Size Control of the Mechanism of Exciton Polarization in Metal Oxide Nanocrystals through Fermi Level Pinning

Light-matter interaction incertain aliovalently doped metaloxide nanocrystals (NCs) results in the generation of localized surfaceplasmon resonance (LSPR) in the near- to mid-infrared, allowing fortheir implementation in various technologies, including photovoltaics,sensing, and electrochromics. These materials could also facilitatecoupling between plasmonic and semiconducting properties, making themhighly interesting for electronic and quantum information technologies.In the absence of dopants, free charge carriers can arise from nativedefects such as oxygen vacancies. Here we show using magnetic circulardichroism spectroscopy that the exciton splitting in In2O3 NCs is induced by both localized and delocalized electronsand that contributions from the two mechanisms are strongly dependenton the NC size, owing to Fermi level pinning and the formation ofa surface depletion layer. In large NCs, the angular momentum transferfrom delocalized cyclotron electrons to the excitonic states is thedominant mechanism of exciton polarization. This process diminisheswith decreasing NC size, owing to the rapidly reduced volume of theplasmonic core. On the other hand, exciton polarization in small NCsis dominated by localized electron-spin-induced splitting of the excitonicstates. This mechanism is independent of NC size, suggesting thatwave functions of localized spin states on NC surfaces do not overlapwith the excitonic states. The results of this work demonstrate thatthe effects of individual and collective electronic properties onexcitonic states can be simultaneously controlled by NC size, makingmetal oxide NCs a promising class of materials for quantum, spintronic,and photonic technologies.

Automated summary

In certain aliovalently doped metal oxide nanocrystals, light-matter interaction results in the generation of localized surface plasmon resonance (LSPR), making them highly interesting for various technologies. The exciton splitting in In2O3 NCs is induced by both localized and delocalized electrons, and the contribution from these two mechanisms depends on the NC size. In large NCs, the angular momentum transfer from delocalized cyclotron electrons is the dominant mechanism, while in small NCs, exciton polarization is dominated by localized electron-spin-induced splitting.