent when the device is driven continuously, rather than in pulsed operation. That’s because the device driven continuously runs at a higher temperature, and photo-thermal quenching of the europium-doped nitride phosphors is more prevalent. It is worth noting that at 1.5 A, which is a typical maximum operating current for a 1 mm2 active-area high-power LED, although the junction temperatures of both classes of devices are within 5°C of the estimated 125 °C, the difference in phosphor temperatures is significantly higher. This contributes to the difference in light output and efficiency between the two architectures, which is more than 15 percent. The merits of a lower phosphor temperature and a lower irradiance of phosphor are very welcome, because they enable the flip-chip design to maintain high efficiency into even higher current densities.


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Figure 6: Thin-film architectures excite and

dissipate phosphor heat through one side , roughly equal to the pump-die area. Multiple sides of a flip-

chip allow lower average irradiance and a larger

area to conduct out the heat of conversion for the

same die area as thin-film. Thanks to these benefits,

in DC operation, the five-sided flip-chip emitter is

over 15 percent more efficient at 1.5 A.

The flip-chip design is not the only architecture for reducing photo-quenching. There are also the remote-phosphor configurations that are often seen in lighting modules, and mid-power LED or chip-on-board-type emitters. In these architectures,

blue light is distributed over a large phosphor volume, which helps to maximize efficiency. The downside is a compromise in source brightness, limiting emitter usability. For high brightness applications − such as automotive LEDs, laser-based sources, and forms of architectural lighting that require narrow, collimated beams − photo-thermal quenching of phosphors is a basic limitation. In these applications there is a need for sources with the lowest etendue possible, which means minimizing the emitting area and the angle of the source. In short, as photo-thermal quenching is a basic property of phosphor materials, it will impact LED efficiency. While LED architecture design can be used to mitigate this form of droop, ultimately, the best solution is at the material level. We have shown success in this area through the use of ceramic phosphors.


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GE Lighting Signs KSF Red Phosphor License Agreement with Suijing

Optoelectronics

A new Chinese LED company Suijing Optoelectronics listed on China’s Over The Counter Bulletin Board (OTCCB) has become the latest company to sign a red KSF phosphor license agreement with GE Lighting.

GE Lighting’s licensed its core red phosphor, also known for its chemical compound name Potassium Fluoride Silicon (PFS), global patent to Suijing Optoelectronics.

Earlier this month, Jufei Opto also announced sealing a license agreement deal for the same red phosphor patent with GE Lighting.

Jufei Opto announced the patent can be used to improve the company’s LED products wide color gamut (WCG) performance to match OLED technology, which would improve client satisfaction. The company also signed patent license agreements with GE for backlight WCG performance, and other global backlight market applications. All these have effectively raised the company’s added product value and core competitiveness, which was sued to strengthen the company’s domestic and international clients patent demands.

Suijing Optoelectronics is a company that is an advanced technology company involved in SMD LED R&D, production and sales, especially in the LED backlight component market for small displays. In the LED component market for small backlight applications, the company has entered major

Chinese and international smartphone brands supply chain to form a steady partnership system. In the large LED display backlight application market, the company’s backlight light bar modules began to take off in 2015, and accelerated growth. The product has been applied in a wide range of applications including Chinese smart TVs. Moreover, the company’s advantages in LED backlight technology applications, such as small pitch LED displays and LED flash lights have been the new growth engines for the company.

As a leader in the LED backlight market, Suijing Optoelectronics has valued intellectual property and been active in acquiring core patents authorization. Prior to this, the company signed a white LED patent licensing agreement with Toyoda Gosei on October 2015.

Receiving core patent licensing will become crucial for Suijing Optoelectronics in the future and open up new global business opportunities, and is important development for the Taiwanese company in the international market. Recent developments will also better support its clients international developments, and protect the company by forming a solid patent protection network that can improve its added value and core competitiveness.


15

Lumileds Unveils First Compact UVA Emitter LUXEON UV U1

Leveraging its leading expertise in chip scale packaging, Lumileds today introduced the LUXEON UV U1 LED for use in UV curing, counterfeit detection, analytical instrumentation, inspections and other UVA and Violet (380-420 nm) applications. This third generation of UV LEDs maintains the same micro package size as LUXEON Z UV, but enables a higher power density. LUXEON UV U1 also features a robust design that eliminates materials like silicone over mold, which tends to yellow and crack upon UV exposure, and the elimination of wire bonds that can lead to catastrophic connection failures. “UV LED customers are reliability driven. They tend to run their equipment 24/7 and demand a proven product that will perform as expected for over 20,000 hours. The LUXEON UV U1 is that reliable product,” said Yan Chai, Product Line Director of Lumileds UV LEDs. The LUXEON UV U1 LED is nominally tested at 500mA but can be driven at up to 1A

to achieve higher irradiances. For the application of UV curing at 395 nm, LUXEON UV U1 achieves 700 mW at 500mA and >1300 mW at 1A under 25oC. Compared to the 3.5x3.5 mm2 package size of most UV LEDs, LUXEON UV U1’s unique micro package size delivers superior packing density as well as >5X higher power density. The LUXEON UV U1’s footprint is a drop-in replacement for the LUXEON Z UV, while providing twice the typical radiometric power as its predecessor at 380-390 nm, a popular range for UV curing applications. The surface mount LEDs can be tightly assembled with spacing as small as 200 µm for high system flux density. With a wall plug efficiency exceeding 45+% and thermal management aided by an AlN package, users can avoid the use of more expensive water cooling at the system level.


16

Latest Journals

Luminescence properties of novel Ba2MgWO6:Eu3+ and g-C3N4/Ba2MgWO6:Eu3+

phosphors This work reported the photoluminescence properties of novel red-light-emitting phosphor Ba2MgWO6:Eu3+ prepared by a conventional solid state reaction at high temperature. A broadband sensitized red emission was obtained in Ba2MgWO6:Eu3+ phosphor due to the energy transfer from W6+-O2− groups to Eu3+. The concentration quenching phenomenon and mechanism of Eu3+ in Ba2MgWO6 host was investigated in detail. Based on the obtained results, a series of g-C3N4/Ba2MgWO6:Eu3+ composite phosphors were also prepared. Under the

excitation of ultraviolet light, these composite phosphors show tunable emission from blue to red region, in which white light emission can be obtained in term of appropriate quality proportion of g-C3N4 relative to Ba2MgWO6:Eu3+. This work not only develops a novel red-emitting phosphor for application in white light-emitting diodes, but also enlarges the research scope of g-C3N4 based materials. DOI: 10.1016/j.ijleo.2016.11.208

Crystal structure, tunable luminescence and energy transfer properties of

Na3La(PO4)2:Tb3+, Eu3+ phosphors

A series of Tb3+ and/or Eu3+ doped Na3La(PO4)2 phosphors were successfully synthesized and their crystal structure and photoluminescence (PL) properties were investigated in detail. Double phosphates with the compositions Na3Tb(PO4)2 and Na3Eu(PO4)2 were obtained by the substitution of Tb or Eu for La in Na3La(PO4)2 host. The XRD pattern analysis indicates that these obtained compounds crystallize in the orthorhombic system with space group of Pbc21. The crystal structure of the Na3RE(PO4)2 (RE= Tb, Eu) is made up of isolated PO4 tetrahedra and of sodium and RE atoms arranged in an ordered way. The REOy polyhedral are isolated from one another, resulting in high critical concentration of Tb3+ or Eu3+ activators. Under excitation of near-ultraviolet (NUV) irradiation, Tb3+ doped Na3La(PO4)2 shows a blue-greenish emission with the

predominated peak at 546 nm, while the emission spectra of Eu3+-doped Na3La(PO4)2 exhibits a reddish orange performance due to the 5D0→7FJ transitions of Eu3+ ions. The energy transfer from Tb3+ to Eu3+ in Na3La(PO4)2 host is demonstrated by the luminescence spectra and fluorescence decay dynamics. Meanwhile, the emission color of Na3La(PO4)2:Tb3+,Eu3+ can be tuned from green to red through tuning the Tb3+/Eu3+ ratio. These results indicate that the Na3La(PO4)2:Tb3+,Eu3+ phosphor exhibits broadband NUV absorption and green−reddish orange tunable emission, which might serve as down-converted phosphors for NUV light-emitting diodes. DOI: 10.1039/C6RA26164G


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White Light Emitting MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) Phosphors for WLEDs

A series of MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) phosphors were prepared by the solid state diffusion method. Confirmation of the phase formation and morphological studies were performed by X-ray powder diffraction (XRD) measurements and scanning electron microscopy, respectively. Photoluminescence (PL) properties of these phosphors were thoroughly analyzed and the characteristic emissions of Dy3+ ions were found to arise

from them at an excitation wavelength of 351 nm. The PL emission spectra of the three phosphors were analyzed and compared. The CIE chromaticity coordinates assured that the phosphors produced cool white-light emission and hence, they are potential candidates for UV excited white-LEDs (WLEDs). DOI: 10.1007/s10895-016-1985-y

Synthesis, luminescence properties and electronic structure of Tb3+-doped

Y4−xSiAlO8N:xTb3+ – a novel green phosphor with high thermal stability for

white LEDs A series of novel green Y4−xSiAlO8N:xTb3+ phosphors have been prepared by a high temperature solid state reaction. The phase formation and structural properties were analyzed by X-ray powder diffraction. The XRD results and SEM images show that the Y3+ can be substituted by Tb3+ for the max content of x = 1.5 and the most suitable sintering temperature is about 1500 °C. The PLE spectra of Y4−xSiAlO8N:xTb3+ phosphors exhibit a wide excitation band ranging from 200 to 500 nm, which matches well with the characteristic emission of n-UV chips. Under excitation of 380 nm, the phosphor shows four intense emission bands with emission peaks at 488 nm, 543 nm, 585 nm and 624 nm, respectively. These emissions were attributed to the characteristic 5D4 → 7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions. The optimum doping concentration of Tb3+ was found to be x = 2.0 which indicated that the concentration quenching effect in the Y4−xSiAlO8N:xTb3+ phosphor is very weak.

The critical distance for the Tb3+ ions calculated by the concentration quenching is 3.64 Å. The detailed nonradiative energy transfer mechanism between Tb3+ ions is confirmed to be via a dipole–dipole interaction by the fluorescence decay analysis. Furthermore, with the introduction of Tb3+ ions, the reflectance spectra shows an obvious increment of reflectance in the region of 200–250 nm, which is due to the variation of electronic structure in the conductance band derived from Y3+ ions. Finally, the excellent thermal stability of the phosphors was demonstrated by the temperature dependence of the PL spectra. Compared to the initial intensity at room temperature (293.0 K), the relative PL intensity maintains high value of 96.5% at 475.2 K. The detailed thermal quenching behavior has also been interpreted.

DOI: 10.1039/C6RA24438F


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Photoluminescence study of a broad yellow-emitting phosphor K2ZrSi2O7:Bi3+ The photoluminescence of a novel yellow emitting phosphor K2ZrSi2O7:Bi3+ that contains no rare earth ions was investigated. This phosphor was further evaluated as a color converter for white LEDs. The results indicate that K2ZrSi2O7:Bi3+ has strong absorption in 300–400 nm region due to the 1S0 → 3P1 transition of Bi3+. Upon excitation into the 3P1 level of Bi3+, K2ZrSi2O7:Bi3+ gives bright and broad yellow emission (FWHM ∼ 125 nm) peaking at 560 nm. Except for intensity, the spectral position and shape of the yellow emission band are the same for different concentrations of Bi3+ incorporated K2ZrSi2O7; Both the emission spectra measured at liquid nitrogen temperature (77 K) and room temperature have no splitting and they can be well fitted

by a single Gaussian profile; time resolved luminescence spectra reveal that the shape of the emission spectra remain unchanged with increasing delay time. These results indicate only one type of Bi3+ center exists in K2ZrSi2O7. Accompanied by a decrease of emission intensity, the emission of Bi3+ is blue-shifted upon heating ( max = 560 nm at T = 25 °C vs. max = 550 nm at T = 250 °C), which is ascribed to the thermally active phonon-assisted tunneling from the excited states of lower-energy emission band to those of higher- energy emission band. The white light has been reached using K2ZrSi2O7:Bi3+ as a yellow emitting phosphor. DOI: 10.1016/j.cej.2016.11.003

Broadband Yellowish-Green Emitting Ba4Gd3Na3(PO4)6F2:Eu2+ Phosphor:

Structure Refinement, Energy Transfer, and Thermal Stability

A series of Ba4Gd3Na3(PO4)6F2:Eu2+ phosphors with a broad emitting band have been synthesized by a traditional solid state reaction. The crystal structural and photoluminescence properties of Ba4Gd3Na3(PO4)6F2:Eu2+ are investigated. The different crystallographic sites of Eu2+ in Ba4Gd3Na3(PO4)6F2:Eu2+ phosphors have been verified by means of their photoluminescence (PL) properties and decay times. Energy transfer between Eu2+ ions, analyzed by excitation, emission, and PL

decay behavior, has been indicated to be a dipole–dipole mechanism. Moreover, the luminescence quantum yield as well as the thermal stability of the Ba4Gd3Na3(PO4)6F2:Eu2+ phosphor have been investigated systematically. The as-prepared Ba4Gd3Na3(PO4)6F2:Eu2+ phosphor can act as a promising candidate for n-UV convertible white LEDs. DOI: 10.1021/acs.inorgchem.6b00648


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Novel Patents

Radioactive contamination inspection device

This radioactive contamination inspection device is provided with a plastic scintillator, a light receiving element, a light guide that causes scintillation light emitted from the plastic scintillator to reach the light receiving

element, and a light shielding case having an entrance window, and is further provided with a structure of thin film layers disposed between the plastic scintillator and the entrance window provided in the light shielding case, including a protective film, a light shielding film, and a reflecting film arranged in this order from the entrance window side. The side surface of the light guide is formed of a diffusely reflecting surface, the reflecting film and the plastic scintillator are arranged such that a layer of air is confined therebetween, and the surface of the reflecting film which faces the plastic scintillator is formed of a specular surface. WO 2016195007 A1

Light emitting device and manufacturing method thereof

A light emitting device is provided which as much as possible suppresses the deviation between a design value and the color of the actual light, which is obtained by mixing the light emitted from multiple light emitting elements mounted at high d. and the excitation light from phosphors contained in a resin that seals the light emitting elements; and a manufg. method of said light emitting device is also provided. This light emitting

device comprises a substrate, multiple light emitting elements which are mounted densely on the substrate with the light-emitting surface facing away from the substrate, and a sealing resin which seals the whole of the multiple light emitting elements and which contains multiple types of phosphors, which are in a state deposited on the top surface of the multiple light emitting elements and are excited by light from the multiple light emitting elements. The interval between adjacent light emitting elements is greater than or equal to 5 m and is less than or equal to 120% of the median radius D50 of those phosphors of the multiple types of phosphors that have the greatest av. particle diam. WO 2016194876 A1


20

Light emitting element for display device using exciplex and fluorescent

substance to achieve high emission efficiency

This invention discloses a light-emitting element for a light emitting display which exhibits high emission efficiency without using a rare metal as a light-emitting material. The light-emitting element including a first electrode, a second electrode, and a layer contg. org. compds. between the first electrode and the second electrode is provided. The layer contg. org. compds.

includes a light-emitting layer at least contg. a fluorescent substance. The light-emitting layer includes a fluorescent substance, a first org. compd., and a second org. compd. The combination of the first org. compd. and the second org. compd. forms an exciplex. The exciplex transfers energy to the fluorescent substance, resulting in high emission efficiency for the light-emitting elements. The first org. compd. is a substance having the first skeleton including a benzofuropyrimidine skeleton or a benzothienopyrimidine skeleton. US 20160351833 A1

Wavelength conversion device, light source system and projection system

The invention relates to a wavelength conversion device, a light source system and a projection system. The wavelength conversion device comprises a wavelength conversion element (1) which itself comprises a reflection layer (12), said reflection layer

(12) comprising a first surface (120) and an opposite second surface (121). A light-reflecting layer (11) is positioned on the first surface (120). A first heat-dissipation film (13) is affixed to the second surface (121). The first heat-dissipation film (13) is a graphite heat-dissipation film. The present wavelength conversion device is characterized by high reflectivity and high thermal stability and is capable of maintaining highly efficient stability of light output in high-power light emission conditions.

WO 2016188460 A1


21

Backlight device and liquid crystal display device provided with same

To realize a backlight device in which the color temperature can be adjusted or modified without reducing color purity. A light source constituting a part of the backlight device comprises: a first magenta light-emitting body (60(M1)) comprising a blue LED element (6(B)) and a relatively large quantity of red phosphors (7(R)); a second magenta light-emitting body (60(M2)) comprising a blue LED element (6(B)) and a relatively small quantity of red phosphors (7(R)); and a green light-emitting body (60(G)) comprising a green LED element (6(G)). The light emission intensity of the first magenta light-emitting body (60(M1)), the light emission intensity of the second magenta light-emitting body (60(M2)), and the light emission intensity of the green light-emitting body (60(G)) are independently controlled by a backlight control unit. WO 2016189997 A1

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