研究目的
To study the impact of the chemical composition on phonon-mediated exciton relaxation in core/shell quantum dots (QDs) with a 1-nm core made of PbX and a monolayer shell made of CdX, where X=S and Se.
研究成果
The simulations revealed that despite many similarities in the electronic structure and phonon spectra of PbSe/CdSe and PbS/CdS QDs, rates of charge carrier relaxation differ greatly, with about twice-faster energy relaxation in PbS/CdS than in PbSe/CdSe QDs. The four-state irreversible kinetic model was suggested to describe the relaxation dynamics, predicting 0.9 ps and 0.5 ps relaxation rates in PbSe/CdSe and PbS/CdS QDs, respectively.
研究不足
The study is limited to smaller size QDs (< 3 nm in diameter) due to the computational cost of DFT-based simulations. The PBE functional used in the study underestimates energy bandgaps in semiconductor materials, which may affect the accuracy of the results.
1：Experimental Design and Method Selection:
Time-domain non-adiabatic dynamics (NAMD) based on Density Functional Theory (DFT) and Surface Hopping techniques were applied to study phonon-mediated exciton relaxation in core/shell QDs.
2：Sample Selection and Data Sources:
The study focused on PbS/CdS and PbSe/CdSe core/shell QDs with a 1-nm core and a monolayer shell.
3：List of Experimental Equipment and Materials:
The Vienna Ab initio Simulation Package (VASP) software was used for electronic structure and NAMD calculations at the DFT level of theory within the generalized gradient approximation (GGA) of Perdew, Burke, and Ernzerhof (PBE) exchange-correlation functional.
4：Experimental Procedures and Operational Workflow:
The structures were optimized until the forces between ions became smaller than
5：01 eV/?, heated to 300 K, and adiabatic trajectories up to 4 ps with 5 fs atomic time-step were produced. Data Analysis Methods:
Non-adiabatic coupling terms (NACTs) were calculated in the basis of adiabatic Kohn-Sham (KS) orbitals, and Fewest Switching Surface Hopping (FSSH) simulations were used to sample the hopping probabilities.
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