Measuring the Ultrafast Spectral Diffusion and Vibronic Coupling Dynamics in CdSe Colloidal Quantum Wells using Two-Dimensional Electronic Spectroscopy

• Published in: ACS nano Vol. 17; no. 3; pp. 2411 - 2420
• Main Authors: Nguyen, Hoang Long, Do, Thanh Nhut, Durmusoglu, Emek G., Izmir, Merve, Sarkar, Ritabrata, Pal, Sougata, Prezhdo, Oleg V., Demir, Hilmi Volkan, Tan, Howe-Siang
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14-02-2023
• Subjects: spectral diffusion; energy transfer; vibronic coupling; two-dimensional electronic spectroscopy; exciton; colloidal quantum well
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.2c09606

We measure the ultrafast spectral diffusion, vibronic dynamics, and energy relaxation of a CdSe colloidal quantum wells (CQWs) system at room temperature using two-dimensional electronic spectroscopy (2DES). The energy relaxation of light-hole (LH) excitons and hot carriers to heavy-hole (HH) excitons is resolved with a time scale of ∼210 fs. We observe the equilibration dynamics between the spectroscopically accessible HH excitonic state and a dark state with a time scale of ∼160 fs. We use the center line slope analysis to quantify the spectral diffusion dynamics in HH excitons, which contains an apparent sub-200 fs decay together with oscillatory features resolved at 4 and 25 meV. These observations can be explained by the coupling to various lattice phonon modes. We further perform quantum calculations that can replicate and explain the observed dynamics. The 4 meV mode is observed to be in the near-critically damped regime and may be mediating the transition between the bright and dark HH excitons. These findings show that 2DES can provide a comprehensive and detailed characterization of the ultrafast spectral properties in CQWs and similar nanomaterials.