New Class of Nanocrystal Semiconductors

 


A recent article was published in the American Chemical Society journal ACS Nano. The US Naval Research Laboratory authenticates a new class of semiconductor nanocrystals. The crystals are bright with ground-state excitations. This is a huge advancement for semiconductors. The research could alter current highly efficient light-emitting devices and reach other optotechnologies. 

The lowest-energy exciton in nanocrystals does not emit light well. This is why nanocrystals have earned the nickname “dark” exciton. Nanocrystals also slow the emission of light. The dark exciton can limit a nanocrystal based device’s performance. Examples of these devices include lasers or light-emitting diodes (LED).  Scientists have worked for years to vanquish these dark excitons.

“We set out to find new materials in which the exciton ordering is inverted, so that the lowest energy exciton is bright,” reports John Lyons. He is a Ph.D from the Theory of Advanced Materials section of the Navy. He continues, “Searching through open source databases of materials using criteria informed by our theoretical modeling, we identified over 150 targets. We further narrowed this list with advanced first principles calculations, ending up with 28 candidates for bright-exciton nanomaterials.” 

After more research, scientists discovered that four of these materials can generate bright ground state excitons in nanocrystals. This discovery, made in collaboration with Prof. David Norris from the Federal Institute of Technology Zurich, and Peter Sercel, Ph.D from the Center for Hybrid Organic-Inorganic Semiconductors for Energy, “could pave the way for the development of ultra bright and highly efficient light-emitting devices, lasers and other technologies,” says Lyons.

Alexander Effros is a Ph.D, who is senior author of the paper and with the Material Science division. He gave a statement about the importance of the nanocrystal study. 

“In our research, we have identified several bright-exciton materials that can emit light across a broad spectrum, from infrared to ultraviolet. This versatility makes them very useful for optoelectronic applications. The capability to engineer nanocrystals with bright excitonic states across this wide range opens new avenues for creating better and more efficient LEDs, solar cells and photodetectors.”

The Naval Research Laboratory is working on solving the dark-exciton problem. The Navy scientists are looking to shake up the largely stagnant nanomaterial community by attacking bright-exciton nanostructures as a group head-on. This area of research has been evaded for a long time. 

Today, three of these noted materials are being grown. They are at the Naval Research Laboratory in part with the Nanoscience Institute Program’s Bright Nanocrystal Emitters. They hope to show (without a doubt) this bright-exciton behavior in the laboratory and use it for naval technologies in the future. 

Michael Swift, Ph.D summarizes, “Our findings demonstrate the power of combining high-through put computational screening, pen-and-paper theory, and high-accuracy calculations of electronic structure. No one technique would be enough on its own, but together we discovered new ultrabright nanocrystals and unlocked the power of the bright exciton across unexplored classes of materials.

The future is wide open for development of these nanocrystals! 

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