SUNY/Buffalo Developing High-Efficiency Colloidal Quantum Dot Phosphors
The State University of New York at Buffalo is working to reduce the cost and increase the performance of LEDs for general illumination by developing high-efficiency colloidal quantum dot phosphors to replace conventional phosphors (i.e., those placed directly on the chip). Colloidal quantum dot phosphors are nanocrystal emitters and contain no rare-earth elements. What's more, it's possible to tune the emission wavelength merely by changing their size.
Typical nanocrystals, though efficient at room temperature, contain the toxic element cadmium, and suffer from quenching of the fluorescence at high temperatures (>100°C) and/or at high optical excitation fluxes (>50 W/cm2). SUNY/Buffalo has made significant inroads in creating a viable replacement technology for conventional phosphors by forming indium phosphide-based nanocrystals having unique compositional structures. From a performance standpoint, the researchers have synthesized nanocrystals over the spectral emission range of green through red that have efficiencies in the mid-80 percent range, lose only 5 percent in efficiency at 150°C, and suffer minimal fluorescence loss at least up to excitation levels of 38,000 W/cm2.
These performance values are close to achieving (or surpass) a number of DOE's SSL Multi-Year Program Plan performance targets for phosphors. Though work needs to be done to put these new nanocrystals into white LED products, SUNY/Buffalo's research shows that colloidal quantum dot phosphors can be engineered to overcome many of their initial challenges. In the course of creating these new nanocrystal compositions, the researchers have also managed to significantly reduce Auger recombination, which could result in the future production of important optical devices.