Non-Markovian Exciton-Phonon Interactions in Core-Shell Colloidal Quantum Dots at Femtosecond Timescales

Area of Science:

• Quantum dots
• Colloidal nanocrystals
• Solid-state spectroscopy

Background:

• Colloidal quantum dots (CQDs) are crucial for optoelectronic applications.
• Understanding exciton-phonon coupling is key to controlling CQD properties.
• Markovian spectral diffusion models assume instantaneous, memoryless dephasing.

Purpose of the Study:

• Investigate exciton dynamics in CdSe/CdZnS core-shell quantum dots.
• Probe the influence of lattice phonon modes on exciton coherence.
• Characterize energy-gap fluctuations beyond Markovian assumptions.

Main Methods:

• Two-dimensional coherent spectroscopy (2DCS) at cryogenic temperatures.
• High-resolution femtosecond spectroscopy.
• Comparison with theoretical simulations.

Main Results:

• Observed sidebands in 2D spectra linked to CdSe LO-phonon coupling.
• Deviations from exponential dephasing, challenging Markovian models.
• Evidence for finite-timescale energy-gap fluctuations induced by LO-phonon coupling.

Conclusions:

• LO-phonon coupling induces non-Markovian energy-gap fluctuations.
• Exciton dynamics are directly influenced by nuclear motion timescales.
• 2DCS provides insights into ultrafast processes in nanocrystals.