Nanocrystal-Based LEDs Offer More Efficient Color Conversion

As part of an effort to improve the performance of potential solid-state replacements for general lighting applications, investigators at Los Alamos National Laboratory and at Sandia National Laboratories in Albuquerque, both in New Mexico, have demonstrated that semiconductor nanocrystals acting as color-conversion phosphors can be directly coupled to an LED by nonradiative energy transfer. The approach, which they reported in the June 16 online edition of Nano Letters, improves the color-conversion efficiency of the devices by avoiding the sources of energy loss associated with intermediate steps in traditional color conversion with phosphors.

In the work, the scientists spin-coated a single monolayer of 5.4-nm-diameter CdSe/ZnS core/shell nanocrystals atop an inverted InGaN/GaN quantum-well LED. The spectra of the device under an injected current of a few milliamps displayed a peak at 590 nm generated by the nanocrystals as well as the 420-nm light from the LED. Based on the observed emission intensity from the nanocrystals, they calculated that the overall color-conversion efficiency was 13 percent and estimated that the efficiency by nonradiative energy transfer alone was nearly 10 percent.