One of the main roadblocks to higher efficiencies for warm-white LED light sources is spectrally-wide red-emitting bulk phosphors, which emit a significant amount of their energy either in the far red or infrared where the eyes response is poor or zero. Consequently, employing those phosphors (along with bulk green-yellow emitting ones) will result in desired warmer light sources, however, at the expense of lower efficiency. Colloidal nanocrystals have been touted for years as a solution to this problem; however, they still suffer from unwanted quenching of the quantum efficiency and increases in their spectral width at the elevated temperatures and excitation levels that are attained during operation of high power LEDs. Previously, we have formed a new and novel class of high efficiency non-toxic nanocrystals which overcome these long-standing problems with nanocrystals. However, in common with all other nanocrystals, our materials suffer from efficiency and optical scattering losses when placed in silicone films, the preferred matrix for enclosing the LED down-conversion phosphors. In this project, we will form nanocrystal-based silicone films with high quantum efficiencies and low optical scattering losses, which maintain these properties under LED operation and for optically- dense films. Novel nanocrystal surface region materials will be synthesized, analyzed for performance, and then optimized accordingly in order to enable the maximum efficiency and minimal scattering loss for the silicone-based films. The main goal for the Phase I is for the nano-crystals to extend their current high performance optical properties to silicone-based films and maintain these properties under the harsh environmental conditions of LED operation. Given these properties, the resulting nanocrystal-based silicone films can be placed directly on blue LEDs without losing efficiency. In conjunction with pc-LEDs containing green-yellow emitting bulk phosphors, the resulting phosphor blends can be used to create warm-white LEDs with up to a factor of 1.3 increase in white LED system efficacy while enabling quality white light with a high color rendering. By adding green- and yellow-emitting nanocrystals to the silicone films, further LED system efficacy gains can be made, while enabling custom light sources to be formed. These performance advantages will enable both commercial and consumer customers to lower their general lighting energy costs, obtain higher quality lighting, and reduce their carbon footprint.
