Thermal and vibronic effects on the absorption spectra of II–VI quantum dots: Atomistic origins of the Urbach tail
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134101_1_5.0314509.pdf
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Published version
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7.23 MB
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Author(s)
Alexiu, Alexandra
McIsaac, Alexandra R
Luo, Carina
Kim, Inkoo
Chien, Yu-Che
Rogers, Lin
Van Voorhis, Troy
Date Issued
April 1, 2026
Journal
The Journal of Chemical Physics
Publisher
AIP Publishing
Citation
Alexandra Alexiu, Alexandra R. McIsaac, Carina Luo, Inkoo Kim, Yu-Che Chien, Lin Rogers, Troy Van Voorhis; Thermal and vibronic effects on the absorption spectra of II–VI quantum dots: Atomistic origins of the Urbach tail. J. Chem. Phys. 7 April 2026; 164 (13): 134101.
Version
Final published version
Abstract
Explicit treatments of exciton–phonon coupling and ensemble averaging are often neglected in computational studies of nanocrystal optical properties. Here, we present a simple harmonic approximation framework for predicting temperature-dependent UV–Vis absorption spectra of II–VI quantum dots from first principles, without empirical parameters. Two variants are introduced: the equilibrium harmonic approximation, which captures homogeneous broadening, and the averaged variant, which additionally accounts for configurational sampling and bandgap renormalization. Application to II–VI quantum dot model systems demonstrates nearly quantitative agreement with experiment and clarifies the microscopic origin of the Urbach tail. Atomistic analysis reveals that surface-to-bulk excitations associated with hole trap states exhibit greater sensitivity to thermal fluctuations, leading to broader excitations that form an extended low-energy absorption tail. These findings underscore the need for ab initio treatments of exciton–phonon interactions in predictive models of nanocrystal optoelectronic properties. The harmonic approximation framework provides a practical pathway toward the explicit inclusion of thermal and ensemble effects in future computational studies.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1063/5.0314509
