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

Investigating Organization
Nanomaterials & Nanofabrication Laboratories (NN-Labs, LLC)

Principal Investigator(s)
David Goorskey

Subcontractor
University of Arkansas

Funding Source
Small Business Innovation R&D, Phase I

Award
DOE Share: $99,636

Contract Period
6/20/07 - 3/19/08

The most common and cheapest type of white LED consists of a yellow-emitting phosphor powder 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.  This proposal specifically addresses the LEE issue to improve the overall efficiency of white LEDs allowing them to compete with conventional (and toxic) mercury-vapor fluorescent lamps.  Specific impacts would include providing massive energy savings worldwide, reducing the amount of mercury release into the environment, and providing an economic boost to U.S. LED manufacturers while allowing them to retain technical superiority over foreign corporations.

Specifically, this SBIR Phase I project will incorporate high quantum efficiency doped nanocrystal quantum dots (D-dots™) into high-index TiO2 using sol-gel techniques to form scatter-free nanophosphor composites for white phosphor conversion light emitting diodes (pc-LEDs) which are presently limited by poor light escape efficency at the die-encapsulant interface (due to poor refractive index matching) and back-scattering from the bulk phosphor layer.   Nanophosphors are too small to scatter light and if embedded into a high-index material, can achieve near index matching with the LED die, thereby solving both of these current problems.  D-dots™, a new class of nanocrystal light emitting materials, do not suffer from parasitic reabsorption associated with “intrinsic” quantum dots, are highly stable up to 300oC, and are immune to photo-oxidation under intense UV irradiation, making them ideal candidates for replacing bulk phosphors in white pc-LEDs.  The high performance D-dots™ newly invented by this SBIR team are free of toxic heavy metals such as cadmium in CdSe and CdS quantum dots which have been the traditional workhorses for intrinsic nanocrystal emitters. 

Phase I will focus primarily on integrating yellow-emitting Mn-doped ZnSe D-dots™ into TiO2 sol-gel matrices deposited on near-UV/blue LED dies whereas Phase II will develop additional D-dot™ nanophosphors to improve the color rendering index and luminous efficacy of white LEDs.

Content dated 2/08