Research Project Summary Information
Improving Quality and Performance of Non-Toxic Quantum Dot Based White LEDs(ST8895-1)
White light-emitting diodes (LEDs), as opposed to colored LEDs, contain a combination of colors (typically red, green and blue) that, when added together, make white light. There are currently four approaches to obtain white LEDs: using individual colored LEDs to make white light (much like a TV screen); using a blue LED with a yellowish phosphor (YAG) to make white light; or, using an ultra-violet (UV) or blue LED to excite (or make glow) three different colored quantum dot phosphors mixed together and applied as a paste onto a single LED, or unmixed and applied onto multiple LEDs, to make white light. The challenge with the UV/blue excited white LEDs are that the phosphors available today are too expensive, not bright enough, degrade long before they should and contain toxic materials (e.g., cadmium or lead). The contractor's manufacturing process is expected to reduce the cost constraint and the toxicity concern for using quantum dots for white LEDS.
The project produced non-toxic nanophosphors and applied to LEDs to improve their efficiency, brightness and white color properties. The project also established brightness benchmarks for the new LEDs based on commercially available phosphors used in LEDs; developed a next-generation LED using purification processes to increase the luminescence properties of the semiconductors; conducted accelerated aging and reliability studies on the new LEDs; and conducted a commercial and feasibility study to determine whether large-scale production is cost-effective.
Benefits include energy and demand savings associated with the replacement of incandescent light sources with LEDs. Benefits also include economic development related to new job creation in the Capital District of New York, and reduced environmental and health risks associated with avoided emissions at electricity generating stations.
The project produced non-toxic nanophosphors via solid-state synthesis that, when mixed with an epoxy and applied to LEDs, improved the efficacy, brightness and white color properties of LEDs. Specifically, the project developed next-generation LEDs coated with phosphors produced using purification processes to increase the luminescence properties of the semiconductors. The contractor also conducted accelerated aging and reliability studies on the improved LEDs. The contractor achieved different emission wavelengths from 400-650 nm (blue to red) by tuning the material compositions. The phosphors successfully increased the brightness of commercially available LEDs, with a mean improvement in luminous efficacy of 82% for ultraviolet lumens and 24% for blue lumens. The Contractor's degradation studies showed no lumen depreciation over a period of 96 hours. Future research is needed to further increase the luminous efficacy of the contractor's phosphors and to increase production from small batch quantities to commercial-scale production. Follow-up work by the contractor in phosphor development is necessary to reduce particle sizes to below 50 nm, to develop surface treatments of the phosphor particles (for easy dispersability in organic solvents), and to improve yield of the phosphor quantity from each batch
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