Doping Controls Plasmonics, Electrical Conductivity, and Carrier-Mediated Magnetic Coupling in Fe and Sn Codoped In2O3 Nanocrystals: Local Structure Is the Key

Abstract

Multifunctional Fe–Sn codoped In2O3 colloidal nanocrystals simultaneously exhibiting localized surface plasmon resonance band, high electrical conductivity, and charge mediated magnetic coupling have been developed. Interactions between Sn and Fe dopant ions have been found critical to control all these properties. Sn doping slowly releases free electrons in the colloidal nanocrystals, after reduction of active complex between Sn4+ and interstitial O2–. Unexpectedly, Fe codoping reduces the free electron concentration. Our X-ray absorption fine structure spectroscopy (XAFS) results show that Fe3+ and Sn4+ substitutes In3+ in the In2O3 lattice for all Fe-doped In2O3 NCs and Sn-doped In2O3 NCs. Interestingly, for Fe–Sn codoped NCs, a smaller fraction of Fe3+ gets reduced to Fe2+ by consuming free electrons produced by Sn doping. Therefore, Fe doping can manipulate free electron concentration in Fe–Sn codoped In2O3 nanocrystals, controlling both plasmonic band and electrical conductivity. Free electrons, on the other hand, facilitate magnetic coupling between distant Fe3+ ions. Such charge mediated magnetic coupling is useful for spin-based applications.