Julian CareyWhile phosphors were used for decades in fluorescent lighting, they were deep-ultraviolet driven and not suited for use with blue LEDs, which emit light at a frequency of around 455nm.As adoption of LEDs for general lighting applications has grown, so has the demand for new phosphor solutions developed to convert blue light into a range of light colors, creating various color temperatures of white light.

The development of these new advanced phosphor solutions has spawned new patents, creating a more intellectual property (IP) intensive environment for LED component, LED light source and luminaire manufacturers to analyze and manage.They must not only select phosphor materials that give them the light quality, stability and reliability required by specific applications, but they must also navigate the patent landscape.

Phosphor growth drivers
Growth in LED-based lighting in North America is estimated to average 38% between 2012 and 2016, according to a recent McKinsey & Company report.Now that we are seeing LED use transition into general lighting – thanks to reduced pricing and accessibility of products with LED technology – quality of light has become the predominant requirement.This, in turn, has led to a demand for more advanced phosphor solutions and a much more complex mixing strategy.Generally, a two- or even three-phosphor strategy is needed to attain high color rendering index (CRI) and high R9, an indication of how well the light shows deep, saturated shades of red.

Phosphor materials are coated on blue-emitting LED chips to create white light with a variety of specific color qualities, depending on the chemistry of the phosphor material. Intematix’s portfolio of phosphor products include aluminate, garnet, nitride and silicate families which emit green, yellow, red, and orange light.In addition to mixing strategy, phosphor solutions for general lighting require a high degree of ruggedness.They are based on very tough molecular structures and are lasting for upwards of 50,000 hours.Thus, today’s primary lighting phosphor options are green aluminate (such as GAL) , red nitride, and yttrium-aluminum-garnet or YAG.  Not only do these materials have long lifetimes, but they also have high thermal stability, independent of lifetime.For example, if you go as high as 200°C with GAL, you will only lose a very small degree of brightness – this very high degree of stability means that manufacturers can drive their LEDs harder and still lower costs.

History of phosphor IP
“High-brightness” LEDs were originally developed around the 1990s by early producers of gallium nitride (GaN)-based blue LEDs in Japan after researchers from Nichia and a professor from Nagoya University shared their formulation.  The combination of blue LED chips with YAG phosphor was patented by Nichia in 1996 via U.S. “925 Patent” No. 5,998,925.

As market research firm Yole Développement points out, while LED phosphor IP is complex and rich with thousands of patent families, only a few patents have provided significant returns to their owners in terms of market share, freedom of exploitation, or additional revenue streams from royalties.Some of those patents are on the verge of expiring within the next five to 10 years – most notably, Nichia’s 925 patent, which is set to expire in 2017. The expiration of this patent will remove a significant barrier and will allow broader use of the YAG materials covered by the patent.

As the industry matures, breakthrough innovations and industry-redefining fundamental patents will diminish.While patent activity remains strong, it is now focused on emerging compositions, mostly addressing the need for more efficient and cost-effective red and green phosphors to be used in display and general lighting applications.However, differentiation opportunities remain, and the development of any new composition with disruptive potential could still greatly benefit its inventor.

Color innovations
Today, phosphor makers such as Intematix are further addressing the trend toward high-quality light with patented advanced phosphor technology.In addition to being the only company that makes its GAL formulation, Intematix also holds patents that cover different wide-spectrum green phosphors called LuAGs (for lutetium-aluminum-garnet).GAL generally offers a broader spectrum, higher thermal stability, higher CRI and higher quality of light compared to LuAG formulations, but owning IP that covers both GAL and various LuAG formulations enables Intematix to offer the more extensive portfolio of broad greens and reds essential to high-quality LED light.

Remote-phosphor technology separates the phosphor element from the LED plate, illuminating the blue LED from behind the remote phosphor plate to emit pure white light. This technology, used in products such as the Intematix ChromaLit Linear, is rapidly gaining acceptance for a variety of applications that require uniform illumination and high efficiency.Intematix’s recently granted patent covers its new XR Red Nitride formulation.Intematix’s XR products offer similar high performance and reliability compared to traditional CASN-based red nitride products, but have a fundamentally different structure than the CASN products, which differentiates them from an IP perspective.The Intematix XR products are also designed to have notable performance characteristics like color stability over life and long wavelengths to improve CRI and R9.

One of the key metrics for phosphor performance is quantum efficiency (QE), which involves taking one photon and replacing it with another photon.High-quality, advanced phosphors such as those from Intematix can reach as high as 97% QE.  Also important are high-performance characteristics at the individual particle level, which can be very small, including the particle finish, shape and even its coloration and size.All of these things come into play in the effort to make LEDs brighter, more uniform and reliable and they are additional dimensions to manufacturing technology IP.

China’s growing role
Until 2008, Chinese LED packaging firms obtained phosphors primarily from imports alone.Then, many LED packaging firms began moving from Taiwan to China, favoring suppliers with whom they had worked previously and therefore trusted.Following the entrance of domestic players, reliance on imports dropped to 80% in 2010 and 60% in 2011.

Lack of LED IP in general, and phosphor IP in particular, is a major issue for China-based LED packaging firms established on the mainland.So most Chinese companies face significant restrictions in exporting LED lighting products.  To remedy this, various Chinese phosphor companies and academic institutions have begun to pursue research and development activities. However, as major compositions and configurations have already been protected, any innovations are often limited in scope or applicability and have so far been unable to unlock foreign markets to domestic LED makers.

Thus, Chinese and other LED makers, who will need an IP-strong solution to enable future export of their products, can gain a strategic advantage from implementing phosphor IP such as that provided by Intematix, which has not only a strong patent portfolio, but also a large local manufacturing and service base in China.The coming expiration of the Nichia 925 patent will also improve Chinese LED makers’ ability to export their production and remove barriers to marketing and selling YAG products.

IP in novel phosphor solutions
Application methodologies for phosphor are becoming more diverse. One example is the implementation of remote phosphor. This technology involves bonding phosphor to a substrate, instead of incorporating it into the LED die package, and then (in Intematix’s case) adding a reflective coating on top of the remote phosphor optic, which maintains a white appearance even when the product is powered off. The phosphor can be coated on two-dimensional shapes or formed into three-dimensional ones. Separating the phosphor from the blue-pump LEDs prevents heat from the LED causing any degradation in the phosphor, and thus prevents color shift over time. This approach provides a low-glare system capable of higher system efficiency, increased reliability and less color shift over time.

Remote phosphors can be used in many different ways for a majority of lighting applications. A few examples include LED retrofit light bulbs, portable consumer lighting, downlights, decorative lighting, appliances, task lighting, spot and modules.The addition of remote phosphors to the landscape has led to additional IP frameworks at the component and application levels.The most recent Nanomarkets Report, LED Phosphor Markets 2014, lists Intematix as one of the IP leaders in remote phosphor technology. The company’s portfolio of differentiated IP for both its standard and remote phosphor products and their application allows customers considerable latitude when designing the major categories of lighting systems.

Innovation in phosphor solutions has played a large role in the rapid advancement of LED lighting quality, efficacy and affordability for displays, lighting, automotive and many other applications. It’s expected that designers of LED lighting components and systems will increasingly deploy and manage their use of IP to maximize the marketability and sales of their products worldwide.