Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence
Abstract
:1. Introduction
2. Results and Discussion
2.1. Pump-Probe Transients vs. Pump Fluence
2.2. Oscillations in Transient Traces of CdSe QDs Dissolved in Toluene
2.3. Specific Features of Coherent Phonons Produced in CdSe Revealed by FFT
2.4. Amplitude of Oscillations Revealed by FFT vs. Pump Fluence
2.5. Analysis of the CWT Spectrogram Obtained for Varied Pump Fluence
3. Materials and Methods
3.1. Femtosecond Laser Photolysis Setup
3.2. Materials
3.3. Synthesis of CdSe Nanocrystals
4. Conclusions
- (1)
- Coherent LO phonon oscillations are significantly chirped. An especially significant chirp manifests itself at time delays shorter than ~300 fs. The chirp sign is changed when pump fluence approaches the value of ~0.8 mJ/cm2. This fluence threshold matches the fluence where the amplitude of LO phonon oscillations reaches the maximum value.
- (2)
- The coherent response of CdSe exhibits the antiresonance dip (destructive interference) at ~6 THz in the overlap region between the coherent phonon and electronic responses. The obtained data suggests that: (a) this effect is related to the coherent excitation of the coupled phonons and charge carriers; (b) the dynamical interference between short-lived Rabi oscillations is resulting from close electronic states (fine structure) of the exciton and long-lived coherent phonons in CdSe QDs. This data agrees with the conclusion that the Fano interference always starts from the destructive one when the corresponding optical phonon being coherent [47].
- (3)
- The damping rate enhances with the increase of pump fluence.
- (4)
- The anharmonic coupling occurs between optical and acoustic phonons.
Supplementary Materials
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Nadtochenko, V.; Denisov, N.; Aybush, A.; Gostev, F.; Shelaev, I.; Titov, A.; Umanskiy, S.; Cherepanov, A.D. Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence. Nanomaterials 2017, 7, 371. https://doi.org/10.3390/nano7110371
Nadtochenko V, Denisov N, Aybush A, Gostev F, Shelaev I, Titov A, Umanskiy S, Cherepanov AD. Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence. Nanomaterials. 2017; 7(11):371. https://doi.org/10.3390/nano7110371
Chicago/Turabian StyleNadtochenko, Victor, Nikolay Denisov, Arseniy Aybush, Fedor Gostev, Ivan Shelaev, Andrey Titov, Stanislav Umanskiy, and And Dmitry Cherepanov. 2017. "Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence" Nanomaterials 7, no. 11: 371. https://doi.org/10.3390/nano7110371