Electric field and exciton structure in CdSe nanocrystals

TL;DR

This paper theoretically investigates the quantum Stark effect in CdSe nanocrystals, analyzing exciton structure, energy shifts, and optical properties under electric fields, with results aligning with experimental observations.

Contribution

It provides a detailed theoretical analysis of exciton behavior and optical properties in CdSe nanocrystals under electric fields, including symmetry and selection rules, extending prior models.

Findings

Exciton binding energy dependence on electric field is reduced for small quantum dots.

Electric field induces quenching of optical spectra and anomalous emission line behavior.

Results agree with experimental photoluminescence data.

Abstract

Quantum Stark effect in semiconductor nanocrystals is theoretically investigated, using the effective mass formalism within a $4\times 4$ Baldereschi-Lipari Hamiltonian model for the hole states. General expressions are reported for the hole eigenfunctions at zero electric field. Electron and hole single particle energies as functions of the electric field ($\mathbf{E}_{QD}$) are reported. Stark shift and binding energy of the excitonic levels are obtained by full diagonalization of the correlated electron-hole Hamiltonian in presence of the external field. Particularly, the structure of the lower excitonic states and their symmetry properties in CdSe nanocrystals are studied. It is found that the dependence of the exciton binding energy upon the applied field is strongly reduced for small quantum dot radius. Optical selection rules for absorption and luminescence are obtained. The electric-field induced quenching of the optical spectra as a function of $\mathbf{E}_{QD}$ is studied in terms of the exciton dipole matrix element. It is predicted that photoluminescence spectra present anomalous field dependence of the emission lines. These results agree in magnitude with experimental observation and with the main features of photoluminescence experiments in nanostructures.