Abstract
We report femtosecond stimulated Raman spectroscopy (FSRS) measurements on dispersions of CdSe semiconductor nanocrystals (NCs) as a function of particle size and pump fluence. Upon photoexcitation, we observe depletion of stimulated Raman gain corresponding to generation of longitudinal optical (LO) phonons followed by recovery on picosecond timescales. At higher fluences, production of multiple excitons slows recovery of FSRS signals, which we attribute to sustained increases of LO phonon populations due to multiexcitonic Auger heating. Owing to the discretized electronic structure of these NCs, such heating cannot be readily monitored via electronic spectroscopic analysis of high-energy band tails as has been performed for higher-dimensional materials. Notably, recovery timescales exceed those of the biexcitonic Auger recombination process and as such reveal overall thermalization timescales likely owing to an acoustic phonon thermalization bottleneck that dictates the cooling timescale.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4481-4487 |
| Number of pages | 7 |
| Journal | Journal of Physical Chemistry Letters |
| Volume | 9 |
| Issue number | 16 |
| DOIs | |
| State | Published - Aug 16 2018 |
Funding
This work was performed, in part, at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science User Facility and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, DOE under Grant DE-FG02-99ER14999 (M.R.W.) and by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1324585 (S.M.H). We acknowledge support from the NSF DMREF Program under Award DMR-1629383. We thank Dr. Maria Chan for help with Figure S1. S.M.H. thanks M. Krzyaniak for help with Matlab as well as T. Ueltschi and M. McAnally for insightful conversations about FSRS. This work was performed in part, at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science User Facility and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, DOE under Grant DE-FG02-99ER14999 (M.R.W.) and by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1324585 (S.M.H). We acknowledge support from the NSF DMREF Program under Award DMR-1629383.
ASJC Scopus subject areas
- General Materials Science
- Physical and Theoretical Chemistry