NanoCrystals May Hold Key to 'Natural' LED Light

18. června 2013 v 5:41 |  solar photovoltaic system
According to new research, minuscule crystals that are glowing in different colors may be the ingredient that has thus far been missing from natural-like LED lighting.
Light-emitting diodes, which are commonly known LEDs, are promoted by many thanks to their energy-saving capability. The lights use incandescents and fluorescents that can produce single-color light as seen in items like street lights or children's toys.
Developing the LED light that creates a broad spectrum has proved, thus far, to be difficult. Making a light that gives off a natural and warm lighting effect is even more difficult. LEDs create their lighting effect through the passing of electrons through a semiconductor material, which is more often than not tied to materials called phosphors.
"But it's hard to get one phosphor that makes the broad range of colors needed to replicate the sun," said John Budai, a scientist in ORNL's Materials Science and Technology division. "One approach to generating warm-white light is to hit a mixture of phosphors with ultraviolet radiation from an LED to stimulate many colors needed for white light."
Budai, works with the University of Georgia and Oak Ridge and Argonne national laboratories in order to better understand the crystals. Zhengwei Pan's group at the Georgia grew what were called nanocrystals in order to avoid the use of rare-earth elements like europium.
"What's amazing about these compounds is that they glow in lots of different colors-some are orange, purple, green or yellow," Budai said. "The next question became: why are they different colors? It turns out that the atomic structures are very different."
Budai spent time studying the structure of the materials at the atomic level. He utilized x-rays from the Argonne Advanced Photon Source, finding two types of crystals.
"Only the green ones were a known crystal structure," Budai said. "The other two, the yellow and blue, don't grow in big crystals; they only grow with these atomic arrangements in these tiny nanocrystals. That's why they have different photoluminescent properties."
Using atom arrangement, the team looked to create differing colors of phosphors to exhibit separate diffraction patterns. That allowed researchers to analyze specific structures of given crystals.
"What that means in terms of how the electrons around the atoms interact to make light is much harder," Budai said. "We haven't completely solved that yet. That's the continuing research. We have a lot of clues, but we don't know everything." More information about the program is available on the web site at

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