Controlling the Mechanism of Excitonic Splitting in In2O3 Nanocrystals by Carrier Delocalization.

Abstract

Degenerately doped metal oxide nanocrystals have emerged as infrared plasmonic materials with promising applications in optoelectronics, surface-enhanced infrared spectroscopies, and sensing. They also have potential for technological applications in electronics and photonics owing to the possibility of coupling between plasmon and exciton in the absence of a heterojunction. Here, we demonstrate the control of excitonic splitting in In2O3 nanocrystals upon excitation with circularly polarized light in an external magnetic field by simultaneous control of the electronic structure of donor defects and the nanocrystal host lattice. Using variable-temperature-variable-field magnetic circular dichroism spectroscopy, we show that the nanocrystal band splitting has two distinct contributions in plasmonic In2O3 nanocrystals. Temperature-independent splitting arises from the cyclotron magnetoplasmonic modes, which impart angular momentum to the conduction band excited states near the Fermi level, and increases with the intensity of the corresponding plasmon resonance. Temperature-dependent splitting is associated with the localized electron spins trapped in defect states. The ratio of the two components can be controlled by the formation of oxygen vacancies or introduction of aliovalent dopants. Using these experimental results in conjunction with the density functional theory modeling, relative contribution of the two mechanisms is discussed in the context of the perturbation theory taking into account energy separation between the nanocrystal excited states and the localized defect states. The results of this work demonstrate the ability to control carrier polarization in nonmagnetic metal oxide nanocrystals using both individual and collective electronic properties and allow for their application as an emerging class of multifunctional materials with strongly interacting degrees of freedom.