Amazing stuff!
"... The lowest energy, or ground-state excitons in nanocrystals are bad at emitting light, hence the name dark exciton. Dark excitons act like a speed bump, slowing down the emission of light and limiting the performance of nanocrystal-based devices. ..."
" U.S. Naval Research Laboratory (NRL) scientists confirm the identification of a new class of semiconductor nanocrystals with bright ground-state excitons, a significant advancement in the field of optoelectronics ..."
From the abstract:
"While semiconductor nanocrystals provide versatile fluorescent materials for light-emitting devices, their brightness suffers from the “dark exciton”─an optically inactive electronic state into which nanocrystals relax before emitting. Recently, a theoretical mechanism, the Rashba effect, was discovered that can overcome this limitation by inverting the lowest-lying levels and creating a bright excitonic ground state. However, no methodology is available to systematically identify materials that exhibit this inversion, hindering the development of superbright nanocrystals and their devices. Here, based on a detailed understanding of the Rashba mechanism, we demonstrate a procedure that reveals previously unknown “bright-exciton” nanocrystals. We first define physical criteria to reduce over 500,000 known solids to 173 targets. Higher-level first-principles calculations then refine this list to 28 candidates. From these, we select five with high oscillator strength and develop effective-mass models to determine the nature of their lowest excitonic state. We confirm that four of the five solids yield bright ground-state excitons in nanocrystals. Thus, our results provide a badly needed roadmap for experimental investigation of bright-exciton nanomaterials."
NRL [US Naval Research Laboratory] Scientists Identify New Class of Semiconductor Nanocrystals (original news release)
Graphical abstract
No comments:
Post a Comment