August 09 ElectroIndustry - 15

Quantum Dots Lighting Up LED Technology SETH COE-SULLIVAN PHD AND SRIDHAR SADASIVAN PHD, QD VISION, INC. NANOTECHNOLOGY New energy-efficient lighting solutions involving LED-based solid-state lighting are beginning to emerge. The long lifetime, low energy usage, and continuous improvement in efficiency are helping to position LED lighting as the most promising solution for the future. Along with solutions, however, come new problems. Today’s efficient LED lights produce “cool” white light while consumers prefer ”warm” white light. Warm white LED lamps are at least 30 percent less efficient than cool white LED lamps. Recently, light-emitting quantum dots (QDs) have been developed to address the color quality and efficiency of LEDbased lighting systems. These nanomaterials are used in place of conventional phosphors to create high-efficiency warm white LED lighting systems. The first lighting products taking advantage of the color quality and power efficiency possible with QDs are being introduced in 2009. emission color of the QDs can be tuned throughout the visible and infrared spectrum by simply changing the particle size. The key properties that are of interest to lighting are the narrow band emission and the quantum efficiency (QE) of quantum dots. The narrow emission of QDs relative to conventional phosphors translates into increased efficiency. The high QE of the quantum dots ensures efficient conversion of bluish-yellow cool white light to reddish warm white light. The Need: Successful Commercialization of Quantum Dots As the interest in these nanomaterials grows, the ability to uniformly assess key attributes becomes critical. One critical performance parameter is the QE, as it is a good predictor of LED lamp performance. The most meaningful information for the lighting community would be the QE under conditions approximating those experienced in actual usage. Two distinctly different measurement approaches are being followed to date. Thus, it is critical that a standard measurement protocol be developed to measure QE. The U.S. National Committee TAG to IEC TC 113 for Nanoelectrotechnologies is now in the process of developing a new standard for characterizing the QE of QDs and nanophosphors. The intent is to standardize a measurement methodology that will be consistent with existing equipment and testing procedures used in the lighting industry. The Challenge: Creating Efficient Warm White Light with Quantum Dots To meet consumer demand for energy-efficient LED light that has the same color quality as incandescent lamps, the challenge is to create an indoor light source that reproduces the colors of various objects faithfully while producing the familiar “warm” white light. The white light from present-day LEDs is created using a combination of a blue LED chip and luminescent phosphors. A yellow phosphor is used to absorb some of the blue light and emit a broad spectrum yellow light ranging from the green to the orange end of the spectrum. The resultant white light is cool and does not reproduce colors of various objects well. To create a warm white light with high quality, a red phosphor is used in addition to yellow. The red phosphor used in the LED emits broad spectrum light that extends all the way into near infrared, which is not visible to human eye. The result is warm white LED light, but the solution is much less efficient than the cool white LED package. These inefficiencies can be remedied by QDs, nanoscale tunable emitters with a very narrow band emission profi le. The narrow light emissive properties of QDs come from their small size (typically 2-12 nm) and the resulting quantum confinement. The A Quantum Dot Future Previous LED solutions and lighting solutions in general have traded warm white light with high color quality for efficiency. QD technology is now available to overcome the previous limitations imposed by this trade-off. High efficiency translates into lower overall cost, as fewer LED chips are required to reach a desired brightness. To successfully drive adoption of these materials in the industry, it is imperative that standards are in place. They minimize development time as partnering companies can start with meaningful performance data and expectations. In addition, they provide a consistent way of comparing QD solution with other LED chip solutions. ei August 09 • NEMA electroindustry 15

August 09 ElectroIndustry

Table of Contents for the Digital Edition of August 09 ElectroIndustry