Improved Light Extraction Efficiencies of White pc-LEDs for SSL by using Non-Toxic, Non-Scattering, Bright, and Stable Doped ZnSe Quantum Dot Nanophosphors

With the potential to drastically reduce the US and world-wide electrical energy consumption, white light emitting diodes (LEDs) comprise a very rapidly growing market in the general illumination and specialized lighting sectors. Already, white LEDs are more efficient than tungsten filament bulbs and are rapidly gaining on fluorescent lamps. The most common and cheapest type of LED, the phosphor conversion LED (pc-LED), consists of a yellow-emitting phosphor powder embedded in a silicone or epoxy encapsulant material surrounding a blue-emitting LED die. One serious challenge is improving the light extraction efficiency (LEE), often referred to as ¿package efficiency,¿ of pc-LEDs. The LEE presently is limited by poor light escape efficiency at the die-encapsulant interface (due to poor refractive index matching) and by back-scattering from the bulk phosphor layer. This project will use a sol-gel technique to incorporate high-quantum-efficiency, doped nanocrystal quantum dots (d-dots) into high-index TiO2, in order to form scatter-free nanophosphor composites for white pc-LEDs. Because the nanophosphors are too small to scatter light, they can achieve near index matching with the LED die if embedded into a high-index material, thereby solving both of the current problems. Phase I will focus primarily on integrating yellow-emitting Mn-doped ZnSe into TiO2 sol-gel matrices deposited on near-UV/blue LED dies. Phase II will develop additional d-dot nanophosphors to improve the color rendering index and luminous efficacy of white LEDs. Commercial Applications and other Benefits as described by the awardee: The technology should improve the overall efficiency of white LEDs, allowing them to compete with conventional, but toxic mercury-vapor fluorescent lamps. Specific impacts would include massive energy savings, reduced mercury release into the environment, an economic boost to US LED manufacturers, and the establishment of a successful high-tech industry in the traditionally rural state of Arkansas.