The broader impacts/commercial potential of this Small Business Innovation Research (SBIR) Phase I project is that it will enable white LEDs to produce significantly better quality light at up to 30% higher efficiencies. Accordingly, the proposed nano-phosphors will enable faster market adoption of LED lighting at a lower overall cost to the end consumer due to their higher efficiencies. Since general lighting is a large component of total energy consumption, e.g., ~20% in the U.S., the nano-phosphors will enable significantly added energy savings at an earlier date compared to the status quo of employing conventional phosphors. With regard to light quality, the nano-phosphors will enable custom, desirable light sources to be formed, for example, that of natural sunlight. Since the nano-phosphors maintain high efficiency under the conditions of high temperature and very high optical flux, they should also help enable next generation optoelectronic devices, such as, optically-pumped, visibly-tunable lasers. Successfully encapsulating the nanocrystals in glass will also make the nano-phosphors more technologically viable in these other high impact areas. Accordingly, R&D will be accelerated due to the availability of nano-phosphors with these enhanced performance characteristics, leading to faster market introduction of additional next generation optoelectronic devices.
This Small Business Innovation Research Phase I project aims to take novel InP-based quantum dots, which have outstanding optical performance, and put them in a form suitable for usage by the LED and lighting fixture industries. To enhance the adoption of LED lighting, manufacturers currently seek high-performance, spectrally-narrow, red-emitting phosphors to replace conventional red phosphors that result in large LED efficiency losses. The InP-based nano-phosphors have the advantages of quantum dots, namely, negligible optical scattering, emission range throughout the visible spectrum, and narrow spectral width, but also maintain high efficiency under the extreme operating conditions of the LEDs. To be practical for LED manufacturers, the nano-phosphors need to be placed in a silicone matrix. To achieve this, the nanocrystals will be encapsulated by a thin shell of glass. In order to maintain efficiency following glass shelling, the semiconductor shell surrounding the nanocrystals will be altered and the conventional glass shelling procedures will be modified.
Solid state lighting, based on combining blue LEDs with green- and red-emitting phosphors to form white-light LEDs, will become a dominant source of general lighting over the next 5-10 years. Current phosphors are based on rare-earth materials for their emission characteristics. Though efficient, the red-emitting rare-earth-based phosphors emit a significant portion of their light in either the far red or infrared, where the human eye response is poor or zero. In addition, recently the rare-earths have had supply issues and have become significantly more expensive. A well-known means for overcoming these issues is to form phosphors from nanomaterials. Nanomaterials are very small semiconductor particles (a factor of 10,000 smaller than the thickness of the human hair), whose properties can be tailored based on their material composition and specific size. Most groups working in this area have formed Cd-based nanomaterials due to the long history of those types of materials. However, Cadmium is a toxic carcinogen and Cd-based nanomaterials still have some performance shortfalls which limit their ability to be drop-in replacements for current rare-earth-based LED phosphors. In order to overcome the shortcomings associated with phosphor-based nanomaterials, we previously formed Cd-free nanomaterials based on a novel material composition. As a result of this new composition, most of the drawbacks associated with nanomaterial-based phosphors were eliminated. One remaining issue is that the Cd-free red-emitting nanomaterials emit some light in the far-red (though less than that of rare-earth based phosphors), thus limiting the overall LED efficiency. Our SBIR project worked on three means for removing this unwanted emission component. The first approach modified the procedure for synthesizing the nanomaterials while keeping the composition the same; the second and third approaches made changes to the composition while employing our typical synthetic approach. Very good progress was made with the first approach in removing the unwanted far-red emission component, though some work needs to be done to further optimize the resulting nanomaterial efficiency. Of the two compositional approaches, one of them turned out to be very effective, resulting in a reduction of the unwanted red emission component, while causing only ~10% loss in efficiency. Overall, the best method will be to combine this compositional approach with the modified synthetic procedure in order to obtain the desired narrower (no far-red emission) red emission, while maintaining high efficiency when placing the nanomaterials directly on top of the blue LEDs. As a result of the project work, we have two solid approaches for eliminating one of the last hurdles which remain prior to successful replacement of the conventional rare-earth based phosphors with our Cd-free nanomaterials. Once the hurdles are eliminated, our nanomaterials will enable up to a 35% increase in overall white LED efficiency. Given the large percentage of energy use associated with general lighting (~18% in the US), this will result in considerable cost savings in addition to large reductions in carbon emissions. Nanomaterials also have the nice property that through a straightforward change in their size, their emission properties can be simply tuned, for example, changing from a red-emitter to an orange emitter. Through this property, custom LED light sources can be simply formed, in addition to LED light sources with improved color quality (for example, better matched to natural sunlight). Overall, the project results will help pave the way for efficient non-toxic nanomaterial-based LED phosphors which will enable both more-efficient and better-quality general lighting.
