1.1:Current Assessment of LED Phosphors Technologies

by:Getian     2020-07-27

Increasing demand for luminous efficacy, a high color rendering index, and cost-effectiveness is fueling the lighting industry. LED phosphors, will therefore enjoy an expanding market that will generate shipments equal to 800 metric tons in 2019.

Phosphors are the critical luminescent materials for LEDs. In a white LED, for example, the phosphor emits up to 95% of the visible lumens. Existing phosphors have been able to provide LEDs with 100% greater increase in LED efficacy and a 50% to 200% decline in price. The use of phosphors has also helped in reducing the price of high-quality LEDs by a huge amount.

In LED applications, phosphor penetration will continue growing as long as lower cost per lumen, a high CRI, and a lower cost of ownership is demonstrated. It is also believed that phosphor choice may help in eliminating consumers' perception of LED lamps as being cold, dull, and above all, unaffordable.

Another critical factor affecting the field is the IPs owned by the companies in the phosphor space. This factor has and will continue to shape this market. Other important factor that is likely to continue structuring the phosphor sector is the 'division of labor' based on both supplier size and geography.

Analysis of this market indicates that large phosphor players will continue improving their products through the deployment of efficient production lines while smaller players will seek novel phosphor solutions

1.2:Emerging Requirements for LED Phosphors

For now the standard, blue chip Ce:YAG combination is the most popular in the market. Green and red phosphors are steadily growing their market share, particularly for applications that require a high CRI and good color reproducibility, such as general lighting and liquid crystal display (LCD) backlights in cell phones and flat-panel displays.

Intensified competition is being observed for new green/red phosphors. Companies like Intematix (U.S.) and Mitsubishi Chemical are actively working in this area and strengthening their IP. In the coming years, thrust of important R&D work in phosphors needs to be in the areas discussed below.

Color-mixed solutions: There is considerable room in the market for color-mixed solutions. The workhorse for current lighting products is phosphor-converted blue light. There is still potential for energy improvement and cost reduction in this technology.

Color rendering indices: For high-quality LED solutions, the key factor is to increase the CRI at various color temperatures while maintaining high efficiency. Phosphors having broad emission spectra (except for the red phosphors, where a small bandwidth is needed to avoid NIR-losses), or those that emit various wavelengths with minimized re-absorption are needed.

Color consistency over time must also be guaranteed. Color conversion requires temperature-stable phosphor solutions, while RGB (red, green, blue) solutions require color controls that compensate for the divergent aging properties of LEDs having different colors.

To take advantage of these opportunities, an understanding of the color mixing mechanism at the molecular level is required. And, also the ability to maintain the same color impression during the lifetime of a single lamp and between individual lamps is needed. This goal however looks difficult to achieve, as the temperature and aging behavior of red, amber, and blue LEDs is different.

1.3:Materials Trends: Novel Products and New IP

All commercially available phosphors are heavily patent-protected items and have become the basis for much of the IP litigation in the industry today. However, an active search for novel phosphors is beginning and there lies plenty of opportunity for entrepreneurs and businesses to enter this area and create novel IP.

Garnets, silicates, aluminates, sulfides, selenides, nitrides, and oxynitrides are considered as key materials for technical development of new phosphors. There are interesting trends occurring with many of these materials, particularly with respect to intellectual property issues.

Garnet: The IP related to Ce3 doped yttrium aluminum garnet (Ce:YAG), or yellow phosphors, is mainly controlled by Nichia (Japan). Compositional modifications give CRI of approximately 70-80%. This color quality is acceptable for applications such as backlights for portable displays and indicators, which currently dominate the LED market and result in garnets dominating the phosphor market.

Silicates: Something similar is expected to occur in the silicate sector. As Nichia's critical IP is set to expire in the next few years, an increasing number of phosphor manufacturers are offering YAG compositions as well.

Sulfides and selenides: Sulfides and selenides are mainly patent-protected by Lumileds. However, in addition to any limitations that IP places on the use of these materials, this class of material has not been popular because it is sensitive to moisture and has poor stability and a low QE (quantum efficiency). There are also some regulatory issues due to the presence of sulfur compounds.

Despite all these negatives, we are seeing opportunities in this space, because when combined with YAG:Ce, however, warm white light LEDs are produced.

Nitrides and oxynitrides: A new approach is to add red and/or green phosphors to nitrides or oxynitrides to improve performance. This technology is currently controlled by Denka (Japan) and Mitsubishi Chemicals (Japan) through strong IP.

The problem here is that the price of these materials is, five-to-tenfold higher than that of yellow phosphors. Thus, what we are seeing is that many research groups are scrambling to develop better and cheaper converters, and a large number of patents have been filed in the last two years.

One important example is Intematix's (U.S.) latest U.S. patents (numbers 8,529,791 and 8,475,683), which describe green aluminate (GAL) technology for rendering high CRI for solid-state lighting (SSL). Companies are also investigating tungstates, molybdates, and carbidonitrides as alternative candidates.

Other technologies: There are various other phosphor technologies that can be successful. These technologies include:

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