Exciton polarizability and absorption spectra in CdSe/ZnS nanocrystal quantum dots in electric fields

Abstract

The effects of an external electric field on the exciton polarizability and absorption spectra in CdSe/ZnS nanocrystal quantum dots have been investigated theoretically by using an exact diagonalization method within the effective-mass approximation. The results show that the application of an external electric field causes the splitting of degenerated states introducing new interband transitions (1s-1p0 and 1p0-1s), resulting in the increase of the excitonic absorption coefficients of the 1s-1p0 and 1p0-1s transitions due to the enhancement of the electric-field-induced coupling between the 1s and 1p0 states. The excitonic absorption intensity of 1s-1s, 1p-1-1p-1, and 1p1-1p1 transitions decreases with the increase of the electric field strength. A red-shift in the absorption spectra of 1s-1s, 1p-1-1p-1, 1p1-1p1, 1s-1p0, and 1p0-1s interband transitions is observed while the absorption peak of 1p0-1p0 interband transition is first blue-shifted and then red-shifted with increasing the electric field strength, which is attributed to the quantum-confined Stark effect (QCSE). The exciton polarizability increases monotonically with increasing the dot radius. The fitting expressions of the Stark shift and exciton polarizability have been proposed for the interband transitions in the strong confinement regime. Therefore, the emission wavelength and intensity of the output of optoelectronic nanodevices can be manipulated using an external electric field.