Text Box: Exciton-phonon coupling in semiconductor nanocrystals

Exciton-phonon coupling (EPC) refers to the dependence of electron-hole state energies on displacement of the nuclei along a phonon coordinate.  The magnitude and frequency distribution of EPC influences the efficiencies of important photophysical processes including carrier multiplication and interfacial charge separation.  Resonance Raman scattering is an ideal method to probe EPC experimentally, and in collaboration with David Kelley’s group we are carrying out Raman studies as a function of nanocrystal size, composition, and surface chemistry.  The experimental work is coupled with computational studies that combine fully atomistic calculations of the phonon modes and frequencies with effective mass, particle-in-a-sphere models for the electron and hole wavefunctions and fully quantum mechanical simulations of the resonance Raman intensities.  By measuring and modeling both absolute Raman scattering cross-sections and excitation profiles, we have demonstrated that EPC is fairly constant over a range of CdSe and ZnSe quantum dots of very different sizes, and also is little affected by adding a CdS shell to delocalize the electron wavefunction.  However, ZnSe/CdSe alloyed quantum dots exhibit strongly enhanced EPC which we attribute to localization of the hole wavefunction in locally Cd-rich regions within a random alloy.  


Recent publications in this field

Anne Myers Kelley.  Electron-phonon coupling in CdSe nanocrystals from an atomistic phonon model.  ACS Nano 5, 5254-5262 (2011).

Anne Myers Kelley, Quanqin Dai, Zhong-Jie Jiang, Joshua A. Baker, and David F. Kelley.  Resonance Raman spectra of wurtzite and zincblende CdSe nanocrystals.  Chem. Phys. 422, 272-276 (2013).

Anne Myers Kelley.  Resonance Raman overtone intensities and electron-phonon coupling strengths in semiconductor nanocrystals.  J. Phys. Chem. A 117, 6143-5149 (2013).

Joshua A. Baker, David F. Kelley, and Anne Myers Kelley.  Resonance Raman and photoluminescence excitation profiles and excited-state dynamics in CdSe nanocrystals.  J. Chem. Phys. 139, 024702 (2013).

Jonathan D. Mooney, Jonathan I. Saari, Anne Myers Kelley, Brenna R. Walsh, Michael Krause, and Patanjali Kambhampati.  Control of phonons in semiconductor quantum dots via femtosecond pulse chirp-influenced wavepacket dynamics and polarization.  J. Phys. Chem. B 117, 15651-15658 (2013).

Chen Lin, David F. Kelley, Mikaela Rico, and Anne Myers Kelley.  The “surface optical” phonon in CdSe nanocrystals.  ACS Nano 8, 3928-3838 (2014).

Chen Lin, Ke Gong, David F. Kelley, and Anne Myers Kelley.  Size-dependent exciton-phonon coupling in CdSe nanocrystals through resonance Raman excitation profile analysis.  J. Phys. Chem. C 119, 7491-7498 (2015).

Chen Lin, Ke Gong, David F. Kelley, and Anne Myers Kelley.  Electron-phonon coupling in CdSe/CdS core/shell quantum dots.  ACS Nano 9, 8131-8141 (2015).

Anne Myers Kelley.  Comparison of three empirical force fields for phonon calculations in CdSe quantum dots.  J. Chem. Phys. 144, 214702 (2016). 

Ke Gong, David F. Kelley, and Anne Myers Kelley.   Resonance Raman spectroscopy and electron-phonon coupling in zinc selenide quantum dots.  J. Phys. Chem. C 120, 29533-29539 (2016).

Ke Gong, David F. Kelley, and Anne Myers Kelley.  Non-uniform excitonic charge distribution enhances exciton-phonon coupling in ZnSe/CdSe alloyed quantum dots.  J. Phys. Chem. Letters 8, 626-630 (2017).