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

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 multiband k.p theory, we analyze 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. The implication of this mechanism is 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.