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Both absorption and emission of light in semiconductor quantum dots occur through excitation or recombination of confined electron−hole pairs, or excitons, with tunable size-dependent resonant frequencies that are ideal for applications in various fields. Some of these applications require control over quantum dot shape uniformity, while for others, control over energy splittings among exciton states emitting light in different polarizations and/or between bright and dark exciton states is of key importance. These splittings, known as exciton fine structure, are very sensitive to the nanocrystal shape. Theoretically, nanocrystals of spheroidal shape are often considered, and their nonsphericity is treated perturbatively as stemming from a linear uniaxial deformation of a sphere. Here, we compare this treatment with a nonperturbative model of a cylindrical box, free of any restrictions on the cylinder’s aspect ratio. This comparison allows one to understand the limits of validity of the traditional perturbative model and offers insights into the relative importance of various mechanisms controlling the exciton fine structure. These insights are relevant to both colloidal nanocrystals and epitaxial quantum dots of III−V and II−VI semiconductors.
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Reductive pathways in molten inorganic salts enable colloidal synthesis of III-V semiconductor nanocrystals
Colloidal quantum dots, with their size-tunable optoelectronic properties and scalable synthesis, enable applications in which inexpensive high-performance semiconductors are needed. Synthesis science breakthroughs have been key to the realization of quantum dot technologies, but important group III–group V semiconductors, including colloidal gallium arsenide (GaAs), still cannot be synthesized with existing approaches. The high-temperature molten salt colloidal synthesis introduced in this work enables the preparation of previously intractable colloidal materials. We directly nucleated and grew colloidal quantum dots in molten inorganic salts by harnessing molten salt redox chemistry and using surfactant additives for nanocrystal shape control. Synthesis temperatures above 425°C are critical for realizing photoluminescent GaAs quantum dots, which emphasizes the importance of high temperatures enabled by molten salt solvents. We generalize the methodology and demonstrate nearly a dozen III-V solid-solution nanocrystal compositions that have not been previously reported.
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- Award ID(s):
- 2011854
- PAR ID:
- 10590288
- Publisher / Repository:
- American Association for the Advancement of Science
- Date Published:
- Journal Name:
- Science
- Volume:
- 386
- Issue:
- 6720
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 401 to 407
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1126/science.ado7088
