Electronic Origin of Linearly Polarized Emission in CdSe/CdS Dot-in-Rod Heterostructures

TL;DR

This study reveals that shear strain is the primary electronic factor causing linear polarization in CdSe/CdS dot-in-rod nanostructures, enabling polarization control through structural design.

Contribution

It identifies shear strain as the main electronic mechanism behind polarization, combining it with dielectric effects for improved emission control.

Findings

Shear strain favors light hole excitons, enhancing polarization.

Piezoelectric effects accelerate radiative recombination.

Long, thin shells increase linear polarization.

Abstract

Seeded CdSe/CdS nanorods exhibit intense polarized emission along the rod main axis. The degree of linear polarization cannot be explained by dielectric effects alone, an additional electronic contribution is present whose nature has not been settled up to date. Using multi-band k.p theory, we analyse the potential influence of several factors affecting excitonic emission and show that shear strain is the main electronic mechanism promoting linear polarization. It favors energetically light hole excitons over heavy hole ones, via deformation potential, and makes their radiative recombination faster via piezoelectricity. Implications of this mechanism are that linear emission can be enhanced by growing long but thin CdS shells around large, prolate CdSe cores, which indeed supports and rationalizes recent experimental findings. Together with the well-known dielectric effects, these results pave the way for controlled degree of linear polarization in dot-in-rods through dedicated structural design.