Enhanced Optical Efficiency Package Incorporating Nanotechnology Based Downconverter and High Refractive Index Encapsulant for AlInGaN High Flux White LED Lamp with High Luminous Efficiency LED Phosphor Performance (Phase I)
Investigating Organization
Nanocrystals Technology
Principal Investigator(s)
Rameshwar Bhargava
Subcontractor
None
Funding Source
Small Business Innovation Research
Award
DOE Share: $99,933
Contract Period
7/1/03 - 4/30/04
Nanocrystals Technology LP (NCT) has developed unique nanotechnology-based materials that will cost-effectively enhance performance of white LED lamps for general illumination applications. These innovations include optically non-scattering efficient downconverter Nanophosphors and high refractive index (HRI) Nanocomposites that enhance both the Package Optical Efficiency (POE) and Light Extraction Efficiency (LEE) of white LED lamp at the package level.
Today in white LEDs, blue-to-white light conversion is exclusively achieved by using YAG:Ce 3+, an efficient broad-band, yellow-green phosphor. One of the drawbacks of this system is that the mixing of blue/yellow color not only produces halo effect, but also yields inferior color rendering. Absorption process in phosphors such as YAG:Ce 3+, involve impurity states of rare-earth (RE) emission that have low absorption coefficient of about 40 cm-1 in the region of interest. The low absorption in RE systems requires larger size particles and increased scattering to enhance the net absorption. Nanocrystals has demonstrated that in nanophosphors, the absorption coefficient associated within intra-atomic states of the RE-activator is enhanced by two orders of magnitude. These nanophosphors ,when optimized, would eliminate the required scattering conditions and the halo effect.
NCT has developed nanocomposites of refractive index of 1.8. This was achieved by incorporating TiO2 nanoparticles with proprietary coating that are dispersed uniformly to yield optically transparent nanocomposites. The HRI encapsulants were used to demonstrate >25% improvement in efficiency of green and red LEDs. Furthermore, we have incorporated YAG:Ce 3+ bulk phosphor of refractive index 1.85 in nanocomposite encapsulant of refractive index 1.8. The matched refractive indices render the downconverter nanocomposite optically transparent. These optically transparent HRI nanocomposites containing bulk YAG-phosphor increase the efficiency of white LEDs by 40% over the current LEDs that use the same YAG-phosphor and encapsulant of refractive index of 1.5.
Projected 50% enhancement in POE due to the optically non-scattering downconverter, when combined with an additional ~40% enhancement in LEE due to HRI encapsulant, would lead to a good color-quality, high-luminous efficacy white LED lamp with ~ 95 lm/W using present AlInGaN blue LED die/chip with wall-plug-efficiency of 25%. With improved LED chip efficiency in the future, the use of HRI nanocomposites and nanophosphors will allow us to achieve luminous efficacy of 200 lm/W.