Nonradiative processes govern efficiencies of semiconductor nanocrystal (NC)-based devices. A central process is hot exciton cooling, or the nonradiative relaxation of a highly excited electron/hole pair to form a band-edge exciton. Due to quantum confinement effects, the timescale and mechanism of cooling are not well understood. A mismatch between electronic energy gaps and phonon frequencies has led to the hypothesis of a phonon bottleneck and extremely slow cooling, while enhanced electron-hole interactions have suggested ultrafast cooling. Experimental measurements of the cooling timescale range six orders of magnitude. Here, we develop an atomistic approach to describe phonon-mediated exciton dynamics and simulate cooling in NCs of experimentally relevant sizes. We find that cooling occurs on ~30 fs timescales in CdSe NCs, in agreement with the most recent measurements, and that the phonon bottleneck is circumvented through a cascade of multiphonon-mediated relaxation events. Furthermore, we identify NC handles for tuning the cooling timescale.
Jasrasaria, Dipti and Rabani, Eran. "Circumventing the phonon bottleneck by multiphonon-mediated hot exciton cooling at the nanoscale." npj Computational Materials, vol. 9, no. 1, Aug. 2023. https://doi.org/10.1038/s41524-023-01102-8
Jasrasaria, Dipti, & Rabani, Eran (2023). Circumventing the phonon bottleneck by multiphonon-mediated hot exciton cooling at the nanoscale. npj Computational Materials, 9(1). https://doi.org/10.1038/s41524-023-01102-8
Jasrasaria, Dipti, and Rabani, Eran, "Circumventing the phonon bottleneck by multiphonon-mediated hot exciton cooling at the nanoscale," npj Computational Materials 9, no. 1 (2023), https://doi.org/10.1038/s41524-023-01102-8
@article{osti_2217263,
author = {Jasrasaria, Dipti and Rabani, Eran},
title = {Circumventing the phonon bottleneck by multiphonon-mediated hot exciton cooling at the nanoscale},
annote = {Abstract Nonradiative processes govern efficiencies of semiconductor nanocrystal (NC)-based devices. A central process is hot exciton cooling, or the nonradiative relaxation of a highly excited electron/hole pair to form a band-edge exciton. Due to quantum confinement effects, the timescale and mechanism of cooling are not well understood. A mismatch between electronic energy gaps and phonon frequencies has led to the hypothesis of a phonon bottleneck and extremely slow cooling, while enhanced electron-hole interactions have suggested ultrafast cooling. Experimental measurements of the cooling timescale range six orders of magnitude. Here, we develop an atomistic approach to describe phonon-mediated exciton dynamics and simulate cooling in NCs of experimentally relevant sizes. We find that cooling occurs on ~30 fs timescales in CdSe NCs, in agreement with the most recent measurements, and that the phonon bottleneck is circumvented through a cascade of multiphonon-mediated relaxation events. Furthermore, we identify NC handles for tuning the cooling timescale.},
doi = {10.1038/s41524-023-01102-8},
url = {https://www.osti.gov/biblio/2217263},
journal = {npj Computational Materials},
issn = {ISSN 2057-3960},
number = {1},
volume = {9},
place = {United Kingdom},
publisher = {Nature Publishing Group},
year = {2023},
month = {08}}
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 370, Issue 1972https://doi.org/10.1098/rsta.2011.0204